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Micro servos in a Middle Phase wing.

Where should I put these servos?

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David Davis22/03/2013 09:28:44
3851 forum posts
741 photos

I am building a Chris Foss Middle Phase for a club colleage. He's provided me with a three-channel kit to convert to ailerons. I've cut out the trailing edge to allow for 1.5 inch TE stock ailerons and reduced the dihedral to 1 inch under each tip.

He's also provided me with micro servos of indeterminate make measuring approximately 25mm x 25mm x 12mm. Where should I postion the servos in the wing? Should I remove the foam and build a balsa box and glue the the servos permanently in place? If so should I use epoxy or something like silicone as the adhesive?

I have some plastic micro servo mounts but if I were to use these I would have to remove more foam and probably weaken the wing.

All advice from experienced glider guiders gratefully received.

Tom Satinet22/03/2013 09:42:44
519 forum posts

I think because the wing is fairly thick you can pretty much drive the ailerons from where you want. Bear in mind the "standard" middle phase has a single aileron servo driving both ailerons from their inner tips, and they fly fine.

I would position the ailerons at something like 40% of the length of the aileron. Back to front positioning is behind the spar on most gliders, but the middle phase doesn't have spar of course, so i would just position them beyond a 3rd back from the leading edge at least (they say this is the most critical area of the aerofoil). Nearer the trailing edge than the leading edge seems sensible (TLAR).

I think building a box for the servos is a good idea - what about ply? Then you can glue the servo in with a small amount of glue and they will come back out again if needs be. .

Peewhit22/03/2013 13:30:52
795 forum posts
264 photos

Hi David,

I have done this with both a Middlephase and a Phase 6.

Servo positioning is not that critical.

The further inboard the less inertia and therefore faster roll rate, yet the closer to the centre of the aileron length, the better control.

I opted for the pushrods at the centre of the ailerons.

Install the servos in the thickest part of the wing and build a box with ply (3/32" or so).

Wrap the servos in insulating tape, sand down lightly and wipe with white spirit, meths or isopropyl alcohol. Glue in place using epoxy thickened with microbaloons.

If the servo needs to be replaced simply cut the tape, take out the servo and peel the tape from the epoxy. You are left with a lovely servo shaped hole.

David Davis26/08/2013 18:37:33
3851 forum posts
741 photos

I took your advice Peewhit but encased the servos in automotive filler rather than epoxy.

The model is covered in flourescent yellow Solartex, the owner's choice. It hasn't been flown yet.

I would insert an image from my album but the cybernetics won't allow me to do so this evening for some reason, ....and people wonder why i have such a jaundiced view of computers.

face 8

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