Why still no dive acceleration difference?

[mayshine]

:confused:Dear All

Why thru so many versions still the very big defect--same dive acceleration

for all aircrafts---is not fixed?

As we know, FW,spit,p47,la....and so on have their own respective dive
acceleration which to some extence dominate the result of the combat.

It is really uncomfortable when diving in a Fw with a La almost neck to neck

Why it is not fixed, is it because of the limit of IL2 engine?

[JtD]

Because in game, g applies the same to all aircraft. Just like in real life.

[mayshine]

thanks for concerning

however i want to correct u

G does affect everything on earth the same

however the air friction does not, plus the motor power, the shape of the plane, the weight of the plane

with the air friction, the feather obviously can not reach the ground as fast as the stone ball.

this make dive acceleration very different.

please go WIKI if u do not fully understand

[mayshine]

also it has been record in RAF documents for the acceleration difference test of different spit fire. a lot of doc support those differences.

And thru the BBC history, u can clearly hear the old pilots saying their P47
can easly catch up with the FW190 when diving which other lighter planes can
not, even D9 dora can not compete the diving acceleration of P47

[mayshine]

I do appriciate D team's effort

and love so much the IL2 sim which brings me a lot of fun

However, to be serious

IL2 will forever be a HANDICAP without this problem fixed

almost 10 years since the publish, man, I am slightly not patient enough now

[Robo.]

almost 10 years since the publish, man, I am slightly not patient enough now

But the diving speeds do vary in Il-2. Plus you can't compete with say a Lavochkin fighter against a 190 as you'd lose parts of your aircraft when diving too fast anyway. With all due respect I don't understand what you mean, perhaps you can give an example (starting altitude, engine settings etc).

[mayshine]

I meant the speed increase difference in certain period during diving.

for example, spit early type may have speed increase from 200KM/H to 400KM/H in 10 sec during diving
while spit late type will have the speed increase from 200KM/H to 500KM/H in 10 sec during diving at same altitude and throttle condition

In 4.11 ver and before, La will share the same speed increase with FW 190 when chasing after it till critical speed limit during the diving

It's a bit late here, I will post the test documentation from from archive tomorrow

Hope this explaination can help to clarify.

[IceFire]

Have you actually done tests in-game or are you just thinking that this is the case? I'm not trying to be obtuse but years ago I did some testing with a couple of players side by side and there was an obvious difference between different types of aircraft. It wasn't quite as pronounced as some people thought they would be... but it was there. I wish we still had the tracks but this was years and years ago.

[fruitbat]

Have you actually done tests in-game or are you just thinking that this is the case? I'm not trying to be obtuse but years ago I did some testing with a couple of players side by side and there was an obvious difference between different types of aircraft. It wasn't quite as pronounced as some people thought they would be... but it was there. I wish we still had the tracks but this was years and years ago.

I agree.

Only a couple of weeks ago a squad mate and myself were practising for a SEOW mission (HSFX i know, but), and we were testing how to best fight J2M's up high in a 47, and we did some side by side dive tests. All planes do not dive the same for sure.

[mayshine]

please please

now set a quick mission

altitude 2000.

u will find Fw190A9 1944 be at 720km/h before hit the ground with 100 throttle

try La5 1942 same, 720km/h before hit the ground 100 throttle


please do that test. it is easy and fast to prove the defect

also please remember to press the "pause" botton before crash

[fruitbat]

please please try it from 10000m, and see the difference.

[mayshine]

I am serious, do not take it as a joke

Please go WIKI if u do not understand what i am talking about.

Sorry for anything offensive

please also go Il2 compare to check La5 1942 and Fw190A9 ---- altitude vs TAS

U will really support me if u read the diagram and understand the difference.

"La5 1942 can not compare Fw190A9 in TAS at all Altitude except within 2km steep diving."

does it sound rediculous?

[mayshine]

also please make sure u understand the difference between

diving speed limit

&

diving speed acceleration

[fruitbat]

also please make sure u understand the difference between

diving speed limit

&

diving speed acceleration

I do understand the difference. i also understand that 2000m is not enough to show much, and that its not just the speed at the bottom, its the time to get there. Put them both side by side with to people in, and do the test from higher, and then come back.

It may well be that it should be more pronounced, but you will notice differences.

[mayshine]

I think you are incorrect

1. 2000m dive for la5 1942 will increase it's speed from 260km to 720km which is it's limit
more distance is meanless, it will be shreded into pieces.

2. certain distance of 2000m, fixed speed at the start (260km/h) and fixed speed at
the end (720km/h), the acceleration rate is FIXED,
u can not reach the same speed by the end with different acc. rate, isn't it?

3. the case u mentioned diving from 10000m and see the difference does not because
of the acceleration, may be it is because of the speed limit.
limit of la is 720km, 860km for 190A9.
La of cause can not follow you thru out the diving if you start from 10000m

4. my point is: the distance between la5 and FW should be increasing once start diving
instead of maintaining the distance till the critial speed limit of La5

[fruitbat]

I think you are incorrect



Well i'm certainly not from tests myself and DD_squawk did with respect to J2M's and P47's, we noticed one plane pulling away from the other, way way before the Vne of either plane.

Unless you have the 2 planes side by side, you won't and can't see it, have you tried this with someone else?

[mayshine]

Well

I have suffered a lot in dogfight server in which I was caught up by La with same E stage
under 3000m.

That's why i start to reseach this issue~~~:)

[mayshine]

dear D team member / admin

please see the fomular

set:
accelerate rate= a
starting speed=v0
end speed=vt
distance=x

The accelerate=a=(vt^2-v0^2)/(2x)
=(720km/h^2-260km/h^2)/(2*2000m)
=8.7m/s
=almost just G itself

this is the dive accclerate rate for everything in IL2,

for every bomber and piston fighter,

for both feather and rock in Il2 if any.

so simple and unrealistic

is this all we got in IL2 even in the future?

[Korn]

wrong post, pls delete, sorry

[realhammer]

I did a test, 90° dive at 5000m, 30% fuel, default weapon,
accelerate time 300km/h~700km/h:
LA5FN 12.43s
FW190A6 12.95s
P47-D27 12.25s
TEMPEST MK.V 12.23s
almost the same?

[realhammer]

I did a test, 90° dive at 5000m, 30% fuel, default weapon,
accelerate time 300km/h~700km/h:
LA5FN 12.43s
FW190A6 12.95s
P47-D27 12.25s
TEMPEST MK.V 12.23s
almost the same?

it's a shame to P47 and TEMPEST

[mayshine]

it's a shame to P47 and TEMPEST

yes I am agree with that.

It is a shame to all heavy interceptive fighters

think about it :

One of the biggest advantages of these heavy fighters is to dive to get
the speed advantage and then pull into a hammer action verticlely,

However, these heavy fighters are emasculated so far in all versions

[JtD]

Up to level top speed, the better climbing plane accelerates better. Looking at the planes given, based on level speed and climb rate, the order should be Tempest, P-47, La-5FN and Fw 190A-6 and the differences small. All true.

If you want bigger differences, don't dive vertically, use a shallow dive, and try higher speeds. Take a Fw 190A-9 and a Spitfire IX 25lb, start at 550 km/h at 1.5km altitude and dive them to a place 15 km away. Check their speeds.

[FC99]

In TAIC test between the Zero and P-47 when they started the dive from 10000ft at 220MPH IAS and dived until Zero reached maximum allowed speed (325MPH IAS). It took 30 seconds for that and the P-47 had 100 yards advantage over Zero.

Disapointing, isn't it? :grin:

[Luno13]

100 meters is close enough to get shot down.

I guess those planes are only good divers if they're fast to begin with. You should never be slow in a P-47. If you're at the same speed as a Zero, you've already lost.

[BadAim]

These aircraft are not all that much different. They are similar in size weight power and performance, it only makes sense that they perform similarly, besides a vertical dive will be measuring the effects of gravity much more than any other factor.

As for relative performance in a fight, how the pilot uses the strong points of his aircraft against the weak points of his opponent is much more important than the actual performance. I get my butt kicked by guys in inferior aircraft all the time because they are better pilots.

[Untamo]

S!

In situations with me flying a Zero vs. a Spit or P-47 or whatnot, if we start in same E situ me in the six of the other plane (where else ;) ), they always easily extend away after a short dive. I almost never get near the Vne because of the slow acceleration.

Zero is a kite that just doesn't have the mass for the dive acceleration and it clearly can be seen in-game.

[mayshine]

In TAIC test between the Zero and P-47 when they started the dive from 10000ft at 220MPH IAS and dived until Zero reached maximum allowed speed (325MPH IAS). It took 30 seconds for that and the P-47 had 100 yards advantage over Zero.

Disapointing, isn't it? :grin:

yes, should have been more pronounced

[mayshine]

These aircraft are not all that much different. They are similar in size weight power and performance, it only makes sense that they perform similarly, besides a vertical dive will be measuring the effects of gravity much more than any other factor.

As for relative performance in a fight, how the pilot uses the strong points of his aircraft against the weak points of his opponent is much more important than the actual performance. I get my butt kicked by guys in inferior aircraft all the time because they are better pilots.

I do not agree

1. cut wing and round end wing are different very much from each other
2. power are different, Tempest has 2000 HP while Zero has only 1200 HP.
3. weight for La is around 2000kg when FW is 4000Kg or more

I dont think they can perform in the same way during the diving

[mayshine]

S!

In situations with me flying a Zero vs. a Spit or P-47 or whatnot, if we start in same E situ me in the six of the other plane (where else ;) ), they always easily extend away after a short dive. I almost never get near the Vne because of the slow acceleration.

Zero is a kite that just doesn't have the mass for the dive acceleration and it clearly can be seen in-game.

how about La5, it is also a light plane with out mass enough to perform
a fast dive....why i can not get rid of it in FW till it reachs it's critical speed
limit??

[FC99]

yes, should have been more pronounced
TAIC is "Technical Air Intelligence Center".It was established Washington, D.C. (Anacostia) in 1944, as a joint Army-Navy organization with British participation. To this center was assigned the responsibility of collection, evaluation, and dissemination of all technical intelligence on the Japanese Air Forces.

That's why they tested P-47 and Zero (lot of other planes as well) and 100 yards(~100m ) was the difference between real planes in test. If you think that difference should be bigger than maybe you have to adjust your expectations to match the reality.

[zxwings]

In TAIC test between the Zero and P-47 when they started the dive from 10000ft at 220MPH IAS and dived until Zero reached maximum allowed speed (325MPH IAS). It took 30 seconds for that and the P-47 had 100 yards advantage over Zero.

Disapointing, isn't it? :grin:
Diving vertically down? Or at what angle to the ground?

[JtD]

From the top of my head, 30 degrees.

[SaQSoN]

yes, should have been more pronounced

We all here agree, that real life rarely meets our expectations. Particularly, when someone thinks, he is wa-a-ay much better pilot, then he actually is. :lol:

[BadAim]

I do not agree

1. cut wing and round end wing are different very much from each other
2. power are different, Tempest has 2000 HP while Zero has only 1200 HP.
3. weight for La is around 2000kg when FW is 4000Kg or more

I dont think they can perform in the same way during the diving

The only person I heard talking about the Zero was talking about real pilots flying real aircraft during a real war.

The aircraft that you were talking about were contemporary competing designs which in the big picture had similar overall performance, that was what I was referring to.

Now please go ahead and and continue arguing the same point ad nauseum for our amusement.

[BadAim]

We all here agree, that real life rarely meets our expectations. Particularly, when someone thinks, he is wa-a-ay much better pilot, then he actually is. :lol:

LOL, what he said.....a man's got to know his limitations.

[csThor]

Diving vertically down? Or at what angle to the ground?

[Smart@ss comment] Maybe they measured the distance between the two impact craters. http://usefulshortcuts.com/imgs/skype-basic/emoticon-0136-giggle.gif [/Smart@ss comment]


;)

[jameson]

I've posted this before but for the OP and others who seem to have little idea: The soundtrack is great BTW.

http://www.youtube.com/watch?v=_NWaHlnI_LQ

[mayshine]

Badaim, Saqson

Teasing and joking doesnt help you to improve yourself:-x

I am not here without proof or prepare

why can not you guys sit down and do the reaserch seriously

What u r laughing only shows your ignorance

I am disapointing with your "senior member" title

[mayshine]

u will have to calculate a lot of factors before you can laught at me

shape, zero floating resistance, engine power, weight, propeller type and condition, deformation for the plane at different speed...and so on

Who were laughting at this topic are really simple mind and ignorant

I am here to help to improve IL2, to provide simers the best expierience,
instead of seeing some jokers.

--------------------------

--------------------------------------------------------------------------------

D team member, and who do not want to be the joker

Please check this like for ME262 compare documentation

http://www.wwiiaircraftperformance.o...erman-jets.pdf


and do the test in the Il2 4.11

here is the test in IL2 4.11 for the diving

starting altitude 5000m, throttle 100, stating speed 300km/h,
testing scope : 300 to 700 km/h

the result is below

Bf109G6as： 12s

Me262：11.7s


Isnt it showing something ridiculous?

[mayshine]

D team member, and who do not want to be the joker

Please check this like for ME262 compare documentation

http://www.wwiiaircraftperformance.org/me262/RAE-german-jets.pdf


and do the test in the Il2 4.11

here is the test in IL2 4.11 for the diving

starting altitude 5000m, throttle 100, stating speed 300km/h,
testing scope : 300 to 700 km/h

the result is below

Bf109G6as： 12s

Me262：11.7s


Isnt it showing something ridiculous?

[mayshine]

TAIC is "Technical Air Intelligence Center".It was established Washington, D.C. (Anacostia) in 1944, as a joint Army-Navy organization with British participation. To this center was assigned the responsibility of collection, evaluation, and dissemination of all technical intelligence on the Japanese Air Forces.

That's why they tested P-47 and Zero (lot of other planes as well) and 100 yards(~100m ) was the difference between real planes in test. If you think that difference should be bigger than maybe you have to adjust your expectations to match the reality.

-----------------

please show your link of the documentation or so

Is it a memior or serious testing documentation?

I have docs showing the diving difference between different aircrafts

[mayshine]

From the top of my head, 30 degrees.



in game test we clearly found that the almost verticle diving will cost only

12 seconds from 300km to 700km

what will take "30 seconds to gain 100 yard"

what kind of steep dive will take 30 seconds???

[mayshine]

D team member and Non jokers

the pic below will talk

http://www.wwiiaircraftperformance.org/wade-dive.jpg

http://www.wwiiaircraftperformance.org/wade-data.jpg

[AndyJWest]

the pic below will talk
Not withut (a) telling us where the initial document is from, and (b) telling us what it is supposed to represent.

And what the heck has the second image got to do with dive acceleration rates?

Either find some data from actual tests on real aircraft that proves the Technical Air Intelligence Center results are wrong, or drop the issue. So far, all we have had is speculation and waffle from you.

[mayshine]

Not withut (a) telling us where the initial document is from, and (b) telling us what it is supposed to represent.

And what the heck has the second image got to do with dive acceleration rates?

Either find some data from actual tests on real aircraft that proves the Technical Air Intelligence Center results are wrong, or drop the issue. So far, all we have had is speculation and waffle from you.

The second image is showing the details of the planes only, the first is showing the diving diffrerence, and obviously it is not dive speed limit

you want to improve the Il2 or u want to win some dispute?

I have other souce showing the difference,

you can apply the same question to all source i provide coz it is internet.

if you do want to win a dispute instead of reaserching ,

let me tell you

you WIN!!!


I propose these only because I LOVE IL2


Thats all

[AndyJWest]

Go away, do the research. Provide the evidence, then bring it here. Real evidence. With actual data describing the results from properly defined tests. Not pictures that tell us nothing at all.

Or f*** off and troll somewhere else.

[SaQSoN]

Here's one more real life disappointment for you:
I am disapointing with your "senior member" title
Who cares?

[mayshine]

Go away, do the research. Provide the evidence, then bring it here. Real evidence. With actual data describing the results from properly defined tests. Not pictures that tell us nothing at all.

Or f*** off and troll somewhere else.


Really good, the one who do the reaserch and help to improve

deserves f*** off somwhere

really well, this is the way you treat serious people

Really nice

I found the potential problem, and come to 1c, to D team, to see some
help i can provide or some improvement can be made

I even spend time to serch the net and do the test myself.

now, Instead of being listened and think again and double check

I deserve f*** off

Really nice,

what a real simer

[mayshine]

Here's one more real life disappointment for you:

Who cares?


no problem you dont respect yourself, no one else will

[mayshine]

Go away, do the research. Provide the evidence, then bring it here. Real evidence. With actual data describing the results from properly defined tests. Not pictures that tell us nothing at all.

Or f*** off and troll somewhere else.

I found the potential problem, and come to 1c, to D team, to see some
help i can provide or some improvement can be made

I even spend time to serch the net and do the tests myself

Now, instead of being listened and thinking again and double check

I deserve f*** off

Really nice,

what a real simer

[AndyJWest]

Could some kind moderator please lock this pointless thread, and preferably block the clueless troll?

[mayshine]

Could some kind moderator please lock this pointless thread, and preferably block the clueless troll?


let me see if it will be locked

Let someone reasonable judge if this is point less

The one who raise the personal attack should be BANed indeed

Let me tell you

some other groups/teams now are seriously treating the diving issue

acutually it is not a easy issue to be solved.

it is very very complicated issue may invole IL2 engine defect.

I tell you again, I am not someone who wander around for nothing

I am here coz I lay hope to Dteam and Il2

[mayshine]

Could some kind moderator please lock this pointless thread, and preferably block the clueless troll?


and baning someone for saying something real but not comfortable is the Freedom institution your country so proud of?

you attacked me and u want me baned. woo....

[AndyJWest]

and baning someone for saying something real but not comfortable is the Freedom institution your country so proud of?

you attacked me and u want me baned. woo....

No. Telling clueless trolls to f*** off is what my country is proud of. :-P

[FC99]

-----------------

please show your link of the documentation or so

Is it a memior or serious testing documentation?

I have docs showing the diving difference between different aircrafts

TAIC is very serious, have you read what I wrote about it? Report that deal with A6M5 and P-38,P-51 and P-47 is TAIC report No 38. A6M5 was tested against some Navy planes too,F6F-5, F4U-1D and FM-2. Results are published as TAIC Report No 17.

So far you didn't provided any evidence that would suggest that there is something fundamentally wrong with the game. IIRC Your picture that shows dives is from the post war magazine article.

And you will be hard pressed to find any RL test with planes diving at 90 deg straight into the ground or any 90 deg diving test for that matter, ~45 deg maximum angle during the dive is more typical.

[mayshine]

No. Telling clueless trolls to f*** off is what my country is proud of. :-P

I would like to advice you;

the best way to avoid telling the wrong one to f*** of

is to read more book and start calculation.

[mayshine]

TAIC is very serious, have you read what I wrote about it? Report that deal with A6M5 and P-38,P-51 and P-47 is TAIC report No 38. A6M5 was tested against some Navy planes too,F6F-5, F4U-1D and FM-2. Results are published as TAIC Report No 17.

So far you didn't provided any evidence that would suggest that there is something fundamentally wrong with the game. IIRC Your picture that shows dives is from the post war magazine article.

And you will be hard pressed to find any RL test with planes diving at 90 deg straight into the ground or any 90 deg diving test for that matter, ~45 deg maximum angle during the dive is more typical.

would you please show me the link or so, I am new here

I am not here to attack someone

acctually I will be happy if I am proved wrong coz I will not have to be
plaged by this issue anymore and can fully enjoy the Il2

However, thru my/our calculation, things are different with those shown
in Il2

acutually, I do not believe the 45 degree dive is similar to 90 degree seriously

and this is the the blank point we are trying to figure out.

Fw 190 defence action will always start with a split s followed by a certain period of almost 90 degree dive

so the veticle dive has it's meaning

[mayshine]

letme show you some clue here

with the speed increased, the back-drag force will increase pronouncely
due to 1, deformation , 2, propeller pitch, 3, propeller tip speed,4, air wave darging force.

with this backward force increased largely.

the heavier aircraft should prevail in the diving.

roughly it is the result I got, and I am quite comfident it is meaningful
and to some extence correct.

[AndyJWest]

air wave darging force

rofl!

[mayshine]

rofl!

I am not native speaker, but i am trying to solve something

the point is to express

you'd better continue to wish I am baned

by the way

can you speak Chinese well?

[AndyJWest]

can you speak Chinese well?

No. But you are trying to communicate in English - and failing.

[mayshine]

No. But you are trying to communicate in English - and failing.

sounds u r happy to find this

instead of finding some truth

[JtD]

mayshine, I've recommended you to do this test:Take a Fw 190A-9 and a Spitfire IX 25lb, start at 550 km/h at 1.5km altitude and dive them to a place 15 km away. Check their speeds.Have you done it?

I can also assure you that the issue has been brought up again and again over the years and that il-2 is fairly accurate at typical combat speeds. The limitations will be reached only when you reach very high speeds, where the effects of near sonic flight are not as strong as they are in real life.

[mayshine]

mayshine, I've recommended you to do this test:Have you done it?

I can also assure you that the issue has been brought up again and again over the years and that il-2 is fairly accurate at typical combat speeds. The limitations will be reached only when you reach very high speeds, where the effects of near sonic flight are not as strong as they are in real life.

I fairly know this, I start Il2 by 2004,

of cause spit will lag behind when it is closing to it's limit and start shaking

but

what I want to propose is fast and verticle dive

a intensive speed increasing dive, u sure they will perform in the same way?

obviously 15Km is not a steep dive

[mayshine]

by the way

even one man I knew who knows Oleg and now part of paticipation of the "world of Plane"

he doubt the steep dive in IL2

[JtD]

In terms of physics:

dive acceleration = earth gravitational constant + excess thrust / mass

It is easy to see that as long as excess thrust is larger than zero, mass will reduce the planes acceleration. Excess thrust will be less than zero when the plane is above level speed for that power setting. Also, in typical flying conditions, earth gravitational constant >> excess thrust / mass, so excess thrust / mass doesn't really matter.

If you don't care about physics, at least search for the TAIC test FC99 mentioned, read it, and adjust your expectations. That time would be a lot better spend than making another dozen posts on the issue here.

[mayshine]

In terms of physics:

dive acceleration = earth gravitational constant + excess thrust / mass

It is easy to see that as long as excess thrust is larger than zero, mass will reduce the planes acceleration. Excess thrust will be less than zero when the plane is above level speed for that power setting. Also, in typical flying conditions, earth gravitational constant >> excess thrust / mass, so excess thrust / mass doesn't really matter.

If you don't care about physics, at least search for the TAIC test FC99 mentioned, read it, and adjust your expectations. That time would be a lot better spend than making another dozen posts on the issue here.

Good , finnally I found some one who pose the formular

but I want to correct u in some point

G actually the advantage to heavy planes

see my formular posed previously.

F= ma, a=(m*g - back force)/m

when the backward force become larger and larger

the mass * G will become more and more helpful to speed up the plane.

that means the plane will bigger mass and less back force will be faster

and the back force is complicate,

it is regarded to the strenght of the plane, air wave darg force, pro pitch
propeller tip speed, the shape of the wing, wing load and so on

I dare not to simplify all this in to a univeral A = 8.7m/s as I calculated
previously

Do you still think I do not know physics?

[mayshine]

to make it more obvious

set g=10, m = 10 , back force = 50

first plane mass = 2m
second plane mass = 1m

F=ma

a1: a2
= (2m*g-backforce)/2m : (m*g-backforce)/m
=150/20:50/10
=7.5:5

a1 is 50% faster

[FC99]

So in this extreme case plane have 2,5m/s advantage in acceleration. What will be the difference in distance after 12-13 seconds?

And in the end try with different values for drag for each plane like it is in most real life cases.

[mayshine]

Planes don't fly in vacuum. Your diving physics is missing drag.



I just put everything simply in to the "backforce"

even the air fricition and what so ever are supposed to be within the "back force"

and

if the missing drag u mentioned is the drag force by the engine

JTD have already said Mass*G >> engine thrust or so

"earth gravitational constant >> excess thrust / mass, so excess thrust / mass doesn't really matter."

he is wrong?

[FC99]

prove that,

I just put everything simply in to the "backforce"

even the air fricition and what so ever are supposed to be within the "back force"

and

if the missing drag u mentioned is the drag force by the engine

JTD have already said Mass*G >> engine thrust or so

"earth gravitational constant >> excess thrust / mass, so excess thrust / mass doesn't really matter."

please proof I flew in vacuum

I edited my previous post I wrote first version before you posted the calculation with "backforce". As you can calculate than do the full calculation and show us the results which proves how the game is wrong.

Just out of curiosity, how much difference you expect in dives?

[mayshine]

So in this extreme case plane have 2,5m/s advantage in acceleration. What will be the difference in distance after 12-13 seconds?

And in the end try with different values for drag for each plane like it is in most real life cases.


come on!!!

in this extreme case it is not 2,5m/s advantage

its 50 % speed acceleration advantage

se FW = a1, La = a2
by the time la dive to from 300 to 500km/h , FW will get the speed of 600km/h

enought to do a verticle hammer action.


u know I can feel a lot of people are just defending theirself instead of
looking for truth

[mayshine]

I edited my previous post I wrote first version before you posted the calculation with "backforce". As you can calculate than do the full calculation and show us the results which proves how the game is wrong.

Just out of curiosity, how much difference you expect in dives?

sorry I am not sure, but certainly will be different for current version

please do not be offenced,

you know I just try to........

acutually i am happy to be wrong

However I will try to provide more figures in the coming days

so late here now

[Arrow]

So in this extreme case plane have 2,5m/s advantage in acceleration. What will be the difference in distance after 12-13 seconds?

And in the end try with different values for drag for each plane like it is in most real life cases.

yep, and it is only valid for 90 degree dive. You will have to multiply gravity force (mxg) with sine of the dive angle (assuming zero degrees of AoA) in a very simplified case. In the end, the final effect is marginal as tests show and as it is correctly modeled in Il-2 that has the basic physics 100% right.

[FC99]

come on!!!

in this extreme case it is not 2,5m/s advantage

its 50 % speed acceleration advantage

se FW = a1, La = a2
by the time la dive to from 300 to 500km/h , FW will get the speed of 600km/h

enought to do a verticle hammer action.


u know I can feel a lot of people are just defending theirself instead of
looking for truth

I should be more precise and use m/s^2, I meant acceleration in my post and I still call it just 2,5m/s^2.

Even with this numbers distance between the planes will be less than 200m. Now plug in real numbers for FW and La and do the calculation again. When you include real numbers for mass, drag and thrust difference between La and FW will be very small.

[BadAim]

LOL! You are so funny Mayshine. You tell us we aren't listening, and we don't know what we're talking about, but you have not listened to a bloody word anyone has said here, then you have the unmitigated gall to say that you would be happy to be proven wrong. That's Bull.

