Polikarpov TIS The Polkarpov TIS was a heavily - armed Soviet heavy fighter designed during the early 1940s . Only two prototypes were built because its intended engines proved to be too unreliable to be placed into production and the engines ' manufacturer lacked the resources to fix the problems . The second prototype crashed in September 1944 and the program was canceled after the death of Nikolai Nikolaevich Polikarpov , the chief designer of his eponymous OKB , earlier that year . Design and development . The original request for proposals for a heavy escort fighter ( " Tyazholyy Istrebitel ' Soprovozhdeniya " ) was received at the Polikarpov OKB in November 1938 , but the press of work with the I - 180 and SPB prototypes prevented any significant design work until the third quarter of 1940 . Mikhail Yangel was appointed head designer , but his job was complicated by multiple changes in the role of the aircraft from escort fighter to interceptor , dive bomber , and eventually reconnaissance . The prototype , internally designated as aircraft or TIS " A " , was a low - wing , all - metal , cantilever monoplane with two Mikulin AM - 37 engines and a twin tail . The monocoque fuselage had four ShKAS machine gun s in the nose , each with 1 , 000 rounds . The pilot and the gunner / radio - operator were seated back - to - back , separated by an armor plate , under sliding canopies . The gunner had a dorsal ShKAS on a TSS - 1 mount with 750 rounds that could be used once his canopy was slid forward . He also had a ventral ShKAS mounted below the armored floor that he could access by raising a hatch in the floor and kneeling down to fire the machine guns . The ventral gun was provided with 500 rounds of ammunition . A UBK machine gun with 400 rounds and a ShVAK cannon with 350 rounds were mounted in each wing root . Underneath the wings were two racks each capable of carrying a single FAB - 500 bomb . The wing had automatic leading edge slats and four split flaps separated by the engine nacelles . The single wheel landing gear retracted into the rear part of the nacelles , as did the tailwheel into the fuselage . The ' A ' prototype first flew in September 1941 and reached a speed of at altitude . It suffered from a lack of directional stability and the engines were unreliable and vibrated above . Factory No . 51 attempted to fix the stability problem in late September by increasing the area of the rear fins , but was unsuccessful . Flight testing continued in October in Novosibirsk , to where the LII ( — Flight Research Institute ) had been evacuated . Eliminating the stability problem took until March 1942 , although the engines remained as unreliable as ever . By the summer of 1942 it was clear that the Mikulin OKB lacked the resources to fix the problems with the AM - 37 and that the TIS would need a new engine , but the OKB ' s resources were fully utilized on the I - 185 and ITP programs and the TIS program was put on hold . Work did not resume on the TIS until the second half of 1943 , after the I - 185 had been canceled , and the Mikulin AM - 39 engine was selected . A new prototype was built , internally called the " MA " , with a completely revised armament . Two ShVAK cannon replaced the nose ShKAS machine guns and a UBT machine gun in a VUB - 1 mount replaced the dorsal ShKAS , while the ventral machine gun was removed entirely . Two Shpitalny Sh - 37 or 111P cannon replaced the wing root guns . The intended AM - 39s were unavailable and therefore two Mikulin AM - 38 Fs were used as a temporary expedient . The engine radiators were moved from the nacelles into the wings . They were fed by inlets in the leading edge and outlets on the undersurface of the wing . Operational history . The " MA " was flight tested from June to September 1944 and generally met its expected performance figures . The engines were optimized for low altitudes and the aircraft could only reach a maximum speed of and a ceiling of . It did , however , have an initial climb rate of and , on the basis of the flight tests , it was concluded that it would be capable reaching at and would take 6 . 4 minutes to reach once the AM - 39s were fitted . A brake failure on 29 June damaged the " MA " , which required a month to repair , but a crash - landing on 16 September caused by the failure of the undercarriage to extend proved to be the death knell for the TIS program . The OKB was being shut down after Polikarpov ' s death at the end of June and there was no one willing to champion the TIS .