Sikorsky Product History

Sikorsky S-76

Background

The S-76 was launched in the 1975 timeframe as the first Sikorsky model to be designed for commercial rather than military missions in order to increase the commercial portion of the company’s business. Its intended missions included the transport of workers to and from offshore oil rigs in a 12 passenger version and transport of business executives in a 6 passenger VIP version. Funding for its design, development and certification was provided from company sources. The technology basis for the S-76 was the Utility Tactical Transport Aircraft System (UTTAS) that had been awarded to Sikorsky in 1972. In particular, the rotor blade aerodynamic and structural features including blade airfoil, twist, swept tip and titanium spar were all embodied in the S-76. The UTTAS elastomeric main rotor head design as well as the cross beam bearingless tail rotor design was also applied to the S-76.

The Sikorsky S-76® is an intermediate class twin engine commercial helicopter powered by two turboshaft engines, which drive both the main and tail rotors, each with four blades. The S-76 landing gear is retractable.

The S-76 was announced at The HAA (now HAI) Convention in Las Vegas, Nevada in February 1975.

S-76A Executive Transport Helicopter

The sleek lines of the S-76 combined with significant advancements in rotor technologies and with improved engine fuel consumption, resulted in a helicopter having excellent efficiency.

The executive transport version was designed with a quiet cabin which would provide a work environment during flight and allow conversations without the need for headsets. The S-76 was designed to replace small business jets for short to medium business trips.

Sikorsky’s development of the UH-60 Black Hawk served as the basis for the S-74, which was later re-designated the S-76 Spirit in honor of the U.S. Bicentennial. The design accommodates 2 pilots and 12 passengers, to accommodate an oil rig crew change, and was initially powered by two Allison 250 C30 turboshaft engines of 650 shp (Takeoff Power) each. The prototype first flew on March 13, 1977. The name Spirit was officially dropped by the company on October 9, 1980 due to unanticipated complications when Spirit was translated into certain foreign languages.

S-76A Oil Rig Crew Change

The first production variant was the S-76A. In 1982 this model set 12 world records for speed and time to climb in its weight class. A closed course 500 km (311 mi) speed record was set at 214.8 mph.

Several airlines operate the S-76A on scheduled services including Helijet International of Vancouver, British Columbia, Canada. Helijet International was recognized in February 2012 as the operator of the world’s highest flight time Sikorsky S-76® airframe an S-76A™ helicopter (Serial Number 760074) with 37,025 flight hours.

S-76A Serial Number 700074 Landing

The Executive S-76 has become the “First Choice” for Fortunes 500 companies. The Queen’s Helicopter Flight which transports Queen Elizabeth II and the Royal Family has flown a Sikorsky S-76C+ since 1998. In 2009 a Sikorsky S-76C++ took over the duties

The Queen’s Helicopter Flight S-76C++

Although not in the original target market, Air Ambulance (EMS) has developed as an S-76 market based on its high dash speed, long range, and room for 2 patients plus equipment which are not available in the EMS competition.

S-76 Air Ambulances

S-76 Development Timeline

Program Start
Start of the Sikorsky S-76 development.
Public Introduction
S-76 introduced at the 1975 Helicopter Association of America (now Helicopter Association International) Convention in Las Vegas, Nevada.
Detailed Design Complete
Detailed design of the Sikorsky S-76 completed.
Prototype Rollout
First production prototype rollout in Stratford, Connecticut.
First Flight
First flight of S-76 (Aircraft No. 2) at Sikorsky Development Flight Center in West Palm Beach, Florida.
FAA Certification Issued
S-76 is FAA Certification under Part 29 Category A for VFR and IFR operations.
First Delivery
First Production S-76 Aircraft delivered to Air Logistics, New Iberia, Louisiana.
S-76A Introduced
The S-76A Mark II aircraft is unveiled to the public.
S-76A+ Introduced
The S-76A+ aircraft with the Arriel engine is introduced.
S-76A++ Introduced
The S-76A++ aircraft is introduced.
S-76B Receives FAA Certification
The S-76B aircraft receives FAA certification.
S-76C Receives FAA Certification
The S-76C aircraft receives FAA certification.
S-76C+ Receives FAA Certification
The S-76C+ aircraft receives FAA certification.
S-76C++ Receives FAA Certification
The S-76C++ aircraft receives FAA certification.
January 1975
February 1975
April 1976
January 11, 1977
March 13, 1977
November 21, 1978
February 27, 1979
1982
1986
1987
October 31, 1985
March 15, 1991
June 21, 1996
January 3, 2006

