Late in 1942 work was well advanced at Mikoyan factories on a parallel fighter referred internally as the "A" Series. They were prototypes that Mikoyan hoped to fullfil a VP (an order from Soviet Air Ministry) requirement for a high altittude interceptor. The first of those, the I-220, was a new design of mixed construction with a metallic part forward of the cockpit and a wooden monocoque aft and wings with steel and auxiliary spars with spruce outer pannel ribs. The first prototype rolled out from production line in June 1943 and flew for the first time the next month, in July 1943. It was initially powered by a Mikulin AM-38F engine rated at 1700hp and was armed with two 20mm ShVAK cannons. In January 1944 it was refitted with a Mikulin AM-39 engine rated at 1800hp with fly tests continuing until August 1944. A second prototype was built in September 1944 and was armed with four 20mm ShVAK cannons, being the first fighter armed with such number of such cannons. The official designation given by the Soviet Air Ministry was MiG-11.
The second series of the "A" fighters was the I-221, which was fitted with a turbo-supercharged Mikulin AM-39A engine rated at 1700hp and with a centrifugal compressor, paired with a TK-2B turbo-superchargers developed by the TsIAM. That setting allowed a maximum ceiling of 13000m (42650ft). Unlike its most direct predecessor, the I-220, it was of dural construction instead of wooden monocoque and the outer wing pannels were also extended. It was armed with two 20mm ShVAK cannons placed above the engine. It flew for the first time on 2nd December 1943 but the programme came to an abrupt ending when, after some tests, one of the piston fractured causing the fighter to crash.
The next in the series, the I-222, was powered by a Mikulin Am-39B-1 engine rated at 1750hp with a TK-300B supercharger on its port side. It was armed with two 20mm ShVAK cannons mounted in a cowl above the nose. It had the same wooden monocoque structure of the previous I-220 and used a pressurized cockpit, designed by Shchyerbakov of welded dural sheet with inflatable rubber seals and pressurized by air tapped from the compressor. The cockpit was the first to be air conditioned in any Soviet fighter ever. It flew for the first time on 7th May 1944, but, although a mass production was expected, the course of the war made the need for a high altittude fighter pointless as the Luftwaffe had lost the high-altittude bombing capability. Priorities, therefore changed and, even if development programme continued, all proposals for series manufacturing were discarded.
The work continued on that "A" series with the I-224 and I-225, named internally as 4A and 5A respectively, even if the VP was just of mere scientifical interest as there wasn't any need for this type of fighter. The I-225 was expected to be tested three months before the I-224 and therefore, the first of two prototypes flew for the first time on 21st July 1944. It was powered by a Mikulin AM-42B 12-cylinder liquid-cooled vee engine equipped with a TK-300B turbo-supercharger on the starboard side, yielding a power of 2000hp. It featured a Shchyerbakov pressure armoured cockpit and an armament of four 20mm ShVAK cannons. It was made entirely out of metal and shortly after the first flight, it achieved the speed of 439mph (707Km/h) at 8500m (27885ft) high. Unfortunately, two days later, after many flight tests, the engine seized at just 15m (50ft) high and the aircraft crashed beyond repair. it wasn't until 14th March 1945 that the second prototype flew for the first time, as the Soviet Air Ministry was prioritizing the I-250. During subsequent testing, the I-225-02, powered by a Mikulin AM-42FB engine, attained a speed of 451mph (726km/h), which at the time it was believed to be the fastest speed ever achieved by a Soviet fighter. However, that record went for the Yakovlev Yak-3M.
The last of the "A" series, flew for the first time on 20th October 1944 and was powered by a Mikulin AM-39B engine which yielded 1750hp of power, equipped with a TK-300B turbo-supercharger on the starboard side. It was armed with two 20mm ShVAK cannons placed in a cowling above the engine and featured a particular exhaust system with four aft-facing ejection "chimneys". It gained an altittude of 14100m (46260ft) high durin its brief flight testing programme which ended when a supercharger malfunctioned and set the engine in an uncontrollable fire.
All these prototypes, from I-221 to I-225, were assigned the designation of MiG-7 by the Soviet Air Ministry.
Sources:
1. Salamander Books - The Complete Book of Fighters
2. http://www.airwar.ru/enc/fww2/mig7.html (translated)
3. http://www.airwar.ru/enc/fww2/i220.html (translated)
4. Signal Squadron - Aircraft In action 204 - Early Mig Fighters in Action
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