P-38 kill ratio...out of whack.

[Vinkman]

were you able to see what we've been talking about in my gut-wrenchingly exciting film?

Cap1 my appologies, I did not get to watch the film yet, but I should have time this evening.

[Shuffler]

Hits vinkman over the head with the empty dvd box..... ok where did you put the cap1 movie.....

 

[CAP1]

Hits vinkman over the head with the empty dvd box..... ok where did you put the cap1 movie.....

 

in the supermegamightyagonizinglyexc itinglyinteresting stack?

[TnDep]

in the supermegamightyagonizinglyexcitinglyinteresting stack?

  it's in the corner

[CAP1]

  it's in the corner

[Captain Virgil Hilts]

Thats not what I said at all and certainly not what I meant. I will make it clear though... Kelly Johnson and every other engineer in the world at that time thought that the speed of sound was a wall and there never would be a way past it.

Uh, could you find me a quote from Kelly Johnson stating that? I've read all sorts of stuff on that subject, and never read that Johnson considered the speed of sound to be an impenetrable barrier. He certainly makes no mention of it with regards to the P-38 and compression. As early as 1936/1937, he made notes of the problems of compression, before any plane had experienced it. But nothing about the speed of sound and never being able to exceed it. Besides, he knew the P-38 would never approach the speed of sound.

[CAP1]

Uh, could you find me a quote from Kelly Johnson stating that? I've read all sorts of stuff on that subject, and never read that Johnson considered the speed of sound to be an impenetrable barrier. He certainly makes no mention of it with regards to the P-38 and compression. As early as 1936/1937, he made notes of the problems of compression, before any plane had experienced it. But nothing about the speed of sound and never being able to exceed it. Besides, he knew the P-38 would never approach the speed of sound.

i actually just found this very interesting read.


http://history.nasa.gov/SP-4219/Chapter3.html

[Chalenge]

Uh, could you find me a quote from Kelly Johnson stating that? I've read all sorts of stuff on that subject, and never read that Johnson considered the speed of sound to be an impenetrable barrier. He certainly makes no mention of it with regards to the P-38 and compression. As early as 1936/1937, he made notes of the problems of compression, before any plane had experienced it. But nothing about the speed of sound and never being able to exceed it. Besides, he knew the P-38 would never approach the speed of sound.

He said that about compressibility actually (and AFTER the sound barrier had already been broken which says something). I believe the interview was with Pamela Reynolds-Wood for her book "P-38 Lightning" but I cannot find a referencing citation to it online.

“ I broke an ulcer over compressibility on the P-38 because we flew into a speed range where no one had ever been before, and we had difficulty convincing people that it wasn't the funny-looking airplane itself, but a fundamental physical problem. We found out what happened when the Lightning shed its tail and we worked during the whole war to get 15 more knots [28 km/h] of speed out of the P-38. We saw compressibility as a brick wall for a long time. Then we learned how to get through it. ”

[EskimoJoe]

This thread is going to rack up more total views than the rules thread 

[texastc316]

Rules thread?

[CAP1]

well, we're catching up to the corvette/porsche thread. 

[Captain Virgil Hilts]

He said that about compressibility actually (and AFTER the sound barrier had already been broken which says something). I believe the interview was with Pamela Reynolds-Wood for her book "P-38 Lightning" but I cannot find a referencing citation to it online.

Compressability was a brick wall the P-38 never really got through, because of the wing design. Had they used a different wing profile, they'd wouldn't have run into the problem, at least not until over 500MPH or so. They made the P-38 go faster without entering compression, a couple of times. But it never got past the point where compression was not an issue. Levier said the dive flaps were good to 0.75 Mach, a boost of about 0.07 Mach, as without them, compression happened at 0.67 Mach, where in 1937, Johnson had said it would happen at 0.65 Mach. But the wing of the P-38 was always the problem, and where it joined the fuselage made it worse. Had they been able to use a thinner and sleeker wing, compression might not have happened until 0.70 Mach or more. But the P-38 would not have been as maneuverable, nor would it have climbed as well, and the range on internal fuel would have been very short, like the Spitfire.

