The Sikorsky S-76 is a medium-size commercial utility helicopter designed and produced by the American helicopter manufacturer Sikorsky Aircraft. It is the company's first helicopter specifically developed for the civilian market.
The S-76 was developed during the mid-1970s, originally being designated S-74 but renamed in honor of the U.S. Bicentennial. Drawing upon its recently-developed S-70 helicopter, it features twin turboshaft engines, four-bladed main and tail rotors, and retractable landing gear. On 13 March 1977, the prototype performed its maiden flight. The initial production variant was the S-76A, the first deliveries of which took place on 27 February 1979. Several improved models were produced over time, including the S-76 Mk II launched in 1982, and the S-76B in 1987. Development of the S-76D was particularly troubled, being delayed by four years of delays due to flight envelope issues; it was finally certified for operation on 12 October 2012.
The S-76 initially encountered strong demand from the off-shore oil drilling industry; later on, demand shifted towards the VIP sector of the market. It performed several noteworthy flights, such as the first circumnavigation of the world in an east-to-west direction by a helicopter, and an autonomous demonstration flight during 2016. Sikorsky also used individual helicopters, often heavily modified for the purpose, for experimental purposes and to support other programmes. Demand for the S-76 waned during the 2010s, newer helicopters such as the AgustaWestland AW139 proved to be stiff competition. During March 2022, Sikorsky halted new orders for the S-76, but stated that it was looking at opportunities for future overseas manufacturing with foreign partners.
Development
The development of the S-76 commenced during the mid-1970s as the S-74. The S-74 was subsequently redesignated the S-76 in honor of the U.S. Bicentennial. The company had set the design goal of producing a medium helicopter suitable for corporate transportation and the oil drilling industry. Sikorsky's design work on the S-70 helicopter (which was selected for use by the United States Army as the UH-60 Black Hawk) was utilized in the development of the S-76, incorporating S-70 design technology in its rotor blades and rotor heads.[5][6]: 1378 It was the first Sikorsky helicopter designed purely for commercial rather than military use.[6]: 1377
On 13 March 1977, the prototype performed its maiden flight.[7] On 21 November 1978, initial US Federal Aviation Administrationtype certification was granted, while the first customer delivery took place on 27 February 1979.[8]: 142, 144 During late 1978, the S-76 was officially named "Spirit",[8]: 144 however, this name was officially dropped by Sikorsky on 9 October 1980, reportedly due to translation issues into some foreign languages.[5][9]
The first production variant was the S-76A. Several improved models were produced over time. During 1982, the S-76 Mk II, equipped with more powerful engines and other refinements, was introduced. In 1987, production of the S-76B, powered by Pratt & Whitney Canada PT6B-36A and Pratt & Whitney Canada PT6B-36B engines; it was capable to attaining a maximum speed of 155 kn (287 km/h) at sea level. By early 2001, in excess of 500 S-76s had been delivered.[7]
During the early 2000s, the S-76C+ was the main version in production; it was equipped with twin Turbomeca Arriel 2S1 engines with FADEC and a HoneywellEFIS suite.[7] This version also incorporated active noise suppression, vibration dampers and a composite main rotor. On 3 January 2006, the S-76 C++ replaced earlier versions in production; it is powered by twin Turbomeca Arriel 2S2 engines and incorporates an improved and quieter transmission as well as minor changes in the interior equipment and avionics. By January 2006, Sikorsky had secured 92 orders for this model.[citation needed]
Development of the follow-on S-76D was subject to four years of delays due to technical problems in expanding the flight envelope. On 7 February 2009, the prototype conducted its first flight, and type certification was initially expected during 2011 while deliveries were forecast to start at the end of that year. The FAA issued certification on 12 October 2012. Three prototypes were used in the certification program, with one aircraft used to certify the optional rotor electric ice-protection system. The "D" model is powered by 1,050 hp (783 kW) Pratt & Whitney Canada PW210S engines driving composite rotors and incorporates active vibration control. Performance is substantially improved with the added power, but initial certification retains the same 11,700 lb (5,307 kg) gross weight and maximum 155 kn (287 km/h) cruise speed as earlier models.[10][11][12]
The rate of manufacturing noticeably declined during the 2010s; only a dozen S-76s were delivered between 2016 and 2020.[13] During September 2013, it was announced that the Chinese manufacturer Changhe Aircraft Industries Corporation had been contracted to produce the S-76D airframe.[14] By 2022 April, in excess of 875 S-76s had reportedly been built.[4]
During March 2022, Sikorsky announced that it had halted new orders for the S-76 while potential overseas manufacturing partners and licensing opportunities were being evaluated. Reasons for the hold included decreasing sales volume, the high cost of supply and manufacturing, and the prohibitive costs associated with adapting the S-76 to meet increasing safety mandates. This move effectively ended production of the S-76 following the completion of the three orders that were outstanding, and represented a withdrawal by Sikorsky from the medium commercial helicopter market.[15][16] Sikorsky has stated that it will continue to actively manufacture spare parts for the S-76 at its Connecticut facility.[13]
