Sikorsky S-76 & S-92 (2024)

* In the 1970s, the Sikorsky company introduced a new light helicopter,the "S-76", primarily but not entirely for civil use. The S-76 provedsuccessful, with Sikorsky then introducing a larger helicopter, the "S-92".This document provides a history and description of the S-76 and S-92.A list of illustration credits is included at the end.

[1] S-76 ORIGINS / S-76A & S-76B

* In early 1975, Sikorsky announced the development of a new commercialhelicopter, originally designated the "S-74", this machine to be the firstSikorsky helicopter designed from the outset for civilian use. It was soonrenamed the "S-76 Spirit", to capitalize on the American bicentennial in 1976-- though the "Spirit" of the name part would be dropped in a few years,since that name didn't come out right in some foreign languages.

The S-76 was based on S-70 Black Hawk technology, with a configurationsomewhat along the lines of the Agusta A109 and the Bell 222 helicopters, butlarger. The first of four S-76 prototypes performed its initial flight on 13March 1977. The type received FAA certification in April 1978. Deliveriesof the initial "S-76A" production version began in early 1979.

Sales of the S-76A were slow at the outset, due to the sluggish economy andvarious minor technical problems with the machine. The economy began torecover in the early 1980s, and Sikorsky relaunched the type in 1982 in theform of a modest production improvement designated the "S-76 Mark II",featuring an improved ventilation system, modifications to the dynamicsystem, and more maintenance access panels. Kits were provided to updateS-76As to S-76 Mark II standard. There was also an "S-76 Utility" version ofthe S-76 Mark II, with a sliding door on both sides and stronger floors.

* The S-76 Mark II was a sleek machine of main-tail rotor configuration, withaccommodations for one or two crew -- dual controls were optional -- and amaximum of 12 passengers, though other various passenger arrangements wereavailable, including a four-passenger "office in the sky" layout. A widerange of luxury interiors could be installed as per customer specification.There were front-hinged doors on both sides of the cockpit, as well as doorson each side of the passenger cabin; the cabin doors were front-hinged bydefault, but rear-sliding doors were used on utility or search and rescue(SAR) configurations. There was a baggage hold behind the passenger cabin,with doors on each side of the fuselage. The utility version could be fittedwith litters for the medical evacuation role. Avionics included radio,navigation aids, and a wide range of options, such as weather radar.

The S-76 Mark II was powered by twin Allison 250-230S turboshaft engines witha maximum continuous rating 485 kW (557 HP) each. The original S-76A used 5%less powerful Allisons. The transmission system was rated at 969 kW (1,300HP) and could absorb the full power of both engines. The engine systemincluded a fire detection and extinguisher system.

The S-76 Mark II used four-bladed main and tail rotors, similar to thosedeveloped for the S-70 Black Hawk, but scaled down. The main rotor hadtitanium spars surrounded by Nomex polymer honeycomb and sheathed withfiberglass. There were titanium-nickel abrasion strips on the leading edgeof the blades, plus swept tips made of Kevlar polymer. The tail rotor was ofcomposite construction. There was an all-moving tailplane for flight trim.

 ___________________________________________________________________ SIKORSKY S-76 MARK II: ___________________________________________________________________ main rotor diameter: 13.41 meters (44 feet) tail rotor diameter: 2.44 meters (8 feet) fuselage length: 13.22 meters (43 feet 4 inches) footprint length: 16.0 meters (52 feet 6 inches) height (tail rotor): 4.42 meters (14 feet 6 inches) empty weight: 2,540 kilograms (5,600 pounds) max sling load: 1,500 kilograms (3,300 pounds) max loaded weight: 4,672 kilograms (10,300 pounds) max cruise speed: 270 KPH (165 MPH / 145 KT) service ceiling: 4,575 meters (15,000 feet) range: 750 kilometers (465 MI / 405 NMI) ___________________________________________________________________ 

The S-76 Mark II had retractable tricycle landing gear, with single wheels onall gear assemblies, the nose gear retracting backwards, the main geartucking up and back into the fuselage. The utility variant had an option fortaller fixed landing gear with low-pressure tires, to provide betterclearance on rough terrain -- which raised the height of the helicopterby 10 centimeters (4 inches). Other options for the S-76 included a cargohook, rescue hoist, imaging turret under the nose, inflatable flotation bags,or engine inlet dust filters. Combined sales of the these first-generationS-76s amounted to a total of 283 machines.

