The Polikarpov I-17 was a rare example of a Polikarpov fighter powered by an inline engine, and was developed in an attempt to improve on the speed of radial engined fighters.
The I-17 was produced after Stalin ordered Polikarpov to design a fighter capable of reaching 500kph (310mph). In order to achieve this Polikarpov decided to use an inline engine. This allowed him to produce an aircraft with a slim fuselage, reducing drag but also producing a very cramped design. The first aircraft, the TsKB-15, was powered by an imported Hispano-Suiza 12 Ybres engine capable of providing 750hp, and was to be armed with four wing mounted 7.62mm machine guns.
The TsKB-15 made its maiden flight on 1 September 1934, and reached a top speed of 455kph/ 282mph. Stability was better than on the I-16, and so work on a second prototype was approved.
The second aircraft, the TsKB-19, was similar to the first prototype, but was powered by the M-100 engine, a Soviet copy of the Hispano-Suiza. It was more heavily armed, with a 20mm cannon, and had a new undercarriage. Speed rose to the required 500kph, but the narrow cockpit was judged to be unsuitable for service use.
A third prototype, the TsKB-33 with a surface-evaporation steam cooling system was completed. The I-17 was also used as the basis for a number of other experimental aircraft, including the TsKB-43 of 1936, which would have been powered by a Gnone-Rhone 14Krsd and the TsKB-25/ I-19.