Advances in Modeling and Control of Tethered Unmanned Helicopters to Enhance Hovering Performance

The hovering capabilities of unmanned helicopters can be seriously affected by wind. One possible solution for improving hovering performance under such circumstances is the use of a tethered setup that takes advantage of the tension exerted on the cable that links the helicopter to the ground. This paper presents a more elaborate strategy for helicopter control in this augmented setup, that extends previous work on the subject by the authors. Particularly, a combination of classical PID control laws, together with model inversion blocks, constitutes the basis of the new controller. Additionally, feed-forward action for counteracting rotational couplings is also taken into account. The resulting nonlinear control structure considers also a viscoelastic model of the tether which accurately reproduce the behavior of real ropes. Several simulations under artificially generated wind influences are presented to endorse the validity of the new proposed controller.