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Old 02-15-2019, 02:57 PM
Abuelo's Avatar
Join Date: Sep 2013
Location: Arizona desert
Posts: 331
Default Dihedral effect on swept wing

A buddy built a powered glider type plane with forward swept wings and had some stability and turning issues with it. We got most of these sorted but still have a question we don't know then answer to.

"Miss Tempe" has a 60" span ( two 30" panels), 8" root chord, 5" tip chord, flat bottom conventional airfoil, 4 per panel dihedral, and 5 forward sweep as measured at the leading edge. No tip plates or fences, high wing, rudder, elevator, and throttle only. As built the C/G was about 33% of the MAC but she flew better with the C/G moved forward to around 25%. Weight all up was 19 oz. See the rather poor photo.

I understand that rear sweep adds effective dihedral, found references to anywhere from1 per each 5 to 10 sweep. (References are inconsistent but may represent unknown factors in the overall design.) But what about forward sweep? Does that add effective dihedral or subtract dihedral? I'm thinking it subtracts which would account for the turning difficulty as the effective dihedral was down to 3.5 or 3.0, depending. I also think a fence along the root would have kept any span wise air flow on the wing.

The builder is leaning toward replacing the wing with a 0 dihedral KF2 and ailerons. I'm thinking he could cut the original wing and add a couple more degrees dihedral and would be OK. Another option is a second KF2 with dihedral and no ailerons.

Thoughts and comments? All appreciated.
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