A version of this article appears in the July 14 edition of Aviation Week & Space Technology.
Before the end of this year, if the latest timetable holds, the first will begin coming together in Shanghai. The program has been repeatedly delayed but, in a sense, it is behind schedule on schedule—that is, when it was launched in 2008, industry executives widely expected the aircraft to be delivered not in 2016, as then promised, but in 2018, which a few weeks ago finally became the official target.
Now the question is whether the 158-seat airliner will prove to need more than 10 years to develop—which hardly seems to be helped by a now-confirmed decision to include a titanium-alloy wing spar fabricated with 3-D printing.
In general, the C919 is being designed with current but not next-generation technology. The compromise is intended to make the aircraft as efficient as possible without overtaxing the state-owned manufacturer’s inexperienced engineering and management teams.
The 3-D-printed titanium-alloy spar seems to be a notable exception. The 3-meter (10-ft.) piece, developed for the C919 by Northwestern Polytechnical University in Xian, will be used in the production aircraft, a Comac official told a conference in Shanghai last month, following earlier reports of the part’s development. The university is a key center of aeronautics research here. Each C919 will presumably have two such spars.
There may be less to the announcement than meets the eye, however. The term 3-D printing is normally understood to mean making a piece completely with an additive process. That would be a huge achievement for a certifiable titanium spar, carrying some of the greatest loads in the airframe. Conceivably, the Chinese may be referring to a less difficult additive fabrication technique in which features are applied to parts made by other processes, such as forging.
A further technical advance for the C919 is linkage of the pilots’ side-stick controllers, Comac says. While rejecting the traditional yoke arrangement used by, Comac decided that the side sticks should move together, so the pilot-not-flying would have a visual and tactile indication of what the pilot flying was doing, the official said at the June conference. Resistance in the sticks will change according to flight conditions. is supplying the C919’s flight-control system; is building the avionics core processing system and displays; Parker is charged with the flight-control actuation system.
The C919 is being designed for dispatch reliability of 99.7% two years after entering service, another Comac said at the meeting, the SAE 2014 Aviation Technology Forum (see table).
Comac Chief Financial Officer Tian Min said in May that the first C919 would fly by the end of 2015. Previous forecasts cited October 2015, and the initial target of 2014—set when the program was launched six years ago. All efforts are being made to assemble the first flying C919 airframe in the second half of this year, according to Comac.
The C919 program launched the, but the engine design changed when adopted the turbofan for the . This had positive and negative effects. The benefit: CFM improved the specification and, importantly, offered commonality with the Airbus aircraft, whose production volume will be far higher than the C919’s. The detriment: The C919 design had to be revised to accommodate the changed engine, adding months to its development program.
One of the greatest challenges in developing the C919 is specifying requirements of systems and, more particularly, subsystems and the items that comprise the subsystems. The first Comac engineer cited said the manufacturer had the ability to set out a fraction of the requirements that Boeing could.
It is not entirely clear how the aircraft is being developed under such circumstances. Suppliers are being asked to help far more than they would be in an Airbus or Boeing program, but for many items the answers must come from the airframe developer—in this case, Comac.
For structural and mechanical details, an inexperienced manufacturer will usually just have to play safe and specify greater strength—and therefore weight—than would a company that had been through the process several times before. This helps explain why the C919 shows no great weight advantage over the closely comparable A320, despite availability of technology more than 20 years newer than what was feasible for the Airbus narrowbody.
SAE standards for certification were a focus of the conference. The non-profit association helps the industry by sharing knowledge on achieving airworthiness certification. Comac engineers at the conference were keen for guidance.
But, as SAE’s Airplane Safety Assessment Committee chairman, John Dalton, told them, the standards take them only halfway, by setting out what information a manufacturer can show to satisfy a regulator but not exactly how that information is derived. In working out how to conduct tests to produce the data, each manufacturer needs to work it out for itself, or get help from another.
Dalton is also a technical fellow at Boeing.
|C919 Maintainability Targets|
|Utilization||10 hr. a day|
|Dispatch reliability 2 years after EIS*||99.7% or more|
|Mean flight time between failures||40 hr. or more|
|Inflight shutdown rate||0.005 per flight hour or less|
|Mean time to repair||30 min. or less|
|Direct maintenance||0.6 man-hours per flight hour|
|Transit maintenance||25 min. or less|
|Direct maintenance cost||3% less than similar aircraft|
|Direct engine maintenance cost||Same or less than similar aircraft|
|Engine removal or installation||4 hr. or less|
|APU removal or installation time||45 min. or less|
|Failure detection rate||More than 98%|
|False alarm rate||2% or less|
|*Entry into service|