Story ID: GP777aerodynamics03092015
Boeing Unveils Efficiency ‘Bridge’ to 777X
By: Gregory Polek
Caption: New aerodynamic features promise to help cut fuel burn by 2 percent
Word Count: 427
Boeing has revealed five new distinct aerodynamic improvements in the 777 as it continues to prepare for the transition to the 777X starting in 2018. While appearing on March 9 at the International Society of Transport Aircraft Traders conference in Phoenix, Boeing Commercial Airplanes marketing vice president Randy Tinseth said the aerodynamic changes, coupled with engine efficiency improvements and 1,200 pounds worth of weight reductions, will result in a 2 percent reduction in fuel burn by the third quarter of 2016.

Changes include a so-called divergent trailing edge, in which designers add a trailing edge device to the underside of the wing, outboard of the aileron. The profile of the device increases camber of the outboard wing, resulting in outboard wing efficiency.

Next, improved elevator seals reduce drag while revised pitch trim software logic allows the elevator to augment the stabilizer trim during cruise flight, reducing profile and induced drag. Another design change involves making the slat trailing edge 60 percent thinner, resulting in lower drag. Still another revision involves a change to the inboard flap track fairing to “optimize” span-loading and reduce profile drag. Meanwhile, a new passenger window and seal design results in a more flush fit with the fuselage skin, reducing excrescence drag. Finally, Boeing’s enhanced tail skid protection integrated into the fly-by-wire control laws eliminates the need for a physical tailskid on the 777-300ER.

“The other thing about these airplanes is that we’re adding new features that will allow our customers to add up to fourteen seats,” said Tinseth. “So this combination of more fuel efficiency and more seats will yield about 5 percent improvement in efficiency per seat.”

The latest set of changes embodies Boeing’s latest effort to execute a smooth transition between the 777 and the new 777X. The company continues to plan for a roughly 100-unit annual output until the new airplane enters production in 2018, while Airbus concedes a need to cut production of the A330 from nine airplanes a month to just six starting in the first quarter of next year. Boeing estimates it will need to sell between 40 and 60 current generation 777s a year to maintain its 8.7 monthly rate. Last year it sold 63 of the big twins.

“As we’re looking at our backlog, as we’re looking at our production, our first focus was to fill the production line in 2016. And we’re to the point where we’re essentially sold out,” said Tinseth. “I think we’re well positioned for 2017 and when we get to ’18 we’ll handle it.”