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Sikorsky S-74 / S-76 Spirit

sikorsk-s76a
S-76A


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 S-74. The designation was changed to S-76 to tie-in with the USA bicentennial and later named Spirit. Sikorsky used the H-76 Eagle unofficial designation to promote a military version of this model Sikorsky

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 The rotor hub is made according to the latest techniques to minimize maintenance: the normal bearings have in fact been replaced by elastomeric ones needing no lubrication, and special dampers virtually eliminate vibration.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 650 shp Allison 250-C30 turbines. There is a single 1030 litre 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 1.19 cu.m. The S-76 can also be fitted with an external cargo hook to carry 2270kg.

Building of the four prototypes began in May 1976 and the second prototype (N762SA) was the first to fly, on 13 March 1977, complete with IFR avionics.

Sikorsky had deposits on 87 ships as of February 1, 1977, and the first fully certificated IFR production aircraft was delivered to Air Logistics of Lafayette, Louisiana, on 27 February 1979. 

 

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The 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, each with a maximum continuous power rating of 870 shp (649 kW), the S-76B incorporates aerodynamic refinements developed for the UH-60. S-76B meets FAR Pt 29 category A IFR requirements with a 48 per cent increase in take-off performance and a commensurate increase in useful load under hot and high conditions.

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.

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.
Military sales of the S-76 had been few until the introduction of a dedicated, armed version, the twin-PT6B-powered 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 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.

In February 1987 the H-76 Eagle armed helicopter completed successful weapons firing trials using a new four-station pitch compensated armament pylon (PCAP), and during the tests the GIAT M621 20mm cannon pod and VS-MD-H mine dispenser were used on the H-76 for the first time. The PCAP is one of several integrated improvements aimed at reducing pilot workload and giving greater weapons accuracy. The integrated armament management system (IAMS) can be controlled from the collective lever, activating both the PCAP and headup display.

The H-76N naval version is offered with either PT6B or Allison 250-C34S engines. The S-76N is a navalised version of the S-76C.

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.

The S-76 Shadow had a nose radar housing and fly-by-wire controls grafted onto the front section.

Sales of the Spirit in all its civil forms were approaching the 500 mark by 1993.

The S-76C+ model has a maximum gross weight of 11,700 lb and a maximum cruise speed of 160 kt.

To expand the S-76 market, Sikorsky introduced the Sikorsky Shares fractional ownership program, the first of its type to be offered by a leading helicopter manufacturer. Sikorsky Shares uses a pricing plan that is based on "flight units" rather than the conventional approach of charging per flight hour.

Variants:

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
Production version powered by Pratt & Whitney PT6B-36 turboshafts

S-76C
Alternative 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

Specifications:

H-76 Eagle
Engine: 2 x P&WC PT6B-36
Instant pwr: 715 kW
Rotor dia: 13.4 m
Length: 13.2 m
No blades: 4
Empty wt: 2545 kg
MTOW: 5176 kg
Payload: 2315 kg
Max speed: 145 kts
ROC: 410 m/min
Fuel cap (aux): 1060 lt (415 lt)
Max range: 748 km
HIGE: 1890 m
HOGE: 5350 ft
Service ceiling: 11,500 ft
Crew: 2
Pax: 12

S-76
Engine: 2 x Allison 250-C30, 650 shp
TBO: 1500 hrs
Main rotor: 44 ft
Seats: 14
Length: 52.5 ft
Height: 14.5 ft
Max ramp weight: 10,300 lbs
Max takeoff weight: 10,300 lbs
Standard empty weight: 5600 lbs
Max useful load: 4700 lbs
Max landing weight: 10,300 lbs
Max sling load: 3300 lbs
Disc loading: 6.6 lbs/sq.ft
Power loading: 7.9 lbs/hp
Max usable fuel: 1875 lbs
Max rate of climb: 1800 fpm
Service ceiling: 15,000 ft
Hover in ground effect: 6200 ft
Hover out of ground effect: 2800 ft
Max speed: 155 kts
Normal cruise @ 3000 ft: 145 kts
Fuel flow @ normal cruise: 490 pph
Endurance @ normal cruise: 3.6 hr

S-76B
Engine: 2 x P&WC PT6B-36B
Instant pwr: 730 kW
Rotor dia: 13.4 m
MTOW: 5300 kg
Useful load: 1855 kg
Max cruise: 155 kts
Max range: 828 km
Crew: 2
Pax: 12
Seats: 14

S-76C
Engine: 2 x Turbomeca Arriel 1S1
Instant pwr: 540 kW
Rotor dia: 13.4 m
MTOW: 5310 kg
Useful load: 2072 kg
Max cruise: 155 kts
Max range: 643 km
Crew: 2
Pax: 12
Seats: 14

S-76C+
Engine: 2 x Turbomeca Arriel 2S1
Instant pwr: 638 kW
Rotor dia: 13.4 m
MTOW: 5310 kg
Useful load: 2057 kg
Max range: 889 km
Crew: 2
Pax: 12
Seats: 14

 

S-76C++
Engine: 2 x Turbomeca Arriel 2S1
Instant pwr: 638 kW


S-76N
Engine: 2 x Turbomeca Arriel 2S1

S-76 Mk.II
Engine: 2 x Allison 250-C30S turboshaft, 509kW
Main rotor diameter: 13.41m
Length with rotors turning: 16.0m
Height: 4.41m
Max take-off weight: 4672kg
Empty weight: 2540kg
Cruising speed: 269km/h
Service ceiling: 4570m
Range with 12 passengers: 748km

 

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