The Polikarpov line of aircraft under the flag of the Soviet Union began with the "I-1", the first indigenously designed and developed Soviet monoplane fighter. The design stemmed from Nikolai Polikarpov himself , aided by I.M. Kostkin, and the two brought about a modern single-seater that utilized a low-set monoplane wing planform. The prototype - IL-400 - achieved a first-flight on August 15th, 1923 but the I-1 series, as a whole, proved quite forgettable in the annals of Soviet aviation history.
The wooden aircraft was powered by an American "Liberty" L-12 water-cooled engine of 400 horsepower driving a two-blade propeller at the nose. The pilot sat in an open-air cockpit ahead of midships and the fuselage was given a well-tapered form with slab sides. The wing mainplanes were straight in their general design and featured clipped tips. The tail unit was traditional with a sole vertical fin and fuselage-mounted horizontal planes. The undercarriage was wheeled (under center mass) and incorporated a tail skid at the rear.
During its initial flight, IL-400 showcased such longitudinal instability that it led to a crash. This forced a major reworking of the design both internally and externally. Wooden construction still prevailed but thinner wings were implemented as well as a corrugated dural skinning technique. This revised form became IL400b (IL-2) and achieved its own first flight on July 18th, 1924. It was envisioned that the finalized military product would carry a pair of 7.62 machine guns set to fire over the nose and through the spinning propeller blades by way of interrupter gear.
Soviet authorities liked what they saw in the Polikarpov product and, after completing state trials, an order for eight aircraft was placed. This was then followed by an order for twenty-five more though completed to an all-wood construction standard. The finalized fighting model, I-1M-5 (IL-3), achieved a first flight on March 16th, 1926. This was powered by the local, license-produced copy of the Liberty engine designated "M-5".
Including the two prototypes, only 35 I-1 series aircraft were completed in all. The design was still found to be inherent unstable in certain envelopes and generally underpowered for a fighting type. Additionally, quality control from the Polikarpov facility brought the series down further and restricted its official deployment to Soviet aviation units. The first Soviet "exit-by-parachute" from an aircraft was done by Mikhail Gromov, this by necessity when his I-1 could not be recovered from a spin (June 1927).
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2 x 7.62mm machine guns over the nose set to fire through the spinning propeller blades by way of interrupter gear.
I-1 - Base Series Designation
IL-400 - Initial all-wood prototype; Liberty L-12 engine of 400hp.
IL-400b (IL-2) - Second prototype with metal skin; revised thinner wing sections; redesigned internally and externally.
I-1M-5 (IL-3) - Revised IL-400b with all-wood construction; M-5 400hp engine; 33 examples completed.
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