Abstract
Effects of camber and camber-change due to elastic deflection for aspect ratio 4.25 wings were examined for the classical unsteady problem of rectilinear translational acceleration. Direct force measurements and flow visualization by laser illumination of fluorescent dye allowed for the tracking of force history vs. evolution of the flowfield of rigid flat, rigid cambered, and flexible membranous wings. At low incidence (10 degrees and below), Wagner's approximation provides an accurate prediction of the time-evolution of lift for the rigid wings, beyond which flow separation leads to peaks in the force history and the camber-effect is no longer additive to the incidence effect. Both the rigid uncambered and cambered wings reach peak lift at 35 degrees, whereas the flexible wing experiences a form of stall-delay and reaches peak lift at 50 degrees. Due to the aeroelasticity of the flexible membrane, flow over the suction surface remains attached for much higher incidence angles than for the rigid wings. For incidence angles less than 30 degrees, the flexible wing's peak lift is lower than that of its rigid counterparts. However, beyond 30 degrees, the flexible wing experiences an aeroelastically-induced stall delay that allows lift to exceed the rigid analogs.