You are engaging in mental masturbation, pure and simple.

Have fun.

[BlackBerry]

TAIC is very serious, have you read what I wrote about it? Report that deal with A6M5 and P-38,P-51 and P-47 is TAIC report No 38. A6M5 was tested against some Navy planes too,F6F-5, F4U-1D and FM-2. Results are published as TAIC Report No 17.

So far you didn't provided any evidence that would suggest that there is something fundamentally wrong with the game. IIRC Your picture that shows dives is from the post war magazine article.

And you will be hard pressed to find any RL test with planes diving at 90 deg straight into the ground or any 90 deg diving test for that matter, ~45 deg maximum angle during the dive is more typical.


1)FC99, 30 degree dive is very different from 60 degree dive,leave alone 90 vertival.

http://www.wwiiaircraftperformance.org/japan/zeke52-taic38.pdf

P51D and zeke，@10000ft，begin dive at 200MPH（IAS），after 27s， reach 325IAS ，P51D is 200 yards ahead of zeke。

This test is probably a shallow dive(30 degree), in my opinion, if dive in 45-60 degree, P51D will get much more advantage. So we need more data on 45 degree dive.


2)

http://www.wwiiaircraftperformance.org/sl-wade.html


Efficient streamlining and maximum speed both influence the dive, although a jet propelled aircraft will invariably have the advantage, particularly at the higher speeds, when the conventional fighter is progressively more handicapped by airscrew drag, and the accessory protuberances common to all conventionally powered fighters.

As speed building up, the drag force of airscrew increases sharply because the tip of airscrew is approvching sonic.

Does il2 model this increasing drag of propeller? Does il2 model enginee exhaust gas boost at high speed?

3) http://www.spitfireperformance.com/spit9v109g.html

... I had the throttle open and I rolled over and headed on a course to cut the angle toward the 109s, which had separated a little. I wound on nose-heavy trim so essential to keep the aircraft in a high-speed dive. The Spit responded eagerly as I dove more steeply than the 109s, with Red Two and Three no doubt following, although I could not see them. The controls got very heavy as the airspeed needle moved far right at 480 mph. (Corrected for altitude, true airspeed approached 600 mph.) I could see that I was gaining on the nearest Me 109. That was something new. We were already half-way to Sicily; that was no problem. We knew from years of experience, dating back to the boys who had been in the Battle of Britain, that the 109 with its slim thirty-two foot wing was initially faster in a dive than we were. But we accepted that compromise happily in exchange for our broad superior-lift wing with its better climb and turn. One couldn't have it both ways. In any case, I was closing on this Me 109, which I recognised as a G. Perhaps he wasn't using full throttle.

We were down to 5,000 feet and our dive had become quite shallow. I could see the Sicilian coast a few miles ahead. Now I was within range at 300 yards, and I let him have a good squirt. The first strikes were on the port radiator from which white smoke poured, indicating a glycol coolant leak. I knew I had him before the engine broke out in heavy black smoke. (Bf 109 G-4 "Black 14" of 2(H)/14, flown by Leutnant Friedrich Zander, shot down 10 June 1943)




In il2, Does bf109 outdive spitfire at initial stage of dive?

[JtD]

This test is probably a shallow dive(30 degree), in my opinion, if dive in 45-60 degree, P51D will get much more advantage.Accelerating from 200 to 325 the difference will be mostly the same, if diving for 27 s the difference will be bigger. However, in a steeper dive the limiting speed of 325 IAS will be reached sooner, therefore you'll be diving for less than 27 s, and separation will be smaller.

[BlackBerry]

Accelerating from 200 to 325 the difference will be mostly the same, if diving for 27 s the difference will be bigger. However, in a steeper dive the limiting speed of 325 IAS will be reached sooner, therefore you'll be diving for less than 27 s, and separation will be smaller.

http://www.wwiiaircraftperformance.org/japan/zeke52-taic38.pdf

page 3-4


There is a "zoom"(should be nearly 90 degree upwards) test about P51D and Zeke with same cruising speed and altitude, side by side.


If il2-4.11m perfectly reproduce this "zoom" record, this thread's "boom" discuss can be closed.

[FC99]

1)FC99, 30 degree dive is very different from 60 degree dive,leave alone 90 vertival.

Not really, as JtD already pointed, time is big factor here. If you dive vertically you will reach max allowed speed very fast and you will have not enough time to build big separation. And remember, when we are talking about planes like P-51 or P-47 and A6M5 we are talking about polar opposites of WWII fighter world.

That's basically the biggest difference you can expect and it is still not some huge separation some are wishing for.

Let's go back to mayshine's calculation for a moment.

set g=10, m = 10 , back force = 50

plane mass = 2m
second plane mass = 1m

F=ma

a1: a2
= (2m*g-backforce)/2m : (m*g-backforce)/m
=150/20:50/10
=7.5:5
Now let's put some real numbers for mass. I'll use FW190A5 and La5 values for mass. For now we will assume that drag(backforce) is the same although drag is somewhat higher for FW, I'll use drag = 4000 for both planes in time =0.

Acceleration

FW
(4100*10-4000)/(4100)=9,02

La5

(3300*10-4000)/(3300)=8,79


How much difference you can expect if they started the vertical dive from 2000m to the ground with starting speed = 260 Kmh?


page 3-4


There is a "zoom"(should be nearly 90 degree upwards) test about P51D and Zeke with same cruising speed and altitude, side by side.


If il2-4.11m perfectly reproduce this "zoom" record, this thread's "boom" discuss can be closed.
Zoom is not necessarily 90 deg and in case of WWII fighters 90 deg zooms are mostly useless due to low power/weight ratio.

But again, difference is very small just 300 ft(~100m) from cruise flight up to 500ft after the zoom from dive. Considering that everything under 500m (~1600ft) is shooting distance for most Il2 players it is not enough to just put your plane into dive or zoom and expect that will solve all of your problems.

[Treetop64]

yes, should have been more pronounced

According to what? Your own personal expectations?

[AndyJWest]

So what does this document tell us? "The condition of the Zeke 52 during test was good, so that significant comparative combat results were obtained, but certain airframe discrepancies prevented obtaining maximum speed and climb performance" - or in plain English, the Zeke tested was either underpowered, damaged, or both.

And what else do we learn? That this Zeke was slower in level flight than a P-51D, P-38J and P-47D. No surprise there. That it was more manoeuvrable at low speeds than the US fighters. Again, no surprise. But what do the dive tests tell us? That in the tests conducted, an underpowered/damaged Zeke can't out-accelerate the US fighters starting from 200 IAS or so. Zek vs P-51D, 10,000ft - after 27 seconds, when the Zeke reached 'red line' 325 IAS, the P-51D was 200 yards ahead. Not a lot, and presumably a 'good' Zeke would be doing better. Similar results with the P-38J. The P-47D out-dived this Zeke, but with less of a margin.

As for Blackberry's comments about vertical zooms, that is too ignorant to be worth commenting on.

[mayshine]

FC99 do you know the drag formular?

I am working on it and found some problem in the speed.

I shall propose the result after double check


the formular is

Drag force (air friction to plane itself)

Drag= air drag coefficient*0.5*air density*air speed^2*wing demension

air drag coefficient should be the result from the lab and in Il2 data

can you just use the digit provided in Il2 software data?

coz your team are easier to dig out the date encoded

and see the difference in my simplified model between planes

(m*g-drag)/m

[BlackBerry]

So what does this document tell us? "The condition of the Zeke 52 during test was good, so that significant comparative combat results were obtained, but certain airframe discrepancies prevented obtaining maximum speed and climb performance" - or in plain English, the Zeke tested was either underpowered, damaged, or both.

And what else do we learn? That this Zeke was slower in level flight than a P-51D, P-38J and P-47D. No surprise there. That it was more manoeuvrable at low speeds than the US fighters. Again, no surprise. But what do the dive tests tell us? That in the tests conducted, an underpowered/damaged Zeke can't out-accelerate the US fighters starting from 200 IAS or so. Zek vs P-51D, 10,000ft - after 27 seconds, when the Zeke reached 'red line' 325 IAS, the P-51D was 200 yards ahead. Not a lot, and presumably a 'good' Zeke would be doing better. Similar results with the P-38J. The P-47D out-dived this Zeke, but with less of a margin.

As for Blackberry's comments about vertical zooms, that is too ignorant to be worth commenting on.

Good comment.zeke was lightly damaged.

BTW,the weight of a/c plays important role in a dive, the steeper the diving is, the more dive accelaration for heavier a/c.

In a steep dive, p47D may outdives p51d a liitle although p47's has less margin in a shallow dive than p51d over zeke.

[BlackBerry]

Not really, as JtD already pointed, time is big factor here. If you dive vertically you will reach max allowed speed very fast and you will have not enough time to build big separation. And remember, when we are talking about planes like P-51 or P-47 and A6M5 we are talking about polar opposites of WWII fighter world.

That's basically the biggest difference you can expect and it is still not some huge separation some are wishing for.

Let's go back to mayshine's calculation for a moment.

Now let's put some real numbers for mass. I'll use FW190A5 and La5 values for mass. For now we will assume that drag(backforce) is the same although drag is somewhat higher for FW, I'll use drag = 4000 for both planes in time =0.

How much difference you can expect if they started the vertical dive from 2000m to the ground with starting speed = 260 Kmh?


Zoom is not necessarily 90 deg and in case of WWII fighters 90 deg zooms are mostly useless due to low power/weight ratio.

But again, difference is very small just 300 ft(~100m) from cruise flight up to 500ft after the zoom from dive. Considering that everything under 500m (~1600ft) is shooting distance for most Il2 players it is not enough to just put your plane into dive or zoom and expect that will solve all of your problems.



Backforce increases sharply as speed build up. The heavier a/c is, the more ability of retaining high speed which is above a/c's maximum level speed.


In P51-zeke's test, they just did a shallow dive and then zoomed up. The zoom's beginning speed must be lower than 325PMH IAS.


At first, they zoomed up from cruising speed,that was 210MPH IAS=250MPH TAS, when P51d reach 130MPH=150MPH TAS, zeke was 90m lower. So how much kinetic energy was spent to get altitude?

0.5(250^2-150^2)= 20000

If they begin from 325MPH IAS=389MPH TAS

0.5(389^2-150^2)= 64410

We assume that there is a linear relationship between "kinetic energy" and P51D's zoom advantge to "damaged" zeke52.

So this time, p51d should be 3.22*90=290metres higher.


That is to say, when p51d @325MPH IAS@10000ft, and find a (lightly damaged) zeke on his 6 with same altitude and speed. And the distant between them are 450 metres. P51D may try a zoom, and will probably (450+290)=740m higher than zeke when p51d's speed drops to130 MPH IAS.

Surely 740m is enough for avioding being hit by zeke's cannon.

Forthermore, let's assume zeke could bear 450 IAS@10000ft, if they zoom from 450MPH IAS=539MPH TAS

0.5(539^2-150^2)= 134010=6.7 times of so called small "90m",that is 603 metres higher.

Surprising？Somebody will say zeke was underpowered and lightly damaged， I admit it， however， our caculating basis is on medium-low speed data, merely 210MPH to 130MPH IAS, it seems that p51d's zoom advantage will be more remarkable in high speed zooming, given by same amount of kinetic energy consumed.

Perhaps, p51d will gain sth.300meters advantage over 109 by starting a high speed (450MPH IAS)zoom, who knows? You can not simply deny that possibility.

[FC99]

FC99 do you know the drag formular?

I am working on it and found some problem in the speed.

I shall propose the result after double check


the formular is

Drag force (air friction to plane itself)

Drag= air drag coefficient*0.5*air density*air speed^2*wing demension

air drag coefficient should be the result from the lab and in Il2 data

can you just use the digit provided in Il2 software data?

coz your team are easier to dig out the date encoded

and see the difference in my simplified model between planes

(m*g-drag)/m

FWA5 0,0236
La5 0,025

Why don't you just work backwards and calculate how much different planes should be for separation after dive to meet your expectations.
BTW how big the difference should be in your opinion after 2000m vertical dive?

The heavier a/c is, the more ability of retaining high speed which is above a/c's maximum level speed.
If everything else is equal.


In P51-zeke's test, they just did a shallow dive and then zoomed up. The zoom's beginning speed must be lower than 325PMH IAS.


At first, they zoomed up from cruising speed,that was 210MPH IAS=250MPH TAS, when P51d reach 130MPH=150MPH TAS, zeke was 90m lower. So how much kinetic energy was spent to get altitude?

0.5(250^2-150^2)= 20000

If they begin from 325MPH IAS=389MPH TAS

0.5(389^2-150^2)= 64410

We assume that there is a linear relationship between "kinetic energy" and P51D's zoom advantge to "damaged" zeke52.

So this time, p51d should be 3.22*90=290metres higher.


That is to say, when p51d @325MPH IAS@10000ft, and find a (lightly damaged) zeke on his 6 with same altitude and speed. And the distant between them are 450 metres. P51D may try a zoom, and will probably (450+290)=740m higher than zeke when p51d's speed drops to130 MPH IAS.

Surely 740m is enough for avioding being hit by zeke's cannon.
Distance between them will not be converted into altitude and if P-51 zoom at 90deg up as you suggested previously A6M5 will just cut the corner, use more energy efficient maneuver , close the distance to P-51 and in the end it will have nice fat P-51 close and slow right in its gunsight.

Happens online all the time.



Perhaps, p51d will gain sth.300meters advantage over 109 by starting a high speed (450MPH IAS)zoom, who knows? You can not simply deny that possibility.Maybe, maybe not. Anyway, question is not about couple hundreds meters, it's obvious that some expects lot more than that. When you are slow on top of the zoom and enemy is 300 m behind you you are dead meat, more often than not and when that happens, it's not the problem with the game physics, it's pilot's error, as simple as that.

[K_Freddie]

It has been known for years that the game accelleration rates are not that accurate. I think the documents from which the games rates are taken are from shallow test dives (as mentioned) so cannot really be extrapolated to 90 degree dives.

In this situation, there probably should be large initial differences due to weight, power and friction, as this was guaranteed escape tactic for the FW, P47 and others, against the lighter aircraft. Maybe TD can tweak the FM's in this area.
:)

[FC99]

It has been known for years that the game accelleration rates are not that accurate. I think the documents from which the games rates are taken are from shallow test dives (as mentioned) so cannot really be extrapolated to 90 degree dives.


Acceleration rate in dive is product of thrust, gravity and drag. Same equations are used no matter the plane attitude. Gravity is the same in the game no matter what the plane is doing. Thrust and drag are inside reasonable margins under level flights and climbs so there is no reason to believe that they are wrong during dive, especially during the initial phase.


Maybe TD can tweak the FM's in this area.
:)
We could but we prefer to have FM as realistic as possible.

[K_Freddie]

The final test would be P47-vs-something else.

We all know that the p47 'dropped like a brick'... if this doesn't happen in comparison to other a/c... we quiet simply have a FM problem .. period!
;)

This is a valid, if not 'niche' point brought up by mayshine.. whether anybody likes it or not, is irrelevant.
and..
Yes Yes.. we've done the aeronautics and formulae ad-nauseum ;)

[K_Freddie]

Thrust and drag are inside reasonable margins under level flights and climbs so there is no reason to believe that they are wrong during dive, especially during the initial phase.

Interesting.... and you actually believe this statement to be the 'absolute truth'

It is time to rethink FM policy... :)

[AndyJWest]

It is time to rethink FM policy...

Based on guesswork, or data?

[JtD]

We all know that the p47 'dropped like a brick'...
Actually, it's not "we all know", but "some think". I know that it dropped faster than a brick, and it does in game. A brick neither produces the thrust a P-47 produces, nor is it anywhere near as aerodynamic. However, this applies to about all WW2 fighter aircraft.

Anyway, you are more than welcome to do the research, dig up a few tests and take it from there.

[BlackBerry]

Acceleration rate in dive is product of thrust, gravity and drag. Same equations are used no matter the plane attitude. Gravity is the same in the game no matter what the plane is doing. Thrust and drag are inside reasonable margins under level flights and climbs so there is no reason to believe that they are wrong during dive, especially during the initial phase.



We could but we prefer to have FM as realistic as possible.

especially during the initial phase.............

I have a question, does bf109g6as outdive spitfire IX or fw190A8 during the initial phase in 4.11m?

[BlackBerry]

Bf-109-G2
[Mass] kg
Empty 2320.0
TakeOff 2830.0

[Squares] m^2
Wing 16.16
Aileron 1.02
Flap 2.00
Stabilizer 1.90
Elevator 1.20
Keel 0.70
Rudder 1.10

[Polares]
lineCyCoeff 0.094
Cy0_0 0.15.............................................. .
AOACritH_0 21.0............................................
AOACritL_0 -16.0...........................................
CyCritH_0 1.48.............................................. .
CyCritL_0 -1.0230048.....................................
CxMin_0 0.027............................................. ..
parabCxCoeff_0 6.7E-4....................................

Spitfire.LF.IXC
[Mass]
Empty 2650.0
TakeOff 3300.0

[Squares]
Wing 19.0
Aileron 1.32
Flap 2.125
Stabilizer 1.90
Elevator 1.20
Keel 0.85
Rudder 1.10

[Polares]
lineCyCoeff 0.092
AOAMinCx_Shift 0.0
Cy0_0 0.1
AOACritH_0 16.0
AOACritL_0 -17.0
CyCritH_0 1.4
CyCritL_0 -0.7
CxMin_0 0.0232
parabCxCoeff_0 5.4E-4


P-47D-27
[Mass]
Empty 4630.0
TakeOff 6583.0

[Squares]
Wing 25.87
Aileron 1.45
Flap 2.76
Stabilizer 3.50
Elevator 2.05
Keel 1.30
Rudder 1.10

[Polares]
lineCyCoeff 0.092
AOAMinCx_Shift 0.9
Cy0_0 0.17
AOACritH_0 16.0
AOACritL_0 -15.0
CyCritH_0 1.25
CyCritL_0 -0.8
CxMin_0 0.0256
parabCxCoeff_0 4.8E-4


Bf-109G-2 = 0.027 * 16.16 = 0.43632
Spitfire.LF.IXC = 0.0232 * 19.0 = 0.4408
P-47D-27 = 0.0256 * 25.87 = 0.662272


Bf-109G-2
0.43632/2830 = 1.5417667844522968197879858657244e-4

Spitfire.LF.IXC
0.4408/3300 = 1.3357575757575757575757575757576e-4

P-47D-27
0.662272/6583 = 1.0060337232264924806319307306699e-4

[Crumpp]

JtD says:

Because in game, g applies the same to all aircraft. Just like in real life.


Tell me you don't touch any of the flight models.....

Excess thrust......not the same!

:rolleyes:

[FC99]

The final test would be P47-vs-something else.

We all know that the p47 'dropped like a brick'... if this doesn't happen in comparison to other a/c... we quiet simply have a FM problem .. period!
;)

This is a valid, if not 'niche' point brought up by mayshine.. whether anybody likes it or not, is irrelevant.
and..
Yes Yes.. we've done the aeronautics and formulae ad-nauseum ;)
Mayshine's question has been answered, dive acceleration difference exist in game already.

And P-47 falls like the brick in comparison with most other aircrafts.


I have a question, does bf109g6as outdive spitfire IX or fw190A8 during the initial phase in 4.11m?
Depending on initial conditions and your definition of "initial phase" that's probably possible.

FM data you posted for several planes looks like 4.11 data.


Because in game, g applies the same to all aircraft. Just like in real life.Tell me you don't touch any of the flight models.....

Excess thrust......not the same!

:rolleyes:

And JtD is wrong in what exactly? AFAIK F=mg, g is a constant and is the same for every object in game.

[Crumpp]

And JtD is wrong in what exactly? AFAIK F=mg, g is a constant and is the same for every object in game.


Of course it is Fatcat. This is not the issue and completely irrelevant as to why your FM's would not exhibit any differences in dive acceleration. It does not answer the original poster's question.

Take the force triangle for a dive. A component of weight contributes to thrust based on the angle of dive. The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....

Then apply the same formula...

Force = Mass x Acceleration

Rearrange it to solve for Acceleration: The acceleration of gravity is considered constant but acceleration is not constant.

Acceleration = Force/Mass

You then have the aircrafts acceleration rate to the equilibrium point.

Now I am not a computer programmer but I am sure there is a way to look at the code to see if it following those principles.

[JtD]

It does not answer the original poster's question.

But it does. The original poster asked in the topics title why there are no dive acceleration differences. There aren't because gravity is the same for all planes. As soon as you consider anything else, the dive accelerations are different. Had he asked why all the dive accelerations are different, the question would have required a much more complex answer.
The answer was specifically given to the question asked.

[Crumpp]

The amount of excess thrust determines an aircraft dive acceleration.

The acceleration of gravity is constant but that excess thrust is not constant. It is a characteristic of the design and each aircraft will have a different acceleration in a dive.

[K_Freddie]

Probably something to do with engine type/power and propellor type... Just guessing as I know sweet ....all, you know ;)

[Whacker]

But it does. The original poster asked in the topics title why there are no dive acceleration differences. There aren't because gravity is the same for all planes. As soon as you consider anything else, the dive accelerations are different. Had he asked why all the dive accelerations are different, the question would have required a much more complex answer.
The answer was specifically given to the question asked.

Dive acceleration is not solely a function of gravity.

One must also account for frictional coefficients and powerplant thrust as they relate to the specific "dive" profile being discussed, as well as each individual aircraft's operational guidelines and parameters. It's not a simple answer by any means.

If anyone has a direct link to that TAIC study report, please post it, I'd be very interested to read it.

[Crumpp]

http://img338.imageshack.us/img338/3665/p47fw190.jpg (http://imageshack.us/photo/my-images/338/p47fw190.jpg/)

http://img571.imageshack.us/img571/2213/p47fw1902.jpg (http://imageshack.us/photo/my-images/571/p47fw1902.jpg/)

http://img155.imageshack.us/img155/806/p47fw1903.jpg (http://imageshack.us/photo/my-images/155/p47fw1903.jpg/)

http://img805.imageshack.us/img805/6062/p47fw1904.jpg (http://imageshack.us/photo/my-images/805/p47fw1904.jpg/)

as well as each individual aircraft's operational guidelines and parameters.

Excellent point.

[JtD]

Dive acceleration is not solely a function of gravity...I know. So once more: If someone asks why dive accelerations are the _same_, he doesn't want to know about thrust, drag and whatnotelse. Because these are reasons for _different_ dive accelerations.

[FC99]

Of course it is Fatcat. This is not the issue and completely irrelevant as to why your FM's would not exhibit any differences in dive acceleration. It does not answer the original poster's question.
Who says that there is no difference in dive acceleration. Whole premises in initial question is wrong. There is a difference in dive acceleration.


Take the force triangle for a dive. A component of weight contributes to thrust based on the angle of dive. The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....
You are missing the point here, people want dive acceleration "fixed" as there is some magical switch that is turned on when plane start to dive but there is no such thing. All you have are Thrust, Lift,Drag and Weight acting on a plane no matter what's the plane attitude.

If you change something you will change plane behavior in all flight regimes not only in dive. If you have plane behavior modeled reasonably well in level flight and climb than there is no reason to believe that dive behavior is wrong.

Where game has its problems are extreme parts of flight envelope but that's not what the thread starter asked.


BTW Long ago I made tests and posted it on CWOS but it's lost now. But anybody can repeat it.It's simple.

1. Start the plane at alt above the initial testing point. Use no cockpit view to get TAS and stabilize the plane at desired TAS.

2. Keep the TAS constant and measure the time required to pass from the start altitude to end altitude.

3. Repeat for all planes you want to test, try it with no power and full power.

4. Compare the results.


As the test measure the time required to get from StartAlt to EndAlt it also measure the distance traveled. Test requirement is that TAS is kept constant so difference in time from let's say 4000m to 2000m will mean that planes passed different distances which in turn means that their diving angle was different.

Plane that needed longest to get to EndAlt is the best diving among the tested planes because it needed smallest help from gravity to keep its speed. Consequently it will dive fastest in a dive that is performed at same diving angle.

[BlackBerry]

Who says that there is no difference in dive acceleration. Whole premises in initial question is wrong. There is a difference in dive acceleration.

You are missing the point here, people want dive acceleration "fixed" as there is some magical switch that is turned on when plane start to dive but there is no such thing. All you have are Thrust, Lift,Drag and Weight acting on a plane no matter what's the plane attitude.

If you change something you will change plane behavior in all flight regimes not only in dive. If you have plane behavior modeled reasonably well in level flight and climb than there is no reason to believe that dive behavior is wrong.

Where game has its problems are extreme parts of flight envelope but that's not what the thread starter asked.


BTW Long ago I made tests and posted it on CWOS but it's lost now. But anybody can repeat it.It's simple.

1. Start the plane at alt above the initial testing point. Use no cockpit view to get TAS and stabilize the plane at desired TAS.

2. Keep the TAS constant and measure the time required to pass from the start altitude to end altitude.

3. Repeat for all planes you want to test, try it with no power and full power.

4. Compare the results.


As the test measure the time required to get from StartAlt to EndAlt it also measure the distance traveled. Test requirement is that TAS is kept constant so difference in time from let's say 4000m to 2000m will mean that planes passed different distances which in turn means that their diving angle was different.

Plane that needed longest to get to EndAlt is the best diving among the tested planes because it needed smallest help from gravity to keep its speed. Consequently it will dive fastest in a dive that is performed at same diving angle.

I tried：4.11m Tempest mkv vs p51c engine overheat off, radiator closed

From 3000m altitude to 2000m, keeping speed=700TAS

2minutes and 2 second for tempest mkv
2minute and 30 second for p51c

So, p51c outdives tempest? No. Tempest mkv definitely outdives p51c!

BTW, this kind of "dive" is very shallow, smaller than 10 degree.

[BlackBerry]

When P51 dives to 4500 m=15000ft altitude, and reaches 640km/h=400 mph IAS, that is 1.25*640=800 km/h=222m/s TAS, the mach number is equal to 222/322=0.69. That's fuselage speed.

However, the speed of tip of airscrew is far more 0.69 mach.

4-blade hamilton airscrew,10.5 feet diametre, the reduction ratio of airscrew rotating to engine is 0.477. 3000rpm engine, 1431rpm=23.85r/s airscrew, the rotating speed of tip is：3.14*10.5*0.303*23.85=238m/s

So the combination speed is: (238^2+222^2)^0.5=325 m/s.

