XP-39 II - The Groundhog Day Thread

[DerAdlerIstGelandet]

Hello XBe02Drvr,

One of the other things worth noting is that with the CoG at 30.2% MAC, the stick only needs to move 1 inch to go from CL 0.2 to CLmax of 1.4.
In combination with very light stick forces, this is not a good thing.
This is why I have commented that control harmony was poor. Aileron forces were noted as fairly high.
It gets a bit better at 2.7 inches with CoG at the forward end of the range.

- Ivan.

Aaaaarrrrggghhhh, stop scarying me!!!

 

[Ivan1GFP]

Aaaaarrrrggghhhh, stop scarying me!!!

Halloween IS coming up!

 

[P-39 Expert]

In other words, when you're trying to recover from the unwarned high G stall/snaproll out of your turn when you were trying to pull enough lead on your victim to get a shot, and there you are recovering from an upset right in front of his wingman's guns. GAME OVER. That matter of fact test pilot language is full of pitfalls for those who don't understand the context.

Once again you missed the context. That statement was made in reference to simple, coordinated, one G stalls in various configurations and maneuvers. It then went on to glaze the reader's eyes over with a lengthy discussion of sideslip angles and control surface deflections ("test pilot talk"), the gist of which was that any stall at higher G with even the slightest sideslip will result in a sharp roll without warning AGAINST aileron deflection. After you've read that sort of test pilot verbiage and then gone out and banged your helmet HARD against the side of the canopy while your world turned sharply upside down in the hands of Zeus a few times, you develop a sense of context. If you're as hard headed as I am, it takes a few tries and an aching neck before enlightenment dawns. Once preconceived notions give way to understanding, it's kind of fun. You're no longer sitting in the airplane and driving it; you're wearing it like a tightly strapped backpack, and it becomes an extension of your body and your will.


Cherry picking again. In several places it stated in low key unobtrusive language that the test aircraft fell short of USAAF published standards in one way or another, most notably stick free static stability (displacement oscillation damping) and stick force gradient/G. That last one is a biggie. A 14.4 lb pull (thumb and fingertips of your right hand) can put 8Gs on you and your aircraft at "normal" (30.2% MAC) CG. The plane can take it; you can't. This is well below USAAF minimum standard, and WAY below desirable values.
That super light stick force gradient combined with the no-warning abrupt stall under G load sets up a scenario which may not be apparent to nonflyers, the accelerated secondary stall. If the pilot pulls hard enough in a high G maneuver to stall the plane and the ailerons and rudder aren't perfectly coordinated, the resulting sudden snap AGAINST the ailerons is apt to set the adrenaline pumping and the right arm tensing. As the plane sorts itself out and is once again flying and the windshield is full of trees getting bigger FAST, the resulting pull on the stick is apt to be greater than the 7-8 pounds required for a smooth manageable pullout, and a secondary stall results at 4 or 5 Gs with another departure from controlled flight, recovery, and panicked secondary stall, until altitude runs out. Desirable stick force gradients are a lesson written in blood.
BTW, they somehow managed to ballast the test airplane to a 24% MAC CG, where it managed a much more reasonable stick force gradient.
Not trying to scare anybody, just verifying some of the less than complimentary opinions that have circulated about the plane. No silk purses here.

"In ANY condition, at ANY time after the stall occurred, recovery could be effected promptly by applying down elevator". Stated in the report more than once. I read the entire report.

Chuck Yeager's favorite plane. Until he got a Merlin P-51.

 

[fubar57]

Chuck Yeager never flew it in combat

 

[P-39 Expert]

My understanding was that the Russians also pushed the Allison way past the USAAC's limits. The price was more frequent overhauls. It would be interesting to know how many V-1710s the USA sent to Russia. outside of those mounted in aircraft.

I have read that they used combat power 3000rpm from takeoff until they returned from their mission. Engine life was something like 50 hours. Of course with only 87 gallons of gas and no drop tank their missions were only on the order of about a half hour.

 

[Ivan1GFP]

"In ANY condition, at ANY time after the stall occurred, recovery could be effected promptly by applying down elevator". Stated in the report more than once. I read the entire report.

Hello P-39 Expert,

That recovery might be just a LITTLE slower if your aeroplane just snap rolled and is inverted.

Chuck Yeager's favorite plane. Until he got a Merlin P-51.

His comment about the P-39 was that he was willing to fight anyone AT LOW ALTITUDE.
Apparently he didn't think it had any useful high altitude capability either.

.......

Have you thought about what it meant for the P-39D-1 to have a CoG at 30.2% MAC when loaded to 7600 pounds?
This is not light for a P-39D. There isn't a lot to leave off to get down to that weight which is only about 50 pounds below its normal loaded weight.

- Ivan.

 

[GregP]

Make Me Operations

Don't give me a P-38 with props that counter-rotate
They'll loop, roll and spin but they'll soon auger in
Don't give me a P-38!

CHORUS:
Just make me Operations
Way out on some lonely atoll
For I am too young to die
I just want to go home.*

Don't give me a P-39 with an engine that's mounted behind
She'll tumble and spin, she'll auger you in
Don't give me a P-39.

Don't give me an old Thunderbolt. It gave many pilots a jolt
It looks like a jug and it flies like a tug
Don't give me an old Thunderbolt!

Don't give me a Peter Four Oh, a hell of an airplane, I know
A ground loopin' bastard. You're sure to get plastered
Don't give me a Peter Four Oh.

