S-76 Spirit

S-76 Spirit

Sikorsky S-76 is a multi-role, medium-size utility helicopter manufactured by Sikorsky Aircraft, a subsidiary of Sikorsky Aircraft. It was principally designed and developed for CHC Helicopter Corporation, Canada. The maiden flight of S-76 took place on 13 March 1977. More than 800 S-76 helicopters have been delivered to various operators worldwide.

Operations carried out by the S-76 include executive passenger transport (VIP), emergency medical services (EMS), search-and-rescue operations (SAR) and offshore passenger and material transportation. The S-76 can accommodate 14 people including two pilots. It has a retractable landing gear.

Sikorsky Aircraft Corporation received Federal Aviation Administration (FAA) certification for its S-76C++, a variant of the S-76, in January 2006.

In October 2012, the FAA issued the Type Certificate for S-76D helicopter, the newest variant of S-76. The first S-76D helicopter was delivered in the last quarter of 2013.

In April 2014, the Civil Aviation Administration of China (CAAC) issued a validation type certificate for the S-76D helicopter.

Design

The S-76 is of conventional configuration, with a four-bladed fully articulated main rotor and a four-bladed anti-torque rotor on the port side of the tailboom. Two turboshaft engines are located above the passenger cabin. In the prototypes and initial production aircraft, these engines were Allison 250-C30s, a new version of the popular Allison 250 engine developed specially for the S-76, with a single-stage centrifugal compressor instead of the multi-stage axial/centrifugal compressor of earlier models of the engine, rated at 650 shp (480 kW) for takeoff. These engines are connected to the main rotor by the main gearbox, a three-stage unit with a bull gear as its final stage rather than the planetary gear used by previous generations of Sikorsky helicopters. This arrangement has 30% fewer parts and lower costs than a more conventional design.

The main rotor hub has a single piece aluminum hub with elastomeric bearings designed not to require lubrication or any other kind of maintenance throughout its design life. The main rotor blades have titanium spars and incorporate a ten degree twist to give an even loading when hovering, while they use a non-symmetrical airfoil section with a drooped leading edge. The rotor tips are tapered and swept back. Flight controls are servo-assisted, with a Stability Augmentation System fitted. A retractable nosewheel undercarriage is fitted, which gives the S-76A a 6 knots (6.9 mph; 11 km/h) increase in cruising speed; emergency flotation gear can be fitted using helium-filled bags to increase buoyancy in the event of a forced landing on water.

The fuselage of the aircraft is of mixed metal and composites construction; the nose is composed of fiberglass while the cabin primarily employs a light alloy honeycomb structure, the semi-monocoque tailboom is also constructed of light alloy. Two pilots (or a pilot and a passenger) sit side by side in the cockpit, situated ahead of the cabin, which can accommodate a further 12 passengers in three rows of four, or four to eight passengers in more luxurious executive seating.

Development

Sikorsky Aircraft Corporation commissioned the development of a medium business helicopter, UH-60 Black Hawk, in the 1970s. The company focused on airlines that were using medium business helicopters and the oil drilling industry. Sikorsky built the S-74, which was renamed the S-76 Spirit. The S-76 Spirit was equipped with two Allison 250 C30 turbo shafts with the capacity to generate 478kW of power each.

In 1982 the S-76A, also known as the S-76 Mk II, was developed. The S-76A provides high-range climbing. It is being operated by Helijet Airways of Vancouver, British Columbia, Canada.

In 1987 an advanced version, S-76B, was introduced. It can fly at speeds of 155k at sea level. About 500 S-76s were delivered by early 2001. Turbomeca Arriel 2S1 engines were deployed in the S-76C+ until December 2005. The main rotor of the S-76C+ was manufactured using composite material. Increased active noise and vibration dampers were used to provide more comfort for passengers. Production of the S-76C+ was completed in December 2005.

The S-76C++, which features an intake air filter and an improved and quieter transmission, was launched later. It is equipped with upgraded interior equipment and electronics. The production of S-76C++ was completed in January 2006. The helicopter is powered by a Turboméca Arriel 2S2 turbo shaft engine.

The S-76D is equipped with a Pratt and Whitney 210S engine. The dual FADEC-controlled engine can produce about 1,050shp of power. Active Vibration Control System (AVCS) and four-bladed composite main rotor are installed for smooth operation.

The revolutions per minute (rpm) of the rotor are self-adjusted. The higher rpm is applied during takeoff and lower rpm setting is applied for enhancing cruise range.

The maiden flight of S-76D took place in February 2009. The helicopter entered production phase in December 2009. Final assembly production started a year later in December 2010, with the first flight test of the second prototype complete in March 2010.

Cabin of S-76C aircraft

The S-76C++ helicopter has a large rectangular cabin. The length and width of the cabin are 2.41m and 1.93m respectively. The height and area of the cabin are 1.35m and 4.65m² respectively. The baggage volume and cabin volume are 1.08m³ and 5.78m³ respectively.

The helicopter also has a spacious cabin interior, an AVCS, reduced interior noise, two cabin doors with pop-out windows and two cockpit doors.

S-76C Cockpit

The cockpit is equipped with a Honeywell primus weather radar, dual comm / nav radios, an automatic direction finder, dual attitude and heading reference systems (AHRS) and air data computers, a radio altimeter, a mode C transponder, dual VORs with glideslope, distance measuring equipment (DME) and a cockpit voice recorder (CVR).

Avionics

The avionics suite installed in the cockpit of the S-76C++ includes a Honeywell four-tube electronic flight instrument system (EFIS), a four-axis fully coupled autopilot, an integrated instrument display system (IIDS) and a Honeywell enhanced ground proximity warning system (EGPWS).

