Bakshaev RK-I / RK-M-11 / LIG-7



Increasing the wing area produces a noticeable increase in lift caused by the laws of aerodynamics. With more lift the crash speed becomes lower and therefore the aircraft can stay in the air with less "effort". The increase in speed demands a decrease in the surface and therefore an increase in the load on each point of the wing
Air combat aircraft seek to increase performance at the cost of greater driving power and a decrease in wing area, but even this type of aircraft is forced to carry out operations at low speeds such as approach and landing.
Aeronautical development has brought different solutions to this problem, among which the use of flaps and variable geometry in aviation stand out. In the 1930s in the USSR the aeronautical engineer Georgi Ivanovich Bakshayev proposed an interesting method to achieve the same effect. The practical implementation of his theory came to light in the form of the RK aircraft "Razdvizhnoe Krylo", which was successfully tested in 1937.
The RK owes its name to the strange telescopic wing configuration (Razdvizhnoe Krylo - sliding wing), being also known as LIG-7 to indicate its development within the Leningrad Civil Aviation Fleet Institute. The main objective of this model was to obtain the smallest wing area for horizontal flight operations and its increase during takeoff and landing.
Designed as a conventional type two-seater monoplane with a 100 hp M-11 engine, this airplane was used as a test bed for a variable surface experimental wing. The RK was conceived as a low-wing monoplane aircraft braced by cables. This wing, made of wood, was characterized by having a wingspan of 11.3 meters, a constant chord (1.5 m) and a great aspect ratio, which allowed for improved performance during flight at cruising speed. With an M6 wing profile, the internal structure was designed on the basis of two wooden stringers. The covering was fabric. The wing featured bracing cables running from the top of the cabin and from a special cabin structure located in the ventral region.
Rear view of the RK in configuration with the segments collected.
During takeoffs and landings, lift was increased by the extension of 6 telescopic sections, which increased the surface area of ​​the wing to occupy two thirds of the wingspan, giving a total area of ​​23.85 sq.m. Each section, constructed of plywood, was 500mm wide with a 40mm overlap. The profile in this case was the TsAGI-846. The sections featured lightweight support ribs in the inner section constructed of pine and 2mm thick plywood overlay. The extension or retraction system was achieved by means of a steel cable that was operated manually from the cockpit. During the flight all sections were hidden inside the fuselage. The outer wing section with ailerons (one third of the wingspan) was not covered by the sections.
Front view of the RK in configuration with the segments extended.
The RK was ready for testing in 1937. The entire system worked well, with a retraction time of 20 to 30 seconds and extraction time of between 30 and 40 seconds. Retraction and extension were found to be easier in the air than on the ground.
The designers took overload and symmetry into account in the extraction / retraction process and this allowed for no negative effects during in-flight system testing. The center of gravity was established at 26% of the length.
The effect achieved during takeoff and landings was remarkable and the technology proved applicable. The speed did not increase considerably with the collected system, since it maintained a 20% resistance caused by the installation of the structure. Despite this, it was clear that the positive impact of this technology would be extremely useful on larger and faster aircraft, where resistance to wing advancement increases.
This advantage was of little use in civil aircraft. For this reason in 1938 Bakshayev proposed to develop an airplane to set speed records with this Klimov M-105 alar and power plant principle , but the project received no support, however an order was received to build a single-seater fighter using the Alar technology of the RK that was due to be ready for testing in 1940 and was known as Bakshayev RK-I (RK-800).
Engine: 1 x 100 hp M-11 piston engine
Wingspan: 11.3m
Length: 7.34 m
Wingspan of extended sections: 6.27 m
Wing area with retracted sections: 16.56 m²
Wing area with extended sections: 23.85 m²
Empty weight: 667kg
Loaded weight: 897kg
Wing load with sections retracted: 54.2 kg / m²
Wing loading with extended sections: 37.6 kg / m²
Power Load: 9.0kg / hp
Fuel and oil weight: 70 kg
Speed ​​at sea level with sections retracted: 150 km / h
Speed ​​at sea level with extended sections: 144 km / h
Landing speed with sections retracted: 100km / h
Landing speed with extended sections: 75km / h
Landing run with sections retracted: 210 m in 12 seconds
Landing run with sections extended: 110m in 9 seconds
Take-off run with sections retracted: 250m in 14 seconds
Take-off run with sections extended: 135m in 9 seconds
Range with sections retracted: 400 km
Range with extended sections: 370 km
Autonomy: 3.0 h
Ceiling: 2900m
Ascent time to 1000m: 7.5 minutes
Ascent time to 2000m: 19.5 minutes
Accommodation: 2