Polikarpov I - 6 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 ( — Landplane Department ) , later redesignated as OPO - 1 ( — 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 . 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 . 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 . 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 , 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 . 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 gun s , 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 after his initial sentence of death had been commuted to ten years of imprisonment in a labor camp .