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Jungmann
08-26-2004, 03:09 PM
Bought the farm enough times in a flat spin in a P-39 to begin to wonder if this particular nasty characteristic was due to the mid-mounted engine? Something to do with control ineffectiveness in the spin, and lack of weight in the nose to pull the AOA down and recover?

Aero engineers, please weigh in.

And has anybody experienced the "tumble" P-39 pilots spoke about? Apparently an uncontolled a** over tit maneuver--some 39 pilots got into it, some said they never saw it. Is it in the model?

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Jungmann

Jungmann
08-26-2004, 03:09 PM
Bought the farm enough times in a flat spin in a P-39 to begin to wonder if this particular nasty characteristic was due to the mid-mounted engine? Something to do with control ineffectiveness in the spin, and lack of weight in the nose to pull the AOA down and recover?

Aero engineers, please weigh in.

And has anybody experienced the "tumble" P-39 pilots spoke about? Apparently an uncontolled a** over tit maneuver--some 39 pilots got into it, some said they never saw it. Is it in the model?

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Jungmann

VW-IceFire
08-26-2004, 03:55 PM
Largely caused because of the center of gravity of the plane being in the middle instead of towards the front like in most planes.

This is of course because the engine is mounted there and the 37mm cannon takes up some of the area at the front.

Definately a problem for this plane...anothe reason why the USAAF didn't like it. The later models apparently had some correction to this problem so it was less servere but still an issue.

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El Turo
08-26-2004, 04:05 PM
Compare a picture of a spitfire and P-39 side by side and you'll notice that the cockpit and wings (among other things) are positioned quite differently to make up for the engine placement and CG.

The "tumble" and vaunted instability of the p-39 are vastly inflated and perpetuated mythology.

The pilots hated the ergonomics of the plane, hated having the engine behind them in case of a forced landing and hated the mid-to-high altitude performance of the plane. Speaking to the rate of fire and muzzle velocity, one veteran I spoke with described the 37mm cannon to me as a nearly useless softball pitching machine.

Because they disliked the aircraft, many pilots began a smear crusade to get rid of the things in favor of better aircraft. The army air corps ran many test flights with cameras and instrumentation to try and repeat the claims of tumbling and were never able to substantiate the reports.

That's the real truth.

Late,

~T.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
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~V.

F19_Ob
08-26-2004, 04:08 PM
The russians lightened the p39 as much as they could, pulling out all kinds of stuff from it and removing unescessary guns.
Several times I have encountered that they put in leadweights to balance it better.

'Golodnikow' describes and confirms this also in this interview about the p39 in russia. Here:

http://airforce.users.ru/lend-lease/english/articles/golodnikov/part3.htm


U might want to peek at his opinions about the other planes he flew in combat ( I-16 , Hurricane, p40, p39) and the others he tested aswell as his opinions about the enemy planes.

4 interviews in all. Begin with the first then:

http://airforce.users.ru/lend-lease/english/articles/golodnikov/part1.htm

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XyZspineZyX
08-26-2004, 04:58 PM
I'd also heard the tumbling to be caused by emptying the heavy 37mm ammo in the nose, which would shift the CoG in combat.

Not sure how true or untrue that is, but it sounds plausible that loosing off a goodly % of that large, heavy ammo would shift your CoG, and if you didn't trim to adjust for it...

Huckebein_UK
08-26-2004, 05:03 PM
The same could be said for any plane that didn't have the guns mounted on the centre of gravity though, couldn't it? No reason it should effect the P-39 any more than, say, the Yak-9k...

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Jungmann
08-26-2004, 05:13 PM
I know the P-39 was controversial in the USAAF. But Chuck Yeager trained on one out of Hamilton Field, Calif, before he went overseas, and he says in print he loved the airplane, could do anything he wanted with it, no vices, etc. On the other hand, he was (and is) a master stick and rudder man--I wonder if the pilot's opinion about the plane correlates to the pilot skill?

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Jungmann

El Turo
08-26-2004, 05:19 PM
The P51 was dangerously unstable.



...if you flew it like a ****** with a full fuselage tank.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,
reloading my rifle.

~V.

XyZspineZyX
08-26-2004, 06:06 PM
Huckebein, the weight of ammo in a P-39 is probably a LOT more than the weight of ammo of ShVaks. You have to factor the weight of the gun, the weight of the ammo, and the belts and other coupling required to mount the gun and keep it operating.

berg417448
08-26-2004, 06:26 PM
In test pilot A.M "Tex" Johnston's biography he mentioned that the 37mm shell casings were too large to be ejected in flight without potential of damage to the aircraft.

He further mentioned that although the flight and shop manuals were specific that the aircraft must not be flown in non-combat situations without the proper ballast in the nose, the regulations were sometimes violated ...sometimes with disasterous results.

WTE_Galway
08-26-2004, 06:34 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>--I wonder if the pilot's opinion about the plane correlates to the pilot skill?

