What are winglets, the aesthetically-pleasing aerodynamic marvels found on most planes?

Have you ever snagged a window seat, looked out and wondered what was protruding off the end of the wing — a mostly vertical extension of the wing itself?

Some may curve upward, making a seamless transition from horizontal to vertical. Others may look angular. Some might even be split in two, extending both above and below the wing.

These are called winglets, and they're an aerodynamic marvel that has — with some notable exceptions — become a staple of airliners over the past 30 years. But how do they work, and what are the differences between the styles? We're here to tell you.

Winglets cut down on a phenomenon called wake vortices that trail off the tips of an aircraft's wings. These vortices can cause significant drag, making aircraft less efficient.

Winglets are technically small wings that generate lift and can cut down on the amount of drag created, therefore reducing fuel consumption and increasing an aircraft's range.

While winglets do add weight to an aircraft, the amount of efficiency they provide generally makes their extra weight worthwhile on all but the shortest flights.

Winglets are most efficient during the cruise portion of a flight, as well as during the actual takeoff and landing when an aircraft is in what's known as a "high angle of attack," which is defined as the difference between where a wing is pointed and where it's going.

Winglets can come in different shapes and sizes. Here are some of the winglets you might encounter during your travels.

Conventional canted winglet

Aircraft: Boeing 747-400, Airbus A330-200 and -300, Airbus A340, Canadair Regional Jet, Embraer E-Jets.

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These early winglets were direct descendants of the original winglet research that took place at NASA in the late 1970s. Engineers had known about the potential for wingtip devices. However, Richard Whitcomb at the agency's Langley Research Center is widely credited with improving the concept to the point where winglets became commercially viable.

Whitcomb modified a KC-135 (the U.S. Air Force's workhorse aerial tanker) with the winglets he designed. His research revealed that the winglets boosted the KC-135s range by as much as 7%.

Blended winglet

Aircraft: Boeing 737-300, -500, -700, -800, -900 and -900ER, Boeing 757-200, -300, Boeing 767-300ER, various corporate aircraft.

Blended winglets came about in the early 1990s as a way to improve upon Whitcomb's angular winglet design. In Whitcomb's original design, winglets transition from the horizontal wing structure to vertical at an obtuse angle. This creates interference drag, a phenomenon that occurs when different airflows on different surfaces mix. By smoothing out that transition, blended winglets cut down on drag and make the winglets more efficient.

Blended winglets were pioneered by a company called Aviation Partners, which later formed a joint venture with Boeing called Aviation Partners Boeing.

The first Boeing 737s flew with blended winglets in 2001 and later became a ubiquitous feature of the type. Blended winglets on the 737 could be retrofit after delivery or installed in Boeing's Renton factory — an option most customers took. Blended winglets later came to the 757 in 2005 and the 767-300 in 2009.

Split scimitar winglet

Aircraft: Boeing 737-700, -800, -900, -900ER.

Split Scimitar winglets, another Aviation Partners Boeing product, offer about 2% additional fuel savings over blended winglets and entered service in 2014. Split Scimitar winglets look like blended winglets — with the addition of a downward-facing winglet, called a ventral strake — and are another Aviation Partners Boeing innovation.

Advanced-technology winglet

Aircraft: Boeing 737 MAX.

From certain angles, this winglet can sometimes look like a split scimitar winglet, but it works a bit differently.

The advanced-technology winglet is found exclusively on the 737 MAX and comes standard. It includes both an upper and a lower airfoil.

The upper airfoil creates a lifting motion toward the fuselage. The lower airfoil creates a lifting motion away from the fuselage, countering the upper airfoil and increasing the efficiency of the wing. (An airfoil is a structure on a plane designed to generate lift.)

Boeing says this winglet increases fuel efficiency by another 1.5% over the winglets found on the 737 NG.

Sharklet

Aircraft: Newer A320ceo family aircraft, all A320neo family aircraft, A330neo, A350.

Sharklets largely resemble blended winglets — a seamless curve upward — and generally work the same way.

Sharklets are essentially a different term that Airbus coined for blended winglets (Airbus sued Aviation Partners in 2011 over its blended winglet patent and both parties settled the case in 2018). The first sharklet-equipped A320 aircraft was delivered in December 2012. Sharklets come standard on A320neo family aircraft.

When sharklets debuted on the A320, Airbus promised a 4% reduction in fuel burn and a 100 nautical mile range improvement.

The Airbus A350 comes standard with sharklets as well. However, these sharklets are much larger and have a different shape than the sharklets found on A320 family aircraft.

Wingtip fence

Aircraft: Older A320ceo family aircraft, A300-600, A310, A380.

These early-design winglets are made to address wake vortices below the wing, in addition to the aerodynamic benefits that they provide above the wing.

They're a hallmark of 1980s-era Airbus design, though they also appeared in a supersized form a generation later on the A380 superjumbo. Triangular-shaped, these fences meet the wing at a right angle and protrude both above and below the wing.

Bottom line

Next time you're flying and stare out at the wing, you now know what those winglets at the end of it are for, and can identify the type of winglet on your plane.

There are other types of winglets we didn't cover here. Also, aircraft like the Boeing 777 and 787 lack winglets. Adding winglets would have made the 777 too large for some airports, while Boeing engineers determined that the uniquely-shaped 787 wing was efficient enough without winglets.

Boeing's newest jet, the massive 777X, also doesn't include winglets. However, it features folding wingtips that allow it to use smaller gates at airports. It's already a defining feature of this new aircraft, which is slated to enter service in 2025.