Sikorsky S-52

Sikorsky Aircraft began designing the S-52 in late 1945.Harding 1990, p. 228. 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. The prototype pioneered the use of all-metal main and tail rotor blades along with offset flapping hinges for the main rotor, which allowed greater maneuverability and would become a trademark Sikorsky design feature. The aircraft was granted a Civil Aeronautics Authority type 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.{{cite web|title= S-52 |last1= Devine |first1= Vinny |url= http://www.sikorskyarchives.com/S-52.php |date= June 2012 |website= Sikorsky Product History |publisher= Igor Sikorsky Historical Archives |access-date= 3 August 2022}}

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 an absolute height of 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 was the first helicopter to be flown in a loop, as flown by Harold E. Thompson on 19 May 1949.{{cite book|title=Guinness World Records 2019|date=22 January 2019|publisher=Portable Press, 2019|isbn=9781684127184|pages=164}}

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. 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 replacing the earlier tricycle arrangement. The production S-52-3 (HO5S-1) incorporated a downward sloping (anhedral) v-tail stabilizer.FAA type certificate 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.Flight manual, page 5 The pilot-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 during medevac missions.

The S-52 also served as the basis of the turbine-powered S-59 (originally designated S-52-5 or YH-18B), 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.

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.Rawlins, p. 44. 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.

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

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 search and rescue, and were placed in storage beginning in April 1954.

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.{{cite web |last1=Wallace |first1=Brent |last2=Swartz |first2=Kenneth I. |url=https://evtol.news/news/orlando-helicopters-electric-sikorsky-s-52 |title=Orlando Helicopter's Electric Sikorsky S-52 |work=Vertiflite |date=January–February 2022 |access-date=4 August 2022}} 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.

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 {{convert|60|hp|kW|abbr=on}} 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 {{convert|240|hp|kW|abbr=on}} 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.

A restored HO5S-1—then one of the only flyable examples of the type—is featured in the 2022 film Devotion.{{cite magazine |last=Busha |first=Jim |date=November 2022 |title=Bond of Brothers |url=https://cdn.coverstand.com/53731/764215/fb058ba9f90dacce5abcdcfddf3b8771cdc778e5.1.pdf |url-access=subscription |magazine=EAA Sport Aviation |location=Oshkosh, Wisconsin |publisher=Experimental Aircraft Association |access-date=November 7, 2022 |pages=52–63}}{{cite press release |last=Wiseman |first=Andreas |date=February 1, 2021 | url=https://www.jetwhine.com/2021/02/devotion-bearcats-corsairs-real-moviemaking-oh-my/ | title=Devotion: Bearcats, Corsairs, & Real Moviemaking Oh My! |publisher=Black Label Media |access-date=November 7, 2022}}

File:S-52-3.jpg

;S-52-1

:Two-seat prototype, first flown in 1948. Four built.

;S-52-2

:Improved three/four-seat variant.{{cite magazine|url=http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%201024.html|magazine=Flight International|date=7 August 1953|page=178|title=Sikorsky S-52 Series – A Successful Little Helicopter and its Background}}

;S-52-3

:Variant of the S-52-2 for the United States Navy and Coast Guard, designated HO5S-1 and HO5S-1G.Andrade 1979, p. 195

;YH-18A

:Four S-52-2s for evaluation by the United States Army, two later converted into XH-39s.Andrade 1979, p. 119

;HO5S-1

File:Sikorsky HO5S‑1.jpg]]

: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 turboshaft-powered prototype modified from two YH-18As.Andrade 1979, p. 122

;Experimental Electric S-52

:Model S-52-2 battery-powered prototype using four 60-hp (45-kW) alternating current (AC) starter/generators and fourteen 72-Volt lead acid batteries producing 240–300 hp (180– 225 kW) for 10 minutes.{{cite web|url = https://evtol.news/news/orlando-helicopters-electric-sikorsky-s-52|title = Orlando Helicopter's Electric Sikorsky S-52 |magazine=Vertiflite |date=Jan 2022 |first1=Brent |last1=Wallace |first2=Kenneth |last2 =Swartz|access-date = 30 October 2022}}

;Vertical Hummingbird

:Sold by Vertical Aviation Technologies of Sanford, Florida, the Hummingbird 300L 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 an IO-540 — a vertically mounted, opposed six-cylinder air-cooled engine.{{cite web|url = https://vertical-aviation.com/specification|title = Hummingbird 300L |access-date = 30 October 2022}}

File:Marine HO5S-1 of VMO-6 evacuates wounded in Korea 1953.JPEG

;{{HON}}

• Honduran Air ForceHagedorn 1986, p. 63.

;{{USA}}

• United States Army
• United States Coast GuardPearcy 1991, pp. 292–293.
• United States Marine Corps{{Citation needed|date=January 2013}}
• United States Navy{{Citation needed|date=January 2013}}

File:Sikorsky HO5S-1 3-view line drawing.png

{{Aircraft specs

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|gross weight lb=2400

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|max takeoff weight lb=2700

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|eng1 name=Franklin 6V6-245-B16F

|eng1 type=air-cooled six-cylinder horizontally-opposed piston engine

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{{aircontent

|related=

• Sikorsky XH-39
• Vertical Hummingbird

|similar aircraft=

|lists=

• List of civil aircraft
• List of military aircraft of the United States
• List of rotorcraft

}}

{{reflist}}

• FAA Type Data Certificate, Helicopter Specification No. 1H2, rev. 3; 7 July 1961.
• GAA Rotorcraft Flight Manual for Model S-52-3 Helicopter, Publication No. SA4045-10 Register 2, Sikorsky Aircraft Division of United Aircraft, 1952.
• Bridgman, Leonard. Jane's All The World's Aircraft 1951–52. London: Sampson Low, Marston & Company, Ltd, 1951.
• Donald, David, ed. "Sikorsky S-52". Encyclopedia of World Aircraft. Etobicoke, Ontario: Prospero Books, 1997. {{ISBN|1-85605-375-X}}.
• Hagedorn, Daniel P. "From Caudillos to COIN" Air Enthusiast, Thirty-one, July–November 1986. pp. 55–70.
• Harding, Stephen. "Sikorsky H-28". U.S. Army Aircraft Since 1947. Shrewsbury, England: Airlife, 1990. {{ISBN|1-85310-102-8}}.
• Pearcy, Arthur. U.S. Coast Guard Aircraft Since 1916. Shrewsbury, England: Airlife, 1991. {{ISBN|1-85310-118-4}}.
• Polmar, Norman, and Floyd D. Kennedy, Jr. Military Helicopters of the World. Annapolis, MD: Naval Institute Press, 1981. {{ISBN|0870213830}}.
• Rawlins, Eugene W. Marines and Helicopters 1946 - 1962. History and Museums Division Headquarters USMC, 1976. {{ISBN|9781500102852}}. https://www.usmcu.edu/Portals/218/Marines%20and%20Helicopters%201946-1962%20%20PCN%2019000306900.pdf

{{Commons category|Sikorsky S-52}}

• [http://www.globalsecurity.org/military/systems/aircraft/h-18.htm H-18 page on GlobalSecurity.org]
• [http://www.helis.com/database/model/1141/ HELIS.com Sikorsky S-52/H-18/HO5S Database]

{{Sikorsky Aircraft}}

{{USN helicopters}}

{{USAF helicopters}}

Category:1950s United States helicopters

Single engine aircraft

Category:1950s United States military utility aircraft

S-052

Category:Aircraft first flown in 1947