Engineers look at alternative mount designs for Advanced derivative to allow use of powerplants with larger fans

Boeing engineers are studying alternative engine mount designs to increase ground clearance for the proposed 747 Advanced. The move would enable the use of 7E7 derivative engines with larger fan diameters up to 2.8m (110in), says the company, which plans to finalise the design in 2005.

The change, which is accompanied by parallel studies to enable "bleed" variants of the 7E7 engines to be plumbed into the legacy systems of the 747, is widely seen as vital to the credibility of the Advanced study and to any chance of its launch. The planned efficiencies of the 7E7 engines, irrespective of the chosen finalists, are pivotal to the 747 Advanced study and Boeing is anxious to reassure potential customers that the full benefits of 7E7 technology could be available to allow the derivative family to enter service in 2009.

Market interest in its proposed 747 Advanced family remains "hefty" says John Quinlivan, vice-president and general manager of the Everett site and 747, 767 and 777 programmes, who adds that industry concerns over ground clearance and bleed are being addressed (Flight International, 5-11 August).

"We've found we can get a bit bigger than that," says Quinlivan, referring to the baseline 747 engine fan diameter inlet limit of just over 2.6m. Although current 7E7 engine studies are divided between smaller and larger fan sizes to meet the short-range and stretch thrust requirements, the mid-60,000lb thrust (267kN) needs of the 747 derivative family still sit within the range. "We have also found a way around the bleed issue," says Quinlivan.

He adds that, combined with advances in composite and aluminium materials selected for the 7E7, together with a range of aerodynamic improvements already outlined for the Advanced, Boeing's latest analysis suggests direct operating costs for the passenger version will be up to 13% better than the current -400, and up to 19% better for the Advanced freighter versus the -400F.

"Those are huge benefits we didn't see on earlier 747 derivative studies," Quinlivan adds.

Market indications show the freight market is recovering more quickly than the passenger market, and it is likely that Boeing could launch the freighter variant first. Quinlivan says the company does not have to commit to this until around 30 months before the projected 2009 service entry target. He adds that upturns in the freight and passenger markets could see more 747-400 orders to bridge the gap until the possible Advanced production begins around 2008.

Source: Flight International