Old 05-31-2016, 06:30 AM
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Join Date: May 2010
Location: Wichita, KS
Posts: 3,958
Unhappy What the heck is wrong with my giant wing?

Iím having trouble with my new flying wing and Iím at a loss for a solution.

The problem in a nutshell is this Ė as it picks up speed, it pitches down. (And as it pitches down, it picks up speed.) Unless I catch it *immediately*, this self-reinforcing behavior quickly gets out of hand and ends with it lawn darting into the ground at high speed.

This is *not* a motor angle problem; it happens in an unpowered glide, as well.

The wing is pretty big Ė 60Ē Ė if that makes any difference.

Itís using a relatively fat airfoil, but I donít think itís an airfoil problem; Iím using a version of this same airfoil on three other flying wings in my hangar.

When I first tossed the plane up, I had the CG pretty far forward and it felt very nose-heavy. It required ridonculous amounts of up reflex and all the elevator I had to keep the nose up enough for level flight. Iíve been slowly moving the CG back and the flight characteristics seem to be improving as I do so Ė though it still requires a lot of up reflex Ė but it has retained this one fatal habit.

In two sessions, Iíve put it nose-first into the ground, hard, from pretty significant altitude. Iíd like to stop that before itís destroyed beyond all recovery.

Iím hoping thereís a rule of thumb Iím unfamiliar with that diagnoses this problem. Any thoughts?

Hereís some video from the first flights. You can see the problem start to develop several times before it gets away from me and the plane finally augers in.

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