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R-4 / H-4

The H-4 designation was initially applied to the the Vought-Sikorsky R-4 that flew in 1948. The R-4 was the world's first production helicopter and the Air Force's first service helicopter. The original military model, the XR-4, was developed from the famous experimental VS-300 helicopter, invented by Igor Sikorsky and publicly demonstrated in 1940.

As early as 1910, while still in Europe, Igor Sikorsky had designed and built a coaxial helicopter with a 25-horsepower engine driving two 16-foot contra-rotating rotors through a concentric shaft. Unfortunately, the machine could lift only its own weight. In 1919, six years after building the world's first successful four-engine aircraft, Sikorsky emigrated from Russia and settled in Connecticut where he continued to pursue the manufacturing of large land and seaplanes . Then, in 1938, he again turned his talent to the field of rotary-wing aircraft and began the most difficult construction of all helicopter designs - the single rotor. While his past experiments had been with the coaxial configuration, Sikorsky preferred the single lifting rotor with a small anti-torque tail rotor . He considered it to be the best rotor arrangement for a helicopter rather than the more popular side-by-side or tandem lifting rotors.

The United Aircraft (Vought-Sikorsky) VS-300 was an experimental helicopter designed and piloted by Igor Sikorsky. Igor's nightmare, constructed of struts, metal tubing, sheet metal, and a pulley belt system, could be radically redesigned overnight. The final version bares little resemblance to the original. Using this craft, Sikorsky perfected cyclic pitch control of the main rotor and the use of the tail rotor to balance torque and provide logitudinal control, the method of control used in all modern helicopters.

The VS-300 made the first true controlled flight of a helicopter December 8, 1941. Realizing the potential value of Sikorsky's new helicopter, the U.S. Army Air Corps awarded a contract to Vought-Sikorsky on 10 January 1941 for an experimental machine, the XR-4, which was to be built on an expanded scale of the VS-300.The Air Corps was acting under a 1939 interservice agreement which gave the Army the initial responsibility for the development of all US helicopters.

The VS-300 was the prototype for three Sikorsky R-series helicopters. Exactly one year later the first R-4 flew at the Sikorsky plant, with subsequent improved versions, the R-5 and R-6, taking to the air in August and October of 1943. Enlarged in size to suit a 450-horsepower engine, the R-5 eventually proved to be the most successful of the three types. The R-4 and R-6 were powered by 175- and 245-horsepower engines, respectively. The R-series helicopters each had a three-bladed main rotor and a three-bladed vertical controllable-pitch anti-torque and steering tail rotor. In 1948, the US Army Air Force (USAAF) changed the designation from R (Rotorcraft) to H (Helicopter).

The Sikorsky (model S-47) R-4 (British name Hoverfly MK I), was the first mass-produced military helicopter. The XR-4 (VS-316A), first flown in 14 January 1942, had a fabric covered tubular steel fuselage. Model numbers ranged from A through C. The XR-4 made its initial flight on January 13, 1942 and as a result of its successful flight tests, the AAF ordered 3 YR-4As and 27 YR-4Bs for service testing and flight training. The YR-4B was a two-place side-by-side, observation, reconnaissance, and MedEvac helicopter, with one external litter. Of these 30, one went to Burma and one to Alaska, while several others were assigned to the U.S. Navy, U.S. Coast Guard and British Royal Navy. They showed such promise that the AAF ordered 100 R-4Bs.

During the early part of World War II, the Navy Department initially visualized the helicopter as an aid in combating German submarines which were seriously menacing United States and Allied shipping. Original plans called for the helicopters, piloted by Coast Guard flyers, to accompany ocean convoys and operate as scout aircraft from platforms constructed on the merchant ships. The Navy accepted delivery of its first helicopter, the R-4 (HNX-1), on 16 October 1943 and assigned it to the United States Coast Guard, Coast Guard Air Station, Floyd Bennett Field, Brooklyn, New York.Testing of the helicopter's suitability as an antisubmarine weapon began the following month. At first, the HNS-1 appeared promising, but open sea shipboard trials in January 1944 showed the helicopter to be too difficult to handle and the operation was deemed too hazardous with the present state of the helicopter's development.

The R-4 was first used in combat in May 1944. In a letter to a friend, Col. Philip G. Cochran, Commanding Officer (CO) of the 1st Air Commando Group, wrote "Today the 'egg-beater' went into action and the damn thing acted like it had good sense."

The model R4-B entered service in 1945. Many were fitted with twin pontoons for use aboard ships or over water. A YR-4, equipped with pontoons, made the first helicopter deck landing on the S.S. Bunker Hill on May 6, 1943. An Army YR-4B performed the first military/MedEvac rescue behind enemy lines in Burma on April 25-26, 1944. Taxed-to-the-limit, powered by only a 185 hp Warner R550-1 engine, it required the YR-4B pilot four trips over a two day period to rescue the downed Stinson L-1 Vigilant pilot and three British casualties. R-4Bs were used by the U.S. Army Air Force, U.S. Navy (as the HNS-1), U.S. Coast Guard, as well as the British Royal Air Force and the Royal Navy (as the Hoverfly MK I). The R-4B was replaced by the versatile Sikorsky (model S-51) R-5D shortly after World War II.

This aircraft is unrelated to the later HO-4 (later OH-4A), Bell model 206 JetRanger, which was designed as an entry in the Light Observation Helicopter [LOH] competition.

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