Don't give me a P-51, it was all right for fighting the hun
But with coolant tank dry. you'll run out of sky
Don't give me a P-51.

Don't give me a P-61, for night flying is no fun
They say it's a lark. but I'm scared of the dark
Don't give me a P-61.

 

[glennasher]

Chuck Yeager never flew it in combat

And he wasn't an average, everyday pilot, either, he was pretty gifted at the job. An average schmuck like me would have been in serious trouble with a 39.
There's a reason we gave them to the Russians, we didn't really want them. That's been abundantly clear. I'm pretty sure the only reason we used them at all, was because that's all we had available for awhile.
And after the "new and improved" P-63 came out, we (the US) used it for target practice, which says enough, right there. We used it for TARGET PRACTICE. I don't much give a rip what the Russians did with it, we used it for TARGET PRACTICE. Enough said.

 

[P-39 Expert]

Hello P-39 Expert,

That recovery might be just a LITTLE slower if your aeroplane just snap rolled and is inverted.



His comment about the P-39 was that he was willing to fight anyone AT LOW ALTITUDE.
Apparently he didn't think it had any useful high altitude capability either.

.......

Have you thought about what it meant for the P-39D-1 to have a CoG at 30.2% MAC when loaded to 7600 pounds?
This is not light for a P-39D. There isn't a lot to leave off to get down to that weight which is only about 50 pounds below its normal loaded weight.

- Ivan.

P-39D was a dog at 7650lbs. Could be made competitive by losing the nose armor and the .30s. Move the radio up from the tail cone for balance. For the umpteenth time.

 

[P-39 Expert]

And he wasn't an average, everyday pilot, either, he was pretty gifted at the job. An average schmuck like me would have been in serious trouble with a 39.
There's a reason we gave them to the Russians, we didn't really want them. That's been abundantly clear. I'm pretty sure the only reason we used them at all, was because that's all we had available for awhile.
And after the "new and improved" P-63 came out, we (the US) used it for target practice, which says enough, right there. We used it for TARGET PRACTICE. I don't much give a rip what the Russians did with it, we used it for TARGET PRACTICE. Enough said.

The Russians beat the Luftwaffe with the P-39, after they lightened it a little.

 

[DerAdlerIstGelandet]

And he wasn't an average, everyday pilot, either, he was pretty gifted at the job. An average schmuck like me would have been in serious trouble with a 39.
There's a reason we gave them to the Russians, we didn't really want them. That's been abundantly clear. I'm pretty sure the only reason we used them at all, was because that's all we had available for awhile.
And after the "new and improved" P-63 came out, we (the US) used it for target practice, which says enough, right there. We used it for TARGET PRACTICE. I don't much give a rip what the Russians did with it, we used it for TARGET PRACTICE. Enough said.

For god sakes, stop scaring me!!!

 

[fubar57]

And for the umpteenth time, if it was that easy, why didn't Bell do it?

 

[glennasher]

The Russians beat the Luftwaffe with the P-39, after they lightened it a little.

Of course they did, all those Yaks and Lavochkins, Migs and others had nothing whatsoever to do with that, right?

 

[DerAdlerIstGelandet]

And for the umpteenth time, if it was that easy, why didn't Bell do it?

They were not experts.



And they were scared.

 

[GrauGeist]

Of course they did, all those Yaks and Lavochkins, Migs and others had nothing whatsoever to do with that, right?

Or the P-40, depending on who you talk to...

 

[XBe02Drvr]

One of the other things worth noting is that with the CoG ta 30.2% MAC, the stick only needs to move 1 inch to go from CL 0.2 to CLmax of 1.4.

Only test pilots notice or care how much travel of the controls it takes to make various maneuvers, unless they threaten to hit their stops, or are so extreme as to be awkward in the cockpit. (6'5" instructor in a J3 Cub trying to keep hands and feet clear while student enters and recovers from spins.) What matters to everyday pilots is control pressures, not control displacements.

 

[XBe02Drvr]

"In ANY condition, at ANY time after the stall occurred, recovery could be effected promptly by applying down elevator". Stated in the report more than once. I read the entire report.

Chuck Yeager's favorite plane. Until he got a Merlin P-51.

And like the prudent pilot he was, he saw to it his "favorite plane" was ballasted so that it's behavior was safe and responsive. Less renowned and less experienced pilots who had to fly it "loaded for bear" weren't so privileged.

 

[FLYBOYJ]

The Russians beat the Luftwaffe with the P-39, after they lightened it a little.

The Russians beat the Luftwaffe with superior numbers, the P-39 was just part of the equation.

 

[GrauGeist]

Yeager never flew the P-39 in combat, though.
He was assigned to the 363rd FS, 357th FG and he may have flown a P-39 stateside, but the 357th FG was the first 8th AF outfit supplied with the Mustang in February 1944.

 

[Ivan1GFP]

P-39D was a dog at 7650lbs. Could be made competitive by losing the nose armor and the .30s. Move the radio up from the tail cone for balance. For the umpteenth time.

Hello P-39 Expert,

For the umpteenth time:
If this is really your response after all the information and explanations and evidence presented to you, either you are incapable of understanding weight and balance of aircraft or cannot comprehend how this information fits together.
You can wish whatever you want, but there were many intelligent and skilled people on the scene when YOU were not and I would trust their conclusions over yours. You clearly do not qualify as a P-39 "Expert".

- Ivan.