Motahari, N., Turbeville, F., Hiremath, N., and Komerath, N., "Aerodynamic Load Maps of Vehicle Shapes at Arbitrary Attitude," SAE Technical Paper 2015-01-2574, 2015, doi:10.4271/2015-01-2574.
The interest in flying cars comes with the question of characterizing aerodynamic loads on shapes that go beyond traditional aircraft shapes. When carried as slung loads under aircraft, vehicles can encounter severe aerodynamic loads, which may also cause them to go into divergent oscillations that can threaten the vehicle and aircraft. Slung loads can encounter the wind at arbitrary attitudes. Flight test certification for every vehicle-aircraft combination is prohibitive. Characterizing the aerodynamic loads with sufficient resolution for use in dynamic simulation, has in the past been extremely arduous. Sharp changes that drive instabilities arise over small ranges of yaw and pitch. With the Continuous Rotation technique developed by our group, aerodynamic load characterization is viable and efficient. With two well-chosen attitude sweeps and appropriate transformations, the entire 6-DOF load map can be obtained, for several rates. The paper describes application of the method to scale models of various vehicles of interest, and the decomposition of the air load features into various fluid dynamic phenomena. Rate effects are also measured and investigated using both 6-DOF load measurements at varying rates of motion, and hot-wire anemometry data from the wake. Generalized aerodynamic load prediction by reference to canonical shapes, is explored. Unsteady effects are conclusively shown to be absent. Starting with generalized empirically-based load prediction for cylinders and rectangular shapes that we have already demonstrated, the uncertainty in load prediction for some vehicles of interest is examined. Models of a truck, a HumVee and a Sentinel vehicle reminiscent of a Tactical Response Vehicle, are used as examples.