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Old Apr 13, 2004, 05:06 PM
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Grand Rapids, MI
Joined Mar 2004
83 Posts
Servo recom. for lrg plane crashed once by elev. flutter


I was flying a large plane on 4/10/04, and noticed a glitch in pitch control. I immediately tried to land the plane, but within seconds, I completely lost pitch control and the plane crashed after I leveled it out and cut the throttle. This was a large scratch built plane, loosely based on the Sig Four Star, with a 34cc engine and smoke system, which was a huge investment for me. The engine is a Quadra 35, with one of the Dario Brisighella "unbalanced" flywheels, for vibration reduction. The engine was mounted with vibration isolators to the firewall. This plane contained a new Futaba 6EXA radio with S004 BB servos. Post crash inspection revealed a stripped out elevator servo. The servo was directly connected via a short control rod (pre crash photos attached). The linkage was slop free. Elevator is 2 layers of coroplast, with an essentially gapless hinge. I have recently learned that elevator flutter is the likely cause of the gear train failure. What do you recommend for a Hitec servo model? I usually buy from Tower Hobbies for convenience. Their catalog doesn't show specifications. I read about someone using the following in their large plane:

Servos: Rudder - 1 Hitec 5945 (181oz) w/ pull pull
Elevator - 2 Hitec 5625 (131oz)
Ailerons - 2 Hitec 5625 (131oz)

I also plan to replace gutter pipe control horns with something stiffer, possibly moving control rod further from surface (and compensating with larger servo arm).

Will any mass balancing be necessary for this? It's easier said than done, and if added in lumps, could make it worse.

Finally, I plan to use 2 servos on elevator for insurance.

What can be recommended for this set-up? Any help would be greatly appreciated.

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