Ground effect in cars
Encyclopedia
Ground effect is term applied to a series of aerodynamic effects used in car design, which has been exploited to create downforce
Downforce
Downforce is a downwards thrust created by the aerodynamic characteristics of a car. The purpose of downforce is to allow a car to travel faster through a corner by increasing the vertical force on the tires, thus creating more grip....

, particularly in racing cars. This has been the successor to the earlier dominant aerodynamic theory of streamlining. IndyCar
IndyCar
IndyCar is the trade name of an American-based open-wheel auto racing sanctioning body. IndyCar sanctions three racing series, the premier IZOD IndyCar Series with its centerpiece Indianapolis 500, and developmental series Firestone Indy Lights and the U.S...

s employ ground effect to some extent, but Formula One
Formula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...

 and most other racing series worldwide currently use design constraints to heavily limit its effectiveness.

Theory

In racing cars, a designer's aim is for increased downforce, increasing grip and allowing for greater cornering speeds. (Starting in the mid 1960s 'wings', or inverted airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....

s, were routinely used in the design of racing cars to increase downforce, but this is not ground effect.) Substantial further downforce is available by understanding the ground to be part of the aerodynamic system in question. This kind of ground effect is easily illustrated by taking a tarpaulin
Tarpaulin
A tarpaulin, colloquially tarp, is a large sheet of strong, flexible, water-resistant or waterproof material, often cloth such as canvas or polyester coated with urethane, or made of plastics such as polyethylene. In some places such as Australia, and in military slang, a tarp may be known as a...

 out on a windy day and holding it close to the ground: it can be observed that when close enough to the ground the tarp will suddenly be sucked towards the ground. This is due to Bernoulli's principle
Bernoulli's principle
In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy...

; as the tarp gets closer to the ground, the cross sectional area available for the air passing between it and the ground shrinks. This causes the air to accelerate and as a result pressure under the tarp drops while the pressure on top is basically unaffected, and together this results in a net downward force. The same principles apply to cars.

The Bernoulli principle is not the only mechanic in generating ground effect downforce. A very large part of ground effect performance comes from taking advantage of viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

. In the tarp example above neither the tarp or the ground is moving. The boundary layer
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...

 between the two surfaces works to slow down the air between them which lessens the Bernoulli effect. However when a car moves over the ground the boundary layer on the ground becomes helpful. In the reference frame of the car, the ground is moving backwards at some speed. As the ground moves, it pulls on the air above it and causes it to move faster. This enhances the Bernoulli effect and increases downforce. It is an example of Couette flow
Couette flow
In fluid dynamics, Couette flow refers to the laminar flow of a viscous fluid in the space between two parallel plates, one of which is moving relative to the other. The flow is driven by virtue of viscous drag force acting on the fluid and the applied pressure gradient parallel to the plates...

.

History

Jim Hall
Jim Hall (race car driver)
Jim Hall is a former racecar driver and constructor from the United States. He competed in Formula One from to , participating in 12 World Championship Grands Prix and numerous non-Championship races....

 built Chaparral cars to both these principles. His 1961 car attempted to use the shaped underside method but there were too many other aerodynamic problems with the car for it to work properly. His 1966 cars used a dramatic high wing for their downforce. His Chaparral 2J "sucker car" of 1970 was revolutionary. It had two fans at the rear of the car driven by a dedicated two-stroke engine; it also had "skirts", which left only a minimal gap between car and ground, to seal the cavity from the atmosphere. Although it did not win a race, some competition had lobbied for its ban, which came into place at the end of that year. Movable aerodynamic devices were banned from most branches of the sport.

Formula One
Formula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...

 was the next setting for ground effect in racing cars. Several Formula One designs came close to the ground effect solution which would eventually be implemented by Lotus. In 1968 and 1969, Tony Rudd
Tony Rudd
Anthony Cyril "Tony" Rudd was an engineer involved in aero engine design and motor racing, with particular associations with BRM and Lotus.- Early life and war service :...

 and Peter Wright at British Racing Motors
British Racing Motors
British Racing Motors was a British Formula One motor racing team. Founded in 1945, it raced from 1950 to 1977, competing in 197 Grands Prix and winning 17. In 1962, BRM won the Constructors' Title. At the same time, its driver, Graham Hill became World Champion...

