Question

If dimples on a golf ball make it travel further then why don't they use dimples on aircraft?

Asked by: David Nelson

Answer

You may have noticed the important difference between golf balls and airplanes that answers your question - airplanes are not round!

The dimples on a golfball help the laminar flow of air travel around the ball a little farther than it would flow around a smooth ball. Since air in laminar flow has a higher pressure than turbulent air, the laminar flow behind the ball creates less of a 'sucking' effect behind the ball which would substantially slow it down. The ball must be spherical, but spheres are poorly shaped for flight through air because the rapidly decreasing diameter as one moves from the front of the ball (i.e. whatever part faces the direction of motion) to the back of the ball would require the air to rapidly come back togethergether behind the ball. No can do - the airstream breaks up into many fast moving swirls and eddys which due to their low pressure exert less force on the back of the ball than the smoothly flowing air exerts on the front. Voila, drag.

A plane avoids this same problem in a different way. By having a tapering tail, the airstream is allowed to come back together more gradually, and therefore does not become turbulent. Ditto submarines, Porche 944's, footballs, dolphins, and anything else that has long, tapering edge facing away from the direction of travel. (But those new helmets that Olympic skiers wear to get the same effect still look funny!)

Answered by: Rob Landolfi, Science Teacher, Rockville, MD

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