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Help needed mounting 2 servos on the wings

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Help needed mounting 2 servos on the wings

Old 08-19-2008, 08:23 PM
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Default Help needed mounting 2 servos on the wings

The old-fashioned "bell-crank" mechanism that uses a single servo to control the ailerons for my Senior Falcon is completely SHOT to the point of where the plane just isn't airworthy.... This plane is over 30 years old and I love it more than any other plane I have, or probably ever WILL have. Doc gave it to me and I'd LOVE to teach my son to fly it one day and tell him that his grand-daddy built this plane. To me, this plane just has that "magical" quality about it that I can't define.

It's also special for 2 other reasons (1) you DON'T see one flying anymore EVER so it's unique and as beautiful as any freshly covered plane in the world (to me) and in it's own way and (2) because no matter WHERE I go or who I talk to (especially the older veterans) I hear "HEY! I learned to fly on one of those! That's one of the best aircraft I've ever flown." Fixing it and getting it airborne again has really become a labor of love, even though my friend with the handmade giant scale P51D calls it a "lead sled"(it's a pretty heavy plane, but the Webra 10ccm (.61) with an 11x8 prop was what Doc used on it without any probmes. My friend told me to put it in a corner and forget about it.... Two words: H*LL NO!!!!!!!!!! This plane is very dear and special to me and I want to pass it on to my son one day and teach HIM to fly it. It also doesn't hurt that it's also mostly a heavy gauge/weight balsa + plywood crafted plane so it can really withstand some MASSIVE punishment (not that I'm planning to, but "just in case"....) I've heard that Doc pulled more than a couple of "doozies" over the years with this bird !

I've talked to alot of very experienced builders recently and they ALL said the same thing: Get rid of that "bell-crank" system and mount 1 servo on each wing attached directly to each aileron, then link the servos with a Y-connector. I've got the servos (I need the connecting rods + Y-cable....) and even some really great wood to use as a mount (a 2'x2' sheet of 1/8" thick "cabinet quality" wood; very light and very strong).

I've never done ANYTHING like this before, but I really want to. Does anyone have any tips for getting the servo mounting holes aligned perfectly? (the wing has a tough covering -almost a hard plastic, but it's not - it's much lighter- and a foam core in the middle with a semi-symetrical profile so depth isn't going to be an issue) I know they have to be EXACT in location AND totally symetrical. I'm going to mount them where they can directly connect to the control horns on the ailerons -which are mounted 8"-10" away from the fuselage down the ailerons.

I'm going to have to cut through the covering and then "dig" a hole in the foam core big enough to fit the servo and a pair of cross beams/support mounts to screw the servos to. I don't want to RUIN this wing (even though it IS the third wing this plane has had; my benefactor -father-in-law aka "Doc" is a great surgeon, a skilled "full scale" pilot and a talented builder of all kinds of things (including his full size "real" kit plane!) , but he was a LOUSY RC pilot [:@] ).

Has anyone got any tips for such an undertaking? I don't want to "hatchet job" it. Any ideas, suggestions, or experience in making sure the symetry of the servos is perfect are GREATLY APPRECIATED !!!!!!!!! I'm not even really sure WHERE to measure from (where to make the "zero point" in terms of drafting/design) I'm sure there's SOMEONE OUTHERE with a trick or a technique in doing this right that could help me do this without making a total mess of it.

PLEASE HELP !!!!!!!!!!!

I'm including a picture from the "new" design of the Falcon from Goldberg. This is what I'm trying to accomplish. (unfortunatly, the ARF kit it now comes in has the position already located and cut it's it's almost a "drop-in-and-plug-up" simple operation..... )
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Old 08-19-2008, 08:40 PM
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Default RE: Help needed mounting 2 servos on the wings

You are not only going to have to dig out the hole for the servo, but you will also need to thread a servo lead through each wing. And if the servo leads aren't long enough to reach the fuselage, you will need to connect a servo extension or Y harness somewhere along the span of the wing.

It's really not a terribly difficult task, but you will probably have to strip and recover the bottom of the wing. Otherwise, you will end up with a patch job.

It may be easier to repair the torque rods than to make this modification. That's what I would try first.

If I were going to the dual servo setup, I would probably strip the bottom of the wing, build up a little wooden box to mount the servo into, and epoxy that into the foam. You'll need to cut a groove to run the servo lead, and then cover it all back up. I would try to get the servo close to the middle of the wing, and try to line up the control horn on a hinge line, but that's probably not critical.

Good luck, and I hope you get the old girl back in the air. Be sure and post some pictures. If you can post a picture of the current setup, you may get some advice on how to make it work as it originally worked. There's really nothing wrong with one central servo and torque rods.
Old 08-19-2008, 09:09 PM
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Default RE: Help needed mounting 2 servos on the wings

I would use a razor knife and heated chisel to hog out cavities for the servos to drop into. Then drop a heated tube or stiff wire into the wing from the center section and from the servo pocket until you create an interconnecting pathway for the wiring. Once you get all the prep work over with, then "pot" the servos into the wing. A forum search should show some threads about "potting" servos.
The actual pin point symetry of the servo mounting doesn't have to be as exact as you make it sound, close is good enough
Old 08-19-2008, 11:07 PM
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Default RE: Help needed mounting 2 servos on the wings

I found a picture of the underside of the Falcon's wing. As you can see, the bellcrank setup is not only shot, it catches and grabs unevenly inside the wing at the pivot hinges. It's just not an efficient or easy to use (much less setup!) configuration. Even if I got the servo mounted and the bellcrank soldered back together, the hang-ups inside the wing really put a strain on the servo and I'd rather not take that chance.

On the surface it "looks" easy to fix and configure, but the space is SOOOO limited and cramped that setting the bellcrank is just not a good idea. I've had 3 different builders look at it and evaluate it and they ALL agreed that the best thing would be to replace it with wing-mounted servos.

The plastic coating is pretty tough so If I make an incision to slip a wire into, covering it back up with something (even clear tape, would be easy to do

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Old 08-20-2008, 02:22 AM
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Default RE: Help needed mounting 2 servos on the wings

You can alway install a servo with more torque and just leave it.

If you want to go dual servo. I'd cut where the bell cranks are at. I'm pretty there's holes already where the bell cranks are at.
A drimel is nice to have. You can just drop a string through to pull the servo's wire where the old linkage is at. This way you don't have
to cut more than you have to. If it's just a foam core wing..I'd just ream/enlarge the holes (for servo leads) with an allen wrench..it's not far from the center anyway.

I've applied film on wings with plastic skin. I have a couple of extra ASAP that's like that.
Old 08-22-2008, 06:22 PM
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Default RE: Help needed mounting 2 servos on the wings

Just a quick tip on cutting foam. Hobbico makes a soldering iron that holds a # 55 X-acto blade. Works great. Also works great on cutting through the Mon O Cote were necessary on stab. fin for glueing to fuse.

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