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The Sikorsky S-76 & S-92

v1.0.1 / 01 jul 15 / greg goebel

* In the 1970s, the Sikorsky company introduced a new light helicopter, the "S-76", primarily but not entirely for civil use. The S-76 proved successful, with Sikorsky then introducing a larger helicopter, the "S-92". This document provides a history and description of the S-76 and S-92.

Sikorsky S-76C


[1] S-76 ORIGINS / S-76A & S-76B
[2] MILITARY S-76 VARIANTS & SPECIAL MODIFICATIONS
[3] S-76C & S-76D
[4] S-92 HELIBUS
[5] H-92 SUPERHAWK / CH-148 CYCLONE
[6] COMMENTS, SOURCES, & REVISION HISTORY

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

* In early 1975, Sikorsky announced the development of a new commercial helicopter, originally designated the "S-74", this machine to be the first Sikorsky helicopter designed from the outset for civilian use. It was soon renamed 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 Blackhawk technology, with a configuration somewhat along the lines of the Agusta A109 and the Bell 222 helicopters, but larger. The first of four S-76 prototypes performed its initial flight on 13 March 1977. The type received FAA certification in April 1978. Deliveries of the initial "S-76A" production version began in early 1979.

Sikorsky S-76A++

Sales of the S-76A were slow at the outset, due to the sluggish economy and various minor technical problems with the machine. The economy began to recover in the early 1980s, and Sikorsky relaunched the type in 1982 in the form of a modest production improvement designated the "S-76 Mark II", featuring an improved ventilation system, modifications to the dynamic system, and more maintenance access panels. Kits were provided to update S-76As to S-76 Mark II standard. There was also an "S-76 Utility" version of the 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, with accommodations for one or two crew -- dual controls were optional -- and a maximum of 12 passengers, though other various passenger arrangements were available, including a four-passenger "office in the sky" layout. A wide range of luxury interiors could be installed as per customer specification. There were front-hinged doors on both sides of the cockpit, as well as doors on each side of the passenger cabin; the cabin doors were front-hinged by default, 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 fitted with 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 with a 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 (1,300 HP) and could absorb the full power of both engines. The engine system included a fire detection and extinguisher system.

The S-76 Mark II used four-bladed main and tail rotors, similar to those developed for the S-70 Blackhawk, but scaled down. The main rotor had titanium spars surrounded by Nomex polymer honeycomb and sheathed with fiberglass. There were titanium-nickel abrasion strips on the leading edge of the blades, plus swept tips made of Kevlar polymer. The tail rotor was of composite construction. There was an all-moving tailplane for flight trim.

   SIKORSKY S-76 MARK II:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   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
   _____________________   _________________   _______________________
 
   * Due to the higher landing gear, the utility variant was 10 centimeters
     (4 inches) taller.

The S-76 Mark II had retractable tricycle landing gear, with single wheels on all gear assemblies, the nose gear retracting backwards, the main gear tucking up and back into the fuselage. The utility variant had an option for taller fixed landing gear with low-pressure tires, to provide better clearance on rough terrain. Other options for the S-76 included a cargo hook, rescue hoist, imaging turret under the nose, inflatable flotation bags, or engine inlet dust filters. Combined sales of the these first-generation S-76s amounted to a total of 283 machines.

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

The engine installation was of course modified, while the area of the tailfin was reduced slightly -- providing a distinguishing feature relative to earlier variants, in which the tailboom extended beyond the rear of the tailfin, this extension being eliminated in the S-76B. Otherwise, details of and options for the S-76B were much like those of the S-76 Mark II. The first prototype conducted its initial flight on 22 June 1984, leading to FAA certification in early 1987. 101 were sold through end of production in 1997.

