|R-5 / H-5|
|Sikorsky YH-5A at National Museum of the United States Air Force, retired from Eglin AFB, Florida, in March 1955.|
|First flight||18 September 1943|
|Primary users||United States Army Air Forces
|Number built||over 300|
|Developed from||Sikorsky R-4|
The Sikorsky H-5, (aka R-5, S-51, HO2S-1, HO3S-1) (R-5 until 1948; company designation VS-327) was a helicopter built by Sikorsky Aircraft Corporation, formerly used by the United States Air Force, and its predecessor, the United States Army Air Forces, as well as the United States Navy and United States Coast Guard (with the designations HO2S and HO3S). It was also used by the United States Post Office Department. In December 1946, an agreement was signed between the British company Westland Aircraft and Sikorsky to produce a British version of the H-5 or S-51, to be manufactured under license in Britain as the Westland-Sikorsky WS-51 Dragonfly. By the time production ceased in 1951, more than 300 examples of all types of the S-51/H-5 had been built.
Design and development
The H-5, originally designated the R-5 by the military, was designed to provide a helicopter having greater useful load, endurance, speed, and service ceiling than the Sikorsky R-4. The R-5 differed from the R-4 by having an increased rotor diameter and a new, longer fuselage for two persons in tandem. Larger than the R-4 or the later R-6, the R-5 was fitted with a more powerful Wasp Junior 450-hp radial engine, and quickly proved itself the most successful of the three types. The first XR-5 of four ordered made its initial flight on 18 August 1943. In March 1944, the United States Army Air Force ordered 26 YR-5As for service testing, and in February 1945, the first YR-5A was delivered. This order was followed by a production contract for 100, outfitted with racks for two litters (stretchers); only 34 were actually delivered.
Sikorsky soon developed a modified version of the YR-5A, the S-51, featuring a greater rotor diameter, greater carrying capacity and gross weight, which first flew on 16 February 1946. With room for three passengers plus pilot, the S-51 was initially intended to appeal to civilian as well as military operators, and was the first helicopter to be sold to a commercial user. Eleven S-51s were ordered by the USAF and designated the R-5F, while ninety went to the Navy as the HO3S-1, commonly referred to as the 'Horse'.
In Britain, Westland Aircraft began production in 1946 of the Westland-Sikorsky S-51 Dragonfly for the Royal Navy and the Royal Air Force, all of which were powered by a 500 hp Alvis Leonides engine. This gave an improved top speed of 103 mph and a service ceiling of 14,000 ft. In total, 133 Westland-Sikorsky Dragonfly helicopters were built. A considerably modified version was also developed by Westland as the Westland Widgeon, but the type was never adopted for service.
The U.S. Navy ordered four S-51s "off-the-shelf" from Sikorsky in late 1946 for use in the Antarctic and Operation Highjump, placing them into naval inventory as the HO3S-1. Carried aboard the seaplane tender USS Pine Island, on Christmas Day 1946 an HO3S-1 of VX-3 piloted by Lieutenant Commander Walter M. Sessums became the first helicopter to fly in the Antarctic. Having proved its capabilities, the initial naval HO3S-1 order was followed by subsequent purchases of an additional 42 aircraft in 1948. The Navy equipped several warship classes with HO3S-1 utility helos, including aircraft carriers, seaplane tenders, icebreakers, Des Moines-class cruisers, and Iowa-class battleships. By February 1948, the Marine Corps had equipped HMX-1, its first regular Marine Helicopter Transport Squadron, with six HO3S-1 aircraft. With a passenger load of only three lightly dressed persons, the HO3S-1s were primarily operated in the utility role by the marines; for the transport role, an additional nine tandem-rotor Piasecki-built HRP-1 helicopters were later added to the squadron. Eventually, the U.S. Navy would acquire a total of 88 HO3S-1 (S-51) helicopters.
Twenty-one Sikorsky YR-5As were fitted with a third seat, rescue hoist, auxiliary external fuel tank, and nosewheel; the United States Navy evaluated three, as the HO2S-1. Five more were converted as dual-control YR-5Es.
Several H-5Hs were converted in 1949 to a unique medical-evacuation role, with casualty stretchers loaded sideways through blister-hatches on the side of the fuselage. The back stretcher station was located just forward of the tail boom and the main stretcher station was located behind the crew cabin. The forward stretcher station could accommodate two casualties, who were accessible to the medic in flight, while the back stretcher station handled only one, not accessible to the medic during the flight. Very little information is known about the operational use of this modification by the USAF, this being abandoned shortly after tests in 1950.