Unfotunatly, sonic speed at 4500m altitude is 322m/s, that is to say, the tip of airscew is 1 mach. There is no mach number "concept" in il2's model at all, how can I believe that il2 simulates 1 Mach aerodynamics very well?

http://en.wikipedia.org/wiki/Indicated_airspeed

In aneroid instruments the indicated airspeed drops-off with increasing altitude as air density decreases. This leads to an apparent falling-off of airspeed at higher altitudes. For this and other reasons never exceed speeds (abbreviated VNE) are often given at several differing altitudes in some aircraft's operating manuals, the VNE IAS figure falling as height is increased, as shown in the sample table below.
Diving below mph IAS
30,000*ft 370
25,000*ft 410
20,000*ft 450
15,000*ft 490
10,000*ft 540

Ref: Pilot's Notes for Tempest V Sabre IIA Engine - Air Ministry A.P.2458C-PN


Tempest could dive to 450 mph IAS below 20000ft, aha, tempest's big rotol 14-ft airscrew, 3800rpm, 450mph IAS, the tip of rotol must be supersonic, so is P51's hamilton, thus the efficiency curves of their airscrews play an important role when they dive to high speed.

Why tempest outdives p51? For more efficiency airscew @ supersonic? Maybe. For much more heavier fuselage? Probably.

All in all, il2's model is lack of supersonic simulation, that's why we couldn't experience what tempest/p51 should be. That's why tempest couldn't outdive dora easily in game.

[FC99]

When P51 dives to 4500 m=15000ft altitude, and reaches 640km/h=400 mph IAS,
Why 400mph IAS ? Why not any other number?

Unfotunatly, sonic speed at 4500m altitude is 322m/s, that is to say, the tip of airscew is 1 mach. There is no mach number "concept" in il2's model at all, how can I believe that il2 simulates 1 Mach aerodynamics very well?Prop planes can't break sonic barrier so it's not that important for Il2 to have highly detailed Mach model.


Tempest could dive to 450 mph IAS below 20000ft, aha, tempest's big rotol 14-ft airscrew, 3800rpm, 450mph IAS, the tip of rotol must be supersonic, so is P51's hamilton, thus the efficiency curves of their airscrews play an important role when they dive to high speed.
Yes it does.

Why tempest outdives p51? For more efficiency airscew @ supersonic? Maybe. For much more heavier fuselage? Probably.
It does? Maybe, depends which models you take for comparison .

All in all, il2's model is lack of supersonic simulation, that's why we couldn't experience what tempest/p51 should be. That's why tempest couldn't outdive dora easily in game.
It should out dive Dora easily, why ?

[BlackBerry]

Why 400mph IAS ? Why not any other number?

It's very common to dive to 400-450MPH IAS for WWII late aircrafts such as P51, P47,Tempest, fw190, etc.


Prop planes can't break sonic barrier so it's not that important for Il2 to have highly detailed Mach model.

Prop planes can't break sonic barrier, but Prop planes' propeller CAN often break sonic barrier in a dive, it's an unfortunate fact for il2.

As early as 1904 when Wright brothers made the first a/c, they knew both airscrew and wing are "same thing".

The twisted airfoil (aerofoil) shape of modern aircraft propellers was pioneered by the Wright brothers. They realised that a propeller is essentially the same as a wing, and were able to use data from their earlier wind tunnel experiments on wings. They also realised that the angle of attack of the blades needed to vary along the length of the blade, thus it was necessary to introduce a twist along the length of the blades. Their original propeller blades were only about 5% less efficient than the modern equivalent, some 100 years later.[2]

http://en.wikipedia.org/wiki/Propeller_(aircraft)




Their original propeller blades were only about 5% less efficient than the modern equivalent, some 100 years later.........


That conclusion is based on low Mach data, for supersonic airscrew, the story is totally diefferent.


In my opinion, the airscrew theory/simulation is the weakness of il2's FM.

It does? Maybe, depends which models you take for comparison .

Tempest MKV 9lbs boost outdives P51B(Mustang III) 18lbs boost.

Dive
For the same reasons as the zoom climb, the Tempest pulls ahead. As the speed is increased it does so more rapidly. The fact is it has the best acceleration in the dive yet seen at this Unit.

http://www.hawkertempest.se/TacticalTrials.htm


Speed and acceleration in the dive is an essential quality to a successful fighter, but a decisive conclusion on the order of superiority is largely dependant on throttle settings, and the maximum speed in straight and level flight of the individual aircraft. Here again, however, by carrying out a number of tests under different conditions, it is reasonable to assume that the Meteor is well ahead of its rivals, followed by the Tempest, Thunderbolt, Mustang and Spitfire in that order.

http://www.wwiiaircraftperformance.org/sl-wade.html

[MadBlaster]

if you simply want to test 'drag' without digging into the code, I think it better to do it with the engine off (i.e., no thrust test).

- go into fmb and set your spawn kph to zero and start a track in cockpit view.

- spawn your plane say 5000 meters and leave the engine off.

- close your rads, neutral your trims, set you prop pitch to 100%.

-push nose into 90 degree vertical.

-end the track when your plane hits the beach at zero alt.

-go back and look at track. look at speedometer at say 20 second mark per track time. (e.g., speed says 400 kph at 20 seconds for this plane)

-repeat with another plane and compare results.

- For the thrust piece, you can use devicelink to get an idea. There is an acceleration parameter that can be graphed/logged. You can see the effect of adjusting throttle and prop pitch. Prop pitch changes and its effect on acceleration is modeled. The csp may be slower to change blade angle than the vdms. At least, that's how it feels like to me. The fw vdm has a torque limiter. I think p factor is also modeled. You can produce de-celeration by adjusting blade angle, according to devicelink.

[BlackBerry]

Crumpp, your very good information.

Especially this one, P47d4 vs fw190a5? a6?

I bet that il2 4.11m can't simulate this.

9504
(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

There are some interesting records:

1) bf109g6as initially outdives spitfire IX LF, but spitfire overtakes 109 as speed building up.

2)fw190a5 initially outdives p47d, but p47d overtakes fw190a5 as speed building up.

3)Tempest and 109G's initial dive acceleration are roughly same, but Tempest outdives 109G easily as speed building up.


When speed building up, what happens to P47/P51/Tempest? There airscrew tips reach/break sonic barrier??? howabout 109/190's airscrew?

If Daidalos Team solve this "supersonic" issue, we''ll appreciate that.

[MadBlaster]

Doesn't changing the blade angle keep the prop from going sonic in a dive?

[BlackBerry]

Doesn't changing the blade angle keep the prop from going sonic in a dive?

That doesn't make sense because airscrew tip's speed is irrelevant to blade angle.

Airscrew aerodynamics is quite complex, one need to read a whole book to master that.

[MadBlaster]

I'm not an engineer or a pilot. I understand that tip speed means velocity at the tip of the prop and it's faster at the tip then near the center. Theres some formula that describes rotational velocity.

my point is when they built these planes, I imagine the didn't want the tip to be breaking the sound barrier all the time, so they put governors on the engines and design the props to keep it from doing that. if your in a dive and ram air is pushing your prop to rpm limits, I'm pretty sure the operators manual is going to tell you that isn't so good and you need to change the pitch angle and slow the rpms/reduce the tip speeds or something might break or do damage when you get near your never exceed speeds.

Going back to your tempest example, will the pilot not try to do something to mitigate the effects of sonic tip speeds? Or simply, the prop design specs try to engineer that out of the equation as much as possible? It seems in your analysis, you assume not, that it is simply a function of prop length, max rpms of the engine and forward velocity. I just don't know if that is realistic. To me, it seems that tips speed breaking the sound barrier would be a rare event. So, not sure why it needs detailed modeling.

But then again, I only learn aviation stuff from playing this game.;)


Edit:

Relates to what I was thinking about. http://en.wikipedia.org/wiki/Scimitar_propeller

This can be controlled to some degree by adding more blades to the prop, absorbing more power at a lower rotational speed. This is why some WWII fighters started with two-blade props and were using five-blade designs by the end of the war. The only downside to this approach is that adding blades makes the propeller harder to balance and maintain. At some point, though, the forward speed of the plane combined with the rotational speed of the propeller will once again result in wave drag problems. For most aircraft, this will occur at speeds over about 450 mph.

A method of decreasing wave drag was discovered by German researchers in WWII: sweeping the wing backward. Today, almost all aircraft designed to fly much above 450 mph (700 km/h) use a swept wing. In the 1940s, NACA started researching propellers with similar sweep. Since the inside of the prop is moving more slowly than the outside, the blade becomes progressively more swept toward the outside, leading to a curved shape similar to that of a scimitar.

[JtD]

BlackBerry, I think what you're saying about Tempest vs. P-51C is about right, even if your sources are vague and not always the right ones (you're quoting a comparison between Tempest and Typhoon, for instance). A direct test between the P-51C and the Tempest V revealed that the "Tempest tends to pull away" - which is a marginal advantage for the Tempest. You've tested a marginal advantage for the P-51.
Given the average accuracy of the flight models, which was aiming at a 5%, this is something that simply may happen between individual planes, it is no indication that the general algorithm is wrong.
Mach effects are modelled, not extensive enough for accurate high speed performance imho, but they are there.
The differences in initial acceleration between individual planes is there, if you fly them properly. Some of the acceleration differences you see as simple statements "this one is better" has a lot to do with engine management. If say an Fw 190 and a P-47 cruise side by side and then go into a full power dive, the guy in the 190 slams the throttle forward and off he goes, while the guy in the P-47 adjusts mixture, then rpm and then the throttle and then starts to accelerate. Gives the 190 a two second head start. But even without considering this, if you compare a 190A-4FR with a P-47D-22 at medium altitude in 4.11, you'll be getting something similar to the test you quoted.

[BlackBerry]

BlackBerry, I think what you're saying about Tempest vs. P-51C is about right, even if your sources are vague and not always the right ones (you're quoting a comparison between Tempest and Typhoon, for instance). A direct test between the P-51C and the Tempest V revealed that the "Tempest tends to pull away" - which is a marginal advantage for the Tempest. You've tested a marginal advantage for the P-51.
Given the average accuracy of the flight models, which was aiming at a 5%, this is something that simply may happen between individual planes, it is no indication that the general algorithm is wrong.
Mach effects are modelled, not extensive enough for accurate high speed performance imho, but they are there.
The differences in initial acceleration between individual planes is there, if you fly them properly. Some of the acceleration differences you see as simple statements "this one is better" has a lot to do with engine management. If say an Fw 190 and a P-47 cruise side by side and then go into a full power dive, the guy in the 190 slams the throttle forward and off he goes, while the guy in the P-47 adjusts mixture, then rpm and then the throttle and then starts to accelerate. Gives the 190 a two second head start. But even without considering this, if you compare a 190A-4FR with a P-47D-22 at medium altitude in 4.11, you'll be getting something similar to the test you quoted.


JTD, I'll make clear that I am not saying the il2 FM is wrong, on the contrary, I believe il2 is the best simulation of WII a/c, especially 4.11m has achieved "structute failure" at high G manoeuver. Well done Daidalos Team! And many of us just hope il2 go further to become PERFECT.


In il2 FM, the wing drag coeffiecent is a constant, since most a/c fly below 0.8 Mach, the result is very accurate. However, there is small flaw in high speed diving. See picture below:

9519
Even the best prop diver---Tempest MKV can hardly reach 0.8 Mach in diving----maximum permissible airspeeds 540m.p.h. IAS below 10000 ft, but the airsrew==a twisted and rotating "wing" could exceed 0.8 Mach with its "tip" in a high speed dive.

As long as we could simulate "the balance of propeller power", il2 will be nearly perfect. Don't forget those exhaust tubes just behind airscrew! Exhaust boost!

9515

In WWII, US had NACA-16 series airfoil(eg. 4-blade Hamilton), UK had ARA-D airfoil, German had Gottingen airfoil.

I just suspect that those engineers of Hamilton or Rotol intently designed very big 4-blade airscrews in order to optimise high mach performance at high speed.


P51D----Hamilton Standard, four-blade, hydraulic, constant speed, 11 feet 2 inches, non-feathering

Bf109----The propeller is a V.D.M.9 - 12087. Three bladed metal constant-speed with electric pitch change, hand controlled or automatic. Diam. 9' 10" Max. blade width 11 5/8".

Tempest MKV----All versions of the Sabre drove four-bladed, 14 ft (4.267 m) diameter de Havilland Hydromatic or Rotol propellers.

Fw190A9----Three types of propeller were authorised for use on the A-9: the VDM 9-112176A wooden propeller, 3.5 m (11 ft 6 in) in diameter, was the preferred option, however, many A-9s were fitted with the standard VDM 9-12067A metal propeller and some had a VDM 9-12153A metal propeller with external, bolt on balance weights.

P47D----The P-47D-16, D-20, D-22 and D-23 were similar to the P-47D-15 with minor improvements in the fuel system, engine subsystems, a jettisonable canopy, and a bulletproof windshield. Beginning with the block 22 aircraft, the original narrow-chorded Curtiss propeller was replaced by propellers with larger blades, the Evansville plant switching to a new Curtiss propeller with a diameter of 13 ft (3.96 m) and the Long Island plant using a Hamilton Standard propeller with a diameter of 13 ft 2 in (4.01 m). With the bigger propellers having barely 6 in (152 mm) of ground clearance, Thunderbolt pilots had to learn to be careful on takeoffs to keep the tail down until they obtained adequate ground clearance, and on landings to flare the aircraft properly.

Last but not least, I believe the high-speed dive and zoom advantage of P51P47Tempest is their most important tactic in combat, and is the most amazing aspect of their flight characters.

If they can outzoom from high-speed against opponent for 300 metres higher; if they can outdive rival for more kinetic energy(sth. equals to 300 metres Potential Energy ). What will happen?

As we all known, Bf109s are very good at climbing(low speed,max climb), usually, in low-medium altitude, Bf109 has 1000ft/minute climbing advantage to their opponents.

Bf109's Energy fight: When finding enemy at rear, same energy, 700-800m away , 109 will probably climb, after 2 minutes(Be patient! Be careful about the 3rd one!), 109 will establish 600 meters higher advantage over the opponent who follows the 109. And then, 109 will fight back by using this 600 meters "extra" energy. This kind of story takes place again and again and again in most il2 servers.

P51P47Tempest could also "E-fight" in different style: diving and zooming. If a P51 find a 109 at rear, same energy, 700-800m away, P51 can dive to 650km/h IAS ( by split S), if 109 follows, he will find P51 is gaining on him, that is, P51 is quite faster than him, and the distant between them has been enlarged to 1000 m, and then, P51 will zoom at 60 degree (Be patient! Be careful about the 3rd one!), of course 109 will cut the coner, but P51 has zoom advantage so that 109 could not get close to shooting range during zooming period. Roughly P51 will find himself 600 m higher than 109, and this is the time to fight back.


1v1 is quite funny, teamwork of E-fighting will be more attractive, believe it or not. If you have some advantage, be good at using it, don't waste it, don't spoil it, be patient.

[JtD]

"the balance of propeller power"Which is already modelled including Mach effects. Like I said, some aspects are there. This is one.

[Crumpp]

When speed building up, what happens to P47/P51/Tempest? There airscrew tips reach/break sonic barrier??? howabout 109/190's airscrew?


IIRC, the FW-190 tested is a G series by WerkNummer.

The maximum helical tip velocity is extremely important to any propeller design. At about mach .85 most propellers will begin to dramatically decrease efficiency as the normal shock formation disrupts flow. Yes, they break the sound barrier.

You can see the effect in any fast aircraft equipped with a CSP and the ability to over speed the propeller. Climb to about 12,500 feet, preferably on a hot summer day and set the aircraft for 75% cruise. If you increase to maximum rpm and manifold pressure, you will see a drop in your airspeed.

Maybe one could simulate the effect just by decreasing propeller efficiency sharply at Mach .85.

As you stated, propellers are extremely complicated and there are lots of trade-offs in design. For example, adding blades does increase the co-efficient of power but adding blades decreases propeller efficiency. The materials one chooses also has a large effect on propeller design. Metal blades have good power absorption but are fatigue limited. The primary reason for a metal propeller is cheap production and erosion resistance. Metal propellers have excellent erosion resistance so they be flown in the rain. Wooden blades have even better power absorption and unlimited fatigue life. Wooden blades can delaminate in the rain and require some sort of protection in order not to erode. The German wooden propellers were wrapped in metal mesh, fabric covered, and covered with a thick resin.

In the event of a prop strike, metal transferred more force to the engine resulting in more damage. Wooden propellers tend to act like a circuit breaker and disintegrate transferring less force to the engine. It is cheaper to replace a propeller than an engine.

[BlackBerry]

Let's discuss this record.

(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.


Jtd's explanation:
The differences in initial acceleration between individual planes is there, if you fly them properly. Some of the acceleration differences you see as simple statements "this one is better" has a lot to do with engine management. If say an Fw 190 and a P-47 cruise side by side and then go into a full power dive, the guy in the 190 slams the throttle forward and off he goes, while the guy in the P-47 adjusts mixture, then rpm and then the throttle and then starts to accelerate. Gives the 190 a two second head start. But even without considering this, if you compare a 190A-4FR with a P-47D-22 at medium altitude in 4.11, you'll be getting something similar to the test you quoted.

It sound reasonable, in a real world combat, the engine management can't be neglected, but this is a "test" to determine dive accelaration so P47 should prepare for diving: at first setting rich-mixture, rpm/pitch to 3000rpm, throttle to 40% so that actual engine rpm is 2000 or so(although pitch is fine), criusing side by side with fw190 @250mph IAS. Next step for P47 is just slam the throttle forward and dive.

BTW, I am doubt fw190A4 could PULL AWAY RAPIDLY from P47d at initial dive in 4.11m.

My GUESS about that historical test:

When diving from 250mph to 380 mph or so, the speed of tip of P47's airscrew firstly reached 0.8 Mach than fw190's due to its greater rotating speed. When P47's reached 0.8 Mach and suffered from obvious airscrew efficience drop while 190's remained at BELOW 0.8 Mach, 190 had more thrust and outdove P47 rapidly.

But 380mph IAS(just my estimate) is the turning point, where P47's tip breaks sound barrier, and the drag coefficient of airscrew tip DECREASES, P47's efficiency INCREASES as we known that the majority of airscrew thrust is from tip section of propeller. From 380mph to 450mph, it was 190's turn to suffer from efficiency drop due to it's 0.8-1.0 Mach tip speed, P47 began to catch up with 190, and the P47's hugh weight advantage boosted its taking over because the higher speed, the more important role of weight. Therefore P47's diving accelarartion became astonishing-------quickly catched up fw190 200yard ahead, and passed 190 with MUCH GREATER SPEED like "thunderbolt".

[MadBlaster]

It's good thinking. I'll take a shot.

I think if the props on both planes are nearing 450 TAS and running inefficiently, you must fall back to the drags of the planes themselves. We know that the wing loading on p47-22 is greater than fw 190A. We also know that fw190A out turns a p47-22 based on the fan plots. So, I think we can conclude that the p47 is simple more aerodynamically streamlined for diving (less draggy) and this is why it eventually catches up and surpasses the 190A in a dive. I don't think the p47 prop all of a sudden gets more efficient when it breaks the sound barrier, but I could be wrong about that. Anyway, it is not the weight of the p47, but more so that the 190 wing simply generates more lift and that creates a drag. Yes, there is a weight difference. But if both planes were shaped as same sized spheres and one is twice as heavy as the other, I think you won't get that much separation.

Also ot, don't ever dive after a p51 in 109. Climb, pursue and hope he turns. If he is diving away from his home base, you have him. Simply cut off the angle. ;)

[BlackBerry]

It's good thinking. I'll take a shot.

I think if the props on both planes are nearing 450 TAS and running inefficiently, you must fall back to the drags of the planes themselves. We know that the wing loading on p47-22 is greater than fw 190A. We also know that fw190A out turns a p47-22 based on the fan plots. So, I think we can conclude that the p47 is simple more aerodynamically streamlined for diving (less draggy) and this is why it eventually catches up and surpasses the 190A in a dive. I don't think the p47 prop all of a sudden gets more efficient when it breaks the sound barrier, but I could be wrong about that. Anyway, it is not the weight of the p47, but more so that the 190 wing simply generates more lift and that creates a drag. Yes, there is a weight difference. But if both planes were shaped as same sized spheres and one is twice as heavy as the other, I think you won't get that much separation.

Also ot, don't ever dive after a p51 in 109. Climb, pursue and hope he turns. If he is diving away from his home base, you have him. Simply cut off the angle. ;)


The "no-lift" drag coefficeint for P47D-37 is "0.0256",it's a constant below 0.8 Mach. The test 0f 1943 December between fw190G and P47D was definitely below 0.8 Mach. You can see that P47 has a big wing of 25.87 square meters:

P-47D-27 = 0.0256 * 25.87 = 0.662272

0.662272 is also a constant, if you want to get drag force of the wind, multiple speed^2:

0.662272X(250mph)^2

I have no fw190G's data, fw190G-1 based on A4; G-2 based on A5, they are both 1.42ata( 42").

let's put aside propeller's thrust at first, only gravity and wind drag(there are some induced force but I just calculate roughly).


gXweightXcos(60)-dragcoefficentX(speed)^2= (dive-accelaration)Xweight

that is

dive-accelaration=gXcos(60)-dragcoefficentX(speed)^2/weight

P47's weight is almost twice of fw190A4, so at 250mph speed it's almost impossible for fw190 to outdive P47 in il2 4.11m. But in real world, fw190 pulled away rapidly!

The only factor we didn't include is the detailed airscrew efficeiency curve espicielly when tip reachs 0.8-1.0 Mach and above.
Spitfire.LF.IXC
[Mass]
Empty 2650.0
TakeOff 3300.0

[Squares]
Wing 19.0
Aileron 1.32
Flap 2.125
Stabilizer 1.90
Elevator 1.20
Keel 0.85
Rudder 1.10

[Polares]
lineCyCoeff 0.092
AOAMinCx_Shift 0.0
Cy0_0 0.1
AOACritH_0 16.0
AOACritL_0 -17.0
CyCritH_0 1.4
CyCritL_0 -0.7
CxMin_0 0.0232
parabCxCoeff_0 5.4E-4




P-47D-27
[Mass]
Empty 4630.0
TakeOff 6583.0

[Squares]
Wing 25.87
Aileron 1.45
Flap 2.76
Stabilizer 3.50
Elevator 2.05
Keel 1.30
Rudder 1.10

[Polares]
lineCyCoeff 0.092
AOAMinCx_Shift 0.9
Cy0_0 0.17
AOACritH_0 16.0
AOACritL_0 -15.0
CyCritH_0 1.25
CyCritL_0 -0.8
CxMin_0 0.0256
parabCxCoeff_0 4.8E-4


Bf-109G-2 = 0.027 * 16.16 = 0.43632
Spitfire.LF.IXC = 0.0232 * 19.0 = 0.4408
P-47D-27 = 0.0256 * 25.87 = 0.662272



Someone says

On the R-2800 engines the Reduction Gear ratio was about 50%, the crankshaft would produce about 50% more power strokes per revolution than a direct drive engine. On the dash 21 (P-47 Thunderbolt) engine it was 16:8 ratio. On most other R-2800 engines the ratio is 16:9, 16 revolutions of the engine give 9 revolutions of the prop. The numbers have no common multiple, it's a vibration control function.

The R-1830 of the C-47, and R-2800, and that R-4360 are geared engines, notice how large the nose case is - where the "crankshaft" and the prop meet.


R-2800 engine, 2700rpm, 50% reduction for airscrew=1350rpm, 4m diametre. On the ground when engine at full rpm, the propeller's tip's rotating speed is:

3.14X4X1350/60=282m/s=282/340=0.83 Mach

Wow, it's seems that P47's designer just want to make the tip speed approach sonic as soon as posssible. Why? The supersonic state for airscrew's tip? We all know P47 was intently designed for high altitude escort where the sonic speed is samller than 340m/s on the ground, and P47 often dives at hight speed at high aititude, therefore P47's airscrew tip must often beyond 1 Mach.

airscrew=the twisted and rotating "wing" above 1 Mach, what does this mean in il2?

Again we analysis 1943's test.
(C)

(1) 10000 feet to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

When p47 flew on 10000 feet@250 mph IAS,what's the speed of propeller's tip?

At 5,000' TAS = IAS + 9%
At 10,000' TAS = IAS + 16%
At 15,000' TAS = IAS + 25%
At 20,000' TAS = IAS + 36%
At 25,000' TAS = IAS + 49%
At 30,000' TAS = IAS + 64%

250 mph IAS=290mph TAS=130m/s, rotating speed is 282m/s, combination speed is 310m/s, Mach number=310/328=0.945Mach

When slam throttle full forwards and dives 60 degree, P47's airscrew will probably be the first one to suffer from sonic barrier.0.95-1.0 Mach. This is probably the reason why P47 was outdived by fw190G from 250 mph(initial diving stage). As speed building up to 650km/h or so (3000ft altitude), mach number=1.

(Probably)Fw190's airscrew tip entered 0.9-1.0 Mach later than P47, that's why 190 outdove P47 at the begining, but when both of them were all suffering from low airscrew efficiency at high speed, P47 will gain on 190, the formula I'v posted above demonstrates this clearly.


When P47 dives to 7500 altitude @800 km/h TAS, and tip mach number is 1.16. Hamilton standard airscrew is NACA-16 series which is laminar flow airfoil.

<<Static characteristics of Hamilton Standard propellers having Clark Y and NACA 16 series blade sections>>
http://digital.library.unt.edu/ark:/67531/metadc62146/m1/

[MadBlaster]

hmm, before I read further, I think we need zero lift drag coefficient for 190 to say that weight is the deciding factor. wiki says 27.87 m² for p47 wing area and 18.30 m² for 190A. Agree with you that denominator (i.e., weight) is almost twice as large for p47 verses 190, but numerator? To keep simple math, assume zero drag coeff=1 for both planes, 190 weighs "1" and p47 weighs "2" (weight on relative basis to each other). Then drag coefficient portion of numerator

-dragcoefficentX(speed)^2/weight

where you did this -> P-47D-27 = 0.0256 * 25.87 = 0.662272 (i assume your using 25.87 for wing area)

(i.e., use 1 instead of .0256 and 1 for speed since same for both planes and 2 for weight p47 and 1 for weight of 190)

27.87/2 (p47) or 18.3/1 (190) is bigger??? The latter is bigger, and since it is a subtraction from this gXcos(60), wing area and/or differences in zero drag coeff may be the deciding factor in the calculation of dive acceleration, not the weight. And if this is the case, dive acceleration is less for 190 than p47. Sorry,if this is confusing. It's late here.

