DLR tests unmanned high-altitude solar aircraft HAP-alpha on the ground
The autonomous solar aircraft HAP-alpha can operate at high altitudes and replace satellites. It was pulled across a taxiway for the first time.
The HAP-alpha is being pulled by a tractor vehicle on a launch trolley across the airfield's taxiway.
(Image: DLR (CC BY-NC-ND 3.0))
The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR) has conducted ground tests in preparation for the maiden flight of the high-altitude solar aircraft HAP-alpha (High Altitude Platforms – HAP). In addition to completing taxi tests, essential flight systems and the stability of the unmanned aircraft were checked. As early as spring 2025, DLR had carried out static flutter tests on HAP-alpha to check the general aircraft structure for its strength. The aircraft has now been completely assembled for the first time at DLR's National Experimental Centre for Unmanned Aerial Systems in Cochstedt and had to undergo further ground tests.
Withstand real flight conditions
The elastic structure of the airframe was subjected to vibrations that can occur during takeoff and flight. This is to check whether the aircraft can withstand real flight conditions. The effects of the resulting vibrations are monitored by high-precision measuring systems. However, the wings and the tail unit were still uncovered during these tests to avoid damaging the aircraft's delicate structure.
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DLR also conducted a taxi test. The HAP-alpha was loaded onto a special trailer, the launch trolley, and secured using a patented mechanism. The launch trolley was pulled by a tractor across the taxiway of the in-house airfield, as a DLR video on Facebook shows.
First test flights in 2026
The combination will also be used in the upcoming flight tests. The aircraft, fixed on the launch trolley, can be released via the fastening mechanism as soon as the required angle of attack for takeoff is reached. HAP-alpha then takes off independently. Landing occurs with the engines off on skids.
DLR plans further measurements and integration work on the aircraft for the first quarter of 2026. After flight clearance, the maiden flight and further test flights will initially be carried out at low altitudes up to 150 m at the Cochstedt site. However, HAP-alpha has been developed for flight operations at altitudes up to 20 km. Test flights at this altitude are planned to take place later in remote areas – for example, over the sea.
Payloads up to about 5 kilograms
The solar aircraft HAP-alpha, powered by two electric motors, has a wingspan of 27 m and weighs around 138 kg. It is designed for slow flight at altitudes of 20 km to remain in the air energy-efficiently for a longer period. It can carry payloads of up to approximately 5 kg.
The autonomous aircraft is intended for aviation applications, such as Earth observation and communication tasks in crisis areas at any location, thus eliminating the need for non-geostationary satellites. The use of such an aircraft is intended to be more cost-effective than satellites, as the aircraft is reusable and can be equipped and used for different tasks. The costs for the aircraft itself are also lower.
A total of 16 DLR institutes and facilities are involved in the development of the high-altitude solar aircraft HAP-alpha. The development work is coordinated by DLR's Institute of Flight Systems.
(olb)
