The SK aircraft was designed in the 26th department of TsAGI (designer Matus Ruvimovich Bisnovat) since 1938 as an experimental device designed to achieve maximum flight speeds of the order of 700–800 km/h. Such high values ​​​​with the M 105 engine were hoped to be obtained, first of all, due to especially high-quality aerodynamics and a small wing with an area of 9.5 m², with a high specific load (up to 220 kg / m²). At the same time, it was supposed to study several interchangeable wings with different profiles, to determine the characteristics of stability and controllability at a high specific load on the wing.

The fuselage of the SK aircraft is maximally compressed, with a midsection of only 0.85 m², with a cockpit canopy made flush with the top line of the fuselage. During takeoff and landing, the pilot's seat was raised, at the same time the visor was tilted up, covering the pilot's head.

The wing is two-spar, one-piece, very cleanly made in terms of production. Wing profile NACA 230. Additional cleanliness of the surface of the wing was achieved through the use of a special putty with cork dust applied to the fabric glued over the metal surface. This technique made it possible to polish the surface of the wing to a mirror finish. To reduce takeoff and landing speed on the wing, special retractable flaps designed by TsAGI - Vlasov were used. In the takeoff position, the flaps were extended, forming an additional bearing surface, in the landing position, they were lowered, changing the wing profile in the area of ​​​​their installation. The main landing gear, hydraulically removed towards the axis of the aircraft, was equipped with very small wheels - 500 × 150 mm. Crutch wheel, oriented when taxiing on the ground and completely retractable in flight. An additional innovation in the SK was a special engine liquid cooling system, in which the radiator area was reduced to 0.17 m², and water circulated at a pressure of 1.1 kgf / cm².

The place of manufacture of the aircraft was called the experimental workshops of TsAGI, at the same time the aircraft plant No.156 was indicated, where the final assembly was carried out. Flights of the experimental SK began in the spring of 1940, initially on skis without retracting the landing gear. Test pilot G. M. Shiyanov flew. Insufficient longitudinal and lateral stability was noted, engine oil was heated. On March 26, 1940, during the landing, an asynchronous opening of the landing flaps occurred, which almost led to an accident.

During the continuation of tests on an aircraft with a flight weight of 2100 kg, it was possible to achieve a flight speed of 577 km / h at an altitude of 5500 m. For the first stage of the experiments, this value was considered quite sufficient. All flight stability tests were completed on 5 July 1940, and the test report was prepared by 1 August. The main drawback of the aircraft was the lack of a conventional pilot's lantern, which greatly complicates the performance of flights. This and other shortcomings were supposed to be eliminated on the second SK, called the "understudy", or SK-2.

Photo	Description
	Drawing SK-1
	Bisnovat SK-1. May 20, 1940

High Speed Fighter Bisnovat

SK-2 — A high-speed fighter developed at TsAGI by Bisnovat. First flight - November 10, 1940.

The aircraft had a metal structure with a rivet in the back, the canvas was used only in the skin of the ailerons and rudders. The aircraft had an unusually small wing measuring 9.57 m². The aircraft was equipped with a serial M-105 engine with a variable pitch propeller VISh-52.

The cockpit canopy was of the usual type with an emergency release mechanism, the oil cooler was moved to the forward lower part of the fuselage, the engine suction pipes are located at the root of the wing.

With the M-105 engine with a power of 1050 h. p. and the VISh-52 propeller, the SK-2 aircraft developed a maximum speed at an altitude of 4900 m up to 660 km / h, and at an altitude of 2700 m - 645 km / h. To climb to a height of 5000 m, 4 minutes were enough for him. 20 s. The service ceiling was 10,300 m. The takeoff weight of the SK-2 was only 2,300 kg. Despite the high specific wing loading (240 kg / m²), the SK-2 had quite satisfactory takeoff and landing characteristics. The length of its takeoff run did not exceed 350 m, and the run - 500 m.

When assessing the speed characteristics, it should be borne in mind that the SK-2 had no weapons. Converting it into a fighter (installing machine guns, armored backs, sight, etc.) would reduce the speed by several tens of kilometers.

Photo	Description
	Drawing SK-2

The experience in the development of the SK-2, and especially the materials for testing them in the air, were subsequently taken into account and used in the design of fighters, in which, along with the increase in engine power, the specific load on the wing also increased.

Feedback from the pilots about the aircraft: "Flight. The aircraft has sufficient positive stability in the longitudinal and directional relation; in the lateral relation, the stability of the aircraft is close to neutral. The aircraft" tightly "sits in the air and is easily controlled ...

Planning and landing. The landing approach is made at 240 km / h, a lower speed makes the landing unpleasant. Landing visibility is good. Guards allow go-around and flight in any mode. When the flaps are deflected, the plane becomes more stable and lowers the nose, the trajectory becomes steep.

The landing of the aircraft is simple and pleasant, but requires precise approach to the ground ... The landing gear cushioning works well, the mileage after landing with the wheel unbraked is very stable and keeping the direction does not require tension. "

In 1940 M.R. Bisnovat wrote to the People's Commissariat of the Aviation Industry: “Despite the fact that flight tests have not yet been completed, the material we received is of great value. For the first time, we started flying on a TsAGI-SK aircraft with a specific load of over 200 kg / m² and received positive results in the take-off run, the run and the turns at high landing speeds. Thus, the "theory" of the impossibility of using large specific loads as a speed reserve was overturned "

Bibliography

• "The history of designs of planes in USSR 1938-1950" /Vadim Shavrov/
• Lost victories of Soviet aviation /Mikhail Maslov/