The Sikorsky S-52 is a utility helicopter developed by Sikorsky Aircraft in the late 1940s. It was used by the U.S. Navy, Marine Corps, and Coast Guard.[2] The S-52 was the first US helicopter with all-metal rotor blades. Initially a two-seater, it was developed into the four-seat S-52-2 and S-52-3. It was designated HO5S-1 by the U.S. Navy and Marine Corps, HO5S-1G by the Coast Guard, and YH-18A by the U.S. Army, and was used extensively by civil operators after being retired by the military.

S-52
S-52-3.jpg
Sikorsky S-52-3
Role
Helicopter
Manufacturer
Sikorsky Aircraft
First flight
12 February 1947
Introduction
April 1951
Status
In service
Primary users
United States Navy
United States Army
United States Marine Corps
United States Coast Guard
Number built
93[1]
Variants
Sikorsky XH-39
Vertical Hummingbird
Design and development

Operational history
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The U.S. Navy operated the aircraft as a utility type and it was used by the Marine Corps for observation and scouting in the Korean War.[8] The Marine Corps also extensively used the HO5S for medevac in that war, as it could carry two wounded marines on stretchers internally, which was considered an advantage over the Bell HTL, which could only carry stretchers externally.[4]

Four S-52s were evaluated by the U.S. Army for utility use in 1950, as the YH-18A, but not purchased in quantity.[3] YH-18A serial number 42-2890 was later rebuilt as an XH-39 prototype.[4]

In September 1952, eight S-52-3 aircraft were delivered to the U.S. Coast Guard as the HO5S-1G, but were found to be too slow, small, and short-ranged for the air-sea rescue mission, and were placed in storage beginning in April 1954.[4]

Many former military S-52 aircraft were demilitarized, rebuilt, and licensed for civil use, and in 1964, Orlando Helicopter Airways (OHA) acquired the type certificate and parts inventory from Sikorsky.[4][9] In the early 1960s, OHA founder Fred Clark had used a fleet of three S-52 aircraft for powerline inspections and to shuttle VIPs and members of the news media between Orlando, Florida, and the Kennedy Space Center at Cape Canaveral. OHA would eventually acquire at least 17 S-52 aircraft, which were extensively used for long-distance powerline inspection flights—a role that Clark found the S-52 to be well suited for, as it was more comfortable to fly and had a longer range than the then-prevalent Bell 47.[9]

In 1981, a NASA scientist contacted Clark, proposing to develop a proof of concept electric-powered crewed helicopter. OHA had a hurricane-damaged former Marine Corps HO5S-1 in storage, and using NASA funds, the aircraft was rebuilt with four salvaged 60 hp (45 kW) electric starter motors from disused turboshaft engines along with fourteen 72V lead-acid batteries. In 1983, the aircraft was briefly flown under onboard electric power, but proved to have motor synchronization problems. OHA obtained additional funding from NASA, hoping to replace the troublesome four-motor setup with a single 240 hp (180 kW) torpedo motor that would eliminate the transmission, but was unable to obtain the desired motor from the U.S. Navy; OHA consequently stored the aircraft indefinitely in 1984 and the project was eventually abandoned. Although ultimately unsuccessful, the electric-powered HO5S-1 is believed to be the first crewed eVTOL aircraft to have flown using onboard battery power rather than a cable tethered to a ground-based power supply.[9]

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