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control question

Old 04-10-2006, 10:22 AM
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I just recently finished building a Quickie 500 type airplane that was kitted to be a "Sunday flyer", tricycle gear, canopy etc... Basically it is an old school low wing Quickie made back in the mid eighties that I found on the hobby shop shelf.
After messing around with the configuration a bit, I ended up building it just like a Quickie racer, tail dragger, and a OS 40 FX with a Mac tuned pipe I had laying around doing nothing, looped up over the top side of the fuse.

I took it out Sunday and it leapt into the air, no lack of power on this one. The only problem I seem to be having with it is when it approaches its top speed; the tail (pitch) will start to violently pitch up and down uncontrollably. It will stop as soon as I back of the throttle a little bit. Now I would assume some kind of flutter problem with the elevator, but the kicker is that this same action will occur when you take the A/C vertical and just when it is about to lose forward speed and you roll it over, the tail will start to pitch in a wild oscillation again.

Any Idea what my problem could be? Is it a control problem, servo or aerodynamic issue? Any input would be appreciated.
Old 04-10-2006, 10:35 AM
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Default RE: control question

If it's elevator flutter you will certainly hear it. It sounds terrible. Can you press hard on the elevator surface without it flexing ...you should be able to press real hard.
It might also be the elevator servo that goes berserk! What servo do you have??

Jan K
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Old 04-10-2006, 10:58 AM
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Default RE: control question


Thanks for the quick response.

No, I do not hear flutter at all. I have had a flutter problem before (on a different airplane) and know the sound well. When it starts to ocilliate, it is very large up and down movements, like four or five foot up and down pitch movements, very un-nerving.

I am using Hitec servos, HS-322HD, I have used this type of servo in many different models and have had no issues with it before. There is no real unusual play in the elevator, no more than the rudder or my other airplanes.

BTW, the pic of your quickie pretty much sums up what my plane looks like, add a tuned pipe on top and that is it.

Also noted the pic of your elevator linkage. I am building a similar setup in another airplane that I am covering right now. This airplane was also from that same hobbystore. It is called a Rainbow Runner, and I would swear that the Ultra Sport was a direct copy of this airplane, just changed the shape of the tial a little bit. Anyway, It is being built for the sole purpose of being a speed plane and I was looking for ways to keep the drag down. Linkage buried in the fuse. No gear except for a single mono wheel in the belly, like a sailplane, fully sheeted the wings and a Jett 50, it should scream. I just dont want any issues like I am having with the Quicky Sport.

Old 04-10-2006, 11:54 PM
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Default RE: control question

I'm apt to think it might be your servo, I had a similar problem with the 322 also, It for some reason lost it's center point under certain conditions and drove me nuts trying to figure it out, I changed the servo to a HS425 and it went away, I only use the 322's and others in it's class for throttle now, Better servos are cheaper than new planes. The 322 is a good sport servo but lacks when it comes to higher performance taskes like a screaming fast 500. Another club member had one and that thing moved.

Old 04-11-2006, 12:48 AM
Rod Bender
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Default RE: control question

By no means am I well schooled on this, but what about your mounting location of the control horn on the elevator? I read somewhere that the pushrod connection point should be at the hinge point. Not sure if this is attributed to your issue, but it talked about anomalies that occurred when it was not mounted correctly.... Greg

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