Small, winglike devices mounted at the tips of wings.

Winglets, sometimes known as Whitcomb winglets, after their developer, Richard Whitcomb of the National Aeronautics and Space Administration (NASA), are placed at the tips of the wings of many airline, commuter, and business class aircraft. They look like small wings and are usually attached to the main wingtip at an angle that tilts them slightly outward from vertical. In some cases, a winglet will include elements extending both above and below the wingtip, although many extend only upward from the wing.

Many people believe that the primary purpose of a winglet is to reduce or eliminate the swirling flow, or trailing vortex, beginning at an airplane’s wingtip as air moves around the tip to the low-pressure region above the wing, but this is not the winglet’s primary purpose. Although a winglet may somewhat alter this tornado-like vortex that flows from the wingtip of every airplane, its main purpose is to use that flow to create a thrust.

A properly designed winglet is mounted on a wingtip at a slight angle to the oncoming airflow, and the combination of the swirling flow around an aircraft’s wingtip with the oncoming flow causes a “lift” on the winglet, which is directed both inward along the wing and forward. This forward force is essentially a thrust that counteracts some of the normal drag of the airplane, improving its lift-to-drag ratio and giving it better range in flight.

A similar improvement in a wing’s lift-to-drag ratio could also be obtained by using a wing of greater span that gives a higher aspect ratio. The aircraft designer who wishes to make such an improvement may choose either to extend the wingspan or to use winglets. The latter choice may depend on factors such as the ability of the airplane to fit through hangar doors and between allowable airport gate widths.

• Barnard, R. H., and D. R. Philpott. Aircraft Flight. 2d ed. Essex, England: Addison Wesley Longman, 1995. An excellent, nonmathematical text on aeronautics, with well-done illustrations and physical descriptions, rather than equations, that explain virtually all aspects of flight.
• Bertin, John J., and Michael L. Smith. Aerodynamics for Engineers. 3d ed. Englewood Cliffs, N.J.: Prentice Hall, 1998. An engineering textbook with detailed technical examinations of a wide range of wing and airfoil aerodynamics theories and solutions.
• Stinton, Darrol. The Design of the Airplane. London: Blackwell Science, 1997. An outstanding reference, slightly technical but well-written and well-illustrated, on the design of all types of aircraft.

Aerodynamics

Airplanes

Forces of flight

National Aeronautics and Space Administration

Wake turbulence

Richard Whitcomb

Wing designs