Wing stress

[GScholz]

Interesting in that there is no delineation between Design Limit (usually within elastic/Yield stress) and Ultimate (Failure and in US 1.5xLimit)

The failure load of steel and aluminum is typically 1.5 times the yield load.

[drgondog]

The failure load of steel and aluminum is typically 1.5 times the yield load.

  Correct,

Curiously since the airframe business I was in when I was a structures guy dealt with such materials ( and early composites and titanium forgings) that might be the reason that was our standard in US.. for normal flight loads and cycles.. greatly reduced for critical components in high frequency reversible loads such as helicopter engine mounts, etc,

[drgondog]

Supermarine Type 224 was also to be called Spitfire, hence there sometimes being confusion.

drgondog,

Yes, there were increases in strength for the Spitfire's wing, though I don't recall when they showed up.  Mk V or VIII perhaps.

Gaston,

It would do you a wonder of good to invest the time and money in some physics and aerospace engineering classes.

Karnak - does that mean the load profiles in the above spec were at Ultimate?.. wow, if so - unless that was Late in the development cycle when GWs had pretty well max'ed out...

[GScholz]

I'm fairly certain they are limit loads. While British specifications typically were a bit lighter on the limit load (btw. P-51H was designed after the British specs, thus the slightly lower limit load), they weren't THAT different. The Jerries also typically designed their fighters to an 8G limit load.

[GScholz]

I seem to remember an old discussion here years ago about the P-38's limit load. Having been designed as an high alt interceptor it only had a limit load of 6G, if my memory serves me. Also someone here thought it was the cause of the death of an American ace in the Pacific.

[drgondog]

I seem to remember an old discussion here years ago about the P-38's limit load. Having been designed as an high alt interceptor it only had a limit load of 6G, if my memory serves me. Also someone here thought it was the cause of the death of an American ace in the Pacific.

I would tend to doubt that Lockheed set a limit/ultimate load spec - but as in the case of the XP-51 designed to 8/12G Limit and ultimate load factor for 8000 pounds GW, that limit load reduced to 6.4/9.6 at 10,000 pounds for the P-51D.  The P-51H was 11 Ultimate and 7.4 Limit at 8000.

I suspect, because I can't prove otherwise, that the Load Factors were based on YP-38 basic weight which was 1600 pounds less than the basic weight of the P38J... by the time the full internal combat load was attained it grew another 1500 pounds.. and the limit load dropped dramatically to the "6G" range.

[icepac]

Speed also plays a factor.

You can't ignore the force that is pulling the wings backwards because of your speed.

That has to be factored in and it complicates things greatly concerning at what G loading you will experience wing failure.

[J.A.W.]

There are other factors.. Planes such as the P-38 & Typhoon were among the 1st to really
encounter compressibility effects in high speed dives.. with tails falling off & uncontrollable
terminal dives.. both an aero & fatigue stress dynamic..

The P-38 needed & got 'dive flap' spoilers that enabled control to be regained..
but remained fundamentally low Mach/Vne limited.

The Typhoon needed the Tempest wing to really solve its issues..
 [ but received the beneficial thinner Tempest tail-plane in the late-production versions]

Typhoon Vne/dive speed limit of 520mph IAS @ 10,000ft ..
..was still ~100mph higher than the P-38 though.

[Mace2004]

 
  The amazing thing is, they appear to never have tested how much those wings actually bent in an actual horizontal turn with a low-wing nose-puller... To this day even...

  I've been looking for those wing in-flight turn stress tests for years now... And no, dive-pull-outs don't count, and that is what they do if they do it: I checked... This is because in a dive, the propeller is, in large part, unloaded by the extra dive speed...

  For those who know my thinking about this, I think 3 G of turning at full power could equal 6 G of wing stress on these WWII fighter types, and the pilot limit of 6-7 Gs could mean 9-10 Gs of actual wing stress: Well within the ultimate failure limit...

  Those who claim this is a violation of physical laws seem to confuse force and energy... I remember reading the claim (elsewhere) that this is is like claiming a perpetual motion machine... This shows you how clueless are those who claim this violates physical laws...

  Unlike energy, yes you can get more force out of something than you put in... If you don't think this is true, you don't understand the difference between force and energy...

  Gaston

Wait...what???

[nrshida]

Unlike energy, yes you can get more force out of something than you put in... If you don't think this is true, you don't understand the difference between force and energy...

Don't you hold with those fangled laws of thermodynamics then Gaston?

Quite right, how is the perpetual motion machine coming along? 

[Franz Von Werra]

TEST:
Go to dueling arena, or training arena, I forget which... take off from the '30k base'... it will drop you in flight, then dive the plane: get to high speed, pull back!!!

I did this long ago, most planes break their wings, but some don't! Long lost list, need to make new!

[pembquist]

For your amusement http://youtu.be/OhwLojNerMU

From my reading you don't often get much warning from flutter induced failure. The film clips are often super slow mo and an excited control surface can in reality just fly off in a half second.

Here is a flutter analysis of a famous amateur build airplane. What is interesting is that in investigating the flutter characteristics of adding more fuel capacity they found a configuration that lowered flutter speed to 160 knots, (this is a 300 mph airplane.) 

[Zacherof]

Thanks for the responses guys. I hink I have what I want now

[Franz Von Werra]

wing stress is over rated! 

http://www.youtube.com/watch?v=SXQ5uoMBnuE

[Gaston]

Don't you hold with those fangled laws of thermodynamics then Gaston?

Quite right, how is the perpetual motion machine coming along? 

  What? Do you mean to say you can't get more force out of something than you put in? Oh ok, that was not what you meant. Thank God....

   Gaston