The R-5 had been designated under the United States Army Air Force system, a series starting with R-1 and proceeding up to about R-16. In 1947 with the start of the United States Air Force, there was a new system, and many aircraft, but not all, were redesignated. The R-6 became the H-6. The United States Army broke off with its own designation system in the 1950s, resulting in new designations for its helicopter projects (such as the HO-6). In 1962 under the new tri-service system (see 1962 United States Tri-Service aircraft designation system), many navy and army aircraft were given the low numbers. Under the 1962 system, the low H numbers were given to new aircraft. For example, H-6 was given to the HO-6, which entered service as the Cayuse.
During its service life, the H-5/SO3S-1 was used for utility, rescue, and mercy missions throughout the world, including flights during Operation Highjump in the Antarctic. While the extra power of the H-5 made it significantly more useful than its R-4 and R-6 cousins, the H-5/HO3S-1 suffered, like most early small tandem-seat single-rotor machines, from center of gravity problems. As a matter of routine, the helicopter was equipped with two iron-bar weights – each in a canvas case – one of 25 lb (11 kg) & one of 50 lb (23 kg). Flying with no passengers – both weights were placed forward alongside the pilot. With three passengers, both weights were normally placed in the baggage compartment. However, in conditions of high ambient temperatures, which reduced lift due to the lowered air density, all weights were jettisoned. If the weights could not be recovered later, pilots on future missions were forced to utilize rocks or other improvised weights next to the pilot after offloading three passengers, or else travel at a very slow 25 knots (46 km/h; 29 mph).
The H-5/SO3S-1 gained its greatest fame, during the Korean War when it was called upon repeatedly to rescue United Nations pilots shot down behind enemy lines and to evacuate wounded personnel from frontline areas, before being replaced in most roles by the H-19 Chickasaw. In 1957, the last H-5 and HO3S-1 helicopters were retired from active U.S. military service.
- Prototype based on the VS.372 with two seats and tailwheel landing gear, powered by a 450hp R-985-AN-5, five built
- As the XR-5 with minor modifications, 26 built including two to the United States Navy as the HO2S-1
- Production rescue model with provision for two external stretchers, 34 built later re-designated H-5A
- Modified R-5A, not built
- Modified R-5A, not built
- Modified R-5As with nosewheel landing gear, rescue hoist, twenty conversion later re-designated H-5D
- Modified YR-5As with dual controls, five conversions later re-designated YH-5E
- Civil model S-51 four-seaters bought in 1947, 11 built later re-designated H-5F
- R-5A redesignated
- R-5D redesignated
- YR-5E redesignated
- R-5F redesignated
- Four-seater as H-5F with rescue equipment, 39 bought
- As H-5G with updated equipment, 16 built
- Two YR-5As to the United States Navy later passed to the United States Coast Guard, order for 34 cancelled
- Four-seat version for the USN similar to the H-5F, 88 built
- HO3S-1 for the United States Coast Guard, nine built
- Was a naval version of the H-5H, not built
- One HO3S-1 modified in 1950 with a redesigned rotor
- Civil four-seat transport version; four purchased for inventory for U.S. Navy
- Argentine Air Force – (Secretaria de Aeronautica) 
- Argentine Coast Guard 
- Argentine Federal Police - 
- Royal Australian Air Force – Three in service from 1947 to 1964.
- South Africa
- South African Air Force – Used for DDT spraying to combat malaria in Zululand in the 1950s.
- United Kingdom
- United States
- Los Angeles Airways
- United States Army
- United States Air Force
- United States Coast Guard
- United States Navy
- United States Post Office Department
- YH-5A (s/n 43-46620) is on display at the National Museum of the United States Air Force at Wright-Patterson AFB near Dayton, Ohio. The aircraft is one of 26 ordered in 1944. It was obtained from Eglin Air Force Base, Florida, in March 1955.
