|Sikorsky S-64 / CH-54 "Tarhe"|
Sikorsky's first crane helicopter, the S-60, was a research vehicle designed and built from funds shared between the U.S. Navy and the parent company. Work on the design started in May 1958, the idea being to produce a minimum 'backbone' airframe beneath which a close-fitting or suspended heavy payload could be supported. To speed development and minimise actual flight testing, the S-60 was given the already tried and tested power-plant, rotor and transmission systems of the S-56 helicopter. The 2100hp Pratt & Whitney R-2800 engines were similarly mounted, in outrigged pods into which the main undercarriage wheels could be partially retracted. A 5443kg payload could be attached or suspended beneath the fuselage boom, and by pivoting his seat to face aft the co-pilot could supervise loading and unloading. The S-60, registered N807, first flew on 25 March 1959 and was demonstrated extensively until it was lost during a test flight in April 1961.
By this time, however, Sikorsky had already begun to build a prototype of the bigger S-64, and this machine (N325Y) was flown on 9 May 1962. The S-64, also envisaged as an airborne prime mover, retained the same basic rotor system as the S-60, though employing a 6-blade main rotor. It differed from the smaller machine in having a pair of 4050shp JFTD-12A shaft turbines mounted side-by-side on top of the fuselage boom, and had no fin area below the boom. Ground clearance beneath this boom is 2.84m and the main wheel track is 6.02m, hence loads of considerable size can be fitted underneath the S-64. A feature of this aircraft is that the landing gear can be lengthened and shortened hydraulically, so that the helicopter can 'crouch' on to its load, raise it off the ground and then, if desired, taxi with it to a more suitable take-off point. Two additional prototypes, N305Y and N306Y, were completed for evaluation by the Federal German forces. Re-registered D-9510 and D-9511, they were operated under the aegis of the former Weser Flugzeugbau.
After evaluation of the original prototype at Fort Benning, Georgia, the U.S. Army placed a pre-series order in June 1963 for six S-64A's with the military designation CH-54A. Five of these were delivered and have operated with some distinction with the 478th Aviation Company supporting the U.S. Army's 1st Cavalry Division in Vietnam. Eighteen more CH-54A's were ordered in 1966, and total orders stood at about sixty in 1968, later aircraft having uprated -4A engines of 4620shp each. Loads which can be lifted by the S-64A/CH-54A include trucks or palletised containers holding a field hospital unit, 48 casualty litters, 67 troops or 10382kg of cargo; one CH-54A in Vietnam has successfully lifted 87 troops.
Meanwhile a Sikorsky-owned S-64A and the sixth aircraft of the U.S. Army's original order have been used to further the acceptance of the type for the civil market, where it should prove valuable for such operations as ship-to-shore loading or unloading of cargo vessels or support of offshore oil rigs. During 1967, N325Y carried out tests on behalf of the Los Angeles Airport Department with the 23-seat Budd XB-1 Skylounge pod, designed to speed connection between the city's airports and the city centre. Also under development is the S-64B/CH-54B, an enlarged three-turbine version designed to lift a 16329kg payload.
K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968
Sikorsky began designing flying cranes with the development of the S-56, which, although used in the early stages of the Vietnam War to lift and carry slung loads, was really an assault and troop transport helicopter. Using the dynamic components of this aircraft, i.e. the five-blade main rotor, four-blade anti-torque rotor and two Pratt & Whitney R-2800 engines in two outrigged pods, Sikorsky built the Model S-60 in 1959, with a fuselage reduced to the bare essentials, all the payload being carried externally. Before the S-60 was destroyed in April 1961, Sikorsky had already begun the S-64 Skycrane project. The new helicopter was similar in structure to its predecessor but had a six-blade main rotor and two 4050shp Pratt & Whitney JFTD-12A turbines installed side-by-side. The height of the tricycle landing gear could be adjusted to adapt it to the payload. The S-64 had 2.84m clearance between the ground and the bottom of the fuselage, while the main landing gear wheels on two downward-sloping strut supports were set 6.02m apart. In this way, very large loads could be carried, including a special container for 23 passengers.
The German Bundeswehr was interested in the flying crane and Weser Flugzeugbau lost no time in acquiring the production license. Two S-64A prototypes built in the United States were sent to Germany for evaluation by the Army Air Corps. Meanwhile, the US Army carried out its own tests on the new Sikorsky helicopter and six were ordered in June 1963 with the designation YCH-54A. Another 18 were later added to the order, followed by further contracts for a total of 90 aircraft.
The first six flying cranes were assigned to the First Cavalry Divison (Airmobile) operating in Vietnam. The cranes' performance there was outstanding (one of them set a world record on 29 April 1965 by carrying a pod with 90 passengers). Other exploits by the Tarhe (as the US Army S-64 was called) during the Vietnam War included the lifting of bulldozers and tanks and retrieval of damaged aircraft.
