PZL Bielsko SZD-21 Kobusz
Developed between 1958 and 1964, and one of the very few sailplanes designed especially for aerobatics, this high performance single-seater first flew in prototype form as the SZD-21-2 Kobuz 2 on 3 June 1961, and was designed by Trzeciak. lt was developed into the Kobuz 3, the prototype of which was built at the No 4 ZSLS (Sport Aviation Equipment Plant) at Wroclaw, and flew for the first time on 10 December 1964, piloted by S.Skrzydlewski.
An initial production batch of three Kobuz 3s followed in 1965. The Kobuz 3 differed from the Mk 2 in having the cockpit moved forward and the pilot in a semi-reclining instead of a fully reclining seat, a slightly longer and more pointed nose, a wing of 0.5m greater span with plywood stressed-skin covering, and a taller fin and rudder with the low-set tailplane moved back to underneath the rudder. The Kobuz 3 is stressed to airframe limits of + 7G to -5G, and has a cantilever mid-set laminar flow wing built as a sparless torsion box structure with plywood and foam sandwich skinning; the two section ailerons are fabric-covered and flaps as well as air brakes are featured. The monocoque fuselage is built in two portions and is covered with a glassfibre and plywood skin; the cockpit has provision for an oxygen installation and R/T radio. A manually-retractable monowheel is fitted, plus a tail bumper. The cantilever tail unit is structurally similar to the wing, and has a fabric-covered rudder and elevators.
SZD-21-2B Kobuz 3
Wingspan: 45 ft 11.5 in / 14.0 m
Wing area:145.3 sqft
Aspect ratio: 14.52
Length: 23 ft 7.5 in / 7.3 m
Height: 6 ft 3 in / 1.9 m
Max take off weight: 884.2 lb / 401.0 kg
Max. speed: 108 kts / 200 kph
Glide ratio: 30.0