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Old Jun 02, 2016, 03:14 PM
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In need of ideas

While getting ready for this weekends TD contest I assembles my Muller Cobra to make some adjustments on the flaps. I noticed I have a dead aileron. On closer look the servo is dead. I plug in a new servo and all it does is cycle from one extreme to another. I plug the servo directly into the RX and all is fine. After some probing with a multi meter it would appear that the wire within the wing has developed a short. When the signal wire and positive wire are probed at the same time I am reading connectivity instead of an open. OK so the wire has to be replaced. The question is how? The wire seems to be glued in place. This is a veneer sheeted foam wing. The only solution I can think of is to sharpen a long brass tube and try to cut a new hole through the core. Does anyone else have a better suggestion?
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Old Jun 02, 2016, 03:21 PM
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Shawn,
Cutting a long hole with a brass tube is a pain. If you're going to do it, file a few notches in the boring end of the tube and cut your way in.

My preferred method, since you will be replacing the wire would be to burn a channel. This is cleaner, but takes some time, jigging, and practice. You could do this ~ 1/2" away from the existing channel, then access on either end.

If you like, I'd be glad to do this chore with/for you, understanding your hand issue. Give me a call (I'll pm my number).

JT
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Old Jun 02, 2016, 03:22 PM
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Yes, the wires are locked in the foam, no large open channel for them to run through on a Muller wing. Put a flat tip on a piece of music wire and drill it up the wing? Gonna be tough, that's a long run.
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Old Jun 02, 2016, 03:26 PM
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Burning a channel is probably the way to go like Jim said. Taking him up on his generous offer is probably a good idea. It isn't hard to do, but experience helps - especially since you will be doing it on a finished wing.

Tom
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Old Jun 02, 2016, 03:29 PM
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Mueller wings were a pain because of the way they buried the wires in epoxy. I would have to think that the short must be at either end and not in the middle of the run. Perhaps you can chip away some of the epoxy and find the offender?

Otherwise Jim has the right idea. Those furniture wings sure were beautiful!
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Old Jun 02, 2016, 03:36 PM
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Thanks guys, spoke with JT and am headed over to his place.
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Old Jun 02, 2016, 05:39 PM
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The deed is done. New channel burned cleanly just ahead of the old wire location, centered in thickness. Opened up access at servos bays and strung new wires. Shawn should have this flying again in short order, just needs to do a little soldering.
JT
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Old Jun 02, 2016, 10:59 PM
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Thanks to JT the job is complete. Both aileron and flap wires have been replaced, I found a 4 pin header that was a good match to what is installed into the fuse. The sailplane is charging right now waiting for tomorrow's practice session. Big thanks to JT.
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Old Jun 03, 2016, 09:37 PM
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JT IS the guy. A good friend is beyond value.

One thing to perhaps make the job easier if it's ever needed to be done again - use the old wires to guide the brass tube for the new hole.
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Old Jun 03, 2016, 11:34 PM
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I thought about that but the original wires are right up against the wing sheeting and I would have been cutting through a mix of epoxy and foam. I could just picture the tube coming through the sheeting.
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