Official Fulqrum Publishing forum
Page 14 of 34 « First 41213 14 151624 Last »
Show 100 post(s) from this thread on one page

Official Fulqrum Publishing forum (http://forum.fulqrumpublishing.com/index.php)
-   Daidalos Team discussions (http://forum.fulqrumpublishing.com/forumdisplay.php?f=202)
-   -   Why still no dive acceleration difference? (http://forum.fulqrumpublishing.com/showthread.php?t=31464)

BlackBerry 05-13-2012 02:46 AM
1 Attachment(s)
Quote:
Originally Posted by MadBlaster (Post 424466)
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

Attachment 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 05-13-2012 06:22 AM
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 05-13-2012 08:23 AM
Quote:
Originally Posted by MadBlaster (Post 424690)
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 05-13-2012 09:38 AM
Quote:
Originally Posted by BlackBerry (Post 424730)
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 05-13-2012 11:03 AM
1 Attachment(s)
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.

Quote:
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/Convent...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.o...90a8-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.o...ed-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.
Attachment 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 05-13-2012 01:39 PM
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.:)

Quote:
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 05-13-2012 04:05 PM
Quote:
Originally Posted by BlackBerry (Post 424807)
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.o...90a8-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.o...ed-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.
Attachment 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 05-14-2012 12:55 AM
Quote:
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?

Quote:
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.

Quote:
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 05-14-2012 02:49 AM
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 05-14-2012 03:52 AM
Quote:
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?




Quote:
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.
Quote:
(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.


All times are GMT. The time now is 10:56 PM.
Page 14 of 34 « First 41213 14 151624 Last »
Show 100 post(s) from this thread on one page

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright © 2007 Fulqrum Publishing. All rights reserved.