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The Aerodynamic Development of the Formula One Car

Contents

• Bernoulli's Principle
• Formula One
• Early Developments
• Lotus 72
• JPS Lotus 72D
• Lotus 78 and 79
• Flat Bottoms
• Rear Downforce
• Raised Noses
• Improving the Show
• Summary
• Glossary

Aerodynamics is a branch of fluid mechanics that deals with the motion of air and other gaseous fluids, and with the forces acting on bodies in motion relative to such fluids. The motion of an aircraft through the air, the wind forces exerted on a structure, and the operation of a windmill are all examples of aerodynamic action.

One of the fundamental laws governing the motion of fluids is Daniel Bernoulli's principle, which relates an increase in flow velocity to a decrease in pressure. For example, for the same volume of air at the entry to the venturi tube below to pass through the constriction in the middle, the air must speed up. Based on Newton's theory that energy cannot be created or destroyed, just transferred, this increased speed must have a corresponding decrease in pressure, if the same volume of air is to move through the tube. As the air exits the constriction, it slows and regains its original pressure.

This is better explained by a simple, familiar situation. If, when driving at speed on a Motorway, you open a window a couple of centimetres, you can feel a rush of air entering through the air-vents. The air going by the window has to speed up to get out of the way of the car. When air speeds up, it loses pressure. The lower pressure of the air speeding past the window sucks more air out of the window, increasing flow into the car through the vents, to replace the lost air.

Bernoulli's principle is used in aerodynamics to explain the lift of an airplane wing in flight. A wing is so designed that air flows more rapidly over its upper surface than its lower one, leading to a decrease in pressure on the top surface as compared to the bottom. The resulting pressure difference provides the lift that sustains the aircraft in flight. If the wing is turned upside-down, the resultant force is downwards. This explains how performance cars corner at such high speeds. The 'downforce' produced pushes the tyres into the road giving more grip.

Another important aspect of aerodynamics is the drag, or resistance, acting on solid bodies moving through air. The drag forces exerted by the air flowing over an airplane, for example, must be overcome by the thrust force developed by the engine. These drag forces can be significantly reduced by streamlining the body. For bodies that are not fully streamlined, the drag force increases approximately with the square of the speed as they move rapidly through the air. The power required, for example, to drive an automobile steadily at medium or high speed is primarily absorbed in overcoming air resistance. The more streamline a vehicle is, the less power it needs to obtain high speeds, and therefore is more economical.

Motor sport is used as a proving ground for the development of technologies that are subsequently applied to road going vehicles, and this has inspired a great deal of aerodynamic research in recent years. Intensive aerodynamic development has become an increasingly important priority within Formula One Grand Prix car design since the mid-70's. The techniques for investigating this crucial area of performance, have evolved to such a level, that any modern front-line F1 team has exclusive access to its own wind tunnel facilities.

For more than 50 years, aeronautical engineers have employed wind tunnel development to shape the future path of their aircraft designs. The wind tunnel provides the opportunity for the proposed design to be subjected to aerodynamic forces. Carefully monitoring and plotting of the aerodynamic pressures can accurately obtain a clear picture of the prototype shapes aerodynamic potential.

In the 1960's the use of soft rubber compounds and wider tyres, pioneered particularly by Lotus, demonstrated that good road adhesion and hence cornering ability, was just as important as raw engine power in producing fast lap times. The tyre width factor came as something of a surprise. In simple school experiments on sliding friction between hard surfaces, the friction resistance force is found to be independent of the contact area. It came as a similar surprise to find that the friction could be greater than the contact force between the two surfaces, apparently giving a coefficient greater than one.

The desire to further increase the tyre adhesion led the major revolution in racing car design, the introduction of inverted wings, which produce negative lift or 'downforce'. Since the tyres lateral adhesion is roughly proportional to the downloading on it, or the friction between tyre and road, adding aerodynamic downforce to the weight component improves the adhesion.

In addition to enhancing the cornering ability, aerodynamic downforce allows the tyres to transmit a greater thrust force without wheel spin, and hence the acceleration will be increased. Without aerodynamic downforce, high-performance racing cars have sufficient power to produce wheel spin at more than 100mph.

New aerodynamic wings were fixed at a set angle on the car. However, a major disadvantage of a fixed wing is that it produces high drag when set for cornering. Therefore, when wings were first introduced to Formula One, they were provided with a mechanism for controlling the incidence angle. On the straight, the wing could be feathered to a zero angle to minimise drag, but on braking and entering a corner, the angle of attack was increased negatively to provide downforce. Front wings were soon added, and as a further refinement, Brabham introduced split wing surfaces with independently variable incidence. These enabled a greater downforce to be applied to the inside wheel to offset the effects of body roll. In the early experiments of 1968, Brabham and Ferrari mounted a wing onto the body. Lotus mounted the wing directly on to the unsprung wheel assembly, so that the downforce would be transmitted directly onto the tyre and its contact with the road. In order to take the wing out of the turbulence from the body, Lotus pioneered the use of very high mounted wings, an arrangement that was taken up by a number of other competitors.

