Heavy Bomber First flight: 1933 Kalinin

A potential competitor to TB-4, the seven-motor K-7, was no more fortunate. Like ANT 20, it was designed in parallel in civil (passenger) and military versions. The preliminary design of the K-7 was prepared in 1931.

The car was distinguished by many non-standard design solutions. Kalinin used a two-girder fuselage and landing gear in the form of two huge cowl-powered bogies with twin two-meter wheels. At the same time, the chassis did not have any depreciation, the designer decided that it would be enough to use special low-pressure balloon wheels.

In the parking position, the fuselage was horizontal, like in modern aircraft with a nose wheel. The control was supposed to use electric servomechanisms (in fact, never created). The armament of the military version consisted of four cannons and eight machine guns, which provided spherical shelling. At the same time, from any direction the enemy met fire from three shooting points.

The arrows had to get to the installations at the ends of the tail booms on electrified carts moving along the rails. The maximum bomb load was 14 tons (with a take-off weight of 43 tons). With 6,000 kg of bombs, the K-7 had a range of 2,400 km. The bomber's crew was supposed to consist of 19 people, including the boatswain (he is also a reserve shooter and paramedic). An airship, like a naval one, was to be commanded by a commander freed from other functions. On instructions from the Air Force, he was supposed to sit in a special armored retractable wheelhouse behind the cockpit.

At first, they wanted to make the plane a six-engine, but as the design progressed, the weight grew and the designer added a seventh M-34 engine, placing it with a pusher propeller on the trailing edge of the wing in the middle between the tail booms.

In 1932, the design was completed and a full-size wooden model of a passenger car was manufactured. As a civilian, without weapons, they began to build the first prototype. A special building was built for the assembly of the K-7, which followed the contours of the aircraft. The commission that evaluated the project under the leadership of Professor N.A. Zhemchuzhina wrote in her response: "The K-7 aircraft by its design, regardless of the expected flight data from it, represents a major step forward in aircraft construction ...".

August 21, K-7 made its first flight in a circle. Further, after each flight, certain alterations followed. On September 13, an order was received to convert the prototype aircraft into a military one, and to stop work on the passenger version.

In November, it was already required to present the K-7 for state tests. Kalinin did not fit in either the timeframe or the allotted money. They did not have time to execute the order. On November 21, when measuring the maximum speed, the plane suddenly lost control, crashed into the ground and burned down. On December 29, the GUAP ordered the construction of two more experimental K-7s in the military version, taking into account the shortcomings of the first vehicle. But they soon came to the conclusion that Kalinin's plane did not have significant advantages over the more advanced MG. Work went sluggishly until 1935. Then, more than half of the second copy of the K-7 was mothballed and then dismantled.

By 1935, the priorities in equipping the Air Force with aircraft gradually changed. Interest in slow-moving giants has disappeared. The unhurried huge bomb carriers were replaced by fast and maneuverable SB and DB-3 .

Photo	Description
	Drawing K-7
	Full-size wooden model of the fuselage and center section of Kalinin's K-7. Judging by the layout, it was originally planned to install two of the six engines in the landing gear nacelles. However, this unconventional solution was subsequently abandoned.
	K-7 Kalinin in flight - the only photo that has come down to us.

• The history of designs of planes in USSR 1938-1950 /Vadim Shavrov/
• Aircraft of the country of the Soviets. 1917-1970 /Simakov B.L./