[BlackBerry]

hmm, before I read further, I think we need zero lift drag coefficient for 190 to say that weight is the deciding factor. wiki says 27.87 m² for p47 wing area and 18.30 m² for 190A. Agree with you that denominator (i.e., weight) is almost twice as large for p47 verses 190, but numerator? To keep simple math, assume zero drag coeff=1 for both planes, 190 weighs "1" and p47 weighs "2" (weight on relative basis to each other). Then drag coefficient portion of numerator

-dragcoefficentX(speed)^2/weight

where you did this -> P-47D-27 = 0.0256 * 25.87 = 0.662272 (i assume your using 25.87 for wing area)

(i.e., use 1 instead of .0256 and 1 for speed since same for both planes and 2 for weight p47 and 1 for weight of 190)

27.87/2 (p47) or 18.3/1 (190) is bigger??? The latter is bigger, and since it is a subtraction from this gXcos(60), wing area and/or differences in zero drag coeff may be the deciding factor in the calculation of dive acceleration, not the weight. And if this is the case, dive acceleration is less for 190 than p47. Sorry,if this is confusing. It's late here.

27.87/2=13.93 much smaller than 18.3, so P47 has smaller subtraction from this g*cos(60).


BTW, this link says VDM 3m diametre has a 0.54 prop reduction gearing. Fw190A8 :VDM 9-12176A10 ft, 11 ¾ in. diameter 390 lbs

BMW-801D 2700rpm



FockeWulf190BMW 801D radialVDM prop mechanism was built into the nose case of the engine itself, along with 1.72 to 1 cooling fan drive, 0.54 prop reduction gearing, magneto, oil pump, and front camshaft drive.

http://www.enginehistory.org/Convention/2005/Presentations/FeyTom/P09%20VDM%20Electric.pdf

So in 1943's test, @10000ft ,250mph IAS, fw190A4's propeller tip speed=(254^2+130^2)^0.5=286m/s=0.87Mach, less than 0.95 Mach of P47's.

Some P47's has 16:9 reduction which provides higher Mach number (1.05Mach ).

In conclusion, My opinion is that when p47 and fw190a4 at full engine 2700rpm dive from @10000ft ,250mph IAS, fw190's tip speed is about 0.87mach while p47's is around 0.945-1.05 Mach. Probably at that time P47's propeller's efficiency is quite lower than fw190, so p47 was outdove rapidly at initial diving stage.
9525

[MadBlaster]

Your conclusion seems reasonable to me. I was digging into that hamilton clark link, it says the machs for best efficiencies were in the .7-.9 range. I would assume that plays out at cruising speeds.

[Crumpp]

Wow, it's seems that P47's designer just want to make the tip speed approach sonic as soon as posssible. Why?

4 meter diameter compared to a 3 meter diameter....

4 meters is a big prop and they have to push the tip speeds. Keep in mind, diameter is the most important factor in propeller design.

Good design can compensate, though.

it says the machs for best efficiencies were in the .7-.9 range.

They were not dumb at Republic!
:grin:

This is probably the reason why P47 was outdived by fw190G from 250 mph(initial diving stage).

I did not check over your math but your final conclusion is absolutely right.

[BlackBerry]

Crumpp, thank your comments，I think I've found the answer！ the NACA report of Hamilton standard tells us everything：1350rpm propeller 13ft diameter CSP just like P47's with the exception of 3-blade vs 4-blade.

http://digital.library.unt.edu/ark:/67531/metadc62146/m1/

There were two airfoil being tested， Clark Y airfoil was before WWII, not laminar. NACA16 was during WWII, NACA16 airfoil is laminar flow profile, and the test shows that there is no advantage of NACA16 airfoil when propeller's tip speed is 1Mach and when "advance ratio" is above 2.0, but there is no more than 3% efficiency benefit from NACA16 when "advanc ratio" is between 1.2 and 2.0.

advance ratio= TAS/(rpm*diameter)

fw190:3 meter propeller, 1400 rpm
p47d: 4 meter propeller, 1400 rpm

You can see Figure 24, when tip speed is 1 Mach, the more advance ratio, the lower efficiency. So we now come to know why Repulic engineer wanted as big propeller as possible because they wanted smaller advance ratio! When fw190 and P47 dive to same high TAS, the P47 has smaller advance ratio and higher efficiency AS LONG AS BOTH PROPELLER'S TIP SPEED IS AROUND 1 MACH. Republic engineers were right: since high TAS diving(efficiency loss)is inevitable for P47, why not prefer low "advance ratio" while accepting the high mach number of 4 meters big propeller's tip?

The complete formular of diving 65 degree is below:

acceleration=g*cos(65)-dragcoefficent*(TAS)^2/weight+Propellerthrust/weight

A simple math question: if you are P4D7's pilot fighting against a fw190G(both arr 250mph TAS @10000ft ), how can you get higher dive acceleration? On the right of formular there are three parts:

1) g*cos(65)
You have nothing to do with it, every a/c shares same value.

2) dragcoefficent*(TAS)^2/weight

Your huge weight is your advantage, and the bigger TAS, the more important role this part plays. So you should build up speed ASAP.

3) Propellerthrust/weight

Unfortunately the third part is your enemy's advantage. Although P47's efficiency is almost same as fw190's, your huge weight is your shortcoming.The NACA report says when tip speed is above 0.9 mach, the drag coefficient of tip increase rapidly, and when tip speed is 1.0 mach and advance ratio is above 2.0, the efficiency of propeller drops sharply. @250 IAS ,p47's advance ratio is about 1.32, not high, but as speed slightly building up, efficiency drops quicker than 0.5-0.8 Mach curve.

http://digital.library.unt.edu/ark:/67531/metadc62146/m1/43/
http://digital.library.unt.edu/ark:/67531/metadc62146/m1/13/
http://digital.library.unt.edu/ark:/67531/metadc62146/m1/11/

You are now 250mph TAS @10000ft, your tip speed is 1 mach, and you will suffer from compressibility loss while your enemy dose NOT. The fw190 has more thrust than you, his weight is less than you, therefore his thrust/weight is much greater than you so that he can overcome your advantage----the second part of formular.

What should you do ? The answer is very simple and as same as the conclusion we've got from 2nd part of formular:

BUILD UP SPEED ASAP.

Drag him down!!! Yes, your tip speed will be always above 1 mach but now fw190's is also around 1 mach, he is now suffering from compressibility just like you, furthermore, his advance ratio(J) will much bigger than you, so his propeller efficiency drops more sharply than you. Now, the third part of formular is NOT enemy's advantage any more. You've succeded in eliminating his advantage and retaining and enlarging yours.

Congratulations from Republic engineers! You now have energy advantage by diving to high TAS, you are extending your distant now, do what you want to do. :)

The last thing is that if il2 4.11 models the compressibility loss of propeller efficiency . If not, there are 2 probem with its FM.

1) every piston a/c dives faster than it shoud be @ high TAS.

2)For those a/c like P47, the advantage of high TAS diving acceleration has been ignored, so is it's Low TAS diving accelaration shortcoming.

Now we can perfectly explain the fact of 1943 Dec test between fw190G and P47D, and many other comparation such as spitfire vs bf109 initial and final diving difference.

BTW, it's stupid for P47 to dive in a shallow angle with zeke which demonstrates the 6 ton thunderbolt has only a littile advantage(100yards)to the "kite"----Zeke52. I can image those angry faces of the Republic's engineers.:cool:


As for P51d, He has similar high TAS diving acceleration with P47, but the reason is not much depending on huge weight, it is very low coefficient of laminar wing. pls look at 2nd part of formular.

[MadBlaster]

about this part of the equation, Propellerthrust/weight ->

Simply lower the rpms to bring the p47 tips speeds down to optimal range .7-.9? Won't that give you better acceleration? It seems to work that way in game. Starting at 250 mph, full throttle, and 100% pp, nose trim 2 notches down, rads closed. if I nose it down into dive and crank down the prop pitch to 0% quickly and then bring it back up to ~77% and gradually lower throttle to about 77% in a dive from 250 mph, the planes gets to ~ 400 mph ias very quickly.

[BlackBerry]

about this part of the equation, Propellerthrust/weight ->

Simply lower the rpms to bring the p47 tips speeds down to optimal range .7-.9? Won't that give you better acceleration? It seems to work that way in game. Starting at 250 mph, full throttle, and 100% pp, nose trim 2 notches down, rads closed. if I nose it down into dive and crank down the prop pitch to 0% quickly and then bring it back up to ~77% and gradually lower throttle to about 77% in a dive from 250 mph, the planes gets to ~ 400 mph ias very quickly.


Yes, that works. But even you can get same propeller efficiency as 190, your weight is too great to overcome, Propellerthrust/weight is still inferior to 190's.

We need to know if 190's airscrew tip compressibility loss is modelled or not at high mach number where 190's huge "advance ratio" making efficiency even worse than P47's.

[MadBlaster]

agree, but better to do it than not if your p47 guy. for 190 guy, you have revealed something that I think goes ignored. sometimes it is good to over ride the vdm auto prop pitch control and go to manual mode for same reason, to keep tip speeds at optimal ranges.

[mayshine]

Thanks to BlackBerry and everyone,

all your threads have done greatly to help me to understand more.

and may be there is a chance to involve the Prop calculation in IL2

to knock down Cliff of Dover and be the most perfect all the way?

Sorry for offensive language to someone l

I am tricky and want this topic to enjoy a long life and drag more men
to research in their full strenth,

So that I deliberately use somewhat offensive language.

sorry again JTD or so

[BlackBerry]

agree, but better to do it than not if your p47 guy. for 190 guy, you have revealed something that I think goes ignored. sometimes it is good to over ride the vdm auto prop pitch control and go to manual mode for same reason, to keep tip speeds at optimal ranges.

That dosn't help much, I'll show you how terribly drop of propeller efficiency for SMALLER propeller.

Again, NACA Figure24, Both fw190's 3 meter prop. and p47's 4-meter prop @19500ft , 1350rpm for propeller CSP,

1)A point=126m/s TAS=453km/h TAS=323km/h IAS

P47's advance ratio=126/(4*22.5)=1.4

fw190's advance ratio=126/(3*22.5)=1.86

2)B point=180m/s TAS=648km/h TAS=462km/h IAS

P47's advance ratio=2.0
fw190's advance ratio=2.66

3)C point=216m/s TAS=777km/h TAS=555km/h IAS=345m.p.h. IAS

P47's advance ratio=2.4

fw190's advance ratio=3.2

9534

B piont--->When both p47 and fw190 dive to 20000ft/462km/h IAS=287m.p.h. IAS, p47's efficiency is 70%, almost twice of fw190's 38%!

C point---->When dive to 20000ft/555km/h IAS=345 mph IAS, fw190 almost lost its propellerthrust while p47's remaining 55%.

So when speed building up @high altitude, the third part of acceleration formular will also be p47's advantage. Thus we could image how "Thunderbolt" really is!

P47's exhaust turbine boost leads to the lost of exhaust boost for propeller, but that can't help fw190 much.

Finally, we can completely understand why Republic's engineers want the biggest propeller as possible.

[MadBlaster]

interesting. I'm suggesting that at point A with a canister of mw50 on board that the 190 guy trade high rpms and prop efficiency while TAS is low, for thrust 'instantaneously' (limited by rate of change of the blade angle) by over-riding auto prop pitch (slower response). The prop would not be spinning at 1350 rpm. It has a load on now, so is spinning at say the lower end of the power curve for the bmw engine, guesstimate, 1050 rpm. Point C for 190 is irrelevant because dive speed limitations are upon him. The race is for point B. How long does it take for p47 turbo to spool up??? How long does it take to get power from mw50???

[BlackBerry]

interesting. I'm suggesting that at point A with a canister of mw50 on board that the 190 guy trade high rpms and prop efficiency while TAS is low, for thrust 'instantaneously' (limited by rate of change of the blade angle) by over-riding auto prop pitch (slower response). The prop would not be spinning at 1350 rpm. It has a load on now, so is spinning at say the lower end of the power curve for the bmw engine, guesstimate, 1050 rpm. Point C for 190 is irrelevant because dive speed limitations are upon him. The race is for point B. How long does it take for p47 turbo to spool up??? How long does it take to get power from mw50???


1) German tried MW50 on BMW801 but finally gave up. It's said that MW50 is harmful to BMW801's piston. 1945 version Dora's Jumo213A(liquid cooled) was equipped with MW50. However, 20000ft(6000m) is probably above 190's FTH, so there is little benifit from WEP.

At "A" point, if fw190 uses 1050rpm propeller, tip rotating speed is 165m/s, TAS is 126m/s, Mach number=207/310=0.67. Quite below 0.9mach. But I'd to say the propeller's has a certain optimised rpm, if you use full 100% throttle while reducing propeller's rpm incorrectly, you will lose efficiency. Your propeller probably couldn't absorb engine's output.

2) C point is above fw190's max allowable diving limit?

3)I don't know how long does it take for p47 turbo to spool up. I guess it's several seconds?

4)Last but not least, Do you have the information of Dora's 41276.16 V propeller? The size of it, the reduction ratio etc. As we all known before 4.11m, Dora flys so fast.

[MadBlaster]

1) German tried MW50 on BMW801 but finally gave up. It's said that MW50 is harmful to BMW801's piston. 1945 version Dora's Jumo213A(liquid cooled) was equipped with MW50. However, 20000ft(6000m) is probably above 190's FTH, so there is little benifit from WEP.

ah, okay. I read wiki they had used a version of a-4. But if it didn't work, it's not relevant. Lets leave out the dora/jumo too. Actually, iirc, dora was modified to handle mw50 at higher alts than 109 @ 6000 meters. Definitely the Ta 152 was. And then there was the gm1 (forgot the name). Actually, I fly UP 3.0 RC4 which uses 4.10 as base. Haven't tried 4.11 yet. But I checked all the fw190As in ultrapack, and none have mw50. some have the added fuel injection. so there you go.


At "A" point, if fw190 uses 1050rpm propeller, tip rotating speed is 165m/s, TAS is 126m/s, Mach number=207/310=0.67. Quite below 0.9mach. But I'd to say the propeller's has a certain optimised rpm, if you use full 100% throttle while reducing propeller's rpm incorrectly, you will lose efficiency. Your propeller probably couldn't absorb engine's output.

yea, I was thinking like a range of acceptable efficiency (going back to the .7-.9 range for the p47 prop). so your running auto pitch at about 400 kph about to start your dive. then you go manual mode using the vdm 3 way switch. So you quickly run up the rpms (toggle the switch) and atas ~1.4 to get the tip speed at the high end of the mach range. then put the load on by toggling the three way switch to the other position and slowly back off the atas as your in your dive. your accelerating, tas is going up and prop efficiency is going down. When your rpms are at 2100 on the indicator and your at the low end of the mach range for the prop, you go to auto prop pitch and your atas are running ~1.0 or so and your prop self adjusts to the TAS at that moment . Assuming they engineered out the rate of change on the blade angle so that you do not lose power in the transition. I think its like 3 degrees every one second or something like that. I forgot. All this happens very fast. like in a few seconds. I coded a 3 way switch in glovepie to do this, btw.

2) C point is above fw190's max allowable diving limit?

yes, but getting close. your tas is still increasing. its time to make a decision
and there is only one thing to do. p47 has a lot more headroom @ 1000 kph.

3)I don't know how long does it take for p47 turbo to spool up. I guess it's several seconds?

yes. i think so. I was thinking mw50 is instant satisfaction verses turbo lag. but since mw50 not on a4. but dora, yes. So we can ask DT if turbo lag is modeled correctly.

4)Last but not least, Do you have the information of Dora's 41276.16 V propeller? The size of it, the reduction ratio etc. As we all known before 4.11m, Dora flys so fast.

sorry,I'd have to google. I wasn't really intending to change discussion to dora. It's a different plane. jumo was way better engine. much higher rpms capability. I guess that is germans partial answer to opponent with bigger prop size. in ultrapack doras, there is a torque limiter. So you can crank a load from say 3700 rpm to 3000 rpm with mw50 on max ata. then you have to switch it off/cut ata and you can crank the load from 3000rpm to say 2700 rpm. .

[BlackBerry]

I know you are trying to get best propeller efficiency by adjusting rpm manually, thinking that fw190 is quite an automatic plane but the pilot is oblidged to be so busy....

I'll carefully calculate Fw190 A8's prop. efficiency.

BMW-801D 2700rpm VDM 3m diametre has a 0.54 prop reduction gearing. Fw190A8 :VDM 9-12176A, 10 ft, 11 ¾ in. diameter 390 lbs

FockeWulf190 BMW 801D radial VDM prop mechanism was built into the nose case of the engine itself, along with 1.72 to 1 cooling fan drive, 0.54 prop reduction gearing, magneto, oil pump, and front camshaft drive.

http://www.enginehistory.org/Convention/2005/Presentations/FeyTom/P09%20VDM%20Electric.pdf


Prop diameter: 11.98feet=3.33 metre

Prop rpm: 2700*0.54=1458rpm =24.2 rps(100% pitch)

Notice that "B" point is just Fw190A8 max. level speed @19500 ft, that is 648km/h=180m/s

advance ratio=180/(3.33*24.2)=2.23

P47's advance ratio=2.0

So fw190's ratio is NOT so bad as 2.66, just 2.23. My 3-meter vs 4-meter comparation is just a demonstration of how important the diameter of prop. is.
http://www.wwiiaircraftperformance.org/fw190/fw190a8-level.jpg


You can see Fw190A8 gets its max. level by using 2700rpm-engine, this is the best rpm for A8, if you fly A8 at "B" point, don't decrease rpm because this will increase your advance ratio, which leads to the moving to rightside on the curve.

http://www.wwiiaircraftperformance.org/fw190/fw190-a8-level-speed-13nov43.jpg

At "B" point, A8's tip speed=(180^2+253^2)^0.5=310m/s.

Mach number is 310/316=0.981 Mach, almost 1 Mach.

That means @19500ft, fw190A8 have to make it's propeller's tip speed just equal to 1 Mach, this is the best result, if you decrease rpm, you lose efficiency because "advance ratio" will be greater.

Actually, fw190A8's prop. working piont is "D" with efficiency 0f 60%+, less than P47's 70%, if P47 using 16:9 reduction, thundebolt's working point is "E", 75% efficiency.
9555
I am not saying that manual operating rpm is useless, it may help you a bit, but not much.

P47's efficiency advantage may or may NOT overcome its huge weight at high speed, but at least P47 could shrink the third part of the formular which is propitious to fw190. Even fw190 could maintain 100% efficiency all along diving, the importance of 3rd part of firmualar will also be less and less. Don't forget another foumular:

output(HP)=speed(m/s)*thrust(KN)

When you double your speed, the 3rd part of formular will become 50% (and even smaller due to efficiency lose) important as before, the 2nd part will become 400% important as before.
When P47 building up speed quickly, fw190A is doomed to be outdived.

[BlackBerry]

This thread is about diving acceleration, not level flying.

"B" point is just fw190a8 's max. level ,only 648km/h TAS, while P51B could reach 715km/h (444mph)@20000ft, and 670km/h for P47D.

It's very very easy for P51P47 dive to "C" point(777km/h TAS) which is only 100-60km/h higher than there max. level flght. At "C" point fw190a8 prop. efficiency only 36%!

The max. permitted dive speed @20000ft for Tempest is 450 mph IAS=1014 km/h TAS, P47P51 are probably the same. Sir, when diving at 850km/h TAS@20000ft, can you imagine how frustrated fw190A8 is?


I think I've expressed enough my opinion. Let's read a paragragh from wiki to understand why the author wrote "energy-saving" dive. "energy saving" means P47's opponents bleeding their energy heavily when fighting against P47 at high TAS. I wish Daidalos team could make il2 perfect by giving us REAL thunderbolt , Mustang, and Tempest.:)

The P-47's initial success in combat was primarily due to tactics, using rolls (the P-47 had an excellent roll rate) and energy-saving dive and zoom climbs from high altitude to outmaneuver German fighters. Both the Bf 109 and Fw 190 could, like the Spitfire, out-turn and out-climb the early model P-47s at low altitude, although at altitudes above 15,000*ft, the P-47 could turn inside both the Bf 109 and Fw 190. Once paddle blade propellers were added to the P-47 in early 1944, climb performance improved significantly,[33] enabling the P-47 to match the climb performance of any German fighter at all altitudes[citation needed]. While both German fighters could break hard downwards, and leave all models of the Spitfire trailing,[29] no German piston-engined aircraft could out-dive the Thunderbolt. In a "bounce," with their rapid acceleration downhill coupled with the pulverizing effect of eight .50s, these aircraft were deadly.[34] The Thunderbolt was the fastest-diving American aircraft of the war—it could reach speeds of 550*mph (480*kn, 885*km/h). Major Robert S. "Bob" Johnson described the experience of diving the big fighter by writing, "the Thunderbolt 'howled' and ran for the earth".[35] Some P-47 pilots claimed to have broken the sound barrier, but later research revealed that because of the pressure buildup inside the pitot tube at high speeds, airspeed readings became unpredictably exaggerated. But German pilots gradually learned to avoid diving away from a Thunderbolt. Kurt Bühligen, a high-scoring German fighter ace with 112 victories, recalled:
"The P-47 was very heavy, too heavy for some maneuvers. We would see it coming from behind, and pull up fast and the P-47 couldn’t follow and we came around and got on its tail in this way".[36]

[MadBlaster]

I know you are trying to get best propeller efficiency by adjusting rpm manually, thinking that fw190 is quite an automatic plane but the pilot is oblidged to be so busy....

I'll carefully calculate Fw190 A8's prop. efficiency.




Prop diameter: 11.98feet=3.33 metre

Prop rpm: 2700*0.54=1458rpm =24.2 rps(100% pitch)

Notice that "B" point is just Fw190A8 max. level speed @19500 ft, that is 648km/h=180m/s

advance ratio=180/(3.33*24.2)=2.23

P47's advance ratio=2.0

So fw190's ratio is NOT so bad as 2.66, just 2.23. My 3-meter vs 4-meter comparation is just a demonstration of how important the diameter of prop. is.
http://www.wwiiaircraftperformance.org/fw190/fw190a8-level.jpg


You can see Fw190A8 gets its max. level by using 2700rpm-engine, this is the best rpm for A8, if you fly A8 at "B" point, don't decrease rpm because this will increase your advance ratio, which leads to the moving to rightside on the curve.

http://www.wwiiaircraftperformance.org/fw190/fw190-a8-level-speed-13nov43.jpg

At "B" point, A8's tip speed=(180^2+253^2)^0.5=310m/s.

Mach number is 310/316=0.981 Mach, almost 1 Mach.

That means @19500ft, fw190A8 have to make it's propeller's tip speed just equal to 1 Mach, this is the best result, if you decrease rpm, you lose efficiency because "advance ratio" will be greater.

Actually, fw190A8's prop. working piont is "D" with efficiency 0f 60%+, less than P47's 70%, if P47 using 16:9 reduction, thundebolt's working point is "E", 75% efficiency.
9555
I am not saying that manual operating rpm is useless, it may help you a bit, but not much.

P47's efficiency advantage may or may NOT overcome its huge weight at high speed, but at least P47 could shrink the third part of the formular which is propitious to fw190. Even fw190 could maintain 100% efficiency all along diving, the importance of 3rd part of firmualar will also be less and less. Don't forget another foumular:

output(HP)=speed(m/s)*thrust(KN)

When you double your speed, the 3rd part of formular will become 50% (and even smaller due to efficiency lose) important as before, the 2nd part will become 400% important as before.
When P47 building up speed quickly, fw190A is doomed to be outdived.

yes. recall, at point A when you enter the dive at ~400 kph, your rpms are at ~2100. So going manual mode allows you to spool up the engine to 2700 rpm at cruise speeds and transfer that power in short order to the prop for better acceleration than auto mode would give you. most of the time you fly in auto mode. just certain situations, you apply manual mode adjustments to the power band, imo. entering a dive, nearing stall speed, ground taxi, air braking, etc.

But to maintain top speed at level flight, agree. don't use manual mode for that.

Maybe they called it 'thunderbolt' because of the dive limit?

Okay, I'm out. Thanks for the discussion.:cool:

[BlackBerry]

Maybe they called it 'thunderbolt' because of the dive limit?

It's dive acceleration not dive limit made P47 succesful in history.

It's totally useless for having 1 Mach dive limit when your enemy could outdive you with better acceleration within 0.7 Mach and pull to level run away. Even if you fly the same a/c 500m behind your wingman, you couldn't catch up him when following his dive, could you?


While both German fighters could break hard downwards, and leave all models of the Spitfire trailing[/B], no German piston-engined aircraft could out-dive the Thunderbolt.


Although SpitfireIX/XIV has the same dive limit(if not better than) as fw190A/bf109G, he couldn't over take Germans in a dive.

Speed and altitude records
The Spitfire Mk XI flown by Sqn. Ldr. Martindale, seen here after its flight on 27 April 1944 during which it was damaged achieving a true airspeed of 606 mph (975 km/h).Beginning in late 1943, high-speed diving trials were undertaken at Farnborough to investigate the handling characteristics of aircraft travelling at speeds near the sound barrier (i.e., the onset of compressibility effects). Because it had the highest limiting Mach number of any aircraft at that time, a Spitfire XI was chosen to take part in these trials. Due to the high altitudes necessary for these dives, a fully feathering Rotol propeller was fitted to prevent overspeeding. It was during these trials that EN409, flown by Squadron Leader J. R. Tobin, reached 606 mph (975 km/h, Mach 0.891) in a 45° dive. In April 1944, the same aircraft suffered engine failure in another dive while being flown by Squadron Leader Anthony F. Martindale, RAFVR, when the propeller and reduction gear broke off. Martindale successfully glided the Spitfire 20 mi (32 km) back to the airfield and landed safely.[120] Martindale was awarded the Air Force Cross for his exploits.[121]

A Spitfire was modified by the RAE for high speed testing of the stabilator (then known as the "flying tail") of the Miles M.52 supersonic research aircraft. RAE test pilot Eric Brown stated that he tested this successfully during October and November 1944, attaining Mach 0.86 in a dive.[122]

On 5 February 1952, a Spitfire 19 of 81 Squadron based at Kai Tek in Hong Kong reached probably the highest altitude ever achieved by a Spitfire. The pilot, Flight Lieutenant Ted Powles,[123] was on a routine flight to survey outside-air temperature and report on other meteorological conditions at various altitudes in preparation for a proposed new air service through the area. He climbed to 50,000 ft (15,240 m) indicated altitude, with a true altitude of 51,550 ft (15,712 m). The cabin pressure fell below a safe level and, in trying to reduce altitude, he entered an uncontrollable dive which shook the aircraft violently. He eventually regained control somewhere below 3,000 ft (900 m) and landed safely with no discernible damage to his aircraft. Evaluation of the recorded flight data suggested that, in the dive, he achieved a speed of 690 mph (1,110 km/h, Mach 0.96), which would have been the highest speed ever reached by a propeller-driven aircraft, but it has been speculated this figure resulted from inherent instrument errors.[120]

That any operational aircraft off the production line, cannons sprouting from its wings and warts and all, could readily be controlled at this speed when the early jet aircraft such as Meteors, Vampires, P-80s, etc, could not, was certainly extraordinary.—Jeffrey Quill

[124]The critical Mach number of the Spitfire's original elliptical wing was higher than the subsequently-used laminar-flow-section, straight-tapering-planform wing of the follow-on Supermarine Spiteful, Seafang and Attacker, illustrating that Reginald Mitchell's practical engineering approach to the problems of high-speed flight had paid off.[125]

[MadBlaster]

mach 1, sound barrier and 'loud noise'. what is 'thunder'??? get it now??? What other WW2 prop planes had mach 1 dive limit??? I can't recall any other that did. Even the great Ta 152 falls short. So, if Republic makes the only plane that can get to sound barrier with out breaking up, calling it 'thunderbolt', seems a good fit to me. So, I simply was speculating on the origination of name. :rolleyes:

"it's totally useless for having 1 Mach dive limit when your enemy could outdive you with better acceleration within 0.7 Mach and pull to level run away. Even if you fly the same a/c 500m behind your wingman, you couldn't catch up him when following his dive, could you?"


