Aeroelastic behavior of inflatable wings: Wind tunnel and flight testing

Wind tunnel investigations have been conducted in order to determine the aerodynamic and structural deflection characteristics of a new inflatable wing design for unmanned aerial vehicles (UAVs). The wings were tested over a range of dynamic pressures from 0 to 400 N/m² and angles of attack from 0° to 16° corresponding to below the minimum stall speed up to speeds resulting in wing buckling. Since the inflatable wing stiffness varies as a function of the internal inflation pressure, the inflation pressure was varied below the design pressure in order to examine the effect of reduced stiffness on wingtip twist and bending. In order to accurately record deflections across the entire wing, photogrammetry was used as the measurement technique. The inflatable wings display a wash-in deformation behavior, increasing the span-wise angle of attack as the wing bends. In order to actively alter the shape of the wing, two wing warping mechanisms (mechanical servos and nitinol actuators) were examined. Wing mounted servos were found to be an effective method of wing warping for control comparable to conventional ailerons as demonstrated by flight tests.