Discusses the Sikorsky R-4 rotor helicopter designed by Igor Sikorsky. History of the helicopter; Impact of the first working unit on the design of the helicopter in 2003; Modernization of the VS-300 model to the upgraded R-4 model by the U.S. Army Air Corps; Success of the prototype XR-4 model's developmental test flights and long range trip; Structural design and material composition; Design evolution and analysis.