Structural Failure

For an aircraft that did this the wings appear to come off far FAR too easily...

http://www.bbc.com/future/story/20160505-the-spitfires-that-nearly-broke-the-sound-barrier

A Spit XI has completely different wing structure than a IX. The test is somewhere online btw maybe it was on WWII aircraft performance, not sure. If I remember correctly the engineers themselves doubted the results of that test our it was severely damaged. Can't really remember.

The VII brought in changes to the fuselage not wings, IIRC the only difference between the IX and XI in terms of wings was the removal of guns and the addition of wing fuel tanks

Come on Krupi, you're bright enough to spot the lack of detail in the article and the differences in the forces.

The article states it was the speed of the dive responsible for the warping into a slightly swept shape.

Well I think you can't ignore the significantly thicker aluminum sheets being used on the Mk XI wings. These contribute a large share to structural integrity. It is really not appropriate in my eyes to compare a Mk IX wing to a Mk XI one.

If the wing skin thickness was increased, what was the thickness of each wing skin?

Please look it up yourself, it's not hard to find blueprints. There is even a section about it in Spitfire the History including sketches.

Thanks for the reply which should have been easy to answer.

Spit: the History doesn't have the info that I could find.

Apparently the D wing the used a strengthened D nose, which I was unaware of.

I would like to know more about this change, I assume it was to do with the addition of fuel tanks along the D nose and the pressure that they exerted on the skin.

Apart from that and the lack of guns there was no difference, it wasn't until the Mk21 where any real structural changes occurred.

Yeah the leading edge dural plate was about twice as thick and there was an extra dural sheet inserted orthogonal to close off the tank volume. Ammo compartments were reinforced with struts and some other small changes.

I am 99% sure there is a section in Spitfire The History where I read the specifics. When I come home from vacation I'll gladly post the page number.

I do not see a bug detailed anywhere. Unless provided, thread is redundant and can be closed or moved to the offtopic/general section.

Well I lost two wings in what I would consider normal combat manoeuvre situations this evening so yes, I think there is a problem in this regard.

It is easily possible to overload the Spitfire with the elevators alone by exceeding cc. 10 g. Its manual explicitely warns against that.

What g-loads do you record when the wing fails?

Manual warns indeed, but it doesnt mean that wings break exactly at 10 G. Usually manuals set more conservative numbers to protect both pilots and machines. Nothing unusual would be in this department.

Though I think I already posted that one some time ago:

It would be actually interesting to know what load was reached when OP broke his wings, personally so far I managed to do so once by silly maneuvering but that was at very beginning. Since then not once they broke and I still insist that before one would approach the load to damage wing spars pilot would already be unconscious.

Manual warns indeed, but it doesnt mean that wings break exactly at 10 G. Usually manuals set more conservative numbers to protect both pilots and machines. Nothing unusual would be in this department.

Nor are there any Spitfire "manuals" that specify 10 G as the structural limit. Without any such evidence, it's just pure speculation that Spitfires invariably broke up at around 10 G because of the elevators alone.

Here are details of the IX's wing construction from

Spitfire Mk IX & XVI Engineered:

Though I think I already posted that one some time ago:

 

It would be actually interesting to know what load was reached when OP broke his wings, personally so far I managed to do so once by silly maneuvering but that was at very beginning. Since then not once they broke and I still insist that before one would approach the load to damage wing spars pilot would already be unconscious.

The usual average WW 2 pilot could blackout between 4 to 6.5 g, depending on the pilot and the cockpit environment: unconsciousness could occur without warning during high speed pullouts etc of 3 to 10 g.

Interestingly from the engineering book it says that the PR spitfire had reduced skin thickness!

The leading edge dural sheet of Mk XI and XIX and was 10 gauge.

This is a PR XI / XIX wing btw I found over google pics (all credit to the photographer), you can see even in the photo the thick leading edge skin. It is also the only part of the skin thats not completely eroded.

I wasn't doubting your claim.

