S-76®Helicopter

 

 

 

s-76-1

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Background

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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.

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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.

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S-76-2

S-76A Executive Transport Helicopter

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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.

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S-76-3

.S-76A Oil Rig Crew Change

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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.

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S-76-4

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

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S-76-5

The Queen's Helicopter Flight S-76C++

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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.

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S-76-6

S-76 Air Ambulances

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S-76 Development Timeline

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  • January 1975 Program Turn On
  • February 1975: S-76 introduced at the HAA (now HAI) convention in Las Vegas, Nevada
  • April 1976 Completed Detail Design
  • January 11, 1977: First production prototype rollout in Stratford Connecticut.

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S-76-7

S-76 Rollout January 11, 1977

 

  • March 13, 1977: First flight, Aircraft No. 2, at Sikorsky Development Flight Center in West Palm Beach, Florida.

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S-76-8

.S-76 First Flight March 13, 1977

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  • November 21, 1978: FAA Certification under Part 29 Category A for VFR and IFR operations.
  • February 27, 1979 First Production Aircraft delivered to Air Logistics, New Iberia, Louisiana.

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S-76-9

S-76 First Delivery February, 27, 1979

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  • March 26, 1979 S-76 was a contender for the USCG Short Range Recovery (SRR) Program for a helicopter to replace the Sikorsky HH-52A.  The requirement was for 90 helicopters.  A decision was made to withdraw from the competition due to the USCG requirements that the US Government obtain rights in data for the design, which was company funded, and a requirement for a firm fixed price for the Avionics Development.
  • 1982 S-76A Mark II introduced
  • 1986 S-76A+ with Arriel Engine introduced
  • 1987 S-76A++ introduced
  • October 31, 1985 FAA Certification of the S-76B
  • March 15, 1991 FAA Certification of the S-76C
  • June 21, 1996 FAA Certification of the S-76C+
  • January 3, 2006 FAA Certification of the S-76C++

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Configuration Features

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S-76-10

.S-76A Cutaway Drawing

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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. 

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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.

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S-76-12

.S-76 Main Rotor Blade Construction Details

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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.

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S-76-12


S-76 Flight Controls and Mixer

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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-76-13

.S-76 Tail Rotor Construction Detail

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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.

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S-76-14

.S-76 Main Gearbox Drive Train

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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.

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S-76-15


S-76 Main Rotor and Bifilar Vibration Absorbers

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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.  

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S-76-16

. Advanced Composites used on theS-76

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Model/1st Delivery

Engines (Max. Continuous Power)

Improvements

Gross Weight

 

S-76A
1979

Allison 250-C30 (557 shp)

 

10,500 lbs

 

S-76 Mark II
1982

Allison 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+
1986

Turbomeca Arriel 1S (701 shp)

Increased performance and engine reliability

10,500 lbs

 

S-76A++
1987

Turbomeca Arriel 1S1 (725 shp)

Increased engine power

10,500 lbs

 

S-76B
1985

P& 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-76C
1991

Turbomeca Arriel 2S (730 shp)

Incorporated the
S-76B strengthened Transmission and Airframe. Arriel engines used for weight savings and fuel economy

11,700 lbs

 

S-76C+
1996

Turbomeca Arriel 2S1 (787 shp)

FADEC Engine Controls.  QUIETZONE® main gearbox

 

11,700 lbs

 

S-76C++
2006

Turbomeca Arriel 2S2 (832 shp)

FADEC Engine Controls & Inlet Barrier Filters.  QUIETZONE® main gearbox

11,700 lbs

 

S-76D

P& W Canada PW210S (1077 shp)

The S-76D is in development in 2012. For current information refer to .Sikorsky web

11,700 lbs

 

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S-76C++ BASELINE CONFIGURATION

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Airframe

  • Large, rectangular cabin
  • Reduced interior noise
  • Two cabin doors with pop-out egress windows (optional)
  • Two jettisonable cockpit doors
  • Retractable tricycle landing gear
  • Built-in work platforms to access engines and hydraulic deck

