Nikitin-Shevchenko IS-4
Both the Italians and Russians drew the wrong conclusions from the air combats fought during the Spanish Civil War.
The two countries invested abundant resources in building the next generation of biplane fighters that would go into service in 1940.
The Polikarpov I-15, I-152 and I-153 were defeated by the Nakajima Ki.27 and the Mitsubishi A5M in the Far East and by the Bf 109 in the West Front.
Why then the devotion of the Soviet designers to the biplanes?
Basically, a biplane fighter has a higher ceiling and climbing speed and better manoeuvrability than a monoplane equipped with an engine of similar power. It also needs a shorter landing strip for take-off.
All these advantages were counterbalanced by the higher speed of the monoplane but, for the Russian designers, it was not clear if the new French engines with more than 1,000 hp. could be manufactured under licence by the Soviet industry of 1940.
Thus, a compromise was achieved giving way to a variable geometry fighter able to take off as a biplane and change into a monoplane when in flight.
The IS-1, created by the OKB-30 design team, looked very much alike the Polikarpov I-153 in the outside and used for testing the folding mechanism of the lower wing in June 1940.
The IS-2 was driven by a more powerful engine and was more streamlined but its performances were inferior to the Polikarpov I-16 ones.
The IS-4 had been the final version for production, with sliding canopy and retractable nose wheel undercarriage, powered by one 1,650 hp. M-120 engine of 16 cylinders in “X” driving a three bladed variable-pitch 3SMV-1 propeller.
When the failure of the M-120 production was known, an AM-37 of 12 cylinders ‘Vee’ was installed in the prototype for the first flights that took place during the summer of 1941.
As a consequence of the German attack, the airplane was dismantled and transported to the inner country.
The need to produce a massive quantity of conventional fighters prevented the manufacturing of additional units of IS-4
Another two designs are known. The IS-14 of 1941, that was equipped with one M-105 engine and the landing gear of a Curtiss P-40, and the IS-18 of 1942, with an M-71F of 2,000 hp. including the novelty of a landing gear that was independent from the wings folding system. A jet variant with variable swept wing was designed in 1947.
IS-4 (Technical data)
Type
: Variable geometry interceptor fighter. Phase: Flight tests. Wings: Gull type in the upper wing with aluminium structure and cladding, foldable lower wing with wood structure and cladding. Tail surfaces: aluminium structure and fabric cladding. Fuselage: Steel tubes structure and cladding of aluminium in the front and of wood in the rear. Landing gear: Retractable tricycle type in the central section of the fuselage with fixed tail wheel. Engine: One Mikulin AM-37 of 12 cylinders in “V”, liquid cooled and with 1,400 hp. driving a 3SMV.1 three-bladed propeller of 3.10 m of diameter. Fuel tank: between the housing of the landing gear and the pilot cockpit and another under the pilot seat. Armament: Two Beresin BS machine guns of 12.7 mm (outboard) and two ShKAS of 7.62 mm in the upper wing. Wingspan: Upper wing 8.6 m, lower wing 7.1 m. Length: 8.64 m. Height: 3.8 m. Wing area: 20.83 sq. m. Maximum weight: (with the M-120 engine) 2,900 kg. Maximum speed: (with the M-120 engine and a monoplane configuration) 720 km/h. Ceiling: (with the M-120 engine and biplane configuration) 12,500 m.
