Author Topic: P-39 wondering... (Read 621 times)

lo-muf · « **on:** November 10, 2002, 02:12:06 PM »

Hi, I have a question that follows me since some time, among other questions like: who I am, where are we going, what's the meaning of life. The question is: why the English, who had completely ruined a nice project of an average ground attack plane by fitting a Rolls Royce Merlin into a P-51B, did not the very same thing with a P-39 Airacobra (which they had under the name of P-400)? Yes, it's the well known "what if" territory but this plane was already fast with the Allison, the brit engine could only add more speed to a 37mm cannon making of it a nice performer in the ETO as a pure fighter rather than mere ground attack stuff...

Was the Merlin too heavy to fit it in the Airacobra fuselage, so the plane simply would have been seated on his tail? Was too big the delusion so the P-39 didn't had another chance to improve his design?
Or simply was too risky to divert a badly needed engine for the Spitfire/Lancaster to a big flying question mark?

All written above cames when you don't have a woman, so I eventually apologize for the raving

whgates3 · « **Reply #1 on:** November 10, 2002, 03:01:02 PM »

the P-39 had dangerous flying characteristics - tendency to tumble & get into unrecoverable (inverted, flat) spins.
low rate of fire on 37mm made it somewhat difficult to use in air-to-air combat, but not too hard against ground targets

palef · « **Reply #2 on:** November 10, 2002, 03:35:44 PM »

Quote

Originally posted by whgates3
the P-39 had dangerous flying characteristics - tendency to tumble & get into unrecoverable (inverted, flat) spins.
low rate of fire on 37mm made it somewhat difficult to use in air-to-air combat, but not too hard against ground targets

The "tumbling" issue reported about the P39 is apocryphal.

"Earl" who flew P39s, P400s (export variant of P39) and P47s in WWII, and Skyraiders in Vietnam, and played AW denied that the handling characteristics of the the P39 were any more lethal than any other high-powered prop aircraft and put these comments down to pilot conservatism. If it looks right it will fly right is a maxim that Pilots and Designers tend to stick to and to some people the idea that the engine was behind them, and the propshaft ran between their legs made it "look" wrong. As Earl said if you hit the ground at 300mph it doesn't matter if the engine is behind or in front you're going to die.

The Russians made good use of the P39 and P63 in both Ground Attack and Med Alt fighter roles. Perception and urban legend did the P39 in in Western eyes anyway, more so than any unpleasant handling characteristics.

palef.

Pongo · « **Reply #3 on:** November 10, 2002, 04:30:20 PM »

Using soviet success with the p39 to refute the stall issue is misgueded. They identified exactly the same behavior in thier tests.

Innominate · « **Reply #4 on:** November 10, 2002, 04:34:13 PM »

The 37mm cannon sounds good but isnt of much use in a dogfight. (Try furballling in a Yak9t sometime)

palef · « **Reply #5 on:** November 10, 2002, 04:40:33 PM »

Quote

Originally posted by Pongo
Using soviet success with the p39 to refute the stall issue is misgueded. They identified exactly the same behavior in thier tests.

Pongo, Earl was quick to point out that all aircraft have handling issues that require you to either stay in the envelope or ride the edge of it. If you have a documented sequence of events that happen if you exceed that envelope, why do it?

I repeat that the P39 was regarded as 2nd rate because of tumbling and flat spins is misleading at best.

palef

HoHun · « **Reply #6 on:** November 10, 2002, 05:18:50 PM »

Hi Palef,

>The "tumbling" issue reported about the P39 is apocryphal.

I used to think the same until recently I found a translation of a paragraph from the "Tsagi" book on WW2 aircraft, in this case on the P-63:

"In order to become acquainted with the new aircraft the VVS sent test pilot A, G Of kochetkova and testing engineer F. P. Suprun to the USA. Spin characteristics was the problem, which interested Soviet specialists the most. G. Kochstkov was interested in flight testing the aircraft under these conditions. And it turned out that the assurances Bell that the P-63 would not enter into flat spin, were unfounded. In a test flight A. G. Kochetkov proved that like its predecessor the P-63 had a tendency towards flat spins. After numerous, but futile attempts to pull the fighter out of the spin he was forced to bail out of the aircraft and parachute to the ground. This test forced the aircraft to go through a number of design in order to move the center of gravity forward. Additional flight limitations were also introduced. "

>"Earl" who flew P39s, P400s (export variant of P39) and P47s in WWII, and Skyraiders in Vietnam, and played AW denied that the handling characteristics of the the P39 were any more lethal than any other high-powered prop aircraft and put these comments down to pilot conservatism.