<HR></BLOCKQUOTE>


yes .. that never seems to occur to peopl eon here

a statement made 50 years ago (when most planes were lethal to the inexperienced) by a 10,000 hour test pilot with combat time that a plane "is easy to fly and difficult to spin" is taken to mean that a weekend warrior flying with a plastic joystick on a PC should be able to do advanced aerobatics on the simulated version with no training whatsoever http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Cragger
08-26-2004, 09:25 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Jungmann:
I know the P-39 was controversial in the USAAF. But Chuck Yeager trained on one out of Hamilton Field, Calif, before he went overseas, and he says in print he loved the airplane, could do anything he wanted with it, no vices, etc. On the other hand, he was (and is) a master stick and rudder man--I wonder if the pilot's opinion about the plane correlates to the pilot skill?

http://img.photobucket.com/albums/v365/Jungmann/IL-Sig3.jpg

Jungmann<HR></BLOCKQUOTE>

The P-39 is also the first aircraft to nearly end his flying career as at an early stage. During a mock attack on some bombers the engine seized on his P-39 forcing him to hit the silk. When the chute's canopy opened the shock broke his back, fortunately for history no spinal cord damage occured.

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mortoma
08-27-2004, 09:35 AM
Yea but Cragger, that's not the fault of the P-39 is it?? The engine can sieze in any aircraft, and also the same parachute accident could have happened no matter what aircraft he was flying.
So your point is irrelevant to the the P-39 stability/spin issue and whether or not it was a widow maker.

Covino
08-27-2004, 09:58 AM
The P-39's came out of flat spins a little harder because its center of gravity was a bit further back than normal. More nose weight can help "lead" the plane back into a normal flight path when tumbling through the air.

Also, you'll notice the tail section of the plan is a little short (especially considering the aft center of gravity of the plane). This made the plane a bit unstable.

It was a good training aircraft though. Pilots liked its tricycle landing gear for easier takeoffs and landings (the hardest part of flying aside from combat).

El Turo
08-27-2004, 10:44 AM
What do you notice about the relationship between wing/engine/cockpit placement in each of these designs and how they relate to the CG?

Let go of the mythology.

http://www.lowapproach.com/Images/p39.jpg
http://www.mebsuta.com/jpg/spitfire.jpg
http://www.sanchez-j.nom.fr/Ferte-Alais/99/Me109-02.gif

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,
reloading my rifle.

~V.

BinaryFalcon
08-27-2004, 10:56 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by H_Butcher:
What do you notice about the relationship between wing/engine/cockpit placement in each of these designs and how they relate to the CG?

Let go of the mythology.

<HR></BLOCKQUOTE>

I'm not sure I understand what you mean when you write, "Let go of the mythology".

While I don't know the actual CG location of the planes in the pictures you posted, based on what I know of the planes themselves and planes in general, here's roughly where I'd expect to find them:

P-63: Right about the end of the exhaust stack, probably just forward of the aft end of it.

Spitfire: Right around the forward edge of the wingwalk compound.

109: Just about centered on the panel line between the last small panel and the forward edge of the windscreen.

The P-63 would be farthest aft, with the CG likely located behind the pilot. The other two aircraft would have the CG located most likely forward of the pilot. At least that's what I'd expect.

I'm not quite sure how this would relate to the "mythology" though, as a farther aft CG will generally make the aircraft more difficult to recover if it should go into a spin.

Jungmann
08-27-2004, 12:11 PM
Reaching back with a muzzy memory to my old flying days, it seems to me the CG was always about one-third back from the leading edge of the wing at the point of maximum lift, no matter what the design--wings more forward on the fuselage, wings more aft, high wing, low wing. And the task of the warplane designer was to keep the expendable weight (fuel, ammo, bombs) as near this point as possible (thus fuel and ammo in the wings, fuel in front or back or even--190--underneath the pilot, bombs right under the CG) so that as these weights were dropped or burned or fired off, it wouldn't affect the CG that much. A p-63/p39 type design would need the wings forward on the fuselage to place the CG on that 1/3 of the wings point, given the significant weight of the engine aft of the wings on that long lever.

But somebody raised an interesting point--that as the ammo from the P39/63nose guns--especially the heavy 37mm rounds--were fired off, did that drastically affect the CG, and thus the pitch stability of the A/C?

And we know how a late P-51 with a full fuselage tank was dangerously unstable in pitch until about half of the 45 gallons had been burned off--a trade off of range for stabiltiy

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Jungmann

Cragger
08-27-2004, 12:34 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by mortoma:
Yea but Cragger, that's not the fault of the P-39 is it?? The engine can sieze in any aircraft, and also the same parachute accident could have happened no matter what aircraft he was flying.
So your point is irrelevant to the the P-39 stability/spin issue and whether or not it was a widow maker.<HR></BLOCKQUOTE>

Actually the problem was inherent to the P-39s design. The transfer case and reduction box that ran between the pilots feet was more prone to failures. Investigation of the accident indicated that the transfer case siezed which is good as the engine siezing.

