I-222 (3A) - a high-altitude fighter-interceptor with a pressurized cabin, an AM-39B engine and two TK-2B turbochargers. The aircraft was designed and built on the basis of the I-221 fighter, but had a pressurized cockpit and improved visibility to the rear hemisphere. The aircraft was presented for testing on March 15, 1944. An experimental AM-39B No.01 engine was installed on the aircraft. In addition, an air-to-air radiator was installed in the cooling system of the air entering the engine carburetor instead of the water-air radiator, which made it possible, despite the installation of a pressurized cabin, to prevent an increase in the flight weight of the aircraft. The shell of the pressurized cabin was made of AMTs aluminum alloy. During production, the mechanical sealing system of the lantern was replaced with a pneumatic one. The maximum design speed was supposed to be 689 km / h at an altitude of 12,500 m, and a practical ceiling of 13,000-14,000 m. The armament included two synchronous 20-mm SSh-20 cannons with 100 rounds of ammunition.

On April 28, 1944, the I-222 fighter was transferred to the LIS of plant No.155, and on May 7, the first flight was performed on it. The originally installed three-bladed propeller of the AV-5L series was later replaced by the four-bladed AV-9L-230. In the period from July 26 to August 9, 1944, during tests, the vehicle was purged in a full-scale TsAGI wind tunnel. Based on the results of the purge, the aircraft was modified: new slats and an increased VVR were installed. On September 1, I-222 performed a test flight with some improvements. During the factory flight tests, 39 flights were performed. However, the I-222 did not reach the specified height due to the drop in oil and gasoline pressure, as well as the unstable operation of the propeller group. The fighter confidently ascended only an altitude of 12000 m.The altitude limit of the AM-39B No.01 engine with two TK-2B turbochargers in the climb mode at the second speed of the PTsN was 11,300 m.

On October 19, 1944, the I-222 fighter was transferred to the LII to continue testing, where the aircraft made three flights, after which on January 26, 1945, the engine was removed from it after develop a resource and sent to plant No 300. In July, after a bulkhead, the engine was installed on the plane, but a drop in oil pressure to an altitude of 6,000 m was noted, as a result of which, after five flights, the engine had to be removed again and sent to the factory, from where it never returned. In the absence of a new engine, work on the aircraft was discontinued.

LIS - Letno Ispytatel'naya Stantsiya - letno ispytatel'naya stantsiya - Flight Test Station

LII - Letno Issledovatel'skiy Institut - Flight Research Institute

TsAGI - Tsentral'nyy aerogidrodinamicheskiy institut - Central Aerohydrodynamic Institute

NKAP - Narodnyy Komissariat Aviatsionnoy Promyshlennosti - People's Commissariat of Aviation Industry

TK - Turbo Kompressor - Turbo Compressor

PTsN - Privodnoy Tsentrobezhnyy Nagnetatel' - Driven Centrifugal Supercharger

I-224 (4A) is a high-altitude fighter-interceptor with a pressurized cabin, an AM-39FB engine and a TK-300B turbocharger developed by OKB-300. In addition to the I-222 fighter, a second copy of the aircraft with a pressurized cabin was built, which was named I-224 and code "4A". In contrast to the I-222, the I-224 fighter was equipped with an experienced forced AM-39FB No. 02 engine and one TK-300B turbocharger on the right exhaust manifold, as well as a four-blade propeller AV-9L-26B with a diameter of 3.5 m and a blade width of 400 mm. The armament consisted of one synchronous 20 mm B-20 cannon with 100 rounds of ammunition. The overload provided for the installation of a second B-20 gun with the same ammunition.

The aircraft was taken out of production on August 4, 1944. Lead engineer K.P. Kovalevsky and test pilot G.M. Shiyanov were appointed to carry out factory tests in accordance with the order of the NKAP No. 562 of September 15, 1944. The first flight of the I-224 took place on September 16, 1944. During the factory tests, only 5 flights were performed, since on September 28 the aircraft crashed during an emergency landing due to engine failure. The repair lasted until December 23 due to the late delivery of the new motor. Meanwhile, in accordance with the order of the NKAP No. 615 of October 19, 1944, the aircraft was ordered to be transferred to the LII.

On December 28, 1944, the I-224 fighter, after the completion of repairs, was transferred to the LII to continue testing. In February 1945, the motor was replaced due to the appearance of metal chips in the oil filter. In July, the aircraft reached an altitude of 13,700 m. At the same time, the pilot did not note any shortcomings in the operation of his units and pressurized cabin. However, after replacing the TK-300B with a new one, improved in altitude, the engine began to shake at nominal and medium operating modes. The reason for this was the surge of the turbocharger. In this regard, in November, the TK-300B was replaced with the former one, with which the I-224 climbed to 13,700 m.

The tests were completed on October 26, 1945. The pressurized cabin was fully worked out on the aircraft and the practical ceiling of 14100 m was reached, which exceeded the GKO task by 100 m. The altitude limit of the engine at the second speed of the PNC in the climb mode was 11600 m.

In January 1946, repairs were completed on the aircraft after operation at the LII and prepared for transfer to state tests at the State Research Institute of the Air Force. Also, at the request of plant No. 300, in order to eliminate the surge of the turbocharger, the suction pipe from the air-to-air radiator to the carburetors was finalized. A controlled damper was installed on it for bypassing air into the atmosphere when a TC surge appeared in flight. However, soon at plant No. 300 they decided to replace the AM-39FB engine with the AM-44 engine with direct injection. The new engine was received on July 31, but due to its lack of knowledge, it was not possible to present the I-224 for state tests. By Resolution of the Council of Ministers No. 2548-1065 of November 30, 1946, work on the I-222 and I-224 aircraft was stopped.

