M.Simons The World's Vintage Sailplanes 1908-45
THE SG SERIES
The ZASPL was a Polish equivalent of the German academic flying groups. It was formed at Lwow Technical University when Waclaw Czerwinski and Szeczepan Grzeszczyk were students there. The SG-21, named Lwow after the city, was
designed by Grzeszczyk to the same official specification as Czerwinski's CW-5. It was a cantilever sailplane, test flown by its designer in October 1931. A few days later Grzeszczyk broke the national duration record with a flight of 7 hours 52 minutes. Many other record flights were made by this prototype over the next two years. These early successes led to an official order for another, improved version, the SG-28, which flew in mid 1932. Piloted by Boleslaw Baranowski it broke the Polish altitude record (1270 metres) and duration record (10 hours 40 minutes).
The SG-21 and SG-28 were both taken to Germany in 1932 to compete in the Rhoen competitions. It was very rare for non-German sailplanes and pilots to fly at these meetings. The main difference between these two sailplanes was in the choice of wing profiles. Both used aerofoils designed by the Warsaw Aerodynamic Institute, No 100 for the SG-21 and Numbers 192, 248 and 289, progressively changing along the span for the SG-28. The SG-28 had an improved fuselage with an enclosed wooden canopy, with transparent panels let in, instead of the open cockpit of the earlier aircraft.
From the SG-28 Grzeszczyk developed the SG-3 in 1932. Three were built in time for the 1933 soaring season and further small batches for several years afterwards, each series incorporating minor improvements. This type in its various marks became one of the most popular sailplanes in Poland.
The structural design was orthodox, with single-spar wings and plywood covered ‘D'-nose torsion box, and a semi-monocoque plywood fuselage of egg-shaped cross section. Various cockpit canopies were fitted at different times, the final form being a light, steel tubular framework covered with transparent plastic.
The SG-3 bis/36 was a major redesign, with straight taper and ‘gull’ dihedral, Goettingen 549 aerofoil, and greater wingspan. The new sailplane achieved complete dominance at the 1936 Polish National Championships. The distance and altitude records (332.2 km and 3435 m) fell to the type during the meeting. In 1937 an SG-3 bis/36 again won the contest.
In 1938 new airworthiness requirements were introduced in Poland and all the SG sailplanes required strengthening. They were grounded until this work had been completed. By the time they were flying again, newer and faster sailplanes were in service and the SG types had lost their place at the top of the lists.
SG-3: Span. 17.00 m. Wing area. 16.5 sq m. Aspect ratio. 17.5. Empty weight, 149 kg. Flying weight, 225 kg. Wing loading, 13.7kg/sqm. Aerofoils, Warsaw 192 at root, 336 at tip.
SG-3 bis/36: Span, 17.60 m. Wing area, 16.7 sq m. Aspect ratio, 18.5. Empty weight, 156 kg. Flying weight. 236 kg. Wing loading. 14.1 kg/sq m. Aerofoil, Goettingen 549.