Sikorsky S-55 "Chickasaw" / H-19 / HO4S / HRS

1949


On 1 May 1949, Sikorsky's technical department was given a very important task: it was asked to create a new helicopter in just seven months, which would be capable of carrying ten passengers in addition to a crew of two.

The first of the five YH-19 prototypes ordered by the US Air Force for evaluation flew on 10 November 1949 and was characterized by a blunt-ended fuselage, which lacked the broad, triangular fillet connecting the fuselage to the tail boom which distinguished all the later series aircraft. Another characteristic of the YH-19 was the horizontal stabilizer applied to the starboard side of the tail, which was replaced in the production aircraft by two anhedral tail surfaces.

In 1951, the US Air Force ordered a batch of H-19As fitted with the same 550hp Pratt & Whitney R-1340-57 engine as the prototypes. Production continued with the H-19B which had a 700hp Wright R-1300-3 engine and a larger diameter main rotor; a total of 270 were built for the US Air Force, including the SH-19B version for use as a transport aircraft. From 1952, the Army also ordered the H-19, beginning with 72 H-19Cs. They were subsequently nicknamed "Chickasaw" and redesignated UH-19C and UH-19D in 1962.

Versions of the S-55 were also acquired by the US Navy, which signed its first contract on 28 April 1950. Between August 1950 and January 1958, the US Navy received 119 helicopters, including ten HO4S-1 (equivalent to the H-19A) and 61 HO4S-2 (about 30 of these were built as HO4S-3G for the US Coast Guard). The Marines received 99 HRS-2 and 84 HRS-3, which corresponded to the HO4S series and were used as troop transports. The aircraft assigned to the SAR divisions of the MATS and US Army Aviation arrived in Korea when the war was nearly over, whereas the Marines were able to test their HRS-1s for rapid assault operations which anticipated full-scale landing operations.

Various techniques and roles were first tested with the S-55 in Korea which were later to form the basis of new military doctrine, such as landing operations behind enemy lines, troop support, recovery of damaged vehicles and their capacity for counterattack and engagement. Another primary task of the helicopter was casualty evacuation or the rescuing of pilots who had come down behind the enemy lines. In the ambulance role, the S-55 could carry up to six stretchers, five of which could be hoisted on board using a mechanical winch fixed outside the cabin. The spacious cabin was designed to accommodate various seating arrangements or freight; it could take up to ten men or a load of approximately 1300kg.

The most distinctive feature of the Sikorsky aircraft was the location of the engine in the nose, to enable the cabin to be placed at the center of gravity, thus allowing for considerable variations in payload without affecting stability. Special attention was also paid to the question of maintenance. The main parts were easily dismantled in an average of 12-15 hours and were all designed for ease of access (the engine, for example, could be changed in two hours, even without special equipment, and daily inspections took a maximum of 15-20 minutes). The S-55 had a monocoque metal fuselage with aluminum and magnesium light alloy bulkheads and skin. The three-blade main rotor had long-life metal blades (they demonstrated a life of over 20000 hours in lab tests). The fuel was contained in two crash resistant tanks situated beneath the cabin in the lower part of the fuselage and had a total capacity of 700 liters. Each leg of the quadricycle undercarriage had its own shock absorber for maximum stability during take-off and landing and manoeuvres on the ground. Floats could also be fitted to the legs for emergency landings on water, or the undercarriage could be replaced by permanent metal amphibious landing gear.

The S-55 received American civil type approval on 25 March 1952 and the model with the Pratt & Whitney R-1340 engines became the S-55A, while the version with the Wright engine was designated S-55B. In 1952, the helicopter became the first rotary wing craft to be used for commercial links in Europe; it was then flown by the Belgian airline Sabena between the chief towns in Belgium and Lille, Rotterdam, Bonn and Cologne.

In ten years, Sikorsky produced 1067 S-55s in military version for no fewer than 30 operators throughout the world. Another 547 were built under license (notably by Westland in England under the name Whirlwind).


G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984


Sikorsky H-19C

Developed by Sikorsky during the late 1940s, the Model S-55 made its first flight in November 1949. The Air Force ordered five YH-19 prototypes for service test and evaluation shortly thereafter, and in 1951 purchased fifty H-19A production machines. Near the end of 1951 the Air Force accepted the first of an eventual 270 more powerful and slightly modified H-19B aircraft, and at the same time loaned a single H-19A to the Army for operational evaluation in the utility transport and aeromedical evacuation roles. The H-19 performed both with far greater ability than any other helicopter then in Army service, and in the fall of 1951 the Army ordered the first batch of an eventual seventy-two H-19C aircraft (serials 51-14242 through -14313). In late 1952 orders were placed for the first of some 301 examples of the more capable H-19D variant, sixty-one of which were transferred to friendly nations under various military assistance programmes.

