How do you prep a molded wing for horn? - RC Groups
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Aug 20, 2004, 12:34 AM
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How do you prep a molded wing for horn?

I was getting ready to attach the elevator horn to the elevator on the Lea-V when I got to thinking... Do I want to scratch or sand the elevator first and then attach the horn to the elevator with epoxy? What method do you use? Scratch? Sand? Drill holes? CA? Epoxy (slow cure or fast cure)?
The horns supplied with the Lea appear to be made of fiberglass.
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Aug 20, 2004, 01:29 AM
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CrazyGaijin's Avatar
Make your own horns out of thin epoxy glass circuit board FRP material allowing them to extend into the control surface itself- in other words make them the size of the horn above ground plus the exact section of the control surface. They will get glued "in" not "on".

Carefully mark the surface where you want the horn to go, no wider than the FRP horn cross-section. Make it as close to the hinge line as you can: on the inside your horn will probably be visible if you open the control surface and look behind the wiper.

Drill some small holes carefully by hand using a sharp 1.5mm drill in a pin vise, only into the surface skin!

Finish the thin slot in the syrface with a sharp knife.

Carefully dig into the balsa skin working towards the other skin (but not through it....). You should have a hole slightly bigger underground than the skin slot.

Now carefully sand the horn end to fit exactly in the small hole you made (it will be a bit too large) and roughen the horn where its inside the hole. Test the horn size and angle with servo and rod to ensure its going to give you enough control throw for spoilerons and flaps yet no play. If you have the hinge on the same side as the horn, be very careful not to make too small a horn as you'll get flutter. You need some length from the horn rod hole to hinge line.

Epoxy it in the hole. If you can, add a little epoxy on the inside of the hinge line (under the wiper).

This is a strong and reliable method.
Aug 20, 2004, 01:33 AM
Electric Airplane Junkie
bhchan's Avatar
Cut a slot on the surface on the side of the horn, just wide and long enough to fit the horn in. Put masking tape around the cut out, leave about 1/8" of wing skin around the slot uncovered. Lightly sand the exposed area. IF the plane was built correctly, there should be a hard point to mount the horn, a healthy glop of epoxy/microballoon mix at the area where the horn should be installed. If so, make sure all the material in the slot is cleared all the way to the inside of the other skin. Rough sand part of the horn that will contact with the epoxy. Mix a batch of 15 minutes epoxy and let it flow into the slot. wet of horn with more epoxy and slide it into the slot. Let a generous epoxy built up on the surface. Make sure the horn is at the correct location and not leaning. When the epoxy cured, remove the masking tape and you are done.

Brian, an EAJ

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