08 July 2010

The Mikoyan I-320 Interceptor

One of the best aspects of being an avgeek comes when you find out about an aircraft you never knew even flew. I recently got the vastly upgraded edition of OKB Mikoyan and learned about the I-320 two-seat all-weather interceptor. From several different angles it looks a lot like the MiG-17 and it's clearly derived from that aircraft. In the late 1940s the Soviet Ministry of Defense issued a specification for a long-range interceptor- three bids were submitted from the OKBs of Lavochkin, Sukhoi, and Mikoyan. Late to the party but accepted for consideration was also a design from OKB Yakovlev. All of the designs were twin-jet aircraft.

Mikoyan's submission had the internal designation I-320/R-1 and it was designed and built in 1949- in tandem with the development of the famous MiG-15/17 family of jet fighters, accounting for its similarities in general layout. The main difference, however, was that the I-320 was a much larger and heavier aircraft with two crew and two engines. The engines were uniquely mounted in a stepped-tandem arrangement. The forward jet engine was mounted low in the forward fuselage with its exhaust semi-recessed underneath the fuselage just behind the cockpit. The aft engine was mounted in the aft fuselage just behind the wings much in the same way as the single engine of the MiG-15/17 with its exhaust at the end of the fuselage under the cruciform tail. The large nose intake had two splitters instead of the one intake splitter of the smaller MiG-15/17. The central portion of the nose intake fed the forward engine and the two lateral portions fed ducts that ran on each side of the cockpit to the aft engine.

The pilot and radar operator sat side-by-side under a broad cockpit canopy. This way both crew could scan the radar scopes and the radar operator had full dual controls and could relieve the pilot on long air patrols. The Toriy-A radar was mounted in a bullet-shaped projection above the nose intake and two 37mm cannons flanked the intake on each side of the nose.

Powered by two Klimov RD-45 engines of 5,000 lbs thrust, the I-320 was rolled out in April 1949 and made its first flight that month. Mikoyan's flight tests continued through 1950 and the aircraft was then delivered to the Soviet air defense forces, the PVO, for state acceptance and combat testing. The first version of the I-320, the R-1, didn't get accepted due to some stability issues at high speeds. Following the R-1 version in flight testing was the R-2 version which had more powerful Klimov VK-1 engines (the VK-1 was an upgraded and more reliable version of the earlier RD-45 engine used on the R-1 variant), aerodynamic refinements, and a third 37mm cannon mounted under the nose. With better performance in testing with the PVO, the R-2 got a more advanced Korshun radar to replace the earlier Toriy-A unit. During operational testing in 1951, a 37mm shell exploded in the feed belt and damaged the R-2's nose.

Mikoyan took the opportunity to try and rectify some of the stability issues dogging the I-320 as the R-2 was being repaired. As a result, it was redesignated as the R-3 version. The repaired and upgraded aircraft made its first flight on 31 March 1951 and it would make 60 flights during state acceptance trials for a total of nearly 46 flight hours. However, the I-320 never went into production as its performance was deemed inadequate. With the cancellation of Lavochkin's design, the La-200, and the crash of the Sukhoi entry, the Su-15 (the first use of the designation, not to be confused with the later and totally different Su-15 "Flagon" interceptor), Yakovlev's late entry won the competition and went into production as the Yak-25. For a while, though, Mikoyan retained the R-1 and the R-3 versions of the I-320 interceptor to develop instrument landing systems for the Soviet Air Force.

Source: OKB Mikoyan: A History of the Design Bureau and its Aircraft by Yefim Gordon and Dmitriy Komissarov. Midland Publishing, 2009, p127-130.

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