Thread: Discussion What won't my Kestrel fly?
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Old Sep 24, 2012, 08:42 PM
kcaldwel is offline
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Joined Jan 2007
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I've looked at your powered attempt video a few times, and it sure looks like only the right elevator is up in the final dive.

I have my own bird-like planform 2m sailplane model half done. It has Dr. Drela's AG 44 to 46 series, with the flap in the 2 degree reflexed position. My e-glider has quite a bit lower wing loading than yours but bigger wing chords, so it's Re range might be a bit different. The AG 4* airfoils have excellent low Re performance, and have very low Cm (moment coefficient) with the flap reflexed. This reduces the tail load on a short coupled airplane, and makes it more efficient because the tail doesn't have to lift downward so much with a stable CG position. My model's low wing loading should help with slow flight, because the max Cl is a bit lower with the reflexed flap. It is a bit of an experiment, so I'm not planning on movable flaps at least initially.

Your Eppler 197 isn't very good below Re = 200k, so it wouldn't be the best glider airfoil for smaller chords and slow flight. For powered flight, if the stall is OK, the airfoil isn't too critical unless you are trying to optimize the design. I think a lower Cm airfoil with better low Re performance would be a better choice for your Kestrel (Mk2 ?).

http://www.charlesriverrc.org/articl...t-airfoils.htm

Kevin
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