* In 1983, Sikorsky began work on the "S-76B", which was an S-76 Mark II withtwin Pratt & Whitney Canada (PWC) PT6B-36 turboshaft engines with 716 kW (960SHP) each. The power rating of the main rotor transmission system wasincreased to 1,118 kW (1,500 SHP). The increased power raised the maximumtake-off weight by 500 kilograms (1,100 pounds).

The engine installation was of course modified, while the area of the tailfinwas reduced slightly -- providing a distinguishing feature relative toearlier variants, in which the tailboom extended beyond the rear of thetailfin, this extension being eliminated in the S-76B. Otherwise, details ofand options for the S-76B were much like those of the S-76 Mark II. Thefirst prototype conducted its initial flight on 22 June 1984, leading to FAAcertification in early 1987. 101 were sold through end of production in1997.

[2] MILITARY S-76 VARIANTS & SPECIAL MODIFICATIONS

* Over a dozen government services, such as the Queen's Flight in the UK andthe Spanish Air Force, obtained variants of the S-76 for VIP, utility, or SARuse, but these machines had little in the way of military optimizations,except possibly military-standard radios and the like. The Philippinesobtained twelve "AUH-76" militarized S-76 Mark II machines -- some of themin SAR and utility configuration, some as light attack helicopters. Detailsof the attack configuration are not clear, but imagery suggests they wereonly modest modifications of the stock S-76, featuring a stores pylon on eachside of the lower fuselage for a single unguided rocket launcher pod orpossibly some other store, and provision for an M60 7.62-millimeter(0.30-caliber) machine gun on a pintle mount firing out each side. There wasno visible sighting system; presumably the pilot aimed the rockets with acockpit reticle sight.

Moving along from the AUH-76, from 1985 Sikorsky promoted an "H-76 Eagle"gunship derivative of the S-76, with self-sealing fuel tanks, armored seats,provisions for door guns and a "Multi-Purpose Pylon System (MPSS)", providingweapons pylons to provide four stores attachments. Possible external storesincluded:

• Machine gun or cannon pods.
• Unguided rocket pods.
• Antitank rocket launchers for TOW or Hellfire.
• Light antiship missiles such as the Sea Skua.
• Light anti-aircraft missiles such as the Stinger.

Roof or mast-mounted sights could be fitted, as well as other sensor /targeting gear and defensive countermeasures. The Eagle could be used as anarmed transport, with a load of seven fully-equipped troops. For the medicalevacuation role, three litters and a bench for two medical attendants couldbe fitted. A demonstrator was flown for several years, but nobody bit on theconcept.

Sikorsky also tried to promote a navalized version of the Eagle designatedthe "H-76N", with an anti-shipping subvariant fitted with Ferranti Sea Sprayor other targeting radar under the nose, and armament of two Sea Skua orother antishipping missiles; along with an anti-submarine subvariant withdipping sonar and two Sting Ray or similar homing torpedoes. Possibleoptions included a roof or mast-mounted "forward looking infrared (FLIR)"imager, countermeasures gear, and a data link. There was no interest inthe H-76N, and it never got beyond promotional literature.

* The S-76 has been used as an experiment and trials platform. In 1981, theUS Army awarded Sikorsky with a contract to build an "S-75" demonstratorhelicopter under the "Advanced Composite Airframe Program (ACAP)", which wasintended to investigate the utility of lightweight composite materials inhelicopter airframe construction. Sikorsky essentially took the drive systemof an S-76A and put it into a composite airframe with a fair resemblance tothat of the S-76, though the tricycle landing gear was non-retractable; thelanding gear also featured shock absorbers to improve safety in hard landing,complementing crash-resistant seats. A static test airframe was built alongwith the flight demonstrator.

