The battle of wing extensions for new single-aisle

"Dual feather winglet."

This is the new solution proposed by Boeing for the new 737MAX. The winglet on the 737 MAX will have two tips, one bending up, the other down.

The company previously had estimated the MAX would offer fuel savings of 10 percent to 12 percent compared to the current 737, with this solution the additional saving is 1.5 percent on fuel.

"Incorporating this advanced technology into the 737 MAX design will give our customers even more advantage in today's volatile fuel-price environment," Jim Albaugh, president of Boeing Commercial Airplanes, said in the statement. Boeing launched the upgraded 737 MAX last August to compete with the A320 new engine option, or A320neo, which rival Airbus announced in late 2010. Both re-engined single-aisle jets are expected to offer improved fuel savings.

"The concept is more efficient than any other wing-tip device in the single-aisle market because the effective wing span increase is uniquely balanced between the upper and lower parts of the winglet," said Michael Teal, chief project engineer for the  737 MAX. Boeing said the dual feather winglet was validated during wind tunnel testing of the 737 MAX. The new winglet fits existing airport gate constraints "while providing more effective span, thereby reducing drag," the company said. "We have assessed the risk and understand how to leverage this new technology on the MAX within our current schedule," said Teal. "This puts us on track to deliver substantial additional fuel savings to our customers in 2017." The company estimates the 737 MAX will use 18 percent less fuel than the current Airbus A320.

In 2009, Airbus announced it would offer fuel-saving wing tips that the company calls "sharklets" as an option on the A320. The neo adds winglets — Airbus calls them "sharklets" — to the current A320 design, but they are very similar to the upward swooping winglets on today's 737s.

Because the 737 already has winglets, Airbus executives have argued that the MAX cannot gain the extra 3.5 percent fuel-burn improvement the European plane-maker will gain by adding winglets to the neo. Wednesday's announcement of a radical new Boeing winglet design undercuts that argument. Boeing had previously claimed a 5 percent fuel-burn advantage over the neo. Spokeswoman Lauren Penning said the new MAX wingtip's incremental fuel-burn advantage adds up to a further 1.5 percent advantage compared with the neo. Airbus hotly disputes Boeing's figures. Before news of the "dual feather" winglet, Airbus had been claiming the neo would burn 8 to 11 percent less fuel than the MAX, depending on which sub-models are compared.

Airbus hotly disputes Boeing's figures. Before news of the "dual feather" winglet, Airbus had been claiming the neo would burn 8 to 11 percent less fuel than the MAX, depending on which sub-models are compared.

Airbus spokeswoman Mary Anne Greczyn said Wednesday the company's engineers looked at the option of a split-tip winglet for the neo but decided on the "sharklet" design. Separately, Boeing revealed that the MAX will require a slight bump in the door of the nose landing gear. That's because the nose gear must be extended by 8 inches, compared with the current 737, to lift the wing and allow sufficient ground clearance for the new, bigger CFM engines. To fit the longer nose gear into the wheel well without major structural changes, Boeing is shaping the landing-gear door so that it bulges outward to accommodate the tires. That will add some drag, but Teal said the impact is "negligible." The projected fuel-burn improvement takes into account all the changes, negative and positive.Airbus has produced the first new-build A320 with Sharklets. Depicted here at its roll-out in Toulouse, MSN 5098 will be one of several A320 Family aircraft in the certification flight-test campaign starting in May this year and lasting around 600 flight hours. These Sharklet tests follow the successful ‘early flight-test’ campaign with Airbus’ A320 MSN 001 test aircraft.

In a conference call with journalists, Michael Teal, chief project engineer for the 737 MAX, called the concept "the most advanced wingtip technology in the single-aisle market." The design is innovative. No commercial airplanes in service today have anything similar, though the concept resembles a split-tip winglet design Seattle-based Aviation Partners is flight testing. Winglets in general add extra wing surface without extending the overall wing span. They increase the wing's lift while their shape reduces the drag caused by air vortices at the wingtip. Teal said the split ends of the new wingtip maximize the aerodynamic gain without adding as much weight as a longer, single winglet would.

The overall MAX wing span will be just a few inches longer than the current 737. Teal said the upper feather of the new winglet is close to the size of today's 737 winglets, which are nearly 8 feet tall. The lower feather will be shorter to ensure sufficient ground clearance. Boeing aerodynamicists came up with the design using computer simulations, then tested it in two advanced wind tunnels, Teal said.

He said the new winglets can be incorporated into the overall design within the previously announced schedule, which will see the MAX enter service in 2017. Final details for the jet's design and manufacturing will be pinned down next year. Last fall, at a Las Vegas business-jet conference, a somewhat similar design called the Blended Split-Tip Scimitar Winglet was showcased by Aviation Partners, which pioneered winglet technology and works with Boeing in a joint venture that produces winglets for the 737.