HO5S/H-18 (Sikorsky S-52) Helicopter

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.[2] 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.

Sikorsky Aircraft began designing the S-52 in late 1945.[3] The prototype S-52, first flown in 1947, was a two-seater and used a 178 hp (133 kW) Franklin air-cooled flat-six piston engine.[2]
The two-seat version was modified into the S-52-2, a four-seat helicopter using a 245 hp (183 kW) 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,[1] a three-blade rotor, and quadricycle fixed landing gear. The production S-52-3 (HO5S-1) incorporated a downward sloping (anhedral) v-tail stabilizer.[4] 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.[5] The pilot-in-command occupied the right front seat.
The first American helicopter to have all-metal rotor blades,[1][2] the prototype[2] set several speed and height records in 1948, including 129.6 mph (204.2 km/h) on a 3 km (2 mi) course, 122.75 mph (197.54 km/h) on a 1 km (1,100 yd) circuit, and an absolute height of 21,220 ft (6,468 m).[1] It was capable of hover out of ground effect at 5,900 ft (1,798 m) or 9,200 ft (2,804 m) in ground effect.[1] The S-52 is widely believed to be the first helicopter to be looped, as flown by Harold E. Thompson in 1949.[citation needed]
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 (against the S-52’s three) and retractable tricycle gear.[1]

The Navy operated the aircraft as a utility type, and it was used by the Marines for observation and scouting in Korea,[6] 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.[3]
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.

Two-seat prototype, first flown in 1948.[7]
Improved three/four-seat variant.[7]
Variant of the S-52-2 for the United States Navy and Coast Guard, designated H05S-1 and HO5S-1G.[8]
Four S-52-2s for evaluation by the United States Army,[3] two later converted into XH-39s.[9]