22 November 1933:
The K-7 Disaster
The design and construction of the K-7 took five years. She had a span of 208 ft., weighed about 20 tons and accommodated 120 passengers. She was considered a big stride forward in the approach to the “all-wing” aircraft, and most of the accommodation and equipment was in the wing. A few days before the accident the existence of the K-7 was revealed to the general public by “Pravda.” It was declared that the aircraft represented a “victory of the utmost political importance,” as she was constructed entirely of Soviet steel from the mills at Duiepropetrovsk. Hitherto Russia had [imported] materials for her aircraft.
—The Aircraft Engineer, Supplement to FLIGHT, 30 November 1933, at Page 1201.
The K-7 was designed by Konstantin Alekseevich Kalinin and built over a two-year period at the Kharkov State Aircraft Manufacturing Company factory at Kharkov, Ukraine. It was intended as either a heavy bomber in military service or as a civil transport. The K-7 was the largest airplane built up to that time.
The K-7 was an effort to perfect a “wing only” aircraft. The tail surfaces were supported by tail booms. It was operated by a crew of 11 and could carry up to 120 passengers in compartments inside the wings. The K-7 was 28.00 meters (91 feet, 10.4 inches) long with a wingspan of 53.00 meters (173 feet, 10.6 inches). The extremely large wing had an area of 254.00 meters².
As originally built the airplane was powered by six 2,896.1-cubic-inch-displacement (47.459 liter) liquid-cooled, supercharged, Mikulin AM-34 single overhead cam (SOHC) 60° V-12 engines mounted in nacelles on the leading edge of the wing. The engines were rated at 750 horsepower, each, and drove two-bladed propellers. When it was determined that power was insufficient, a seventh and then an eighth engine were added to the trailing edge in pusher configuration.
The K-7 had an empty weight of 21,000 kilograms and maximum weight of 40,000 kilograms. It’s cruise speed was 204 kilometers per hour (127 miles per hour) and the maximum speed was 234 kilometers per hour (145 miles per hour). The service ceiling was 5,500 meters (18,045 feet) and the range was 1,000 kilometers (621 miles).
In military configuration, the K-7 would be armed with 20 mm cannon and 7.62 mm machineguns. A bomb load of up to 16,000 kilograms (35,274 pounds) would be carried.
The Kalinin K-7 made only 7 test flights before it crashed. 15 of the 20 persons aboard were killed. Kalinin was not among the dead, as had been report by Flight in the article above. One of the two tail booms failed. Some suggested that sabotage was involved. A government commission determined that the structure of the tailbooms was sufficiently strong, but that oscillations induced by aerodynamic flutter led to the failure.
During World War I, Konstantin Kalinin was awarded the Order of Sv.Stanislav. He had been given the Order of the Red Banner of Labor in 1935. However, during the Stalin purges, on 23 October 1938, he was executed as an enemy of the state.
© 2018, Bryan R. Swopes