Huh? We already know that the fw190a-4 was quicker off the line in the dive! Go back and read your own posts and theory as to why. I already stated your conclusion seemed reasonable. I don't know why you seem to be contradicting your own conclusion now? Most of the other prop planes couldn't touch that dive limit, so p47 acceleration is moot beyond their dive limits. But it did not have the best acceleration in the dive as per the test record.

Also, even if fw 190 does get some lucky shots off in the first part of the dive, p47 is built like a tank. Good chance it gets home.;)

[BlackBerry]

mach 1, sound barrier and 'loud noise'. what is 'thunder'??? get it now??? What other WW2 prop planes had mach 1 dive limit??? I can't recall any other that did. Even the great Ta 152 falls short. So, if Republic makes the only plane that can get to sound barrier with out breaking up, calling it 'thunderbolt', seems a good fit to me. So, I simply was speculating on the origination of name.


It's totally useless for having 0.85 Mach dive limit when your enemy could outdive you with better acceleration within 0.7 Mach and pull to level run away.

It's totally useless for having 0.75 Mach dive limit when your enemy could outdive you with better acceleration within 0.65 Mach and pull to level run away.

It's totally useless for having 0.65 Mach dive limit when your enemy could outdive you with better acceleration within 0.55 Mach and pull to level run away.

Now, do you understand me?




Huh? We already know that the fw190a-4 was quicker off the line in the dive! Go back and read your own posts and theory as to why. I already stated your conclusion seemed reasonable. I don't know why you seem to be contradicting your own conclusion now? Most of the other prop planes couldn't touch that dive limit, so p47 acceleration is moot beyond their dive limits. But it did not have the best acceleration in the dive as per the test record.

It seems that you misundertand me. P47 can outdive fw190 WITHIN fw190's dive limit.
(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

In your opinion, fw190 from 3000m @400km/h dive to deck will lost its wings?
No, no, no.
When hit ground, the speed of fw190 is BELOW its diving limit. But fw190 was outdived by P47, wasn't it?

I'll use estimated numbers to show you, if you don't aunderstand, I 'll give up.

acceleration=g*cos(65)-dragcoefficent*(TAS)^2/weight+Propellerthrust/weight


1)from 400km/h to 570km/h,Fw190G outdives P47D
acceleration=g*cos(65)-dragcoefficent*(TAS)^2/weight+Propellerthrust/weight

For fw190G:acceleration=4.1-1.5+3.5=6.1 m/s^2

For P47D:acceleration=4.1-1+2=5.1 m/s^2


6.1>5.1, So fw190G outdives P47D.



2)from 570km/h to 750km/h, P47D doutdives fw190G

For fw190G:acceleration==4.1-5+1=0.1m/s^2

For P47D:acceleration=4.1-3.3+1=1.8 m/s^2


1.8>0.1,So P47D outdives fw190G.

[MadBlaster]

(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.


Okay, I guess it is just a words mix up. Look at the underline bold above. You posted it from the test record. It says 190 was quicker off the line. This is from the test record. You reasoned it out. I agreed. Then you said this:


It's dive acceleration not dive limit made P47 succesful in history.


which contradicts the test observation we have been talking about. So, imho, I don't think it's p47 acceleration abilities in a dive that gave it the name 'ThunderBolt'. http://en.wikipedia.org/wiki/Thunder It is the fact that it had a dive limit capability like no other prop plane at that time, near the sound barrier. It took time for p47 to catch up and pass the 190. It was not the quickest. It was the fastest. So, I don't think you can say dive acceleration was it's leading attribute in history. There's nothing to argue here. I think we just got a word mix up.:)


The wings obviously did not fall off the 190 in that test. So, I guess we can assume that at that dive angle, starting altitude, starting speed...etc, that the 190 stayed within the dive limits. Probably a vertical dive angle is a different story and the wings fall off.

[BlackBerry]

What's name for P47 isn't important, you may call it "old woman", but p47's acceleration is still one of the best.

In 1943 July, p47 was equipped with old naca-16 propeller whose efficiency is low at low TAS, but when P47 had a paddle prop., story changed.

I guess fw190G can only slightly outdive P47 (paddle) at the beginning.

[Crumpp]

Hi Blackberry,

You have drawn some of the right conclusions but there is some work required still.

First of all, these are constant speed propellers. They change pitch as required. I am sure you got confused looking at that single F4U graph but it is a fact, you cannot compare CSP propellers at different advance ratios.

The advance ratio does not tell you a thing except in the context of that specific pitch angle. Now what you are doing is how that pitch stops are determined. A good propeller design will keep the polar at the flat area on the top as the pitch of the blade changes throughout the flight envelope.

This is what a complete CSP efficiency over advance ratio graph looks like:

http://img403.imageshack.us/img403/8361/advanceratio.jpg (http://imageshack.us/photo/my-images/403/advanceratio.jpg/)

The best aircraft/engine for this propeller will achieve Vmax at ~2.2 advance ratio and the propeller will have the stops at 15 degrees and 45 degrees.

That is the advantage of a CSP, you maintain peak efficiency over a wide range of velocities.

The F4U graph looks like it comparing airfoil selection at a specific velocity.

[MadBlaster]

I think he knows that. The example is a bit rigged. Same max rpms, similar reduction ratios. The main difference being the diameter. He started it out by calculating max tip speed as peak efficiency. So, have to look at his advance ratio calcs on a relative performance basis verses comparing one prop to the other.

[BlackBerry]

Hi Blackberry,

You have drawn some of the right conclusions but there is some work required still.

First of all, these are constant speed propellers. They change pitch as required. I am sure you got confused looking at that single F4U graph but it is a fact, you cannot compare CSP propellers at different advance ratios.

The advance ratio does not tell you a thing except in the context of that specific pitch angle. Now what you are doing is how that pitch stops are determined. A good propeller design will keep the polar at the flat area on the top as the pitch of the blade changes throughout the flight envelope.

This is what a complete CSP efficiency over advance ratio graph looks like:

http://img403.imageshack.us/img403/8361/advanceratio.jpg (http://imageshack.us/photo/my-images/403/advanceratio.jpg/)

The best aircraft/engine for this propeller will achieve Vmax at ~2.2 advance ratio and the propeller will have the stops at 15 degrees and 45 degrees.

That is the advantage of a CSP, you maintain peak efficiency over a wide range of velocities.

The F4U graph looks like it comparing airfoil selection at a specific velocity.

Thanks for correcting me, you are right, the NACA16 vs Clark-Y diagram is at a specific velocity=640km/h TAS, and at a specific altitude= 6000m(19500ft)

advance ratio=J= V/(n*D)

V=177 m/s, D=4.1m(13.5ft), when J varies from 1.0 to 2.5, the propeller's rpm is from 2590 to 1036 respectively, and engine rpm is between 5180 and 2072rpm(reduction ratio=0.5:1). But 5158rpm is far more than engine's max. rpm, Thus the working range of 3-blade 4.1m diameter CSP is the "red curve", other part of curve is just the calculated result.


Larger prop. will always benifit from lower advance ratio when other things being equal.

9568

3-blade CSP diagram
9569
4-blade CSP diagram
9570

It seems that 4-blade CSP with larger diameter prop, is FAR MORE efficient than 3-blade with smaller size, especially when advance ratio is very high(diving).

Assume 3-blade diagram is Fw190A8, 2700rpm engine , reduction 0.54:1, 1458rpm for 3.3m Propeller

Assume 4-blade diagram is P47D, 2700rpm engine , reduction 0.5:1 or 0.56:1, 1350rpm or 1518rpm for 4.0m Propeller

When both Fw190A8 and P47D dive to 6000m altitude @ 950km/h TAS=264m/s TAS=680km/h IAS=421m.p.h IAS. This speed is within Tempest MKV's permitted dive limit.

Propeller efficiency for P47D:82%-85% , advance ratio=3 or 2.6

Propeller efficiency for Fw190A8:0%. advance ratio=3.3

:shock:What a surprise! It's very wise for allied to drag fw190A to such a high speed, and make fw190a lost its power!

The most important is whether il2 4.11m models detailed prop. efficiency curve? Is there Mach number in il2's FM code? Crumpp Do you know?

[BlackBerry]

To demostrate how important of 4-blade design compared to 3-blade, we can calculate Tempest MKV.

engine rpm 3700 or 3850, reduction ratio=0.274, prop. rpm=1013rpm or 1055 rpm ;propeller diameter=14ft=4.24m

When dive to 6000m altitude @ 950km/h TAS=264m/s TAS=680km/h IAS=421m.p.h IAS. This speed is within Tempest MKV's permitted dive limit.


advance ratio=J=V/(d*n)=264/(4.24*1012/60)=3.7 even bigger than Fw190A8!

If Tempest was equipped with 3-blade prop, it will be badly outdived by Fw190A8, but Tempest slightly outdive P47 and P51! The reason is 4-blade prop. which provides efficiency 78%@950km/h TAS.

During the war many types of fighter aircraft were produced out of the designers bag, some never even reached the prototype stage, others failed to reach Service requirements, but not a few made the grade and are now house hold words the world over. The best known in this country are, of course, the Hurricane and Spitfire, the Typhoon, Mustang and Thunderbolt, and latterly the Tempest and Meteor. Each came out in many guises and fulfilled many roles, some of which they were never designed for, but all did a grand job of work, and were at one time or another indispensable to the work of the R.A.F. Fighter Command.


The Aeroplane June 21st 1946.

http://www.wwiiaircraftperformance.org/wade-dive.jpg

1)The best diver, Meteor, of course, not" handicapped by airscrew drag"

2)Tempest MKV(9lbs boost), the best piston diver, 4-blade prop. 5 tons, streamlined

3)Thunderbolt(P47D), the best American piston diver, 4-blade prop, 7 tons.

4) Mustang(P51B/C 18lbs boost), one of the best diver, 4-blade prop, 3.5 ton , very low drag coefficiency of laminar flow wing.

5) Fw190A8A6? Bf109G6as Spitfire IX,XIV, these a/c are outdived by P47P51Tempy. Why?

Fw190A,as heavy as P51, but not laminar flow wing, lighter than P47/Tempy. only 3-blade prop. low prop efficiency at high speed.
Bf109G6as, very good at initial dive stage, but not very heavy, 3-blade prop.
Spitfire IX, XIV, 4-blade prop. not heavy, initially outdived by 109, but can catch up with 109 due to 4-blade efficienvy at high speed, over take 109? not sure.

[BlackBerry]

3-blade and 4-blade diagrams are from university textbook of aerodynamics.

I don't know those props are modern or WWII era. So they are just for demonstrate, but apperently, xfu4-1 13.5ft naca16 or clark y propeller is much inferior to that 3-blade diagram. For example, 400mph @6000m xf4u's efficiency is 70%, advance ratio=2, while in that 3-blade diagrams, could reach 85%+. So this implies that fw190a8 will completely lose its power much below 950km/h@6000m. Sad news for germans, because bf109/fw190 including Ta152 are equipped with 3-blade prop. while allied had 4-blade after 1942. Even worse for soviet planes, la5/la7,yak are light, small size plane which means their dive acceleration are poor within 730km/h.

BWT, prop. efficiency decreases when altitude grows, and I don't know whether those diagrams are sea level or 9000 m.


I am afraid that the efficiency diagrams of WWII era are difficult to find. The last choice is "ansys" which is powerful software in simulating propeller.

[Crumpp]

To demostrate how important of 4-blade design compared to 3-blade,

That is a very generic graph with absolutely no conditions given. It is impossible to draw conclusions from about aircraft dive performance.

Good design can achieve the same efficiency and thrust with either 3 blades or 4 blades at the power levels of WWII aircraft.

As for propeller efficiency, there is a good reason why n=.85 is a good assumption to make for CSP propeller efficiency. Take the top of your single pitch effiiciency curve for the F4U and that is the efficiency a CSP will maintain throughout the envelope. It will adjust the blade angle to maintain that.

Examine n under various conditions and advance ratios in this article. This is a good primer for propeller performance btw.

You will see that n has a very small variance and even remains the same at different advance ratio because of the shape of the curve at that blade angle.

http://www.nar-associates.com/technical-flying/propeller/cruise_propeller_efficiency_screen.pdf

More blades = more drag but those airplanes have more thrust than the blades add drag because of their weight.

Align those aircraft by weight and you will see the important of it to achieving a high Vne.

That being said, mach limits and dynamic pressure limits have a much more practical impact on determining Vne.

Fw190A8A6? Bf109G6as Spitfire IX,XIV, these a/c are outdived by P47P51Tempy. Why?


Weight = additional available thrust. The propeller thrust is going to zero at the equilibrium point. It will vary but it not nearly the factor that weight becomes....

The excess propeller thrust is why the Bf-109 and FW-190 have such high initial dive acelerations under the conditions the article is talking about. If you dove all of those aircraft from Vmax, they would have no excess propeller thrust and would be using a component of weight as thrust.

Fw190A,as heavy as P51

Maybe, maybe not. Using the load plans, the P51D has the potential to add 550 more pounds of thrust at take off weight to increase its Vmax depending on the angle of dive. Granted that is not very much give the relationship of velocity and power. Power requirements are cubed in relation to velocity. Keep in mind your graphical representation from the 1940's flying magazine does not give us a scale but only shows relative advantage.

The radial of the FW190 will consume more gas and oil so its weight will change faster but the P51 has more gas and potential to change weight at a slower rate. The P51 also has a lower Drag picture so does not require as much thrust to achieve a higher speed. That is why it is faster than the FW-190A8 with a less powerful engine. Laminar flow has what is termed the "drag bucket" in the middle of the polar that occurs around cruise co-efficients of lift. It has no bearing on either low speed or Vmax performance except that laminar flow airfoils as a general characteristic exhibit lower CLmax. For your games purposes, that is irrelevant as you do not have to guess CLmax but can easily calculate it from stall speed with a given weight.

The Mustang achieves a higher Vmax in level flight so it was also achieve a higher Vmax in a dive provided it does not reach mach limitations or dynamic pressure limitations.

You can see from this sustained turn performance analysis the general effects of thrust and aerodynamic limitations of these designs.

http://img837.imageshack.us/img837/5403/p51d5vsfw190a8.png (http://imageshack.us/photo/my-images/837/p51d5vsfw190a8.png/)

[Crumpp]

Summary of propeller design:

Fewer blades = more efficiency

Fewer blades = lower power loading

More blades = better power loading

More blades = less efficiency

Larger disc size = better power loading

Larger disc size = faster tip speeds = lower efficiency = good for low speed work

Smaller disc = slower tip speeds = higher efficiency = good for high speed work

Propellers are undoubtedly the most complicated piece of engineering on an aircraft.

You can also bet that all the engineers during WWII did their homework. I know Mtt and Focke Wulf both tested 4 bladed designs on their aircraft. It was found that what one design made up in efficiency, it lost in power loading and vice versa. As such Focke Wulf concluded that was no appreciable difference other than weight savings on the 3 bladed propeller.

The German propeller designer took the approach of widening the blade chord to increase power loading and using a better material. The allies added more blades and accepted the weight increase. Both are perfectly acceptable approaches to increasing performance with very little to choose from.

The most efficient propeller would have one very long and wide blade. It would revolve rather slowly and acelerate rather poorly.

All the best,

Crumpp

[BlackBerry]

Power requirements are cubed in relation to velocity.
Yes, but don't forget compressibility at 500mph=800km/h which P47P51Tempest could dive to. As for wing airfoil drag, there are extra 250HP is consumed by Compressibility.
http://history.nasa.gov/SP-4219/Chapter3.html
http://history.nasa.gov/SP-4219/4219-081.jpg
Graph and sketch hand-drawn by John Stack, 1933. The effect of compressibility on the power required for a hypothetical airplane.This sketch was subsequently sent to the October 1933 Committee Meeting of the NACA in Washington. From the John Stack papers at the NASA Langley Archives.

More blades = more drag but those airplanes have more thrust than the blades add drag because of their weight.
You can also bet that all the engineers during WWII did their homework. I know Mtt and Focke Wulf both tested 4 bladed designs on their aircraft. It was found that what one design made up in efficiency, it lost in power loading and vice versa. As such Focke Wulf concluded that was no appreciable difference other than weight savings on the 3 bladed propeller.

The German propeller designer took the approach of widening the blade chord to increase power loading and using a better material. The allies added more blades and accepted the weight(drag) increase. Both are perfectly acceptable approaches to increasing performance with very little to choose from.


Yes, all the engineers during WWII did their homework. However, why allied engineers accepted the weight(drag) increased by the 4th blade, and why german engineers denied?

allied side:
The most valuable link of wind tunnel is here:
http://history.nasa.gov/SP-440/contents.htm
German side:

http://wp1113056.wp148.webpack.hosteurope.de/ABL/20-forschung/laminarfluegel/laminarfluegel_en.htm

The measurements were repeated for different Reynold Numbers and different lift coefficients. For the lowest Reynold Number (4 millions) the point of transition was measured at 50% depth on the upper surface. It moved to the leading edge with increasing Reynold Number, arriving at 20% for Re=7,5 millions. Measurements with different laminar flow airfoils including the Mustang airfoil were later continued in the large high-speed wind tunnel of the DVL, Berlin up to Reynold Numbers of 20 millions. These measurements clearly revealed the fact that the laminar flow effect completely disappeared at real flight Reynold Numbers. This was an expected but sobering result.


Allied said laminar airfoil actually reduced drag in P51, but german believed it's an impossible goal when Reynold Numbers is high(real flight ).

Who made the mistakes?

This unclassified file<<where we stand>> at Page 45 says:

http://www.governmentattic.org/vonK/WhereWeStand_VKarman_V2.pdf



According to the German aerodynamicist Schlichting, German work on laminarflow airfoils did not start until about the end of 1938. By 1940, Schlichting considered that the fundamentals were known. Drag coefficients as low as 0.0027 were reached at a Reynolds Number of 5 x 10^6, but the German scientists were unable to retain the low drag at higher Reynolds Numbers. They were handicapped by lack of suitable low-turbulence wind tunnels. On one occasion, Prandtl reported: "Suitable wind tunnels for the conduct of airfoil investigations at sufficiently high Reynolds Number and at low turbulence are lacking in Germany. On the other hand, it is known that in the U. S. A. particular installations created for this purpose are working exceptionally vigorously in this field."

Tests were made on a Japanese laminar flow airfoil, on·three airfoils derived from one member of an obsolete NACA Series 27215 (which was described in a captured French secret report), and on a few airfoils designed by Schlichting. The Germans also 45 had some information on a Russian laminar flow airfoil obtained from a captured report.
The Germans never used laminar flow airfoils on aircraft. They were astonished and mystified by the performance of the Mustang and made many wind-tunnel and flight "tests. They gave the following tabulation of wing profile drag coeffiicients
(obtained by momentum method) for a number of airplanes at lift coefficient of 0.2:
He-177 0.0109
Me-109B 0.0101
Mustang 0.0072
Ju-288 0.0102
FW-190 0.0089

The German comment is: "The drag of this only foreign original airfoil tested up till now is far below the drag of all German wings tested in which it should be remembered that it was tested without any smoothing layer." Another writer says: "A comparison of flight measurements shows quite unmistakably that the Mustang is far superior aerodynamically to all other airplanes and that it maintains this superiority in spite of its considerably greater wing area."
Allied Developments.
The NACA began investigations of laminar flow airfoils in a low-turbulence wind tunnel in the spring of 1938, and the encouraging nature of the results obtained (without details) were described in the Wilbur Wright Lecture of the Royal Aeronautical Society on 25 May 1939, and in the NACA Annual Report for 1939. In June, 1939, an advance confidential report by Jacobs was released. A summary was published in March, 1942 in confidential form. The most recent summary was relaesed in March, 1945, and this summary has been kept up to date by supplementary sheets.
As indicated in the summary of German developments, the Allies are far ahead in low-turbulence wind tunnel equipment and in knowledge of laminar flow airfoils and their application to aircaft. Drag coefficients as low as 0.003 at a Reynolds Number of 20 x 10^6 have been obtained. A summary of the present state of knowledge is given in the NACA restricted report L5C05, "Summary of Airfoil Data," by Abbott, von Doenhoff, and Stivers,
March, 1945.

Probablly German wind tunnel failed in testing laminar flow airfoil in WWII. German tested none-laminar 3-blade vs 4-blade prop. and drew the conclusion of "not appreciable" for 4-blade, but if they test laminar 3-blade vs laminar 4-blade prop, they will finally find the advantage of 4-blade low drag propeller.

Hamilton Standard :NACA-16 laminar flow airfoil,4-blade prop. widely used in P47P51 etc.
UK de Havilland Propellers was established in 1935, as a division of the de Havilland Aircraft company when that company acquired a license from the Hamilton Standard company of America for the manufacture of variable pitch propellers. The division was incorporated as a separate company on 27 April 1947. SpitfireIX,XIV, Tempest also have laminar flow airfoil,4-blade prop.

As XF4U-1 diagram indicated, 3-blade NACA16(laminar) and 3-blade Clark-Y propeller are roughly the same efficiency(within 3%), after 1942 alomost all allied laminar prop had 4 blade, later Spitfire even had 5-blade prop. There must be enough reason for allied engineers to prefer 4-blade. If allied found that was no appreciable difference other than weight savings on the 3 bladed propeller, they would drop 4-blade design just like Germans did. Those two diagrams from university textbook maybe demonstrate the difference between 3-blade laminar and 4-blade laminar propellers. We need exam it in future, Perhaps the diving difference mystery is just within propeller's efficiency diagrams.

If il2 FM couldn't model detailed compressibility of wing and propeller between 0.8-1.0 mach, it will never be perfect in simulating WWII late a/c.

[BlackBerry]

http://history.nasa.gov/SP-4103/ch8.htm


The NACA's failure to discover and develop jet propulsion should not be allowed to mask its real and significant contributions to American aerial victory in World War II. Though air power was not the sole, [195] or even the most, important ingredient of American victory in the war, it was a key ingredient; without the NACA, American aerial superiority would have been less complete, less early. Every American airplane that fought in the war, every aircraft engine, had been tested and improved in NACA facilities. Most of this cleanup and testing was incremental and anonymous, hard to trace to the NACA, and difficult to evaluate. With military officers, NACA engineers, and aircraft designers and manufacturers all poring over the same test results in an effort to improve the flying qualities of an aircraft, the credit for improvements must be spread widely. Some examples of NACA contributions can be isolated, as when the Committee predicted that the B-32 would fail and recommended that its development be abandoned. In some cases, the prescribed NACA fix for a problem aircraft was rejected by the manufacturer, as when Kelly Johnson of Lockheed ignored the first solution proposed by the NACA for the problems his P-38 was experiencing.45

Two Committee achievements during the war were so obviously useful and noteworthy that the NACA took great pride in citing them. The first investigation undertaken at the new Ames laboratory - icing research - was so useful not only to military bombers operating at high altitudes and through all kinds of weather, but also to commercial operators, that it won for its principal investigator, Lewis A. Rodert, the Collier trophy of 1946. The low-drag wings of the P-51 Mustang, the result of years of NACA research on wing characteristics, became a hallmark of NACA achievement. Though some questioned that these laminar-flow wings (as they were often and incorrectly called) were responsible for the unparalleled performance of the Mustang, most agreed that they were a significant contribution to airfoil development and drag reduction. John Victory was pleased to report in later years that captured German documents revealed an inability by the Germans to account for the superior performance of the Mustang, even after they captured one intact and tested it, because their wind tunnels could not duplicate the low turbulence produced by the NACA.


So German's conclusion is not valid for allied laminar flow 3-blade vs 4-blade comparation. German never used laminar flow airfoil in wings, nor the propellers.

Xf4u-1 test speed is not high, merely 640km/h TAS, we don't know the difference between naca16 and Clark y at high speed, 750km/h,800km/h, etc.

Is that possible for 4-blade laminar type prop provides more power loading than 3-blade of traditional airfoil while keep the drag level remain same?

[Crumpp]

German never used laminar flow airfoil in wings, nor the propellers.


The Germans were well aware of the mustang and laminar flow. Their conclusions agreed with the NACA's, that laminar flow is very difficult to achieve under field conditions and the benefits would not be attainable in a frontline fighter.

http://img33.imageshack.us/img33/2650/p51wingdrag.jpg (http://imageshack.us/photo/my-images/33/p51wingdrag.jpg/)

http://img84.imageshack.us/img84/6954/laminarflowreynolds3.jpg (http://imageshack.us/photo/my-images/84/laminarflowreynolds3.jpg/)

[Crumpp]

Allied said laminar airfoil actually reduced drag in P51, but german believed it's an impossible goal when Reynold Numbers is high(real flight ).


I own and operate an aircraft with laminar flow wings.

You have to keep the wing and leading edge absolutely spotless and polished to see any benefit.

Dirt, bugs, and a rough surface will destroy the laminar flow drag bucket.

Lastly, the benefits of a laminar flow airfoil is not a factor at Vmax or Vs. It occurs in the vicinity of the cruise design point.

Look at the polar for a laminar flow airfoil.

[Crumpp]

However, why allied engineers accepted the weight(drag) increased by the 4th blade, and why german engineers denied?


You do know a Clark Y is not a laminar flow airfoil?

You use a propeller analysis for a Clark Y and then start talking about the benefits of laminar flow.

I am also not sure what I supposed to remember with compressibility effects. Transonic drag rise is included in the statements I made. It is one of the components of drag our thrust must overcome.

I am confused as to what you want to say now.

You are right in that the dive limits of WWII aircraft leave very little to chose. They all hit the wall about the same point. The diagram you form the 1940's enthusiast magazined has no scaling information at all.

I will attempt to answer your question as to why the Germans chose three blades and the allies four blades.

The Germans increased the chord to raise the coefficient of power. The Allies added a blade to increase the coefficient of power.

The Germans were resource and production limited so not having to produce another blade is attractive. Saving weight in any airplane is attractive. The German fighters had sychronized weapons firing through the propeller disc. Less blades means more bullets on any given target.

