The Effect of Ship Size on the Flying Qualities of Maritime Helicopters

This paper describes the use of Computational Fluid Dynamics (CFD) to produce unsteady ship airwakes to investigate the effect of ship size on the pilot workload at the helicopter-ship dynamic interface. A ship model was created to represent modern naval vessels and geometrically scaled to represent smaller and larger scale ships that currently operate maritime helicopters. An unsteady airwake for each ship was computed at 40 knots for both the Headwind and Green 45° Wind Over Deck (WOD) conditions, while the mid-scale ship was also computed at 30 knots. Using Strouhal scaling, the mid-scale ship airwake was scaled both in terms of velocity and ship size. Comparisons of the resulting small and large scaled data were made with the computed CFD data and the use of Strouhal scaling was found to a feasible method for the modification of airwake data. An offline analysis using a SH60B Seahawk-like helicopter was used to determine the impact of the ship size on the pilot workload. As the ship size increased, so did the levels of predicted pilot workload due to the increasing energy contained within the turbulent wake as the ship size was increased.