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Race Tech 101: Wings on Racecars
The first time I saw a racecar with a wing on it, I thought
it was dumb. But, thinking about it a while, I realized that
racers are practical people competing in an intense environment.
If those wings didn't do any good, they wouldn't be using them.
What I finally figured out was the upside down wings provide
additional force on the tires in excess of the weight of the
car, allowing the tires to produce more grip. Wings on an airplane
generate an upward force that's called lift. If you turn the
wing upside down, mount it on a car, and move it through the
air you get negative lift which we call downforce. More force
pressing the car down with no extra weight on the car makes the
car brake, accelerate, and turn better.
Slower Top Speeds but Faster Laps
Done properly, aerodynamic improvements to racing cars are
almost free performance improvements. For an open-wheeled car
especially, the tires produce a huge amount of aerodynamic drag.
If a clever designer is able to reduce this drag by cleaning
up the air flow over the bodywork and around the tires, wings
and other downforce-producing devices can improve the car's performance
with little or no penalty. Even when added aerodynamic devices
produce some drag along with downforce, the car can turn faster
laps. The car can actually have a slower top speed due to increased
aero drag and still turn faster laps because of more grip in
How Wings Produce Lift
When you're driving on the freeway and you open your car window
an inch or so, you get a rush of air coming into the car from
the vents. This is the same natural occurrence that allows a
wing to generate lift. The air going by the window has to speed
up to get out of the way of the car. When air speeds up, it loses
pressure. The lower pressure of the air speeding past the car
window sucks more air out the window, increasing flow into the
car through the vent. An airplane wing has a shape that causes
the air going over its upper surface to speed up more than the
air going under it. The air on top loses pressure and the difference
in pressure top to bottom times the area of the wing generates
a lifting force.
In 1738 Daniel Bernoulli, a Swiss physicist, observed and
measured fluid flow behavior causing him to propose that a fluid
loses pressure as it speeds up. Moving air has static pressure
and dynamic pressure. The total of the two is called the total
pressure and that remains the same whether the air is still or
moving. Static pressure plus dynamic pressure is total pressure,
a constant at sea level.
Any fluid (air or water, for instance) has no dynamic pressure
when still. When a car is motionless, the air inside and outside
has no dynamic pressure and the static pressure is the same both
places. When you put your hand out the window of a moving car,
you feel the momentum of the air as it runs into your hand. This
pressure you feel is called the dynamic pressure and it increases
the faster you go.
The graphic above shows a fluid flowing in a pipe that gets
smaller. For the same flow volume the fluid has to speed up in
the smaller pipe. The guages measure static pressure (in the
pipe wall, 90 degrees to the flow) and total pressure (parallel
to the flow). When the fluid speeds up total pressure stays the
same while static pressure decreases.
Through experiments, Bernoulli found out that this pressure
difference increases with the square of the airspeed. That means
the pressure loss goes up by a multiple of four when the speed
doubles. If you can accurately measure the difference between
these two pressures, you can find out how much the speed of the
That lower pressure air going by outside your car window is
what causes lift on airplane wings and downforce on racecars.
The curved upper surface of the wing (on a plane) makes the air
speed up to get around the wing in the same time as the air on
the bottom going a shorter distance. This speed difference creates
a pressure difference because the faster air on top loses static
pressure as it gains dynamic pressure. When the pressure on the
bottom of the wing is higher than the pressure above the wing,
we get a pressure difference and a lifting force.
Turn a wing upside down, put it on a car moving through the
air-you get downforce.