The combination of high mounting, variable incidence mechanisms and direct connection to the unsprung wheel assembly resulted in a flimsy and vulnerable structure that was susceptible to accidental damage. Following serious accidents at the Spanish Grand Prix in 1969, stringent regulations governing the use of wings were introduced, and these are still in force. They are essentially:

1. The maximum height, width and locations are controlled.
2. Aerodynamic devices have to be of fixed geometry (no variable incidence).
3. They have to be rigidly attached to the body work.

The last two regulations have caused significant problems. The fixed incidence means that a compromise has to be achieved between the improved cornering due to high downforce, and reduced straight line speed resulting from the high trailing vortex drag. The optimum compromise differs according to the nature of the circuit, and considerable effort in practice sessions goes into trying to achieve the right balance.

For the 1970 season Lotus developed the new 72, which, after disappointing early performances, proved to be perhaps the outstanding car of the early 70's. The 72 had new features such as the 'shovel' nose with twin fins, inboard front brakes, and torsion bar suspension. The adoption of mid-mounted radiators was taken from the current practice in sports cars, and the aim was to achieve good air penetration by having as small a nose as possible. Another new feature of the 72 was the three rear aerofoils.

In 1970, Jochen Rindt joined the Gold Leaf Team Lotus. After a slow start, Rindt and the 72 found winning form at Zandvoort, in Holland, where he also took pole position. Rindt subsequently won the French, British, and German Grands Prix. As the season progressed, a number of modifications were made to the cars, including a stiffened monocoque, and an air collector box above the fuel injection system, something else that was copied by other teams.

During practice for the Italian Grand Prix, Rindt ran his car without wings to gain straight-line speed, and crashed with fatal results. A prolonged Italian investigation finally decided that the front brake-shaft had failed, causing Rindt to lose control, but his fatal injuries were the result of badly installed safety barriers. Rindt was the first, and hopefully last, posthumous World Champion.

Team leadership was taken by newcomer Emerson Fittipaldi, who won in only his fourth race, one month after Rindt's death. For 1971 more minor changes were made to the car; suspension modifications, a one piece rear wing, and low-profile tyres. In this form the car was known as the 72D.

With an inexperienced driver line-up, there were no wins that season, and for 1972 the cars were painted black and gold and entered as 'John Players Specials'. Changes were few, but they now featured revised air-boxes, a revised rear wing, a new oil tank design, and more suspension modifications. Fittipaldi enjoyed fine success, winning that year's World Championship, and he still remains the youngest Champion in the history of the sport at just 25 years and 8 months old.

Much credit for effective early wind tunnel work has been attributed to Shadow designer Tony Southgate during the mid-70's. However, Team Lotus designer Peter Wright was the man who made some of the most significant discoveries. This led to the development of Colin Chapman's 'ground effect' Lotus 78 and the Championship winning type 79.

Whilst working with models of the still secret Lotus 78, Wright, almost by chance, stumbled over the development that was destined to have enormous implications for F1 car design over the five years that followed.

Wright had been studying the complexities of airflow beneath racing cars ever since the late 1960's when he had worked at BRM. During the course of his tests to finalise the Lotus 78's basic aerodynamic configuration, an assessment was carried out as to whether the water radiators could be incorporated within the leading edge of the inverted wing side-pods. In this configuration, Wright began to obtain non-repeatable results with the wind tunnel model. What followed was a break-through of momentous significance that would open the door to new areas of understanding of under-car airflow. This established a basic yard-stick that would remain valid even after wing section underbody profiles were banned in F1 at the end of the 1982 season.

On closer examination, Wright detected that the model's side pods were sagging, and as they moved closer to the tunnel floor, so the downforce increased. The Lotus research team explored this phenomenon with a degree of fascination, quickly cutting up some makeshift card-board sides that extended the model's pods right down to the ground. Thus tested, their results indicated that the downforce had doubled, opening the way for skirted ground-effect F1 racers.

If the type 77 had started the team along the road back to a competitive status, the type 78 sharply focused the thinking towards the benefits offered by ground-effect aerodynamics. The Lotus 79 carried that philosophy a giant step further. The design concept called for a brand new car with a slim monocoque, central fuel cell and inboard suspension all round; in short, every facet of its performance succumbed to excellent aerodynamics.

Unfortunately, title sponsor JPS left, and the new 80 model was too advanced to tame. Reining champion Mario Andretti only scored 14 points, with a best of 1 third place, compared to 64 points and 6 wins the previous year. However, the basic layout of this revolutionary car can still be seen on Formula One machines today.

For 1981 and 82, teams were required to run fixed aerodynamic skirts, beneath which a 6cm ground clearance requirement was made, obliging them to run impossibly hard suspension in an effort to control the under car aerodynamics. Throughout these seasons, spring rates gradually climbed to 1365kg (3000lb) as designers fought to control the fixed skirt aerodynamics, quickly spawning a breed of 200mph go-karts.

Having got rid of sliding skirts, the next challenge to F1 aerodynamicist came at the start of 1983, when sculptured under-body tunnels were prohibited. As from the start of that season, flat bottoms were required for F1 cars from the trailing edge of the front wheels, to the leading edge of the rear wheels.

