Heavy Escort Fighter
The new version, the TIS(MA), differed not only in having the more powerful engines, but also in armament. In the F1 forward fuselage section two 20mm ShVAK guns with 120 rounds each replaced the four ShKAS machine guns. The wing centre section mounting included yel another two guns of 45mm 111P-type with 45 rounds per gun (the prototype had two 37mm guns). The lower mounting for a ShKAS machine gun was removed, and in the aft part of the canopy the standard upper gun mounting of a VUB-1 bomber was installed, carrying a UBT machine gun with 200 rounds.
The powerplant installation was designed tor AM-39s but, owing to the non-availability of these engines, AM-38Fs from the I1-2 attack aeroplane were installed, supposedly as a temporary measure.
Compared with the first version of the fighter, the radiators were moved from the engine nacelles into the wings, where they were housed in special tunnels with leading edge air intakes and outlets in the undersurface of the wing. The altitude tolerance of AM-38F was only 5,400ft (1,650m), which made it impossible to achieve high speeds at altitude. The TIS(MA)'s speed at ground level 319mph (514km/h), and at its critical altitude the speed was 332mph (535km/h). The service ceiling was only 21,600ft (6,600m). but its rate of climb at sea level at a flying weight of 18,2351b (8.280kg) was 13.5m/sec, which was not bad for a twin-engine fighter. The performance differed from the estimated figures by no more than 1.5%, and on the basis of the flight test data it was concluded that the TIS with AM-39s could reach a maximum speed at 23,500ft (7,150m) of 403mph (650km/h) and climb to 16,400ft (5,000m) in 6.4 minutes. During the flight tests undertaken by Gavrilov from June to September 1944, 15 flights were made with a total flying time of about nine hours. Damage caused to the fighter by a brake failure on 29th June was repaired in a month, but the TIS was ill-fated. On 16th September 1944 it was damaged again during a belly-landing caused by non-lowering of the undercarriage. It was not restored. Its chief designer, Nikolay Polikarpov, had died earlier, on 30th July 1944.