The H-19 was of all-metal pod-and-boom construction, had quadricycle wheeled landing gear, and carried its single piston engine in its nose. The engine was linked to the gear drive of the three-bladed main rotor by a long extension shaft, and was easily accessible via two large clamshell doors. The innovative arrangement of powerplant and drivetrain allowed the placement of a large and unobstructed box-like passenger/cargo cabin directly below the main rotor blades, thus ensuring that loads of varying sizes and composition would not adversely affect the craft's centre of gravity. The H-19's two-man cockpit was placed above and slightly forward of the passenger/cargo cabin, with the seats placed one either size of the drive shaft, and offered excellent visibility to the front and sides. The craft's high-set tailboom carried a vertical tailplane and a two-bladed anti-torque rotor, and was faired into the rear of the fuselage by a triangular fin. The Army's H-19C was essentially identical to the Air Force H-19A and, like that aircraft, was powered by a 600hp R-1340-57 engine and had two small fins fitted to the lower rear of the tailboom in an inverted 'V’. The H-19D was the Army's version of the Air Force -B model and shared that aircraft's more powerful 700hp engine, downward-sloping tailboom, repositioned horizontal tail fins, and smaller-diameter tail rotor.

The H-19 Chickasaw holds the distinction of being the Army's first true transport helicopter and, as such, played an important role in the initial formulation of Army doctrine regarding air mobility and the battlefield employment of troop-carrying helicopters. The Chickasaw made its combat debut during the last stages of the Korean War (having arrived in Korea in January 1953 in the hands of the 6th Transportation Company), and went on to serve in Southeast Asia during the first years of the Vietnam War. In 1962 the H-19C and H-19D were redesignated as, respectively, the UH-19C and UH-19D, and examples of both variants remained in Army service well into the mid-1960s.


S.Harding "U.S.Army Aircraft since 1947", 1990


Sikorsky S-55

In 1948 Sikorsky received a contract for five Sikorsky S-55 utility helicopters for US Air Force evaluation under the designation YH-19. The first of these was powered by a 410kW Pratt & Whitney R-1340-57 mounted in the nose to drive the main rotor gearbox through a long extension shaft, and flew on 10 November 1949. The 447kW version of the R-1340-57 powered 50 production H-19A helicopters, while the 522kW Wright R-1300-3 replaced it in 270 H-19B helicopters, many of which were fitted with rescue hoists and designated SH-19. The US Navy placed its first order on 28 April 1950, for 10 HO4S-1 machines (similar to the H-19A), which were followed by 61 HO4S-3 aircraft based on the H-19B; the HO4S-3G was a US Coast Guard rescue version. Initial troop and assault transport versions were designated HRS-1 and HRS-2, similar to the HO4S-1, 151 of which were delivered from April 1952. Eighty-four HRS-3 helicopters with Wright R-1300-3 engines were also built. The US Army's 72 H-19C and 338 H-19D helicopters, known as the Chickasaw, were equivalent to the H-1 9A and H-19B respectively. Licence-production was undertaken by SNCA du Sud Est in France and by Westland in the UK, the latter developing versions with the Alvis Leonides Major piston engine and with the Bristol Siddeley Gnome turboshaft under the family name Whirlwind.

In 1964 Orlando Helicopter Airways Inc, of Sanford, Florida, was founded by Fred P. Clark to support, and in some cases, re-start production of Sikorsky helicopters no longer built by the parent company. In addition to a huge spares resource, Orlando Helicopters now holds the FAA type certificates for all H-19 and S-55 models. Several versions of the S-55 have since been developed by the firm. These include the OHA-S-55 Hen-Camper, a fully fitted out VIP version seating four passengers. New equipment includes a shower, wash-basin and toilet, air conditioning, carpeting and sound-proofing. An optional hydraulic winch, cargo sling or exterior spot-light can also be fitted. The Heli-Camper is powered by an overhauled and reconditioned 596kW Wright-Cyclone R-1300-3D engine.

The OHA-S-55 Nite-Writer is an unprecedented aerial advertising helicopter fitted with a 12.2m x 2.4m array of computer-controlled lights which can display messages and graphics, visible over a distance of 3.2km. More in demand is the OHA-S-55 Bearcat, for which Orlando has developed a quick-change hopper and spray system for crop and fertiliser spraying or seed spreading. Certified in 1991, the Bearcat is powered by a Pratt & Whitney R-1340 engine, which can run on automotive fuel, is fitted with a 'quiet' exhaust, and sells for an affordable $300,000.

In October 1985 the company signed an agreement with China's Guangzhou Machinery Tool Company to licence-build OHA-S-55 Bearcats. Under a 20-year joint venture Guangzhou Orlando Helicopters would first assemble American-built parts before progressing to manufacturing entire units. For carrying heavy external loads, such as logging or construction work, Orlando has developed the OHA-S-55 Heavy Lift which can deal with underslung weights of up to 1361kg. The company has also moved into a unique military market through modifying its S-55s for the US Army Missile Command. As QS-55 Aggressors they have been extensively modified to resemble Mil Mi-24 'Hind-E's as flying targets. The Aggressors can be flown by a pilot or as drones (with dummy pilots in their cockpits) and have a new five-bladed main rotor, extensively redesigned nose, stub wings, and chaff and flare dispensers. A second, more aggressive military version is the armed OHA-AT 55 Defender, design of which began in 1990. Re-engined with a Garrett TPE331-3 turboshaft or a Wright R-1330-3 radial, the Defender also features a stub wing with pylons capable of carrying up to 500kg of weapons, and a five-bladed rotor. Capable of carrying up to 10 fully-equipped troops, the Defender can also be fitted out to accommodate six stretchers and two attendants.

