The RK (Razdvizhnoye Krylo – extending wing) (a.k.a. LIG-7) was a two-seat cabin aircraft designed and built in the USSR from April 1936.
In 1930 the LIIPS (- Leningrad institute for sail and communications engineers) formed a UK GVF (- training centre for civil air fleet), in turn the UK GVF formed the NIAI (Naoochno-Issledovatel'skiy Aero-Institoot - scientific test aero-institute) which became the focus of several good design engineers who were given command of individual OKB (Osboye Konstrooktorskoye Byuro – personal design/construction bureau).
Along with contemporary aircraft designers, in the USSR and abroad, Grigorii Ivanovich Bakshayev was interested in the concept of variable geometry aircraft, where the size and/or shape of wings are altered according to the stage of flight, or desired characteristics. One methods of achieving this was with a telescopic wing, where wing sections of bigger aerofoil section and area are telescoped out over the original wing. He designed the RK to use a telescopic wing with six sections, of gradually increasing size, extending outwards from the fuselage to the demands of the pilot.
The airframe of the RK was a simple structure of steel tube fuselage and a wire braced monoplane wing of constant M-6 section constructed of wood. The extending wing sections were each 460 mm wide and were extended by the observer in the rear cockpit operating a hand-crank connected to cables via a pulley system to pull each section out in turn, with each section pulling the next behind it. Successful flight tests starting in 1937 led to authorisation for a fighter with telescopic wings to be designed and built; The RK-I (Razdvizhnoye Krylo - Istrebitel – extending wing fighter).