It makes perfect sense that they had to increase the thickness of the leading edge, I was just pointing out that they apparently also removed material elsewhere.

Nor are there any Spitfire "manuals" that specify 10 G as the structural limit. Without any such evidence, it's just pure speculation that Spitfires invariably broke up at around 10 G because of the elevators alone.

I didnt state it does or it should, merely that manual warns, as it does warn indeed - about use of controls with care.

It would be interesting to find out those reports mentioned on the picture carried by Accident Branch at Farnborough.

It was just coincidence that I looked up the thickness and posted it Krupi, no worries. I dont know the rest of the plating gauge, I only have a drawing of the XI/XIX D-Box tank.

There was a high speed dive test performed with BS310 (Mk IX) in March 44. They tested to Mach .83. The results were in a nutshell: the elevators became very heavy, the aircraft developed a longitudinal pitching movement and there was considerable turbulence around the cockpit. No structural damage though.

Skin wrinkling in high G dive bombing pull outs or when flying armed recce was apparently a concern for the RAF. No. 125 reported several such incidents within a few weeks and it was investigated in November 44. No mention of broken wings though.

I guess the prop will be the limiting factor in high speed dives anyway, as above Mach .85 the drag of the prop sykrockets and will likely be shed to pieces before anything else.

I didnt state it does or it should, merely that manual warns, as it does warn indeed - about use of controls with care.

 

It would be interesting to find out those reports mentioned on the picture carried by Accident Branch at Farnborough.

No problem - I was agreeing with you, but also disagreeing with an earlier claim that had been posted, to the effect that the structure failed at around 10 G because of the elevators alone: there is nothing in any Spitfire manual that "explicitly" says that. :smilewink:

...

There was a high speed dive test performed with BS310 (Mk IX) in March 44. They tested to Mach .83. The results were in a nutshell: the elevators became very heavy, the aircraft developed a longitudinal pitching movement and there was considerable turbulence around the cockpit. No structural damage though.

....

I guess the prop will be the limiting factor in high speed dives anyway, as above Mach .85 the drag of the prop sykrockets and will likely be shed to pieces before anything else.

Mach .83 or even less could already be enough for the wings to be in transonic speed.

On the topic, it seems quite easy to loose wings in Spit. I don't think that the modeling of the wings structural integrity might be the issue but rather the failure is caused by extreamly sensitive elevator.

When pulling out from a high speed dive Spit requires to be really gentle with applying back pressure on the stick.

I don't have the Spitfire myself, but it's interesting seeing this discussion, as it reminds me how the 109's wing tips would snap if you so much as sneezed on them back when it was released, and it was more or less unflyable.

So it's probably "just beta things" for the spit too.

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I don't have the Spitfire myself, but it's interesting seeing this discussion, as it reminds me how the 109's wing tips would snap if you so much as sneezed on them back when it was released, and it was more or less unflyable.

 

So it's probably "just beta things" for the spit too.

 

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Yes, I recall that :joystick:

I hope you are right, unfortunately I haven't had the time to go back and thoroughly test the dive speeds again.

Perhaps firmek is right and I just overtightened the turn during my pull out.

Manual warns indeed, but it doesnt mean that wings break exactly at 10 G. Usually manuals set more conservative numbers to protect both pilots and machines. Nothing unusual would be in this department.

More or less. Individual machines vary and most manufacturer's are likely on the safe side to avoid... unpleasant complaints from the customer and the unfortunate end user's families. Anyway, if you have regular failures below 10 g, it means probably a similar issue that the K-4 beta head. Hence why the point of failure needs t be established, otherwise it not much of a bug report. All wings will fail at some point.

Anyway, here is the page from the Spitfire II manual addressing this issue, it might prove useful for better understanding the diving and control limitations for this plane, perhaps even more so for the more forgetful who may have already seen this dozens of times, but perhaps not nearly enough, considering the denial that such Spitfire manual would have ever existed. :music_whistling: