An experimental technique for evaluating the aerodynamic impact of ship superstructures on helicopter operations

Ship–helicopter operating limits for military frigates and destroyers are often restricted in difficult weather conditions because of excessive pilot workload caused by the ship airwake. Despite the importance of the helicopter as a naval tactical system, there is a scarcity of guidance for naval architects with respect to the aerodynamic impact of ship superstructure designs on helicopter operations. This paper describes an experimental investigation into the potential benefits of some aerodynamic modifications to a model-scale generic ship. A model-scale helicopter with a motored main rotor, mounted on a six-axis force balance, has been used to measure the unsteady forces and moments imposed by the airwake. The helicopter has been held, immersed in the unsteady airwakes of a baseline and modified ship geometries, at important locations through the landing approach path for two oblique starboard wind-over-deck angles. Root-mean-square forces and moments have been derived from the time-histories recorded by the force balance. All the ship modifications were found to significantly reduce root-mean-square forces and moments, compared with the baseline ship geometry. Particularly promising design concepts are a side-flap and a notch modification which both showed consistent improvements of 25–50% in root-mean-square loads, in both wind conditions and through various flight paths.

► Aerodynamic modifications to a generic frigate superstructure were made.
► The impact of the modifications on a model-scale helicopter was investigated.
► Ship modifications significantly reduced unsteady loading of the helicopter.
► Positive development of helicopter friendly ship design features.