A radical new nacelle concept is moving closer to completion. The system designed and built by Nexcelle, a joint venture between GE Aviation's Middle River Aircraft Systems and Aircelle (Safran), has successfully completed an initial test campaign on a flying test bed. The first shipset designated for the initial flight-test aircraft is on its way, via the engine manufacturer, to the customer airframer this summer.

Nexcelle's next-generation nacelle for CFM's Leap 1-C will fly on the COMAC C919 airliner. The system combines Nexcelle's one-piece composite O-Duct, which replaces the two-piece 'D' doors on a traditional thrust reverser, with a pylon specific to the system. When deployed, the O-Duct moves aft to the reverse thrust position, eliminating drag links in the engine’s secondary flow-path and increasing the efficiency of the reverser. The O-Duct combines with a bespoke nacelle and a new pylon to deliver weight, drag and fuel-burn reduction, and provide greater ease of maintenance.

“This is the first truly integrated propulsion system,” says Nexcelle president Michel Abella. “The structure of the nacelle, the main structure of the engine, and part of the pylon were designed concurrently.”

The nacelle flew for the first time in October on board one of GE's two Boeing 747 flying test bed aircraft in California, since when “GE has completed 20 flights without any issue on our nacelle,” Abella reports.

While the tests have proven the mechanical concept, there is no clear data yet supporting Nexcelle's ambitions to demonstrate a reduced fuel burn from the system.

“The installation of the propulsion system on a 747 aircraft, even if it has a specific pylon in order to be matched with the wing, is extremely hard to do,” Abella explains. “All three elements of the propulsion system – the pylon, the engine structures, and the nacelle structures – contribute to the fuel burn. This has been assessed by CFM, discussed with COMAC, and reviewed several times. I'm pretty sure that our customer (CFM) may have some indication of where they are altogether with the propulsion system, but we do not have that information. From our viewpoint, the testing validated the mechanical behavior of the nacelle and the actuation system, so we are confident.”

Getting the system on to the customer's aircraft is obviously critical to establishing how much of an impact the novel design may have on the commercial aviation market.

“We are already very satisfied with what we have seen on the flying test bed, and the way we have executed the maintainability tasks on the ground, so we know the capability is there,” says Abella. “But now we have to have the demonstration of these capabilities by our final customer, the operators of these aircraft. We have to prove the efficiency of the nacelle, prove that it's easy to maintain and to operate both inside and on the ground. We have to prove it's cost-efficient in terms of cost of ownership. It will take time.”

Nacelles have already been delivered to CFM in France for running-engine tests and internal measurements inspection, while delivery of components for two nacelles destined for the first flight test aircraft are underway now. Podding will take place in Toulouse before the nacelles are shipped to China. Test flights will be preceded by a rollout. Though Nexcelle cannot confirm a target timetable, Abella says the company is delivering in line with agreed schedules.

The other program for which Nexcelle is supplying nacelles – GE's PassporT powerplant for Bombardier's Global 7000 and 8000 business jets – is also running on time. Components have been delivered to GE in Peebles, Ohio, ahead of podding. Once completed, the shipset will be delivered to Bombardier to equip the first flight test aircraft, which will be a 7000 model. Testing on GE's 747 has taken place, with a second campaign due later this year.

While the PassporT nacelle does not use O-Duct technology, there are common elements to both programs. Abella points to the extensive use of composites and acoustic treatments across both systems, and highlights the cowl solution which appears on both products.

There is still room for further optimization of the design. “We have an extended one-piece aluminum inlet outer barrel for reduction of aerodynamic drag, and we're considering this to be composite, in order to reduce overall weight,” Abella says. “We have devoted a lot of effort in order to reduce weight and provide best reverse thrust efficiency. We are beating the specification that we have received from the customer with that reverse efficiency.”