How winglets work

A little bend makes aircraft quieter and more effi­cient: designed to improve lift, winglets are up- or down­turned extensions at the tips of wings.

07.2018

A little bend makes aircraft quieter and more fuel-efficient: winglets—upturned or down­turned extensions at the tips of wings—improve an air­craft’s environ­mental perfor­mance by reducing drag and increasing lift.

Inspired by nature: Birds of prey have long wingtip feathers that they can spread out like a fan, which reduces air resist­ance and increases lift and speed. Richard T. Whitcomb, a specialist in aero­dynamics at NASA, adapted this principle for aviation in the 1970s, at a time when the oil crisis had caused prices for aviation fuel to sky­rocket. According to Whitcomb's calcu­lations, an additional vertical wing saves fuel because it increases the lift-to-drag ratio.

The principle: An aircraft’s lift is generated by low pres­sure on the upper surface of the wing and high pressure on the lower surface of the wing. Air flows up around the wing to balance out the low pres­sure. This air move­ment creates vortices, particu­larly at the wingtips, which coun­ter­act lift and increase kerosene consumption. Winglets are able to reduce these vortices.

How it works: Winglets break down the vortices at the wingtips into smaller eddies, which partly cancel each other out. This reduces flow resist­ance and improves lift—the air­craft rises faster and there­fore generates less noise while taking off. It also needs less energy in flight, which increases its range.

Net benefit: Winglets increase the weight of an air­craft, both with their own weight and also because of the structural rein­force­ments that need to be made to the wings. However, this negative effect is com­pen­sated for by the reduc­tion in fuel con­sump­tion, particularly on long-haul flights. The net outcome is that winglets lower fuel con­sump­tion by up to five percent.

Evolution: Wingtip designs can be very different. Airbus initially fitted com­mer­cial aircraft with wingtip fences, which have sur­faces extending both above and below the wingtip. Boeing devel­oped blended winglets, which are attached to the wing to form a smooth curve. More recent Airbus models have Sharklets, which curve up and back.

Taller than a man: Depending on the design, winglets can be quite large. The largest examples, measuring 3.45 meters, are fitted to the wings of the Boeing 767-300ER.

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