At a stroke, the governing body had wiped out millions of pounds worth of research and sent designers back to the drawing board. The new cars were a totally different animal. The long side pods now tended to produce lift, so they were kept short, as used on the Tyrrell 011, Williams FW08C, and Brabham BT-52.

The new Toleman team had entered Formula One at the end of 1982. The major rule change had forced designer Rory Byrne's ground effect TG183 to be totally repackaged to conform with the 1983 flat bottom regulations. He opted for a full-width nose section into which the water radiators were housed. The concept also derived additional rear downforce by the positioning of an aerofoil ahead of the rear wing centre line, at a point where it could take advantage of the maximum chassis width regulations. It complemented the conventional rear wing, which was positioned slightly lower, behind the rear axle line.

On the face of it, getting downforce to the rear of the car, does not look a particularly difficult problem, the engine and gearbox ensuring that the rear-ward weight bias of the basic chassis helps matters considerably. However, the reality is that the front wing uses so much of the air that there is precious little energy left for the rear wing. The optimum function of a wing is achieved when the airflow to and from it, is not interrupted. Clearly, the rear wing has the biggest problem from the point of airflow to the wing, with it being broken up and disrupted by the wheels, cockpit fairings and rollover bars. With Formula One regulations strictly limiting the height at which the rear wing is positioned, there is a restriction on the amount of scope available to a designer for raising it to a level where there is no problem with a disrupted flow.

The result of these design problems was the low-line Brabham BT55 used in 1986. It was powered by a specially made BMW engine canted over at 72° to make the back of the car as low as possible, and smooth the air flow to the rear wing. Unfortunately, although the BT55 developed up to 30% more downforce than its immediate predecessor, somewhere along the line it also picked up an excessive amount of drag. Added to the problem of lost power due to poor oil circulation in an angled engine, the whole package was a disaster.

Nevertheless, no F1 designer would ever underestimate the benefit to be gained by reducing the frontal area of the car. This prompted 1986 Williams FW11B drivers Nelson Piquet and Nigel Mansell to try and sit as low in the car as possible, each hoping to out-do each-other. Mansell discovered that by removing his seat, he lowered his position in the car by just 1.5 centimetres, which translated into an additional 25kg of downforce.

Running flat-bottomed cars as close to the ground as possible, increases the flow rate due to the constricted space under the car. Speeding the air up causes it to lose pressure, and suck the car even closer to the ground. However, it is not that simple. The air must be expanded to its original pressure through a rear diffuser after it leaves the flat bottom to reduce drag. The 1990 McLaren MP4-5B had one of the most fascinating diffusers before the rules limited their width and distance behind the rear axle line.

During 1990, Tyrrell took a radical step equal to the impact that Colin Chapman made with the Lotus 79. Designer Harvey Postlethwaite and aerodynamicist Jean-Claude Migeot raised the nose of the 019 to increase airflow under the flat underbody. The front wing halves were fixed off an anhedral mounting on the nose, and the lower suspension wishbones attached underneath. This elegant, and simple concept produced significantly more downforce without the need to use a larger rear wing. The straight-line performance of the admittedly very light and compact new 019, raised more than a few eye-brows throughout the season.

The splitter under the nose successfully regroups the airflow prior to its rush under the flat bottom, ensuring a high-energy feed as well as shortening the effective length of the underbody, reducing pitch sensitivity.

Following the deaths of Roland Ratzenberger and Ayrton Senna at Imola in 1994, the FIA, the governing body of motorsport, produced some rapidly imposed rule changes, which had the effect of cutting back down force quite significantly. Some rule changes were immediate, and removed a small percentage of downforce. The new rule brought in for 1995, was a large increase in the minimum permitted ground clearance over a large proportion of the underbody, creating a 'stepped floor'. This produced a substantial reduction in downforce levels (as much as 40 per cent), and also lessened the car's sensitivity, which made them more predictable, and hence safer to drive.

During 1996, the FIA commissioned studies into aerodynamics of cars following each other closely, in an apparent attempt to find a general configuration that would enable close running and overtaking to occur, increasing the spectacle.

It seems the studies indicated that if the total downforce was reduced, far from making it easier for cars to follow each other, things actually got worse, causing an adverse effect on the following car. Interestingly, the emphasis of these studies switched for a while from aerodynamics to tyres. Ultimately the FIA decided to introduce 'grooved' tyres into Formula One in 1998, in the hope that reducing the amount of rubber in contact with the road will reduce grip, and hence cornering speeds. At the same time, the cars are 20cm narrower too, which reduces the frontal area and increases straight line speed, with a corresponding increase in braking distances, theoretically promoting 'out-braking' maneuvers.

Over the past decade, racing car technology has reached unimaginable heights of sophistication. This development has been funded - and accelerated - largely by the enormous sponsorship investment, reflecting the global television interest focused on the FIA Formula One World Championship. Motor racing is now a multi million dollar business. Gaining the technical edge can make the difference between a run-of-the-mill contender and pace-setter at the front of the field. Aerodynamics has been the turning point in the design of modern F1 machines, and this keeps the designers busy for 12 months-a-year with constant developments.