Sikorsky S-76
Introduction
The S-76 is a twin-engine “medium” helicopter.
The aircraft primarily provides crew transportation for the oil and gas industry (mainly offshore) and has a secondary role as a EMS / search-and-rescue platform.
Outside these two core areas, the type is well established in VVIP transportation and has seen some limited deployment for humanitarian relief and conflict-zone logistical support missions.
Sikorsky(owned by Lockheed Martin) has now decided not to accept any new orders for the S-76.
History and Development
The S-76 was originally designed as the S-74 but was renamed the S-76 as a reference to 1776, the year of US independence.
The S-76 was the first Sikorsky helicopter designed purely for commercial rather than military use. However, Sikorsky’s design work on the military S-70 helicopter (which was selected for use by the United States Army as the UH-60 Black Hawk) was utilized significantly in the development of the S-76. For example, S-70 design technology was incorporated into the rotor blades and rotor heads of the S-76.
The S-76 construction design has a four-bladed fully articulated main rotor and a four-bladed anti-torque tail rotor. The engines are located above the passenger cabin and the engines are connected to the main gearbox which transfers the drive from the engines to rotate the main and tail rotors. The main gear box also drives the hydraulic pumps and provides mounting for the control servos and other monitoring systems.
The main rotor head is constructed using an aluminium alloy hub with elastomeric bearings which require no lubrication The main rotor blades are constructed using a titanium spar and have an aerodynamic twist built into them giving amore balanced distribution of loading in the hover. They also feature a drooped leading edge and tapered and sweep on the tips.
The flight control system includes Main and tail rotor dual hydraulic servo actuators to provide the control movement supported by dual flight director computers controlling the flight path and stability of the helicopter.
The S76 fuselage is constructed using a mix of aluminium and composite construction. The fuselage is supported with a tricycle undercarriage system with a nose undercarriage and two main undercarriage units. The undercarriage is retractable in flight to reduce drag. The fuselage is also capable of having emergency flotation system installed with four flotation bags to allow landing on water in emergency situation. The seating in the S76 allows for one or two pilots in the cockpit with up to twelve passenger seats in the cabin in three rows of four seats. The cabin can also be configured for low density VVIP seating or with medical or SAR interiors.
The S-76 prototype first flew on March13, 1977. Initial US FAA type certification was granted on November 21, 1978, with the first customer delivery on February 27, 1979. The S-76 was originally brand-named "Spirit" late but this branding did not continue.
The first production variant was the S-76A. In 1982, this model set class records for range, climb, speed and ceiling. Several airlines still operate the S-76A on scheduled services including Helijet Airways. The S-76 "Mk II" was introduced in 1982 followed by the S-76B in 1987 and S-76C in 1990. The main driver in the various variant changes were changes to more powerful and sophisticated engines. The "B" variant was powered by P&WC engines while the C variant saw a return to the Turbomeca engines that had been installed on the"A+/++" variant.
The S-76C is the variant most commonly flying today and itself has three variants (C, C+ and C++). The S-76C++ is powered by twin Turbomeca Arriel 2S2 engines with FADEC anda Honeywell EFIS suite. The differences between the S-76C variants are primarily the power of the engines but also modernised avionics.
Development of the (final) S-76D variant was subject to four years of delays due to technical problems in expanding the flight envelope. The prototype flew in February 2009 but FAA certification did not occur until October 2012. 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 kts (287 km/h) cruise speed as earlier models. The maximum operating mass has subsequently been increased to 11,875lbs (5,386 Kg)
Variants and Engine Types
· 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+: S-76A’s were fitted with two Turbomeca Arriel 1S turboshaft engines.
· S-76A++: S-76A helicopters fitted with two Turbomeca Arriel 1S1 turboshaft engines.
· S-76B: Powered by two Pratt & Whitney CanadaPT6B-36A or Pratt & Whitney Canada PT6B-36B turboshaft engines.
· S-76C: Powered by two Turbomeca Arriel 1S1 turboshaft engines.
· S-76C+: Uprated version, fitted with improved Turbomeca Arriel 2S1 turboshafts with FADEC.
· S-76C++: Turbomeca Arriel 2S2
· S-76D: Powered by two Pratt & Whitney Canada PW210S. Also features a Thales Top deck avionics suite and improved noise signature over all previous variants.
Safety Performance
The S76 has seen several incidents and accidents in its history. Many of these being categorised in the Loss of control (LOC) or Controlled flight into Terrain (CFIT) categories.
Some fatal accidents of note are as follows:
In 1980/1981 two aircraft were lost due to failure of the main rotor spindles.
In 2002 an aircraft was lost due to inflight failure of a main rotor blade.
In 2004 an aircraft was lost due to failure of a main rotor servo actuator.
In 2015 two aircraft were lost due to failure of the main servo input control rod.
In 2020 basketball playerKobe Bryant was killed in a S-76 crash in the US.
The Future
As the S76 is effectively out of production now the future is in the use of the existing fleet.
The S76C++ is the most popular used variant of the S-76 and is particularly highly regarded by Brazilian offshore operators. However, some operators prefer the older S76C variants due to lower operating costs.
Production
S-76 production was initially set up at the Sikorsky production facility in Stratford CT in the USA, production was later transferred to the Sikorsky facility in Coatesville, PA,USA. Sikorsky has now stopped receiving orders for new S-76 helicopters, and therefore production is now closed.
Offshore Oil and Gas
The S-76 continues to support the O&G markets in North America and Latin America, as well as in Africa and in Asia. The O&G work is carried out mainly by the S76C+/C++ andD models.
The S-76 (including the"D" model) does not meet the latest IOGP requirements which has caused its reduced share of O&G market. The popularity and performance of the AW139 has seen a big movement of O&G support away from the S76 to theAW139. With the introduction of the H160 into this segment of the market offering the latest compliance standards as well as innovative noise and fuel reduction the S-76 is now behind the competition.
VIP / Private
The S-76 continues to have a strong presence in the VIP markets around the world.
Public Service (SAR, EMS,Police)
The S76 has in the past seen good service in the public service market in SAR and other roles.
However, in comparison to aircraft such as the AW139, AW189 and H135/H145 its role in public service has been limited and is very likely to remain so. Only in the US does the S-76continue to have a significant presence in the HEMS market.
Costs and Values
S-76 operating costs are reported to be comparable with other helicopters in the medium twin category.
The rental price for a S-76C++is in the range of US$32K to US$36K per month.
Maintenance
Inspections
The primary maintenance events on the S-76C++ are as follows:
Airframe inspections:
Hourly inspections at 100hrs, 300hrs, 600hrs and 1500hrs.
Calendar inspection at 12months and 24 months.
Engine inspections at: 600hrs
The engine overhaul interval is 4000 hrs.
Power by the hour products
Airframe:
Heli-One offers support options for the airframe components.
Eagle Copters offer a support option for the airframe components.
Engine:
Safran offers SPH support contracts for the Arriel2S engines (S-76C++)
P&WC offer support contracts for the PW210S engines (S-76D)
External Links
The Sikorsky home page for the S-76: https://www.lockheedmartin.com/en-us/products/sikorsky-s-76-helicopter.html
The Wikipedia page for the S-76: https://en.wikipedia.org/wiki/Sikorsky_S-76