Sikorsky has revealed the first images of the Phase IV main gearbox (MGB) designed for the new S-92A+ helicopter, while insisting the update reflects the company’s long-term commitment both to the heavy-twin and the broader civil market.
The Connecticut airframer has previously shared graphics of the Phase IV gearbox for the 19-passenger S-92.
But as the Verticon helicopter exposition opens in Dallas this week, the company has for the first time released photographs of the massive aluminium component, which notably includes a new auxiliary oil system that activates if the main oil system fails, providing pilots with much more time to land.
Sikorsky, a division of Lockheed Martin, recently also revealed the Phase IV gearbox to reporters at its Stratford manufacturing site. The company has produced four of the components, completed 800h of testing and expects Federal Aviation Administration (FAA) certification this year.
Executives are quick to note the company has spent $100 million over a decade developing the Phase IV gearbox, though they expect it will never be profitable.
“We’ve invested more than it’s worth commercially… in the sense that I don’t have a business case to have made that investment,” says Sikorsky vice-president of global commercial and military systems Leon Silva. “It sends a message that we’re not only committed to safety, but we’re committed to the S-92… Not everything makes money.”
Sikorsky’s production is now dominated by military helicopters. Of the 90 aircraft it delivered in 2024, just one – an S-92 – was a baseline civilian type, with the balance mostly being UH-60 Black Hawk variants, according to data from the General Aviation Manufacturers Association.
Sikorsky stopped producing its medium-twin S-76 several years ago, leaving the S-92, which has been in service since 2004, as its only in-production civilian helicopter. The global S-92 fleet stands at 276 aircraft, including the basic commerical transport variant and VIP, head-of-state and search-and-rescue models. The S-92 competes to varying degrees with the Airbus Helicopters H225 and H175, Leonardo Helicopters AW189 and – eventually – Bell’s long-delayed 525.
Powered by twin 2,695shp (2,010kW) GE Aerospace CT7-8A6 turboshafts, S-92s are widely used to service offshore oil and gas platforms. A handful of accidents years ago were traced to gearbox oil loss. Operators more recently have struggled to keep some S-92s flying due to shortages of parts, including MGBs.
Sikorsky insists that parts shortages are easing. The current in-service Phase III gearbox, made from magnesium, is incredibly reliable, and many customers are perfectly happy to continue operating that hardware, especially after Sikorsky last year received regulatory approval for some Phase III gearbox components to be run to 5,500h, up from a prior limit of 4,300h, the company says.
Still, Sikorsky developed the aluminium Phase IV gearbox to provide extra safety and to ease component shortages. While still awaiting certification, the Phase IV model is offered as part of Sikorsky’s new A+ version of the heavy-twin and is available as a retrofit for in-service S-92s.
“Why would you invest $100 million in something… that doesn’t really change the revenue stream? [Because] it drives and provides a more-safe aircraft,” says Sikorsky vice-president and general manager Rich Benton. “A lot of our S-92s are used in the oil and gas industry… There’s not a lot of places to land [offshore].”
Executives decline to speculate how many retrofits they might sell or the cost of the A+ updates.
“We are working proposals, pricing,” Silva says. “We are going to be talking to a lot of customers during Verticon… We’re curious to see how much interest there will be in this kind of an upgrade.”
The S-92’s current gearbox lubrication system consists of oil contained within the gearbox housing.
For the Phase IV model, Sikorsky added piping around the gearbox’s exterior that supplies oil automatically from an independent secondary reserve if oil pressure drops below a threshold, says Sikorsky aeronautical engineer Kevin Wittke. The auxiliary system contains far less oil than the main system but is intended to operate only until the aircraft lands.
“If you have any sort of failure on the lubrication… it basically lets you fly the aircraft without having any concern with respect to the gearbox, and land anywhere you need,” Silva says. “You don’t need to land in the water. You don’t have a 30-minute restriction.”
Sikorsky has not said how long the S-92A+ will be permitted to fly while using the backup system. But at its production and engineering transmission test stand in Stratford, Sikorsky engineers subjected a Phase IV gearbox to some 15h of operation while supplied with oil only from the auxiliary system.
“We basically eliminated the main oil system and went on the auxiliary system,” Silva says. “And we took that gearbox apart and it was in very, very good shape.”
For the tests, the team let the main lubrication system eject oil until the auxiliary system activated, then ran the gearbox for 7.5h before inspecting the components. Finding them in “excellent condition”, they completed a second test.
“We’re trying to test through a certain amount of time to substantiate for FAA certification,” says Wittke. “What we demonstrated is, once again, that you can go and finish the mission from wherever you are, however far offshore… to get to a suitable landing [area].”
