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Control surface substitution.

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fulcona

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Dec 20, 2004
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In making a control surface (rudder,aileron etc.) could it be possible to replace the .032 Aluminum spar with one made of fiberglass? The reason I ask is that I no longer have access to the bending brake that I used years ago when I first made these pieces. A while back I discovered that my rudder had a slight twist to it that couldn’t be corrected. I made another one in composite but it turned out way too heavy. So I’m going back to the original style, (RV type). I was thinking of making the spar and skin stiffeners (anything that needs to be bent) in fiberglass because it would be easy to do and then rivet the skins to them. When riveting the aluminum skins to the fiberglass piecesI would back up the backside with a thin aluminum strip or aluminum washers. Think it would work?
 

Dan Thomas

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In making a control surface (rudder,aileron etc.) could it be possible to replace the .032 Aluminum spar with one made of fiberglass? The reason I ask is that I no longer have access to the bending brake that I used years ago when I first made these pieces. A while back I discovered that my rudder had a slight twist to it that couldn’t be corrected. I made another one in composite but it turned out way too heavy. So I’m going back to the original style, (RV type). I was thinking of making the spar and skin stiffeners (anything that needs to be bent) in fiberglass because it would be easy to do and then rivet the skins to them. When riveting the aluminum skins to the fiberglass piecesI would back up the backside with a thin aluminum strip or aluminum washers. Think it would work?
Temperature changes could get you. Aluminum expands and contracts a lot more than fiberglass as the temperature changes, and the rivets might start tearing the holes in both surfaces. Vibration also causes problems. Fiberglass also weighs more, and weight is the enemy of any airplane. You already found that out with the rudder.
Find a friendly HVAC shop and use their brake. You might have to make some radius shims, since they usually use a pretty sharp edge on their light-gauge steel sheet.
 

wsimpso1

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Rebuild in kind is the best scheme. Changing materials is component redesign, particularly when it means large changes in moduli or big disparities between spar and skins. Are you qualified to do structural design of new control surfaces?

Most of us belong to an EAA chapter. Someone must own a brake.

Billski
 

fulcona

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Dec 20, 2004
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We don’t have an EAA chapter anymore in our city but I’ll search for a bending brake. Thanks
 

TFF

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Industrial Machine shops, wood buck, angle iron homemade brake. They require a little extra effort than one at your fingertips. The fiberglass, might as will make a complete tail surface instead of one piece. The parts have to be different to take care of the materials. Not a one to one substitute.
 

Pops

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Before we built a 8' brake in building Bearhawks we took the spar webs to a HVAC shop and told them of the bend allowance and no scratches allowed. They bent the right bend allowance but didn't wipe the bed of the brake clean and all the parts had huge deep scratches. Scrap aluminum.
Ordered the replacement aluminum from Wicks. They offered to sear the aluminum to the right size and bend the webs for a very small fee. I couldn't believe it. Did a perfect job.
 

Victor Bravo

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Dave's brake looks like it has bolts going through the flange in the aluminum (under the clamped steel angle). Unless I'm missing something, the width of a bent flange is severely limited with this brake. It looks FINE for bending a 3/4 or 1 inch flange, but looks like anything wider than that is a problem.
 

BJC

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Before we built a 8' brake in building Bearhawks we took the spar webs to a HVAC shop and told them of the bend allowance and no scratches allowed. They bent the right bend allowance but didn't wipe the bed of the brake clean and all the parts had huge deep scratches. Scrap aluminum.
Ordered the replacement aluminum from Wicks. They offered to sear the aluminum to the right size and bend the webs for a very small fee. I couldn't believe it. Did a perfect job.
Some years ago, I needed to make some 8’ bends in 0.032 2024. Called a local HVAC shop, talked to the owner, later went and met him, told him what I needed to do, and was given the use of a (IIRC) 10’ shear and an 8’ brake. Went in on a Friday evening after the shop had closed, found the equipment clean, sheared and bent for a couple of hours, reset the brake to “as found”, cleaned up, loaded up, and locked up. Tried to pay the owner, but he wouldn’t take anything. I think that he did let me buy him lunch one day.

People can be very helpful and sharing if one approaches them honestly, politely, and respectfully.


BJC
 

Pops

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You can make all kinds of bending brakes from scrap steel.
Picture of the 30" brake for bending .032 ,4130 steel for tail ribs. Will bend down to 3/8" channels. Takes lots of clamping pressure. One 10 ton jack in the middle and 2-- 6 tons on the ends. Use large wrenches for handles to make in easier for storage.
Also a picture of a small , heavy duty 12" brake for bending 4130 steel fittings .
 

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Dan Thomas

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MANY bending brakes make very sharp bends that are NOT OK for airplane parts. For .032" aluminum you're going to want a 1/16" or 1/8" radius at the bend.
You take some sheet--some softer stuff like mild steel or 5052 aluminum--and form a strip of that over the sharp nose first. If the radius needs to be larger you form a second strip over the first, moving the nose back to accomodate the extra thickness. Then you form your part over those strips. This is standard practice in a lot of shops.
 

Dan Thomas

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Homemade brakes are ok for short or light stuff, but they distort on longer or heavier bends and you get some lousy parts. The center of the brake will open up some during the bending, and that messes up the radius of the part in that area. It can result in a curved part.

I'm lucky. A local HVAC shop a block away let me use their big brakes, and now my son, less than an hour away, has two brakes--a small box brake and huge old pan brake. Eight feet at least. Power shear too as well as a smaller foot shear. And I'm not even building an airplane, just restoring an old aluminum runabout boat.
 
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