The larger CH-54B version with twin 4800shp turbines and 2300kg more lifting power, went into service with the US Army in 1969; 29 were built. Sikorsky also offered the Skycrane to commercial operators. The models S-64E (civil version of the CH-54A) and S-64F (derived from the CH-54B) were produced, while plans for a triple turbine version were not realized.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
In 1958 Sikorsky began design work on the Model S-60 twin-engined heavy-lift helicopter, a machine that incorporated the pod-mounted piston engines and dynamic components of the earlier Model S-56/CH-37. The S-60's fuselage was extremely simple, consisting of a central 'backbone' which supported the podded engines, main and tail rotor systems, and a nose-mounted crew cabin. Bulk cargo and passengers were intended to be carried in large rectangular pods that could be attached to the underside of the aircraft's central spine, whereas vehicles and other out-sized loads were to be sling-hoisted. One S-60 was built for Navy evaluation, but the craft was found to be underpowered for its intended roles and Sikorsky took the design back to the drawing boards for extensive reworking. The reconfigured machine, which was allotted the company designation S-64A, made its first flight in May 1962 under the watchful eyes of Army observers.
The S-64A retained the S-60's unique (and somewhat insect-like) layout but was more streamlined and was powered by two 4500shp Pratt & Whitney T73-P-1 turboshafts mounted atop the central spine directly beneath the six-bladed, fully-articulated main rotor. The switch to turbine power produced significant increases in both performance and lifting ability, and in June 1963 the Army ordered six examples for operational test and evaluation. These aircraft, designated YCH-54A Tarhes and allotted the serial numbers 64-14202 through -14207, were delivered to the Fort Benning-based 478th Aviation Company beginning in June 1964. This unit subsequently took four of the machines to Vietnam for a thorough field evaluation, upon the successful conclusion of which the Army placed orders for fifty-four CH-54A production aircraft. In 1969 these machines were joined by the first of an eventual thirty-seven CH-54Bs (serials 69-18462 through -18498). The -B model Tarhe differed from the earlier -A primarily in having more powerful engines, high-lift rotor blades, a modified main rotor gearbox and rotor head, a payload capacity increased by some 5000 pounds, and dual-wheeled main landing gear. The CH-54B went on to set several international helicopter payload and time-to-altitude records that are only now being broken by the latest generation of Western and Soviet heavy-lift rotorcraft.
The first production CH-54s began reaching Vietnam in 1965, and the type quickly proved its value as a 'flying crane' by routinely sling-lifting such outsized and weighty cargoes as artillery pieces, armoured vehicles and recovered aircraft. The Tarhes' universal cargo pods also proved very useful, for they could be used to carry up to eighty-seven troops in addition to serving as mobile hospitals, command posts or barracks. On several occasions, CH-54s even served as makeshift bombers; they were among the few American aircraft in Southeast Asia that were capable of carrying, and dropping, the 10000 pound 'daisy-cutter' bombs used to create instant helicopter landing zones by flattening all vegetation (and most structures) within an area several hundred yards in diameter.
During the late 1960s and early 1970s the Tarhe was gradually superseded in front-line service by the CH-47B and -C Chinook, and all surviving CH-54s were subsequently transferred to the Army Reserve and National Guard. Withdrawal from frontline units did not signal the Tarhe's immediate demise, however, for as of early 1986 seventy-one -A model machines are shared among Georgia, Kansas, Mississippi, Nevada and Pennsylvania, while the twenty-six surviving -Bs serve in Alaska, Alabama and Connecticut. These scrupulously maintained machines remain among the most capable aircraft available to the Army, and current plans call for the CH-54 to remain active in the Reserve and Guard until well into the 1990s.
S.Harding "U.S.Army Aircraft since 1947", 1990
Sikorsky's first 'flying crane' helicopter was the Sikorsky S-60, developed from the S-56 and retaining that machine's powerplant, transmission and rotor system. Work began in May 1958 and the prototype was flown on 2 March 1969; it was capable of lifting a 5443kg payload beneath the fuselage boom, and the co-pilot could turn his seat to face aft to control loading and unloading. The prototype S-60 crashed in April 1961, but by then Sikorsky had begun construction of an enlarged version, with a six-bladed main rotor driven by two 3020kW JFTD-12A turboshaft engines. Designated S-64, the prototype flew on 9 May 1962 and was followed by two further machines for evaluation by the Federal German armed forces. This did not result in German orders, but the US Army placed an order for six S-64A helicopters in June 1963, under the designation CH-54A Tarhe. This version was powered by 3356kW Pratt & Whitney T73-P-1 engines, and production eventually totalled approximately 60; 10 CH-54B helicopters were built with 3579kW T73P-700 engines. The Tarhe served in a heavy-lift role in Vietnam, with the 478th and the 291st Aviation Companies.
Only 97 Tarhes were built for the United States Army between 1964 and 1972. In the later years of its life, the type was largely relegated to Army National Guard units, seven of which were still equipped with it by the beginning of the 1990s. Progressively replaced by the (less-capable) CH-47D, the last unit to give up its CH-54s was D Company, 113th Aviation, of the Nevada Army National Guard, based in Reno, in 1993. On 1 February 1992 Sikorsky sold the rights for the S-64 to Erickson Air-Crane Co. of Central Point, Oregon, who have so far undertaken no production.