 (BRM) experimented on track and in the wind tunnel with long aerodynamic section side panniers to clean up the turbulent airflow between the front and rear wheels. Both left the team shortly after and the idea was not taken further. Robin Herd at March Engineering
March Engineering
March Engineering was a Formula One constructor and manufacturer of customer racing cars from the United Kingdom. Although only moderately successful in Grand Prix competition, March racing cars enjoyed much better achievement in other categories of competition including Formula Two, Formula Three,...

, on a suggestion from Wright, used a similar concept on the 1970 March Formula One car. In both cars the sidepods were too far away from the ground for significant ground effect to be generated, and the idea of sealing the space under the wing section to the ground had not yet been developed.

At about the same time, Shawn Buckley began his work in 1969 at the Univ. of California - Berkeley on undercar aerodynamics sponsored by Colin Chapman
Colin Chapman
Anthony Colin Bruce Chapman CBE was an influential British designer, inventor, and builder in the automotive industry, and founder of Lotus Cars....

, founder of Formula One Lotus
Team Lotus
Team Lotus was the motorsport sister company of English sports car manufacturer Lotus Cars. The team ran cars in many motorsport series including Formula One, Formula Two, Formula Ford, Formula Junior, IndyCar and sports car racing...

. Buckley had previously designed the first high wing used in an IndyCar
IndyCar
IndyCar is the trade name of an American-based open-wheel auto racing sanctioning body. IndyCar sanctions three racing series, the premier IZOD IndyCar Series with its centerpiece Indianapolis 500, and developmental series Firestone Indy Lights and the U.S...

, Jerry Eisert's "Bat Car" of the 1966 Indianapolis 500
1966 Indianapolis 500
Results of the 1966 Indianapolis 500 held at Indianapolis on Monday, May 30, 1966....

. By proper shaping of the car's underside, the air speed there could be increased, lowering the pressure and pulling the car down onto the track. His test vehicles had a Venturi
Venturi effect
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is named after Giovanni Battista Venturi , an Italian physicist.-Background:...

-like channel beneath the cars sealed by flexible side skirts that separated the channel from above-car aerodynamics. He investigated how flow separation on the undersurface channel could be influenced by boundary layer suction and divergence parameters of the underbody surface. Later, as a mechanical engineering professor at MIT, Buckley worked with Lotus developing the Lotus 78
Lotus 78
The Lotus 78 'wing car' was a Formula One racing car used in the and seasons. It was designed by Peter Wright, Colin Chapman, Martin Ogilvie and Tony Rudd, and was the car that started the ground effect revolution in Formula One.-Concept:...

.

On a different tack, Brabham designer Gordon Murray used air dams at the front of his Brabham BT44
Brabham BT44
The Brabham BT44 was a Formula One racing car designed by Gordon Murray, Brabham's chief designer. An update of the partially successful BT42 of 1973, the BT44 was a simple design with a standard Ford DFV/Hewland gearbox combination, but was very clean aerodynamically. Murray had an eye for clean...

s in 1974 to exclude air from flowing under the vehicle. Upon discovering that these tended to wear away with the pitching movement of the car, he placed them further back and discovered that a small area of negative pressure was formed under the car, generating a useful amount of downforce - around 150 lbs. McLaren produced similar underbody details for their McLaren M23 design.
In 1977 Rudd and Wright, now at Lotus, developed the Lotus 78
Lotus 78
The Lotus 78 'wing car' was a Formula One racing car used in the and seasons. It was designed by Peter Wright, Colin Chapman, Martin Ogilvie and Tony Rudd, and was the car that started the ground effect revolution in Formula One.-Concept:...

 'wing car', based on a concept from Lotus
Team Lotus
Team Lotus was the motorsport sister company of English sports car manufacturer Lotus Cars. The team ran cars in many motorsport series including Formula One, Formula Two, Formula Ford, Formula Junior, IndyCar and sports car racing...

 owner and designer Colin Chapman
Colin Chapman
Anthony Colin Bruce Chapman CBE was an influential British designer, inventor, and builder in the automotive industry, and founder of Lotus Cars....

