Boeing adds 3% to 747-8 empty weight estimate

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Boeing has updated the empty weight of the 747-8 passenger variant to reflect a 3% increase driven by additional design changes since the previous estimate set in 2008.

The empty weight of the 747-8 has now risen by about 6,800kg (15,000lb) to 220,000kg, according to Boeing's latest update to airport planning documents. Actual weights in service vary with each airline.

The weight of the 747-8 grew during the development phase as Boeing engineers struggled with the initial design of the new supercritical airfoil.

"We changed the airfoils on the 747-8 to a deeper chord supercritical design," says Boeing. "This caused the weight of the wing to increase."

Boeing had previously also described a migrating series of weight-related design problems in the development phase. Changes to the wing shifted the centre of gravity. That shift, in turn, required Boeing to redesign portions of the tail to rebalance the loads, which caused further design changes elsewhere.

But Boeing remains confident that the effort to attach a supercritical wing to the 747 airframe achieved at least most of the desired results.

The 747-8 carries 51 more passengers and 25% more cargo than the 747-400, while consuming about 15% less fuel, says Boeing.

Last May, launch customer Lufthansa measured the difference in fuel consumption as more than 10% - within the carrier's expected range - but this was still less than was promised.

Boeing has a programme to introduce an improved version of the General Electric GEnx-2B engine in 2014. The performance improvement package engine has an audited estimate to reduce fuel consumption by 1.6%.