M.Simons The World's Vintage Sailplanes 1908-45
Little is known about the GN-7 except the general appearance shown in the drawing and the bare technical data listed. The general background to the design is that during the early 1930s the Russian gliding movement began to develop,
as elsewhere, a great interest in cross country soaring and the emphasis shifted from slow, slope soaring types toward heavier, faster sailplanes with high aspect ratio cantilever wings. One outcome was the DK-2, designed by D. N. Koliesnikov, which flew at the 1934, 10th National Soaring Championship. This had a ‘gull’-type wing, following contemporary fashions in Western Europe.
Soon afterward the engineers Antonov and Groshev collaborated to produce the AG-1, a 15.2 metre sailplane of advanced design. It had a ‘gull' wing, but the rather difficult and costly business of building a curved mainspar was avoided by building a wide centre section integrally with the fuselage, with a sharp dihedral angle. The outer wings were then attached to this, with no dihedral, when rigging. A similar dodge was used by the Huetter brothers with the small H-28. The AG-1 was equipped with Schrenk flaps under the trailing edge of the centre section, and these were found very effective as landing aids. In the AG-1, some very good distance flights were made, especially one of 326.5 km by Rastorguyev, but it seems that only one was ever built.
Groshev went his own way after this successful design, and produced the GN-7. In most respects this was a 16.8 metre version of the AG-1, retaining the ‘gull’ wing with the wide centre section. The flaps seem to have been omitted. The wing joined the fuselage at a high mid position whereas the AG-1 had had a high wing with rather elaborate root fairings. No doubt to control the greater span in yaw, the rudder of the GN-7 was made very tall. The wing loading was less than that of the earlier type.
Other than these few facts, nothing more is known. That the GN-7 was both a very good sailplane and popular with pilots is indicated by the fact that it was produced in some quantity by the Moscow Sailplane Factory. Its list of national records is very long. Rastorguyev’s world record distance of 652.256 km in 1937 being the culmination of a successful series of increasingly long flights, and not, as western commentators believed at the time, an isolated lucky venture.
GN-7: Wingspan. 16.80 m. Wing area, 12.8 sq m. Aspect ratio. 22. Aerofoil. Goettingen 549. Empty weight. 200 kg. Flying weight. 304 kg. Wing loading, 23.8 kg/sq m. Best glide ratio, 1:28.