Cockpit

 

  • Honeywell four-tube EFIS and Collins Proline II avionics suite
  • Four-axis fully coupled autopilot
  • Integrated Instrument Display System (IIDS)
  • Honeywell Enhanced Ground Proximity Warning Systems (EGPWS)
  •  406 MHz Emergency Location Transmitter (ELT)
  • Cockpit Voice Recorder
  • Honeywell Primus® Weather radar
  • Dual comm/nav radios
  • Automatic direction finder
  • Dual AHRS and air data computers
  • Radio altimeter
  • Mode C transponder
  • Dual VOR's with glideslope
  • DME
  • CVR

basic configuration

Powerplant and fuel system

 

  • Two Turbomeca Arriel 2S2 engines with dual FADEC
  • Engine inlet barrier filters
  • Suction fuel system - 281 gallons

Rotor and drive system

 

  • QUIETZONE® main gearbox
  • Four main rotor blades with an articulated hub
  • Four all composite tail rotor blades
  • Dual redundant and isolated flight controls

Electrical

 

  • Dual engine-driven starter-generators
  • Dual static inverters
  • Retractable Controllable Landing Light
  • Fixed Landing Light On Right Main Landing Gear
  • Single transmission-driven AC generator

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S-76C++ OPTIONS

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      • Honeywell EVXP (Enhanced Vibration X Pert) and HUMS (Health and Utilization Monitoring System) offers a vibration monitoring and automatic engine exceedance system that captures monitors and records operational flight data.
      • 50 or 106 gallon Auxiliary Fuel tanks
      • A search and rescue package to allow automatic search, approach, and hover under instrument conditions.
      • FLIR and sliding doors

 

General Arrangement Drawing (S-76C++)

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3 VIEW

.S-76C++ 3-view Drawing

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General Characteristics and Performance (S-76C++ Standard)

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WEIGHTS

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Empty Weight

7,007 lbs.

 

Maximum Gross Weight

11,700 lbs.

 

External Loads Gross Weight/Hook Limit

11,700 lbs.

3,300 lbs.

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GENERAL DATA

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Crew seating capacity

IFR 2 Pilots

 

VFR 1 Pilot

Seating capacity, airline-style seating

IFR 12 passengers

 

VFR 13 passengers

Baggage compartment volume

42 cu ft     1.19 cu m

Fuel capacity (internal, standard)

272 US gal   1030 L

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PERFORMANCE

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Maximum Gross Weight

11,700 lbs

5,30  kg

Maximum Cruise Speed

155 kts

287 kph

Maximum Range Cruise Speed

137 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 Level

3,300 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

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AIRCRAFT DIMENSIONS

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Main rotor diameter (blade tip circle)

44’ 0”          13.41 m

Tail rotor diameter (blade tip circle)

8' 0"             3.35 m

Fuselage length

44' 1"           13.44 m

Fuselage width

7’ 0"             2.13 m

Length over-all (including rotors)

52' 6"           16.0 m

Height over-all

14’ 6”           4.41m

Width

7' 0"             2.13m

Main landing gear tread

8' 0"             2.44  m

Wheel base

20' 4"             6.20 m

Passenger cabin length (with bulkhead)

20' 0"             6.10 m

Passenger cabin width

  6' 7"             2.01 m

Passenger cabin height

  6' 0"            1.83 m

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Production History


S-76 Deliveries by Model

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S-76A and S-76+       307 Built
S-76B                          103 Built
S-76C and S-76C+    191 Built
S-76C++                     213 Built through 2011.

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Related Models

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Military

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

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S-76-18


AUH-76 Gunship Demonstrator

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

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S-76-19

H-76 Eagle Gunship

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  • H-76N Planned naval version proposed to New Zealand

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S-76-20

Artist’s Conception of S-76N

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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.

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S-76-21


S-76A SHADOW

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  • 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.

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S-76B Fantail helicopter

 

 

Prepared by Vinny Devine
April 2012

 

last update SEPTEMBER 11, 2012

 

 

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