The Kalinin K-7 was a heavy experimental aircraft built in the Soviet Union in the early 1930s. Designed by World War I aviator Konstantin Kalinin, with a wingspan close to that of a B-52 and a much greater wing area, the K-7 was one of the largest aircraft built before the jet age. It had an unusual (to say the least) configuration with twin booms and large under-wing pods housing fixed landing gear and machine gun turrets. In the passenger version, seats were arranged inside the 7.5-foot thick wings. Think about that for a moment, and picture yourself getting on an airplane and walking into the wing to find your seat.
The airframe was welded from chrome-molybdenum steel. The original design called for six engines in the wing leading edge. But when the projected loaded weight was exceeded, two more engines were added to the trailing edges of each wing, one right and one left of the central passenger pod. (V. Nemecek, however, states in his book, The History of Soviet Aircraft from 1918, that only one extra pusher engine was added to each wing.) In either case, this was one strange airplane.
The K-7´s very brief first flight on 11 August 1933 revealed instability and serious vibration caused by the airframe resonating with the engine frequency. The solution to this “flutter” was to shorten and strengthen the tail booms, little being known then about the natural frequencies of structures and their response to vibration.
On 21 November 1933 during a speed test on the eleventh flight, the port tail boom vibrated, fractured, jammed the elevator and caused the giant aircraft to crash, killing 14 people on board and one on the ground. Although two more prototypes were ordered, the project was canceled in 1935 before they could be completed.
Undaunted by this disaster, Kalinin’s team began construction of two further K-7s, but the vicissitudes of Stalin’s Russia saw the project abandoned. In 1938, Kalinin was arrested on trumped-up espionage and sabotage charges and executed. To fail on an expensive project under Stalin was particularly hazardous to one’s health.
Although the pictures accompanying this post may appear to be of different K-7s, they aren’t. I didn’t realize this until I mentioned the airplane to my brother Sam, an aeronautical and astronautical engineer.
Take a close look at the third picture and note the addition of cannons. I wondered aloud to Sam about what it would be like to be sitting in the thing when they were fired. He’s familiar with the aircraft, said the pictures showing the cannons were “Photoshop Specials,” and assured me the K-7 could never get off the ground in that configuration.
But you know, in spite of that inconvenience, Stalin might have liked the airplane better . . .