Themes > Science > Physics > Fluid Dynamics > Flying the flag for fluid dynamics > Aerodynamics > Low-speed steady aerodynamics / hydrodynamics > Aerodynamics In Car Racing > Design and Test

Chassis designers and builders are constantly at work evaluating the the race car as a total aerodynamic system. Rule modifications and safety regulations designed to reduce cornering speeds keep engineers seeking alternative aerodynamic advantages. Currently there are only three chassis designs used in competition for the 1994 season.
    Indy Car Chassis Constructors
  1. Lola
  2. Penske
  3. Reynard
Not only are there only three chassis designs in current competition, but there are only four engines available to the teams.
    Engines
  1. Ford Cosworth XB V8
  2. Ilmor Indy V8
  3. Honda Indy V8
  4. Menard V6
A fifth engine, the Mercedes V8 was used by the Penske team only once in the Indy 500. In addition, these engines are leased from the factories and are not rebuilt by the teams. They are replaced with new engines, by CART regulations. This enables car manufacturers to continue their developmental programs in racing and maintains a competitive balance in the series. The engines have been downsized in order to produce a more efficient aerodynamic car design. Still capable of producing between 750-800hp, the engine size is important in reducing the size of the car. Ian Bisco, vice-president and general manager of Cosworth Inc. in the United States explains, "To give you an idea of the what a difference the compactness makes to the car, one of our designers claims that at 230 mph the difference between the old car (1992) and the new car, is like giving the engine another 20hp." Engineers and Constructors design new cars with the overall aerodynamic efficiency of the car as the starting point.

Designing a new Chassis

Indy car construction is governed by CART rules and evolving regulations designed to afford the driver the best protection possible. Whether the chassis is mass-produced or custom built, research and development takes months to get an efficient design on the track. Lola Cars Ltd. of Cambridgeshire, England is the major supplier of Indy car chassis (32 out of 50 chassis used in 1994). Since Lola supplies chassis to the majority of teams, design flaws are seen quickly and feedback is constant. Teams that design and build their own chassis such as Penske, do not get the same amount of feedback. Feedback and performance data provide builders a starting point for their next effort.

Chassis designers rely on CAD (computer-aided design) tools and software to design the "monocoque", or tub. CAD insures accuracy and allows quick part modification. Currently over 50% of the parts on an indy car are designed on a CAD system. A large scale drawing board is still used however, allowing designers the full view of the chassis. The design team will go through several steps:

  1. 40%-scale plans:
      The major components of car are then placed into this scheme, the engine, the gearbox, the sidepods and the fuel tank in an overall package. The idea is to get the weight distribution worked out for model fabrication.
  2. 40%-scale model (suitable for wind tunnel testing):
      During this testing components such as the chasis shape, underwing, sidepods and radiator, are reconfigured and reshaped to optimize the the aeroshape of the car.
  3. Detailed drawings:
      Based on the wind tunnel testing these drawings will be the final working plans for the chassis.

Wind tunnel testing is used extensively when designing a new car. The model is placed in the test section of the wind tunnel where airflow measurements are recorded. The rolling road wind tunnel uses a quarter scale model and a moving belt beneath the model to simulate the relative motion between the vehicle and the road. Wind tunnel simulation is of particular interest for racing teams where:
  1. Ground clearance is minimal.
  2. Downforce/drag statistics can be measured.
  3. The small differences in aerodynamic characteristics can mean winning or losing.
The Rahal/Hogan racing team uses the Aeronautical and Astronautical Research Laboratory in Columbus Ohio. This 7 X 10-ft. subsonic wind tunnel simulates high-speed ground aerodynamics on a 40%-size Indy car model. The model rides on a moving ground plane or rolling road while a model support system controls the vehicle ride height. In this type of wind tunnel simulation, the ground surface should move at a velocity equal and opposite to that of the vehicle. Measurements are recorded on aerodynamic forces for the entire vehicle, with particular attention on wheel rotation and underbody flow characteristics. This type of testing allows the designers to physically test out ground effects, including wing configurations and underbody surface pressures. Wind tunnel testing allows constructors to test new designs in response to modifications in regulations.

At the conclusion of the 1992 Indy car racing season, the CART technical committee modified existing regulations to afford the drivers more protection (particularly in response to forward impacts). The 1993 car must be 5 inches longer to better protect the drivers legs and knees. More material (carbon fiber) was to be used in the chassis construction, and the internal size of the chassis was larger than the 1992 car. In addition, regulations were modified to reduce cornering speeds on the speedway circuits. The aerodynamics of the car were decreased by restricting the size of the underwing (venturi) to 8 inches in height and by reducing the size of the speedway rear wing to its present dimensions (32 inches in height x 43 inches wide). A new, smaller Chevrolet engine was also available. These regulation changes, coupled with the development of a new, smaller engine, meant that chassis design would be new for 1993. This gave engineers the opportunity to redesign the underwing of the car to comply with the new regulations. Team designers utilized wind tunnel testing to determine the best aerodynamic setup for the new design. Nigel Bennett, Penske team designer said, "We test in the wind tunnel over 100 days per year, and have a full time aerodynamic team. No change of shape on an external part of the car is made without it being tested in the wind tunnel." According to Bennett, "The results from the rolling road wind tunnel tests, (undertaken at South Hampton University in England) are extremely accurate in predicting downforce and drag figures the actual car produces on the track."

Computational Fluid Dynamics (CFD) Another tool aiding in the development of desired aerodynamic characteristics is Computational Fluid Dynamics (CFD).


Information provided by: http://www.nas.nasa.gov