A small number of civilian Sikorsky-built S-55s are still in use, chiefly in the United States, but the type has now disappeared from the world's military inventories.

D.Donald "The Complete Encyclopedia of World Aircraft", 1997

The S-55 is a 12-seat utility helicopter suitable for passenger, air mail or cargo transport and for air rescue and military service. The prototype flew on 9 November 1949 and the 1,000th Sikorsky-built helicopter of the basic S-55 type was delivered to the US Marine Corps in mid-1956.

Apart from being adopted by the USAF, US Army Field Forces, US Navy, US Marine Corps and US Coast Guard, the S-55 was also built under licence in the United Kingdom by Westland Aircraft and in France by Sud-Aviation. The British-built S-55 known as the Westland Whirlwind, went into service with the Royal Air Force and the Royal Navy.

VERSIONS

S-55: Standard civil version with 447kW Pratt & Whitney R-1340 engine, friction clutch and straight tailboom.

S-55A: With 522kW Wright R-1300-3 engine, hydromechanical clutch and inclined tailboom.

S-55C: As S-55, but with inclined tailboom.

H-19A: 410kW Pratt & Whitney R-1340-57 engine. For USAF AUW 3,263kg. Crew of two, plus 10 troops or six stretchers.

H-19B: 522kW Wright R-1300-3 engine. For USAF. Rotor diameter 16.16m. AUW 3,900kg. Crew of two, plus 10 troops or six stretchers.

H-19C: Same as H-19A for US Army Field Forces.

H-19D: Same as H-19B for US Army Field Forces.

HO4S-1 and -2: 410kW Pratt & Whitney R-1340 engine. Similar to H-19A. For US Navy for anti-submarine duties.

HO4S-2G: For US Coast Guard. HO4S-2 fitted for rescue duties.

HO4S-3: 522kW Wright R-1300 engine. Similar to H-19B. For US Navy for anti-submarine duties.

HRS-1 and -2: 410kW Pratt & Whitney R-1340 engine. Similar to H-19A. For US Marine Corps for assault transport duties. Crew of two and eight fully armed troops.

HRS-3: 522kW Wright R-1300 engine. Similar to H-19B. US Marine Corps assault transport.

Westland Whirlwind: Licence-built S-55; first flown November 1952. Installation of Wright R-1300 engines produced the Whirlwind Mk 3 in 1953, followed by the Mk 4 with new P&W R-1340 engines for use in the tropics; then Alvis Leonides Major engine. First turbine-powered aircraft, fitted with Gnome engine, flew in February 1959. More than 400 built for UK armed forces; early 100 exported. The description and specification which follow refer in general to all models:

DESIGN FEATURES: Three-blade main rotor and two-blade anti-torque tail rotor. All-metal structures.

STRUCTURE: Except for the chrome-molybdenum steel-tube rotor pylon, structure is of aluminium and magnesium semi-monocoque construction. On commercial versions with R-1300 engine, the tailcone has been sloped down approximately 3.5° to increase clearance of main rotor in a rough landing.

LANDING GEAR: Quadricycle type. Wheel track 3.35m. Alternative gear includes all-metal amphibious landing gear or permanently inflated rubber bag flotation gear. For use with the normal wheels, 'doughnut' pontoons were available which are stowed deflated on each wheel axle and can be inflated in under 5 seconds, when needed for landing on water.

POWER PLANT: One Pratt & Whitney R-1340 S3H2 Wasp radial air-cooled engine rated at 410kW at 1,525m and with 447kW available for take-off at 915m, or one Wright R-1300-3 radial air-cooled engine rated at 522kW at 2,222m and with 596kW available for take-off at 1,675m. Engine on angular mounting in nose of fuselage with sloping shaft drive to rotor gear box below head. With the R-1300 engine, a hydromechanical clutch with free wheel system is used in the drive to the main transmission, and the drive-shaft from the free wheel unit to the main transmission has flexible rubber couplings on each end. Large clamshell doors in nose of fuselage allow complete accessibility to engine from ground level. Internal fuel capacity 700 litres.

ACCOMMODATION: Pilot's compartment above main cabin seats two side by side with dual controls. Cabin located below main lifting rotor may seat from 7 (commercial) to 10 (military) passengers, the 10 passengers being seated three against front and rear walls and two on each side, all facing inwards. Up to six stretchers may be carried, which can be loaded by optional hydraulic power-operated hoist while aircraft is hovering. Pilot's compartment may be entered from the outside or from the cabin so that co-pilot may act as attendant.


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