P-400 (and P-39) veteran M. F. Kirby mentioned that he never heard of a single instance of the P-39 doing the feared flat spin, but he also pointed out that the pilots did their best to avoid getting into any kind of spin anyway.

Regards,

Henning (HoHun)

palef · « **Reply #7 on:** November 10, 2002, 06:44:38 PM »

Thanks HoHun!

Always nice to update the ol' database.

It would be very nice to get hold of an English translation of Tsagi.

Regards

palef

J_A_B · « **Reply #8 on:** November 10, 2002, 07:20:26 PM »

The Merlin engine was no better than the Allison. It was a little smaller but was actually less durable to damage and abuse.

The reason the P-51B performed so much better than the P-51A was it had a better propeller and supercharger. The Merlin's slightly smaller size and different layout made it easier to fit the 2-stage/2 speed supercharger into the limited space.

The P-40E was modified to carry a Merlin engine and a number of planes of this type were built (known as P-40F), but since it had the same propeller and lousy supercharger it didn't perform much better at all. The P-39 would be no different.

Eventually an improved version of the P-39 known as the P-63 was built. It featured an improved Allison engine, 4-blade propeller and a better supercharger and it did indeed have pretty good performance (and it still hads that 37mm cannon). Top speed was over 400 MPH at altitude.

Also of note is a late-model P-40 (XP-40Q) was built with a 4-blade propeller and a good supercharger (once again it still had an Allison). Speed increased from around 370 MPH for the P-40N up to about 420 MPH for the XP-40Q.

J_A_B

Daff · « **Reply #9 on:** November 10, 2002, 07:24:52 PM »

Bell tested the P-39 extensivly and found the only thing close to a 'tumble', was if the stick was held back through the stall, the plane would do a series of whip-stalls, which when seen from the ground, could look like a tumble.
Centering the stick would set the plane in to a normal spin and normal recovery procedures could be used.

What the P-39 did have, was the lightest controls of any aircraft in WW2 (number escapes me...3.5lbs/G??) and also the most sensitive controls, making it easy to overfly it, giving the P-39 it's bad reputation.

Daff

-ammo- · « **Reply #10 on:** November 10, 2002, 08:28:20 PM »

Without going back to reference this, I believe that the reason the P-39/P-400 program was not pursued like the P-51 and the P-47 program was purely political. Fitted with the Merlin, this Airframe would undoubtedly have been a fine performer both in the attack role and with some armement alterations, inn the air to air role.

Daff · « **Reply #11 on:** November 10, 2002, 09:26:45 PM »

^^ Yes, the P-39 was the cleanest airframe of any of the US WW2 fighters and had some kind of charging option for higher alts been seriously pursued it could have been a serious contender in the ETO.

Daff

Guppy · « **Reply #12 on:** November 10, 2002, 09:47:03 PM »

Quote

Originally posted by -ammo-
Without going back to reference this, I believe that the reason the P-39/P-400 program was not pursued like the P-51 and the P-47 program was purely political.

Wasn't the P-39's range a bit of an issue? If I recall my numbers correctly, the P-39 only carried 120 USG internally, versus 159 USG for the P-40 and 180 USG for the P-51 (without fuselage tank)...

While we're on the subject of the P-39, does anyone recall the comparative tests done against the captured A6M2? One of my references quotes the test report as stating that the P-39D began the test using 70" of manifold pressure! (The engine then - surprise, surprise - began to detonate and they reduced power to 52" MP.)

Does anyone have any idea why the evaluation group would try such an extreme level of overboost?

kreighund · « **Reply #13 on:** November 10, 2002, 11:11:27 PM »

It was not uncommon in the field for "local mods" to take place..the engine manufacturers tended to make restrictions on performance on the safe side....the field engine mechanics knowing better "eh..eh..eh" would soup-up the engine a bit...like when we overclock our cpu for faster performance..

If you remove the boost protection from the engine you could get 70" of manifold pressure..but look out...

funkedup · « **Reply #14 on:** November 11, 2002, 12:00:18 AM »

Another thing to consider is that the design of the reduction gear and driveshaft for the P-39 was not a trivial task and it was customized for the V-1710. If the V-1650 were substituted it would have required design of a new drivetrain suitable for that engine.

On the other hand, versions of the V-1650 already existed which were suitable for installation in the Mustang, so replacing the V-1710 with the V-1650 was a somewhat easier task in that aircraft.