Sikorsky switched from magnesium to aluminium for the Phase IV gearbox because magnesium, while lighter, is more prone to defects and more difficult to bore and to repair, and because order lead times are longer for magnesium than aluminium.
“There are very few companies that actually can pour magnesium,” Silva says, adding that magnesium requires specific welding techniques to avoid igniting.
With the S-92A+ update, the company has also introduced a “gross weight expansion” kit that, through structural tweaks and other measures, increases the helicopter’s maximum take-off weight by 544kg (1,200lb), to 12,565kg, letting operators carry more passengers, cargo or fuel.
“Twelve hundred pounds, actually, in the helicopter world, is a big step,” Silva says. “There are some applications around the world where the S-92 currently is the only machine that can actually get out to those distances with any significant load, and this will make it make it even better.”
BEYOND THE S-92
S-92s will continue flying for decades, but Sikorsky is now advancing its vision for the future of commercial vertical take-off and landing (VTOL) aircraft. “We are in a transition phase,” says Silva.
The vision involves a family of hybrid-electric aircraft, with varying degrees of autonomy, designed for roughly the same missions now served by helicopters: city-to-city flights of about 200 miles and regional flights of about 400 miles.
“We are interested in vehicles that operate within where normal helicopters operate, and… roughly double the range,” says Igor Cherepinsky, director of Sikorsky Innovations, the company’s rapid-development division. Sikorsky is evaluating “a family of products… [with] a high degree of commonality when it comes to systems” – a strategy intended to contain development, manufacturing and operating costs.
The company has already rolled out four aircraft designs as part of its long-term development plan.
One – a 52kg (115lb) unmanned all-electric rotor-blown wing demonstrator, in a tail-sitter configuration – has already flown. The others, all to be powered by hybrid-electric systems, include the tiltwing HEX Demonstrator, the nine-12-passenger tiltwing Regional Air Mobility Concept and a helicopter called e-76 Concept.
The strategy marks a shift from several years ago, when Sikorsky had focused on the electric air taxi segment. The company has pivoted due to battery limitations and a desire to target traditional helicopter markets.
On 10 March, Sikorsky disclosed that in January it completed 30 “transitional” flights of the rotor-blown wing demonstrator. The twin-prop aircraft, with a 3.1m (10.3ft) wingspan, takes off vertically and then transitions to forward flight. It runs on Sikorsky’s Matrix autonomous flight-control technology.
“The vehicle was built to basically demonstrate transition and make sure we understood the physics of transition,” and to help Sikorsky “develop controllers for bigger” such aircraft, Cherepinsky says. The company envisions future variants as excelling at search and rescue, humanitarian response, surveillance and reconnaissance missions.
Cherepinsky clarifies that the e-76 Concept will not involve Sikorsky directly developing a hybrid version of its S-76. Rather, it will use the S-76 as a “platform” to study possibly developing a hybrid-electric helicopter of roughly the S-76’s size. For the project, Sikorsky will evaluate both “mild hybridisation” – with a relatively small amount of power from electric systems – and a system that is “more electric than not”.
“Hybridising a conventional helicopter lets us reduce both the load and the size of conventional turbines, bring in electric drivetrains and batteries, [and] lets us recover energy,” Cherepinsky adds. “It’s really all the same reasons why hybrid cars exist.”
Sikorsky’s HEX Demonstrator is to be a twin-propeller, roughly 4,000kg unmanned hybrid-electric aircraft powered by a single CT7 turbine and a turbo-generator, which will convert mechanical power into electricity.
“We take 1.2 megawatts of power produced by a jet engine, convert it all to electricity, send it to our wings and convert it all back into mechanical energy to spin the rotors. It’s not as easy as it sounds,” Cherepinsky says. “We are designing power electronics, motors [and] flight controls ourselves.”
The company intends to keep a lid on costs by producing HEX from 3D-printed components; Cherepinsky says it will have no parts made by forging or casting.
HEX development has been slower than anticipated. Sikorsky is now building a “power systems testbed” composed of the aircraft’s “dynamic components” but not its wings or fuselage. The company intends eventually to fly that testbed in a hover. It aims to complete first flight of the actual HEX Demonstrator in late 2027 or early 2028.
“As we’re adding that technology in, we’re learning how to make those components. It’s costing time,” Cherepinsky says. ”A year or two to go through and really revolutionise some manufacturing [of] parts is absolutely worth it to us.”
Longer term, Sikorsky views HEX as informing development of a hybrid-electric tiltwing weighing 6,350-6,804kg and capable of carrying 9-12 passenger on routes of up to roughly 400nm.
“We’re going to attempt to break the paradigm that VTOL has traditionally been more expensive than pure fixed-wing aircraft,” Cherepinsky says. “We intend to start actually putting out products in this area.“
