Airbus expects that the A350-900 will suffer a fuel burn penalty of "about 1%" as a result of the empty weight being 2.2t greater than the planned specification at service entry but payload/range performance will be maintained.
In a detailed technical update for journalists in Toulouse today, A350 chief engineer Gordon McConnell confirmed that following the completion of the first detailed "structural sizing" of the A350-900, Airbus has established that the manufacturer’s weight empty is 2.2t greater than target and that "similar deltas" are expected for the -800 and -1000.
"At this point we think that we’ve got good maturity on the weight estimate and, although it’s not the result we wanted, it is prudent for us to take the decision to increase the maximum take-off weight by 3t across the family," says McConnell. The target service-entry MWE for the A350-900 was 113.5t, but this has risen to 115.7t, he adds.
The previously quoted MTOWs for the -800, -900 and -1000 were 245t, 265t and 295t, respectively. McConnell says that while payload/range performance has been maintained through the MTOW increase "we think there will be a small impact on fuel burn of about a 1%". However there will no impact on take-off performance or the need for additional engine thrust, says McConnell, except "at some specific airfields where discussions have been held with Rolls-Royce about where we’ll need a percent or two more" thrust.
Weight reduction efforts are ongoing to mitigate the impact of the weight growth, says McConnell, who adds that when the details of the weight growth were provided to customers last week at the programme progress review (PPR) in Madrid, they were "quite understanding about what we are doing". He adds that there is "no issue" with performance guarantees.
Several elements have contributed to the rise in MWE over specification, says McConnell: "This was the first sizing of the electrical structural network [needed to provide current return with the composite fuselage frames] and we had to add some weight for that which we didn’t expect. There have also been some improvements in the aerodynamics of the wing to reduce drag which has cost us some increase in loads and therefore weight."
He adds that the work Airbus has been doing with systems suppliers "has allowed us to get a more accurate weight for the system equipment and the installation".
The A350-900 remains on target to reach the detailed definition freeze by the end of the year, with first flight in early 2012 and service entry in mid-2013 with Qatar Airways after an 18 month flight-test programme.