Experimental Investigation of Unsteady Inflow for a Helicopter Model in Shipboard Operations

State-space representation of the dynamic inflow is an essential element in rotorcraft flight mechanics modeling and simulation. Identification of a reliable low-order model which is able to predict the transient response of the inflow as well as the steady part, becomes even more important during the maneuvering flights. The objective of this paper is to exploit an experimental setup, consists of a helicopter model and a simplified ship geometry, to investigate the possible effect of the wake interactions with environmental elements such as ground effect or airwake of the ship, on the time constants associated with the buildup of the inflow states. A series of wind tunnel tests were performed, simulating various flight conditions, including hover and forward flight, inside and outside of the ground effect, and the rotor over the deck of the SFS1 at two different positions with respect to the ship super-structure, with the wind coming from two different directions. After trimming the rotor at each flight condition, a sequence of pitch excitation commands were applied to the collective, lateral and longitudinal cyclic in order to excite the induced flow of the rotor. The frequency analysis of the measured aerodynamic loads shows the variation of the time lag, while rotor is operating in the same trim condition, but different positions with respect to the ground or the flight deck.