High-Lift Systems for Racing Cars
Summary
- Multi-Element Wing Systems
- Endplates
- Seals and Skirts
- Side Pods
- Venturi Channels
- Other Devices
- Selected References
Listed below are a few major high-lift (e.g. downforce) devices. Most of the devices
and technical solutions are often the results of the current regulations, and do not
necessary apply to the latest designs.
Wing design is the most appropriate approach toward the improvement of the
aerodynamic characteristics. Besides the wing the design there is often the
opportunity to increase the downforce by using wings with several elements (2 in the
Indy and Formula 1 front wing; 5 or more in a Formula 1 rear wing).
The benefits of adding a trailing-edge flap, and possibly a leading-edge slat, are
a well known problem in aeronautics. Wings with a larger number of elements,
appropriately designed and placed, can provide even higher values of downforce (at
the cost of a far higher drag).
The wings are rather short (they are said to have a low aspect-ratio), and
three-dimensional effects (e.g. cross-flow velocities) act to reduce considerably the
values of downforce predicted for the wing section. The problem is further
complicated by the fact that the wing is usually working in a perturbed, turbulent
and unsteady field.
End plates (side fins) are mounted on low aspect-ratio wings to reduce the
three-dimensional effects on the wing, by creating a physical bound to the tip flow
that would tend to spill from the pressure to the suction side of the wing. Their
effect is a function of their size as compared to the wing size.
Some recent developments in Formula 1 have led to the introduction of intermediate
fences on the lower side, whose function is to further reduce the three-dimensional
effects, by creating a limit to the deviation of the boundary layer flow from the
plane of symmetry.
Seals and skirts have been introduced by Chaparral and Lotus, respectively. The idea
behind this solution is that by sealing the gap between the underbody and the outer
field, airflow leakage from the pressure side (outer field) and suction side
(underbody) is prevented. Sealing skirts were widely employed in the late 1970s
Formula 1 races.
Large side pods increase the area on which the aerodynamic lift operates, and thus can
yield larger values of downforce, besides working as safer shelter for the driver. Their
effectiveness is considerable, with and without Venturi channels.
Simple fluid dynamics says that flow that accelerates looses pressure. This is in fact the
nozzle effect (or Venturi effect), when flow in a convergent nozzle accelerates and looses
pressure. Pressure is then recovered in the diffuser.
By shaping the underbody as an inverted wing, or with appropriate channels, or even
with a simple scant angle that work with the Venturi effect, the overall pressure
between the underbody and the ground decreases.
Here we list some other devices/solutions aimed at increasing the downforce. They include:
These are small plates mounted vertically (or almost) at the trailing edge of the
wing, in order to provide a further increase in downforce or lift. This is a good
when a re-design of the wing is not affordable, or when drag is not an issue (or
both).
Spoilers and dams (front spoilers) are devices placed in the back and front, respectively,
to increase the downforce (rear spoilers nowdays are common features also in production
cars.)
The rear spoiler produces a deviation of the flow, so as to create a pressure increase in
the rear deck, and hence the negative lift. It also promotes rear separation (e.g. drag),
by creating an area of relatively flat pressure (wake).
Dams are front spoilers, generally placed under the nose of the car for lift and drag
gains and for cooling airflow enhancement.
Multi-Element Wings
Figure 1: Rear Wing of Indy car (2-element)
Wing Endplates
Seals and Skirts
Side pods
Venturi Channels
Other Devices
Gurney Flaps
Figure 2: Gurney flap
Spoilers and Dams
Body Work
|
The need for generating high values of downforce makes engineering go around the regulations. This sometimes produces details called body work, which are not simply cosmetic changes, but can make a difference of a few tens of a percent. Fig. 3 at right is an example of small wings placed ahead of the rear wheels of a 1997 CART Indy. Besides generating a little extra downforce, these wings works as to deflect the flow from the wheels. |
– |
Figure 3: Small Wings |
Related Material
(on CD-ROM)- Multi-Element Wing Systems
- Gurney Flaps
Selected References
- Clancy JC. Aerodynamics, John Wiley, New York, 1975.
- Schlichting H, Truckenbrodt E. Aerodynamics of the Airplane, McGraw-Hill, New York, 1979, Chapter 8 (Aerodynamics of the Flaps and Control Surfaces).
