The Piasecki H -21 Workhorse (factory name: PD -22 ) was a transport helicopter with two main rotors in tandem configuration. He could carry a two-man crew to fully equipped 20 soldiers and was used inter alia in the Vietnam War.
The development of the H -21 goes to the model Piasecki PV -3 back, better known under the U.S. Navy designation HRP -1 Rescuer (first flight in March 1945). 1949 was followed by the derived version of PV -17 ( HRP -2 Rescuer ), which had a completely new hull from all metal, while the power plant was (440 kW ( 600 hp) Pratt & Whitney R -1340 ) unchanged.
On April 11, 1952, derived from the HRP -2 H -21 (factory designation PD -22) first flew. With its 845 kW radial engine it did have almost twice as much engine power as the HRP -1. The serial production began in 1954 with the H -21A, Piasecki as the " Workhorse " ( workhorse ) refers. By the end of production in 1959, still a B and a C version was produced, which were equipped with a more powerful engine. In the U.S. armed forces of the H -21 became known as " Shawnee ", which was, as usual, borrowed from a Native American tribal name.
When the Piasecki Aircraft Corporation was renamed in May 1956 in Vertol Aircraft Corporation, the internal name of this helicopter by PD -22 changed in Model V- 43rd The term reform of the U.S. armed forces then took the identifier CH -21 ( Cargo Helicopter, Eng. Helicopter for transport ) with itself. Of the U.S. soldiers he got the nickname " Flying Banana " (flying banana, due to the curved shape of the hull ) or "Army Mule " (Army Mule in the style of " Workhorse ").