As for the stability legacy of the P-39.. meh who knows Yeager enjoyed any aircraft that flew practically. In his whole autobiography he never really said anything negative of the aircraft he flew, fought in, and tested. Not on the X-1 that nearly killed him thru its loss of control effectiveness at critical mach, or the X-1A that fell to inertia coupling, nor the P-80s who's turbine decided to leave thru the side of the fuselage, or the trainer who's engine failed and he crash landed nearly into a farmer's house and nearly got court martialed over. Or the F4 he ejected from and recived burns over half his face from the rocket nose hitting him in the head after he releaed from the seat. He just loved to fly and was a firm if not the premire believer that "Its the man not the machine".

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Cragger
08-27-2004, 12:35 PM
Actually I should say Loves to fly because he still test flys aircraft at request for the USAF and NASA.

http://www.centennialofflight.gov/essay/Explorers_Record_Setters_and_Daredevils/yeager/EX30G4.htm

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LilHorse
08-27-2004, 01:55 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Stiglr:
Huckebein, the weight of ammo in a P-39 is probably a LOT more than the weight of ammo of ShVaks. You have to factor the weight of the gun, the weight of the ammo, and the belts and other coupling required to mount the gun and keep it operating.<HR></BLOCKQUOTE>

Yer. And let's not forget that even if you emptied the ammo in a Yak 9 you still had a big ol' engine UP FRONT. The shift of the CG back would be very slight.

El Turo
08-27-2004, 01:56 PM
Also, it is important to note that for quite some time, the "pull power in spin" step in spin recovery was not included in P39 training if you can believe it. When speaking with WWII veterans that flew it, they said that this accounted for a lot of accidents/deaths. With power off, it was exceptionally standard and routine to recover from a spin, but with power-on it was nearly impossible even from 15,000ft and above.

Regards,

~T.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,
reloading my rifle.

~V.

BpGemini
08-27-2004, 02:14 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Jungmann:
On the other hand, he was (and is) a master stick and rudder man--I wonder if the pilot's opinion about the plane correlates to the pilot skill?
<HR></BLOCKQUOTE>



Of course it does. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-tongue.gif

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RedSpar
08-27-2004, 02:58 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> Originally posted by Cragger:
Actually the problem was inherent to the P-39s design. The transfer case and reduction box that ran between the pilots feet was more prone to failures. Investigation of the accident indicated that the transfer case siezed which is good as the engine siezing.<HR></BLOCKQUOTE>

Actually by most accounts the transfer case in the P-39 was a rugged and reliable system. Chuck Yeager was doing high speed testing at the time of his accident and was pushing his P-39 hard.

A majority of the mechanical problems with the P-39 were the earlier versions with the electric ally controlled prop (they would often run wild - later versions were hydraulic) and the early versions of the Allison engine. Oil leaks were also common.

As for an empty 37mm cannon effecting CG, many pilots did notice an effect on the balance of the plane after depleting the cannon. Experienced pilots had no problems dealing with this but greenhorns did on occasion get themselves in trouble.

When the navy tool a look at the P-39 to make a navalized carrier version called the Airabonita, they looked into moving the main wings slightly rearward to improve CG. For whatever reason this was not done and they opted to shift balast and armor around instead. Needless to say the Airabonita never made it into production.

The P-39 really didn't handle _that bad_ it is just the plane recovered differently than most pilots from standard design planes were used to. Once you were accustomed to the flight characteristics of the P-39 (like Chuck Yeager) it really was a pretty honest plane to fly.

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Jungmann
08-27-2004, 05:19 PM
Is Chuck Yeager still flying military? I heard no.

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Cragger
08-28-2004, 02:42 AM
Yeagers last 'official' flight for the USAF was in 1997 piloting a F-15 beyond the speed of sound in celebration for the centinnal of flight and his piloting the X-1 beyond mach 1.

He is still a very active aviation buff, pilot, supporter, and a consultant for both USAF, NASA, Lockheed. There are rumors that he still flys for NASA but he hasn't commented on it if he does or doesn't.

As to Yeager's incident with the P-39. He wasn't doing any real 'testing'. In reality he was goofing off and it got him in trouble. It ain't the first time either. His autobiography is very amusing because he was/is a very spontaneous person that didn't always go by the book.

In reality he broke the speed of sound in the X-1 on the flight before the official speed of sound breaker flight. He ignited all four rockets at once even though he was ordered to do it a pair at a time, just because he wanted to see what it could do. A sonic boom was heard by ground personnell and civilians in the nearby town. However, the USAF wasn't going to let the 'official' mach 1 flight be one done on the pilots of initiative. The second amuzing part of Yeager's X-1 experience was the flight where he broke the speed of sound he had been goofing off again at a ranch and been thrown off his horse breaking a rib. he hide the broken rib from his superiors and had Jack Riley help him figure out a way to close the X-1s hatch using part of a broom stick which he hide under his flight jacket.

I highly encourage anyone to pick up his autobiography because while it is not only informative it truely shows a man doing what he enjoys to the utmost.

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[This message was edited by Cragger on Sat August 28 2004 at 01:50 AM.]