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An experimental aircraft, designated Tu-2P , was created to determine the effectiveness of the use of large-caliber aircraft cannons, intended mainly to combat bombers. The first such RSHR weapon with interchangeable barrels of 57 and 45 mm was created by designers S.E. Rashkov, V.E. Shentsov and S.S. Rozanov. The length of the gun was so great that its breech with ammunition had to be placed in the Tu-2 cargo compartment in the center section area. Since it was a flying laboratory, the rest of the bomber's armament was dismantled, reducing the crew to two people, while the navigator was located in the rear cockpit. Factory flight tests of the gun took place from December 9, 1946 to February 28, 1947. In the spring of the same year, the aircraft was transferred to the Air Force Research Institute. The tests took place at the Research Institute from April 21 to May 30, 1947. Upon completion, it was concluded that: "1. Aviation automatic 57 mm cannon RShR-57 designed and manufactured by OKB-16 of the Ministry of Armament has passed state flight tests and can be recommended for arming fighter-interceptors ... ", however, the aircraft did not go into production - live firing showed low efficiency of the use of large-caliber aircraft cannons.
By the summer of 1948, OKBL-46 of the Ministry of Armaments under the leadership of E.V. Charnko, the Ch-21P automatic aircraft gun of 57/76 mm caliber was created. To test it, the Tu-2 bomber base in OKB-30 A.P. Golubkov created an experimental aircraft for the installation of two such guns. The aircraft, designated Tu-2P, was intended to determine the effectiveness of the use of this weapon when firing at air and ground targets, as well as the behavior of the machine in the air.
Cannons with electro-pneumatic control of firing and reloading were installed parallel to the building horizontal of the fuselage. In this case, the barrels of the guns passed under the floor of the front cockpit. For shooting, they provided an ASP-1N sight, fixed on a telescopic rod.
The muzzle velocity of the cannon projectile, depending on the caliber (57 or 76 mm), was 1087 or 920 m / s, respectively, with a high-explosive fragmentation projectile (OFZT) weighing 2.485 and 4.735 kg. Rate of fire ≈ 80 and 70 rounds per minute, respectively. The cartridges weighed 6.5 and 9 kg, respectively. The ammunition load of the guns did not exceed 15 rounds per barrel.
Factory flight tests of the Tu-2P took place from January 18, 1949 and continued until the end of September 1949 and did not reveal any anomalies in the aircraft's behavior. Tests showed no deformation of the airframe after firing. The Tu-2P was approved for state tests in early December 1949, while the main gun 4-21P remained in prototypes.
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