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Thorp T211 corrugated wing skins

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jsharp

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Feb 28, 2019
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Augusta, GA / USA
Are you sure that's not a three-roll former he has in that picture? I can't see the third roll but it does seem the two rolls I do see are not quite aligned vertically.
It looks like a two roller setup. The leading edge skins might have been pre-bent to the airfoil shape, then run through the roll former to create the corrugations on the panel. This would be possible with with a three roll former (smooth rollers) to shape the skins to the airfoil shape, then process through the two roll corrugation roller. The success in this process would require some development for each panel shape. The consistent shaping of metal through these two rolling and shaping processes is predictable and of course repeatable. For the experienced sheet metal pro, the proper panel size, pre-bending panels to airfoil shape and final corrugation of the sheets, could figured out pretty quickly. As in all things, manipulating a part in this way with two different processes forming the part, has to be done with some planning and setup. The corrugation rolling, will have some affect on the previous bending of the skin to its airfoil shape. In order to assure the "final" form of the skins is the airfoil shape desired, the initial rolling of the flat skin may require adjustment of the the airfoil shape so that after further shaping on the corrugation dies you achieve the desired airfoil. There should not be a significant amount adjustment of the initial airfoil shaping however the second metal forming process will most likely have changed the airfoil shape.
This is very doable... corrugation roll former dimensions and shape are important. If you want a wing with a 2" radius leading edge, you cant do that with 6" diameter rollers. These are elementary considerations however important for those with no experience with this process.
I have always had a curiosity about the Ford Tri-Motor design and especially the design of the outer skin, of which the corrugations provide rigidity and strength in such a clever application of corrugation.
Joe
 

skyscooter

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I have a spare wing panel and will check the skin thickness and post later
I remembered today to check the skin thickness of the T211 beaded wing skins. The skins are .025" thick and are very stiff with the beads. The beads are spaced 3 5/16" apart, 1/4" tall and have about 1/4" radius.
 

BBerson

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I wonder if the beads actually need to go all the way around the nose? My Harbor Freight beader might work up to about 3" from the nose. I would need to turn some new bead rollers. The stock roller is about 3/16" radius. So need twice as big.
Might work on .016" 6061-t6 for an ultralight.
 

skyscooter

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The Seabees wing skin beads didn't go around the leading edge. The leading edge radius has a lot of curvature and makes it pretty stiff. Its wing skins were hydroformed to put the beads and airfoil contour in them and then folded to form the leading edge radius.
 

Mad MAC

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Hamilton New Zealand
I can't say I can think of an example with the beads in, except for something somewhere (I can't remember what) the beads were in and these skins were riveted together through the beads, might have been a helicopter. Out ward may present less of a corrosion risk as the water will run off.
 

Tiger Tim

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Beads in on Aeronca C-2 and C-3 ailerons. IIRC the bead gets carefully crushed flat at the spar and trailing edge for riveting.
 

BBerson

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Interesting Seabee article! Unfortunately page 53 is missing.
I am thinking the Cherokee is decades newer and they chose inward beads with full knowledge of the 1946 Seabee.
 

Turd Ferguson

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I am thinking the Cherokee is decades newer and they chose inward beads with full knowledge of the 1946 Seabee.
The beads on the Cherokee originally faced outward. It was discovered the skins would prematurely crack and when the beads were turned in there was no cracking of the skins. I have a book somewhere on development of the cherokee where that is discussed.
 

Jimstix

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IMHO, beading skins - especially the large wing skins - only makes sense if you have access to metal dies, a large hydroform press, a heat treating facility, and you are going into mass production. If you answer "no" to any of those "if" statements, reassess your plan. Use smooth sheet skins and add ribs spaced about a foot apart.
 

Turd Ferguson

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Pipers reason for beading the skins on the Cherokee was to simplify construction, the Cherokee aileron has 10 parts compared to the Commanche's smooth aileron with 37 parts.

The lightweight Canadian Murphy Maverick from the '90's had fuselage skins "creased" by the builder applying pressure and dragging the butt end of a screwdriver handle on the thin aluminum skin at periodic intervals. Doesn't have to be high tech with hydroform presses to get the benefits.
 

cluttonfred

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The lightweight Canadian Murphy Maverick from the '90's had fuselage skins "creased" by the builder applying pressure and dragging the butt end of a screwdriver handle on the thin aluminum skin at periodic intervals. Doesn't have to be high tech with hydroform presses to get the benefits.
Are you kidding me? Is that all there was to it?!? I always liked the Maverick, it would be great to see somebody do something like that designed around a Verner Scarlett 5V, a sort of baby DHC Beaver.

SPC 1.jpg SPC 1 (1).jpg
 

jsharp

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Feb 28, 2019
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Location
Augusta, GA / USA
I remembered today to check the skin thickness of the T211 beaded wing skins. The skins are .025" thick and are very stiff with the beads. The beads are spaced 3 5/16" apart, 1/4" tall and have about 1/4" radius.
Those skins are rolled in two directions. The beads, and the sheet/skin contour would typically be rolled in one operation however, that may not have been the case with ford. The skin contour and final shape may have been rolled, and then run through the dies on the bead roller (biggest bead roller I have ever seen.
The point is that this material will work harden pretty easily during the beading and rolling process. It would be interesting to know if they left the panels in their work hardened state or perhaps they were annealed after the forming process. The bends from the bead roller are a reasonable radius with no grossly abrupt angles, and neither one of the bending forming processes would necessarily need to be excessive causing extensive work hardening that would make the metal quite brittle and would not be a suitable material forming process without a post forming annealing. So perhaps they determined that after metal forming that the resulting work hardening left the metal ductile enough for their particular application. Ford personnel were experts at sheet metal forming. Would give just about anything to have been a fly on the wall during the design and fabrication of the tri-motor, and of course as a pilot, at least some right seat time..... Great stuff.... Joe
 
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