Configuration Features

S-76A Cutaway Drawing

The S-76 helicopter was designed to serve the off-shore oil market and meet its requirements to carry 12 passengers and a crew of 2 on a 400 nautical mile radius mission with flotation equipment and operate IFR Category A. In order to achieve the design goals, the S-76 employed technologies developed for the UH-60 BLACK HAWK helicopter. Among the features are: titanium and composite main rotor blades, a bearingless composite tail rotor, bifilar vibration absorbers, and a simplified main rotor transmission.

The main rotor blades incorporate composite materials including a hollow titanium spar that is plasma arc welded and hot formed to its oval shape, a fiberglass cover, a redundant graphite root end, a Kevlar tip cap and Nomex honeycomb in the trailing edge. The main rotor blades use an SC1095 airfoil and have a non-linear twist to load the blades evenly in a hover. Tip caps are swept to reduce noise and vibration.

S-76 Main Rotor Blade Construction Details

Ride quality in the S-76 was enhanced by a pitch-cone coupling to a maximum of 17 degrees. The cyclical feathering motion, usually known by the mathematical shorthand “Delta-3”, functions to wash out blade pitch during blade flapping. In other words, when the blade flaps up as it would in turbulence, Delta-3 mechanically washers out some of the pitch angle to prevent tip stall and soften the ride. Delta-3 was incorporated in the S-76 by a phase shifter incorporated in a complex mixer unit.

S-76 Flight Controls and Mixer

The composite bearingless tail rotor principle structural element is the cross beam spar. The cross beam tail rotor is designed to take advantage of the special capabilities of unidirectional graphite composites. The tail rotor consists two assemblies each of which provide two blades for the four bladed tail rotor. The spar which connects opposite blades is made of unidirectional graphite and is laid up in a rectangular cross sectional shape. The resultant beam is flexible in the flapwise and torsional direction but very stiff in the edgewise direction. An airfoil shape is bolted to each end of the cross beam to form one half of the tail rotor. Two of these assemblies are clamped at right angles to form the tail rotor. The resultant tail rotor is free of instabilities and requires no lubrication or maintenance.

S-76 Tail Rotor Construction Detail

The Main Gearbox has as its final reduction a bull gear with two spur gear inputs. This is considerably simpler than the planetary gear system used in previous Sikorsky helicopter models Each engine has a separate power train all the way up to the bull gear through a single spur and a single bevel mesh. The tail takeoff is from the left engine power train. In case of a left engine failure the tail takeoff still drives through the right engine to the bull gear back through the bevel set to the tail take off. The freewheeling units are inside the first spur gear forward of each engine. Using the bull gearing system reduces the number of bearings and gears by a significant number over a conventional planetary gearing approach. This design results in a lower total cost and increased reliability.

S-76 Main Gearbox Drive Train

The main rotor hub is a single piece aluminum forging with elastomeric bearings and Bifilar vibration absorbers tuned to different frequencies to dampen vibrations at the source to reduce cabin noise and protect the airframe from vibration damage.

S-76 Main Rotor and Bifilar Vibration Absorbers

The S-76 fuselage is designed for low drag to improve efficiency. Flush rivets are used, a first for any Sikorsky helicopter. The S-76 was the first Sikorsky commercial helicopter to make extensive use of advanced composites. Kevlar is used for engine cowlings and fairings which is half the weight and twice the strength of fiberglass.

