(CNN) — What caught your eye the last time you looked out of your airplane window? It might have been the winglet, a now ubiquitous appendage at the end of each wing, often used by airlines to display their logo and put their branding in your travel pictures.

But the winglet isn’t there for marketing purposes alone — it actually saves fuel. On average, an aircraft equipped with them can use up to 5% less fuel, and for a typical Boeing 737 commuter plane that can mean 100,000 gallons of fuel a year, according to NASA. The collective savings for airlines are in the billions of dollars.They do so by reducing the natural vortices that form at the wingtips, which can be so strong that smaller aircraft can even flip in mid-air when crossing the wake of very large planes. The effect is so obvious that aerodynamicists were thinking about it even before the Wright brothers completed their first flight. The widespread adoption of winglets, however, is far more recent.

A better design

Winging it: The curves at the end of modern airplane wings are all about efficiency.

Pascal Pigeyre/MasterFilms

As air flows around a plane’s wings, it generates high pressure on the bottom surface and low pressure on the top one, which creates lift. But once the air flowing at the bottom reaches the wingtip, it tends to curl upwards and meet the lower pressure air at the top, generating what is essentially a small tornado. This extends behind the aircraft producing drag, which equals a loss of energy.

“That energy that’s being left in the air is coming from the aircraft,” says Al Bowers, a former chief scientist at NASA’s Neil Armstrong Flight Research Center. “If there were a way to capture more of that energy and keep it on the aircraft, that would result in less energy being wasted in its wake.”

In 1897, British aerodynamicist Frederick W. Lancaster patented “wing endplates,” vertical surfaces to be placed at the end of wings to stop the airflow from the bottom and the top from meeting, reducing drag. “Endplates in many ways act much like winglets do, but the improvement to the lift is rather poor, because flat plates by themselves are not very good aerodynamic surfaces,” explains Bowers.

The idea was refined for modern aircraft in the 1970s by NASA engineer Richard Whitcomb, who imagined vertical wing extensions inspired by the way birds curl up the end of their wings when in need of lift.

“It was Whitcomb who developed the idea that these should be much more aerodynamic surfaces, actually wing-shaped themselves,” says Bowers. “He realized that setting the angle correctly on them would result in a dramatic drag reduction.” The name winglet, meaning little wing, naturally followed.

Whitcomb tested the idea in a wind tunnel and found that winglets could achieve a reduction of drag of about 5%. At the same…

Source: Why modern airplanes have winglets