Overview of reel-out runs per wind speed

The test scenario:

• the kite is parked at zenith (keep it still above your head while in equilibrium)
• then it is steered to the left and takes a dive
• then it is steered towards the planned figure-of-eight that promises the highest power
• it flies figures of eight and reels out

The initial tether length is 150 m, the final length 380 m. The inflow represents the yearly-averaged onshore wind conditions in the Netherlands, based on one full year (2011) of 10-minute wind data from the 213 m tall KNMI meteorological mast at Cabauw, an inland site far from the coast. The vertical wind profile is a power law with the exponent p = 0.234, fitted to the yearly-averaged wind speeds measured at the mast; this gives a much stronger wind shear than at the near-shore Maasvlakte site, reflecting the higher surface roughness of the inland terrain. The wind speed is the ground wind speed, measured at a height of 6 m. The inflow is steady and uniform, without turbulence. A ground-station with 20 kW nominal power and 30 kW peak power is assumed. The nominal reel-out speed is 3.5 m/s, the maximum force 8400 N.

Click on one of the labels to show an additional column group, ctrl+click to deselect, shift+click for multi-select.

The average mechanical power during reel-out, the force, and the speed are shown in the following plot. At about 5.75 m/s the reel-out speed reaches its limit of 3.5 m/s and the average power levels off at about 20 kW. From this wind speed onwards the depower setting is increased with the wind speed.

The optimal trajectory of the kite, the shape of the figure of eight, depends on the tether length and on the wind speed. Below, select the ground wind speed [m/s] to see the shape of the desired and actual trajectory the kite flies. For each figure-of-eight, the AWETrim quasi-static optimizer calculated the optimal trajectory.

The same run in 3D: the flown path in the world frame, coloured by the mechanical winch power, with the ground track underneath and the straight line to the ground station. Drag to rotate, scroll to zoom.

The time series below show, for the same wind speed selected above, the cross-track error, elevation, course/heading tracking, steering, tether force and length, reel-out speed, depower, and the entry state machine over the whole run. The first subplot, `d ', shows the distance between the actual and planned trajectory in degrees.

The plots below show, for the same wind speed selected above, the tether force, reel-out speed and mechanical power over the whole run, and the cumulative mechanical energy.

The plots below show, for the same wind speed selected above, the angle of attack (at the wing centre and the span mean), the wing and effective lift-to-drag ratio, and the apparent wind and kite speed over the whole run.

Acknowledgements

This work has been supported by the MERIDIONAL project, which receives funding from the European Union’s Horizon Europe Program under the grant agreement no. 101084216. The opinions expressed in this document reflect only the author’s view and reflects in no way the European Commission’s opinions. The European Commission is not responsible for any use that may be made of the information it contains.

These results were achieved using the following research software:

• RobustKiteControllers.jl, path-following kite control software by Uwe Fechner, Delft, 2026
• AWETrim was used to provide optimal flight paths, depending on the inflow conditions, written by Oriol Canyon, Delft, 2026
• V3Kite.jl was used as detailed, validated kite model of the V3 kite of TU Delft. It was developed by Jelle Poland, Rotterdam, The Netherlands and Bart van de Lint, Delft, The Netherlands, 2026
• AtmosphericModels.jl provided the wind profile of the Cabauw site