. Its sidepods, bulky constructions between front and rear wheels, were shaped as inverted aerofoils and sealed with flexible "skirts" to the ground. The design of the radiators, embedded into the sidepods, was partly based on that of the de Havilland Mosquito
De Havilland Mosquito
The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...

 aircraft. The team won 5 races that year, and 2 in 1978 while they developed the much improved Lotus 79
Lotus 79
The Lotus 79 was a Formula One car designed in late 1977 by Colin Chapman, Geoff Aldridge, Martin Ogilvie, Tony Rudd and Peter Wright of Lotus. It is considered by many to be one of the most significant and respected racing car designs of all time....

. The most notable contender in 1978 was the Brabham BT46B
Brabham BT46
The Brabham BT46 was a Formula One racing car, designed by Gordon Murray for the Brabham team, owned by Bernie Ecclestone, for the 1978 Formula One season. The car featured several radical design elements, the most obvious of which was the use of flat panel heat exchangers on the bodywork of the...

 Fancar, designed by Gordon Murray
Gordon Murray
Prof. Gordon Murray , is a renowned designer of Formula One race cars and the McLaren F1 road car.-Early life:...

. Its fan, spinning on a horizontal, longitudinal axis at the back of the car, took its power from the main gearbox. The car avoided the sporting ban by claims that the fan's main purpose was for engine cooling as less than 50% of the airflow was used to create a depression under the car. It raced just once, with Niki Lauda
Niki Lauda
Andreas Nikolaus "Niki" Lauda is an Austrian former Formula One racing driver and three-time F1 World Champion. More recently an aviation entrepreneur, he has founded and run two airlines and was manager of the Jaguar Formula One racing team for two years.- Early years in racing :Born in Vienna,...

 winning at the Swedish Grand Prix. The car's supreme advantage was proven after the track became oily. While other cars had to slow, Lauda was able to accelerate over the oil due to the tremendous downforce, which rose with engine speed. The car was also observed to visibly squat when the engine was revved at a standstill. Brabham's owner, Bernie Ecclestone
Bernie Ecclestone
Bernard Charles "Bernie" Ecclestone is an English business magnate, as president and CEO of Formula One Management and Formula One Administration and through his part-ownership of Alpha Prema, the parent company of the Formula One Group of companies. As such, he is generally considered the primary...

, who had recently become president of the Formula One Constructors Association
Formula One Constructors Association
The Formula One Constructors' Association is an organization of the chassis builders who design and build the cars that race in the FIA Formula One World Championship...

, reached an agreement with other teams to withdraw the car after three races. However the Fédération Internationale de l'Automobile
Fédération Internationale de l'Automobile
The Fédération Internationale de l'Automobile is a non-profit association established as the Association Internationale des Automobile Clubs Reconnus on 20 June 1904 to represent the interests of motoring organisations and motor car users...

 (FIA), governing body of Formula One and many other motor sports, decided to ban 'fan cars' with almost immediate effect. The Lotus 79, on the other hand, went on to win six races and the world championship for Mario Andretti
Mario Andretti
Mario Gabriele Andretti is a retired Italian American world champion racing driver, one of the most successful Americans in the history of the sport. He is one of only two drivers to win races in Formula One, IndyCar, World Sportscar Championship and NASCAR...

 and gave team-mate Ronnie Peterson
Ronnie Peterson
Bengt Ronnie Peterson was a Swedish racing driver. He was a two-time runner-up in the FIA Formula One World Drivers' Championship.Peterson began his motor racing career in kart racing, traditionally the discipline where the majority of race drivers begin their careers in open-wheel racing...

 a posthumous second place, demonstrating just how much of an advantage the cars had. In following years other teams copied and improved on the Lotus until cornering speeds became dangerously high, resulting in several severe accidents in 1982; flat undersides became mandatory for 1983. Part of the danger of relying on ground effects to corner at high speeds is the possibility of the sudden removal of this force; if the belly of the car contacts the ground, the flow is constricted too much, resulting in almost total loss of any ground effects. If this occurs in a corner where the driver is relying on this force to stay on the track, its sudden removal can cause the car to abruptly lose most of its traction and skid off the track.

