PZL Bielsko SZD-36A Cobra
The SZD-36 high performance Standard Class single-seater was designed by Dipl-lng Wladislaw Okarmus for the Polish gliding team at the 1970 World Championships at Marfa, Texas. Design work began in October 1968 and the prototype Cobra 15 made its maiden flight on 30 December 1969. At the 1970 World contest, Jan Wroblewski and Franciszek Kepka of the Polish team flew their early production Cobra 15s into 2nd and 3rd places respectively in the Standard Class, and a Cobra 17 - this being the 17m span version - came 5th in the Open Class.
Of all-wood construction with plywood and glassfibre covering, the Cobra 15 has cantilever single-spar shoulder wings with heavy moulded plywood stressed skin covered by glassfibre; the plain ailerons are mass balanced and are of plywood/polystyrene/foam sandwich construction, and there are SZD doubleplate metal glassfibre air brakes in the upper and lower wing surfaces. 45 degree to 45 degree roll rate is less than three seconds. The SZD-39 Cobra 17 is the same as the Cobra 15 except for the increased span (55ft 9.25in) Wortmann profile wing of 23.56 aspect ratio, which has provision for water ballast. The fuselage is an oval section semi-monocoque covered with plywood over the rear part and glassfibre on the forward portion, and there is an aero-tow hook in the lower fuselage forward of the monowheel.
The SZD-36A differs from the SZD-36 in having this hook repositioned about 1 m further forward of the cg with provision for locating it at the cg if required. The monowheel retracts mechanically to lie horizontally in the bottom of the fuselage, and has a brake; there is also a tailskid. The Cobra is distinguished by a sharply swept back fin and rudder with an all-moving mass-balanced tailplane mounted on top of it, with a trim tab on its trailing edge. The pilot sits under a vacuum-formed jettisonable flush-fitting canopy which slides forward to open; there is a small luggage compartment behind the pilot's seat and also a full range of instrumentation, plus provision for an oxygen system with a 4-litre cylinder in the baggage compartment and a radio.
SZD-36A Cobra 15
Altogether 238 Cobras of all versions had been built when production ended in 1977, and the type has been exported to more than 20 countries.
Wing span: 15 m / 49 ft 2.5 in
Wing area : 10.6 sq.m /124.9 sq.ft
Aspect ratio: 19.4
Length: 22 ft 11.25 in
Height: 5 ft 2.25 in
Empty Weight: 257 kg / 567 lb
Payload: 128 kg / 282 lb
Gross Weight: 385 kg / 849 lb
Wing Load: 33.2 kg/sq.m / 6.8 lb/sq.ft
Max speed: 155 mph (in smooth air)
L/DMax: 38 @ 94 kph / 51 kt / 59 mph
MinSink: 0.60 m/s / 1.97 fps / 1.17 kt at 45.5mph
Airfoil: Wortmann FX61-168