Author Topic: P-39 wondering...  (Read 586 times)

Offline GRUNHERZ

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P-39 wondering...
« Reply #15 on: November 11, 2002, 12:09:28 AM »
Simple, while the Brits generally liked their allison mustangs they vehemently hated their P400s and sent them back to the USA. :D

That said I would love to get an early P39D/P400 in US Pacific markings, please!!!

Offline whgates3

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P-39 wondering...
« Reply #16 on: November 11, 2002, 01:33:16 AM »
this is from an interview w/ Dr. Robert Gilruth who worked at Langley Memorial Aeronautical Laboratory '36 - '45 (later he was director of the Manned Spacecraft Center '61 - '72):
...WOLKO: This is again getting back now to Bell Aircraft, on the P-39, did you ever get the P-39 down at Langley to test it?

GILRUTH: Yes.

WOLKO: Was there a tumble problem with that aircraft?

GILRUTH: People thought it did.

WOLKO: That was one of the rumors that went around with the P-39.

GILRUTH: Yes, people tended to think it did. I don't think we were ever that adventurous with it. But it would dig in, and the force per G was pretty nominal until you got to high Gs and then the force per G went to about zero, and it would pull itself in. I know that. I remember that. And that was bad.

WOLKO: Was that because of the engine in the rear?

GILRUTH: I have no idea why. I don't think so. I think it had something to do with the fabric on the elevators. There are all kinds of possibilities. For so many years we just took ailerons and other control surfaces and put canvas over them and dope and when you got to high speed, you had no idea what the shape of that aileron was. It depended so much on the internal pressure, the tension on the fabric and the dynamic pressure.

WOLKO: It could balloon out on you.

GILRUTH: It could balloon out or it could suck in, depending on how it was vented. And similarly with the elevators. So in those days, you could get all kinds of things that you wouldn't understand. It was the British that finally said, "Isn't it time we quit fooling around with the fabric on something as sensitive as that?" My goodness, sure.

WOLKO: So the British were first to put metal skin on their...

here is a pic of Dr. Gilruth showing JFK a small model of the Apollo Command Module


the following is from a section of an autobiography of Robert E. Riddle, at the time flying w/ the 28th squadron in Panama (Later Lt. Riddle became an 11 victory ace w/ the 31st Figther Group, 307th Squadron in the MTO)
"....  Whatever its faults, I actually enjoyed flying the machine.  Besides having a center of gravity far back, little servo tabs on ailerons and elevators made the controls extremely sensitive.  An uncoordinated maneuver could cause the ship to snap roll and in some cases tumble end-over-end until dropping into a flat spin.  The snap roll was much more likely at slow speeds and took it's toll on pilots landing out of a tight circular approach.  But I found that at speed, the P-39 was as easy to hold in a three-G shuddering high speed stall as any other plane I ever flew.   After many complaints and some fatalities attributed to the stalled "tumbling" action,  an experienced Army test pilot was assigned to  investigate.   His report stated that he was unable to induce such a reaction from the ship in any attitude.  But I have seen it happen and a friend of mine twice experienced it while attempting to perfect a vertical circular loop..."

and of course theres this song sung by USAAF pilots
Don't give me a p-39,
With the engine mounted behind,
It'll tumble and roll,
And dig a deep hole
Don't give me a P-39.
It'll stall out and spin,
And soon auger in,
Don't give me a P-39
 
« Last Edit: November 11, 2002, 01:38:43 AM by whgates3 »

Offline HoHun

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P-39 wondering...
« Reply #17 on: November 14, 2002, 03:41:58 PM »
Hi Whgates,

Thanks for the quotes!

>GILRUTH: Yes, people tended to think it did. I don't think we were ever that adventurous with it. But it would dig in, and the force per G was pretty nominal until you got to high Gs and then the force per G went to about zero, and it would pull itself in. I know that. I remember that. And that was bad.

"Bad" sounds like a mild understatement here. What Gilruth describes is the same as the feared "control reversibility" of the P-51 when it had a full fuselage tank.

When the pilot is pulling at the stick to make a hard high-speed turn and the stick force suddenly disappears, he is able to pull more Gs than the aircraft (or the pilot himself) can endure. If the force diminishes before he can react, he actually will pull excessive Gs since he's still applying a force on the stick.

Among the criteria the NACA had defined to ensure military aircraft could be operated safely was a minimum stick force per G to prevent just this kind of self-destructive handling characteristic. (Of course, if it only happened in a certain part of the envelope, it might have escaped the test pilots.)

Regards,

Henning (HoHun)

Offline whgates3

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P-39 wondering...
« Reply #18 on: November 14, 2002, 03:55:08 PM »
ja, the gilruth stuff was kinda off topic, but the dude's résumé is so impressive i had to include it. Lt. Riddle's accout is much more convincing - sounds like the engineers at Langley didn't wring the bird out nearly as thoroughly as the fighter pilot trainees did.  it dose make sense to me that a plabe with it's engine mounted like the P-39s was, would, when outside the flight envelope, tumble or do just about anything and be very tough to recover

Offline HoHun

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P-39 wondering...
« Reply #19 on: November 14, 2002, 04:21:50 PM »
Hi Whgates,

>ja, the gilruth stuff was kinda off topic, but the dude's résumé is so impressive i had to include it.

I'd say there's a close connection to the flat spin topic, though: If you encounter sudden reversibility in an asymmetric flight condition, you might not overstress your aircraft but actually whip it violently into a spin instead.

Regards,

Henning (HoHun)

Offline gripen

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P-39 wondering...
« Reply #20 on: November 14, 2002, 04:54:34 PM »
My impressions is that "tumble" phenomena was connected with center of gravity and I don't know if NACA, AF or manufacturer tested all possible combinations. Maybe it happened just with given CG.

gripen

Offline whgates3

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P-39 wondering...
« Reply #21 on: November 14, 2002, 07:11:33 PM »
the P-51 had handling trouble with a full fuselage tank (~80 gallons or about 700 lbs) and didn't really manuver well (this is according to book i read by a 31st FG pilot) until fuselage tank was down to ~30 gallons.  i would assume that a heavy mass near the CG would cause handling problems due to inertial effects.  if this is the case then the allison engine in the P-39 (nearly 1600 lbs) could be a serious pain in the oscar....
"plabe"...LOL