Sikorsky S-52

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 Corp; 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 (133 kW) Franklin air-cooled flat-6 piston engine.

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-6. It had a semi-monocoque fuselage of pod-and-boom arrangement with large bubble-like front greenhouse, three-blade rotor, and quadricycle fixed landing gear. The production S-52-3 (HO5S-1) incorporated a downward sloping (anhedral) 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 (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 absolute height 21,220 ft (6,468 m). 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. The S-52 is widely believed to be the first helicopter to be looped, as flown by Harold E. Thompson in 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 (against the S-52's three) 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.

Variants



 * S-52-1
 * Two seat prototype, first flown in 1948.


 * S-52-2
 * Improved three/four-seat variant.


 * S-52-3
 * Variant of the S-52-2 for the United States Navy and Coast Guard, designated H05S-1 and HO5S-1G.


 * YH-18A : Four S-52-2s for evaluation by the United States Army, two later converted into XH-39s.


 * HO5S-1
 * Model S-52-3, a United States Navy variant of the four-seat S-52-2, 79 built.


 * HO5S-1G
 * As HO5S-1 for the United States Coast Guard, eight built.


 * XH-39 : Model S-59 turboprop powered prototype modified from two YH-18As.


 * Vertical Hummingbird: Sold by Vertical Aviation Technologies of Sanford, Florida, the Hummingbird 260L is a kit-built design using the basic airframe, blades, main transmission, and tail rotor drive of the Sikorsky S-52 helicopter, but streamlined with a Bell 206 JetRanger nosecone and windshields. The Hummingbird is powered by a Lycoming VO-435—a vertically mounted, opposed six-cylinder 435-cubic-inch engine.

Operators

 * Honduran Air Force
 * United States Army
 * United States Coast Guard
 * United States Marine Corps
 * United States Navy
 * United States Marine Corps
 * United States Navy