Initial flight of the demonstrator was in July 1984, with tests running intothe spring of 1985, after which the S-75 was put into storage. The programprovided a wealth of data useful to future helicopter design. The primaryrationale of the S-75 effort was to support the US Army's "Light HelicopterExperimental" effort, which would evolve into the "RAH-66 Comanche" scoutgunship development program.

The S-76 was used to test other elements of the Comanche. Sikorsky modifiedan S-76A with a one-crew cockpit grafted on to the nose to test technologiesfor the Comanche advanced scout helicopter, particularly improved cockpittechnologies, with the work funded by the US Army. The "Sikorsky HelicopterAdvanced Demonstrator of Operator Workload (SHADOW)" performed its firstflight on 24 June 1985, with the machine put through various trials indifferent configurations for several years.

An S-76B was also configured with a "fenestron" tail or "tailfan" in place ofits normal tail rotor to test that configuration for the Comanche, with thismachine putting on an appearance at the Paris Air Show in 1991. The Comancheprogram suffered from "creeping elaboration" and changes in requirements, tobe finally canceled in 2004, leading to a long-running effort by the Army toobtain a new armed scout helicopter.

[3] S-76C & S-76D

* In 1987, Sikorsky flew an S-76A with a Turbomeca Arriel 1S turboshaftengine, with a continuous rating of 525 kW (700 SHP), this variant beingcertificated from 1988 as the "S-76A+", available as both new production andas an upgrade, with 17 machines built new. The S-76A+ was followed by the"S-76A++", which was strictly an update program, featuring the Arriel 1S1engine, with 540 kW (730 SHP).

The S-76B was similarly updated with the Arriel 1S1 to produce the "S-76C".It was announced in 1989, with initial flight on 18 May 1990, and FAAcertification in 1991. The "S-76C+" featured twin Arriel 2S1 turboshaftswith 638 kW (856 SHP) take-off power. It was certificated in 1996.

The S-76C+ was later followed by the "S-76C++", with further uprated Arriel2S2 engines, plus larger pop-out windows to ease emergency escape, a quietgearbox, a Honeywell health and usage monitoring system (HUMS), and engineinlet filters. The uprated engines permitted carriage of an additional 160kilograms (350 pounds) of payload under "hot and high" conditions. TheS-76C++ was certified in late 2005.

 ___________________________________________________________________ SIKORSKY S-76C+: ___________________________________________________________________ main rotor diameter: 13.41 meters (44 feet) tail rotor diameter: 2.44 meters (8 feet) fuselage length: 13.22 meters (43 feet 4 inches) footprint length: 16.0 meters (52 feet 6 inches) height (tail rotor): 4.42 meters (14 feet 6 inches) empty weight: 3,235 kilograms (7,133 pounds) max sling load: 1,497 kilograms (3,300 pounds) max loaded weight: 5,306 kilograms (11,700 pounds) maximum speed: 287 KPH (178 MPH / 155 KT) service ceiling: 3,841 meters (12,600 feet) range: 713 kilometers (443 MI / 385 NMI) ___________________________________________________________________

These variants were stepping stones to the current "S-76D", with:

• Twin PWC PM210S engines providing 785 kW (1,050 SHP) each.
• A Thales TopDeck integrated flightdeck
• Composite main rotor blades and quiet tail rotor, both with electrical deicing.

The S-76D was faster than the C++, while having better fuel efficiency.Initial flight of the S-76D was on 7 February 2008, with certification in2012, and initial deliveries in late 2013. Over 1,100 S-76 helicopters ofall variants have been sold to date. The machine continues in production.

* From 2013, Sikorsky -- as of 2015, an arm of US defense giant LockheedMartin -- has worked on a "Sikorsky Autonomy Research Aircraft (SARA)", basedon an S-76B. SARA was built as a testbed for an autonomous flight system,bridging the gap from a mere dumb autopilot to a robot helicopter. Theprimary goal of the effort, however, is to develop a helicopter with muchless pilot workload, allowing the pilot to "fly the mission, not theaircraft".

