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Old Dec 26, 2010, 07:24 AM
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High Altitude Flyer
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Fairplay, South Park, CO
Joined Sep 2005
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The moment coefficient (maybe easier understood as a pitching moment) of a wing is dependent upon the critical shaping of the forward 25% of the airfoil, and also is dependent upon the actual implementation & trimming of the control surfaces (ailerons or elevons.) Especially when building a wing with independent servos for each control surface, the trimming of those surfaces combined with a bit of fine-tuning of the wing incidence and balance point result in the pitching moment of the wing being able to be trimmed quite effectively on most builds. (On the first dancer wings with the single aileron servo, I found through test-flying that having ~1/16 "droop" of the trailing edge of each aileron resulted in very good handling across the entire speed range.)

I'm guessing that most foamie scratch-built wings are not shaped to close enough tolerances where the pitching moment is looked at too closely in advance- scratch-builders typically do their control surface linkage adjusting during test flights until they get the best handling they can from a given build, then start thinking about the next build. And, of course, a foam wing can be heat-formed to modify it's contours to a certain extent after the main wing build if desired.

For those making molded wing cores & precise hot-wire cut cores, selecting an airfoil profile for high speed flight tasks with a low pitching moment would be a detail to consider.... but again, with close to full-span trailing edge control surfaces, it may not be as much of an issue with anyone outside of the competition sailplane builders.

Implementations of KF stepped discontinuities in fairly simple structural elements, which result in higher lift and reduced drag, along with more precise control surface response is something that is very much of interest to foamie scratch-builders. There's still a lot to be understood as we test-fly various configurations- (the simulation software may simply not be able to adequately evaluate the affects of these stepped discontinuities on the actual in-flight performance...) and the experimentation along the way is a lot of the fun!

VIKING
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Last edited by viking60; Dec 26, 2010 at 09:58 AM.
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