Impact of variable geometry miniflaps on sailplane flight characteristics

Abstract

Miniflaps (also known as mini-TED, active Gurnay flaps, etc.) located at the wing trailing edge enable to increase wing lift and reduce the aerodynamic drag. Variable geometry miniflaps (VGMF) elaborated at the Estonian Aviation Academy enable to expand the wing area up to 6.5%, when extended, and, at the same time, deflect 16.7 degrees downwards. The use of VGMF is especially promising for reducing the airspeed and sink speed of modern high wing loading sailplanes flying in thermals. The VGMFs were built in cooperation with the Lithuanian company JSC “Sportine Aviacija ir Ko”. They were fixed inside the sailplane LAK-17B trailing flaps. During the test flights, the VGMF effect on the sailplane’s sink speed was measured at different airspeeds and different flap positions. The flight parameters were recorded electronically and later calculated for standard atmosphere. The method of parallel flight was used for comparison. The results indicate that with the flaps position at + 9 degrees, the CAS 79.5 km/h sink speed decreased 0.775–0.555  m/s, i.e. 39.6%. The sailplane’s wing loading was 39.4 kg/m ². With the flaps position at + 15 degrees, the optimal airspeed decreased, but the sink speed, compared to the previous, rose. Cl max increased with the VGMF 1.41–1.58 (i.e. 12%).

Keyword : mini-TED, miniflap, airfoil, sailplane, L/D ratio