Engineering:Polikarpov I-6

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Short description: Soviet Polikarpov biplane fighter
I-6
Polikarpov I-6.jpg
Role Fighter
National origin Soviet Union
Manufacturer Polikarpov
Designer Nikolai Polikarpov
First flight 30 March 1930
Status prototype
Number built 2

The Polikarpov I-6 was a Soviet biplane fighter prototype of the late 1920s. It was designed with traditional wooden construction in comparison with the wood and steel tube construction Polikarpov I-5. Its development took longer than planned and the lead designer, Nikolai Polikarpov, was arrested for industrial sabotage, which only further delayed the project. Only two prototypes were built, as the I-5 was selected for production.

Design and development

Development of the I-6 (Istrebitel'—fighter) began in September 1928 with a deadline for delivery for the first prototype of 1 August 1929 after the first prototypes of the Polikarpov I-3 were completed. Although the new fighter shared many of the characteristics of the earlier design, including the staggered sesquiplane, single-bay, layout of the wings, it was a new design which used a nine-cylinder, single-row, air-cooled Bristol Jupiter radial engine rather the water-cooled inline engine of its predecessor. It was designed by the OSS (Russian: Otdel Sookhoputnykh Samolyotov—Landplane Department), later redesignated as OPO-1 (Russian: Opytnyy Otdel—Experimental Department) of Aviatrest ("Aviation Trust") under the supervision of Nikolai Polikarpov, head designer of the department. It was originally intended to be compared to the I-3, but this was changed to an evaluation of construction methods with the wooden construction I-6 compared to the mixed construction Polikarpov I-5. Both aircraft used the Jupiter VI engine for which a license had recently been negotiated.[1]

The I-6 had an oval-section semi-monocoque fuselage covered with 'shpon', molded birch plywood, with a small headrest faired into the fuselage, although the engine was enclosed in a metal cowling that left the cylinder heads exposed for better cooling. The two-spar wings were covered in plywood and fabric and had a Clark Y profile. Internal bracing wires were fitted to reinforce the wings. The control surfaces were framed in duralumin, but covered in fabric. The duralumin N-type struts that separated the wings, and attached the upper wing to the fuselage, had a teardrop profile. They were reinforced with steel bracing wires. The conventional undercarriage was fixed with rubber shock absorbers. The wooden propeller was given a spinner.[2] The lighter weight of the air-cooled Jupiter engine, which required neither a heavy radiator nor coolant, meant that the I-6 had an empty weight only 62% of that of the I-3.[1]

Polikarpov was arrested and imprisoned by the OGPU in September 1929 for the crime of industrial sabotage when neither the I-6 nor the I-5 projects met their stipulated deadlines,[3] and this delayed the first flight of the I-6 until 30 March 1930. The second prototype was completed shortly thereafter and both aircraft appeared in that year's May Day fly-past over Moscow. Both aircraft likely used imported engines before they were replaced by the Soviet-built copy of the Jupiter, the Shvetsov M-22. One I-6 crashed on 13 June 1930 after the test pilot bailed out, without justification, in the opinion of the Soviet aviation historian Vadim B. Shavrov.[1]

The I-5 and the I-6 were virtually identical in performance, although the I-6 took 15 seconds to complete a full circle versus the 9.5 seconds of the I-5. Both aircraft were armed with two 7.62 mm (0.3 in) PV-1 machine guns, but the production model of the I-5 was expected to be armed with four, although this proved to impose too great a penalty to the I-5's performance. The exact reasons for the selection of the I-5 over the I-6, which was debated for a full year, are not known, but likely relate to both of these factors. Curiously, Polikarpov was not informed of the selection of the I-5 until his release in 1933[1] after his initial sentence of death had been commuted to ten years of imprisonment in a labor camp.[4]

Specifications

Data from Istoriia konstruktskii samoletov v SSSR do 1938 g.[5]

General characteristics

  • Crew: 1
  • Length: 6.8 m (22 ft 4 in)
  • Wingspan: 10 m (32 ft 10 in)
  • Wing area: 20.5 m2 (221 sq ft)
  • Empty weight: 868 kg (1,914 lb)
  • Gross weight: 1,280 kg (2,822 lb)
  • Powerplant: 1 × Shvetsov M-22 9-cylinder air-cooled radial piston engine, 313 kW (420 hp)
  • Propellers: 2-bladed fixed-pitch propeller

Performance

  • Maximum speed: 280 km/h (170 mph, 150 kn)
  • Range: 700 km (430 mi, 380 nmi)
  • Service ceiling: 7,500 m (24,600 ft)
  • Time to altitude: 5,000 m (16,000 ft) in 10 minutes
  • Wing loading: 62 kg/m2 (13 lb/sq ft)
  • Power/mass: 0.245 kW/kg (0.149 hp/lb)
  • Horizontal turn time: 15 sec

Armament

  • Guns: 2 × 7.62  mm (0.30  in) PV-1 machine guns

See also

Related development

Aircraft of comparable role, configuration and era

References

  1. 1.0 1.1 1.2 1.3 Gordon and Dexter, p. 11
  2. Gunston, pp. 298–299
  3. Gordon and Dexter, p. 13
  4. Gordon and Dexter, p. 4
  5. Shavrov, V. B. (1985) (in Russian). Istoriia konstruktskii samoletov v SSSR do 1938 g. (3izd.). Mashinostroenie. ISBN 5-217-03112-3. 

Bibliography

  • Gordon, Yefim; Dexter, Keith (2002). Poliarpov's Biplane Fighters. Red Star. 6. Hinckley, England: Midland Publishing. ISBN 1-85780-141-5. 
  • Green, William; Gordon Swanborough. The Complete Book of Fighters. Godalming, UK: Salamander Books. pp. 415. 
  • Gunston, Bill (1995). The Osprey Encyclopedia of Russian Aircraft 1875-1995. London: Osprey. ISBN 1-85532-405-9.