SARA leveraged off research performed for the US Defense Advanced ResearchProjects Agency (DARPA), under the "Aircrew Labor In-Cockpit AutomationSystem (ALIAS)" program. The company calls the autonomous flight system"MATRIX" technology. The SARA testbed has been put through militaryevaluation from 2018, followed by civil demonstrations. SARA is not intendedfor commercial production, though the MATRIX technology may appear in futureSikorsky products.

[4] S-92 HELIBUS

* In 1992, Sikorsky began studies of a large transport / utility helicopter,conceived originally as the "Growth Hawk", more or less a scale-up of theS-70 Black Hawk. The design actually emerged as the "S-92 Helibus", targetedat airline transport, offshore supply, search-and-rescue, military and VIPtransport. Sikorsky acquired several risk-sharing development partnersincluding Mitsubishi Heavy Industries in Japan; Jingdezhen Helicopter Groupin China; Gamesa in Spain; AIDC in Taiwan; and Embraer in Brazil.

Five prototypes were built to support the S-92 development program, the firstbeing a nonflying ground-test article. The second prototype was the firstmachine to fly, on 23 December 1998. The third prototype featuredsignificant changes, including redesign of the tail rotor configuration andaddition of a 41-centimeter (16-inch) "plug" to extend the nose and improveflight trim. The final two prototypes were flying in 2001, the type beingcertificated by the end of that year; the first S-92A production machine wasdelivered in late 2004.

* The dynamic system of the S-92A was based on that of the S-70, featuringfour-bladed main and tail rotors, the main rotors having drooping / taperedtips. The rotor system was rated to tolerate the impact of a 1-kilogram(2.2-pound) bird at 305 KPH (190 MPH) with no damage to the rotor. The tailrotor faced to the right, with a tailplane offset to the right underneath.

The Helibus was powered by twin GE CT7-8 (T700) turboshaft engines, with"full authority digital engine control (FADEC)" and providing 1,790 kW (2,400HP) each at take-off. An auxiliary power unit (APU) turbine providedstarting and ground power. The first and second prototypes were actuallyfitted with less powerful CT7-6 engines and lacked an APU. The S-92A hadretractable tricycle landing gear, all gear assemblies with dual wheels, thenose gear retracting forward, the main gear retracting back into largesponsons on each side of the helicopter -- the forward part of the sponsonscontaining fuel tanks.

In heliliner configuration, the S-92A had 19 seats with three-across seating,and more luxurious VIP seating arrangements available as options. There wasa drop-down loading ramp in the rear under the tailboom, providing access tothe baggage compartment. In utility configuration, it had 22 tip-up seatsalong the walls of the cabin, plus floor rollers and cargo handling gear, thetail ramp providing access to the cabin for loading and unloading. A bellysling cargo hook was available as an option. Emergency medical serviceconfigurations, with a capacity of six litters, were also offered.

There was a passenger door on the right forward side of the fuselage --usually in the form of a horizontally split door on heliliner machines, thelower half featuring an airstair, and the upper half either tipping up orsliding to the rear; or a rear-sliding door on utility and SAR machines.There was an opening window / emergency exit on the left side of the fuselagematching the door, plus similar windows / emergency exits on both sides ofthe rear fuselage. The cockpit side windows could pop open for crew escape.

 ___________________________________________________________________ SIKORSKY S-92A HELIBUS: ___________________________________________________________________ main rotor diameter: 17.71 meters (58 feet 1 inch) tail rotor diameter: 3.35 meters (11 feet) fuselage length: 17.32 meters (56 feet 10 inches) footprint length: 20.85 meters (68 feet 5 inches) height (tail rotor): 6.45 meters (21 feet 2 inches) empty weight: 7,030 kilograms (15,500 pounds) max loaded weight (internal load): 11,420 kilograms (25,285 pounds) max loaded weight (with sling load): 12,020 kilograms (26,505 pounds) maximum cruise speed: 287 KPH (178 MPH / 155 KT) service ceiling: 4,570 meters (15,000 feet) range: 760 kilometers (472 MI / 410 NMI) Max loaded weight with a sling load, maximum loaded weight with an internal load being about 600 kilograms (1,220 pounds) less. ___________________________________________________________________

