Aerodynamics of cambered membrane flapping wings

The aerodynamics of cambered membrane flapping wings is the focus of this paper. A cambered airfoil was introduced into the wing by shaping metal ribs attached to the membrane skin of the 25-cm-wing-span model. Tests in still air of the flapping wings oriented horizontally and vertically with respect to the gravitational field show no effects on generated aerodynamic forces. The thrust force generated by a 9% camber wing is found to be 30% higher than that of the same size flat wing. The aerodynamic forces and pitching moment generated by flapping wings were measured in a wind tunnel with the flapping wing angle of attack varying from horizontal to vertical. Cambered wings show significantly higher lift and thrust in comparison with flat wings. Adding a dihedral angle to the wings and keeping the flapping amplitude constant improved the cambered wing's performance even further. The aerodynamic coefficients are defined using a reference velocity as a sum of two components: a free stream velocity and a stroke-averaged wing tip flapping velocity. The lift, drag, and pitching moment coefficients obtained using this procedure collapse well for studied advance ratios, especially at lower angles of attack.