The Brditschka HB-21 Hobbylifter is an Austrian two-seat motor-glider characterized by an unconventional design. It was developed in the early 1970s by HB-Flugtechnik, a small firm led by Helmuth W. Brditschka. The HB-21 was designed as an enlarged version of the earlier HB-3, which had first flown on June 23, 1971. The HB-21 itself made its first flight in 1973, introducing a lengthened fuselage and an increased wingspan to accommodate two occupants in a tandem seating arrangement under a three-piece canopy.
Technically, the HB-21 is distinguished by its pusher-propeller configuration, with the engine mounted behind the cockpit to drive a propeller located between the tailbooms or aft fuselage. This layout was intended to maximize visibility for the crew while maintaining a narrow fuselage for gliding efficiency. According to ICAO Doc 8643, the aircraft features a wingspan of 16.2 meters, a length of 7.9 meters, and a height of 2.6 meters. It has a maximum take-off weight (MTOW) of 700 kg and a fuel capacity of 54 liters.
While specific engine models are not firmly documented in available records, the aircraft is powered by a small piston engine. One variant, the HB-21/2400B, is noted in accident reports. Operational data indicates the aircraft is capable of reaching speeds of 165 km/h and possesses a climb performance of approximately 4 m/s. Its maximum range is listed as 350 nautical miles.
Production of the HB-21 was conducted in Austria in very small numbers. While a total production figure is unknown, evidence of series construction exists, such as a specific airframe dated to 1977. The aircraft served exclusively in civil roles, utilized by private owners and flying clubs for recreational touring and glider training. One such civil example, registered as OE-9160, was involved in an incident on June 3, 1987. Today, the HB-21 remains a rarity in the aviation world, with a few examples appearing on the second-hand market in recent decades, reflecting its legacy as an experimental approach to economical private flight.