Ten years ago, GE Aviation and Safran sought to replicate the success of their CFM International joint venture when they agreed at the 2008 Farnborough air show to build a similar partnership for engine nacelles.
The two manufacturers established a 50:50 joint venture between GE's Middle River Aircraft Systems unit and Safran’s nacelle division – which separately manufacture thrust reversers and complete nacelles for a range of engines by different suppliers – and, in 2009, named the new business Nexcelle.
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While nacelles have traditionally been developed separately from engines, the purpose of the new venture is to produce "integrated propulsion systems" in close co-operation with the parents’ aero engine businesses, Nexcelle president Kenneth Onderko tells FlightGlobal.
Now, Nexcelle is nearing serial production for one of two nacelle programmes it has developed to date – for GE's Passport engine. That turbofan, the core of which has been derived from CFM’s Leap unit, powers Bombardier’s Global 7500 business jet, which is scheduled for certification later this year.
AMBITIOUS GOALS
Onderko says Bombardier had set out "very aggressive" weight, performance and noise targets. Achieving the aircraft’s 7,700nm (14,270km) range had, he says, "a lot" to do with an ability to "truly optimise" the overall structure of the engine and nacelle assembly and to avoid steps and gaps in the bypass stream's flow path. "The requirements that Bombardier asked us to achieve were something that we had not been able to do on any programme before," he says.
The bypass stream flows through a single-piece composite barrel that envelops the engine core and which, Nexcelle says, includes "advanced acoustic protection" in order to reduce engine noise. Other features of the nacelle include a "simplified", weight-saving composite cowl, a fixed-nozzle thrust-reverser, and an anti-ice system that distributes hot air more efficiently around the inside of the air intake's leading edge. In order to reduce drag and noise, the leading edge skin is made from a single-piece aluminium sheet, rather than several pieces joined together.
A similar, single-piece inlet lip, albeit on a larger scale, has also been employed on Nexcelle’s second programme: the nacelle for CFM's Leap-1C, the initial powerplant for China's under-development Comac C919. The single-aisle aircraft will later be equipped with the alternative, locally produced CJ-1000 engine.
Nexcelle says the inlet lip surrounding the Leap-1C's 1.96m (77in) diameter fan is "the largest of its kind to enter production on a large commercial jet engine". Like its smaller sibling on the Passport powerplant, the Leap-1C air intake also has a "directed-flow nozzle" de-icing system, which, Nexcelle says, delivers "weight, efficiency and maintainability improvements from traditional nacelle de-icing systems".
NEW DESIGN
Arguably the most exceptional feature of the Leap-1C’s nacelle is its "O-duct" thrust-reverser mechanism. Rather than having two "D-door"-style translating sleeves on conventional nacelles, the new configuration has a single-piece composite structure that slides aft when thrust reverse has been selected. Nexcelle says the electrically driven "O-duct" reduces drag in the airflow path and improves thrust-reverser efficiency.
Other features of the Leap-1C nacelle include an engine mounting system designed to reduce powerplant distortion and a fan cowl that is structurally integrated to the engine.
Onderko says nacelles have been delivered for a third C919 that is scheduled to start flight tests later this year. Entry into service of the C919 is scheduled for 2020-2021.
Integration of the Leap-1C and nacelle takes place in a facility that is jointly operated by CFM and Comac, located on the Chinese manufacturer's premises in Shanghai. Safran is the lead integrator for the Leap-1C nacelle, while GE has a leading role on the Passport nacelle programme.
Onderko believes the partnership between GE and Safran has enabled the two manufacturers to develop more advanced nacelles together than would be possible on their own. "Each company has their expertise; there is some overlap, but in some places not," he says – adding: "They do learn from each other and, I think, the two parent companies in the nacelle business are better today… than they were beforehand."
He notes that while "a lot of financial capital" is required to develop nacelles for new engine programmes, the partnership allows both parents to "bring the best of the best to the table" and share risk, resources and returns.
So what are the next steps for Nexcelle? Onderko says GE and Safran are "obviously" looking for additional engines to be equipped with the joint venture's nacelles. He notes that new designs, such as the O-duct thrust-reverser can be applied to other platforms, but says there are no plans today to roll out that technology.
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Source: FlightGlobal.com
