The Grzeszczyk SG-3 was a Polish single-seat, high performance sailplane first flown in 1933. Between 1934 and 1937 it was Poland's most successful competitor and record setter; about twenty-five were completed.
In 1931-2 Szczepan Grzesczyk designed the Grzeszczyk SG-21 Lwów and SG-28, two high performance sailplanes. Although only one of each was built, they performed well and led to the batch-built Grzeszczyk SG-3. Design was initiated in 1932 and Warsztaty Szybowcowe began construction of three developmental airframes in March 1933. The first flew in July or August. Competing against the CW-5, the SG-3 established itself as the predominant Polish competition and record setting sailplane of its era.
It was an all-wood, single-seat, cantilever high wing aircraft. Its two part wing, mounted on a streamlined central pylon, was built around a single spar with angled drag struts near the fuselage. Plywood covering ran around the leading edge to the spar, forming a torsion resisting D-box, as well as forward of the drag strut. Fabric covered the rest of the wing. SG-3 and SG-3bis wings were similarly built but plans and dihedrals differed. The SG-3 had a rectangular plan centre section filling about 15% of the span, with trapezoidal panels outboard. The SG-3bis had a gull wing of constant taper but with higher dihedral over the inner 30% of the, a greater span and a 6% increase in aspect ratio. They also differed in section: the SG-3 used Warsaw Aerodynamic Institute airfoils but the SG-38bis used the Göttingen 549. The ailerons also differed, with split surfaces on the SG-3 but longer, narrower single surfaces on the SG-3bis.
The fuselage was a ply-skinned semi-monocoque, tapering rearwards most rapidly on the SG=3bis. The enclosed cockpit was ahead of the wing pylon and the wing leading edge and was continuously refined over the three annual production batches (SG-3/34, SG-3/35 and SG-36bis/36). The empennage was similar to that of the SG-21 Lwów and SG-28 with a very narrow, ply-covered fin integral with the fuselage and full, fabric-covered rudder. The rudder balance of early versions had gone by 1936. The chord of the split, tapered and mostly fabric-covered all moving tailplane of the SG-3 was increased in the SG-3bis.
It landed n a sprung, central skid, faired-in on the SG-3bis, and had a small tailskid.
The SG-3 and SG-3bis set many Polish records. These included duration records in 1933 and 1934, the latter lasting 12 h 60 min. In 1936 it set the altitude record at and a distance record of . In 1937 it took the out-and-return distance record to and in the following year Wanda Modlibowska set a women's distance record at .
Twelve competed in the Fourth National Glider Contest, held at Ustianowa in July 1936. Six were SG-3bis and these dominated the competition. One flown Z. Źabski was the overall winner. A SG-3bis, flown by Tadeusz Góra, won the 1937 Contest.By 1938 other designs, like the PWS-101 were starting to out-perform the SG-3bis, which also needed strengthening to meet new cloud-flying regulations. According to Cynk this prevented their participation in the Sixth Contest, though a contract to make the required modifications was agreed. Simons states that this work was judged too costly and most were scrapped, though Samoloty reports that five took part.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Warsztaty Szybowcowe SG-3".
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