|Sikorsky S-76 "Spirit"|
Having concentrated almost exclusively on military aircraft thus far, Sikorsky announced plans in January 1975 for a twin-turbine helicopter for the civil market. The company had carefully evaulated the needs of potential customers and, after having examined various solutions, had already acquired a number of options. Building of the four prototypes began in May 1976 (the designation S-76 was chosen to mark the American bicentennial). The project clearly showed the experience gained with the S-70 combat helicopter. The second prototype was the first to fly, on 13 March 1977, complete with IFR avionics. From the outset, the aircraft was equipped for all-weather operation, as one of its main roles was intended to be the servicing of offshore oil rigs. The four-blade rotor of this air craft is exactly like that of the S-70. The blades are built around a strong titanium spar; the leading edge is also titanium, while the trailing edge has a fiberglass and nylon honeycomb structure. The entire blade is pressurized for maximum structural integrity. The rotor hub is made according to the latest techniques to minimize maintenance: the normal bearings have in fact been replaced by elastomeric ones needing no lubrication, and special dampers virtually eliminate vibration. The powerplant is installed above the fuselage behind the drive shaft and consists of two 650shp Allison 250-C30 turbines. There is a single 1030 liter fuel tank in the fuselage, but supplementary fuel tanks can be carried for longer journeys.
The carefully streamlined fuselage is also of composite structure. The front part is of fiberglass, the cabin section is of light alloy with honeycomb panels, while the tail, which is also of metal, has a semi-monocoque structure. The retractable tricycle landing gear is hydraulically operated. The cabin is normally furnished, with seats for 14 including the crew of two, but can be modified to suit the operator. There is a large baggage compartment at the rear, with a capacity of 1.19m3. The S-76 can also be fitted with an external cargo hook to carry 2270kg.
Over 200 Sikorsky S-76s were in operation throughout the world in 1983 and principal operators include Air Logistics, Okanagan Helicopters, VOTEC in Brazil, and Bristow in the UK. The version currently in production, the S-76 Mk.ll, which won 12 world records in February 1982, has a special variant of the Allison 250 which yields five per cent more power than the previous model.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Growing demands for transport helicopters in support of offshore energy operations led Sikorsky to initiate worldwide market research to establish the requirements of such operators. An important consideration was seating capacity, and in 1975 Sikorsky began the development of a 14-seat commercial helicopter designated Sikorsky S-76 and later named Spirit. The first of four prototypes (N762SA) was flown on 13 March 1977, and the first fully certificated IFR production aircraft was delivered to Air Logistics of Lafayette, Louisiana, on 27 February 1979.
This two-year certification programme resulted from the use of an advanced dynamic systems/powerplant combination evolved for military requirements, but further development continued from the time that production began, leading to an improved S-76 Mk II from 1 March 1982. This differs by having improved cabin ventilation, dynamic system refinements, more access panels to simplify maintenance, and an advanced version of the Allison 250 turboshaft engine that gives an increase in guaranteed power output. In 1983 Sikorsky flew the first S-76B, to replace the Mk II on the production line. Powered by two 771kW Pratt & Whitney PT6B-36As, the S-76B incorporates aerodynamic refinements developed for the UH-60. S-76B meets FAR Pt 29 category A IFR requirements. As a follow-on to the S-76B the S-76C was announced in June 1989, and flew in May 1990. Powered by Turbomeca Arriel 1S1 engines, the 12-seat S-76C has attracted military orders from Hong Kong and Spain, and is also in use with . several off-shore operators.
Military sales of the S-76 had been few until the introduction of a dedicated, armed version, the H-76 Eagle, in 1985. Featuring armed seats, floor and fuel tanks, the Eagle can be armed with a combination of gun pods, rocket pods and even AAMs on its stub pylons. It can be used in gunship, Medevac, troop-transport, or combat SAR roles and has provision for a chin-or mast-mounted sight. It was selected by South Korea as its new light utility helicopter and an order for up 175 is anticipated. Aircraft are being built in the United States initially, with assembly being gradually transferred to Daewoo-Sikorsky Aerospace. Ltd.
The S-76 has also served as a technology demonstrator for several projects. A one-off modification, the SHADOW (Sikorsky Helicopter Advanced Demonstrator and Operator Workload) programme saw an S-76 fitted with an add-on cockpit at the nose to test fly-by-wire, voice-actuated and side-stick control methods, together with helmet-mounted sights, FLIR and HUD combinations and an NVG cockpit. It was used extensively by Boeing/Sikorsky in their First Team submission for the US Army's LHX competition to test a night vision system. A second S-76 was fitted with an anti-torque tail-rotor system, as the Fantail Demonstrator, playing an important part in the selection of the First Team's design by the US Army as the RAH-66 Commanche.
Sales of the Spirit in all its civil forms were approaching the 500 mark by 1993.
S-76: original production version, this designation applicable to aircraft delivered before 1 March 1982
S-76A+: unsold S-76s re-engined with Turbomeca Arriel turboshafts - on demand; produced to special orders only such as SAR aircraft for Royal Hong Kong Auxiliary Air Force with undernose GEC MRTS FLIR turret and searchlight
S-76 Mk II: production all-weather transport from 1 March 1982, superseded by S-76B
S-76 Utility: simplified version of S-76 Mk II with sliding doors, and optional fixed landing gear; available in civil or military versions
AUH-76: armed utility helicopter version, airframe basically as S-76 Utility, but with avionics and armament to permit deployment in various military roles
S-76B: current production version powered by Pratt & Whitney PT6B-36 turboshafts
S-76C: alternative current production version, powered by Turbomeca Arriel 1-S1 turboshafts.
S-76D: projected version available from 1994, to be powered by uprated Turbomeca 2S1s
H-76 Eagle: armed version of S-76B
H-76N: projected naval version announced in 1984; no orders received
D.Donald "The Complete Encyclopedia of World Aircraft", 1997
- When configured for full day and night, all-weather offshore flying, the S-76 generally carries up to 12 passengers.
- Sikorsky sold 428 S-76s to customers in Canada, Mexico, the UK and the US.
- A harmonic control system tested on an S-76 reduced vibration by 90%.
- The S-76 Shadow had a nose radar housing and fly-by-wire controls grafted onto the front section.
- The S-76B is operated in China, Germany, Japan, Korea and the Netherlands.
- The first S-76 prototypes flew in 1977 and deliveries began in 1979.
Alexandra, e-mail, 29.01.2021 Richard Bluett
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