Yakovlev Yak24 "Horse"

In late 1940s, Yakovlev was impressed by the Sikorsky S-51 helicopter. The OKB resembled the S-51 as the Yak-100. It was placed into competition with the Mil Mi-1 but lost a fly-off to the Mi-1. In 1951, Yakovlev and Mil were called by Stalin to create two new helicopters, one to carry a 1200 kg load and the other twice load as much. Both prototypes would be ready in one year. Mil agreed to tackle the smaller machine that became Mil-4, and Yakovlev took the larger that led to the Yak-24 program. In order to build the first prototype extremely quickly, Yakovlev mirrored Piasecki tandem rotor design. The four prototypes were rapidly completed and flight test was began as early as July 1952. It became the largest helicopter in the world when built. Full scale production for Soviet armed forces began in 1955. The later prototypes were publicly demonstrated at Tushino airport, and it was received NATO designation Horse. The Yak-24 served in Soviet Air Force until the far more powerful Mil-6 Hook entered production in 1959. Later Yakovlev scaled up the Yak-24 to the huge Yak-60, but it was again lost to Mil V-22.