Towards fully simulated ship-helicopter operating limits: the importance of ship airwake fidelity

This paper describes the use of Computational Fluid Dynamics (CFD) data to improve the fidelity of helicopter-ship dynamic interface simulation. Two different ship geometries have been investigated and compared in terms of flow topology and pilot workload to determine acceptable fidelity criteria. Time-accurate airwakes for the simple frigate shape (SFS2) and a Type 23 Frigate have been computed for a number of wind-over-deck (WOD) angles to provide a realistic flow field in which to perform simulated deck landings within the FLIGHTLAB flight simulation environment CFD predictions show good agreement with both wind tunnel data and full scale at-sea experimental data. Results from piloted flight trials using the University of Liverpool full-motion simulator are presented in detail. Pilot workload ratings resulting from the trials have been used to generate two Ship-Helicopter Operating Limits (SHOL) diagrams for a Lynx-like helicopter: one operating from the SFS2 and the other from a Type 23 Frigate. By comparing the two SHOLs, assessing pilot workload ratings and analysing flow topology, it can be seen that at certain WOD angles relatively small-scale geometric features give rise to significantly different flow features. Although it is shown that these ship-specific features may not result in different ratings on the five-point deck interface pilot effort scale (DIPES), differences can be detected on finer workload scales. It is suggested that in order to improve fidelity of CFD generated airwakes, geometric features should be included such that any resulting medium to large scale flow features may be captured. Copyright © 2008 by the American Helicopter Society International, Inc. All rights reserved.