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[2] MILITARY S-76 VARIANTS & SPECIAL MODIFICATIONS

* Over a dozen government services, such as the Queen's Flight in the UK and the Spanish Air Force, obtained variants of the S-76 for VIP, utility, or SAR use, but these machines had little in the way of military optimizations, except possibly military-standard radios and the like. The Philippines obtained twelve "AUH-76" militarized S-76 Mark II machines -- some of them in SAR and utility configuration, some as light attack helicopters. Details of the attack configuration are not clear, but imagery suggests they were only modest modifications of the stock S-76, featuring a stores pylon on each side of the lower fuselage for a single unguided rocket launcher pod or possibly 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 was no visible sighting system; presumably the pilot aimed the rockets with a cockpit recticle 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)", providing weapons pylons to provide four stores attachments. Possible external stores included:

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

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

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

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

The S-76 was used to test other elements of the Comanche. Sikorsky modified an S-76A with a one-crew cockpit grafted on to the nose to test technologies for the Comanche advanced scout helicopter, particularly improved cockpit technologies, with the work funded by the US Army. The "Sikorsky Helicopter Advanced Demonstrator of Operator Workload (SHADOW)" performed its first flight on 24 June 1985, with the machine put through various trials in different configurations for several years.

Sikorsky SHADOW

An S-76B was also configured with a "fenestron" tail or "tailfan" in place of its normal tail rotor to test that configuration for the Comanche, with this machine putting on an appearance at the Paris Air Show in 1991. The Comanche program suffered from "creeping elaboration" and changes in requirements, to be finally canceled in 2004, leading to an ongoing by the Army to obtain a new armed scout helicopter.

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

* In 1987, Sikorsky flew an S-76A with a Turbomeca Arriel 1S turboshaft engine, with a continuous rating of 525 kW (700 SHP), this variant being certificated from 1988 as the "S-76A+", available as both new production and as 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 1S1 engine, with 540 kW (730 SHP).

Sikorsky S-76C in Spanish service

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 FAA certification in 1991. The "S-76C+" featured twin Arriel 2S1 turboshafts with 638 kW (856 SHP) takeoff power. It was certificated in 1996.

The S-76C+ was later followed by the "S-76C++", with further uprated Arriel 2S2 engines, plus larger pop-out windows to ease emergency escape, a quiet gearbox, a Honeywell health and usage monitoring system (HUMS), and engine inlet filters. The uprated engines permitted carriage of an additional 160 kilograms (350 pounds) of payload under "hot and high" conditions. The S-76C++ was certified in late 2005.

   SIKORSKY S-76C+:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   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", which features twin PWC PM210S engines with 785 kW (1,050 SHP) each, a Thales TopDeck integrated flightdeck, plus composite main rotor blades and quiet tail rotor, both with electrical deicing. The S-76D is faster than the C++, while having better fuel efficiency. Initial flight of the S-76D was on 7 February 2008, with certification in 2012, and initial deliveries in late 2013. Over 800 S-76 helicopters of all variants have been sold to date.

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[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 the S-70 Blackhawk. The design actually emerged as the "S-92 Helibus", targeted at targeted at airline transport, offshore supply, search-and-rescue, military and VIP transport. Sikorsky acquired several risk-sharing development partners including Mitsubishi Heavy Industries in Japan; Jingdezhen Helicopter Group in China; Gamesa in Spain; AIDC in Taiwan; and EMBRAER in Brazil.

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

* The dynamic system of the S-92 is based on that of the S-70, featuring four-bladed main and tail rotors, the main rotors having drooping / tapered tips. The rotor system is 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 tail rotor faces to the right, with a tailplane offset to the right underneath.

Sikorsky S-92 of Petroleum Helicopters INC

The Helibus is powered by twin GE CT7-8 (T700) turboshaft engines, with "full authority digital engine control (FADEC)" and providing 1,790 kW (2,400 HP) each at takeoff. An auxiliary power unit (APU) turbine provides starting and ground power. The first and second prototypes were actually fitted with less powerful CT7-6 engines and lacked an APU. The S-92 has retractable tricycle landing gear, all gear assemblies with dual wheels, the nose gear retracting forward, the main gear retracting back into large sponsons on each side of the helicopter -- the forward part of the sponsons containing fuel tanks.

In heliliner configuration, the S-92 has 19 seats with three-across seating; more luxurious VIP seating arrangements are also available. There is a drop-down loading ramp in the rear under the tailboom, providing access to the baggage compartment. In utility configuration, it has 22 tip-up seats along the walls of the fuselage, plus floor rollers and cargo handling gear, the tail ramp providing access to the cabin for loading and unloading. A belly sling cargo hook is available as an option. Emergency medical service configurations, with a capacity of six litters, are also available, as are SAR configurations. SAR machines have features including a rescue winch and sliding passenger door; inflatable flotation kit; inflatable life rafts in the front of the sponsons; bulged observation windows; a spotlight; an imaging turret under the nose; plus auxiliary fuel tanks.

