Flapping-wing propulsion as a means of drag reduction for light sailplanes

Abstract

In this paper, flapping-wing propulsion as a means of drag reduction for light sailplanes is investigated numerically. The feasibility of markedly improving minimum sink and L/Dmax performance parameters in light sailplanes by flapping their flexible, high aspect ratio wings at their natural frequencies is considered. Two propulsive systems are explored: a humanpowered system that is used to partially offset airframe drag, and a sustainer system that uses an electric motor with sufficient power for limited climb rates. A numerical analysis is conducted using a strip-theory approach with UPOT (Unsteady Potential code) data. Thrust and power coefficients are computed for 2-D sections. 3-D spanwise load factors are applied to calculate total wing thrust production and power consumption. The results show that theoretical drag reduction in excess of 20%, and improvements of minimum sink by 24% are possible with a human-powered flapping system.