The S-76D’s cockpit is fitted with an avionics suite that includes a Thales Top Deck avionics system, four-axis fully coupled autopilot, an EGPWS, a traffic collision avoidance system (TCAS1), a Honeywell Primus 660 weather radar, a health usage monitoring system (HUMS), a Thales digital map and a Collins Pro Line 21 comm / nav radio suite.

Engine

“The S-76D is equipped with a Pratt & Whitney 210S engine.”

The S-76 is powered by two Turbomeca Arriel 2S2 turbo shaft engines. Each engine can produce a takeoff power of 688kW. The length and height of the engine are 1.156m and 0.6m respectively. The engine can generate maximum continuous power of 621kW.

The engine has simple design that consists of five modules. This provides simpler maintenance and reduces operating cost through optimised acceleration modes. The Arriel 2S2 turbo shaft engine produces 6% more power than the Arriel 2S1 turbo shaft engine. It is also equipped with a double-channel electronic engine control unit (EECU), which measures fuel, ignition timing and other parameters. The endurance of the Arriel 2S2 is 3,000h.

The Arriel 2S2 is suitable for helicopter carrying missions such as EMS, SAR, police, VIP, aerial work, corporate and off-shore liaison.

Performance

The S-76 can fly at a maximum speed of 287km/h. The ferry range and service ceiling of the helicopter are 639km and 4.572m respectively. The maximum takeoff weight of the S-76 is 5,306kg while the empty weight is 3,177kg.

Variants

Civil

  • S-76A: Original production version, powered by two 650 shp (485 kW) Rolls-Royce (Allison) 250-C30 turboshaft engines. Large number modified to S-76A+, A++, C, and C+. 284 manufactured.
  • S-76A Utility: Utility transport version, equipped with sliding doors and a strengthened floor.
  • S-76A+: Unsold S-76s were fitted with two Turbomeca Arriel 1S turboshaft engines. 17 manufactured.
  • S-76A++: S-76 helicopters fitted with two Turbomeca Arriel 1S1 turboshaft engines.
  • S-76A Mk II: Improved all-weather transport version, fitted with more powerful engines, and other detail improvements.
  • S-76B: Powered by two Pratt & Whitney Canada PT6B-36A or Pratt & Whitney Canada PT6B-36B turboshaft engines. 101 built.
  • S-76C: Powered by two 539-kW (981-shp) Turbomeca Arriel 1S1 turboshaft engines. 43 manufactured.
  • S-76C+: Uprated version, fitted with improved Turbomeca Arriel 2S1 turboshafts with FADEC. 35 manufactured.
  • S-76C++: Turbomeca Arriel 2S2
  • S-76D: Powered by two Pratt & Whitney Canada PW210S. Also features a Thales Topdeck avionics suite and improved noise signature over all previous variants.

Military

  • AUH-76: Armed utility transport version, developed from the S-76 Mk. II.
  • H-76 Eagle: Announced in 1985 the Eagle was a military and naval variant of the S-76B, none sold.

Experimental derivatives

  • Sikorsky S-75: The Advanced Composite Airframe Program (ACAP) was an all-composite Sikorsky early LHX proof of concept aircraft. Designated S-75, it mated a new composite airframe with S-76 engines, rotors and powertrain components.
  • Sikorsky S-76 SHADOW: Boeing-Sikorsky MANPRINT study. The original concept of the LHX program was to produce a one-man helicopter that could do more than a two-man aircraft. The Sikorsky (S-76) Helicopter Advance Demonstrator of Operators Workload (SHADOW) had a single-pilot advanced cockpit grafted to its nose. The purpose was to study the MANPRINT or human engineering interface between the pilot and the cockpit controls and displays. The cockpit was the prototype of a single-pilot cockpit designed for use on the prototype RAH-66 Comanche armed reconnaissance helicopter. The cockpit was designed so sensors would feed data to the pilot through helmet-mounted displays. The MANPRINT study determined that single-pilot operation of the Comanche was unsafe, and would result in pilot overload. As result of this study, the Comanche was designed to be operated by a crew of two.

Specifications

Crew 2
Capacity 13
Length (rotors running)
52 ft 6 in (16 m)
Fuselage length (including tail rotor)
Height 14 ft 6 in (4.42 m)
Length (blades folded)
Main rotor diameter 44 ft 0 in (13.41 m)
Tail rotor diameter
Maximum weight 11,700 lb (5,306 kg)
Maximum weight with external load
Empty weight 7,005 lb (3,177 kg)
Maximum speed (Vne)
155 kn (178 mph, 287 km/h)
Cruising speed at sea level
155 kn (178 mph, 287 km/h)
Ascent speed at sea level
 
Ceiling in service
13,800 ft (4,200 m)
Passable distance at sea level with standard reserve
411 nmi (473 mi, 761 km)
Powerplant 2 × Turbomeca Arriel 2S2 turboshaft, 922 shp (688 kW)
Avionics

  • Honeywell four-tube EFIS and Collins Proline II avionics suite
  • Four-axis fully coupled autopilot
  • Integrated Instrument Display System (IIDS)
  • Honeywell ground proximity warning system
  • Honeywell Primus weather radar
  • Dual comm/nav radios
  • Automatic direction finder
  • Dual attitude and heading reference system and air data computers
  • Radio altimeter
  • Mode C transponder
  • Dual VHF omnidirectional range (VOR) and Instrument landing system (ILS)
  • Distance measuring equipment
  • Cockpit voice recorder

Operators

  • Argentine Air Force.
  • China
  • Honduran Air Force
  • Japan Coast Guard – 4 S-76C.
  • Royal Jordanian Air Force.
  • Philippine Air Force – 4 AUH-76.
  • Spanish Air Force – 8 S-76.
  • Royal Thai Navy – 5 S-76.
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