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

   SIKORSKY S-92 HELIBUS:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   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       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-92 features a "glass cockpit" with four large color flat-panel displays, implemented by Rockwell Collins. The machine was designed with a strong emphasis on safety, with redundant fuel, electric, hydraulic, and control systems. The Helibus also features an "active vibration control system", with sensors controlling actuators to damp out vibration, reducing noise and airframe stress; and a "terrain warning system" developed jointly by Sikorsky and Honeywell, since a common cause of helicopter accidents is "controlled flight into terrain". This sensor system uses a 12.7 x 12.7 centimeter (5 x 5 inch) color flat panel cockpit display to provide weather or terrain data, and also provides auditory warnings under emergency conditions. Another interesting feature is a "training mode" that allows flight under simulated "engine out / fully loaded" conditions, with instant recovery at the flip of a switch.

The S-92 was designed for maintainability, Sikorsky estimating that it only requires 20% of the maintenance of the S-61 Sea King. The helicopter incorporates a "health and usage monitoring" system built by Sikorsky and BF Goodrich, and a "maintenance diagnostics" system that allows download of maintenance data into a laptop computer, which is also loaded with a interactive maintenance manual.

Irish Coast Guard S-92

Over 150 S-92 helicopters have been sold to date. While some have been obtained by commercial operators, a number of governments have obtained it as well, for the VIP, utility, or SAR roles. In late 2004, the S-92 won a SAR contract for four machines from the UK's Maritime & Coastguard Agency (MCA) as an interim capability; it was followed up by an order for seven more, to be delivered from 2014. The Irish Coast Guard is also obtaining four S-92s for the SAR mission.

In the spring of 2014, the S-92 also won the US Navy's "VXX" competition, to select the next VIP helicopter for White House service, the program to feature two prototypes and 21 production machines. There had actually been an earlier competition for VXX, with the AgustaWestland AW101 being selected over the S-92 -- but it was cancelled in 2009 due to cost overruns. It was highly likely the S-92 would win the current round, since nobody else bid on it, having difficulties with the specification. Lockheed Martin is teaming with Sikorsky on the "VH-92", with Lockheed Martin providing the specialized kit required and its integration. Initial flight of a proper prototype will be in 2017, with initial fielding in 2020.

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[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:

The only win so far for the fully militarized version was in the summer of 2004, when Sikorsky was awarded the contract for the Canadian Maritime Helicopter Project to replace Canada's notoriously ancient Sea Kings, to be used in utility transport, maritime warfare, and SAR roles. The H-92 beat the AgustaWestland EH-101 Cormorant in the deal.

28 "CH-148" multirole machines were to be provided, with initial deliveries in 2010. For whatever reasons, the program has not gone smoothly, Sikorsky being hit with penalties. The facts are difficult to obtain, with claims that Sikorsky failed to meet contract balanced against claims that the Canadians kept asking for changes.

Sikorsky CH-148

In any case, the CH-148 has 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; an "electronic support measures (ESM)" system to locate and classify radio emitters; and a defensive countermeasures suite. They have pylons outboard of the sponsons to carry munitions, it seems with only homing torpedoes qualified at the outset. It is likely that they will also be able to handle pintle-mounted machine guns, but no details on that issue have been released.

The CH-148 has, at least in principle, inflight refueling capability. Given that the CH-148s will be used for SAR operations in hostile oceanic climes, they are also fitted with inflatable flotation gear, as well as two inflatable life rafts with a capacity of 15 personnel each. All in all, the CH-148 seems like an impressive rotorcraft -- but given its sophisticated operational kit, it's not too surprising that what was apparently seen as an "off the shelf" helicopter at the outset turned out to be more like a machine built to custom specification. It seems the program has finally stabilized, with at least six interim "Block 1" machines to be delivered in 2015, and all 28 CH-148s to be operational in "Block 2" configuration by 2021.

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[6] COMMENTS, SOURCES, & REVISION HISTORY

* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.

Sikorsky S-76

* Sources include:

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

* 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.
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