ORIGINAL: txaggie08

WEll im back rolling on the four star 120, and am coming up to the point i have to decide on servos etc.


Im going to run a homelite 45cc conversion wiht electronic ignition on this plane from BCMA enignes. Theyre a little heavier than the glow motor it was designed for, and between the EI gear the motor, and the firewall reinforcement, im worried about mounting the servos close to the centerline.

Answer, You may want to mount the servos on the outside of the fuselage in the rear, big bird style. This keeps it simple and allows you to inspect linkages easily. You would mount two servos for the elevators and one for the rudder.

I was seriously considering placing the two servo mounts to the rear of the plane. If both will fit i would mount them inboad with an access hatch between the second to last and last formers. It will keep the clean look, but with a hatch i can still get to them after covering. it will also add considerable mass to the extreme rear of the plane. It would also mean very short push rods instead of the longer more flexible ones running from mid plane.

Does anyone see a problem with doing it this way? Obviously im going to run heavy duty extensions to the rear servos. but those arent insanely expensive. ive heard these planes tend to be nose heavy anyway, and the heavier motor is not going to help....


Im was also planning on running 3010 servos in the fuse(or the tower version thats the same torque) and possibly digis on the ailerons(the low profile ones). Ive got a 9650 digital im not using, so it may go on the throttle, but i dont know i might just get a small servo for it. I thought if i used a smaller unit(like the spare 9650 ive got) i could run a VERY short linkage imeadeatly behind the firewall...

Answer; If you are running a gas/ignition engine, you really need to keep all of your electronics at least 12-16" away from the enging and ignition components. Also, you will want to run push rods that are not metal from the throttle servo to the engine. Metal pushrods can act as EMI antenna's and give you problems with interference. There are some really good threads, here on RCU, that cover gas engines and the ins and outs. You may want to read them over, you may come across some information you haven't considered, but could put to good use. Good luck, this should be an interesting project.


Thanks and Gig'em