|Role||Heavy bomber/Civilian transport|
|National origin||Soviet Union|
|Status||Destroyed in crash|
The Kalinin K-7 (Ukrainian: Калинін К-7) was a heavy experimental aircraft designed and tested in the Soviet Union in the early 1930s. It was of unusual configuration with twin booms and large underwing pods housing fixed landing gear and machine gun turrets. In the passenger version, seats were arranged inside the 2.3-meter thick (7 ft 7 in) wings. The airframe was welded from KhMA 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. However, Nemecek states in his book that there was only one further pusher engine added; this agrees with the specification below.
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 biggest aircraft built before the jet age. It had one engine less than the B-52, having an unusual arrangement of six pulling on the wing leading edge and one pushing at the rear.
The K-7 first flew on 11 August 1933. The very brief first flight showed instability and serious vibration caused by the airframe resonating with the engine frequency. The solution to this was thought to be to shorten and strengthen the tail booms, little being known then about the natural frequencies of structures and their response to vibration. The aircraft completed seven test flights before a crash due to structural failure of one of the tail booms on 21 November 1933. However, there appeared recently some speculations in the Russian aviation press about the role of politics and competing design office of A. N. Tupolev, suggesting possible sabotage. The accident killed 14 people aboard and one on the ground. Although two more prototypes were ordered in 1933, the project was cancelled in 1935 before they could be completed.
In 1938 Kalinin was executed as an enemy of the state during the Stalinist purges.
Specifications (K-7) 
Data from Shavrov (1985)
- Crew: minimum 11
- Capacity: 120 passengers in civilian configuration
- Length: 28 m (91 ft 10 in)
- Wingspan: 53 m (173 ft 11 in)
- Height: 12.4m estimated to top of engine shell ()
- Wing area: 454 m² (4,886.8 ft²)
- Empty weight: 24,400 kg (53,793 lb)
- Loaded weight: 38,000 kg (83,776 lb)
- Powerplant: 7 × Mikulin AM-34F V-12 piston engines, 560 kW (750 hp) each
- Maximum speed: 225 km/h (121 knots, 140 mph)
- Service ceiling: 4,000 m (13,123 ft)
- Wing loading: 84 kg/m² (17 lb/ft²)
- Power/mass: 103 W/kg (0.06 hp/lb)
See also 
- Gunston, Bill (1995). The Osprey Encyclopedia of Russian Aircraft 1875–1995. London: Osprey Publishing. ISBN 1-85532-405-9.
- Nemecek, Vaclav (1986). The History of Soviet Aircraft from 1918. Willow Books. ISBN 978-0002180337.
- Shavrov, V. B. (1985). Istoriya konstruktskii samoletov v SSSR do 1938 g. (3 izd.) (in Russian). Mashinostroenie. ISBN 5-217-03112-3.
- Shavrov (1985)
- Nemecek (1986)
- Bill Yenne. The World's Worst Aircraft.
- "Huge Soviet Plane Crashes, Killing 14". New York Times. November 23, 1933.
|Wikimedia Commons has media related to: Kalinin K-7|
- Airplane-Giant K-7 – translation of an article from Russian Modelist-Constructor magazine, December 1989
- Video on YouTube – mostly fake pictures, with the only seemingly real one (of K-7?) at 0:54 in the video