  A previously published algorithm for trajectory tracking control of tethered
wings, i.e. kites, is updated in light of recent experimental evidence. The
algorithm is, furthermore, analyzed in the framework of delay differential
equations. It is shown how the presence of system delay influences the
stability of the control system, and a methodology is derived for gain
selection using the Lambert W function. The validity of the methodology is
demonstrated with simulation results. The analysis sheds light on previously
poorly understood stability problems.
