During a discussion on another forum, the subject of Lazy Bees and Lady Bugs came up. Another poster referred to the polyhedral wing geometry of the Lady Bug, to which I pointed out that on the Lady Bug, the top of the wing is dead flat from tip to tip, the airfoil is constant chord and thickness to the last rib, and tapers in thickness only at the tips. Another participant assured me that this configuration is indeed polyhedral--I guess I can see the logic, but none of the aerodynamics texts I've leafed through over the years for ideas seem to define this. I was under the impression that this is called "effective dihedral"--or does that only apply to sweepback and wing position relative to vertical CG? I'm just curious if anyone can enlighten me as to the proper term for the wing geometry involved in the Lady Bug wing, because whatever it is, it's very stable statically but incredibly maneuverable for a rudder/elevator ship. Thanks.

di = two
poly = many
hedra = side

dihedral = two sides

polyedral = many sides

Since the wing you're discussing has three panels: flat center, two tips canted upward, it has three "sides". Therefore, it's polyhedral.
Maybe you could call it "trihedral" to be exactly precise... And then we could call the common glider wing with four angled panels either "quadrihedral". I'd stay a way from "tetrahedral" because it might be confused with a tetrahedron, a polyhedron with four faces.

You could very likely get an airplane with equivalent performance with only two wing panels joined at the center and then having dihedral. The angle would be different than the "trihedral" look of your Lady Bug, but would likely fly the same.

The flat center, canted tips design originally came about in small aircraft because it made construction of the wing easier. The fuselage could be mounted on a flat spar that had no joint in the center. The spar joints outboard didn't have to be as strong because the loads were less than they would be if there was a center joint. Several homebuilt aircraft have used this type of construction: several of Claude A. Piel's designs, the Thorpe T-18, the Jodel Bebe, and so on.

BuzzBomber- Dihedral simply means having two distinct wing surfaces, but is more often used to describe the angle between those two distinct surfaces. Polyhedral on the other hand suggests that more than two distinct surfaces exist; those surfaces do not necessarily have to be in different geometric planes in order qualify, rather the geometry just has to be different. The effects of dihedral or polyhedral are a function of several factors including sweep of the leading edge(s), angle between surfaces (common definition of dihedral), and to a much lesser extent wing twist, among other items.

Interesting, Bax. Thanks for the input--I guess I was just considering the top of the wing and ignoring the bottom. Rgunder, your mention of the fact that the surface don't have to exist in different geometric planes hit it home for me. When I think of polyhedral, the T-18 and Jodel Bax mentions come to mind, or in models, the "standard" Lazy Bee wing, or the Gentle Lady. For anyone else reading this not familiar with the wing I'm referring to, I've attached a picture. Anyhow, I think I've got my head wrapped around this now--it was just too obvious.