The effect was used in its most effective form in IndyCar
IndyCar
IndyCar is the trade name of an American-based open-wheel auto racing sanctioning body. IndyCar sanctions three racing series, the premier IZOD IndyCar Series with its centerpiece Indianapolis 500, and developmental series Firestone Indy Lights and the U.S...

 designs. Racing series based in Europe and Australia have mainly followed the lead of Formula One and mandated flat undersides for their cars. This heavily constrains the degree to which ground effect can be generated. Nonetheless, as of 2007, Formula One cars still generate a proportion of their overall downforce by this effect: vortices
Vortex
A vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...

 generated at the front of the car are used to seal the gap between the sidepods and the track and a small diffuser is permitted behind the rear wheel centerline to slow down the high speed underbody airflow to free flow conditions. High nose designs, starting with the Tyrrell 019
Tyrrell 019
The Tyrrell 019 was a Formula One racing car, designed by a team led by Harvey Postlethwaite, and built by Tyrrell. It was an evolution of Postlethwaite's first design for Tyrrell, the Tyrrell 018....

 of 1990, optimize the airflow conditions at the front of the car.

While such downforce-producing aerodynamic techniques are often referred to with the catch-all term "ground effect", they are not strictly speaking a result of the same aerodynamic phenomenon as the ground effect which is apparent in aircraft at very low altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

s.

Porpoising

Porpoising is a term that was commonly used to describe a particular fault encountered in ground effect racing cars.

Racing cars had only been using their bodywork to generate downforce for just over a decade when Colin Chapman
Colin Chapman
Anthony Colin Bruce Chapman CBE was an influential British designer, inventor, and builder in the automotive industry, and founder of Lotus Cars....

's Lotus 78
Lotus 78
The Lotus 78 'wing car' was a Formula One racing car used in the and seasons. It was designed by Peter Wright, Colin Chapman, Martin Ogilvie and Tony Rudd, and was the car that started the ground effect revolution in Formula One.-Concept:...

 and 79
Lotus 79
The Lotus 79 was a Formula One car designed in late 1977 by Colin Chapman, Geoff Aldridge, Martin Ogilvie, Tony Rudd and Peter Wright of Lotus. It is considered by many to be one of the most significant and respected racing car designs of all time....

 cars demonstrated that ground effect was the way to go in Formula One, so naturally at this point under-car aerodynamics were still very poorly understood. To compound this problem the teams that were keenest to pursue ground effects tended to be the more poorly-funded British "garagiste" teams, who had little money to spare for wind tunnel testing and tended simply to mimic the front-running Lotuses.

This led to a generation of cars that were designed as much by hunch as by any great knowledge of the finer details, making them extremely pitch sensitive. As the centre of pressure on the sidepod aerofoils moved about depending on the car's speed, attitude and ground clearance, these forces interacted with the car's suspension systems and cars began to resonate, particularly at slow speeds, rocking back and forth - sometimes quite violently. Some drivers were even known to complain of sea-sickness. This back-and-forth rocking motion, like a porpoise
Porpoise
Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...

 diving into and out of the sea as it swims along at speed, is what gives the phenomenon its name.

Ground effects were largely banned from Formula One in the early 1980s, but Group C sportscars and other racing cars continued to suffer from porpoising until gradually better knowledge of ground effects allowed designers to minimise the problem.

See also

  • Automotive aerodynamics
    Automotive aerodynamics
    Automotive aerodynamics is the study of the aerodynamics of road vehicles. The main concerns of automotive aerodynamics are reducing drag , reducing wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds...

  • Venturi effect
    Venturi effect
    The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is named after Giovanni Battista Venturi , an Italian physicist.-Background:...

  • Ground effect in aircraft
  • Ground effect train
    Ground effect train
    A ground effect train is an alternative to a magnetic levitation train. In both cases the object is to prevent the vehicle from making contact with the ground...

  • Formula One car
    Formula One car
    A modern Formula One car is a single-seat, open cockpit, open wheel racing car with substantial front and rear wings, and an engine positioned behind the driver. The regulations governing the cars are unique to the championship...


External links

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