When Boeing’s new 777X taxied out for takeoff for its first flight earlier this year, it shared the look of most modern airliners. Its long fuselage was flanked by two massive engines under its long wings—the tips, known better as “winglets,” turned up in familiar fashion.
This is just the latest chapter in a 120-year-long quest to create a better airplane wing. Today, Boeing, Airbus, Embraer, Gulfstream, Bombardier, and other manufacturers produce multiple aircraft types with winglets, but as recently as the late 1990s, you rarely saw winglets on passenger aircraft.
Here’s what gave rise to the little-known-but-immensely-important winglet.
The idea of turning a wingtip up (or down) dates back to the 19th century. In 1897, English engineer Frederick W. Lanchester patented the placement of end plates vertically at the tip of a wing to control wingtip vortices.
Generally only visible in high moisture conditions, clouds, or fog, vortices appear as twisting ribbons of air behind the wing, almost like mini tornadoes turned sideways. As air flows over the wingtip of a conventional airplane, it tends to roll upward from the high pressure area under the wing to the low-pressure area above it. At speed, airflow over the tip of the wing is also forced backward. This backward flow combines with the upward roll from under the wing to form a vortex.
They may look cool, but they’re a major drag, literally. Vortices cause lift-induced drag, lowering the efficiency of the wing.
Though Lanchester recognized the problem, he never demonstrated his endplate on an aircraft. That feat would be left to Scottish engineer William Sommerville, who in 1910 patented what are considered to be the first functional winglets. Further research was done in the 1920s and 30s, but it wasn’t until World War II that winglets became more common.
Germany’s late-War Heinkel He-162A jet fighter incorporated many advancements including winglets. Integrated by Messerschmitt/Heinkel designer, Alexander Lippisch, the 162A’s winglets turned down instead of up. Their appearance gave rise to the nickname “Lippisch-Ears.” This style of drooped wingtip later became associated with German aerodynamicist Sighard F. Hoerner, whose influence led them to be used on gliders and light aircraft led to a new nickname: “Hoerner tips.”
But as aviation developed in the post-War era, winglets disappeared from most commercial and military aircraft—until 1973’s global oil embargo.
When the Organization of Arab Petroleum Exporting Countries (OPEC) drastically cut oil exports in the fall of 1973, crude oil went from $3 per barrel to almost $12 a barrel by March, 1974. Then (same as now) fuel accounted for 40 to 50 percent of operating costs of a single flight, depending on the type of airliner used. It was no surprise that airlines were hit hard.
The dramatic spike in oil prices got Richard Whitcomb, an aeronautical engineer at NASA’s Langley Research Center, thinking about winglets. He had studied Lanchester’s original concept and surmised that making the vertical surface of a winglet a refined airfoil would more effectively allow it to interact with the wingtip airflow vortices, reducing drag.
Whitcomb began a series of wind tunnel tests using a model of a DC-10, evaluating winglets at different airspeeds with different flap and aileron configurations. He found that adding them to the DC-10 model reduced overall drag by five percent compared to the model without the devices. In the mid-1970s, Boeing made its own engineering study of a 747 with winglets, which predicted a four percent reduction in aero drag.
As the NASA and Boeing studies went forward, Bill Lear’s innovative Learjet Corporation actually put winglets on its prototype Learjet 28 business jet in 1977. It became the first production jet to use winglets. In flight testing, they reportedly increased range by 6.5 percent. Bizjet maker, Gulfstream, also experimented with winglets in the late 1970s, installing them on the Gulfstream III in 1980.
The collective research inspired a test program for an airliner-sized aircraft at the NASA Dryden Flight Research Center in 1979-80. The U.S. Air Force furnished a KC-135 aerial refueling tanker (similar to a Boeing 707) for testing and Boeing built prototype winglets measuring nine feet high and six feet across at the base.
The winglet-equipped KC-135 first flew on July 24, 1979. Another 47 test flights followed, evaluating it against the stock KC-135 configuration. The results were close to what Whitcomb had forecast in his wind tunnel studies, only better. Drag decreased by 6.5 percent according to NASA with a corresponding reduction in fuel consumption.
Despite the added fuel benefits, it still took awhile for the aviation industry to catch on. In the mid 1980s, Boeing was looking to revamp flagging sales of its 747 Jumbo Jet by increasing range and lowering operating costs. The 747-400 was the first commercial airliner ever to feature winglets. According to Boeing, winglets increased the 747-400’s range by 3.5 percent over its 747-300 predecessor.
While it seemed that winglets had finally arrived (McDonnell Douglas’ MD-11 debuted them in 1990), a small Seattle aviation company would be the one to really accelerate winglets as a standard feature in modern aviation.