# Thorp T211 corrugated wing skins

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#### BBerson

##### Light Plane Philosopher
HBA Supporter
Molded composite doesn't make much sense in a home shop either, yet some do it.
The idea of a beaded metal is it is lighter weight and less hours to assemble. I am looking at home alternatives to using a big hydraulic press.

#### cluttonfred

##### Well-Known Member
HBA Supporter
I like the idea of preformed metal, fiberglass, or plastic sections of wing sheeting with internal flange ribs and spar attachment ponts, and enough of a joggle for the next one to lay flat. The sections could be nested for easy shipment and then you build your spars, rivet or bond each secton to the spars and each other one after the other, and your basic wing structure done. Something like this....

#### BJC

##### Well-Known Member
HBA Supporter
If wing skins are almost flat ... aft of the main spar ....
Many modern aerobatic wings are flat from the spar aft.

BJC

#### Victor Bravo

##### Well-Known Member
Molded composite doesn't make much sense in a home shop either, yet some do it.
The idea of a beaded metal is it is lighter weight and less hours to assemble. I am looking at home alternatives to using a big hydraulic press.

You mean mold-less or molded? A lot of people did moldless, AFAIK only a few did molded.

You can use a beading roller instead of a hydraulic press. There were hand-cranked bead rollers made by Peck, Stow & Wilcox (PEXTO) or Roper-Whitney, but these have finite depth yokes (so you can only bead so far from the edge of the metal).

You could come up with some sort of a fixture to hold those beading rollers that uses a larger C-frame, similar to the homebuilder's dimple and rivet tools, they have an 18 or 24 inch throat.

OR, for skins larger than that and you could make some sort of a clever custom fixture - something that mounts the lower die on the floor, then the sheet of metal goes on top of that, then a long hinged arm (hinge bolted to the hangar wall) brings the upper bead roller down on top, and then you put a heavy weight on it to create the forming pressure... then you can roll the sheet in and out of the dies to create a bead in the center of a sheet.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
I have a hand cranked Harbor Freight bead roller. Can't see how it would roll a preformed leading edge skin.
Moldless is too heavy for my ultralight. Molded single ply fiberglass with deep beaded might work.

#### skyscooter

##### Well-Known Member
I am looking at home alternatives to using a big hydraulic press.
My recollection from discussions with the former VLA owner that it was not a big press that did the beads, because I believe it was done at his place with the help from the guy who had prior experience in using the tools to make the various beads in the skins. It may have been as simple as a female mold with the male bead tool on the other side of the skin hit with a hammer to form the bead. I have a spare wing panel and will check the skin thickness and post later

#### WonderousMountain

##### Well-Known Member
Them: How you making your ribs?
Thorp: I'm not.
Them: Shouldn't your wing be smoothe?
Thorp: Seems excessive.
Them: The dies & presses will be unweildy.
Thorp: They stay on the ground.
Them: You'll take extra man hours.
Thorp: I love my job, like I love my flying.
Them: It will never catch on.
Thorp: They will sing praises of me in the annuls.

##### Well-Known Member
If I have my facts straight, mass production is the primary reason why the Seabee was designed the way it was. Same for the Ercoupe. Mass production was the reason the Me-109 was designed the way it was. Mass production is probably the reason Cessna control surfaces have corrugations. The Blanik and Pilatus glider fuselages had external flanges for joining the fuselage halves, not because it was aerodynamically cleaner (it isn't) but because it made production easier in large numbers.

It's about reducing man-hours of riveting and reducing parts count far more than it is about anything else.
Its interesting to think for a minute, about how much tooling costs has come down since those examples. All the route templates are now digital, as are the holes for match tool parts. Die manufacture now costs fractions of what it did then, but even then when did you last see a drop hammer in action. Not to mention someone had to draw all that tooling.

From a Kitplane manufacture point of view the aim is still the same reducing the riveting and the parts count. Throw in Vans domination and one reaches an interesting observation, fir a Kitplane manufacture wanting to get traction in metal kitplanes by distinguishing ones self from Vans, a beaded semi elliptical wings could be as good as a 200K advertising budget (and a lot more permanent) if one can put the wing together as easily as a RV.

I like the idea of preformed metal, fiberglass, or plastic sections of wing sheeting with internal flange ribs and spar attachment ponts, and enough of a joggle for the next one to lay flat. The sections could be nested for easy shipment and then you build your spars, rivet or bond each secton to the spars and each other one after the other, and your basic wing structure done. Something like this....

View attachment 100272
The only example of the that rib structure I can think of in the wild is Bf 109 fuse frames (someone is making new ones but for the life of me I can't find the pictures on the web). A slightly simpler version is clinker built skins where the skin is as wide as the stringer spacing and the trailing edge of the skin is folded down to form the stringer, the Fletcher Fu24 had this on the rudder, it did prove to have low damage tolerance.

#### Turd Ferguson

##### Well-Known Member
Maurice Hovious can make all the skins for a Ford Trimotor. Same principle:

#### BBerson

##### Light Plane Philosopher
HBA Supporter
That looks simple to roll flat sheets. How do they form the leading edge curved skins?
I suppose a similar three roll former could do it on a big radius like the Ford.

#### wktaylor

##### Well-Known Member
Them: How you making your ribs?
Thorp: I'm not.
Them: Shouldn't your wing be smoothe?
Thorp: Seems excessive.
Them: The dies & presses will be unweildy.
Thorp: They stay on the ground.
Them: You'll take extra man hours.
Thorp: I love my job, like I love my flying.
Them: It will never catch on.
Thorp: They will sing praises of me in the annuls.
WonderousMountain… I think You never met/knew John Thorp. This is NOT the man I knew. He was certainly NOT stupid or egotistical and he was very soft spoken... but when he spoke people listened!!!

