Rotorcraft Control Strategy In A Three-Dimensional Wind Shear Environment

Navy pilots have the unique task of landing rotorcraft in an extremely hostile environment. Not only is the landing platform moving with the motions of the ship, but the airwake and turbulence change magnitude and direction as the rotorcraft gets closer to the ship. The pilot control strategy required to hover and land the rotorcraft in this complex three-dimensional flow field can become a very demanding and a limiting factor in the rotorcraft-ship dynamic interface flight envelop. This paper presents a method to synthesize pilot control strategies required in the lateral, longitudinal and vertical axes as functions of the magnitudes of the wind shears, turbulence and ship motions. The linear analysis techniques include the case of reduced-order decoupled rotorcraft dynamics operating in a simple one degree of freedom wind shear to the more general case of coupled rotorcraft dynamics operating in a generalized three-dimensional wind shear environment. The equations of motion are presented in terms of a “dynamic interface matrix,” which is the product of the aerodynamics matrix of the rotorcraft at a specific flight condition and the wind gradient matrix at a specific point on the ship. The dynamic interface matrix couples the rotorcraft and ship and can adversely affect the stability and control characteristics of the shipboard landing task. A small perturbation model of the UH-60B rotorcraft, and a computational fluid dynamics model of the flow field around an LHA-class ship are used to demonstrate the analysis techniques. This method may prove useful for identifying wind over deck flight envelops for specific combinations of rotorcraft, ship and operating conditions.