AerodynamicsEverything You Need to Know About

By Julien Versailles

What is it?• The study of forces

and the resulting motion of objects through the airor

• The study of the flow of air around and through an object

Drag• A mechanical force caused by an object moving through a fluid (liquid or

gas)• The solid body must be in contact with the fluid• There must be motion between the object and the fluid• It is a vector quantity having both a magnitude and direction acting in a

direction opposite to the moving object

Lift and Downforce• Lift is the force that directly

opposes the weight of an object and holds it in the air

• Lift occurs when a solid object turns a moving flow of gas

• A negative lift causes downforce, which is the force that acts to push an object closer to the ground

• Lift and downforce are basically the same except that downforce acts downward and lift acts upward

Airplanes• For any airplane to fly,

you must lift the weight of the airplane

• The airfoils (wings) generate most of the lift to hold the plane in the air

• Jet engines or propellers provide the thrust to push the airplane forward through the air

Newton’s 3rd Law• For every action (force) in nature there is an equal and

opposite reaction• helps to explain the generation of lift from an airplane wing• The air is deflected downward by the action of the wing,

and in reaction the wing is pushed upward

The Bernoulli Effect• If a fluid (gas or liquid) flows around an object at different speeds,

the slower moving fluid will exert more pressure than the fastermoving fluid on the object

•The object will then be forced toward the faster moving fluid•The wing of an airplane is shaped so that the air moving over the top of the wing moves faster than the air beneath it•Since the air pressure under the wing is greater than that above the wing, lift is produced

Racecars• The total aerodynamic

package of the racecar is emphasized now more than ever before

• The focus of their efforts is on the aerodynamic forces of downforce and drag

• Downforce is necessary for maintaining speed through the corners

• The efficient design of a ground effects racecar is based on a downforce/drag compromise

The Chassis• The shape of the chassis is

similar to an upside down airfoil

• The shape of the underbody creates an area of low pressure between the bottom of the car and the racing surface

• The shape of the chassis sucks the car to road, which results in higher cornering speeds

Wings• Airfoils or wings are

also used in the front and rear of the car in an effort to generate more downforce

• The efficiency of a wing is the downforce/drag ratio

The Front Wing Assembly• The first part of the car to

meet the air mass• The flow field here is

better than at other parts of the car because the air here has been disturbed the least

• The wing is designed to produce downforce and guide the air as it moves toward the body and rear of the car

The Rear Wing Assembly• The turbulent air moving

toward the rear of the car will impact the efficiency of the rear wing

• The rear wing is not as aerodynamically efficient as the front wing, yet it must generate more than twice as much downforce to balance the car

Streamlines of Road Cars• As the air flows over the hood of a regular car, it's loses pressure, but

when it reaches the windscreen, it again comes up against a barrier, and briefly reaches a higher pressure

• The higher-pressure area in front of the windscreen creates a downforce

• As the higher-pressure air in front of the windscreen travels over the windscreen, it accelerates, causing the pressure to drop

• lower pressure literally lifts on the car's roof as the air passes over it

The Underside of a Car

• The underside of the car is responsible for creating lift or downforce

• If a car's front end is lower than the rear end, then the widening gap between the underside and the road creates a vacuum, or low-pressure area, and therefore "suction" that equates to downforce

Flow Detachment• Once the air makes it's way to the rear window, the notch created by

the window dropping down to the trunk leaves a vacuum, or low pressure space that the air is not able to fill properly

• As a result, a continuous vacuum sucks in the opposite direction• the resulting lower pressure creates lift that then acts upon the

surface area of the trunk

Applying Aerodynamics• To appreciate the importance of aerodynamics as applied to motor vehicles it must be realized

that, as driving speeds increase, the power needed to overcome air drag multiplies at a very rapid rate

• As an example, let us apply this formula to a car whose engine has to generate 18 HP to overcome the air drag at 80 km/h

• The power needed to double the speed to 160 km is shown in the following example. This is eight times the power needed to travel at 80 km

• If it were possible to reduce the drag by 25% we would need only 108 HP and fuel consumption would be about one-quarter less than what it was before

• It is now obvious why the proper shaping and streamlining of a car pays very significant dividends at little extra cost

Why You Need Aerodynamics• Not only can better

aerodynamics help improve the speed of a car, but it can also better the efficiency of a car

• Proper aerodynamic shaping, has been found to be the most effective and least costly method of increasing fuel economy and performance, especially at higher speeds

Other Important Aspects of Aerodynamics

• Automotive aerodynamics also plays an important role in other related areas including:

high-speed traction, sensitivity to crosswinds, efficient cooling (engine, drive train, exhaust system, and brakes), keeping the front windshield, the windows, the mirrors and the headlights clean, and last but not least, reducing wind noise to a minimum