The Allies and especially the United States had much higher production capacity and nearly unlimited resources. Making more blades and the resources to make them was not an issue. The USAF main fighters used wing mounted weapons that did not fire through the propeller disc.

[MadBlaster]

I don't understand why you guys keep saying weight = thrust. :confused:
Weight=mass*g
-> mass directly proportional to weight and g is constant
greater mass/weight in free fall gives you more inertia to overcome drag forces. Inertia is not thrust. p-47 was big plane with big torque radial engine (not the best drag profile to slip through the air). So it was a trade. A big engine to drive a big prop of a big plane with big drag profile. If p 47 want more acceleration off the line, simply take a steeper dive angle than fw 190 and fill up the tank with fuel and load up on bombs. So, inertia is not constant either. It depends on the loadout and dive angle.

[BlackBerry]

The P51 also has a lower Drag picture so does not require as much thrust to achieve a higher speed. That is why it is faster than the FW-190A8 with a less powerful engine. Laminar flow has what is termed the "drag bucket" in the middle of the polar that occurs around cruise co-efficients of lift.

The Germans were well aware of the mustang and laminar flow. Their conclusions agreed with the NACA's, that laminar flow is very difficult to achieve under field conditions and the benefits would not be attainable in a frontline fighter.

Although there are some arguements about P51's laminar airfoil in a frontline role, Mustang is actually benifitted from this type of airfoil more or less. Isn't it? Same rules applies to NACA-16 laminar propeller airfoil. After WWII, NACA-16 was still widely used in various of propeller's with very low Cd(min) and high critical Mach number.

9612

With regard to German tunnel test on P51 in 1943-1944, they even lost laminar effect when reynolds number reached 20 million due to the lack of low turbulence in wind tunnel which Prandtl had already mentioned. It's no need to remind you who is Prandtl.


Langley Two-Dimensional Low Turbulence Tunnel

http://crgis.ndc.nasa.gov/historic/Low_Turbulence_Pressure_Tunnel


I own and operate an aircraft with laminar flow wings.

You have to keep the wing and leading edge absolutely spotless and polished to see any benefit.

Dirt, bugs, and a rough surface will destroy the laminar flow drag bucket.

Lastly, the benefits of a laminar flow airfoil is not a factor at Vmax or Vs. It occurs in the vicinity of the cruise design point.

Look at the polar for a laminar flow airfoil.

Do you mean there were often Dirt, bugs, and a rough surface on the propellers of P47P51 in WWII?



You do know a Clark Y is not a laminar flow airfoil?

You use a propeller analysis for a Clark Y and then start talking about the benefits of laminar flow.

Clark-Y was Before WWII, NACA-16 was during WWII. There was small peroid for allied using 3-blade laminar NACA16 airfoil beforce they moved to 4-blade. NACA16's section is very different from Clark-Y/RAF-6. Furthermore, although both Clark-Y and RAF-6 were very similar conventional pre-WWII design, there are even some difference between them:

1) Clark-Y has less drag than RAF-6, more suitable for cruising and high speed flying.
2) RAF-6 has more lift, more suitable for taking off.

Thus the difference between NACA16 and Clark-Y/RAF-6 is more profound. In fact RAF-6(UK), Clark-Y(USA) and Gottingen(German) airfoils were the best ones during WWI.

http://www.afwing.com/intro/p51/model.JPG
XP51 prototype model in wind tunnel , 3-blade prop.

http://www.afwing.com/intro/p51/na73x.jpg

NA-73X prototype , 3-blade ,looks like German's 3-balde sharp tip prop.

http://www.afwing.com/intro/p51/mustangI-2.JPG
RAF Mustang I, 3-blade

http://www.afwing.com/intro/p51/xp51-2.jpeg

Another picture of XP-51.

http://www.afwing.com/intro/p51/p51a.jpg
P-51A-10-NA

http://www.afwing.com/intro/p51/p51b5.jpg
P51B prototype , first time with 4-blade (Why 4-blade with 2-stage superchager Merlin engine? For high Mach number of propeller at high altitude?)

When crashed landing, wood propellers do less hatm to engine via shaft.

http://www.afwing.com/intro/p51/XP51g.JPG

Rotol wood 5-blade prop with XP-51G

To sum up, propeller is one of the most complicated components in WWII aircraft, thus deep invastigation should be paid in il2 FM about efficiency curve.

[Crumpp]

Thus the difference between NACA16 and Clark-Y/RAF-6 is more profound.

It was certainly advertised and pushed as such. However like many things advertised, buyer beware.

To our dismay and disappointment, the 16-series propeller showed no advantage at high speeds; in fact the Clark Y appeared slightly
better.

Page 124 tells the story...

http://www.scribd.com/doc/46042585/The-High-Speed-Frontier-Case-Histories-of-Four-NACA-Programs-1920-1950

Although there are some arguements about P51's laminar airfoil in a frontline role, Mustang is actually benifitted from this type of airfoil more or less. Isn't it? Same rules applies to NACA-16 laminar propeller airfoil. After WWII, NACA-16 was still widely used in various of propeller's with very low Cd(min) and high critical Mach number.


No real benefit. Sounds cool though, laminar flow....

Believe it or not, the Davis wing on the B24 actually did see laminar flow benefits under certain conditions. It was total fluke of design but it did achieve laminar flow.

Do you mean there were often Dirt, bugs, and a rough surface on the propellers of P47P51 in WWII?


Yes.

Want some good dings in a propeller, taxi on new pavement. A propeller picks up dirt, rocks, bugs, and anything else in the aircrafts path. Operating from an unimproved strip will result in lots of nicks on the propeller to dress.

Even operating from a nice paved one, you will get nicks in the prop.

Find a Constant Speed Propeller that does not leak some grease too. Anything from the hub goes right up the blade.

[Crumpp]

I don't understand why you guys keep saying weight = thrust.

Use the climb triangle:

The balance of forces in a steady climb show thrust is acting upwards and an element of weight is adding to the drag

As the thrust assists the lift, the lift required is less than in level flight. Verify mathematically by the formula Lift = W.cos gamma

For a steady speed to be maintained the thrust and the two retarding effects of aerodynamic drag and the weight element must be equal.

If Thrust = T, Drag = D and Weight = W, then as a formula it can be written as:

T = D + W sin gamma


When you dive that element of thrust is acting downward and an element of weight is added to thrust.

Our formula is rearranged to become T + W sin gamma = D

Our lift required increases in a dive as thrust acts against lift.

And this still applies at the equilibrium point:

For a steady speed to be maintained the thrust and the two retarding effects of aerodynamic drag and the weight element must be equal.


http://www.theairlinepilots.com/forum/viewtopic.php?p=792&sid=3f2d63d3d764f72c4c9895f5d7f6bd2f

[BlackBerry]

To our dismay and disappointment, the 16-series propeller showed no advantage at high speeds; in fact the Clark Y appeared slightly
better.

Page 124 tells the story...

http://www.scribd.com/doc/46042585/T...rams-1920-1950

How high speed? 400MPH TAS?

I coldn't open this link.

Athough 3-blade Clark-Y airfoil airscrew slightly outperformed 3-blade NACA-16 airfoil, you can't draw the conclusion that 3-blade NACA-16 outperforms or same as 4-blade NACA-16.

Why didn't German keep 2-blade Gottingen airfoil in WWII? 3-blade Gottingen airfoil is better than 2-blade Gottingen?

The Germans were resource and production limited so not having to produce another blade is attractive. Saving weight in any airplane is attractive. The German fighters had sychronized weapons firing through the propeller disc. Less blades means more bullets on any given target.

Don't forget 2-blade Gottingen prop. could save more resource and more friendly to sychronized weapons firing through the propeller disc.

Again, German's 3-blade Gottingen vs 4-blade Gotingen comparation is not valid for 3-blade NACA-16 vs 4-blade NACA-16.

[Crumpp]

The P51

Is a wonderful fighter aircraft. We are restoring one and I can't wait to fly it!

:)

[BlackBerry]

Is a wonderful fighter aircraft. We are restoring one and I can't wait to fly it!

:)

With 4-blade prop. please.:)

[MadBlaster]

lol. yes, vector quantities.:grin:

[BlackBerry]

http://en.wikipedia.org/wiki/Propeller_(aircraft)

A further consideration is the number and the shape of the blades used. Increasing the aspect ratio of the blades reduces drag but the amount of thrust produced depends on blade area, so using high-aspect blades can result in an excessive propeller diameter. A further balance is that using a smaller number of blades reduces interference effects between the blades, but to have sufficient blade area to transmit the available power within a set diameter means a compromise is needed. Increasing the number of blades also decreases the amount of work each blade is required to perform, limiting the local Mach number - a significant performance limit on propellers.

A propeller's performance suffers as the blade speed nears the transonic. As the relative air speed at any section of a propeller is a vector sum of the aircraft speed and the tangential speed due to rotation, a propeller blade tip will reach transonic speed well before the aircraft does. When the airflow over the tip of the blade reaches its critical speed, drag and torque resistance increase rapidly and shock waves form creating a sharp increase in noise. Aircraft with conventional propellers, therefore, do not usually fly faster than Mach 0.6. There have been propeller aircraft which attained up to the Mach 0.8 range, but the low propeller efficiency at this speed makes such applications rare.

There have been efforts to develop propellers for aircraft at high subsonic speeds.[4] The 'fix' is similar to that of transonic wing design. The maximum relative velocity is kept as low as possible by careful control of pitch to allow the blades to have large helix angles; thin blade sections are used and the blades are swept back in a scimitar shape (Scimitar propeller); a large number of blades are used to reduce work per blade and so circulation strength; contra-rotation is used. The propellers designed are more efficient than turbo-fans and their cruising speed (Mach 0.7–0.85) is suitable for airliners, but the noise generated is tremendous (see the Antonov An-70 and Tupolev Tu-95 for examples of such a design).


//////

We will find the proof of 4-blade vs 3-blade, sooner or later.;) When a/c diving, it often creats a sharp increase in noise, which means tip of the blade reaches its critical speed.

[BlackBerry]

http://digital.library.unt.edu/ark:/67531/metadc62616/m1/19/
P47D tested with a Hamilton Standard 6507A-2 3-blade airfoil(NACA-16)

Cp=P/(r*n^3*D^5)

r=air density

We can see when dive to low altitude @0.7 Mach, prop efficiency will be as low as 63%. Fw190A8's 3.3m propeller advance ratio is quite bigger than P47's, so its efficiency should be quite less than 63% if the VDM prop. shares the same airfoil with 6507A-2.

But don't forget Hamilton Standard 6507A-2 has a NACA-16 airfoil. see here

http://digital.library.unt.edu/ark:/67531/metadc63942/m1/3/


Allied also tested Hamilton Standard 6507A-2 with both 3-blade and 4-blade configuration at 0.4 Mach, also here

http://digital.library.unt.edu/ark:/67531/metadc63942/m1/40/

http://digital.library.unt.edu/ark:/67531/metadc63942/m1/43/


Fig 16 and Fig 18

Appearently, 4-blade NACA-16 airfoil shows around 5%-10%+ efficiency advantage over 3-blade cousin even at medium speed. That's one of the reasons p47D picked up 4-blade airscrew.

It's probably that when dive to high-speed fw190a8's 3-blade Gottingen prop. efficiency is much inferior than P47's 3-blade NACA-16 airfoil. But I know Crumpp will argue that Gottingen(WWI standard) outperforms NACA16 at high speed. I'll remind you that NACA-16 airfoil was widely used after WWII until 1970s when computer calculating method helped people designed better airfoils. To sum up, in high speed diving:

1)P47 has less advance ratio than fw190a8.
2)P47 has NACA-16 lower drag airfoil than fw190a8.
3)P47 has 4-blade prop rather than fw190a8's 3-blade.

In future, if someone finds the proof or calculates out that fw190A8 Gottingen 3-blade prop only has 30% efficiency in high speed diving while P47 has 75% with 4-blade NACA-16 airfoil, don't be surprised because that will perfectly explain why Fw190G was badly outdived by P47D at 65 degree in Italy 1943 summer.


How about 0.7 Mach comparation of 3-blade vs 4-blade efficiency? That's more interesting.:-P But I guess the truth will change il2's diving FM.

[Crumpp]

if the VDM prop. shares the same airfoil with 6507A-2.


That is a poor assumption to make.

[Crumpp]

Don't forget 2-blade Gottingen prop. could save more resource and more friendly to sychronized weapons firing through the propeller disc.


This is were your power loading effects the design. A two bladed propeller will not absorb 2000 hp very well.

A 3 Bladed propeller can absorb 2000 hp very well.

[BlackBerry]

This is were your power loading effects the design. A two bladed propeller will not absorb 2000 hp very well.

A 3 Bladed propeller can absorb 2000 hp very well.

Yes, 3-blade is usually enough for 2000hp, but in some special envirenments, I doubt about it.

Crumpp, you have tons of information on a/c, try to find sth. interesting to make il2 diving FM perfect. I know you have all the data of VDM propellers. :)

[TomcatViP]

Wow...interesting thread guys (but I did only read the actual page).

But I think you forgot something BckBr: the large bladed prop will fly easier in the airstream during the dive and will then have a tendency to raise the rpm much higher than a 4 bladed one.

More rpm -> pilot will have to reduce throttle during the dive in order to keep eng safe
More rpm -> more tip blade speed hence more drag

Transonic drag being far higher than low subsonic drag, low rpm is better either for your eng (max pow dive) and for your total drag coef.

But if you are comparing the Jug with the Fw, it 's far better to keep in mlind their difference in weight and the weight/power ratio.

With the latter, you'll understand easily that gravity did play a huge part during WWII in term of improvement of aircraft perf. Hence, a nose down Jug had far better "propulsive" power than a FW190 in the same configuration.

EDIT: oh... and let's not forget that the Jug had a metal prop when the 190 used ones made out of woods. The technology is quite different ( the latter being somewhat newer). Large blades might hve been something difficult to achieve with casted aluminium

[BlackBerry]

Wow...interesting thread guys (but I did only read the actual page).

But I think you forgot something BckBr: the large bladed prop will fly easier in the airstream during the dive and will then have a tendency to raise the rpm much higher than a 4 bladed one.

More rpm -> pilot will have to reduce throttle during the dive in order to keep eng safe
More rpm -> more tip blade speed hence more drag

Transonic drag being far higher than low subsonic drag, low rpm is better either for your eng (max pow dive) and for your total drag coef.

TomcatViP, when fw190a8 flying at max. level speed, it uses 2700 rpm engine. Therefore if fw190A8 dive to a speed much more than its level speed, the engine rotation is definitly 2700rpm. Such as 2500 rpm in a high speed diving is stupid:loss efficiency a lot because of increase of advance ratio.

Let your CSP governer to maintain blade angle and rpm, don't bother thinking about it. And fw190a8's small prop's tip speed is inevitably around critical mach number in a dive, you can't avoid it.

[BlackBerry]

Crummp, you are the expert on propeller aerodynamics. With your help, I've finally got the whole story.

In world war ONE, UK, Germany, USA developed RAF-6, Gottingen, and ClarkY airfoils for propellers respectively. These airfoils are "high drag high lift" conventianal airfoils. At the time, 2-blade fix pitch airscrew were used.

Before WWII, people found it's nessesary to add the 3rd blade to absorb growing horsepower of engine. eg. Bf109B/D->Bf109E. When you add more blade, there are two contrary effects:

1)good thing: better power loading ability
2)bad thing: more drag

At late 1930s, UK/USA/Germany engineers found it's almost no benifit from the 4th blade because the improvement on power loading is completely counteracted by drag increase added by the 4th blade. Allied tested RAF-6/ClarkY with 3-blade and 4-blade configration, drew that conclusion, German Mtt and Focke Wulf also tested , with same result.

http://aerade.cranfield.ac.uk/ara/1938/naca-report-640.pdf

You can also bet that all the engineers during WWII did their homework. I know Mtt and Focke Wulf both tested 4 bladed designs on their aircraft. It was found that what one design made up in efficiency, it lost in power loading and vice versa. As such Focke Wulf concluded that was no appreciable difference other than weight savings on the 3 bladed propeller.


During late period of WWII, every country faced same difficulty: how to improve prop efficiency when more powerful engine equipped with aircrafts?

German engineers found a clever method: use broad chord in 3-blade prop thus they could improve power loading while maintain lower drag than 4-blade. Result was quite good:

I have all the data on VDM propeller series. The wide chord wooden props for the Luftwaffe dropped top level speed by about 4 percent but increased turn and climb rate by about 15 percent. The Luftwaffe conducted several indepth studies. I am sure the USAAF did the same. Blade width does help efficiency to a point.

http://forum2.totalsims.com/viewtopic.php?t=2475

The German propeller designer took the approach of widening the blade chord to increase power loading and using a better material. The allies added more blades and accepted the weight increase. Both are perfectly acceptable approaches to increasing performance with very little to choose from.

Allied finally accept 4-blade prop, eg P51A-P51B. in your opinion, both methods are perfect, and with little to choose.


Question: Since german 3-broad-blade obviuosly outperformed their old 3-blade design , so were allied new 4-blade prop. I've posted the proof of efficiency advantagde of P47's 4-blade hamilton over 3-blade. However, in late 1930s, allied reports on RAF-6/ClarkY already said there is little difference between 4 and 3 blade. What's the problem?


The answer is lamimar airfoil developed during WWII, NACA-16 series. I agree with you with the difficulty maintaining of laminar effect in actual combat envirenments. OK, let's regard NAVA-16 as conventianal airfoil, that is, NACA-16 is "fake" laminar flow airfoil. The next question is: Is there enough difference between two kinds of conventianal airfoils? Of course. In an aerodynamics textbook says:"RAF-6 is suitable for taking off while ClarkY is better in criusing and high speed flight." Notice that there is only slightly section shape difference between RAF-6 and ClarkY. Therefore, being a vast different shape, NACA-16 behavior should be "special". But in some allied test, 3-blade NAVA-16 is even slightly worse than 3-blade ClarkY especially during taking off. Notice that the test speed is probably within 400MPH.

To our dismay and disappointment, the 16-series propeller showed no advantage at high speeds; in fact the Clark Y appeared slightly
better.

Page 124 tells the story...
http://www.scribd.com/doc/46042585/The-High-Speed-Frontier-Case-Histories-of-Four-NACA-Programs-1920-1950

at high speed......how high? 0.7 Mach TAS?

Is the NACA-16 the "new age ClarkY" just like Clark/RAF-6 comparation? that is to say, "new clarkY"--NACA16 is worse than old clark in taking off and better in REALLY high speed when propeller tip approching critical mach number? This is the key of mysterious diving performance difference.

After WWII, as piston engine's power increased to 2400-3000HP, people impelmented 5-6 blade low drag NACA-16 airfoil to absorb it, and this configaration worked perfectly at high mach subsonic flight. This fact reminds us that whether the 4-blade NACA16 propeller outperforms 3-blade high drag/high lift wide-chord airfoils at high diving speed(=0.7mach or so)? There is small clue as Crummp said in 2005:

I have all the data on VDM propeller series. The wide chord wooden props for the Luftwaffe dropped top level speed by about 4 percent but increased turn and climb rate by about 15 percent.The Luftwaffe conducted several indepth studies. I am sure the USAAF did the same. Blade width does help efficiency to a point.

Why decreased in max. level flght? Dose that suggest us the 3-broad blade prop was slightly outperformed by old 3-blade with narrow chord around 0.5 Mach? ? Because of the more drag of 3- broad blade especially when tip mach number approching 0.85 ?This is only level flight, just 0.5Mach/650km/h or so, how about 0.7Mach/850km/h? Could broad design shortcoming--more drag-- become more abvious?

I think you will find that 80 percent is actually very generous. Very few early war props are even close to this figure. The wide chord Schware Wooden Props found on late war LW fighters were just a tad over 80 percent.

while 4-blade NACA16 achived 90% in P47....

http://digital.library.unt.edu/ark:/67531/metadc63942/m1/40/

In my opinon, there is the possibility of 4-blade NACA16 greatly outperformed 3-broad blade at high diving speed(0.7 Mach). To prove this ,we need more data while crummp tons of resource will play the key role. :)

I have all the data on VDM propeller series.
----Crummp

[MadBlaster]

"There is small clue as Crummp said in 2005"

LOL! Seven years ago. No where to run, no where to hide.

[BlackBerry]

"There is small clue as Crummp said in 2005"

LOL! Seven years ago. No where to run, no where to hide.

German 3-broad chord blade prop plane lost 4% top level speed compared with 3-narrow-blade, according to drag fomular, new broad design lost roughly 8% efficiency around 5.5Mach. Why? Because the bad thing--more drag--become more noticable when speed building up?How about 0.7 Mach? Broad chord design will lose 15% efficiency than narrow chord?

There is evidence that 3-blade NACA16 on P47 gets 63% efficiency at 0.7 Mach, so let's assume that ClarkY and Gottingen(narrow chord) share the same performance with everyelse being equal.

But fw190a8's diameter is quite smaller than P47's, then much bigger advance ratio, guess fw190a8 get 45% efficiency at 0.7 Mach?

Allied 4-blade NACA16 outperforms 3-blade NACA16 at 0.4 Mach, with extra 7-10%, probably at 0.7 Mach, 4-blade NACA16 will get 75% efficiency.

45% vs 75%? This is critical for P51P47Temepest's tactics. I strongly suggest il2 developing team simulate the efficiency of WWII late prop at high speed using software such as ANSYS, otherwise, this game could not perfectly simulate western line where the "battles are not forgotten".

[MadBlaster]

what about windmilling and internal friction /cylinder compression of engine? bmw801 only had 14 cyl. p47 had 18 cyl. so, maybe some inefficiency of 3 blade wide was offset by less internal friction in the 801 and that is why they went with 3 blade wide.:-P

[BlackBerry]

what about windmilling and internal friction /cylinder compression of engine? bmw801 only had 14 cyl. p47 had 18 cyl. so, maybe some inefficiency of 3 blade wide was offset by less internal friction in the 801 and that is why they went with 3 blade wide.:-P

bf109k4 ：3-blade prop
spitfire xiv：4-blade prop even 5-blade

Both are liquid cooling engine.

btw，r2800 and bmw801 share almost same front area.

[MadBlaster]

you miss the point.

What a wide 3 blade may lose in "thrust" vector efficiency from more drag , it may gain in 'weight" vector efficiency when "thrust" vector efficiency is at zero in a dive and high TAS. The wider blade means higher tip speed from ram air verses thinner 3 blade. This means greater torque to overcome internal friction from the engine. The pilot can reduce internal friction by lowering manifold pressure, but not completely. The engine will still tend to over-speed and this is mitigated by lowering rpms/coarsening blade pitch. So, internal friction of the engine is more easily overcome by the weight vector with the wider blade I speculate.

One way to measure the internal friction of the engine. What was the cranking force required to start the 801? What was the cranking force required to start the r-2800? If two engines are identical, it takes more cranking force to start an engine with a 4 blade wider diameter prop attached than a 3 blade smaller diameter. The engines were not identical. The r-2800 had more cylinders than the 801. If you take off the props, I suspect it takes more cranking force to start the r-2800. I suspect the p47 had more internal friction to overcome than the fw190. This would hamper dive acceleration.

[Crumpp]

Why decreased in max. level flght?

Inncrease the area of our lifting surface = more drag

If you know how to do sections, then you know the common expression in propeller blade element theory is Cb for chord length and our local section Drag is expressed as:

~D = 1/2pVb^2CbCD

[Cloyd]

OK Gents,

I've read this thread with fascination, but the details are WAAAAY over my head. Do you have a conclusion, ie, IL2 is way off or it is close enough for a $40 flight sim that is a decade old?

Cloyd

[MadBlaster]

lol, I have no idea.

maybe add some sound effects when the tip speeds go mach.

maybe add some sound effects to p47 turbine spinning up.

I did notice in up3, rc4, there seems to be turbo lag in the dial indicator verses the engine rpm indicator. so somebody was thinking good thoughts. i think it was a mod p47, maybe p47B. felt a little more agile than the others too.

[BlackBerry]

OK Gents,

I've read this thread with fascination, but the details are WAAAAY over my head. Do you have a conclusion, ie, IL2 is way off or it is close enough for a $40 flight sim that is a decade old?

Cloyd

Read this article and you will know high-speed propeller was a leading edge issue in WWII when people didn't know much about the transonic aerodynamiacs(0.8-1.0 Mach). They even could NOT precisely test the propeller efficiency at high speed in fullscale wind tunnel.

http://aerade.cranfield.ac.uk/ara/1938/naca-report-640.pdf

Il2 is a very closed simulation when speed is below 0.8 Mach, but when speed of anything(wing, propeller tip,etc) is beyond 0.8 Mach, not very accurate.

[Crumpp]

bf109k4 ：3-blade prop
spitfire xiv：4-blade prop even 5-blade


Try to find a WWII fighter with cowl guns and a 4 bladed propeller. I cannot think of a single one.

[Cloyd]

Read this article and you will know high-speed propeller was a leading edge issue in WWII when people didn't know much about the transonic aerodynamiacs(0.8-1.0 Mach). They even could NOT precisely test the propeller efficiency at high speed in fullscale wind tunnel.

http://aerade.cranfield.ac.uk/ara/1938/naca-report-640.pdf

Il2 is a very closed simulation when speed is below 0.8 Mach, but when speed of anything(wing, propeller tip,etc) is beyond 0.8 Mach, not very accurate.

I have been flying this sim for over a decade, and I really only know how to fly two planes well - I-153 and F4F-3. (Yes, I realize that neither of these was available in the initial release.) Is it safe for me to assume that I don't have to worry about the performance of my preferred rides in the 0.8 to 1.0 Mach range? ;-) ;-) ;-)

Cloyd

[AndyJWest]

If you ever go that fast in an I-153, you have a problem. And almost certainly, no wings... ;)

[TomcatViP]

What I said most importantly :

Transonic drag being far higher than low subsonic drag, low rpm is better either for your eng (max pow dive) and for your total drag coef.


But I hve to agree that was not my best writing :oops:

I think that your answer lies in faisability (large series) and techniques.

Just remember that the very goal of the Clark's Y airfoils series is for an easy craftsmanship (russians abused of this with their wooden series of La, Yack etc... all were made out of Clark Y).

Propeller material:
German = wood (but some 109 had metal..... seems it was not so much a prob ?)
US = casted aluminium

It makes a huge difference in what kind of airfoil you can achieve.

But still it's only my own guess.

Thx for making that thread an interesting one. Pls go further on ;)

EDIT :OOOpss..just forgot to say that the Clark Y airfoils had a flat bottom to ease marksmanship.

[BlackBerry]

Tomcatvip, if you exam the fw190a8 max level flight at 20000ft, you will find the tip of VDM propeller is just 1 Mach.

