I must say that the decision of the placement of weapons demanded significant changes in the design of the aircraft. Was planning to reinforce the front spar by replacing the set braces by a continuous wall with a hole for the installation of the gun. The impact could be reduced by mounting the muzzle brake but the barrel was too close to the hull of the bomber; a jet of hot gases could damage it. The root ribs needed to be redone, providing a window for ammunition handling and removal of cartridges. Also going to do the rib hatch for access to the breech of the gun from the bomb Bay.
To free up space under the instrument, it was necessary to reduce the width centralnogo gas tank. The volume was decreased by almost half. The cannon from the tank must be separated by fire partition. The top and bottom of the wing skin was going to cut hatches for access to the gun.
Mount cannon in the wing was designed by an engineer Grigoriev. The first version, made in late 1936, recognized a failure. Rigidity, according to the calculations, was lower than required. In early 1937 began a new design. It turned out to be much tougher, but has become much harder: 55 kg against 24 kg. This weighting was considered unacceptable. Used in the design of the gun carriage forgings replaced riveted nodes. It is possible to reduce weight up to 31.5 kg Around the same time came to the conclusion that the trunks necessary to push over the nose of the aircraft, abandoning the protective steel plating.
Since the gun was mounted motionlessly, the targeting was provided by the pilot, turning the aircraft. When planning to use semi-automatic optical sight PPN-3 and PPN-4. The unit is semiautomatic, which was corrected, was supposed to be the Navigator, and sighting pipe would mount two – pilot and Navigator. Why the second is not clear, because the Navigator could not change the position of the machine to restore it on the target.
But the modification is SB with guns AJP never came to physical implementation. Work on it ceased in late 1937 or early 1938 More successful was a competing project with cannons ShVAK, which was created in the 7th division of TSAGI under the leadership of engineer Schmidt. The first version called 5-Tokarev (aka 5-SWISS), prepared in 1937, the Number “5” indicated the number of guns. All five guns were in the bomb Bay, their trunks slightly beyond the contour of the sheathing and closed a total fairing. To protect the plating on the trunks davincibles steel pipe – covers.
Ammunition in detachable metal tape housed in boxes and filing sleeves. Each gun had one box with 100 rounds. In the sleeves because they had a different length was from 20 to 50 rounds per gun.
To protect the lining of the forward fuselage in front of the trunks, made of anodized aluminum was replaced by stainless steel thickness 0,8 – 1 mm. Reloading of guns was carried out with compressed air, fire control – electric.
The model ANT-46 denaturaciei without guns, instead of with an extra machine guns
The installation weighed 500 kg. According to the original plan 5-ShVAK was mounted when necessary on any SB, turning it into a multi-seat fighter or heavy bomber.
System 5-ShVAK was installed in the fuselage section SAT and shot back in the dash since April 11, 1937 To April 28, fired only one gun at a time, and 7 September for the first time fired a volley with the whole battery of five guns.
Development of 5-ShVAK was a 4-ShVAK. Guns it was one less – removed the one that was in the center. 4-ShVAK was also distinguished by the improved performance of several nodes. Weight turned lower and are quite reasonable – about 470 kg with ammunition. Ammo slightly decreased to 100 – 130 rounds per gun. 4-ShVAK actually mounted on the aircraft, which was taken to the landfill NIPAW in Noginsk. The guns were adjusted so that the converging gave the fan runs. In Noginsk fired on the ground from January 13, 1938
System 5-ShVAK in the dash, 1937
The total rate reached 3000 RDS./min, second salvo ensured the defeat of any aircraft of the time.
Factory testing installation on NIPAW ended successfully. Representatives of the air force required a significant increase in ammunition – up to 250 – 300 rounds per gun.
But further work on 4-ShVAK stalled. Perhaps this was due to the rapid progress in aviation. High-speed bomber SB, for which the system was created, by 1938, had already begun to lag in its data from the new fighters and some bombers of the West. The rate began to do the new project heavy fighters with higher performance data.
The last case of equipment of the bomber SB cannon armament refers to the November 1940 IN NIPAW the aircraft used as a flying test bench for 23-mm gun MP-6 (Taubina-Baburin). The gun was located in a fairing under the fuselage. Thus equipped the two cars and the end of 1941 were tested on the ground and in the air. Their further fate is unknown.