Re: 1951 Pontiac Chieftain
Posted: Sat Feb 13, 2021 3:23 pm
Ahh so I've got a P38 XJR too.
Well, hopefully not everything....
- p-38-lighning-in-flight.jpg.pc-adaptive.1920.medium.jpg (259.01 KiB) Viewed 2312 times
The Dark Wob
1951 Pontiac Chieftain
Page 116 of 197
Re: 1951 Pontiac Chieftain
Posted: Sat Feb 13, 2021 3:52 pm
Re: 1951 Pontiac Chieftain
Posted: Sat Feb 13, 2021 4:27 pm
Well the early ones had the tails fall off due to compressibility in dives.mercrocker wrote: ↑Sat Feb 13, 2021 3:52 pmWell, hopefully not everything....
p-38-lighning-in-flight.jpg.pc-adaptive.1920.medium.jpg
Re: 1951 Pontiac Chieftain
Posted: Sat Feb 13, 2021 4:30 pm
Didn't know that! Phil was right, then.
Re: 1951 Pontiac Chieftain
Posted: Sat Feb 13, 2021 5:00 pm
There's actually a 133 page and growing P38 thread that covers this and other things on an Alternate History forum that I read.
Compressibility issues were an absolute bastard for planes of that performance, locked ailerons, reversed controls etc..
Compressibility issues were an absolute bastard for planes of that performance, locked ailerons, reversed controls etc..
Re: 1951 Pontiac Chieftain
Posted: Sat Feb 13, 2021 8:13 pm
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Found a leak or two. That crack goes further than I thought.
Re: 1951 Pontiac Chieftain
Posted: Tue Feb 16, 2021 10:38 am
I just came across this.Hooli wrote: ↑Sat Feb 13, 2021 4:27 pmWell the early ones had the tails fall off due to compressibility in dives.mercrocker wrote: ↑Sat Feb 13, 2021 3:52 pmWell, hopefully not everything....
p-38-lighning-in-flight.jpg.pc-adaptive.1920.medium.jpg
It's certainly too much information but you don't have to read it:
To properly understand the compressibility problem in the P-38, one has to understand that the lockup was primarily elevators and not ailerons in that aircraft. This was another problem that aerodynamicists had trouble visualizing. There was AIRLERON lockup, but this was not a main wing problem as it was a HAMMER coming off the pilot pod on the horizontal stabilizer problem, and by hammer I mean a harmonic effect that forcefully oscillated the elevators (flutter) as the shock waves hit until pressure equalized and the control surfaces exceeded both the mechanical control forces available to move them and the tensile strength of the aircraft structure. The tail tore off and that indicated to "Kelly" Johnson, that he had the "tail control" issue. It was in the main wing spar that the "hammer" was set up, but it was definitely a tail control issue. He had to stop that hammer from forming in the first place. It was the era of "intuition", and he mentally visualized the wind flow pattern and had NACA and test pilots test for it to determine if his hunches were correct; to put numbers to the concept he imagined. My guess is that Stack beat him to the root cause, but it was Johnson who figured out where the "unstick at the upper boundary layer occurred. What I do not understand, is why Johnson missed the wing sweepback solution, which was the other way to deform the shock wave?
Sorry for the serious divergence Phil.
Re: 1951 Pontiac Chieftain
Posted: Tue Feb 16, 2021 10:51 am
Interesting that they got the same issue as Typhoons with I think a different cause. The Typhoon was traced to something to do with the elevator balance weights causing tail flutter till the tail fell off.LynehamHerc wrote: ↑Tue Feb 16, 2021 10:38 amI just came across this.Hooli wrote: ↑Sat Feb 13, 2021 4:27 pmWell the early ones had the tails fall off due to compressibility in dives.mercrocker wrote: ↑Sat Feb 13, 2021 3:52 pm
Well, hopefully not everything....
p-38-lighning-in-flight.jpg.pc-adaptive.1920.medium.jpg
It's certainly too much information but you don't have to read it:
To properly understand the compressibility problem in the P-38, one has to understand that the lockup was primarily elevators and not ailerons in that aircraft. This was another problem that aerodynamicists had trouble visualizing. There was AIRLERON lockup, but this was not a main wing problem as it was a HAMMER coming off the pilot pod on the horizontal stabilizer problem, and by hammer I mean a harmonic effect that forcefully oscillated the elevators (flutter) as the shock waves hit until pressure equalized and the control surfaces exceeded both the mechanical control forces available to move them and the tensile strength of the aircraft structure. The tail tore off and that indicated to "Kelly" Johnson, that he had the "tail control" issue. It was in the main wing spar that the "hammer" was set up, but it was definitely a tail control issue. He had to stop that hammer from forming in the first place. It was the era of "intuition", and he mentally visualized the wind flow pattern and had NACA and test pilots test for it to determine if his hunches were correct; to put numbers to the concept he imagined. My guess is that Stack beat him to the root cause, but it was Johnson who figured out where the "unstick at the upper boundary layer occurred. What I do not understand, is why Johnson missed the wing sweepback solution, which was the other way to deform the shock wave?
Sorry for the serious divergence Phil.
Sorry Phil.
Re: 1951 Pontiac Chieftain
Posted: Tue Feb 16, 2021 11:09 am
Is it worth setting up an aircraft saddoes thread and transferring these into it?
Re: 1951 Pontiac Chieftain
Posted: Tue Feb 16, 2021 11:15 am
Could be, I think we had a 'things wot fly' thread once. I'll look for it later.