Evaluation of Two-Hinged Wings

Abstract

Two types of wing geometries imitating wings of birds in gliding fl ight are analyzed with the vortex lattice method in terms of lift-drag ratio and root bending moment while varying the joint positions and joint angles under the constant lift coe ffi cient and constant fl ight velocity conditions. One geometry is, what is sometimes called, a gull wing which has a dihedral inner wing and horizontal outer wing, named “ DH wing. ” On the contrary, the other geometry is a drooped wing which has a horizontal inner wing and anhedral outer wing, named “ HA wing. ” The lift-drag ratio of the HA wing becomes larger when the joint of the anhedral outer wing is closer to the wing tip with a larger anhedral angle, while the root bending moment of the HA wing becomes smaller when the joint of the anhedral outer wing is closer to the wing root with a larger anhedral angle. In contrast, the DH wing has no combination of a joint position and joint angle to improve the lift-drag ratio, and it is found that the HA wing e ff ectively contributes to the reduction of the root bending moment and the lift-drag ratio compared with the DH wing.