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The Sikorsky R-4 was the first production single rotor helicopter. Introduced to the U.S. Army Air Corps in 1941, it served as a rescue and reconnaissance aircraft during World War II.
Igor Sikorsky began to work on helicopter design in 1939, after convincing United Aircraft (now United Technologies Corporation) to provide a small amount of funding for helicopter development. United Aircraft supported this work, and also merged Vought and Sikorsky together to reduce costs. (They were separated at the end of 1942.) The helicopter, designated VS-300, made its first short flight on September 14, 1939 (Fig. 1). After much trial and error, this machine would become the first practical single rotor helicopter and the prototype for most helicopters flying today.
The U.S. Army and the R-4
The success of the VS-300 led to an order from the U.S. Army Air Corps for a production version in January 1941. This helicopter would have two seats and serve as a trainer and observation aircraft. It was designated as the VS-316 by Vought Sikorsky, and as the R-4 by the Army. Twice the weight of the VS- 300, the R-4 would have a larger main rotor, larger tail rotor, and more powerful engine, as well as a two-place cockpit. Design of the R-4 was difficult because development of the VS-300 was continuing at the same time, and design decisions had to be postponed until the results of VS-300 flight testing were available.
The prototype XR-4 made its first flight on January 13, 1942, (Fig. 2) just as war fever was building in the United States following the bombing of Pearl Harbor. After development flight tests by Sikorsky, the helicopter made an epic five-day, 761-mile flight from Sikorsky's factory in Bridgeport, Connecticut, to Wright Field (now Wright Patterson AFB) near Dayton, Ohio, for Army Air Corps evaluation in May 1942.
Initial evaluations were successful, but somewhat strange to the military pilots who had never seen an aircraft that could lift off vertically and fly sideways and backwards. Eventually, service test versions (YR-4B) with a somewhat larger rotor and more powerful engines were ordered for operational evaluation.
After successfully demonstrating their usefulness, a production order for R-4B helicopters was awarded to Sikorsky Aircraft. These were distributed to the...