P-38 structural integrity?

[GScholz]

In the plane description of the P-38 on HTC's website the P-38 is listed as having "Max G Loading- +6/-3.5". Was the P-38 really so structurally weak? In AH I seem to pull lots more G without any damage.

[Batz]

Those limits aren’t cut in stone. In you go over 7gs that doesn’t mean your plane will fall apart. Most limitations, including power settings, are set to minimize maintenance not because the plane or engine would break or blow up if they are exceded.

The 6g limit could mean a limit on the pilot (black out etc) or to limit overall stress on the aircraft.

[Montezuma]

Originally posted by GScholz In the plane description of the P-38 on HTC's website the P-38 is listed as having "Max G Loading- +6/-3.5". Was the P-38 really so structurally weak? In AH I seem to pull lots more G without any damage.

Never had a G stress failure in the P-38, and I am pretty good at ripping my wings off in compression-prone planes like the 38.

[Bodhi]

Stick your head in a 38 boom sometime and look back.  You'll see why they limited the amount of g's...

[GScholz]

I find this very strange since the FW-190A8 is listed at +8/-4, P-51D "+8/-4 @ minimum weight", F4U-1D +7.5/-3.5, and La-5FN "+7.5/-3.5 @ minimum weight".

Why don't these aircraft take damage in AH when they exceed these limits, especially the P-38 with a very low +6 limit?

[Widewing]

Originally posted by Batz
Those limits aren’t cut in stone. In you go over 7gs that doesn’t mean your plane will fall apart. Most limitations, including power settings, are set to minimize maintenance not because the plane or engine would break or blow up if they are exceded.

The 6g limit could mean a limit on the pilot (black out etc) or to limit overall stress on the aircraft.

Typically, American fighers were rated about 2 G below failure loading. Except that is, Grumman aircraft which repeated demonstrated the ability to survive tremendous loads without failure. One F4F survived several high G pullouts with the last one exceeding 12.5 G. This Wildcat was under test and was fully instrumented. There was no damage to the airframe, although the engine A-frame displayed some distortion. So, Grumman swapped in a new power egg and delivered the airplane to the Navy. I have about 1,600 hours in Grumman aircraft and can attest to the sobriquet "Iron Works" as not being without solid basis.

My regards,

Widewing

[GScholz]

So a P-38 would not survive 8 G's?

[HoHun]

Hi Widewing,

>Typically, American fighers were rated about 2 G below failure loading.

Actually, the safety margin is usually given in percent, with 33% and 50% being commonly used in WW2.

Regards,

Henning (HoHun)

[whels]

Originally posted by GScholz
In the plane description of the P-38 on HTC's website the P-38 is listed as having "Max G Loading- +6/-3.5". Was the P-38 really so structurally weak? In AH I seem to pull lots more G without any damage.

the Crew chief for Thomas  McGuire 2nd leading p38 ace of
WW2  said he believe  McGuire died from structural failure on
his last mission. he said there wasnt a p38 that McGuire had flown that didnt come back with rivets popped, and/or wings
bent out of true.

IF a great pilot like him could do that to p38s, just think what
regular pilots might have done.

[Ack-Ack]

McGuire was famous for bring back planes with wings bent from stress and IIRC, it was common to see P-38s return home in such conditions.

In AW I was never able to break the wings of a P-38J, no matter how hard I tried.  In AH I found out that you can snap the wings off of a P-38L if you are fully loaded with ordnance (1,000 pounders and 10 rockets) and pull around 8 Gs pulling out of a 525mph (IAS) dive.  I've never been able to do it while flying without ordnance though.

As a side note about McGuire's crash, there's a theory that he died when his P-38 entered into a spin when he throttled up one engine to full before throttling back on the other and advancing them together.  If you don't do it that way, you can cause the P-38 to enter into a vicious spin and at low altitudes (like Mcguire and his flight was at) it's almost usually fatal.  This coincides with the surviving members of the flight witness reports of hearing one of McGuire's P-38's engine throttling up before he crashed.  Coupled with the fact that McGuire was not flying his normal mount and he violated one of his dictas by not pickling the drop tanks when engaging in combat, it was the final link needed to cause his demise.

Maybe Widewing or Savage have a copy of the report that was done on the crash a few years ago, since I originally got it from one of them.


ack-ack

[FUNKED1]

Originally posted by Batz
Those limits aren’t cut in stone. In you go over 7gs that doesn’t mean your plane will fall apart. Most limitations, including power settings, are set to minimize maintenance not because the plane or engine would break or blow up if they are exceded.

The 6g limit could mean a limit on the pilot (black out etc) or to limit overall stress on the aircraft.

The standard safety factor for aircraft built in the US is 1.5.  If the "book figure" is 6g then 9g is when failure can occur.  6g would be the Limit Load, 9g would be the Ultimate Load, and 9/6 = 1.5 would be the Safety Factor.  It doesn't mean that the thing will fall apart at 9g, just that in the worst possible case (loading, fatigue, corrosion, etc) the most highly stressed part on the airplane will start to fail (break or experience plastic deformation) when you hit 9g.

[GScholz]

Actually Funked, from what I've learned in your example the plane would suffer permanent plastic deformations if it exceeds 6G and would break apart if exceeding 9G. If it's exceeding 6G for a period of time the structure will also eventually fail.

I know the standard is 1.5 today, but I'm not sure that was standard back in WWII.

[FUNKED1]

No, there should not be plastic deformation at Limit Load.
I can tell you that from first hand experience.

The factor of safety is a completely arbitrary number.  It is a factor of ignorance, to account for the difference between real life and the engineer's mathematical model and laboratory experiments.  You figure out what load you need to carry safely, call that the limit load, then multiply by your factor of safety, call that the ultimate load, and design the part so that it will not fail (deform plastically or fracture) at the ultimate load.

Being loaded "for a period of time" (fatigue strength) is a different discussion altogether.   Steels have a fatigue limit, a stress level below which they will never fail, regardless of the number of stress cycles.  Aluminum alloys have no fatigue limit.  At even the lowest levels of stress, they will eventually fail after experiencing enough stress cycles.  Most critical airframe components on WWII aircraft were aluminum, so the airframes had a finite life, regardless of loading.

[Wolfala]

For the first time in my history of flying the P38 - I managed to crack the wings off while in a high G pullout. Amazing.



Wolf