Slung load stabilization across the flight envelope using an active cargo hook

A control methodology for stabilizing an external load using an active cargo hook is demonstrated in simulation. A test load exhibiting instabilities in the form of high amplitude limit cycle oscillations in forward flight is used. A previous study used full-state feedback linear-quadratic regulator to stabilize the load across the flight envelope. This paper will examine the use of output feedback and a reduced order model with relative cable feedback in a linear-quadratic regulator controller. The initial design is tested on a model of an isolated load in a wind tunnel and demonstrated in a single airspeed to provide positive load stability for the originally unstable load. The controller gains are then scheduled across the flight envelope. Simulations with a coupled system of a UH-60 Black Hawk helicopter using an active cargo hook with an external load demonstrate stability across the flight envelope in still air. The efficiency of the active cargo hook controller is finally checked in the presence of varying turbulence intensities.