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        Servo recom. for lrg plane crashed once by elev. flutter

#1 Brad B. Apr 13, 2004 05:06 PM

Servo recom. for lrg plane crashed once by elev. flutter
 
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Hello,

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.

Thanks.

#2 MikeMayberry Apr 19, 2004 01:07 PM

The set up you are considering is a good one.

Mike.

#3 Brad B. Apr 19, 2004 09:59 PM

Quote:

Originally Posted by MikeMayberry
The set up you are considering is a good one.

Mike.

Mike, can you give me a specific recommendation (model numbers)? Will the plain, hi torque MG servos be sufficient? Will digital servos work with my Futaba 6EXA radio? What about the newer servos with the "karbonite gears"? There is a big price range here, so I'd like to use a reliable set-up with minimal risk of failure. Thanks.

Brad

#4 MikeMayberry Apr 20, 2004 11:07 AM

It depends on your skill and how you intend to fly the plane as to what servos would best suit your application. At the lower end the not digital 625/645's would be fine. Stepping up to the digitals will help the plane fly more precise. The Karbonite geared servos would also work. You could use the new HS-635's all the way around.

The ultimate set up is HS-5945's all the way around.

Mike.

#5 Brad B. Apr 20, 2004 11:23 AM

Quote:

Originally Posted by MikeMayberry
It depends on your skill and how you intend to fly the plane as to what servos would best suit your application. At the lower end the not digital 625/645's would be fine. Stepping up to the digitals will help the plane fly more precise. The Karbonite geared servos would also work. You could use the new HS-635's all the way around.

The ultimate set up is HS-5945's all the way around.

Mike.

Mike, This will be average skill level sport flying, nothing precise. Will the digital's work okay with my Futaba set-up? What is advantage of coreless? Does that mean no brushes? My biggest concern is to have a servo that can withstand the onset of flutter (higher torque servos), should it occur and I can catch it in time before it tears something apart. I haven't been able to find out much info on other people's experience with flutter on large planes.

Thanks,
Brad


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