The Sikorsky S-52 was a utility helicopter developed by Sikorsky Aircraft in the late 1940s. It was used by the U.S. Navy, Marines, and Coast Guard. The S-52 was the first US helicopter with all-metal rotor blades. A two-seater, it was developed into the four-seat S-52-2. It was designated HO5S-1 by the U.S. Navy and Marine Corps; HO5S-1G by the Coast Guard; and YH-18A by the Army.
Design and development
Sikorsky Aircraft began designing the S-52 in late 1945. The prototype S-52, first flown in 1947, was a two-seater and used a 178 hp Franklinair-cooledflat-sixpiston engine. The two-seat version was modified into the S-52-2, a four-seat helicopter using a 245 hp Franklin O-425-1 air-cooled flat-six. It had a semi-monocoque fuselage of pod-and-boom arrangement with a large bubble-like front greenhouse, a three-blade rotor, and quadricycle fixed landing gear. The production S-52-3 incorporated a downward sloping v-tail stabilizer. It also had sliding doors on the right forward and left rear sides, and a vertically split front bubble, allowing the left half to swing open in a clamshell fashion. The engine was placed at the aft end of the cabin and was canted forward 30 degrees to couple with the clutch and transmission. The pilot-in-command occupied the right front seat. The first American helicopter to have all-metal rotor blades, the prototype set several speed and height records in 1948, including 129.6 mph on a 3 km course, 122.75 mph on a 1 km circuit, and an absolute height of 21,220 ft. It was capable of hover out of ground effect at 5,900 ft or 9,200 ft in ground effect. The S-52 was the first helicopter to be flown in a loop, as flown by Harold E. Thompson on May 19, 1949. The S-52 also served as the basis of the turbine-powered S-59, which as the XH-39, competed for and lost the contract that produced the Bell UH-1 Iroquois. This aircraft differed in having a four-bladed rotor and retractable tricycle gear.
Operational history
The Navy operated the aircraft as a utility type, and it was used by the Marines for observation and scouting in Korea, where the HO3S proved more popular. Four S-52s were evaluated by the United States Army for utility use in 1950, as the YH-18A, but not purchased in quantity. Many of the former military HO5S-1 units were demilitarized, rebuilt, and licensed as civil aircraft by Orlando Helicopters, who acquired the parts inventory from Sikorsky.
