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Brditschka HB-21
The HB-21, which first flew in 1973, is basically an enlarged version of the HB-3 with an increased wing span and a lengthened forward fuselage seating two people in tandem under a long three-piece cockpit canopy hinged to open sideways.
The HB-3's basic configuration of high wings and a pusher propeller rotating in a cut-out portion of the fuselage is retained. Construction is very similar to the HB-3, the fabric-covered three-piece wooden wings being of birch ply with laminated beech spars; they now have Wortmann aerofoil sections and there are spoilers in the upper surfaces. The fuselage is a steel tube framework covered with glassfibre, and the wooden tail unit has a fixed-incidence tailplane and fabric covered control surfaces. The fixed nosewheel undercarriage has Tost mechanical brakes on the main wheels.



Four prototypes were built which included both the HB-21 R with a 41 hp Rotax 642 two-stroke engine like the HB-3, and the HB-21 L with a 65hp Volkswagen(VW)-Westermayer 1600G 'flat four' motor, the latter being the principal version; both powerplants drove a Hoffman HO 14-175 B 117 LD two-blade fixed-pitch propeller, and both versions have an 11.9 Imp gallon aluminium fuel tank in the wing.
Certification of the HB-21 was granted in February 1978, and a year later 15 had been built.
Span: 53 ft 3.5 in
Length: 25 ft 11 in
Height: 8 ft 6.25 in
Wing area: 204.3 sq ft
Aspect ratio: 13.89
Empty weight: 1,102 lb
Max weight: 1,565 lb
Max speed: 124 mph (in smooth air, power off)
Max cruising speed: 99 mph
Min sinking speed: 3.94 ft/sec at 52 mph
Best glide ratio: 24-26:1 at 65 mph
Max rate of climb: 650 ft/min at sea level
Take-off run: 330 ft
Range with max fuel: 497 miles


HB-21 R
Engine: Rotax 642, 30.6 kW / 41 hp
Wing span: 16.24 m / 53 ft 3.5 in
Length: 7.9 m / 25 ft 11 in
Height: 2.6 m / 8 ft 6.25 in
Wing area: 18.98 sq.m / 204.3 sq ft
Wing section: Wortmann FX-61-184/60-126
Aspect ratio: 13.9
Empty weight: 418 kg / 922 lb
Max weight: 640 kg / 1,411 lb
Water ballast: None
Max wing loading: 33.7 kg/sq.m / 6.9 lb/sq.ft
Max speed: 140 kt / 260 km/h
Stalling speed: 35.5 kt / 66 km/h
Min sinking speed: 0.8 m/sec / 2.6 ft/sec at 43 kt / 80 km/h
Best glide ratio: 28 at 54 kt / 100 km/h
T-O run: 170 m / 558 ft
Rate of climb: 132 m/min / 433 ft/min at S/L
Range: 650 km / 350 nm




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