Glider AK-1, maker: Akademische Fliegergruppe Karlsruhe, Karlsruhe, maiden flight 1971, wingspan 15.0 m, empty weight 300 kg, propulsion: four-cylinder two-stroke engine Hirth F 10 A1a with 19 kW (26 hp). Deutsches Museum, Flugwerft Schleißheim.
In 1971, the AK-1 glider, developed by the Akademische Fliegergruppe (Akaflieg) at Karlsruhe University completed its maiden flight. This innovative design featured a retractable auxiliary engine for self-launching, which influenced the development of motorized gliders with retractable engines. The auxiliary engine also helped bridge thermal lulls and reduce the risk of irregular landings. This first flight marked the culmination of over 15 years of design and construction work by students at Karlsruhe Polytechnic (redesignated a university in 1967). The necessary expertise converged on Akaflieg because students could apply their theoretical knowledge there practically. Scientific support from the academic institutes, along with access to workshops and laboratories for component testing, was similarly crucial to the project’s success. The AK-1 remained in flight service until 2008 and is now exhibited as a technical monument at Deutsches Museum in Munich. Akaflieg Karlsruhe, like other academic flying clubs in Germany, was established in the 1920s. Like other academic sports, one initial motivation for its creation was the ban imposed by the Treaty of Versailles on military pilot training, which led to flying activities at universities in an attempt to replace it. During the Nazi era, Akaflieg was dissolved, and aviation activities were absorbed by a Nazi mass organization. In 1951, Akaflieg was reestablished as an association independent of any externally set aims. The AK-1 marked the beginning of a series of projects for Akaflieg in Karlsruhe. Currently, their most ambitious undertaking is the development of a tailless glider, anticipated to give a further innovative boost to glider design. kn
As early as 1955, Akaflieg Karlsruhe began to develop motorized gliders with good gliding performance. They recognized the significant advantages of self-launch capability, which not only extended the glider’s range but also reduced the need for ground personnel, minimized the risk of landings off the airstrip, and simplified transport logistics. The main problem posed by motorized glider construction is integrating an engine into a glider without significantly compromising the glider’s performance and flight characteristics. In addition to an increase in overall weight, the primary reason for performance degradation due to the engine is aerodynamic. A permanently installed drive unit creates significant air resistance when not in use. A more effective solution was the retractable driving gear, which complicated the design enormously. In 1965, all was finally ready: the preliminary research commissions to investigate tow ropes, winch launches, and the building of a customized launch winch were completed. The Hirth F10 was finally available as a functional drive unit, allowing the design of a motor glider to begin, with the following objectives: (1) Self-launching capability without auxiliary personnel, (2) State-of-the-art gliding performance, (3) Minimal maintenance and overhaul requirements, (4) Weather-resistant construction and materials. The AK-1 took to the skies for the first time on January 9, 1971. On July 7, 1973, it was named Mischl (mutt) by the professor of meteorology, Max Diem, reflecting its hybrid character as both a powered aircraft and a glider. After completing flight tests, it received certification from the Federal Aviation Office and was used by all Akaflieg pilots holding a motor glider license. Its performance met the design targets established in the 1960s. Nowadays it is no longer suitable as a competition aircraft. The proliferation of motor gliders with retractable engines since the 1980s testifies to the merits of the AK-1 design developed in the early 1960s. Mikail Albayrak
The AK-1 glider was the starter’s gun for a whole line of successful research projects. The innovative idea of a retractable engine was an important impetus for the very successful modern hinged-power-unit technology in glider design. Thus, Karlsruhe Akaflieg could write aeronautical history, particularly with the AK-1 as well as with other projects from that time as well. Due to its historical importance, the AK-1 model is on display at Deutsches Museum in Munich since 2011. Mikail Albayrak, first chairman of Akademische Fliegergruppe at Karlsruhe Institute of Technology e.V.