The Brditschka HB-3, HB-21 and HB-23 are a family of motor gliders of unorthodox configuration developed in Austria in the early 1970s. The unusual design was based on work done by Fritz Raab in Germany in the 1960s. The pilot and passengers sit in a fuselage pod with the engine and propeller behind them. The pod also carries the fixed tricycle undercarriage and the high cantilever wing. The tail is carried on a pair of booms that emerge from the top and bottom of the fuselage pod, the upper of which passes through the propeller hub. The HB-21 has a conventional tail and has two seats in tandem accessed by a sidewards-hinged canopy, while the HB-23 has a T-tail and side-by-side seating accessed via gull-wing doors in the canopy. The Militky MB-E1 was a modified HB-3 with an 8-10 kW (11-13 hp) Bosch KM77 electric motor. It was the first full-sized, manned aircraft to be solely electrically powered. Flights of 12 minutes duration at up to an altitude of 380 m (1,247 ft) were just within the Ni-Cd battery's capacity. Its first flight was on 23 October 1973. Variants Brditschka HB-3 Single seat powered sailplane, powered by 31 kW (42 hp) Rotax 642 engine, 12.00 m (39 ft 4 in) wingspan. HB-Flugtechnik HB 21 Tandem two-seat derivative of HB-3 with longer span (16.24 m (53 ft 3 in)) wings. HB-Flugtechnik HB 21/2400 HB-Flugtechnik HB 21/2400 B HB-Flugtechnik HB 21/2400 V1 HB-Flugtechnik HB 21/2400 V2 HB-Flugtechnik HB 23/2400 HB-Flugtechnik HB 23/2400 SP HB-Flugtechnik HB 23/2400 Scanliner Observation version of HB-23 with bubble canopy and provision to carry FLIR or LLTV pods under the wings. HB-Flugtechnik HB 23/2400 V2 Militky MB-E1 electrically powered version.
