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Soft landing on moving vehicle promises weight reduction for UAV

21 January 2016

German researchers have achieved the successful landing of an unmanned, electric, autonomous aircraft travelling at 75km/h on the roof of a moving car.

The speed of the UAV and car are synchronised (clip from YouTube video courtesy of DLR)

For the first time, researchers at the German Aerospace Center (DLR) have successfully demonstrated a technique that enables an ultra-light, long-range, high-altitude unmanned aerial vehicle (UAV) to land on a moving vehicle, thereby avoiding the need for heavy landing gear.

Ultralight solar-powered aircraft can fly at altitudes in excess of 20km and stay airborne for several weeks; weight is crucial for long-duration flights. By omitting the landing gear, the weight of a UAV can be significantly reduced; this allows increased payload, greater range and enhanced performance. Reinforcements to the aircraft structure that would usually be necessary can also be eliminated, contributing to a further reduction in weight.

Combining technologies from the fields of robotics and UAVs, the DLR researchers' system has now been successfully tested using a three-metre, 20 kilogram, electrically powered fixed-wing UAV during flight trials at Mindelheim-Mattsies airfield in Bavaria.

To accomplish this, the researchers fitted a special platform equipped with a number of optical markers to the roof of a car. The aircraft is able to navigate to a position – accurate to within 50 centimetres – above the four-metre-long by five-metre-wide mobile platform. An optical multi-marker tracking system recognises the landing platform and performs a highly accurate calculation of its position relative to the ground vehicle. The landing is then carried out under computer control.

The major advantage of this system is that the movement of the UAV and the ground vehicle are synchronised in real time using special algorithms. With both vehicles moving at the same velocity, the landing resembles a vertical helicopter landing when seen from the ground vehicle. The horizontal velocity components are thus close to zero, making the landing phase simpler and safer.

In the experiments performed to date, flight operations safety rules required a driver to be present in the car. The driver received calculated control commands via a graphical display, which instructed faster or slower driving. In the future, in practical applications, a robotic vehicle without a driver could be used.

Eliminating the landing gear significantly increases the payload capability of a solar-powered aircraft. This in turn creates more space for scientific instruments. The system also simplifies landings in adverse weather conditions including crosswinds or wind gusts.

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