680km/h TAS, 2700rpm engine, 0.54:1 reduction ratio, 3.3m diameter

[TomcatViP]

IMHO it's a by-design parameter. Don't we hev the same result with the larger Hamilton props such as fitted on the P47?

[Crumpp]

IMHO it's a by-design parameter. Don't we hev the same result with the larger Hamilton props such as fitted on the P47?


Yes, the engineers in the 1940's were at the top of their game for subsonic propeller design.

[RegRag1977]

Reading this very interesting topic a question has come to my mind: for what reasons did the enginneers at Focke-Wulf tried a four blades propeller on the Fw190V18 high altitude prototype (were the blades longer? was the propeller similar to those on the P51 and P47?). Anyone knows or have a guess?

[Crumpp]

for what reasons did the enginneers at Focke-Wulf tried a four blades propeller on the Fw190V18 high altitude prototype

They were looking for a counter to the B-29 being able to bomb at 30,000 feet and above.

The Germans had no ability to intercept anything at that altitude. The FW-190V18 was one of the designs examined and tested. The result was the Ta-152 series had better performance at altitude and the program was scrapped.

[RegRag1977]

They were looking for a counter to the B-29 being able to bomb at 30,000 feet and above.

The Germans had no ability to intercept anything at that altitude. The FW-190V18 was one of the designs examined and tested. The result was the Ta-152 series had better performance at altitude and the program was scrapped.

Thanks for the answer Crumpp,

In fact I was very surprised to see a German aircraft with a 4 blades propeller (which is very uncommon, the only other i know is He177 Greif bomber) , so i thought (in my noob mind) this solution would somehow be related to very high altitude flight (after all P47 used 4 blades prop and was designed as a high altitude aircraft, and when the P51 became one too, it switched its three blades for four). To sum up i thought the 4 blades were somehow related to very high altitude rather than to power dive performance. But it was just a noob question :) : anyway i recognize that i don't know anything about aircraft enginneering! Just trying to try to understand "in broad strokes"...

As for what you said about 4 blades propeller and cowling/wingroot weapons firing through the prop disc, although very rare, there were some aircraft with this configuration:

P39-Airacobra late 4 blades prop and P-63 Kingcobra, 2x50. cal (cowling) firing though the prop disc ;

Nakajima Hayate Ia, 4 blades prop and 2xHo103 MGs (cowling) firing through, and on later Ib version 2xHo5 20mm canon (cowling).

I've found any with as much guns (4) as the Fw190 though, perhaps four blades would have killed the high firing rate of these guns?

[JtD]

Hardly, the electrical priming on the Fw could deal with synchronised fire rather easily. Much better than other systems.

[Crumpp]

Hardly, the electrical priming on the Fw could deal with synchronised fire rather easily. Much better than other systems.


Yes it could compared to a mechanical sychronization but the electrical priming cannot change the limitations of the weapon itself.

As for what you said about 4 blades propeller and cowling/wingroot weapons firing through the prop disc, although very rare, there were some aircraft with this configuration:


Interesting and rare....

I was very surprised to see a German aircraft with a 4 blades propeller

If the performance differences had been noteworthy, I think the Germans would have used a 4 bladed design. As it was, they had good propeller designs and increased chord width which accomplishes the exact same goal of being able to load more power onto the disc.

The Germans also used wood in many of their later designs as it is a much better material for power loading than metal.

[BlackBerry]

If the performance differences had been noteworthy, I think the Germans would have used a 4 bladed design. As it was, they had good propeller designs and increased chord width which accomplishes the exact same goal of being able to load more power onto the disc.

I don't believe that. Broad chord 3-blade prop lost 8% efficiency when a/c speed is around 0.55 Mach, although this design outperforms old design a lot when speed is low.

German had no naca16 airfoil, what they used in WWII is just WWI standard-gottingen airfoils and the modified broad chord version.

For all of WWI airfoils(RAF6,ClarkY,Gottingen), 4-blade design is useless, but for the newly developed NACA16, story is different.

[Crumpp]

I don't believe that.

So?

For all of WWI airfoils(RAF6,ClarkY,Gottingen), 4-blade design is useless, but for the newly developed NACA16, story is different.

Did you read the NACA's own findings on the Clark Y and NACA 16 series?

The 16 series has poor lift production and its only real application was in propellers. It was generally considered to be worse than the Clark Y even in that application. The NACA 16 series was supposed be low drag at high speed and designed for the very high transonic realm. It was a real disappointment to the NACA.

Go back a few pages and re-read it. It will confirm there was no difference at speed and the Clark Y was actually better overall.

[BlackBerry]

So?



Did you read the NACA's own findings on the Clark Y and NACA 16 series?

The 16 series has poor lift production and its only real application was in propellers. It was generally considered to be worse than the Clark Y even in that application. The NACA 16 series was supposed be low drag at high speed and designed for the very high transonic realm. It was a real disappointment to the NACA.

Go back a few pages and re-read it. It will confirm there was no difference at speed and the Clark Y was actually better overall.

This is my comprehension. Criticism welcome.

9791

[Crumpp]

That is a nice chart, Blackberry. Couple of things to keep in mind.

NACA 16 is a whole series of airfoils each with their own characteristics. You can make some very general statements about them but for the most part, the only characteristic that really sets them apart is the method they were derived. A method with extremely mixed results and sometimes not so very good agreement between calculator and the wind.

Gottingen is also a series of airfoils each with its own characteristics. These were derived from practical work in the wind tunnel.

http://www.aerospaceweb.org/question/airfoils/q0197.shtml

Once more, just as the NACA was aware and used Gottingen airfoils, so did the German designers use NACA airfoils. The Focke Wulf FW-190A uses the NACA 23015.3 at the root and NACA 23009 at the tip.

[K_Freddie]

Ah!.. the numbers ;)

[BlackBerry]

That is a nice chart, Blackberry. Couple of things to keep in mind.

NACA 16 is a whole series of airfoils each with their own characteristics. You can make some very general statements about them but for the most part, the only characteristic that really sets them apart is the method they were derived. A method with extremely mixed results and sometimes not so very good agreement between calculator and the wind.

Gottingen is also a series of airfoils each with its own characteristics. These were derived from practical work in the wind tunnel.

http://www.aerospaceweb.org/question/airfoils/q0197.shtml

Once more, just as the NACA was aware and used Gottingen airfoils, so did the German designers use NACA airfoils. The Focke Wulf FW-190A uses the NACA 23015.3 at the root and NACA 23009 at the tip.


So I suggest Daidalos Team make detailed prop efficiency model.

[Crumpp]

So I suggest Daidalos Team make detailed prop efficiency model.


On what data???

There is a good reason why n = .85 in a CSP is a valid assumption in subsonic aerodynamics.

[BlackBerry]

On what data???

There is a good reason why n = .85 in a CSP is a valid assumption in subsonic aerodynamics.

P47's 3-blade prop drops to 63% efficiency when diving to 0.7 Mach which is subsonic. When you have 20% efficiency advantage over your opponent, you have 400 extra Horse Power, that's a Huge difference.

To model detailed prop efficiency by softwares such as xfoil, ansys,etc.

[AndyJWest]

P47's 3-blade prop drops to 63% efficiency when diving to 0.7 Mach which is subsonic. When you have 20% efficiency advantage over your opponent, you have 400 extra Horse Power, that's a Huge difference.

To model detailed prop efficiency by softwares such as xfoil, ansys,etc.

You are asking TD to rewrite the entire flight physics modelling based on a single number? Yeah, that's going to happen...

[Crumpp]

P47's 3-blade prop drops to 63% efficiency when diving to 0.7 Mach which is subsonic.

How do you figure?

[BlackBerry]

You are asking TD to rewrite the entire flight physics modelling based on a single number? Yeah, that's going to happen...

I don't know whether detailed propeller efficiency is calculated in il2 FM. Someone told me it's only a simple value. It's ridiculous that a propeller a/c simulation game dosn't provide accurate efficiency curve. Simply setting 85% for all of CSP ? No, that's totally unacceptable.

People will spend quite a lot time to collect different propeller data such as prop diameter, reduction ratio, airfoil section shape, angle, etc. Next step is to use Xfoil/Ansys(software) to calculate complete efficiency curve for every propeller. It's worthy because <<cliff of Dover>> could also benefit from this work. Don't forget 10% efficiency difference will cause 100-200 HP error.

like this:
9813

BTW, efficiency drops as altitude increases. If a CSP get 85% at sea level, there is only 85%*80%=68% at 6000m altitude(800KM/H TAS).
9814

[MadBlaster]

Well, I know for a fact from playing that it takes more elevator trim to maintain level flight the higher the altitude. So, I think we can conclude air density effects on wing lift are modeled. I will take a guess Oleg somehow imbedded the prop efficiency losses in the air density values as well. In other words, he came up with a simplified way of doing a complex operation to save cpu cycles.

[AndyJWest]

I don't know whether detailed propeller efficiency is calculated in il2 FM. Someone told me it's only a simple value. It's ridiculous that a propeller a/c simulation game dosn't provide accurate efficiency curve. Simply setting 85% for all of CSP ? No, that's totally unacceptable.


So now you want TD to rewrite the physics modelling because of something that "Someone told" you... ?

If you can provide verifiable evidence that IL-2 is wrong, do so. But bear in mind that even if you do, this is a ten-year-old game, and is hardly likely to undergo a substantial rewrite that would make little practical difference in terms of relative aircraft performance - at lest, from the evidence I've seen so far. IL-2 gets it wrong at high Mach numbers: but this isn't news. It seems to be fairly consistent in the 'wrongness' anyway, so why worry about it...

As for CloD benefiting from the work, do you have any information at all regarding how this entirely new simulation models such things?

[JtD]

I think this debate has shown a lot more than just a single number WRT real life performance.
It is, however, wrong to assume that the game's model is overly simple and wrong.

[BlackBerry]

How do you figure?

http://digital.library.unt.edu/ark:/67531/metadc62616/m1/19/


3-blade Hamilton standard 6507A-2 on P47D, efficiency varies from 83%-63% when TAS is between 0.25-0.7 Mach.


Diagram 1, Cp/blade=0.9, should be at high altitude.

Diagram 2, Cp/blade=0.8, should be at medium altitude.

Diagram 3, Cp/blade=0.6, should be at low altitude.

[BlackBerry]

So now you want TD to rewrite the physics modelling because of something that "Someone told" you... ?

If you can provide verifiable evidence that IL-2 is wrong, do so. But bear in mind that even if you do, this is a ten-year-old game, and is hardly likely to undergo a substantial rewrite that would make little practical difference in terms of relative aircraft performance - at lest, from the evidence I've seen so far. IL-2 gets it wrong at high Mach numbers: but this isn't news. It seems to be fairly consistent in the 'wrongness' anyway, so why worry about it...

As for CloD benefiting from the work, do you have any information at all regarding how this entirely new simulation models such things?


"Someone" is a man involved in il2 mod developing.

As for relative aircraft performance, if your Tempest MKV(9lbs) get caught by a la7@3000m altitude with same speed, could you just dive in a 60 degree angle to the ground (<720Km/h)and simply get far away from la7 shooting range and then come back to 2500m with a much better "energy saving" zoom ? No, in my experience, you can't achieve that. How could those light--2.5 tons--tiny aircraft--smaller 3-blade ClarkY prop.---la7 dive with same accelaration as a 5-tons-huge aircraft-much bigger 4-blade prop. Tempest MKV?

When TempestMKV/La7 dives to 720km/h=200m/s=0.59Mach on the deck, what's the efficiency?
la7 Shvetson M-82FN 14 cyl. with 2-stage supercharger and direct fuel injection rated at 1,850 hp at 2,500 rpm. VISh-105V-4 3 bladed controllable-pitch metal prop of 10.17 ft (3,10 m) diameter

only 2400-2500rpm engine, merely 3.1meter prop, I don't know the reduction ratio but let's assume 1350rpm for propeller. We know 3-blade 1350rpm 4m Hamilton efficiency is 77% or so at 0.59Mach @ low altitude. Advance ratio for Hamilton=2.22, advance ratio for la7 VISh-105V-4=2.87. wow, 2.87? this ratio is for P47 @0.77Mach.

It's very reasonable for la7 to get only 50% efficiency in this situation. La7 loses extra 35% efficiency? lost 650HP? A piece of Sh*t for La's high speed diving. This soviet monster shows his weakness, haha.

I just suspect 10-year-old il2 FM how to treat prop efficiency. If "someone" tell me what formular il2 uses in FM, everything will be clear.

[Crumpp]

3-blade Hamilton standard 6507A-2 on P47D, efficiency varies from 83%-63% when TAS is between 0.25-0.7 Mach.


Not in the envelope of the aircraft. It is a CSP.

[BlackBerry]

Not in the envelope of the aircraft. It is a CSP.

CSP could maintain constant efficiency roughly when speed of propeller tip is below 0.85. Please check 3-blades efficiency curve, when advance ratio is far greater than 2.2, namely when prop tip is approaching 1 Mach, the story changes. A CSP will lose efficiency inevitably at high speed diving(a/c noise louder and louder).

Btw, CSP will also lose efficiency when TAS is very very low.

[Crumpp]

CSP could maintain constant efficiency roughly when speed of propeller tip is below 0.85. Please check 3-blades efficiency curve, when advance ratio is far greater than 2.2, namely when prop tip is approaching 1 Mach, the story changes. A CSP will lose efficiency inevitably at high speed diving(a/c noise louder and louder).

Btw, CSP will also lose efficiency when TAS is very very low.


You are correct but don't misapply it as it has little bearing on the game shapes in IL2.

The efficiency is nearly constant in any portion of the envelope that design can sustain flight....

That is the beauty of a CSP.

The very nature of power producers is such that the faster they go, the less thrust they produce. The reverse is also a characteristics of power producers. The lower the velocity, the more thrust they produce. That efficiency drop occurs because the propeller blades are stalled just like in very high speed flight. The reason is different but believe me, both realms, high and low speed, produce stalled blade portions. In the low speed realm, we are looking at speeds at taxi and the first part of take off but our thrust force is extremely high at low velocity. Therefore, in the scheme of things, it is a useless detail to include the reduction in efficiency in a dive. The performance is not sustainable in the first place and our reduction in thrust with velocity is already well approximated by:

Crumpp says:
Take the force triangle for a dive. A component of weight contributes to thrust based on the angle of dive. The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....

In other words, the details are included when you make the standard assumption of .85 efficiency.
You could also incorrectly conclude that all subsonic propeller theory violates the very definition of lift because it does not include the fact lift force develops at right angles to the relative wind. This means that in all propellers, regardless of blade stalling will not produce thrust. Why? As the velocity increases the relative wind gradually shifts and eventually lift produced by our propeller no longer parallels the flight path but is deflected upward.
Fortunately we don't have to do that or at least we would not be adding any accuracy by deriving our own approximation of the effect. It is one more thing rolled up in our standard formulation.

[BlackBerry]

The efficiency is nearly constant in any portion of the envelope that design can sustain flight....

That is the beauty of a CSP.


Crumpp, this thread is about DIVE, in a high speed dive, you can easily reach very high TAS which, of course, you can not sustain. Finally, as you pull out of dive and begin to level, the aircraft will slow down to its max. level speed, isn't it? The late dive peroid is a temporary flight process in which you may have 25% efficiency advantage over your opponent bacause both propellers could not maintain constant efficiency(85%), namely your 4-blade prop get 80% and your enemy just have 55%, this is a huge tactic factor. Forthermore, from dive terminal speed to max. level speed, that is the slowdown peroid, you still have efficiency advantage. So how long is your advantage peroid? 40seconds? 1 minute? It depends on your altitude to dive from. You are bleeding his energy in this peroid even if your enemy is the best pilot in the world! You are stealing his energy for 40 seconds by the "hand of God". :)Now you can run away with ease, out of his shooting range. This is called "OUTDIVE".


The very nature of power producers is such that the faster they go, the less thrust they produce. The reverse is also a characteristics of power producers. The lower the velocity, the more thrust they produce. That efficiency drop occurs because the propeller blades are stalled just like in very high speed flight. The reason is different but believe me, both realms, high and low speed, produce stalled blade portions. In the low speed realm, we are looking at speeds at taxi and the first part of take off but our thrust force is extremely high at low velocity. Therefore, in the scheme of things, it is a useless detail to include the reduction in efficiency in a dive. The performance is not sustainable in the first place and our reduction in thrust with velocity is already well approximated by:


As I said above, if you are stealing 500HP from your enemy for 30 seconds, he loses "hundreds meters altitude" energy! Imagine that in a il2 combat you decrease throttle to 65% for 30 seconds, that's suicide.

In a high speed flight, a little thrust will give you a lot power, don't forget:

Power=thrust*speed

It is output power not thrust determines your energy state.

[MadBlaster]

come on now. 30 seconds...40 seconds??? in la7 or tempest or whatever, you cruise at 3000 meters then enter dive, it takes just few seconds to hit max level speeds and few seconds more to hit max dive speeds. not that long.

[Crumpp]

As I said above, if you are stealing 500HP from your enemy for 30 seconds

Who is stealing 500 hp???

How much excess excess thrust does a P47 have at 20,000 feet in level flight at Vmax?

NONE

How much excess thrust does any propeller airplane have at Vmax?

NONE

If our airplanes Vmax is 420mph EAS and we dive to Vne at what speed does our Excess Thrust produced by the Propeller = 0?

Vmax

How much Excess power does a CSP propeller aircraft have from cruise flight to Vmax to devote to a dive excess thrust?

All of the excess thrust produced to Vmax...at Vmax our excess propeller thrust = ZERO

What speed does a CSP equipped aircraft traveling at cruise flight reach zero excess propeller thrust at in a dive?

At Vmax....the same speed as in level flight

What is the design propeller efficiency for a CSP in an aircraft envelope from Vs to Vmax?

n = .85 from Stall to Vmax

[MadBlaster]

Crumpp, that doesn't seem quite right based on the diagram you posted a few pages back. Peak efficiency 2.2 at Vmax. but, you can still move down and to the right of the curve towards less efficient (advance ratio increasing for a given blade pitch) as the tip speeds increase and approach mach??? As long as the efficiciency value is > zero, don't you have some thrust being produced by the propellar?

edit:
referring to post #143.

[Crumpp]

As long as the efficiciency value is > zero, don't you have some thrust being produced by the propellar?


Sure you have some thrust being produced but it is not EXCESS thrust. It is excess thrust that accelerates the airplane.

In a dive from Vmax, the only excess thrust is the component of weight.


Propeller thrust only accelerates the aircraft within its envelope.

[MadBlaster]

okay, I think I get it. you said it three posts back, I just didn't sink when I read that the first time.

[MadBlaster]

btw, this has been a very interesting thread. thnks for your input guys. i learned some things.

[BlackBerry]

Sure you have some thrust being produced but it is not EXCESS thrust. It is excess thrust that accelerates the airplane.

In a dive from Vmax, the only excess thrust is the component of weight.


Propeller thrust only accelerates the aircraft within its envelope.


Crumpp, :grin: I totally disagree with you. Imagine that you are now flying a la7 with 110% throttle and you get Vmax speed. The efficiency of propeller is 80%, yes, you propeller are producing thrust(not big) which is equal to La7's drag force. Namely, La7 is in equilibrium. You have no excess propeller thrust, right? Till now, we should have no bifurcation.

And then you suddenly turn off your engine and feather your propeller, It's obvoius that you are about to lose speed because your engine is dead, but you push the stick forwards and begin to dive. A portion of gravity will help you counteract the dargforce and make you maintain Vmax during your "dead enigine" dive. If you dive in a more steep angle, you could even faster than Vmax. in another word, you are spending altitude to maintain your Vmax or get even more speed.

During your "dead enigine" dive, if you suddenly turn on your 1850HP engine, will you dive faster? Will engine give you excess thrust?

In my opinion, definitely, you will get greater dive acceleration because your propeller efficiency is 80-60%.

In your opinion, prropeller efficiency suddenly become zero from 80% when aircraft speed is somehow higher than Vmax.


Propeller thrust only accelerates the aircraft within its envelope.


Propeller thrust could accelerate the aircraft beyond its envelope, as long as gravity force comes to help aircraft-----DIVE.

[BlackBerry]

come on now. 30 seconds...40 seconds??? in la7 or tempest or whatever, you cruise at 3000 meters then enter dive, it takes just few seconds to hit max level speeds and few seconds more to hit max dive speeds. not that long.

Come on, when my Tempest MKV dives to deck and level fly reaching 780km/h, how long will it take to slow down my Tempest to 600km/h? Only just few seconds?

Are you kidding me?

[MadBlaster]

it depends on what dive angle you took after you turned off your engine at Vmax level and entered your dive. if the dive angle was steep enough, you will continue to accelerate due to gravity. if it is too shallow a dive angle, you will start to slow down. in the latter case, if you are below Vmax in the dive due to too shallow a dive angle and turn on your engine, you have potential excess thrust to tap into and get more acceleration from your prop. However, if you are above Vmax because your dive angle was steep, turning on your engine won't give more acceleration because you can not create excess thrust from your propeller at that point. Your TAS is too high. You are moving down and to the right on your efficiency/advance ratio curve for the given blade angle. Any excess thrust is coming from your dive angle/gravity. When your TAS is high enough that you get no thrust, you should lower your rpms to reduce your drag profile, provided you still have room to your Vne speed.

Come on, when my Tempest MKV dives to deck and level fly reaching 780km/h, how long will it take to slow down my Tempest to 600km/h? Only just few seconds?

Umm, who is chasing who here? Tempest has much more dive room than LA7. Push it to ~ 850 kph in your dive extension and zoom climb out from there. Don't waste the zoom energy to 600 kph unless your exiting the fight. Also, Tempest performs better at lower alt.

Face it BlackBerry, Crumpp won.:-P

[BlackBerry]

However, if you are above Vmax because your dive angle was steep, turning on your engine won't give more acceleration because you can not create excess thrust from your propeller at that point. Your TAS is too high. You are moving down and to the right on your efficiency/advance ratio curve for the given blade angle. Any excess thrust is coming from your dive angle/gravity.


You are wrong, LOL. I'll show you with La7's data. When La7 get Vmax=610km/h at low altitude with 1850 HP engine output.

power=thrust*speed

thrust=power/speed=(engine output)*(prop-efficiency)/speed=1850*0.735KW*85%/(610000/3600)=8KN=816kgf

The thrust force is equal to 816kg weight, that is 33% of la7's weight(2.5 tons).

The air drag force is also 816kg force, so la7's speed is steady=610km/h=170m/s.

If La7 dive in a angle of "A" in order to get a portion of gravity for help.

sin(A)=0.33

A=19.3 degree.

So you can turn off your engine/feather your prop and dive in a 20 degree angle, I'll bet that you can sustain 610km/h WITHOUT ENGINE and WITH THE HELP OF GRAVITY.

If you dive in 45 degree, I promise your "dead engine" La7 will be faster and faster untill lost your wing(>730km/h). When you reach 650km/h, you turn on your engine, the thrust is not as big as 816kg, but still around 500kgf, that is, you add "half ton" thrust to your diving La7.

Believe it or not.

In your opinion, la7's propeller will provide zero thrust @650km/h because this is out of "envelope"/Vmax.

Try it in il2 4.11m with your buddy's la7, you shut down engine when speed is above 610km/h and he is still using 110% power, and check if he could pulll away from you or not.

And try to shut down your enigne when you want to escape from the battle field by high speed diving(above Vmax) and when the enemy is chasing you with his 110% WEP. If you dare do that, you'll be caught by him even his aircraft is slower than you@level flight.


Umm, who is chasing who here? Tempest has much more dive room than LA7. Push it to ~ 850 kph in your dive extension and zoom climb out from there. Don't waste the zoom energy to 600 kph unless your exiting the fight. Also, Tempest performs better at lower alt.



Cruising at 3000 meters and dive! :)In order to prevent the poor la7 from losing his wings, my Tempest MKV will carefully control the speed below 740km/h, and I'll show you how long I can stay in the high speed flying status.

[MadBlaster]

[/QUOTE] In your opinion, la7's propeller will provide zero thrust @650km/h because this is out of "envelope"/Vmax.[QUOTE]


no, that is not what I'm saying. it may provide thrust. but it is not "excess" thrust. that is the key here. excess thrust, excess thrust, excess thrust. it is not excess thrust because Crumpp posted a diagram on csp propellar that shows you can not have peak efficiency beyond Vmax. The only way to get beyond vmax and create excess thrust is to dive at the necessary angle. go back and look how he defined excess thrust. it's the difference between the two force vectors. in level flight, the force vector from gravity has no forward direction. at vmax and level flight, there is no more opportunity to create excess thrust from the prop. you have to dive to create excess thrust and acceleration.

[BlackBerry]

no, that is not what I'm saying. it may provide thrust. but it is not "excess" thrust. that is the key here. excess thrust, excess thrust, excess thrust. it is not excess thrust because Crumpp posted a diagram on csp propellar that shows you can not have peak efficiency beyond Vmax. The only way to get beyond vmax and create excess thrust is to dive at the necessary angle. go back and look how he defined excess thrust. it's the difference between the two force vectors. in level flight, the force vector from gravity has no forward direction. at vmax and level flight, there is no more opportunity to create excess thrust from the prop. you have to dive to create excess thrust and acceleration.


MadBlaster, When your la7 diving at 20 degree with constant speed of 610km/h, the air drag force is completely counteracted by g*sin(20), and you turn on engine, so that you add extra thrust from engine, although the engine thrust is smaller than airdrag force, this is the excess thrust.

Both gravity---g*sin(20) and engine thrust are allied, the sum of these two, are counteracting against air drag force, since the sum of them is greater than air drag( at 610km/h), your la7 speed increases, when you reach 700km/h, air drag is quite more than g*sin(20), so a portion of engine thrust(eg 40%) will be used in completely 100% counteracting air drag. The excess thrust is from the left portion of engine thrust(60%). The more efficiency, the more excess thrust you get, understand?


If you dive at 60 degree angle reaching 700km/h, of course, your engine thrust could not 100% conteract the air drag by itself, so you need gravity--g*sin(60) to help you, if propeller efficiency is high, you need less gravity to help you, and more gravity will be used as excess thrust. if you turn off engine(efficiency=0), you need the most gravity to help, thus minimum excess thrust.

Therefore, excess thrust comes from the sum of gravity and engine thrust. Gravity and engine thrust help each other, this is teamwork, if one of them performs better, the other will have more ability to counteract air drag, Understand? The more propeller efficiency, the more sum, the faster dive.

[BlackBerry]

Who is stealing 500 hp???

How much excess excess thrust does a P47 have at 20,000 feet in level flight at Vmax?

NONE

How much excess thrust does any propeller airplane have at Vmax?

NONE

If our airplanes Vmax is 420mph EAS and we dive to Vne at what speed does our Excess Thrust produced by the Propeller = 0?

