Aachen FVA-21 "Wölbklappenautomatik"
On the initiative of Prof. Dr. Ing. A.W. Quick, the FVA received a research assignment on an "automatic flaps for gliders," which was financially supported by the German Research Foundation DFG in 1972.
Profiles with flaps bring higher soaring performance compared to profiles without flaps, only when the flaps are set correctly according to the needs of the aircraft. The pilot must therefore keep an optimum value depending on wing loading and flight speed.
During cross-country flights, it is necessary to vary the flight speed depends on the average rise in thermal updrafts and the instantaneous decrease or increase in air encountered. The so-conditional permanent adjustment of the flaps constituting an additional burden for the pilot. If the adjustment of the flaps was automatic, the pilot would be relieved or the work load as with a simple-to-fly glider without flaps.
The project was developed for the DFG under Heiner Oberdörster during 1973/73.
After extensive preliminary studies it was concluded to make the regulation of the flaps dependent of the angle of attack of the aircraft. At a point in the hull wall an outwardly wind flag was attached, which gave the respective angle of attack of the aircraft in flight.
Measured at the wind flag angle was converted by a field plate differential sensor into an electrical signal and supplied to a controller. This controlled by electric valves, the adjustment of the flaps by a hydraulic cylinder until the actual value is consistent with the preset value.
For manual adjustment of the flaps the control circuit switches, as well as with landing gear and during takeoff and landing, automatically.
A an LC-3 (an all-metal glider open class with 18 m span and flaps) testbed for the automatic flaps was purchased on highly concessional terms from VFW-Fokker in 1971.
The automatic flaps were installed in the spring of 1974, and on 22 August 1974, the first flight of the complete automatics. In the course of 1974, there were more than 50 flight hours, tested by 20 different pilots.
Flying with the LC-3A ( A = automatic ) was very impressive. The flap lever turned out, as if by magic, to the optimal value. The expectations were confirmed by a long series of measurements and to everyone's surprise, they received for the curve Flight optimal values.
The entire system weighed approx 20kg in the LC-3A. In conversation with some manufacturers of hydraulic devices, however, was soon clear that in reducing the weight of a compromise would be concluded between the weight savings and the consequent increase in the cost of the system. Between 1976 and 1978, Liebherr developed a hydraulic unit which was built in the LS 3a of the FVA.
Thus, the automatic flaps corresponded fully to the demands placed on them and was successfully tested in other aircraft.
Project was Heiner Oberdörster, who took care of the work to the successful completion in 1975.