Why still no dive acceleration difference?

[FC99]

Originally Posted by BlackBerry

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]

Originally Posted by mayshine

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]

Originally Posted by 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.

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]

Originally Posted by FC99

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]

Originally Posted by 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

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?

Originally Posted by BlackBerry

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]

Originally Posted by 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.

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