WattFlyer RC Electric Flight Forums - Discuss radio control eflight - View Single Post - What the heck is wrong with my giant wing?
Old 05-31-2016, 05:56 AM
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Join Date: Mar 2009
Location: Aberdeen, Scotland
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It's the airfoil. Flat bottom 'Clary-Y' type airfoils have a very strong nose down (or negative) pitching moment. You can often 'fudge' the problem by adding lots of reflex on the elevons but that's not a good solution even though on some models it might appear to work ok. When you get to high reflex angles you get problems with flow separation on the elevon which causes unpredictable behavior as well as being very inefficient.

For swept wing you can use lots of twist (washout) but as a rule for a tailless design you should be using a tailless airfoil that has some reflex built into it's camber line to give it a neutral or slightly positive (nose up) pitching moment. Symmetrical airfoils also work ok on swept wings providing efficiency is not your main concern..

One of the MH 6X series airfoils would be good along with a few degrees of twist: http://www.mh-aerotools.de/airfoils/mh60koo.htm

Some good reading:
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