The Effect of Lift Position on Helicopter Recovery to a Twin-Island Aircraft Carrier

This paper describes an investigation of the air flow over the flight deck of a twin-island aircraft carrier with the ship's lifts in a raised and lowered position, and the subsequent change in the aerodynamic loads on a helicopter in hover over the deck. The unsteady flow over the flight deck was simulated using Computational Fluid Dynamics for a 40 kt wind from 60◦ off the starboard. The turbulence intensity and velocity flow field produced over the flight deck for each lift configuration was analyzed and compared. An experimental study was conducted in which the mean and unsteady f low over a 1:200 scale model the aircraft carrier submerged in a large recirculating water channel was measured with the lifts in the raised and lowered position. The CFD prediction of the flow over the full-scale aircraft carrier was compared to the experimental velocity data. To analyze the effect of the two airwakes on a helicopter in hover, a technique known as the Virtual AirDyn was used to quantify the unsteady forces and moments acting on the aircraft. Thirty seconds of time-varying velocity data simulated for each lift configuration was integrated with a flight dynamics model of a helicopter representative of a Seahawk SH-60B. The helicopter was fixed in hover positions over the flight deck and subjected to each unsteady airwake. The resultant unsteady aerodynamic loads acting on the aircraft were analyzed to assess the effect of the lift positions on the helicopter in hover. The results show that for the conditions considered, while the lifts' positions do affect the air flow and the aerodynamic loading, there will only be a limited impact on a recovering helicopter.