Kalinin K-7 was a heavy experimental aircraft designed and tested in the Soviet Union in the early 1930s. K-7 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 (7 ft 7 in) thick 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 V.Nemecek states in his book "The History of Soviet Aircraft from 1918" that there was only one further pusher engine added - this agrees with the specification supplied below.
K-7 first flew on 11 August 1933. Then on 21 November 1933 the aircraft crashed due to structural failure of one of the tail booms, killing 14 people aboard and one on the ground. Although two more prototypes were ordered in 1933, the project was canceled in 1935 before they could be completed
In 1930s the Russian army was obsessed with the idea of creating huge planes. At that time, they were proposed to have as many propellers as possible to help carry those huge flying fortresses into the air. Jet propulsion has not been implemented yet.
Specifications (K-7)
General characteristics
Capacity: 120 passengers in civilian configuration
Length: 28 m (91 ft 10 in)
Wingspan: 53 m (173 ft 11 in)
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
Performance
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)
