Whitcomb, a noted aeronautical engineer at the NASA Langley Research Center, refined the winglet concept with wind tunnel tests and computer studies. A winglet flight test program at the NASA Dryden Flight Research Center in validated Whitcomb's research when the test aircraft -- a military version of the Boeing jetliner -- recorded an increased fuel mileage rate of 6. Since the s, when the price of aviation fuel began spiraling upward, airlines and aircraft manufacturers have looked at many ways to improve the operating efficiency of their aircraft.
Winglets have become one of the industry's most visible fuel-saving technologies and their use continues to expand. Winglets increase an aircraft's operating efficiency by reducing what is called induced drag at the tips of the wings.
An aircraft's wing is shaped to generate negative pressure on the upper surface and positive pressure on the lower surface as the aircraft moves forward. This unequal pressure creates lift across the upper surface and the aircraft is able to leave the ground and fly. Unequal pressure, however, also causes air at each wingtip to flow outward along the lower surface, around the tip, and inboard along the upper surface producing a whirlwind of air called a wingtip vortex.
The effect of these vortices is increased drag and reduced lift that results in less flight efficiency and higher fuel costs. Winglets, which are airfoils operating just like a sailboat tacking upwind, produce a forward thrust inside the circulation field of the vortices and reduce their strength. Weaker vortices mean less drag at the wingtips and lift is restored. Improved wing efficiency translates to more payload, reduced fuel consumption, and a longer cruising range that can allow an air carrier to expand routes and destinations.
To produce as much forward thrust as possible, the winglet's airfoil is designed with the same attention as the airfoil of the wings themselves. Performance improvements generated by winglets, however, depend on factors such as the basic design of the aircraft, engine efficiency, and even the weather in which an aircraft is operating.
The shapes and sizes of winglets, and the angles at which they are mounted with respect to the main wings, differ between the many types and sizes of aircraft produced but they all represent improved efficiency. Aircraft manufacturers and makers of add-on winglets have also reported improved cruising speeds, time-to-climb rates, and higher operating altitudes. The use of winglets throughout the aviation industry in the U. Winglets now appear on powerless hang gliders soaring above mountain ridges and from seaside cliffs.
Sailplane builders around the world have included blended winglets to their designs and the sleek, graceful gliders are silently soaring farther than ever Corporate-size Learjet's were the first commercial aircraft to use winglets. Now, several decades later, winglets are incorporated into the designs of many other business jets such as Gulfstreams and the Global Express: a new aircraft built by Lear's parent company, Bombardier.
Retrofitting winglets to existing business jets is also a fast-growing market within the aviation industry itself. Many winglet marketing firms report their products help increase aircraft roll rates and lower approach and takeoff speeds. Winglets are now quite common on large jetliners and many tower as high as six feet. According to Gregg, that's because the operates from international terminals designed for larger jumbo jets. As a result, Boeing found the performance it was seeking without the need for vertical extensions.
According to Gregg, the first-generation winglets fitted to aircraft such as the Boeing and the McDonnell Douglas MD11 offered up to 2. Second-generation winglets, such as those found on Boeing's workhorse , , and aircraft are much larger than the first-gen models, with greater curvature.
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By adjusting these so that the lift force points slightly forward, a designer can produce the equivalent of thrust. A sailboat tacking sharply upwind creates a similar force with its sail while the keel squeezes the boat forward like a pinched watermelon seed.
If winglets are so great, why don't all airplanes have them? Because winglets are a tradeoff: In the highly visible case of the , an airplane with exceptionally long range, the wings grew so long that folding wingtips were offered to get into tight airport gates.
Dave Akiyama, manager of aerodynamics engineering in Boeing product development, points out that designing winglets can be tricky-they have a tendency to flutter, for example. Span extensions are the easiest and least risky. Unlike those tailfins on cars, winglets really work. Continue or Give a Gift. Daily Planet. Flight Today. History of Flight. Virtual Space. Like this article?
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