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The German Aerospace Center – DLR (Cologne) announces that its high-altitude solar aircraft, HAP-alpha, has completed ground vibration testing (GVT), a key milestone in flight readiness, at its National Experimental Test Center in Cochstedt. Further tests will follow and the first low-altitude flight trial is planned for 2026, subject to ideal weather conditions.

HAP-alpha is highly elastic, solar-powered uncrewed aircraft platform designed to operate in Earth’s lower stratosphere for extended periods, performing a wide range of observation and communications tasks from monitoring shipping lanes and supporting disaster response to providing internet access. The structure, weighing only 138 kilograms and with a 27-meter wingspan, is made entirely of carbon fiber-reinforced polymer (CFRP) — specifically, the DLR uses wound round CFRP spars and ribs made from a CFRP sandwich material.

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“With HAP-alpha, DLR is demonstrating its comprehensive systems expertise in the complete design, development and operation of a new and innovative aircraft, incorporating all disciplines,” explains DLR executive board member for aeronautics, Markus Fischer. “This illustrates our engagement in an important field of innovation, to strengthen Germany as a location for technology and business and to open up new perspectives for our public stakeholders in collaboration and knowledge exchange.”

The now completed GVT is an important milestone for investigating the vibration behavior of an aircraft. The goal is to identify critical vibrations that can occur during flight, takeoff and landing. This determines whether an aircraft is safe and thus airworthy. For HAP-alpha, the successful GVT marks a key step on the way to first flight tests next year, which will involve basic flight maneuvers at low altitude.

During the GVT, numerous sensors were used to record the dynamic properties of the platform, which was fitted with electromechanical vibrators so that its vibration characteristics could be identified. A particular challenge of the GVT on HAP-alpha was its very lightweight and therefore very flexible design.

The acquired data will now be used to update simulation models and predict flight behavior even more precisely, especially during maneuvers, turbulence and gusts of wind. “This allows the project team to focus on the upcoming complete system tests, which will mark the completion of ground testing and enable subsequent flight testing,” says HAP project leader Florian Nikodem from the DLR Institute of Flight Systems.