Thread: Discussion What won't my Kestrel fly?
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Old Sep 24, 2012, 09:33 AM
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Originally Posted by eflightray View Post

A reflexed flying wing, (just the same as many models with cambered wing sections), only needs a little speed change to require an elevator trim change to compensate for that increase in lift.

My Eagle is released on quite low throttle, and the speed gently increased to climb. Full throttle will have it going vertical with me holding full down elevator to stop it looping.

I don't see anything particularly wrong with the Kestrel and the Hawk other than too much throttle.
Climb with throttle is 90% of the time having the CG far forward. High pitch stability will cause a strong pitch up with speed increase. If you like flying it like that, then don't change it, but moving the CG back closer to the neutral point will reduce the pitch up tendency with speed increases.

Of course the elevator will get more sensitive as the CG goes back, so throw will have to be reduced and down trim will have to be added. It is quite possible to fly conventional layout airplanes with the CG right at the neutral point, so there is zero pitch trim with speed changes, assuming the thrust angle is correct. Most DLGs, and many pattern airplanes and sailplanes are flown like that.

The lower pitch damping of short-tailed bird-like models means it is pretty hard for most of us to keep up with the pitch on them with low pitch stability, although Biber flew his Mulibumm with a neutral CG quite successfully:

I still think the yaw stability of the Kestrel is pretty marginal. It might be possible to make it work without an added fin, but it will take some fine tuning of aileron differential and thrust line to get it there. Less throttle is a good idea!

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