D.Donald "The Complete Encyclopedia of World Aircraft", 1997
The S-64 flying crane was designed initially for military transport duties. Equipped with interchangeable pods, it is suitable for use as a troop transport, and for minesweeping, cargo and missile transport, anti-submarine or field hospital operations. Equipment includes a removable 9,072kg hoist, a sling attachment and a load stabiliser to prevent undue sway in cargo winch operations. Attachment points are provided on the fuselage and landing gear to facilitate securing of bulky loads.
S-64A: Under this designation the first of three prototypes flew for the first time 9 May 1962 and was used by the US Army at Fort Benning, Georgia, for testing and demonstration. The second and third prototypes were evaluated by the German armed forces.
CH-54A: Six ordered by US Army in 1963 to investigate the heavylift concept, with emphasis on increasing mobility in the battlefield. Delivery of five CH-54As (originally YCH-54As) to the US Army took place in late 1964 and early 1965. A sixth CH-54A remained at Stratford, with a company-owned S-64, for a programme leading toward a restricted FAA certification, which was awarded 30 July 1965. Further US Army orders followed.
On 18 April 1969, two commercial Skycranes were delivered to Rowan Drilling Company Inc of Houston, Texas, for operation in support of oil exploration and drilling operations in Alaska.
CH-54B: On 4 November 1968 Sikorsky announced that it had received a US Army contract to increase the payload capacity of the CH-54 from 10 to 12.5 tons. The contract called for a number of design improvements to the engine, gearbox, rotor head and structure; altitude performance and hot weather operating capability were also to be improved. Two of the improved flying cranes, designated CH-54B, were accepted by the US Army during 1969.
The original JFTD12-4A engines were replaced by two Pratt & Whitney JFTD12-5As, each rated at 3,579kW, and a gearbox capable of receiving 5,891kW from the two engines was introduced. Single-engine performance was increased, since the new gearbox receives 3,579kW from one engine, compared with 3,020kW on the CH-54A.
A new rotor system was also introduced, utilising a high-lift rotor blade with a chord some 0.064m greater than that of the blades used formerly.
Other changes included the provision of twin wheels on the main landing gear, an improved automatic flight control system and some general structural strengthening throughout the aircraft. Gross weight was increased from 19,050kg to 21,318kg.
S-64E: FAA certification of the improved S-64E for civil use was announced in 1969, for the transportation of external cargo weighing up to 9,072kg.
In January 1972 Erickson Air-Crane Company of Marysville, California, purchased the first S-64E, for logging and other heavylift tasks. The company acquired the S-64 type certificate from Sikorsky in 1992 and is marketing improved versions worldwide.
S-64F: Designation of a commercial version of the S-64.
CUSTOMERS: Versions of the CH-54 are in service with the armed forces of the USA and civil operators.
DESIGN FEATURES: Six-blade, fully articulated main rotor. Four-blade tail rotor. Steel driveshafts. Main gearbox below main rotor, intermediate gearbox at base of tail pylon. Tail gearbox at top of pylon. Main gearbox rated at 4,922kW on CH-54A.
FLYING CONTROLS: Rotor brake standard.
STRUCTURE: Aluminium main blades with aluminium and steel head. Aluminium tail rotor blades with titanium head. Pod and beam type of aluminium and steel semi-monocoque construction.
LANDING GEAR: Non-retractable tricycle type, with single wheel on each unit of CH-54A/S-64E, twin wheels on main units of S-64F. CH-54A/S-64E mainwheel tyres size 38.45 x 12.50-16, pressure 6.55 bars. S-64F mainwheel tyres size 25.65 x 8.50-10, pressure 6.90 bars. Nosewheels and tyres of all versions size 25.65 x 8.50-10, pressure 6.90 bars.
POWER PLANT: (CH-54A/S-64E): Two Pratt & Whitney JFTD12-4A (military T73-P-1) turboshaft engines, each rated at 3,356kW for take-off and with maximum continuous rating of 2,983kW. Two fuel tanks in fuselage, forward and aft of transmission, each with capacity of 1,664 litres. Total standard fuel capacity 3,328 litres. Provision for auxiliary fuel tank of 1,664 litres capacity, raising total fuel capacity to 4,992 litres.
POWER PLANT: (CH-54B/S-64F): Two Pratt & Whitney JFTD12-5A turboshaft engines, each rated at 3,579kW for take-off and with maximum continuous rating of 3,303.5kW. Fuel tanks as for CH-54A/S-64E.
ACCOMMODATION: Pilot and co-pilot side by side at front of cabin. Aft-facing seat for third pilot at rear of cabin, with flying controls. The occupant of this third seat is able to take over control of the aircraft during loading and unloading. Two additional jump seats available in cabin. Payload in interchangeable pods.
Jane's Helicopter Markets and Systems
Technical data for Sikorsky CH-54B
Engine: 2 x Pratt & Whitney T73-700 turboshaft, rated at 3579kW, main rotor diameter: 21.95m, fuselage length: 21.41m, height: 5.67m, take-off weight: 21318kg, empty weight: 8981kg, cruising speed: 169km/h, range with max fuel: 370km, payload: 9000kg in a standard container