Ground effect

In the 1960s, the creators of racing cars began to pay attention to the role of aerodynamics when driving a car along the highway. The use of aerodynamic forces to clamp the tires of the car to the surface of the track allowed cornering at a higher speed. The most obvious solution was the use of wing spoilers and spoilers , which use air to flow over the car body to create downforce. However, this solution has a significant drawback: the surfaces used to provide downforce create additional drag , which reduces the vehicle’s speed when moving in a straight line. The designers tried to correct this shortcoming by controlling the angle of attack of the wing, but soon the moving aerodynamic elements in the design of racing cars were banned by the International Automobile Federation (FIA).

Another possibility of creating downforce was the use of air space under the bottom of the car. If you ensure the acceleration of the air passing in this way, then due to the Venturi effect under the car there is a region of reduced pressure, which creates additional downforce. Another way to reduce the air pressure under the car is to actively pump it out of this area using a fan ^[3] .

Advantages

• Creating substantial downforce with little or no drag.
• When creating a vacuum under the car with a fan, the downforce is not dependent on the speed, which gives an additional advantage when cornering.

Weaknesses

• The ground effect is very sensitive to the gap between the bottom of the car and the surface of the track. To ensure a constant gap, it is necessary to use an extremely stiff suspension, which reduces driver comfort.
• When the car jumps on any roughness of the track, there is a loss of downforce and, as a consequence, controllability. This can lead to an accident with serious consequences.
• When creating a vacuum under the car with a fan, it draws dust and debris from the surface of the track and throws them back, which is dangerous for rivals chasing the car.

The first racing car designer to attempt to use the ground effect was . In 1961, he used a special bottom profile on his car, but did not succeed, and in 1970 he created a modification of the Chaparral 2J , in which the ground effect was created by a pair of fans pumping air driven by a separate engine. In this model, a “skirt” was first applied, covering laterally the gap between the car and the surface of the track. The car took part in races and showed the best result in qualification, but did not achieve victories due to technical problems. At the end of the season, the Chaparral 2J was banned by the because of rivals ’complaints of stones flying out of fans and a violation of FIA rules prohibiting mobile aerodynamic devices ^[4] .

The next example of the effective use of the ground effect was the car Lotus-78 , created under the leadership of Colin Chapman to participate in Formula 1 races in 1977. In the design of the car, a special bottom profile was used, similar to the inverted wing of an airplane, to accelerate the air flow and elastic “skirts” on the sides, isolating the air space under the car. The car was successful and won five races in 1977 and two more in 1978, after which it was replaced by an improved Lotus-79 model, which also used the ground effect.

In 1978, , designer of the Brabham team , in the Brabham BT46B model, tried to use a fan to create a ground effect. He went to the trick and declared the fan an element of the engine cooling system. The car won the first race, but was removed from further competition due to complaints from rivals, repeating the fate of the Chaparral 2J . As a result, the Lotus-79 was out of competition and brought the Lotus team victory in the season.

Already in the next 1979, other Formula 1 teams began to use the ground effect. For several years, it has become a factor determining the appearance and characteristics of Formula 1 cars. But the advantages of the ground effect were accompanied by its disadvantages. The effectiveness of the clip depended on the stability of the gap between the bottom of the car and the surface of the track. Non-ideal aerodynamics led to longitudinal vibrations of the car in motion - it swung from the bow to the stern and back. These problems were fought by using an extremely stiff suspension, which caused the pilots of racing cars to experience strong shaking. The increase in cornering speed led to an increase in lateral overloads, which began to exceed the endurance of the pilots, causing short-term loss of consciousness. Jumping the car on any unevenness or touching the bottom of the track led to the sudden disappearance of the downforce and loss of control of the car.

These factors led to an increase in accident rate, as a result of which the FIA made changes to the rules restricting the use of the ground effect: in 1981, elastic skirts were banned and a minimum ground clearance of 60 mm was set. And since 1983, the rules require racing cars to have a flat bottom from the front to the rear axle ^[5] . Despite these limitations, the ground effect continues to be used to create additional downforce along with wing and spoilers. To accelerate the air flow passing under the car, a raised nose of the car and a diffuser located behind the rear axle are used ^[3] .

The widespread use of various aerodynamic elements in modern racing cars leads to the formation of significant air turbulences behind the car. This complicates their pursuit and overtaking by rivals, which reduces the entertainment of auto racing. The round effect, which is indifferent to such disturbances, can reduce the need for a large number of wing, openings and spoilers and improve the entertainment situation. In 2015, the issue of more intensive use of the ground effect in the technical regulations of Formula 1 for 2017 was actively discussed ^[6] . In the Indikar series, it was decided to again resort to the widespread use of the ground effect since 2018 ^[7] .

Enrico Scalabroni demonstrates the principle of the effect of the ground effect (video)