Vmax

How much Excess power does a CSP propeller aircraft have from cruise flight to Vmax to devote to a dive excess thrust?

All of the excess thrust produced to Vmax...at Vmax our excess propeller thrust = ZERO

What speed does a CSP equipped aircraft traveling at cruise flight reach zero excess propeller thrust at in a dive?

At Vmax....the same speed as in level flight

What is the design propeller efficiency for a CSP in an aircraft envelope from Vs to Vmax?

n = .85 from Stall to Vmax

I've got your logic, Crumpp. If you still believe that engine could NOT provide excess thrust in a high speed dive, simply shut down your engine. There is a saying:

After loses only then understood treasures.

[Crumpp]

no, that is not what I'm saying. it may provide thrust. but it is not "excess" thrust. that is the key here. excess thrust, excess thrust, excess thrust. it is not excess thrust because Crumpp posted a diagram on csp propellar that shows you can not have peak efficiency beyond Vmax. The only way to get beyond vmax and create excess thrust is to dive at the necessary angle. go back and look how he defined excess thrust. it's the difference between the two force vectors. in level flight, the force vector from gravity has no forward direction. at vmax and level flight, there is no more opportunity to create excess thrust from the prop. you have to dive to create excess thrust and acceleration.

You got it!

One small tweak though....

Crumpp posted a diagram on csp propellar that shows you can not have peak efficiency beyond Vmax.

It is not that you cannot have peak efficiency beyond Vmax. You could design such a propeller but there is little point as all performance the airplane cannot sustain is instantaneous. Of course there would be some serious design trade off's to gain such performance as well. A supersonic propeller design would not work very well on a WWII Piston fighter.

http://www.aerospaceweb.org/question/aerodynamics/q0031b.shtml

The CSP is designed to maintain peak efficiency through the designs sustainable envelope.

[BlackBerry]

I drew these pictures. Hope you understand my opinion about excess thrust.

When speed above Vmax, engine thrust is always smaller than air drag force.

9825

9824

[BlackBerry]

You got it!

One small tweak though....



It is not that you cannot have peak efficiency beyond Vmax. You could design such a propeller but there is little point as all performance the airplane cannot sustain is instantaneous. Of course there would be some serious design trade off's to gain such performance as well. A supersonic propeller design would not work very well on a WWII Piston fighter.

http://www.aerospaceweb.org/question/aerodynamics/q0031b.shtml

The CSP is designed to maintain peak efficiency through the designs sustainable envelope.

Speed in IAS.

This is my test in Il2 4.11m, Tempest cruising 250km/h @3000 m altitude, and dive to 700km/h, then I tried to maintain 700km/h by lowing my altitude in a shallow dive, after getting on deck at 700km/h, Tempest was slowed down to Vmax-600 km/h.


In this whole process, there is 70 seconds during which tempest speed is between 650km/h and 700km/h(IAS). And it took 40 seconds to slow down Tempest from 700km/h to 600km/h on the deck. Don't forget this is in low altitude where the air is thick--high density, if you dive at high altitude where air density is much less, you could hold a longer time in high speed.


If a La7 follows me from the very beginning with same energy, I can easily drag him down to his low efficciency zone----650-700 km/h IAS for 70 seconds. During this period, I could steal several hundreds of HP from him for more than 1 minutes, it's a HUGE energy loss for La7.

9826

[BlackBerry]

A supersonic propeller design would not work very well on a WWII Piston fighter.

See here, 3-blade NACA16 propeller on P47D, propeller tip speed is 1.0-1.1 Mach while efficiency is still quite high.

http://digital.library.unt.edu/ark:/67531/metadc62616/m1/7/

9828

here, effect of compressibility on propeller efficiency.

http://digital.library.unt.edu/ark:/67531/metadc62616/m1/25/

[Crumpp]

When speed above Vmax, engine thrust is always smaller than air drag force.


Right...

When speed above Vmax, engine thrust is always smaller than air drag force.


Correct.

You getting lost in the trees Blackberry and cannot see the forest.

Maybe if you go back to my very first post, it will help you to gain a better understanding. You understand what is going on with the actual forces but do seem to be able to recognize it in the math.

The difference between the force on the axis of motion in the dive and the force on the axis of motion for level flight is your initial excess force that will move the aircraft to its new equilibrium point velocity. The derivative between that and equilibrium is your average excess force along that vector....

http://forum.1cpublishing.eu/showpost.php?p=421123&postcount=98

At Vmax, that initial excess force is composed entirely of a component of weight.

We don't have to break anything down. The detail is already there in our calculations. To determine aceleration, we need the amount of excess force along our vector of motion. It is that excess force that causes the aceleration.

If we start our dive at a velocity below Vmax, then our initial thrust force is the difference between that specific velocity propeller thrust and zero at Vmax. Then we add the additional component of weight that shifts to thrust.

The derivative between that and equilibrium is your average excess force along that vector...

Your argument that your game would benefit from a more "detailed" propeller model such as Blade Element Theory in dive performance is not valid.

You are confusing the mathmatical process of summing the forces with what is actually going on with those forces in a moment in time.

We have already considered that moment in time when we determined our derivative.

[MadBlaster]

MadBlaster, When your la7 diving at 20 degree with constant speed of 610km/h, the air drag force is completely counteracted by g*sin(20), and you turn on engine, so that you add extra thrust from engine, although the engine thrust is smaller than airdrag force, this is the excess thrust.

Both gravity---g*sin(20) and engine thrust are allied, the sum of these two, are counteracting against air drag force, since the sum of them is greater than air drag( at 610km/h), your la7 speed increases, when you reach 700km/h, air drag is quite more than g*sin(20), so a portion of engine thrust(eg 40%) will be used in completely 100% counteracting air drag. The excess thrust is from the left portion of engine thrust(60%). The more efficiency, the more excess thrust you get, understand?


If you dive at 60 degree angle reaching 700km/h, of course, your engine thrust could not 100% conteract the air drag by itself, so you need gravity--g*sin(60) to help you, if propeller efficiency is high, you need less gravity to help you, and more gravity will be used as excess thrust. if you turn off engine(efficiency=0), you need the most gravity to help, thus minimum excess thrust.

Therefore, excess thrust comes from the sum of gravity and engine thrust. Gravity and engine thrust help each other, this is teamwork, if one of them performs better, the other will have more ability to counteract air drag, Understand? The more propeller efficiency, the more sum, the faster dive.

yes blackberry. this example is rigged though. if i spawn from 3000 meters and V max with the engine off, I can also create acceleration or de-cceleration simply by changing the angle of the dive and the result is a new terminal velocity/equilibrium. it's the change in the sum of the two vector forces, not simply "the sum of" the two vector forces. the thrust vector is still zero in this case.

But we have been assuming up to now the engine is on, level flight and v max.

[Crumpp]

it's the change in the sum of the two vector forces, not simply "the sum of" the two vector forces.

well said.

You understand Blackberry that is the excess force that moves the aircraft it is new equilibrium point.

The summing of the forces determines the vector of motion but the rate of change in motion along that vector is a function of the excess force.

For example, when the engine is off our thrust = 0 but our drag force remains. The summing of the forces results in a negative vector and our aircraft slows down as it seeks a new equilibrium point.

If the pilot pushes the stick forward to control the angle that he can shift a component of weight in order to counter act that drag force to maintain velocity or even speed up.

[BlackBerry]

To determine aceleration, we need the amount of excess force along our vector of motion. It is that excess force that causes the aceleration.

Right.

However, what is equilibrium point? In my opinion, the equilirium point is the point where all forces are well balanced.

You dive in 45 degree with 110% WEP, your speed is always increasing, BEFORE you reach the so called " equilibrium point", you lost your wings.

Try il2 4.11m, use Tempest, P51D, P47, fw190d,bf109K, La7, to dive in 45 degree with full throttle, you can NEVER find a equilirium point where the speed stops increase.Could you? Could you? Why? The equilirium point is sth 1300km/h! Those planes will explode before reaching 1300km/h, believe it or not. They are not supersonic a/c. :)

If you dive in a very shallow angle, for example, dive at 10 degree, the equilirium point is sth.700-800km/h which piston planes could withstand. Yes, you can reach this equilirium point.


As I said again and again, dive steeply. If you dive at 45-60% degree, you are always accelarating, you are always increasing your speed, therefore, before you pull to level flight, there is no equilirium point at all in your dive.

Since there is no equilirium point, the Newton 2nd rule tells us:

Force=acceleration*mass

Thus:

dive acceleration=(Excess Thrust in steep dive)/aircraft weight=(engine thrust + gravity along dive- air drag)/(aircraft weight.)

Imagine that there are two la7, "A" is equipped with high efficiency propeller, the other "B" with low efficiency prop, anything else being equal.

At any piont on the 45 degree dive, A always has more engine thrust than B, thus A always has bigger excess thrust than B, finally, A always has better dive acceleration than B.

[Crumpp]

You dive in 45 degree with 110% WEP, your speed is always increasing, BEFORE you reach the so called " equilibrium point", you lost your wings.

Try il2 4.11m, use Tempest, P51D, P47, fw190d,bf109K, La7, to dive in 45 degree with full throttle, you can NEVER find a equilirium point where the speed stops increase.Could you? Could you? Why? The equilirium point is sth 1300km/h! Those planes will explode before reaching 1300km/h, believe it or not. They are not supersonic a/c.

What are you talking about here?

Do you need a method to estimate the velocity of the new equilibrium point given the increase in forces?

[Crumpp]

there is no equilirium point at all in your dive.


Sure there is blackberry, you just have not reached it yet.

Your equilibrium point velocity is found by converting the Vmax TAS to EAS. We are going to change altitude and we don't have to constantly mess with density effects.

Now we can use the relationship our parasitic drag component to find our new velocity. You already know the Cdo of the design.

So using the relationship of parasitic drag force and velocity:

Dp2 = Dp1(V2/V1)^2

Re-arrange to solve for velocity:

At 100 KEAS our airplane produces 5000 lbs of parasitic drag. At what velocity will it produce 10000lbs of parasitic drag?

100 KEAS * SQRT(10000 / 5000) = 141 KEAS

If we suddenly gained 5000lbs of thrust (5000lbs plus 5000 lbs) our new equilbrium velocity would be 141 KEAS.

[BlackBerry]

Sure there is blackberry, you just have not reached it yet.

Your equilibrium point velocity is found by converting the Vmax TAS to EAS. We are going to change altitude and we don't have to constantly mess with density effects.

Now we can use the relationship our parasitic drag component to find our new velocity. You already know the Cdo of the design.

So using the relationship of parasitic drag force and velocity:

Dp2 = Dp1(V2/V1)^2

Re-arrange to solve for velocity:

At 100 KEAS our airplane produces 5000 lbs of parasitic drag. At what velocity will it produce 10000lbs of parasitic drag?

100 KEAS * SQRT(10000 / 5000) = 141 KEAS

If we suddenly gained 5000lbs of thrust (5000lbs plus 5000 lbs) our new equilbrium velocity would be 141 KEAS.

When P51 at Vmax=700km/h, what's the air drag force? 1500lbs?

When P51 dive in 45 angle with full throttle, what's the next equilibrium piont speed?

1200km/h!

When Bf109K dive in 45 angle with full throttle, what's the next equilibrium piont speed?

1100km/h!

When P47D dive in 45 angle with full throttle, what's the next equilibrium piont speed?

1300km/h!

When TempestMKV dive in 45 angle with full throttle, what's the next equilibrium piont speed?

1200km/h!


When Dora dive in 45 angle with full throttle, what's the next equilibrium piont speed?

1100km/h!

Since those planes never reach so called the next equilibrium piont, the equilibrium is totally useless in analysis of 45 degree dive acceleration.Since you have to pull your aircraft out of 45 degree angle far before reaching the equilirium point, you are always accelerating in dive, you always have excess thrust during dive, higher efficiency propeller always provides higher thrust.

The sum of gravity and engine thrust is always bigger than air drag force.


I post the picture again, do you understand me?

9831

[MadBlaster]

blackberry, the sim would be very boring if all the forces were balanced in equilibrium. there would be nothing to do!:-P I can only think of one time that occurs, when your on the ground and the engine is off and the wind is zero. equilibrium point is not something that has to manifest to exist. obviously, there are constraints that may make it impossible to achieve (e.g., max dive speed). It is the process of moving from set of conditions to another. Dynamic verses Static. This is the concept that is being pointed out.

[BlackBerry]

blackberry, the sim would be very boring if all the forces were balanced in equilibrium. there would be nothing to do!:-P I can only think of one time that occurs, when your on the ground and the engine is off and the wind is zero. equilibrium point is not something that has to manifest to exist. obviously, there are constraints that may make it impossible to achieve (e.g., max dive speed). It is the process of moving from set of conditions to another. Dynamic verses Static. This is the concept that is being pointed out.

Yes，in 45 degree dive, aircrafts are always unbalanced , aircrafts are always increasing speed, always accelerating.

This is a dynamics process, in this process, if my la7 throttle is 100% while your la7 throttle is 60%, I can always outdive you when moving to the equilibrium point which impossible for real flight.

Why? My la7 100% engine produce more thrust than your 60% engine in 45 degree dive, so I have more excess thrust during the whole dive, finally, I can get better dive acceleration than you. understand?

Even if you turn off fuselage damage in difficulty setting, both of us could achieved "equilibrium" speed:

I, with throttle 100%, equilibrium speed is 1000km/h
You, with throttle 60%, equilibrium speed is 950km/h

I can still pull away from you because my engine give me more thrust. Look this picture, when both of us reach equilibrium point, my air drag force is higher than you, this is to say, my speed is bigger than yours.
9832

Now , do you still believe that engine could not produce excess thrust during high speed>Vmax dive?

[MadBlaster]

Sorry, I need more information because the example keeps changing. What is the speed of the two planes before they go into the dive? Is the one at 100% throttle already at Vmax? Or are they both at Vmax because the the one at 60% dove down from higher altitude previously? Honestly, this example doesn't seem good one. The information is sketchy. Are you trying to trick me?:)

[BlackBerry]

Sorry, I need more information because the example keeps changing. What is the speed of the two planes before they go into the dive? Is the one at 100% throttle already at Vmax? Or are they both at Vmax because the the one at 60% dove down from higher altitude previously? Honestly, this example doesn't seem good one. The information is sketchy. Are you trying to trick me?:)

Imagine there are two tempestMKV named 'X' and 'Y' respectively.

X is equipped with a good CSP, while Y is equipped with a bad CSP. Everything else being equal. both a/c weight equal. drag coefficient equal, engine is equal ......

Within the envelop, within Vmax, both good propeller and bad propeller share same efficiency, they performs identically. good prop=bad prop=85% efficiency

But when dive into 0.6-0.7Mach which is out of a/c envelop, good propeller=80% efficiency, bad propeller=60% efficiency.

At first, both X and Y use 100% throttle in level flight SIDE BY SIDE, because they share same efficiency within evelop, both speeds are Vmax.

Then, both begin to dive at 45 angle, and after a while, both speed are entering 0.6-0.7 Mach, suddenly, "Y" CSP lose efficiency to 60%, while "X" efficiency is still 80%. That is to say, "X" engine could provide more thrust.

Question: Will "X" begin to pull away from "Y" from now?

[MadBlaster]

doesn't make sense. the props can not be identical. the curves would have to be different slopes. "suddenly"...is this realistic if they are identical? no.

But assuming it is realistic, i say tenatively 'yes', Y falls behind from this 'sudden' loss of thrust on the bad prop and gravity has not completely taken over yet, so I guess there is an excess reverse thrust. but I have to think about it some more.

[BlackBerry]

doesn't make sense. the props can not be identical. the curves would have to be different slopes. "suddenly"...is this realistic if they are identical? no.

But assuming it is realistic, i say tenatively 'yes', Y falls behind from this 'sudden' loss of thrust on the bad prop and gravity has not completely taken over yet, so I guess there is an excess reverse thrust. but I have to think about it some more.

You are beginning to understand me.

"X" vs "Y" ,Everything ELSE being euqal, propellers are different: good prop vs bad prop.

During TAS 0.2-0.6 Mach, good prop=bad prop=85%

During TAS 0.6 -0.8 Mach, good prop> bad prop; ie 80%>60%.

"Y" has no more gravity for help because both dive in same angle=45 degree, and both weight=5 tons.

"Y" has no reinforcement.

[MadBlaster]

the example works better for me if you assume the 'sudden' drop in efficiency for the bad prop happens at the margin of the csp peak envelope at/near Vmax/level. And to make it even more emphasis, the efficiency drops from .85 peak to 0 no thrust when 1 more kph is added above Vmax/level in 1 second, as soon as you enter the 45 dive. also, drag force just kicked you back into the peak envelope. okay, yes the bad prop now has excess negative thrust. because in that 1 second you went from max thrust to no thrust from the prop and drag force pushed you back and not enough time has elapsed for excess thrust from 45 weight vector to overcome the momentary loss from the prop. I'm probably missing something.


Now, we know there are no 'sudden' drops in these curves. they have slopes and they are a functions of TAS, RPM, reduction ratio, blade diameters...etc. this example, rigged.

[BlackBerry]

the example works better for me if you assume the 'sudden' drop in efficiency for the bad prop happens at the margin of the csp peak envelope at/near Vmax/level. And to make it even more emphasis, the efficiency drops from .85 peak to 0 no thrust when 1 more kph is added above Vmax/level in 1 second, as soon as you enter the 45 dive. also, drag force just kicked you back into the peak envelope. okay, yes the bad prop now has excess negative thrust. because in that 1 second you went from max thrust to no thrust from the prop and drag force pushed you back and not enough time has elapsed for excess thrust from 45 weight vector to overcome the momentary loss from the prop. I'm probably missing something.


Now, we know there are no 'sudden' drops in these curves. they have slopes and they are a functions of TAS, RPM, reduction ratio, blade diameters...etc. this example, rigged.
Good prop and bad prop share same diameter, same rpm, same advance ratio@same TAS. Their DIFFERENCE IS THE SHAPE OF AIRFOIL SECTION.

TAS Mach / good CSP / bad CSP
0.6 85% 85%
0.61 84% 83%
0.62 83% 80%
0.63 82% 77%
0.64 82% 73%
0.65 81% 70%
0.66 81% 67%
0.67 81% 64%
0.68 80% 60%
0.69 80% 56%
0.70 80% 52%

//////////////////////

Your TempestMKV equipped with bad propeller, my Tempest with good propeller.

If I drag you into a high speed dive, around 0.7 Mach TAS for 40 seconds, what is your energy loses?

To simulate this sharply efficiency drops for bad propeller, you can simply use il2 4.11m, quick mission, spawn @ 5000 m with Tempest mkv, you intently decrease your throttle to 60% during 0.6-0.7 Mach 45 degree dive and 45 degree zoom.

You will feel the energy loss.

[MadBlaster]

putting the weight vector/dive angle to the side for a bit, I think what is missing here in the discussion is the drag vector. Now, beyond peak/vmax. what is happening is the drag vector is slowly overwhelming the thrust of the propeller as it gets more and more inefficient until efficiency is at zero and advance ratio reaches some high number at some given high TAS. So, it is negative excess thrust between those two vectors because drag force is becoming greater than the prop thrust vector (still ignoring the weight vector for now). So, the question is how is the interplay between these two vectors modeled in IL-2. Maybe it is already accounted for in the modeling of the drag force? Like an effectiveness factor or something that is attached to the drag coefficient as the thrust begins to degrade beyond Vmax? I really have no idea, only speculate. :)


edit:
of course, the only way to get beyond vmax is to dive, and its the sum of all forces...etc. so this interplay between opposing thrust and drag vectors gets masked over by weight/dive vector. am i on the right track?

[Crumpp]

Since those planes never reach so called the next equilibrium piont, the equilibrium is totally useless in analysis of 45 degree dive acceleration.

Airplanes certainly do reach their equilibrium point in a dive.

However the most common restriction to dive performance is dynamic pressure limits <flutter> and mach limits.

Completely irrelevant though as the equilibrium point estabilishes the rate of aceleration in the dive.

You can debate it all day long but it does not change the fact it is how performance is predicted.

Maybe it is already accounted for in the modeling of the drag force?

The excess force is what drives the aircraft to equilibrium. It is all accounted for in the formulation.

so this interplay between opposing thrust and drag vectors gets masked over by weight/dive vector. am i on the right track?

The interplay is covered in the derivative.

You start out with the maximum force which is the moment in transitioning that a component of weight has shifted to thrust and the propeller thrust is still at level flight velocity. That is the maximum excess force you will have available.

Let's look at the rectilinear motion equations and solve both a zoom climb problem and a dive problem using the same airplane at the same entry speeds.

We will end our zoom at Vy or best rate of climb speed and end our dive at the equilibrium point.

We are going to just simplify the drag and thrust values to illustrate the mechanics of solving the problem.

Characteristics of our Airplane:

Weight 9000lbs
Thrust in lbs = 1000lbs
Drag in lbs = 500

Zoom climb from 300mph to Vy at a 45 degree angle:
The airplane will move to equilibrium

Entry speed = 300mph = 441fps
Zoom Angle 45 degrees
Vy = 150mph = 220.5fps

Zoom height:

Sum the forces on the flight path -

9000lbs * sin 45 = 6364lbs
1000lbs – 500lbs - 6364lbs = 5864lbs

a = F/m

m = 9000lbs/32.2 = 279.5 lb-s^2/ft
a= 5864lb/279.5lb-s^2/ft
a = 20.98 ft/s^2

s = (V1^2 – V2^2 ) / 2a

s = (441^2 – 220.5^2)/(2 * 20.98ft/s^2) = 3476.18 ft

3476.18 ft * sin 45 = 2458 ft

Now let's dive under the same conditions:

Characteristics of our Airplane:

Weight 9000lbs
Thrust in lbs = 1000lbs
Drag in lbs = 500

Zoom climb from 300mph to Vy at a 45 degree angle:

Entry speed 300mph = 441fps
Angle of Dive 45 degrees

We need a ballpark of our equilibrium speed. A quick method is to use the relationship of Parasitic drag. It is the major drag component at high speed. More detailed analysis will give better results but this is accurate within 10%. 10% is acceptable for climb/dive performance.

441(SQRT 1000/500) = 624fps

At 624 fps, the acceleration about the CG will be zero.

Dive:

Sum the forces on the flight path -

9000lbs * sin 45 = 6364lbs
1000lbs – 500lbs + 6364lbs = 6864lbs

a = F/m

m = 9000lbs/32.2 = 279.5 lb-s^2/ft
a= 6864lb/279.5lb-s^2/ft
a = 24.6 ft/s^2

s = (V1^2 – V2^2 ) / 2a

s = (441^2 – 624^2)/(2 * 24.6ft/s^2) = -3961ft (negative is a vector direction)

3961ft * sin 45 = 2801 ft of altitude lost!!

[Crumpp]

Good prop and bad prop share same diameter,

There are very few airplanes with a "bad propeller". It does happen but is caught very quickly as nothing will line up between predictions and the realized.

Including dive performance....which is how they caught it.

That is why Hawker initiated the study.

[MadBlaster]

Okay that is helpful. What Blackberry is wondering, we know the software does these calculations continuously every few milliseconds. In a high speed dive beyond Vmax where TAS is increasing, does the software recognize the degradation of this value? -> Thrust in lbs = 1000lbs. Or maybe it handles it by applying effectiveness factor to this value ->Drag in lbs = 500? Or maybe it ignores it and keeps both opposing forces as static (i.e., "maximum excess force you will have available")?

[Crumpp]

Okay that is helpful. What Blackberry is wondering, we know the software does these calculations continuously every few milliseconds. In a high speed dive beyond Vmax where TAS is increasing, does the software recognize the degradation of this value? -> Thrust in lbs = 1000lbs. Or maybe it handles it by applying effectiveness factor to this value ->Drag in lbs = 500? Or maybe it ignores it and keeps both opposing forces as static (i.e., "maximum excess force you will have available")?

I can't answer any specific questions about IL2 FM. If it uses standard methods to predict aircraft performance, then it does account for it.

I would be willing to bet it does use standard methods.

Now you know the specific numbers for thrust and drag change. For example here is the P47D22 at Take Off weight from Vs to Vmax:

Thrust available in Pounds
6353.75
6353.75
6353.75
6051.190476
5776.136364
5294.791667
4887.5
4538.392857
4235.833333
3971.09375
3737.5
3630.714286
3529.861111
3434.459459
3344.078947
3258.333333
3176.875
3099.390244
3025.595238
2955.232558
2888.068182
2823.888889
2762.5
2703.723404
2647.395833
2593.367347
2541.5
2491.666667
2443.75
2425.09542

Thrust required in Pounds
1537.476184
1537.476184
1537.476184
1458.574233
1396.29734
1311.942922
1269.557568
1259.393629
1274.840011
1311.284626
1365.430601
1398.36277
1434.870602
1474.747484
1517.813624
1563.911983
1612.9049
1664.671298
1719.104337
1776.109457
1835.602718
1897.509403
1961.762824
2028.303316
2097.07736
2168.036844
2241.138416
2316.342935
2393.614985
2425.09542

[MadBlaster]

yes, from your earlier post on parasitic drag force verse velocity and EAS method.

I suppose you got those numbers from customizing udpgraph tool? I think you must manually configure it somehow, or do calculation off the output file? I don't see those parameters in my version.

[BlackBerry]

We are going to just simplify the drag and thrust values to illustrate the mechanics of solving the problem.

Characteristics of our Airplane:

Weight 9000lbs
Thrust in lbs = 1000lbs
Drag in lbs = 500

Zoom climb from 300mph to Vy at a 45 degree angle:
The airplane will move to equilibrium

Entry speed = 300mph = 441fps
Zoom Angle 45 degrees
Vy = 150mph = 220.5fps

Zoom height:

Sum the forces on the flight path -

9000lbs * sin 45 = 6364lbs
1000lbs – 500lbs - 6364lbs = 5864lbs

a = F/m

m = 9000lbs/32.2 = 279.5 lb-s^2/ft
a= 5864lb/279.5lb-s^2/ft
a = 20.98 ft/s^2

s = (V1^2 – V2^2 ) / 2a

s = (441^2 – 220.5^2)/(2 * 20.98ft/s^2) = 3476.18 ft

3476.18 ft * sin 45 = 2458 ft


Crumpp，when airplane zoom 45 degree from 300mph to 150mph, It takes a quite long time: 20 seconds?

In the whole zoom process, Is the acceleration a constant or a variable ? All your formular is of "constant accelerated motion". That's not correct.

In fact, when airplane begin to zoom, the "a"=20.98ft/s^2, however, after a few seconds, as speed drops, the engine thrust increase to 1100lbs, and the air drag will be 450lbs, so the "a" is no long 20.98, "a" will be smaller than 20.98. The acceleration changes during the whole zoom process, so it's a "variable accelerated motion".

I am surprised, your math model is too simple to get correct result.