Analytical Model Development for Rotors Hovering Above Heaving Surfaces

A potential flow model was developed for rotors hovering in-ground-effect above a heaving surface using a similar methodology to classical, analytical, static ground effect models. Experimental performance measurements for rotors hovering above a surface undergoing single degree-of-freedom heaving motion were used for model validation, and potential mission trends were generated for a representative naval helicopter. Unlike prior empirical models, the current model was able to capture the effect of rotor hub height as well as ground motion parameters. A new thrust ratio was proposed that compared the thrust produced in-ground-effect above a heaving surface to that produced above a static surface. Better agreement was found to occur at the higher collective pitch settings and hub heights, with the model predicting the classical thrust ratio within 5% of the measured value for approximately 75% of the test points. The thrust ratio relative to a static surface was found to produce better agreement, and approximately 80% of the experimental tests points were predicted within 5% of the measured value.