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Nudelman-Suranov NS-45
The Nudelman-Suranov NS-45 was an enlarged version of the Soviet Nudelman-Suranov NS-37 aircraft autocannon. It was evaluated for service on 44 Yakovlev Yak-9K aircraft during World War II, but proved to stress the airframes too much. The NS-45 was also mounted on the prototype Tupolev Tu-1 night fighter after the end of World War II.
== Design and development ==
The NS-45 was created as a result of a July 1943 decision of the State Defense Committee to arm Soviet fighters with 45 mm autocannons. As with the 37 mm autocannons already installed in some Soviet and lend-lease single-engine fighters, the intended method of installation of the 45 mm gun was to have its barrel pass through the engine block and the empty propeller shaft, in this case that of the Yak-9. Consequently, the main difficulty in designing the 45 mm autocannon was the limitation imposed by the engine blocks available for this aircraft. Accounting for the diameter of the 45 mm shell, the Yak-9 engine blocks only allowed a wall thickness of 4 mm for the new gun's barrel,〔 which was almost half the thickness of the barrel wall of the NS-37.〔 (Another source gives 55 mm as the diameter of opening in the engine reducer shaft, resulting in a wall thickness of 3.75 mm for the NS-45 barrel relative to 7.1 mm for the NS-37 barrel, both measured at this spot which was approximately 61 cm away from the muzzle.)
The decision of the Defense Committee was followed by a short design competition between Soviet designs bureaus OKB-15 and OKB-16. The former proposed an enlarged version of their unreliable Shpitalny Sh-37; although they made a prototype that passed factory tests in a LaGG-3, their 45 mm gun was not accepted for state trials because of the known issues with the Sh-37 design. OKB-16 presented an enlarged version of their successful NS-37.〔 The recoil force of the NS-45 peaked at seven tons,〔 a force roughly 40% greater than that experienced with the NS-37 (about 5.5 tons).〔 Consequently, the NS-45 was fitted with a muzzle brake—a first in Soviet aircraft-gun design.〔Широкорад А.Б. (2001) ''История авиационного вооружения'' Харвест (Shirokorad A.B. (2001) ''Istorya aviatsionnogo vooruzhenia'' Harvest. ISBN 985-433-695-6) (''History of aircraft armament''), pages 130-132〕
Concomitantly with the gun design, a new cartridge was developed using the standard 45 mm fragmentation shell of the 21-K anti-aircraft gun. (This projectile had a tracer that burned for eleven seconds and was fitted with the MG-8 contact fuse.) The total length of the new cartridge was limited to the same value as for the NS-37 ammunition—328mm.〔 In order to accommodate the larger shell, the case body (brass) was necked up and also slightly reduced in length from 195 mm of the NS-37 ammunition to 185 mm.〔 The resulting 45 mm cartridge weighted 1.93 kg, of which 1.065 kg was the weight of its shell.〔 The muzzle velocity of the NS-45 was 780 m/s and its rate of fire was around 260-280 rounds per minute.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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