Unsteady load assessment of a scaled-helicopter model in a ship airwake

The paper presents the results of wind tunnel tests to measure unsteady aerodynamic loads on a scaled-helicopter operating in the airwake of a generic frigate model. Rotor loads were measured by a six-axis dynamic balance in a stern landing maneuver simulated by trimming the rotor along a sloped descent trajectory towards the landing spot. The measures allowed to identify not only the average loads but also the frequency spectrum in the range of interest for flight mechanics. The results indicate that for the three tested wind directions, including headwind, 30∘ and 60∘ from the port-side, moving towards the landing spot the unsteadiness is increased. The rate of amplification of the loads for the trajectories not aligned with the wind is significantly higher compared with those measured in the headwind test. Furthermore, a fully dynamic landing maneuver was compared with the sequence of trimmed measures to evaluate the effect of the approach velocity of the helicopter on unsteady loads. A notable reduction in the unsteadiness of the pitch moment was found, while the unsteady thrust and roll moment were more comparable between static and dynamic tests.