A split scimitar winglet on a United jet. The airline is testing the design, a joint venture by Boeing and Aviation Partners, which could reduce the annual use of fuel by 45,000 gallons per plane. Eye-Catching Wingtips, but They Aren’t for Show
By JAD MOUAWAD
Published: October 23, 2013
United Airlines is testing the latest innovation in airplane design that may prompt passengers to do a double take. Called a split scimitar, it’s reminiscent of a medieval sword and is a variation on those doodads, known as winglets, that extend up from the tips of wings.
A winglet at the tip of a Boeing 737 that was lined up for an assembly inspection last year at a Boeing plant in Renton, Wash.
United is trying it out not to win any design awards, but to make the plane slice through the air more efficiently and, ultimately, reduce fuel consumption.
If all goes well, the airline estimates that the new design will help save $200 million a year once installed on its newest Boeing 737-800 and 737-900 models.
It will be introduced by the beginning of next year. United said it could improve a plane’s performance by an extra 2 percent compared with the current winglet design it uses on much of its fleet.
Ever since the Boeing 707 kicked off the jet age more than 60 years ago, the basic design of an airplane has changed little. But new materials, better computing power and more refined mathematical models have allowed aerospace engineers to improve the basic features of large passenger jets, including the performance of their wings.
Winglets reduce drag at the tip of an airplane’s wings and can improve fuel performance by as much as 5 percent a flight. Multiplied over thousands of flights, the savings can exceed a million dollars a year for just one plane.
“They smoothen the airflow over the wings and help improve lift,” said Capt. Joel Booth, United’s managing director of operations planning and fuel efficiency. “It’s an efficiency device.”
The search for improvement in a plane’s efficiency, no matter how small, comes after a surge in the price of fuel, which now accounts for roughly a third of an airline’s costs. Jet fuel is now well above $3 a gallon, up from 85 cents a gallon in 2000.
To offset this increase, airlines have pursued a variety of fuel-saving strategies, like taxiing with just one of two engines running, shutting off the plane’s auxiliary power when parked at the gate, or using more direct flight paths for landing. They have also started trials with green fuels, though those are still more expensive than kerosene for the time being. Delta Air Lines even bought an oil refinery outside Philadelphia last year.
Airlines have taken small steps too, giving pilots electronic tablets to replace their hefty flight manuals, using lighter paper for their in-flight magazines in a bid to cut weight from the cabin, or using lighter seats in coach.
While all these things undoubtedly help, the big difference to the economics of flying will come from more fuel-efficient engines and planes. The Boeing 787, which started flying passengers nearly two years ago, and the Airbus A350, which is in its test phase, promise fuel savings of around 20 percent thanks to their use of lighter materials like carbon composites, though the 787 has had its share of problems given all its technological innovations.
New jet engines that run more efficiently than those of the current generation are also being developed.
But airlines also want to improve the efficiency of their existing planes. That’s where the winglets come in, since those can be bolted onto existing models.
The physics behind winglets has been well understood since the 1960s, when NASA did some research on them. The first came out in the 1980s on business jets, and later equipped the Boeing 747 and the MD-11. At the time, those early models improved performance from 1.5 percent to 3.5 percent.
Nowadays, high fuel prices have made them nearly mandatory for all types of commercial planes.
“There are still some basic physics that we use to minimize the drag on the airplane, and that hasn’t changed over the years,” said Robert D. Gregg, III, the chief aerodynamicist at Boeing Commercial Airplanes.
Designs vary in part because every plane — and every wing — is different. Some business jets have “spiroid” wingtips, like a big “O” at the end of the wing. The double-decker Airbus A380 has arrow-shaped tips. The wingtip on the Airbus A330 is slanted at an angle of about 60 degrees.
Plane makers could improve efficiency simply by extending the length of the wings. But that’s usually impossible, given the constraints imposed by airports and parking gates. The standard for single-aisle planes, for instance, is that the wings must not exceed 36 meters, or 118 feet.
A conventional winglet extends the length of the wing by about eight feet upward, and that is now common on many Boeing 737s.
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