Helicopter Aerodynamic Loading in the Airwake of a Moving Ship

This paper presents an analysis of the unsteady aerodynamic loading of a helicopter immersed in the airwake of a generic destroyer undergoing several ship motion types: static, sinusoidal pitching, regular 2-DOF, and realistic irregular 3-DOF ship motions. The study was a collaborative effort between the National Research Council Canada and the University of Liverpool, where each organization have applied their respective modeling approach (whether by simulation or experiment). It was shown that whilst there were only marginal differences in the mean helicopter loads for each motion type, the effects of ship motion are more apparent in the RMS loads, and the instantaneous load and air-velocity spectra. Dominant peaks in the thrust load spectra, as well as subsequent second and third harmonics, are shown at the ship motion frequency for sinusoidal pitching and regular 2-DOF ship motions, which have been attributed to the interaction between the turning rotor and the moving ship. This analysis provides a foundation for understanding the relationships between ship airwake and helicopter loading, and for extending that understanding to impacts on flight operations.