For the complexity of skin manufacturing, the T-11/-211s were simple to assemble [parts-count], rugged, exceptionally light and fun to fly. FAA certification costs/complexity were stupid back in the 1960s... JT could have made the design 'work successfully' in todays sport aircraft category... without being bleeddry. I suspect that modern sheet metal fabrication methods could have expedited/simplified and manufacturing,]… and made them then dead-nuts dimensionally consistent and smooth

BTW... JT was the layout designer [PE] for the Piper Cherokee [140/160/180] and the Rockwell Commander 112... and of course the designer for the T-11, T-211, T-18, wing Derringer and the Fletcher FU24 and FU-25...

I had a ride in JT's T-11 with JT... The aircraft was exceptionally light, tough, stable, stall resist and relatively fast [O-135[?]].. and he was a very capable smooth pilot... in his 60s. As a kid I learned a lot about aircraft design from Dad's T-18 and the other Thorp designs he kindly discussed with me [a curious teenager]... the 'reasons why?!' HE is the reason I chose to become an aero engineer in the middle of the aerospace crash of the 1970s.

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#### TFF

##### Well-Known Member
With that fancy die, It’s going to naturally want to curve. Keeping it flat will be harder. Lots of pressure up front will make it curve. Small change in depth, multiple passes, and man handling will keep it flat.

#### wktaylor

##### Well-Known Member
There are sheet metal techniques NOT evident in this discussion that make a huge difference in how much easy[er] these skins are to make than meets the eye... with good-quality forming dies and workmanship.

BTW, the obviously difficult parts to form are the wrap-around leading edges... but LH and RH are identical... same raw formed detail!

As far as I can recall JT NEVER designed a wing... for his aircraft... but necessarily a customer's design... that had built-in twist or taper: all were straight 'Hershey bar' and had remarkably stable low speed characteristics... but attained amazing performance/efficiency.

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#### BBerson

##### Light Plane Philosopher
HBA Supporter
There are sheet metal techniques NOT evident in this discussion that make a huge difference in how much easy[er] these skins are to make than meets the eye... with good-quality forming dies and workmanship.

#### Turd Ferguson

##### Well-Known Member
I'd be interested in hearing the fabrication or manufacturing negatives for something like the Emigh A-2 Trojan with wing ribs on the outside of the wing. Seems that would be easy to build today with blind rivets. Those panels are interchangeable left to right, top to bottom.

#### cluttonfred

##### Well-Known Member
HBA Supporter
TF, if you run a search for Emigh Trojan you'll find a number of old threads including a couple on the external ribs and the symmetrical tapered wing sections.

The general consensus was that it could make sense for a factory in a production or kitplane context that can bang out one wing skin shape on a big press or mold and use it four times per plane, which could be worth the downsides of the inherently symmetrical airfoil for a low-cost plane, but for a homebuilder a constant chord wing identical except for the mirror-image spars probably makes more sense.

It's not hard to imagine wing skins with integral stiffeners from the leading edge to the main spar, then a short flat section on top of the spar, then integral stiffeners again to the aileron spar. Cover the front section from the flat around the leading edge to the bottom flat with fabric for clearer aerodynamics.

Then again, shipping big wing skins is also problematic for a kitplane, so doing the corrugated components in smaller sections could make more sense. Maybe a nose-section, an upper rear section, and a lower rear section, all in small 24"/60 cm span pieces for easy shipping? That way you wouldn't need to go with a symmetrical airfoil.

#### Victor Bravo

##### Well-Known Member
That looks simple to roll flat sheets. How do they form the leading edge curved skins?
I suppose a similar three roll former could do it on a big radius like the Ford.
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.

#### Riggerrob

##### Well-Known Member
I like the idea of preformed metal, fiberglass, or plastic sections of wing sheeting with internal flange ribs and spar attachment ponts, and enough of a joggle for the next one to lay flat. The sections could be nested for easy shipment and then you build your spars, rivet or bond each secton to the spars and each other one after the other, and your basic wing structure done. Something like this....

View attachment 100272
Nice sketch dear cluttonfred,

Though I was imagining a simpler configuration more closely resembling the Bede-4 wing sections with straight skins and only a simple 90 degree bend to internal ribs. If you don't mind a .030 step, you don't even have to joggle wing skins.
Molds would be CNCed from high-density particle-board.
Start with roughly 4 foot (1 metre) wing skins and wrap them around a leading edge mandrel.
Then clamp them around the rib mandrel - about 6 inches from the end. Hammer beat the over-hanging metal until it resembles a rib. If overhangs are long enough, they might overlap far enough to rivet together in the centre of the wing.
Alternatively, hydraulically press the sheet aluminum against the MDF mandrel.
I wonder if you could use a huge water tank to apply the same pressure? Set it up in the evening and turn on the water. Next morning, drain water and remove press-formed metal pieces.
A third alternative is a huge lever press with one end bolted to the hangar wall and the far end containing a stirrup. Mount the MDF mandrel close to the hangar wall. With a long enough lever, my 200 pounds can press sheet aluminum.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
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.
A three roll has adjust screws on top. At least both mine do. In any case a three roll can't roll tighter than the roll. It would be difficult (impossible) to roll a tight 1" nose radius. The 1 1/2" roll will bow and is not suitable for flat tempered aluminum, let alone beading.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Hehe, my lever press could be 11% shorter than yours, Riggerob! Seriously, my idea was that the ribs and skin would be integral sections and once you attach them to the spars and to each other then you'd be done with the basic structure.