- National Museum of Naval Aviation in Pensacola, Florida
- United States Army Aviation Museum at Fort Rucker, Alabama
- Aviodrome in Lelystad, Netherlands
- Sikorsky S51A (s/n 51–102) is on display at the South African Air Force Museum at AFB Swartkop outside Pretoria
- YR-5A and WS-51 on display at the Royal Thai Air Force Museum, Don Muang Airport, Bangkok, Thailand
- War Memorial of Korea, Seoul, Republic of Korea
- Carolinas Aviation Museum, Charlotte, North Carolina
- Museu de Antiguidades Mecânicas, Bebedouro, Sâo Paulo Brazil
- Sikorsky HO-3-F (S-51) Dragonfly at Evergreen Aircraft & Space Museum, McMinnville, Oregon.
- H-5A (S-51) on display at the New England Air Museum, Bradley International Airport, Windsor Locks, CT 
Data from United States Military Aircraft since 1909
- Crew: two
- Capacity: two stretchers in external panniers
- Length: 57 ft 1 in (17.40 m)
- Rotor diameter: 48 ft 0 in (14.63 m)
- Height: 13 ft 0 in (3.96 m)
- Disc area: 1,810 sq ft (168.2 m²)
- Empty weight: 3,780 lb (1,718 kg)
- Loaded weight: 4,825 lb (2,193 kg)
- Powerplant: 1 × Pratt & Whitney R-985, 450 hp (335 kW)
- Maximum speed: 92 knots (106 mph, 171 km/h)
- Range: 313 nmi (360 mi, 580 km)
- Service ceiling: 14,400 ft (4,390 m)
- Climb to 10,000 ft (3,050 m): 15 min
- Fitzsimons, Bernard, general editor. Illustrated Encyclopedia of 20th Century Weapons and Warfare (London: Phoebus, 1978), Volume 20, p.2173, "R-5, Sikorsky".
- "What Happens When You Mail a Letter." Popular Science, December 1951.
- Rawlins 1976, p. 2.
- Rawlins 1976, pp. 2–3.
- Rawlins 1976, p. 4.
- Rawlins 1976, pp. 2, 19.
- Rawlins 1976, p. 20.
- "Litter Blisters." Popular Mechanics, February 1950, p. 105.
- Polmar and Kennedy 1981, p. 227.
- Close, Robert A. (Cmdr). Helo Operations. Annapolis, Maryland: U.S. Naval Academy Alumni Association & Foundation, 1945.
- Pictorial PNA
- RAAF Museum
- Bridgman 1951, p. 5a.
- Bridgman 1951, p. 20a.
- Bridgman 1951, p. 59b.
- Bridgman 1951, p. 21a.
- Bridgman 1951, p. 22a.
- United States Air Force Museum 1975, p. 54.
- "Building 5: Helicopters and last propeller fighter." Royal Thai Air Force Museum. Retrieved: 11 January 2011.
- "Helicopters." Evergreen Aircraft & Space Museum. Retrieved: 27 October 2012.
- http://neam.org/index.php?option=com_content&view=article&id=883 "Sikorsky S-51 (H-5A) 'Executive Transport'"
- Swanborough and Bowers 1963, p. 431.
- Bridgman, Leonard. Jane's All The World's Aircraft 1951–52. London: Sampson Low, Marston & Company, Ltd, 1951.
- Fitzsimons, Bernard, ed. Illustrated Encyclopedia of 20th Century Weapons and Warfare, Vol.20. London: Phoebus, 1978. ISBN 978-0-83936-175-6.
- Polmar, Norman and Floyd D. Kennedy, Jr. Military Helicopters of the World: Military Rotary-wing Aircraft Since 1917.. Annapolis, Maryland: Naval Institute Press, 1981. ISBN 0-87021-383-0.
- Rawlins, Eugene W., Lt. Col. Marines and Helicopters 1946–1962. Washington, D.C.: History and Museums Division, U.S. Marine Corps, 1976.
- Swanborough, F.G. and Peter M. Bowers. United States Military Aircraft since 1909. London: Putnam, 1963.
- United States Air Force Museum Guidebook. Wright-Patterson AFB, Ohio: Air Force Museum Foundation, 1975.
|Wikimedia Commons has media related to Sikorsky H-5.|
- Flight (1 April 1948) Westland-Sikorsky S-51
- Sikorsky H-5 page at the National Museum of the United States Air Force
- Sikorsky S-51 First Helicopter in Antarctica. – Argentinian Government. Link in Spanish – Google Translation in English
- 1949 newsreel footage of a Sikorsky S-51 at British Pathe (requires Adobe Flash)
- (1951) AN 01-230HB-1 Handbook Flight Operating Instructions USAF Series H-5A, D, and E Navy Model HO2S-1 Helicopters