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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.

At high angles of attack, the flow over a swept wing generates counter-rotating vortical features. These features can amplify into a nearly sinusoidal fluctuation of velocity components. The result is excitation of twin-fin buffeting, driven at clearly predictable frequencies, or at nearby lock-in frequencies of the fin structure. This is distinct from the traditional model of fin buffeting as a structural resonant response to broadband, large-amplitude excitation from vortex core bursting. Hot-film anemometry was conducted ahead of the vertical fins of a 1:48 scale model of the F-35B aircraft, in the angle of attack range between 18 and 30 degrees. Auto spectral density functions from these data showed a sharp spectral peak in the flow ahead of the fins for angles of attack between 20 and 28 degrees. Small fences placed on the top surface of the wing eliminated the spectral peak, leaving only a broadband turbulent spectrum.