[Vinkman]

i actually just found this very interesting read.


http://history.nasa.gov/SP-4219/Chapter3.html

Per this account, everyone might have been a bit correct. What's clear is that the 38 was designed with laminar non-compressible flow in mind. In the compressible region, both the aerodynamic flow AND the aerodynimic pressures (hence forces) on the plane were not properly calculated.
The only thing not clearly explained (by this article) was why the controls became 'locked' which I assume meant that the stick and evelators couldn't be moved.
Speculation on my part could be the at the shock Normal created by the airfoil settled on the elevator and created and the high pressures which created a force that the pilot could not overcome. OR that the booms and tail section of the plane deflected enough under these (higher than calculated) forces so that the bearing loads, gaps, or other clearances necessary for smooth operation of cable, rod, and hinge mechanisms closed up resulting in the controlls locking up. 

Perhaps the controls lock up is related to the aero elastic study quoted, and "tuck under" and dive [brakes] issues were related to the compressibilty as also stated. Also it could be that the aero elastic deflections calculated in later years where compressible loading could be properly calculated SUPLIMENT the P-38 explanations of the 1930s not contradict them.

With respect to quoting Kelly Johnson or others that worked on the program at the time, remember that these are snapshots in time. Often time engineers will propose a theory and come up with a fix. If the fix works, the theory is excepted. But in cases like this one, where compressible Aerodynamics were not understood and could not be calculated for the many different parts of the airplane, the theory of what was wrong, put forth by the engineers (Johnson included),may have been incomplete. If the Aeroeastic deflection was caused by the changes in loading do to the changes in flow dynamics in the compressible region than fixing the flow dynamics with the dive [brake] may have solved both issues without the P-38 team ever knowing the second one was part of the explanation. Suplimantal explanations could be developed years or even decades later as modeling and analysis techniques improved.


Summary: Because all these problems were occuring at the same time, under the same conditions, they may all be correct but should not singularly be described as "the" compessibility problem.

[Vinkman]

in the supermegamightyagonizinglyexc itinglyinteresting stack?

Cap1

OK I got to watch it and that's it exactly! The Zeek looks to be a bit further back than I usually am, but he's at roughly equal speed when you go up and he follows. It appears he makes the mistake, I think I make quite a bit. He tries to pull lead in the early part of the vertical move in order get a gun solution. Indeed he is firing on the way up and it's a high deflection shot with you below his cowl and out of sight.  This causes his initial turn radius (albiet vertical turn) to be much tighter than yours and he slows too quickly trying to ge the shot. Instead of achieving the same height as you, he stalls out several hundred feet below you. You were 1500 yards ahead when you initiated the move so you may have had enough room for a reversal before he was co alt, but if he didn't screw up, you both should have ended up head to head. Instead you ended up head to tail.

Thanks for recording and posting. Good stuff. 

[CAP1]

Cap1

OK I got to watch it and that's it exactly! The Zeek looks to be a bit further back than I usually am, but he's at roughly equal speed when you go up and he follows. It appears he makes the mistake, I think I make quite a bit. He tries to pull lead in the early part of the vertical move in order get a gun solution. Indeed he is firing on the way up and it's a high deflection shot with you below his cowl and out of sight.  This causes his initial turn radius (albiet vertical turn) to be much tighter than yours and he slows too quickly trying to ge the shot. Instead of achieving the same height as you, he stalls out several hundred feet below you. You were 1500 yards ahead when you initiated the move so you may have had enough room for a reversal before he was co alt, but if he didn't screw up, you both should have ended up head to head. Instead you ended up head to tail.

Thanks for recording and posting. Good stuff. 

you're right. had he continued a lag pursuit(i think), and not tried for those shots, he could've probably continued till i made another mistake, and ended the fight differently.
 if you watch the speeds in the par on the right, you'll see that when he pulls sharply, his speed drops FAST. that was usually his mistake.
 i think you're right, that i too, could've reversed sooner than i did, but i wasn't too sure of what i was doing, so i was holding the climb, till i knew for sure he was stalled. i also felt that had i reversed back down earlier, i may have set up for a ho, and i do all i can to avoid giving the other guy that chance, and i try to avoid em myself too.

 for the record, the guy in the zeek, was a good guy to fight. stubborn too. and i mean stubborn in a good way.

 glad that helped ya.

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