Control Surface Skin Bending

[chris]

I'm getting ready to attempt bending some skins and decided to practice on a slightly short scrap piece of .025. I would like some feedback before I bend the bigger high dollar piece.

Is the bend radius on the trailing edge satisfactory?

[structurespilot]

You must be scratch building eh Chris? My control surface skins came prebent.

Well anyway, I just used this method to make a Piper Navajo Aileron skin and it worked great. First of all deburr the edges baby ass smooth so they don't crack. Scotch brite works good.

To finish off the bend and make it tight and uniform, purchase a length of hinge pin, or rod for whatever diameter you want at the T/E. Tape it to the edge of a peice of 1/8" partical board, or thin scrap wood you have laying around. The wood should be equal length to the rod, but slightly longer than the piece your trying to bend. Place the skin on the table, and the wood and rod in tight to the inside of the bend. Screw the wood /rod to the table so it won't move, on all sides (Thats why the wood needs to be slightly bigger all the way around the piece). But up another piece of wood to the outside of the radius, and screw it to the table too. Then use another piece of flat wood to press down on the piece with even pressure. The hinge pin or rod will stay put, and give you a nice clean radius.

If a T/E radius is too small it will make the controls feel too sesitive, and can be prone to crack propagation. If the T/E radius is too big it will make the contols feel dull. Not sure what sonex wants but I recall something around, 1/8" radius ?

Regards, Norm

[chris]

Yes sir I'm giving scratch building a go. I find it very satisfying to see a part come out of a flat piece of aluminum.

The radius called for is 1/8" It looks really close compared to the full size template in the plans except that it bulges a little right after the curve on the trailing edge. You can see that in the picture of my scrap piece. I was worried that pushing on it more might flatten the trailing edge too much but a 1/4" rod as you suggest would take care of that.

One of my problems is my economy bending brake. Its just not strong enough. I'm going to have to make one of the Dave Clay style brakes. Sounds like a good project for this weekend.

Thanks for the advice.

[structurespilot]

Sorry Chris I must point out that I didn't suggest 1/4". If you already own a break, try taping the rod into the radius, and then flip the skin around, and use the break as a clamp to finish the bend. The rod stops the metal from collapsing to tight.

Good luck, Norm..