| S-52 | |
|---|---|
.jpg) | |
| U.S. Army YH-18A in testing | |
| Role | Helicopter Type of aircraft |
| 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 |
TheSikorsky S-52 is a utilityhelicopter developed bySikorsky Aircraft in the late 1940s. It was used by theU.S. Navy,Marine Corps, andCoast 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 designatedHO5S-1 by the U.S. Navy and Marine Corps,HO5S-1G by the Coast Guard, andYH-18A by theU.S. Army, and was used extensively by civil operators after being retired by the military.
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)Franklinair-cooledflat-sixpiston engine.[2] The prototype pioneered the use of all-metal main and tail rotor blades along with offsetflapping hinges for the main rotor, which allowed greater maneuverability and would become a trademark Sikorsky design feature. The aircraft was granted aCivil Aeronautics Authoritytype certificate on 25 February 1948. The S-52 was soon developed into the S-52-1 with the installation of a more powerful 245 hp (183 kW) Franklin engine.[4]
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 ofground effect at 5,900 ft (1,798 m) or 9,200 ft (2,804 m) in ground effect.[1] The S-52 was the first helicopter to be flown in a loop, as flown byHarold E. Thompson on 19 May 1949.[5]
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, which was moved slightly to the rear to accommodate the enlarged cabin.[4] It had a semi-monocoquefuselage of pod-and-boom arrangement with a large bubble-like front greenhouse,[1] a three-blade rotor, and quadricycle fixedlanding gear replacing the earlier tricycle arrangement.[4] The production S-52-3 (HO5S-1) incorporated a downward sloping (anhedral) v-tail stabilizer.[6] 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.[7] Thepilot-in-command occupied the right front seat, while the front clamshell allowed two patients on stretchers to be loaded into the left side of the aircraft, where they could be attended by a medic in the right rear seat duringmedevac missions.[4]
The S-52 also served as the basis of the turbine-poweredS-59 (originally designated S-52-5 or YH-18B[4]), which as the XH-39, competed for and lost the contract that produced theBell UH-1 Iroquois. This aircraft differed in having a four-bladed rotor (against the S-52's three) and retractable tricycle gear.[1]
The U.S. Navy operated the aircraft as a utility type and it was used by the Marine Corps for observation and scouting in theKorean 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 theBell 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 number42-2890 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 forsearch and rescue, 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 betweenOrlando, Florida, and theKennedy Space Center atCape 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-prevalentBell 47.[9]
In 1981, aNASA scientist contacted Clark, proposing to develop aproof 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 disusedturboshaft 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 crewedeVTOL aircraft to have flown using onboard battery power rather than a cable tethered to a ground-based power supply.[9]
A restored HO5S-1—then one of the only flyable examples of the type—is featured in the 2022 filmDevotion.[10][11]
Data fromJane's All The World's Aircraft 1951–52.[20]
General characteristics
Performance
Related development
Related lists