The S-92A featured a "glass cockpit" with four large color flat-paneldisplays, provided by Rockwell Collins. The machine was designed with astrong emphasis on safety, with redundant fuel, electric, hydraulic, andcontrol systems. The Helibus also featured an "active vibration controlsystem", with sensors controlling actuators to damp out vibration, reducingnoise and airframe stress; and a "terrain warning system" developed jointlyby Sikorsky and Honeywell, since a common cause of helicopter accidents is"controlled flight into terrain". This sensor system used a 12.7 x 12.7centimeter (5 x 5 inch) color flat panel cockpit display to provide weatheror terrain data, and also provided auditory warnings under emergencyconditions. Another interesting feature was a "training mode" that allowedflight under simulated "engine out / fully loaded" conditions, with instantrecovery at the flip of a switch.

The S-92A was designed for maintainability, Sikorsky estimating that it onlyrequired 20% of the maintenance of the S-61 Sea King. The helicopterincorporated a "health and usage monitoring" system built by Sikorsky and BFGoodrich, and a "maintenance diagnostics" system that allowed download ofmaintenance data into a laptop computer, which was also loaded with ainteractive maintenance manual.

A SAR configuration was on offer, which added features including:

• A rescue winch and sliding passenger door,
• Inflatable flotation kit, plus inflatable life rafts in the front of the sponsons.
• A spotlight and an imaging turret.
• Bulged observation windows and auxiliary fuel tanks.

Over 150 S-92A helicopters have been sold to date. An increased grossweight version, raising IGW by 4.5%, was introduced in 2015. While someS-92As have been obtained by commercial operators, a number of governmentshave obtained it as well, for the VIP, utility, or SAR roles. In late 2004,the S-92A won a SAR contract for four machines from the UK's Maritime &Coastguard Agency (MCA) as an interim capability; it was followed up by anorder for seven more, to be delivered from 2014. They were actually operatedby a civilian company, Bristow Helicopters, on contract with the Britishgovernment. The Irish Coast Guard also obtained four S-92As for the SARmission.

In a high-profile win, in the spring of 2014, the S-92A won the US Navy's"VXX" competition, to select the next VIP helicopter for White House service,with 23 machines to be obtained. There had actually been an earliercompetition for VXX, with the AgustaWestland AW101 being selected over theS-92A, but that contract was canceled in 2009 due to cost overruns. It wasdead certain the S-92A would win the second round, since nobody else bid onit, having difficulties with the specification.

Lockheed Martin teamed up with Sikorsky on the "VH-92A", as it was formallydesignated, with Lockheed Martin handling the specialized mission kitrequired and its integration. Initial flight of the first of four test anddevelopment machines was in 2017, with two engineering development machinesfollowing. Low-rate production was authorized in 2021, with first deliveriesin 2022. A total of 23 will be obtained -- development machines will bebrought up to operational standard -- with two reserved for training. SouthKorea, incidentally, obtained three S-92As as VH-92As, with deliveriesin 2007. They were clearly not to the same spec as the US VH-92As.

[5] H-92 SUPERHAWK / CH-148 CYCLONE

* Sikorsky offered a militarized version of the S-92, the "H-92 Superhawk",with customers able to choose from a menu of features:

• Uprated CT7-8C engines, rated at 2,240 kW (3,000 HP) each, to improve lift capacity.
• A manual or power rotor-folding system, and a folding tail rotor.
• A fly-by-wire (FBW) flight control system designed by BAE Systems of the UK, and a Rockwell Collins avionics suite.
• Self-sealing fuel tanks, exhaust infrared suppressors, and improved resistance to projectile damage.

The only win so far for the fully militarized version was in the summer of2004, when Sikorsky was awarded the contract for the Canadian MaritimeHelicopter Project to replace Canada's notoriously ancient and decrepit SeaKings, beating the AgustaWestland AW101 on the deal. The Canadians wanted touse the H-92 in utility transport, maritime warfare, and SAR roles.

