Soviet Heavy Fighters 1926–1949

There were many attempts in various parts of the world to mount heavy-caliber cannons on airborne platforms, although designers rarely considered anything above 40 mm.

 

Grokhovsky G-52 (Object G-52)

If they did, the work hardly ever progressed beyond the initial design stage, as was the case with a German Ju-388 armed with a pair of 50 mm weapons. Very few types were actually built as prototypes, i.e. Mitsubishi Ki-109 with its 75 mm cannon. A small batch of the Ju-88 P-1s, another aircraft toting a 75 mm cannon, was actually manufactured and pressed into service.
In the Soviet Union the challenge was accepted by Grokhovsky design bureau. In 1934 a TB-3 bomber was modified to carry a regimental 76.2 mm M1927 gun in a ventral mount bolted to the fuselage. The arrangement was then successfully ground and flight tested with promising results.
The trials took place between December 15 and 18, 1934. During the first ground tests the crew stations were “manned” by dogs, but as soon as it became apparent that no threat to life existed, human crews took over. The truss gun mount worked well to transfer recoil energy onto the main attachment bolts, which protected the aircraft fuselage structure from significant damage. In fact, the only undesirable effects of test firings were a few torn fuselage skin rivets and slightly cracked panels near the gun’s muzzle. The damage was quickly repaired and the skin panels adjacent to the muzzle were strengthened to better withstand the blast.

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The first live airborne firing of the gun took place on December 17, 1934 with the aircraft flying at 500 m and 150 km/h. During the test Grokhovsky, who often actively participated in flight testing of his own designs, took charge of the crew consisting of Cholobayev and Afanasiev (pilots), Shmidt (navigator) and Shamirov (gunner). Post-test examination of the aircraft showed no damage to the airframe and the official test report stated that “experimental use of 76 mm field guns in airborne applications is possible”.
Delighted by their initial success, the designers didn’t rest on their laurels and quickly converted a stock TB-3 powered by M-17 engines to carry a battery of no fewer than three guns (the original mounts – minus the wheels – and recoil mechanisms were retained). After a series of trials, a 76 mm anti-aircraft gun was mounted internally in the fuselage. Although the gun’s barrel was fairly long, the fuselage had to be shortened, which led to the elimination of the navigator’s station in the nose (it was moved further back into the mid-fuselage section of the aircraft). The barrel sat between the two pilots’ seats and protruded 250 mm beyond the nose. The breech was located just forward of the wing, reaching the aft main spar. The weapon was internally attached to the main spar boxes. To protect the flight deck crew from the gun’s muzzle gases, the barrel was encased in a steel tube between the gun port in the nose and the bulkhead just forward of the flight deck. (FOTOS 6,7)
 The remaining two guns were mounted in the wings, just outside the propeller arcs of the two outboard engines. The wing-mounted weapons were short barrel variants of the 76.2 mm regimental gun, which were selected for their relatively compact size. The guns were placed in truss mounts and bolted to the wing’s main spars. The wing’s structure was reinforced in the area immediately around the weapons.
The modified aircraft, officially designated “Object G-52”, was ready for trials by mid-1935. Each gun was manned by a loader handling a supply of 12 rounds (for wing-mounted guns) or 20 rounds of ammunition (internally-mounted cannon). There was no integrated firing system. Instead, in front of each gun loader there was a panel with an indicator light that went on every time the aircraft commander deemed it necessary to fire. Synchronized firing of the guns was therefore impossible under those conditions. While the fuselage-mounted gun could be fired with a degree of accuracy, the wing-mounted weapons could only achieve one-half of that. Every time the wing guns were fired, the second round inevitably missed its mark due to a yawing moment caused by the recoil of the first cannon. In other words, if in a two-round salvo the first gun to fire was the internal cannon, followed by one of the wing guns, both rounds had a fighting chance of reaching their targets. If, on the other hand, the first gun to fire was one of the wing-mounted weapons, only one round would ever land on or near the target. The designers were hoping to remedy the situation by introducing an elaborate system of strings and pulleys which could be centrally activated by the gunner, but the work stalled and came to nothing.

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“Air Cruisers”