A comparative analysis of helicopter recovery maneuvers on a SFS by means of PIV and balance measurements

The flow field around a frigate is complex due to flow detachments, high velocity gradients, and flow unsteadiness. These flow patterns can endanger helicopter operations around frigates and increase pilot workload above the flight deck. This paper contains a comparative analysis of three different recovery maneuvers: an approach from the stern in the centerline plane (S); a diagonal maneuver (D); and an L-shaped maneuver. The comparison is made using wind tunnel tests with a scaled frigate and a motorized helicopter. For the three maneuvers, velocity contours around the helicopter with Particle Image Velocimetry are obtained. An internal balance is also used to obtain forces and moments on the helicopter during the flight path of the maneuvers. Those measurements show that the wake of the ship mostly affects longitudinal and thrust forces. In addition, pitch torque is highly reduced when the helicopter is behind the frigate superstructure, and the roll moment is also important when the wind angle increases. In the end, an estimation of pilot workload is presented to conclude that L-shaped maneuver is the best for 0 degrees and small WOD angles and D or S recoveries for moderately high negative WOD angles.

Automated summary

This paper compares the effects of three different recovery maneuvers on the flow field around a frigate, using wind tunnel tests and mechanical measurements. The study finds that the stern, diagonal, and L-shaped maneuvers have significant impacts on the helicopter, increasing the pilot's workload on the flight deck. The wake of the ship primarily affects longitudinal and thrust forces, while pitch torque and roll moment become important when the wind angle increases. The evaluation of pilot workload concludes that the L-shaped maneuver is the best for 0 degrees and small WOD angles, and D or S recoveries are preferable for moderately high negative WOD angles.