image credit: Carla Thomas, NASA; image source; larger image

How Things Work: Winglets

The photo shows two NASA F/A18s. The smoke streaming from the wingtip of the one on the right reveals the wingtip vortex, which increases the wing's drag. This vortex occurs because the pressure underneath the wing is greater than the pressure above the wing; this excess pressure generates a flow of air around the wingtip, creating the vortex. These vortices can trail behind the aircraft for miles, creating a hazard for following aircraft, particularly small ones.

To reduce the drag caused by these vortices, "winglets" have been added to the wingtips of some airliners, as you can see in this Wikimedia photo. To learn more, visit How Things Work: Winglets.

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Bottled tornado

Make your own vortex at home--see Bottled tornado for how to do it. And be sure you have an adult with you.

Alternately, you can purchase a connector for the two bottles, with a hole in the middle--just google "vortex bottle" to find a vendor.

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image credit: Odile Labbe, ONERA; image source; larger image

Wing Vortices

This image from ONERA, the French aerospace lab, shows a simulation of the wake of an aircraft, looking along the direction the aircraft is moving. The spirals of moving air are called wingtip vortices. To learn more, visit this animation from the Smithsonian Institution's How Things Fly.

Also, compare the image above with this photo (from PTG Issue 33, in the Archives) showing the pattern of smoke released behind the wingtip of a crop-duster. How well did the simulation model the crop-duster wake?

(This feature was updated on September 21, 2013.)

How Airplanes Fly: A Physical Description of Lift

Visit the Florida International University site How Airplanes Fly: A Physical Description of Lift to understand how the wing of an airplane produces lift. You'll see that the frequently-given explanation based on the Bernoulli principle is not correct.