A novel tracking paradigm for flying geometric trajectories using tethered kites is presented. It is shown how the differential-geometric notion of turning angle can be used as a one-dimensional representation of the kite trajectory, and how this leads to a single-input single-output (SISO) tracking problem. Based on this principle a Lyapunov-based nonlinear adaptive controller is developed that only needs control derivatives of the kite aerodynamic model. The resulting controller is validated using simulations with a point-mass kite model.

Non-powered flight vehicles such as kites can provide a means of transmitting wind energy from higher altitudes to the ground via tethers. Although there have been many proposals for systems to extract wind energy from higher altitudes, this paper focuses on the use of a light lifting body at the end of a tether to generate useful power. Two major configurations are studied: 1) the kite is used to tow a ground vehicle in the cross-wind direction, 2) the kite is flown to generate power using a ground generator. In both cases, the useful work done by the kite is transmitted to the ground through the tether. Both applications require automatic control of the kite. A simplified system model is used to study the nature of the optimal trajectories of the system for different wind speeds. Numerical results illustrate that optimal power generation requires complex three-dimensional kite trajectories, whereas cross-wind towing requires much simpler trajectories. A feedback tracking controller is demonstrated for tracking the kite trajectories in the presence of unsteady winds.

The combination of lightweight flexible membrane design and favorable control characteristics renders tethered inflatable airplanes an attractive option for high-altitude wind power systems. This paper presents an analysis of the flight dynamics and stability of such a Kiteplane operated on a single-line tether with a two-line bridle. The equations of motion of the rigid body model are derived by Lagrange's equation, which implicitly accounts for the kinematic constraints due to the bridle. The tether and bridle are approximated by straight line elements. The aerodynamic force distribution is represented by 4 discrete force vectors according to the major structural elements of the Kiteplane. A case study comprising analytical analysis and numerical simulation reveals, that for the specific kite design investigated, the amount and distribution of lateral aerodynamic surface area is decisive for flight dynamic stability. Depending on the combination of wing dihedral angle and vertical tail plane size, the pendulum motion shows either diverging oscillation, stable oscillation, converging oscillation, aperiodic convergence, or aperiodic divergence. It is concluded that dynamical stability requires a small vertical tail plane and a large dihedral angle to allow for sufficient sideslip and a strong sideslip response.

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