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.^[2]

Brditschka HB-3

Single seat powered sailplane, powered by 31 kW (42 hp) Rotax 642 engine, 12.00 m (39 ft 4 in) wingspan.^[1]

HB-Flugtechnik HB 21

Tandem two-seat derivative of HB-3 with longer span (16.24 m (53 ft 3 in)) wings.^[3]

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.^[4]

HB-Flugtechnik HB 23/2400 V2

Militky MB-E1

electrically powered version.^[2]

Data from Jane's All The World's Aircraft 1990^[4]

General characteristics

• Crew: 1
• Capacity: 1 passenger
• Length: 8.00 m (26 ft 3 in)
• Wingspan: 16.40 m (53 ft 10 in)
• Height: 2.45 m (8 ft 0 in)
• Wing area: 19.07 m² (205.3 sq ft)
• Aspect ratio: 14.1:1
• Airfoil: Wortmann FX-61-184 at root, FX-60-126 at tip
• Empty weight: 560 kg (1,235 lb)
• Max takeoff weight: 760 kg (1,676 lb)
• Fuel capacity: 76 L (17 imp gal; 20 US gal)
• Powerplant: 1 × Volkswagen air-cooled 4-cylinder engine, 73 kW (98 hp)

Performance

• Cruise speed: 180 km/h (110 mph, 97 kn) (max cruise)
• Stall speed: 80 km/h (50 mph, 43 kn) (powered)
• Never exceed speed: 200 km/h (120 mph, 110 kn)
• Range: 800 km (500 mi, 430 nmi)
• Endurance: 6 hours
• Service ceiling: 5,000 m (16,000 ft)
• Maximum glide ratio: 22:1
• Rate of climb: 3.80 m/s (748 ft/min)
• Rate of sink: 1.20 m/s (236 ft/min)
• Takeoff run to 15 m (50 ft): 160 m (525 ft)

Related development

• Raab Krähe

Aircraft of comparable role, configuration, and era

• Edgley Optica
• RFB Fantrainer

• Coates, Andrew (1980). Jane's World Sailplanes & Motor Gliders new edition. London: Jane's. ISBN 0-7106-0017-8.
• Lambert, Mark (1990). Jane's All The World's Aircraft 1990–91. Coulsdon, UK: Jane's Defence Data. ISBN 0-7106-0908-6.
• Taylor, John W R (1974). Jane's All the World's Aircraft 1974-75. London: Jane's Yearbooks. ISBN 0-354-00502-2.
• Taylor, John W. R. (1976). Jane's All The World's Aircraft 1976–77. London: Jane's Yearbooks. ISBN 0-354-00538-3.
• Taylor, Michael J. H. (1989). Jane's Encyclopedia of Aviation. London: Studio Editions. p. 195.
• Simpson, R. W. (1995). Airlife's General Aviation. Shrewsbury: Airlife Publishing. pp. 87–88.

• fsg-grimming.at
• www.lokh.at - HB23 Daten