 The NKAP had asked Mikoyan to begin preliminary design work on a high @-@ altitude interceptor in January 1944 , but ordered two prototypes of an all @-@ metal interceptor using the VRDK for testing in February and March 1945 . The aircraft was to reach an altitude of 5 @,@ 000 m ( 16 @,@ 000 ft ) in 4 @.@ 5 minutes with full power and 5 @.@ 5 minutes using the piston engine alone . Its maximum speed was to be 810 km / h ( 500 mph ) at 7 @,@ 000 m ( 22 @,@ 966 ft ) with full power and 700 km / h ( 430 mph ) at 7 @,@ 000 m ( 22 @,@ 966 ft ) using the VK @-@ 107 by itself . Its intended armament was one 23 mm ( 0 @.@ 91 in ) autocannon and two 12 @.@ 7 mm ( 0 @.@ 50 in ) machine guns . To assist Mikoyan TsAGI was ordered to provide help with aerodynamic and stress calculations and to test a full @-@ size mockup in their wind tunnel in one month 's time . TsIAM was ordered to deliver three VRDK engines with 9 @-@ <unk> ( 2 @,@ 000 lbf ) at 7 @,@ 000 m ( 22 @,@ 966 ft ) with a specific fuel consumption of 1 @,@ 200 kg ( 2 @,@ 600 lb ) per hour . The plane was designated I @-@ 250 by the NKAP ; but the internal OKB designation was N. 
