M.Simons The World's Vintage Sailplanes 1908-45
THE STAKHANOVETS
In Russia there was progress in soaring roughly parallel with that in the rest of Europe, but hardly anything was known about it in the west. A hint was given at the Paris Air Show, in 1936. Several interesting Soviet aircraft ДальшеMore>>>
were exhibited, among them a large two-seat sailplane, the Stakhanovets. The designer was V. Emilyanov and it was obvious that he was an original thinker. The problem with two-seat sailplanes has always been that of positioning the second seat. With pilots side-by-side, both get quite a good view but the drag is high, especially if the seating position is upright as was nearly always the case at the time when the Stakhanovets appeared. Also if the ‘side by side' two-seater is ever flown solo, ballast has to be added to retain safe trim and balance. For high performance a tandem arrangement of seats was better, but then the rear seat had to be more or less under, or inside, the wing roots. Swept forward wings offered a neat solution, for the second pilot would have an excellent view sideways and upward. The upward outlook is especially vital in steeply banked, circling flight in thermals, because it is only by looking upward that the pilot can see where he is being taken by his turn. The swept forward planform had another important advantage. On any tapered wing the tip sections naturally tend to stall earlier than the roots. The practice in Germany was to twist the wings progressively to lower angles of incidence toward the tips, in order to retain control. Unfortunately this feature was a serious disadvantage at high speeds. The tips would quickly reach zero angle of attack relative to the local airflow and any further increase of airspeed would see them actually beginning to flex downward, throwing more load onto the inner parts of the wing, creating great drag. Sweep forward has the effect of delaying tip stalling and so the Stakhanovets needed no geometric wing twist at all, even though it had a very strongly tapered planform. In theory its glide ratio at high speeds would therefore be very good.
The only disadvantages of such a shape were that it tended to complicate stressing and construction. To avoid the constructional problems as far as possible, on the Stakhanovets all the nose ribs were glued to the spar at right angles. When covered with plywood to form the usual ‘D'-nose, they did not create any appreciable extra drag by being set at an angle to the direction of flight. Aft of the spar, the ribs for the fabric covered portion of the wing were aligned parallel to the aircraft’s centre line, which, because of the sweep, required them to be set at a slight angle to the spar. The wing root fittings also needed extra work. Otherwise, Emilyanov’s wing was simple in structure and proved extremely efficient. The Stakhanovets must have been difficult to land in small spaces, since although spoilers were fitted on the upper surfaces of the wings, they proved ineffective, pilots reporting that they made hardly any difference when opened.
The aerofoil at the root was a Soviet design which changed progressively to a 13% thick symmetrical profile at the tips. The extreme tips were bent down to form rubbing blocks.
There is little doubt that the Stakhanovets was, in terms of gliding performance, better than the famous German Kranich. It had a larger span, higher aspect ratio and was at least equally clean aerodynamically. It had the additional advantage of a good, high speed performance because of the untwisted wing. The Stakhanovets broke and re-broke all the important two-seat records. It is not known how many were built.
Technical data:
Stakhanovets: Span, 20.20 m. Wing area. 23.0 sq m. Aspect ratio, 17.74. Empty weight, 294 kg. Flying weight. 454 kg. Wing loading, 19.7 kg/sq m. Aerofoil. CAGI R III at root. 15.6% thick, tapering to symmetrical tip of 13% thickness with no washout.
Wikipedia