The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), in tandem with project leader Airbus Defence and Space, has successfully flight tested a new aircraft as part of the development of future production-ready drones (UAVs, unmanned aerial vehicles). The unmanned, jet-powered technology demonstrator with the project name SAGITTA flew fully autonomously for some seven minutes on a pre-programmed course at the test site in Overberg, South Africa. The innovative flying-wing construction demonstrated excellent flight characteristics during the test. This flight marked the successful completion of the first test phase, which also comprised an extensive series of ground tests.
"The first flight of SAGITTA is another milestone for the cooperation between research and industry," says Rolf Henke, member of the DLR Executive Board responsible for aeronautics research. "Within the framework created by Airbus, we were able to deploy our innovation potential and develop and integrate the demonstrator's complex technologies. Aircraft design is always about integration, so we are delighted when a joint project such as this succeeds on multiple levels."
The demonstrator is the product of the 'Open Innovation' / SAGITTA national initiative launched by Airbus in 2010. The project sees Airbus working together with DLR and institutes from the technical universities of Munich and Chemnitz, the University of the Federal Armed Forces (Universität der Bundeswehr) in Munich, the Ingolstadt University of Applied Sciences to jointly develop advanced technologies for unmanned flight. A feasibility study using a flying wing configuration was carried out before the project was fully realised in the shape of a demonstrator after intensive institutional and university research. Three DLR institutes are involved in the SAGITTA project.
Ultra-light structure with adhesive joints
Researchers from the DLR Institute of Composite Structures and Adaptive Systems faced a major challenge in undertaking the construction of the aircraft's ultra-light structure. Delicate structural components made of paper-thin carbon fibre reinforced polymer (CFRP) layers had to be bonded together for optimal load distribution. "Our researchers had to design and build the individual components in such a way that they fitted together precisely during assembly, because the adhesive layer needed to be thin and uniform for the bond to be strong," explained Martin Wiedemann, Director of the Institute, describing the challenge. "To have had the opportunity to assemble the entire aircraft structure along with most of its critical systems was exciting for us." In future, the SAGITTA test vehicle will also be used to test novel structural components into which active functional elements, such as adjustable flaps, are integrated.
New landing gear system
The DLR Institute of Flight Systems contributed the majority of the critical flight systems, including the retractable landing gear, electrical power supply and cabling, control surface actuators and the fuel system. "These systems were essentially new developments, so they were subjected to extensive qualification tests," says Stefan Levedag, Head of the Institute. "Particular development challenges were the restricted installation space and the high vertical speed during landing." To address this, a landing gear test rig was specially developed and tailored to the requirements of the SAGITTA demonstrator, to optimise and prove the viability of the landing gear system. In addition, flight-qualified electronic components for controlling the systems and a semiconductor-based power distribution unit were developed as central components of the electrical supply system.
Virtual test flights
The DLR Institute of System Dynamics and Control at the site in Oberpfaffenhofen was responsible for the planning, construction and operation of simulation and integration test facilities for the SAGITTA demonstrator during the project. "The simulators developed by us in tandem with the project partners enabled the successful completion of virtual flight and landing tests and provided valuable information regarding the expected flight behaviour," emphasises Johann Bals, Director of the Institute. "These versatile virtual flight capabilities, with the capacity to integrate real hardware and software components, proved to be essential for the evaluation, test capabilities and flight approval throughout the course of the project – from the preliminary design through to system integration and operator training."
The research vehicle was constructed to a scale of 1:4 and measures 3 metres by 3 metres. It is designed as a flying wing and is powered by two 300 N turbines. Its maximum take-off weight is 150 kg. The UAV’s stealth properties are primarily a result of its shape. The airframe is produced completely from carbon fibre composite (CFC) using a number of new manufacturing processes. With the exception of the brakes, it is an 'electronic flying device' that is controlled by electromechanical actuators instead of hydraulic components. The experimental vehicle is not a production-ready product. It is designed to acquire valuable information on new technologies for uncrewed flight systems.