Photo	Description
	Drawing I-224
	I-224

I-225 (5A) is a high-speed high-altitude fighter with an AM-42FB engine and a TK-300B turbocharger developed by OKB-300. At the beginning of 1944, OKB-155, on its own initiative, carried out a modification of the I-220 No.02 fighter for an experimental AM-42B engine with a TK-300B turbocharger. On the plane, which received the name I-225 and the code "5A", an air-to-air radiator was also installed to cool the air entering the engine carburetor, and a three-blade propeller AV-5LV-22A with a diameter of 3.6 m.

The I-225 fighter was put out of production on May 9, 1944 and transferred to the LIS of Plant No.155. The first flight on the aircraft was completed on July 21, 1944. Lead engineer A.G. Brunov and test pilot A.P. Yakimov were approved for factory tests in accordance with the order of the NKAP No.447 of July 24, 1944. On tests, the I-225 reached a speed of 580 km / h near the ground in the nominal mode and 721 km / h at an altitude of 8850 m. The aircraft gained an altitude of 5000 m in 4.5 minutes, and 8000 m in 7.9 minutes. At maximum and combat modes, speed and rate of climb were not determined. However, at the very end of the factory tests, the I-225 crashed. On August 9, 1944, during the determination of the altitude limit at the nominal and maximum engine operating modes at an altitude of 7000-7500 m, a fire broke out due to a break in the main connecting rod of the second cylinder of the AM-42B No.02 engine. At an altitude of 2000-1500 m, pilot A.P. Yakimov left the burning vehicle, while receiving burns.

Drawing I-225 No.1

The second copy of the I-225 fighter was completed in production on February 20, 1945. The first flight was completed on March 14, 1945. Initially, it was planned to install the AM-43 engine on the aircraft, but due to its absence, they put AM-42FB No.01 on it. In addition, the aircraft was equipped with an AMTK-1A turbocharger, an air-to-air radiator, a three-bladed AV-5L-22V propeller with a diameter of 3.6 m, and a pressurized cabin. The armament consisted of four synchronous 20 mm SSh-20 cannons with 100 rounds of ammunition. Experienced guns SSh-20 were planned to be replaced with serial B-20s in the future.

To conduct factory flight tests of the second copy of the I-225, in accordance with the order of the NKAP No.157 of April 17, 1945, the lead engineer A.G. Brunov and test pilot A.P. Deev were approved. However, on April 26, in the 16th flight, the aircraft crashed while flying from a forced landing near the village of Luzgarino in the Shatura region. During the takeoff run, the right landing gear began to retract prematurely, the pilot immediately removed the gas, but the plane nevertheless jumped out onto the arable land, turned 180 °, and the rear fuselage broke off from hitting the ground. Despite serious damage, it was decided to restore the aircraft. In June 1945, after replacing the destroyed fuselage with a new one, the I-225 No.02 left the assembly shop. On factory tests of the second copy of the I-225, a maximum speed of 560 km / h was reached at the ground and 726 km / h at an altitude of 10,000 m, which the aircraft gained in 8.8 minutes. The ascent time to a height of 5000 m was 4 minutes.

Photo	Description
	Drawing I-225 No.2

After replacing the engine, which had exhausted its resource, and a number of control flights to check its altitude limit, the aircraft was sent to the Civil Aviation Research Institute of the Air Force on October 30, 1945 for state tests. However, in the Civil Code of the Research Institute of the Air Force, they could not start flight tests of the I-225 No.02, since a surge of the turbocharger installed on the vehicle was detected in the control flight. In early January 1946, the turbocharger was removed to replace the diffuser and intake pipe from the air-to-air radiator to the carburetors. On the branch pipe, as well as on the I-224, a controlled damper was installed to bypass air into the atmosphere when a surge of the TK appeared in flight.

On January 27, 1946, during the flight, a shaking of the AM-42FB No.04 engine was detected in nominal mode up to an altitude of 6000 m, after which the No.300 plant decided to replace it with an AM-44 engine with direct injection. The flights were interrupted, and on February 13 the aircraft was transferred to factory No.155 to replace the engine, which arrived from factory No.300 only on April 6, 1946. In May, they completed the installation of the AM-44 engine and fired cannon weapons at the shooting range.

The first flight of the I-225 fighter with a new power plant took place on May 31, 1946. At the request of the No.300 plant, the aircraft was tested in June before it was handed over to the State Research Institute of the Air Force to continue state tests, in June the AM-44 engine with a turbocharger was tested AMTK-1A. However, during these tests, a number of significant engine defects were revealed, as a result of which it was not possible to present the I-225 aircraft for the continuation of state tests. By Resolution of the Council of Ministers No. 493-192 of March 11, 1947, work on the aircraft was stopped.

Bibliography

• History of aircraft designs in the USSR, 1938-1950. /V.B. Shavrov/
• Aircraft OKB im. A.I. Mikoyan / AiK No. 9 2000 Evgeny Arseniev/
• MiG-3 fighter /Aviation collection 2015-01. N.V. Yakubovich./
• MiG-3 fighter / Wings 2008-02. Mikhail Maslov./
• MiG-3 fighter - lost opportunities / Aviation and Cosmonautics 2013-05. Andrey Ivitsky./