In September 1951, following a meeting of Joseph Stalin with senior aircraft designers the Soviet Union issued two design specifications for helicopters, with the intent of rapidly accelerating Soviet helicopter development. The requirement for a medium-sized helicopter which could transport 12 people was issued to the Mil Design Bureau, which would result in the Mil Mi-4, while the requirement for a larger helicopter capable of transporting 24 people was given to the Yakovlev Design Bureau under Alexander Yakovlev. Prototypes of both types had to be flying within a year - 'unlimited support' was to be provided for these two programmes by the national research institutes. Yakovlev made two prototypes for flight testing, and two more for static and dynamic ground tests. The first prototype was flown on 3 July 1952. It was powered with two 1,268 kW (1,700 hp) Shvetsov ASh-82V radial engines and was built in a tandem rotor layout, which was not typical for Soviet helicopters, which soon brought it the nickname Letayushchiy Vagon (Russian: Летающий вагон) – 'the Flying Railroad Car'. The engines and transmission system were identical to the already-proven single-engine Mil Mi-4, but the Yak-24 proved to be less successful. Its engines were linked together so each could drive one or both rotors, but such an arrangement caused strong vibrations in the airframe. After the problems were partially solved, the new helicopter was ordered for production by the Soviet Air Force, which began in 1955 at Factory No. 272 in Leningrad. In July 1955, the Yak-24 was first presented to the public in Tushino, and on 17 December 1955 it set two new world payload records, lifting a 2,000 kg (4,409 lb) load to 5,082 m (16,673 ft) and 4,000 kg (8,818 lb) to 2,902 m (9,521 ft). A civilian variant for 30 passengers was the Yak-24A, produced from 1960 in small numbers for Aeroflot. It was also used as a flying crane, lifting an external load of 5,000 kg (11,023 lb). Data on the Yak-24 is inconsistent and sometimes contradictory, the exact number of helicopters produced is unknown, with estimates ranging from 40 to 100 units depending on the source of the data. The exact date of the Yak-24's decommissioning from the Soviet Air Force, and possibly Aeroflot, is unknown. A surviving Yak-24 is preserved at the Central Air Force Museum in Monino, Russia.
