Taking Wing

TAKING WING

IGNITION

TWO-WHEEL CHATTER

Why winglets are sprouting on MotoGP bikes such as the Ducati GP16

Kevin Cameron

When downforce wings are mentioned, everyone instantly assumes that, as in F1, the purpose is to press tires down harder, increasing traction to allow higher corner speeds.

This is not the purpose of the winglets that MotoGP bikes have sprouted as of late because what is downforce while the bike is upright on a straight becomes push-you-off-the-corner force when the bike is leaned over at 58 degrees. No good.

A bike’s aerodynamic center of pressure is high above the ground-maybe as high as 26 to 28 inches. That means the faster a bike’s engine forces it through the air, the more air drag tries to blow it over backward. Many a racer cresting a hill in top gear and having the front end come up suddenly has had to go for the back brake to bring it down. Today’s MotoGP bikes— especially the superpowerful Ducatis-are routinely exceeding 200 mph while still accelerating.

Let’s say our Ducati’s acceleration can lift the bike’s front wheel at speeds up to 140 mph, but above that, gravity wins. Now add the blowover-backward aerodynamic force and you have the front wheel still in the air, and as the bike goes

fasteryet, acceleration decreases but aero force increases. This creates a zone of high-speed acceleration in which the front wheel remains light even though the rider pulls himself forward as far as he can. At high speed, bumps add to front-wheel lightness.

The result? Mysteriously poor high-speed acceleration because the bike’s anti-wheelie electronics are being triggered. This means we have performance we can’t use since the engine has the juice to keep accelerating but front-wheel lightness won’t let it.

To keep the front end down, silence the anti-wheelie system, and accelerate past the Hondas, we add downforce winglets to the front of the bike. To maximize effect we put the winglets where the flow moves faster than the bike itself-around the bulbous nose.

Now for the math: If there’s a total of one square foot of winglet area in Ducati’s two-level “biplane” array, and we estimate 30 pounds per square foot downforce at 140 mph (because such stubby wings are rather inefficient), we’ll have twice this at 200 mph. What’s the cost in induced drag? If winglet lift/drag is half as good as an airliner’s, we get 3.5 pounds of drag at 140 mph and 7 pounds at 200 mph, translating to 1.3 hp at 140 mph and 3.7 hp at 200 mph. Now, if the lift/ drag is more like that of a hang glider, power loss doubles.

Detail engineering and wind tunnel testing seem to be making this work. What fun!