Experimental Characterization of Aerodynamic Behavior of Membrane Wings in Low-Reynolds-Number Flow

An experimental study of the aerodynamic characteristics of a flat-plate membrane wing was conducted. Three different values of membrane prestrain (5, 7, and 10%) were investigated, along with a rigid flat plate, at Reynolds numbers of 13,700, 22,600 and 36,300 and angles of attack up to 27 (leg. It was found that 1) the dependence of the prestall mean lift on model prestrain is negligible, 2) prestall mean lift at a given level of prestrain is a strong function of Reynolds number, and 3) the mean drag increased with a decrease in model prestrain. In addition, the stall angle of attack is weakly dependent on prestrain and increases with increasing Reynolds number. With the exception of the highest Reynolds number, the flexible-model stall angles were found to be similar to the rigid flat-plate results. At the largest Reynolds number, dynamic results for the flexible models revealed large rms values of lift and drag; which generally decrease with increasing angle of attack. In comparison to the flexible models, the rms values for the rigid flat plate were insignificant. An aeroelastic flutter instability is postulated to be the cause of the large dynamic response for the flexible models. This hypothesis is supported by results that were generated using a potential flow-based computational aeroelastic model. These aeroelastic instability-induced vibrations are also proposed as the mechanism by which the flexible models showed better stall characteristics at the highest-tested Reynolds number.