Warbird Information Exchange

Here's the details in an anonymous P-38 wreck. The centre circle is reinforced skinning discussed. The l/h circle shows the (milled?) heavyweight wing joint, which is a similar shape but not structure to the corrugations, being solid, not 'folded'.

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James K

"Switch on the underwater landing lights"
Emilio Largo, Thunderball.

www.VintageAeroWriter.com

Same old story for the TBY. Fuselage skins run mostly .040 to .032...small amount of .025.

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It was a good idea, it just didn't work.

The fittings on the L/H edge are individual bath tubs riveted to each corrugation channel and bolts the skin between the spars together.
The corrugated area has an inner skin. Then the corrugated skin. On top you have the external skin. On Stephen Grey's I installed roughly 1200 Cherry Max rivets on each side from Center to wing attach fittings on the outer skin that was replaced. Also this skin setup runs between the main spar and the rear spar. Also most of the rivets in this area are 1/8" AN426 and required a dimpled hole. The skin was about 10' long.
The corrugated skin allowed a large open area that allowed a self sealing fuel cell to be installed.
Originally they used conventional rivets to secure both inner and outer skins to the corrugated skin. How this was accomplished when you need to buck a rivet that is down a trough of the corrugation that is up to 10 feet deep is still a mystery. I had a visitor at POF tell me they used a mouse type device on the end of a rod. It was rubber shaped like the corrugated trough that supported a metal bar. He said they used a timed air charge on a rivet gun. You pushed a rivet against the rubber supported bar and fired a timed burst from the rivet gun.
Can anybody confirm this?
I'm glad we had the Cherry rivets with a hyd pulling gun although my finger got tired pulling the trigger.
Rich

Yes the 40 is built with 78 degree rivets.dimpled and counter sunk.I had the rivets made by a company in new York. the also made the dimpling dies and set for the low profile headed rivets as well. The are kinda tricky to shoot and its best to cook them and then shoot them.

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Hang The Expense

Warbirds are generally unpressurized occasional use aircraft operating significantly below gross weight (nowadays). In their day they were intended to have a limited life, so fatigue was not much of a consideration, performance was. You're Cessna may have a 1.5 safety factor in the design, but that safety factor was likely calculated at 3 Gs, not 6+ Gs like it was for a fighter. Two completely different animals. The Cessna operates much closer to limit load during its life.

The gent is right about the Philosophy of rivet head to countersink conditions.

The purpose of the skin is primarily to convert bending loads on the entire airframe to tension/compression on beams and stiffeners through Shear on the skin.

The countersink should Not go all the way through the skin to create a knife edge. It is the shank of the rivet that transmits the shear load from the skin to the stiffener/beam below.

The removal of 'local cross section area' would not be as serious if the flush rivet was a 'perfect' fit in the skin, but it never is and the skin can fail locally at the knife edge stressed region as a result... then continue deformation until stabilize or fail further.

This is primary reason the Edge distance is 2x Diameter of head versus 1 1/2 for pan head rivet.

Not saying that knife edges didn't occur - just saying that last 40 years of airframe design says Beware.

The B-24 has skins as thin as .016" on the wing flaps.

Gary