The Polikarpov I-5 was the second of Nikolai Polikarpov's biplane fighters to enter front line service, and was designed while he was working in a prison camp.
Polikarpov's I-5 was the third aircraft to carry that designation. In 1928 an Experimental Aircraft Plan was put in place. In this plan the I-5 was to be of mixed wood and metal construction while the I-6 was to be an all-wooden aircraft. The I-6 was to be ready by 1 August 1939 and the I-5 by 1 September 1939. Polikarpov was given the I-6 project, while the I-5 was to be designed by Pavel O. Sukhoi, who at the time was working under Andrey N. Tupolev. The prototype of this aircraft was given the designation ANT-12.
Neither design was ready by its deadline. The Soviet government's response was to arrest Polikarpov and around 450 other aircraft designers and engineers. Polikarpov was charged with 'infiltrating the aircraft industry as an enemy' and sentenced to death, but he was one of the lucky ones, surviving to form part of a new internal prison design bureau (KB Vnutrennaya Tyurma, or House Arrest). This group was formed in December 1929, and early in 1930 began work at No.7 Hanger of Moscow Plant No.39 'V. R. Menshinskii'. In public the prison group was referred to as the 'Central Design Bureau' or 'TsKB'.
By this point Sukhoi's original I-5 had been abandoned, either because he was busy working on heavy bombers or because of the influence of the GPU, which favoured its own 'in-house' design teams. The second I-5 project was led by Dmitriy P. Grigorovich, but this was very short-lived. Polikarpov was able to convince the head of the design bureau that his design was superior, and work switched to this third I-5.
At this point progress sped up. A full-scale mock-up was approved on 28 March 1930 and the aircraft made its maiden flight on 29 April. The new aircraft was a conventional biplane for the period. It was a single-bay sesquiplane, with a smaller lower wing. The fuselage was made of welded steel tubes, covered with Duralumin from the nose to the cockpit and with fabric after that. The upper wing was made in three parts. The central section was made of Duralumin and was attached to the fuselage using steel N-struts. The outer sections were wooden. The tail was fabric over a metal frame.
The first prototype was given the internal designation VT-11 (Vnutrennaya Tyurma-11 or Internal Prison-11), a designation that was clearly not for public consumption! It was powered by a supercharged Bristol Jupiter VII nine-cylinder air-cooled radial engine providing 450mhp. Each of the cylinders had its own cowling, a very streamlined design that did cause problems with over-heating. It was armed with two PV-1 machine guns carried in the side of the fuselage.
The second prototype made its maiden flight on 22 May 1930. This aircraft is referred to as either the second VT-11 or the VT-12. It differed from the first prototype in having a rounded tail fin and in using the un-supercharged Bristol Jupiter VI engine. The second aircraft had a higher top speed of 161mph, up from the 148mph of the first prototype, but achieved that speed at a lower altitude. Seven pre-production aircraft based on the second prototype were built in August-September 1930, but with a small headrest behind the cockpit.
The third prototype (VT-13) made its maiden flight on 1 July 1930. The propeller spinner used on the first two aircraft was removed and the individual cylinder cowling was replaced with a NACA or Townend-ring cowling. Power was provided by a 450hp M-15 engine.
The second prototype was used for State Acceptance Trials in July-August 1931, and the type was ordered into production on 13 September 1931. Production aircraft were based on the third prototype, and were built at two state aircraft factories - Zavod 21 and Zavod 1. Zavod 1 was first into production, delivering 66 aircraft in 1931 and 76 in 1932. Production there then ended, just as it was coming on line at Zavod 21, which produced ten aircraft in 1932. Full scale production really began in the following year, when 321 aircraft were built and peaked in 1934, with the last 330 aircraft. A total of 142 aircraft had been built at Zavod 1 and 661 at Zavod 21, for a total of 803 aircraft. Most aircraft were built with two machine guns, although some received four.
The I-5 entered service in the Leningrad, Ukraine and Trans-Baikal Military Districts, and by the end of 1933 was the most important fighter aircraft in Soviet Service. By the end of 1934 it had replaced most I-3s and I-4s in service and was being introduced into the navy. This was a period of rapid development in aviation, and the I-5 had a short front line career, being withdraw in 1936-37 in favour of the I-15. Most surviving aircraft were used by training schools.
A sizable number of I-5s were still airworthy when the Germans invaded the Soviet Union in 1941. With many front line aircraft destroyed in the first few days of the battle the I-5 was rushed into combat for the first time in its career, serving as an impromptu ground attack aircraft, often with two bomb racks mounted under the fuselage. Most units that were equipped with the I-5 in this period moved on to more modern aircraft early in 1942.
Twenty aircraft were converted into two-seat trainers by installing a second rear cockpit with full controls. These aircraft were built in 1934, but were apparently not used in service.
Engine: M-22 (licence built Bristol Jupiter)
Wing span: 33.6ft (upper), 24.3ft (lower)
Empty Weight: 2,079lb
Loaded Weight: 2,987lb
Max Speed: 173mph at sea level
Service Ceiling: 24,600ft
Range: 410 miles
Armament: Two 7.62mm PV-1 machine guns