|May 05, 2013, 05:22 PM|
Sheeted wings and launch flutter?
Anyone have any experience with full span flapperons on a poplar sheeted wing?
I plan on cutting the flapperons all the way out to the tip on a AH wing and was wondering if I looking at flutter issues.
All the Wood sheeted DLG's out there either have the flapperons stop short of the tip or use trillerons, and I'm wondering why?
|May 05, 2013, 05:47 PM|
Joined Apr 2009
I wasn't aware of a wood sheeted DLG being available these last few years. It is pretty much all composites now.
Many DLGs have or have had flaperons stop short of the tips. A good part of the reason is the developer doesn't know how to make flaperons durable at the tips, IMHO. Not having them extend to the end of the wing leaves them better protected. It does also reduce flutter chances because there is simply a little less length so it behaves a bit stiffer.
However stopping flaperons short of the tips does cost efficiency. It is like having a prop with angled plates on the ends, when it comes to making turns. More aileron throw and more drag. Trilerons aren't nearly as bad in this regard. Note one also loses control of camber at the tips.
Personally I consider stopping flaperons short of the tips to be a butchering of some aspects of the aerodynamics to compensate for a trivially solvable mechanical issue.
Some planes which do have flaperons go all the way to the tips don't have the hingeline kept at anywhere near a near constant percentage of the chord in this last few inches. That is also decidedly sub-optimal.
It is not that a constant percentage is optimal; it is optimal for camber but sub-optimal for roll control. For roll control the percentage should increase roughly linearly as one goes from the root to the tip. Near zero percentage at root, near 100% at tip! Obviously a bit impractical! Clearly roll and camber have different optimums and it is up to the designer to come up with the desired compromise. Note that stopping short of the tips though isn't optimal for either and is the worst direction for roll efficiency.
I wouldn't be shocked if sometime in the future someone starts making a wing with D-47's driving outer flaperons, and one servo in the fuselage driving inner flaps. That would be more efficient. Or 4 servo wings - more efficient still. These combos would be particularly useful for those who for some reason want rudderless. Either would slightly reduce the yaw while rolling the plane, and either would greatly improve the roll control when the flaps are down because one could drop the inner flaps a lot and leave the ailerons in an efficient position for rolling the plane.
Sorry, too much OT.
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