Downforce

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• the shape of the body, and
• the use of airfoils.

Most racing formulae have a ban on aerodynamic devices that can be adjusted during a race, except during pit stops.

The downforce exerted by a wing is usually expressed as a function of its lift coefficient:

${\displaystyle F=-C_{L}{\frac {1}{2}}\rho v^{2}A}$

where:

• F is downforce (SI unit: newtons)
• C_L is the lift coefficient
• ρ is
  air density
  (SI unit: kg/m³)
• v is velocity (SI unit: m/s)
• A is the area of the wing (SI unit: meters squared), which depends on its wingspan and chord if using top wing area basis for C_L, or the wingspan and thickness of the wing if using frontal area basis

In certain ranges of operating conditions and when the wing is not stalled, the lift coefficient has a constant value: the downforce is then proportional to the square of airspeed.

In aerodynamics, it is usual to use the top-view projected area of the wing as a reference surface to define the lift coefficient.

Body

The rounded and tapered shape of the top of a car is designed to slice through the air and minimize wind resistance.^{[citation needed]} Detailed pieces of bodywork on top of the car can be added to allow a smooth flow of air to reach the downforce-creating elements (e.g., wings or spoilers, and underbody tunnels).^{[citation needed]}

The overall shape of a car resembles an airplane wing. Almost all road cars produce aerodynamic lift as a result of this shape.

Some cars, such as the DeltaWing, do not have wings, and generate all of their downforce through their body.^{[citation needed]}

Airfoils

The magnitude of the downforce created by the wings or spoilers on a car is dependent primarily on three things:

• The shape, including surface area, aspect ratio and cross-section of the device,
• The device's orientation (or angle of attack), and
• The speed of the vehicle.

A larger surface area creates greater downforce and greater drag. The aspect ratio is the width of the airfoil divided by its chord. If the wing is not rectangular, aspect ratio is written AR=b²/s, where AR=aspect ratio, b=span, and s=wing area. Also, a greater angle of attack (or tilt) of the wing or spoiler, creates more downforce, which puts more pressure on the rear wheels and creates more drag.

Front

The function of the airfoils at the front of the car is twofold. They create downforce that enhances the grip of the front tires, while also optimizing (or minimizing disturbance to) the flow of air to the rest of the car. The front wings on an open-wheeled car undergo constant modification as data is gathered from race to race, and are customized for every characteristic of a particular circuit (see top photos). In most series, the wings are even designed for adjustment during the race itself when the car is serviced.

Rear

The flow of air at the rear of the car is affected by the front wings, front wheels, mirrors, driver's helmet, side pods and exhaust. This causes the rear wing to be less aerodynamically efficient than the front wing, Yet, because it must generate more than twice as much downforce as the front wings in order to maintain the handling to balance the car, the rear wing typically has a much larger aspect ratio, and often uses two or more elements to compound the amount of downforce created (see photo at left). Like the front wings, each of these elements can often be adjusted when the car is serviced, before or even during a race, and are the object of constant attention and modification.

Wings in unusual places

Partly as a consequence of rules aimed at reducing downforce from the front and rear wings of F1 cars, several teams have sought to find other places to position wings. Small wings mounted on the rear of the cars' sidepods began to appear in mid-1994, and were virtually standard on all F1 cars in one form or another, until all such devices were outlawed in 2009. Other wings have sprung up in various other places about the car, but these modifications are usually only used at circuits where downforce is most sought, particularly the twisty Hungary and Monaco racetracks.

The 1995 McLaren Mercedes MP4/10 was one of the first cars to feature a "midwing", using a loophole in the regulations to mount a wing on top of the engine cover. This arrangement has since been used by every team on the grid at one time or another, and in the 2007 Monaco Grand Prix all but two teams used them. These midwings are not to be confused either with the roll-hoop mounted cameras which each car carries as standard in all races, or with the bull-horn shaped flow controllers first used by McLaren and since by BMW Sauber, whose primary function is to smooth and redirect the airflow in order to make the rear wing more effective rather than to generate downforce themselves.

A variation on this theme was "X-wings", high wings mounted on the front of the sidepods which used a similar loophole to midwings. These were first used by Tyrrell in 1997, and were last used in the 1998 San Marino Grand Prix, by which time Ferrari, Sauber, Jordan and others had used such an arrangement. However it was decided they would have to be banned in view of the obstruction they caused during refueling and the risk they posed to the driver should a car roll over. (It is rumored that Bernie Ecclestone saw them as being too ugly on television and therefore had them banned).^{[citation needed]}

Various other extra wings have been tried from time to time, but nowadays it is more common for teams to seek to improve the performance of the front and rear wings by the use of various flow controllers such as the afore-mentioned "bull-horns" used by McLaren.

See also

• Bernoulli's principle
• Body kit
• Formula One car
• Grip (auto racing)
• Ground effect in cars
• Lift (force)
• Wind tunnel

Further reading

• Simon McBeath, Competition Car Downforce: A Practical Handbook, SAE International, 2000,
  ISBN 1-85960-662-8
• Simon McBeath, Competition Car Aerodynamics, Sparkford, Haynes, 2006
• Enrico Benzing, Ali / Wings. Progettazione e applicazione su auto da corsa. Their design and application to racing car, Milano, Nada, 2012. Bilingual (Italian-English)

References