The Yak-9 represented further development of the successful Yakovlev Yak-7 fighter, a production version of the lightened Yak-7DI, taking full advantage of the combat experience with its predecessor. Greater availability of duralumin allowed for lighter construction which in turn permitted a number of modifications to the basic design.

The State trials took place from January to April 1944. They revealed a clear superiority in top speed over all other fighters in service on the Eastern front, up to 6,000 m (19,685 ft). The aircraft was simple to fly and stable. Unfortunately, the problems with the M-107A engine and all the M-105 variants from which it derived, persisted: power plant overheating, oil leaks, loss of pressure in climbs, intense vibrations, burningout of spark plugs and a short engine life. Despite these defects, the Yak.9U/VK-107 was ordered into production in April 1944, with 1,134 machines produced by December 1944. [7]

The first unit to use the Yak-9U, between 25 October and 25 December 1944, was 163.IAP. Pilots were ordered not to use the engine at combat speed since this reduced its life to two or three flights only. Nevertheless, in the course of 398 sorties, the unit claimed 27 Focke-Wulf Fw 190As and one Bf 109G-2, for the loss of two Yaks in dogfights, one to flak and four in accidents. The Yak-9U contributed greatly to Soviet air superiority, and the Germans avoided the Yaks “without antenna mast”. [7]

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Normandie Niemen Volume Iii Histoire Du Groupe De Chasse.

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