I-16M-22, TsKB-12 by N.N.Polikarpov

20k b/w drawing, courtesy of Sergey Andreev;

The TsKB-12 project emerged from Summer 1932 modern fighter drawings by N.N.Polikarpov. The original layout had Townend ring covering the engine.

After mock-up tests in the wind tunnel and several structure improvements, question of mass production was raised even before completion of a prototype. Two prototypes were built - TsKB-12 (with M-22 domestic analog of the Bristol Jupiter VI engine) and TsKB-12bis for tests with US built Wright-Cyclone SGR 1820-F-2.

Mixed design plane, using wing spars made of chrome-molibdenium steel alloy, duralumin ribs, and mixed D1 aluminum alloy/fabric skin. Fuselage was built of pine spars and frames, covered with birch cross-grain glued strips 4.0mm-2.5mm thick. Tail plane and ailerons had duralumin frame and fabric cover. Gear retraction system employed cables, since hydraulic systems were not in wide use yet. Enclosed cockpit with forward-sliding canopy was a novelty, and later pilots often flew the TsKB-12, I-16 Type 4 and 5 with open canopy.

56k b/w photo of TsKB-12 during first Winter trials, courtesy of Sergey Andreev;

Number of problems were revealed during flight tests (December 30, 1933 - Spring 1934), specially with landing gear (to be cranked up and down manually) and airplane stability. Short fuselage, together with excellent maneuverability provided serious handling complicity, and test-pilot's (V.F.Chkalov, V.K.Kokkinaki, V.A.Stepanchenok) conclusion was that this is a fighter for skilled pilots only.

In early tests prototype was unarmed, it carried dummy barrels in wings. During trials rudder area was increased and Hamilton-Standard 3-blade propeller was replaced by domestic V-22 two-blade unit. In early 1934 engine cowling was redesigned to solve overheating problem.

28k b/w TSKB-12 with reconfigured engine cowling and domestic propeller (I-16 with M-22 engine) from "History of aircraft construction in the USSR", Vol.1 p.493

The TsKB-12 went into production in mid 1934, and few hundred of this aircraft were built with the M-22. TsKB-12 was followed by the I-16 Type 4 with several design changes. Despite outstanding performance of the aircraft, N.N.Polikarpov started to work on the second prototype ('Dubler' TsKB-12bis) with more powerful engine even before the first TsKB-12 took off.