The S-76 is of a conventional configuration, with a four-bladed fully articulated main rotor and a four-bladed anti-torque rotor on the port side of the tailboom. It is powered by a pair of turboshaft engines, which are located above the passenger cabin.[17] On the prototypes and initial production aircraft, these engines were Allison 250-C30s, a variant of the popular Allison 250 engine that was developed specially for the S-76l it had 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.[8]: 113–114 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 that had been used by previous generations of Sikorsky helicopters. This arrangement has 30% fewer parts and lower costs than a more conventional design.[5][8]: 114
The main rotor is furnished with a single piece aluminum hub fitted with elastomeric bearings, which are designed not to require lubrication or any other kind of maintenance throughout its design life.[5][8]: 114 The main rotor blades have titanium spars and incorporate a ten degree twist to provide 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.[6]: 1378 [8]: 114 The rotor blades on later-build S-76s feature ice protection measures.[13] The flight controls are servo-assisted and have a Stability Augmentation System fitted.[8]: 114,116 A retractable nosewheel undercarriage is fitted, the reduced drag from this arrangement is credited with increasing the S-76A's cruising speed by 6 knots (6.9 mph; 11 km/h). Emergency flotation gear can be fitted, which uses helium-filled bags to increase buoyancy in the event of a forced landing on water.[6]: 1377
The fuselage of the S-76 is made from both metal and composite materials; while the nose is composed of fiberglass, the cabin area primarily employs a light alloyhoneycomb structure, the semi-monocoque tailboom is also constructed of light alloy.[17] A pair of pilots are typically seated in a side-by-side arrangement in the cockpit, situated ahead of the cabin, which can accommodate a further 12 passengers in three rows of four, or between four and eight passengers in a more luxurious executive seating configuration.[8]: 114 Later models can be flown by a single pilot when provisioned with an appropriately configured cockpit.[13] The S-76 was not originally designed with crashworthy fuel systems, leading to difficulties continuing production after an FAA requirement was implemented in April 2020.[16]
Operational history
Early on in its commercial career, the S-76 became popular for offshore operations, such as to oil rigs.[18] Numerous operators have either purchased or leased the type specifically to operate in this sector.[19]
During 1982, the S-76A set multiple class records for range, climb, speed[20][21][22] and ceiling.[23] In June 1995, the S-76 became the first helicopter to circumnavigate the world in an east-to-west direction, piloted by the Australian adventurer Dick Smith.[24]
During the campaigning in the run up to the 2005 United Kingdom general election, both the Labour and the Conservative parties dispensed with conventional 'battle buses' in favour of S-76 helicopters to quickly transport their leaders around the British Isles.[25] According to Jason Lambert, Sikorsky's vice president of commercial and military systems, the S-76 had proven itself to be particularly popular amongst VIP customers.[16] By 2020, according to Sikorsky, ten countries operated S-76s to carry their heads of state.[18]
S-76s have been periodically used to test new technologies and capabilities. The highly-modified S-76 SHADOW (Sikorsky Helicopter Advance Demonstrator of Operators Workload) was built to demonstrate its advanced cockpit for single-pilot operations and to study the human engineering interface between the pilot and the cockpit controls and displays; this was in aid of the RAH-66 Comanche armed reconnaissance helicopter programme.[26] During the 2010s, an S-76 was configured for autonomous operation and demonstrated this ability in June 2016, flying for a distance of around 30 miles (48 km) with no human intervention beyond limited inputs made via a tablet computer, the take off and landing phases were also performed autonomously.[27]
During the 2010s, many S-76 operators elected to replace the type with newer medium-lift rotorcraft, such as the AgustaWestland AW139.[16] In early 2020, it was observed that, while the S-76D was no longer compliant with FAA regulations to permit its sale to US-based customers, sales were still possible to several other countries.[13]
Original production version, powered by two 650 shp (480 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.
Armed utility transport version of the S-76 Mk. II. Delivered in 1983 to the Philippine Air Force. Initially armed with two fixed forward firing M134 7.62 mm minigun (one each side) and a 7-round rocket pod on each side and radar altimeters. When M134 became unserviceable, the guns were replaced with M2P Machine Guns.[30][31]
H-76 Eagle
A militarised variant suitable for naval operations, based on the S-76B, it was announced during 1985 but none were ever sold.
Experimental derivatives
Sikorsky S-76 SHADOW
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.[32]
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.[26]
Operators
Civil
The S-76 is in civil service around the world with airlines, corporations, hospitals, and government operators. The world's largest civilian fleet is the 79 Sikorsky S-76 helicopters operated by CHC Helicopter Corporation.[3]
On 17 July 2002, S-76A G-BJVX, operated by Bristow Helicopters, crashed into the North Sea due to the failure of a main rotor blade. The operator temporarily halted all helicopter flights over the North Sea until operations resumed on 3 September 2002.[50]
^ abcdDevine, Vinny (11 September 2012) [April 2012]. "S-76 Helicopter". Sikorsky Archives. Archived from the original on 13 March 2022. Retrieved 25 April 2022.
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