Copyright © A. Filippone (1997-2005). All Rights Reserved.
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Racing Cars Aerodynamics

Summary


Aerodynamics has played a major role in car racing since the late 1960s, when introduction of the first inverted wings appeared in some formulas. After that time, improved wing systems taken from the aeronautic technology made leaps forward, improving consistently lap times, increasing cornering speeds and vehicle stability. With the introduction of the ground effect a few years later the vehicles used a third element (the underbody) to produce downforce, and hence improve the performances.

Preparing to Race

Preparing to Race

Technology Trends

By studying the trends of the last thirty years we see that aerodynamics is a reason behind the success of a racing car, since tire and engine technology have made a comparatively small progress. Furthermore, tires are not manifactured to fit the particular needs of a single racing team, while engines (in Indy Cars) often are developed in series for more than one team.

Aerodynamics is a subject more open to speculation, interest, advancement. These conclusions lead us to the analysis of the aerodynamic tools: computational aerodynamics, wind tunnel testing, and aerodynamic design and optimization.

St. Louis, May 1997

St. Louis Speedway, MO, May 1997 (About the Photo)

The Role of Aerodynamics

The first design that used aerodynamics other that body streamlining did not appear until the 1960s. By then it was recognized how an increase in downforce would provide more grip to the track and hence more speed. This idea was technically developed by Chevrolet- Chaparral in 1966 with their Can-Am racing car. The engineers mounted an inverted wing on two vertical struts above the rear axial. The wing could be pitched during racing to provide the optimal value of downforce.

These ideas were developed quickly, and a few years later several Formula 1 teams mounted inverted wings on the rear axial, combined with a smaller front wing.

Introduction of Sealing Skirts

Another important innovation was introduced by Chevrolet- Chaparral in 1970. It consisted in reducing the pressure under the car by means of suction and lateral sealing skirts. Their sucker car (model Chaparral 2J) reached cornering speeds of 1.7 g, and soon was considered too dangerous. It was banned after a few races.

Introduction of Ground Effect Cars

The ground effect car was introduced by Team Lotus in their 1978 Formula 1 car. By shaping the underbody with appropriate channels, and using side pods to increase the effective area, the car provided much larger values of downforce. The idea, again, was simple. Ground effect was a known concept in aerodynamics. It just needed a technical solution to be fully exploited.

Effects of Legislations

The step from one development phase to another was interrupted by legislations aimed at cutting the aerodynamic downforce, to secure safe races besides great shows. This may seem a contradiction, because it seems to undermine the primary motivation of car racing: speed.

Downforce

Since the introduction of aerodynamics, it has been clear that the proper distribution of downforce has the most evident impact on car performances. Racing regulations are strongly focused on chassis characteristics, and give strict limits to size, position, and type of devices allowed and and prohibited. Nevertheless, cornering speeds have reached the 4 g (four times the acceleration of gravity).

The Role of the Wind Tunnel

Racing teams have been devoting more and more time to the development of the aerodynamics of their cars. They have done so (and they still do it) with track and wind tunnel testing. Track testing is widely recognized for being too expensive and dependent on many casual events. The advantage, of course, is that the car is tested in its actual configuration in a real world situation.

The wind tunnel is the technical answer of the aerodynamic engineers. The wind tunnels are nowdays very sophisticated, and allow a wide range of studies, including modeling of the car in compete configuration, ground plane simulation, etc.

Tunnels with Moving Ground

One major advancement has been promoted by the use of moving ground planes (previously not used in other branches of aerodynamics). When in the 1970s it was discovered that downforce can be created by means of ground effect, it became essential to simulate the effect of the track on the car performance (on underbody, side pods, exposed wheels, wings).

In a wind tunnel with a stationary ground plane a boundary layer build up under the car, and can interfere with the boundary layer of the lower components. Such a case cannot give the correct answer.

There are several ways to remove the ground boundary layer, but the most effective method is to use a moving belt, with the wheels rotating with the belt. The simulation of rotating wheels could not be more effective. The importance of the exposed wheels in Indy and Formula 1 has been widely recognised, and neglecting this effect may have a large effect on the overall performances.

Racing for Land Speed Records

Running fast is an old occupation, and sometimes a risky one. One of the most fascinating pursuits is the land speed record by vehicles that now resemble rockets on wheels, rather than cars. This record has now surpassed Mach 1 (i.e. the sonic speed).

We report here a few basic aerodynamic considerations. Torda and Morel (1971) pointed out that at high subsonic to low supersonic speed the vehicle generates shock waves that are reflected from the ground.

These shock reflections cause a pressure build-up below the vehicle that have an effect dependent on the speed: at subsonic speed shock wave interference produces additional downforce; at transonic speeds the problem is further complicated by the vehicle clearance; at supersonic speeds the interaction may result in reversal of direction of the lift force.

Since these vehicles are rockets, transonic drag rise can be reduced by increasing the finess ratio. Nose design is also critical. For example, a von Karman ogive is known for having minimum wave drag at transonic speeds.

Related Material

(on CD-ROM)
  • High-Lift Systems
  • Sample Calculations (including full car)
  • The Wind Tunnel
  • High Speed Aerodynamics
  • Aerodynamic Drag
    • Shock Waves
    • Bodies of Minimum Wave Drag

Selected References

  • Katz J. Race Car Aerodynamics, Robert Bentley Publ. Cambridge, MA, 1995.

  • Milliken WF, Milliken DL, Race Car Vehicle Dynamics, SAE International, Warrendale, PA, 1995.

  • Rozhdestvensky KV. Aerodynamics of a Lifting System in Extreme Ground Effect. Springer, 2000.


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Copyright © A. Filippone (1997-2005). All Rights Reserved.