Konstantin Kalinin (1889-1938) had forged his history in aviation as a Red Army pilot during the Russian Civil War (1918-1920). After the war, and having joined the Communist Party (1912-1991), he established a design bureau to continue his affair. Design work resulted in several aircraft of the post-war period, all bearing his name, and this stable included the Kalinin "K-4" and "K-5". The K-5 proved of particular note for it became the most-produced Soviet airliner during its time with some 260 built from 1929 onwards. From this work came about one of the most grand of the Kalinin designs in the mammoth "K-7" - intended for the military bomber role and as a passenger airliner. However, the design only ever remained as an experimental prototype and its future was put very much in doubt after Kalinin himself was executed during Stalin's senior level purges predating World War 2 (1939-1945).
The K-7 was a giant creation, even by modern standards, measuring a length of 91 feet, 10 inches with a wingspan of 173 feet, 11 inches and a height beyond 40 feet. When empty, the airframe weighed at 54,000lbs and this ballooned to 84,000lbs when loaded. Such a beast required no fewer than six engines and a seventh was later added (in a "pusher" configuration aft of the fuselage) when the aircraft required it. The engine types were Mikulin AM-34F 12-cylinder piston engine types, each outputting at 750 horsepower and driving two-bladed propellers. The arrangement allowed for a maximum speed of 140 miles per hour and a service ceiling of 13,125 feet.
Structurally, the aircraft was given a large-area, wide-spanning wing assembly which was noticeably rounded at the wingtips. The cockpit and main crew area were contained in a centralized nacelle which utilized heavy framing for good viewing. Three engine nacelles were buried at the wing leading edges, three installations to either side of the flight deck. Twin booms made up the aft-portion of the fuselage to which these were connected by a large horizontal plane mounted under and between two vertical stabilizers. The undercarriage was fixed within large fairings held under the forward section of the booms, under the wings, and these showcased huge landing wheels. A network of struts connected the gear equipment and fairings to the aircraft structure proper. The framework of the K-7 was completed as welded steel for the required tolerances. A standard operating crew became eleven personnel and the passenger version was slated to carry some 120 passengers in addition to cargo. The military version was envisioned with gun stations at the nose, ahead of each landing gear fairing and at positions midway along the tail booms. Armament was to include both machine guns and autocannons as well as an drop ordnance capacity of over 20,000lbs.
Construction of the K-7 began during 1931 at Kharkov (Ukraine) with a first flight recorded on August 11th, 1933. Two additional prototypes were contracted for. The K-7 would complete just over a handful of test flights during her short tenure aloft before suffering damage during a test in November of 1933. With advancing technologies to be found throughout the period (the K-7 certainly looked the part of obsolete design) and political conflicts within the Communist Party, the K-7 project was formally cancelled in 1935.