28 "CH-148" multirole machines were to be provided, with initial deliveriesin 2010. For whatever reasons, the program did not go smoothly, Sikorskybeing hit with penalties. It's not so clear what happened, with claims thatSikorsky failed to meet contract up against claims that the Canadians keptasking for changes.

In any case, the CH-148 featured:

• A Telephonics AN/APS-143B search radar, in a drum radome under the forward fuselage.
• An infrared imaging turret under the nose.
• A dipping sonar / sonar buoy system, and an "electronic support measures (ESM)" system to locate and classify radio emitters.
• A defensive countermeasures suite.
• Inflight refueling capability, plus inflatable flotation gear, as well as two inflatable life rafts with a capacity of 15 personnel each.

They had pylons outboard of the sponsons to carry munitions, it seems withonly homing torpedoes qualified at the outset. It was plausible, butnot reported, that they could also be fitted with pintle-mounted machineguns.

Given the CH-148's sophisticated operational kit, it's not too surprisingthat what was seen as an "off the shelf" helicopter at the outsetturned out to be more like a machine built to custom specification. Theprogram finally stabilized, with six interim "Block 1" machines beingdelivered in 2015, and all 28 CH-148s to be operational in "Block 2"configuration by the end of 2021.

In the meantime, Sikorsky developed an improved version of the S-92, the"S-92B", which featured:

• MATRIX technology for autonomous flight operations, including automated SAR search patterns.
• Larger cabin windows, needed in particular to support improved emergency egress.
• A new common door adaptable to various missions.
• GE CT7-8A6 engines with better "hot & high" capability.
• A new gearbox, capable of running for a half hour without lubricants.

S-92As could be upgraded to S-92B standard, under the designation of"S-92A+". The S-92B was canceled in 2023 from lack of customer interest,though the S-92A+ upgrade program continued -- if delayed to 2025.

[6] COMMENTS, SOURCES, & REVISION HISTORY

* Sources include:

• "S-92 Trials To Fly Door, Tail Changes" by Stanley W. Kandebo, AVIATION WEEK, 12 February 2001, 48:52.
• "H-92 Powers Up" by Stanley W. Kandebo, AVIATION WEEK, 23 June 2003, 30.

Most of the details were picked out of various volumes of JANE'S ALL THEWORLD'S AIRCRAFT, the online Wikipedia, and press releases.

* Illustration credits:

• Sikorsky S-76B / Cannes-Mandelieu FR / 2006 / Elisabeth Klimesch / GNU Free Documentation License
• Sikorsky S-76A of Ontario Ministry of Health / Ottawa ONT CA / 2003 / John Davies / GNU Free Documentation License
• S-76B of Niigata (JP) Air Rescue / 2011 / ~cp9asngf / Creative Commons Share Alike License
• S-76 SHADOW / Sikorsky
• S-76C of Queen's Helicopter Flight / Cheltenham UK / 2019 / ~James / Creative Commons Share Alike License
• Sikorsky S-76Ds of National Helicopter Services of Trinidad & Tobago / author unknown / public domain
• Sikorsky S-92A of Bristow Norway Air Services / Stavanager Airport / 2017 / Alan Wilson / Creative Commons Share Alike License
• Sikorsky S-92A / 2017 / Ronnie MacDonald / Creative Commons Share Alike License
• Sikorsky VH-92A at White House / 2018 / SGT Hunter Helis, USMC
• CH-148 / Sikorsky

* Revision history:

 v1.0.0 / 01 aug 13 v1.0.1 / 01 jul 15 / 7 more S-92s for UK SAR, S-92 VXX win. v1.0.2 / 01 jun 17 / Review & polish. v1.0.3 / 01 may 19 / Review & polish. v1.0.4 / 01 apr 21 / Review & polish. v1.0.5 / 01 jun 21 / Review & polish for ebook release. v1.0.6 / 01 jun 23 / Review & polish.