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Spitfires, stressed skin effect or not?


geedubelyer

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Hi everyone,

Here's a question for the aficionados. Is it accurate to depict a stressed skin effect on a Spitfire?

In particular I'm thinking of Revell's new Mk.IIa.

 

I have seen images of renovated airframes that do show some "oil canning" on the fuselage but wonder if that is a process of the rejuvination rather than original manufacture (i.e, is modern rivetting stronger than wartime rivetting making the aluminium skin tight on the bulkheads etc). http://www.airliners.net/photo/Supermarine-349-Spitfire/2453899/L/&sid=3b68eaae50797bde04629bc02d157554

 

http://www.airliners.net/photo/Supermarine-300-Spitfire/2198713/L/&sid=3b68eaae50797bde04629bc02d157554

 

Grateful for any insight, cheers.

Edited by geedubelyer
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Hi Guy,

 

I think that it would be appropriate on the Mk.I, Mk.II and Mk.V Spitfires as the thinner gauge wing clad material was noticeably stressed when compared to later Spitfires with thicker skins (probably after the Mk.XIX).

 

detail_spitfire1_05.jpg

 

supermarine_spitfire_mk1a_p9444_10_of_37

 

supermarine_spitfire_mk1a_p9444_27_of_37

 

235%20Supermarine%20Spitfire%20I.jpg

 

iwm-spitfire-mk-i-moving-dec-2012.jpg?w=

 

Spitfire_IIA_P7666.jpg

 

545x385-Overhead-view-of-Spitfire-on-the

 

Derek

Edited by Derek B
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The "oil canning" is just an artefact of stress on the skin. The airframe is not rigid and in flight it flexes and twists to certain extents. That causes the "ripples" in the skin between the bulkheads, ribs and stringers. 

Incidentally, a similar effect can be seen on boats.

One thing to keep in mind is that such effect visible on a plane in flight, especially when photographed doing a "stressful" manoeuvre, may not be visible on the same plane at rest.

Radu

 

 

 is modern rivetting stronger than wartime rivetting making the aluminium skin tight on the bulkheads etc

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I remember reading a book on British aircraft carrier operations during the Korean War. Mention was made of the stress deformations of the Seafires which were were making hard landings on the aircraft carriers. I thought that was noteworthy. The Seafires were replaced with later fighters and fighter bombers that were stronger aircraft.

The title of the book is Furies and Fireflies Over Korea: The story of the men of the Fleet Air Arm, RAF and Commonwealth who Defended South Korea, 1950-1953.  Written by Graham Thomas it was published By Grub Street, London in 2004.

Since a Korean War Build has been called for perhaps the British members of the LSP would like to get into it with British Naval Aircraft. This book would be good for inspiration and the history of the operations. A good number of B/w photos of the Furies and Fireflies are in the book. There are no illustrations of the stress points on the Seafires but the photos of the other aircraft make one drool.

Stephen

 

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Hi folks,

I appreciate the comments that everyone has put forward and the additional images.

 

Looking at the images it would appear that some "oil canning" does occur although it varies in degree of severity somewhat.

 

Edgar, may I thank you for taking the time to post the excerpt from the original notice. It's always fascinating to read actual documentation.

From what you have posted I can see that any wrinkles would need to be very fine indeed if one were to reproduce them in 1/32nd scale.

However, I can't help wondering whether wrinkles produced as a by-product of excessive "g" loading compared to the effect that rivets produce is the same thing? :hmmm:

 

The excerpt begins with "after any abnormal manoeuvres" which suggests to me that the inspection would be looking for signs of extreme stress to the airframe rather than the more normal appearance of metal rivetted to a spar or bulkhead.

 

I can accept that any wrinkle that should n't be there would be a cause for concern but what if the undulations to the surface are caused by thin metal being tightly fastened at the point of manufacture?

I wonder if there is a distinction?

 

Perhaps my best course of action if I wish to depict this effect is to model a restored warbird rather than an original WWII aircraft..... :unsure:

 

Talking of the skin of the aircraft, does anyone know of an on-line resourse resource that details where the panels were overlapped and where the lines of raised rivets toward the tail were please?

 

Cheers.

 

Edit: spelling

Edited by geedubelyer
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Edgar, may I thank you for taking the time to post the excerpt from the original notice. It's always fascinating to read actual documentation.

From what you have posted I can see that any wrinkles would need to be very fine indeed if one were to reproduce them in 1/32nd scale.

However, I can't help wondering whether wrinkles produced as a by-product of excessive "g" loading compared to the effect that rivets produce is the same thing? 

The excerpt begins with "after any abnormal manoeuvres" which suggests to me that the inspection would be looking for signs of extreme stress to the airframe rather than the more normal appearance of metal rivetted to a spar or bulkhead.

 I can accept that any wrinkle that should n't be there would be a cause for concern but what if the undulations to the surface are caused by thin metal being tightly fastened at the point of manufacture?

We're in danger of getting into dog-chasing-his-own-tail territory, here.

The second item, in the between-flights inspection schedule, tells the erk to "Examine the main plane skin for signs of wrinkling." If there were wrinkles already present, how would he know which were new?

Holes, for rivets, were pre-drilled and reamed with a countersink, so that the rivet dropped in and lay flush with the outer surface. The rivet was then held in place by a worker holding a flat lump of steel (known as a "dolly") over it, while a second worker did the riveting work with the gun inside the wing/fuselage. This meant that the "hammer" from the gun was absorbed by the rib/former, not the skin.

On the Mk.I/II the technology of the time didn't allow "blind" (i.e. from the inside) riveting of the wings or tailplane, so one of the lower skins was held in place by countersunk screws fixed into wooden strips let into the ribs.

The whole idea behind the Spitfire was to keep the surfaces as smooth as possible, so it could go as fast as possible, and wrinkles = drag, so couldn't be permitted; even the wing skins were, as much as possible, overlapped along the airflow or front-to-back, to cut down on inbuilt drag.

I do have several top and bottom "maps" of the wing skins, which I'll dig out (they differed in thickness, over the life of the Spitfire, especially as the aircraft got faster,) and try to put a typical example on here.

wingpanelsMkI_zpsc576a275.jpg

Edgar

Edited by Edgar Brooks
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