  The problem of autonomous launch and landing of a tethered rigid aircraft for
airborne wind energy generation is addressed. The system operates with
ground-based power conversion and pumping cycles, where the tether is
repeatedly reeled in and out of a winch installed on the ground and linked to
an electric motor/generator. In order to accelerate the aircraft to take-off
speed, the ground station is augmented with a linear motion system composed by
a slide translating on rails and controlled by a second motor. An onboard
propeller is used to sustain the forward velocity during the ascend of the
aircraft. During landing, a slight tension on the line is kept, while the
onboard control surfaces are used to align the aircraft with the rails and to
land again on them. A model-based, decentralized control approach is proposed,
capable to carry out a full cycle of launch, low-tension flight, and landing
again on the rails. The derived controller is tested via numerical simulations
with a realistic dynamical model of the system, in presence of different wind
speeds and turbulence, and its performance in terms of landing accuracy is
assessed. This study is part of a project aimed to experimentally verify the
launch and landing approach on a small-scale prototype.
