PZL Bielsko SZD-24 Foka / SZD-32 Foka
Appropriately named Foka (or Seal), this high performance Standard Class single-seater was designed by Dipl-lng Wladislaw Okarmus and Mynarski, and first flew in prototype form on 2 May 1960.
Flown by Adam Witek, the Foka gained 3rd place in the Standard class in that year's World Championships at Koln-Butzwerhof, Germany, where the type's design features aroused interest.
Three pre-production aircraft designated SZD-24B Foka 2 were completed early in 1961, and the first major production variant was the SZD-24C Foka 4 Standard, which first flew in September 1961; deliveries to the Polish gliding clubs and to export customers began soon after. A Foka 4, flown by Jan Wroblewski, won the Open Class at the 1965 World Championships at South Cerney, England.
This version was succeeded in production by the SZD-24-4A (or SZD-24D) Foka 4, which first flew in prototype form in February 1962 and later took part in the 1963 World Championships in Argentina. The Mk4 had the same fuselage as the Foka-Standard but the wing structure was redesigned to make it much simpler and less costly to produce while retaining the same aerodynamic shape.
The first production Foka 4A made its first flight on 7 Feburary 1964 and four Mk4As were flown by the Polish team in the 1965 World Championships at South Cerney, Gloucestershire; in one of these Jan Wroblewski won the Open Class and his team-mate E. Makula came 4th, while the Fokas flown by F. Kepka and J. Popiel took 3rd and 4th places in the Standard Class.
Of all-wood construction, the Foka 4A has two-piece cantilever shoulder wings which are sparless torsion box structures with thick plywood sandwich stressed skin covering which replaces the Foka-Standard's plywood and foam skinning; the letter's wing had a central torsion box structure built up of a main spar and two auxiliary spars. There are special SZD plain ailerons of NACA 4415 section. No flaps are fitted but there are SZD metal air brakes at the 60% chord line. The wooden monocoque fuselage is unusual in that the forward part has a modified laminar section, with the maximum depth aft of the pilot's cockpit at 40% wing root chord; the forward section is covered with a plywood/glassfibre sandwich skin. The pilot sits in a fully-reclining seat under a large flush-fitting canopy which slides forward to open; blind flying instrumentation is standard and there is provision for radio and oxygen. The landing gear consists of a long skid under the nose and a non-retractable monowheel located well aft of the eg, plus a tail bumper. The swept fin is integral with the fuselage and, like the tailplane, is an all-wooden sandwich structure; the laminar flow tailplane and elevator slot into the rear fuselage cone below and behind the rudder in a manner very similar to the Zefir 2. The elevator and rudder are fabric-covered and there is a trim tab in the former.
Final production version was the SZD-32A Foka 5 (formerly SZD-24E), which first flew in prototype form on 28 November 1966 and received its Polish C of A on 7 October 1967; this differed from the Mk 4 chiefly in having a roomier cockpit and the one-piece wooden tailplane and elevator repositioned at the top of the fin. The Foka 5 won first prize at the 1968 OSTIV Congress for the best Standard Class sailplane and a Mk 5 flown by Eward Makula finished 8th in the Standard Class in that year's World Championships at Leszno, Poland.
SZD-32A Foka 5
The Foka 5 had several other changes from the Mk 4: the wing section was slightly different and the plywood-covered wing was now a multi-longeron semi-monocoque structure, with spars in the inboard section of each panel only; ailerons and air brakes were the same. The fuselage is now a semi-monocoque of oval section, with the monowheel relocated to be under the eg when the aircraft is empty; its brake is linked with the air brakes and the nose skid is retained. The cockpit canopy is slightly shorter but the pilot has the same blind flying instrumentation and provision for radio and oxygen as on the Mk 4.
Altogether 330 Fokas of all variants had been built when production of the type ended in 1971, and 200 of these were exported to 17 countries.
PZL Bielsko / SZD 24 Foka
PZL Bielsko / SZD 32 Foka 5
Length: 23 ft 6.5 in / 7.2 m
Wingspan: 49 ft 2 in / 15.0 m
Aspect ratio: 18.5
Wing area: 131.321 sq.ft / 12.2 sq.m
Height: 5 ft 3.5 in
Max take off weight: 850 lb / 385.0 kg
Weight empty: 564.5 lb / 256.0 kg
Max. weight carried: 284.4 lb / 129.0 kg
Max. speed: 135 kts / 250 km/h / 155 mph (in smooth air)
Landing speed: 37 kts / 68 km/h
Cruising speed: 46 kts / 86 km/h
Min sinking speed: 2.03 ft/sec at 48 mph
Wing loading: 6.56 lb/sq.ft / 32.0 kg/sq.m
Best glide ratio: 36.3:1 at 53mph