Airbus A350XWB (partie 1)

Longer-than-anticipated design activities for the A350XWB twin widebody are forcing Airbus to delay the aircraft’s final assembly start and first flight by several months.

Nevertheless, the aircraft maker still plans to deliver the first A350-900 as scheduled in mid-2013.

“Three months of buffer have been used,” says A350 program chief Didier Evrard.

The three months were lost on a variety of efforts. One was to take more time to complete detailed finite element model work, fully refining the center wing box configuration, and to optimize fuselage damage tolerance. Extra work was also needed on the fuselage electric structural network.

Under the new schedule, final assembly starts at the end of the third quarter 2011, rather than the end of the second quarter, and first flight has slipped to the third quarter f 2012.

The time also allowed developers to conduct further analysis to shave weight from the total, says program chief engineer Gordon McConnell. On one structural element alone, that effort achieved 60 kg of weight reduction.

Most of the systems development remains on schedule, Evrard says.

The schedule adjustment compresses flight testing to 12 months from 15 months. Airbus will have five test aircraft to log about 2,600 flight test hours.

Meanwhile, wind tunnel testing and computer modeling show that long-range cruise speed is slightly above the Mach 0.85 target. Low-speed performance also has improved, with 475 ft. better takeoff performance and four metric tons higher takeoff weight performance in hot-and-high conditions, McConnell says.

Airbus also has launched a program to create some additional buffer in case it is needed.

There are no changes to the -800 and -1000 schedules, Evrard notes.

Airbus also has set up a special organization to work on the -1000, the largest member of the family. Its design freeze is planned next year. Evrard says the -1000 could feature technology upgrades since the selection was made for the lead version, the -900. Evrard says there are strategic decisions to be made on the -1000 that the personnel focused on birthing the -900 cannot address. Still, the 400 people will have close ties into the overall program to keep the A350 family concept alive, Evrard stresses.

Among the issues to be looked at might be whether composites could be used in parts of the landing gear.

The first Rolls-Royce TrentXWB engine to test is now in assembly for first run at the end of May. Seven engines are to run in the first six months. The TrentXWB will be airborne in the second quarter 2011 on the first A380 (MSN001).

Airbus is working to reach the design freeze for the largest A350 variant, the -1000, in the middle of this year and has revealed the that stretched aircraft will feature a slightly larger wing the -800/900 models.
The 369-seat -1000, which has an 11-frame stretch over the -900, is due to enter service at the end of 2015. A separate A350-1000 design team was set up in 2009, headed by the XWB programme's deputy engineer Alain De-Zotti, which is examining trade-offs for the design, says chief engineer Gordon McConnell. Detailed definition is due to be completed at the end of 2011.
Airbus's operational requirement targets for the -1000 include keeping the approach speed to 150kt (277km/h) at maximum landing weight, compliance with London's QC1 noise requirements for arrival and QC2 for departures, and the capability to reach an initial cruise altitude of 33,000ft (10,000m) in less than 30min.


"With these parameters we were able to do the work to design the wing, and we found that with some changes to the trailing edge we can meet all these requirements," says McConnell.
The wing will feature a trailing-edge extension, which McConnell describes as "quite a big change because it extends the high-lift devices and the ailerons, making the chord bigger by a maximum of around 400mm [15.7in]. We've been able to optimise the flap lift performance as well as gain more performance in the cruise."
The -1000 design team will work this year to finalise the changes over the -800/900, with some other less significant trade-offs to be completed on the configuration. Windtunnel tests will be run this year based on the enlarged wing, covering both performance and loads. "This will allow us to size the structure properly, which will give us a good idea on the weight delta of the aircraft," says McConnell

Airbus aims to meet the A350's mid-2013 service-entry target by compressing the flight-test programme into 12 months, after revealing that it has burnt up some of the development programme's " buffer".
The A350-900's 12-month, 2,600h flight-test programme will begin in mid-2012 with the maiden flight of the first of five development aircraft.
The date for the first flight has slipped by three months because of development delays in the aircraft's structural design, but Airbus is confident it can meet the mid-2013 service entry target for launch customer Qatar Airways by reducing the original 15-month test programme by three months.
"We've got five aircraft in the flight-test programme - which is more than we usually have," says A350 chief engineer Gordon McConnell.
He says that the original 15-month plan had been generous - some customers had questioned why it would take Airbus so long - and the airframer has been running projects with its flight-test and engineering teams to devise ways of compressing it.

One example is the flight manual process, says McConnell: "In the past we've done the aerodynamic testing to freeze the configuration, then the performance testing, and then built the flight manual. We've been working to make that a more concurrent effort."
The flight manual will now be built ahead of flight testing and will then be checked during flight-testing, with adjustments being made when necessary. "We've been able to save quite a lot of time on that critical path," he says.
The first two A350s to fly (MSN001 and 003) will be heavily instrumented. MSN001 will undertake all of the flight-envelope opening at the beginning of programme, to enable the aerodynamic and flight-control configurations to be frozen.
"MSN003 will be more devoted to performance and systems testing, but the two aircraft will be interchangeable because they have the same instrumentation," says McConnell.
The third A350 to fly will be MSN002, which will have a cabin installed. "We'll fly that early in the programme so we can do proper operational testing on the cabin and deliver a mature aircraft to customers," says McConnell.
MSN004 and 005 will undertake operational tests and extended twin-engine operations trials towards the end of the programme, with Airbus planning to have up to four of the first five aircraft airborne before end-2012.