Although, by early 1944, the VP programme was of little more than academic interest, work continued on two further "A" series prototypes, the I-224 and I-225, which had been assigned the Izdeliye designations 4A and 5A respectively. The I-225 was destined to enter flight test three months before the I-224, the first of two prototypes flying on 21 July 1944. This was powered by a Mikulin AM-42B 12-cylinder liquid-cooled Vee engine equipped with a TK-300B turbo-supercharger on its starboard side and affording 2000hp for take-off and 1750hp at 7500m. Featuring a much improved Shchyerbakov pressure cabin, a 64mm armour-glass windscreen, 8mm seat armour and an armament of four synchronised 20mm ShVAK cannon, the I-225 was of all-metal construction and was flown for the first time on 21 July 1944. On 2 August, the I-225 attained 707km/h at 8500m, but, two days later, during its fifteenth flight, the engine of the I-225 seized at an altitude of 15m and the aircraft crashed and proved irreparable. The second prototype was not flown until 14 March 1945 as the OKB was devoting priority to the I-250. During subsequent testing, the I-225-02, which was powered by an AM-42FB engine with similar ratings to the AM-42B, attained 726km/h which, at the time, was believed to be the highest speed attained by a Soviet piston-engined fighter. This distinction had been gained, however, by the M-108-powered Yak-3M.

3-View

A three-view drawing (1663 x 1273)