Advanced Composites used on the S-76

Model/1st DeliveryYear of First DeliveryEngines (Max. Continuous Power)ImprovementsGross Weight 
S-76A 1979Allison 250-C30 (557 shp)10,500 lbs
S-76 Mark II1982Allison 250-C30S (557 shp)40 mods to improve reliability & maintainability. Mods were available as Kits and most S-76As were brought up to the MK II standard. 2 Year, 1,000 hour Warranty added.10,500 lbs
S-76A+1986Turbomeca Arriel 1S (701 shp)Increased performance and engine reliability10,500 lbs
S-76A++1987Turbomeca Arriel 1S1 (725 shp)Increased engine power10,500 lbs
S-76B1985P& W Canada PT6B-36A (887 shp)48% increase in takeoff power. 50% increase in useful load under hot and high conditions. Transmission strengthened and airframe strengthened and lengthened 11,700 lbs
S-76C1991Turbomeca Arriel 2S (730 shp) Incorporated the S-76B strengthened transmission and airframe. Arriel engines used for weight savings and fuel economy11,700 lbs
S-76C+1996Turbomeca Arriel 2S1 (787 shp) FADEC Engine Controls.  QUIETZONE® main gearbox11,700 lbs
S-76C++2006Turbomeca Arriel 2S2 (832 shp) FADEC Engine Controls & Inlet Barrier Filters.  QUIETZONE® main gearbox11,700 lbs
S-76DP& W Canada PW210S (1077 shp)11,700 lbs

General Arrangement Drawing

S-76C++ 3-view Drawing

General Characteristics and Performance

Performance
Standard Day At Sea Level
S-76C++
Maximum Gross Weight 11,700 lbs / 5,300 kg
Maximum Cruise Speed 155 kts / 287 kph
Maximum Range Cruise Speed137 kts / 254 kph
Maximum Range – No Reserve 411 nm / 762 km
HIGE (Hover In Ground Effect) 7,050 ft / 2,149 m
HOGE (Hover In Ground Effect) 11,650 lbs. ,Sea Level3,300 ft / 1,006 m
OEI (One Engine Inoperative) Service ceiling 4,900 ft / 1,493 m
AEO (All Engines Operating) Service Ceiling 13,800 ft / 4,206 m

WeightsS-76++ 
Empty Weight 7,007 lbs.
Maximum Gross Weight11,700 lbs.
External Loads Gross Weight11,700 lbs.
External Loads Gross Hook Limit3,300 lbs.

General DataS-76C++
Crew seating capacityIFR 2 Pilots
VFR 1 Pilot
Seating capacity, airline-style seatingIFR 12 passengers
VFR 13 passengers
Baggage compartment volume42 cu ft / 1.19 cu m
Fuel capacity (internal, standard)272 US gal / 1030 L

Aircraft DimensionsS-76C++
Main rotor diameter (blade tip circle)44’ 0” / 13.41 m
Tail rotor diameter (blade tip circle)8′ 0″ / 3.35 m
Fuselage length44′ 1″ / 13.44 m
Fuselage width7’ 0″ /  2.13 m
Length over-all (including rotors)52′ 6″ / 16.0 m
Height over-all14’ 6” / 4.41m
Width 7′ 0″ / 2.13m
Main landing gear tread8′ 0″ / 2.44  m
Wheel base20′ 4″ / 6.20 m
Passenger cabin length (with bulkhead)20′ 0″ / 6.10 m
Passenger cabin width6′ 7″ / 2.01 m
Passenger cabin height6′ 0″ / 1.83 m

Production History

ModelAircraft Produced
S-76A and S-76+307
S-76B103
S-76C and S-76C+191
S-76C++213
S-76DIn Production

Related Models: Military

AUH-76 Armed utility transport version, developed from the S-76 Mk. II. Four were sold to the Philippine Air Force

AUH-76 Gunship Demonstrator

H-76 Eagle Military version of the S-76B. Designed to provide a lower cost alternative to the AH-64 Apache. One built.

H-76 Eagle Gunship

H-76N Planned naval version proposed to New Zealand

Artist’s Conception of S-76N

Related Models: Experimental

SHADOW (Sikorsky Helicopter Advance Demonstrator of Operator Workload) An S-76A with an extended pilot station added to the nose to develop a fly-by wire flight control system for the RAH-66 Comanche program. A safety pilot flew in the normal pilot position to take control of the helicopter if required.

SHADOW was used to test three and four axis side arm controllers. It also tested unique flight control software concepts such as velocity hold which allowed the pilot to release the stick and the helicopter would continue to fly at the set speed. This and other concepts tested were designed to minimize the pilot’s flying workload so he could concentrate on the mission requirements.

S-76A SHADOW

Fantail S-76B with a fan-in-fin tail rotor to test the configuration for the RAH-66 Comanche which required the ability to do a 180 degree turn in 6 seconds with a 45 knot crosswind under hot and high conditions. This led to a very powerful fan and the ability to fly sidewards at 70 mph.

S-76B Fantail helicopter

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