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The
Overtaking Problem Special Issue |
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Formula 1 news, results and statistics when you need it |
The
Overtaking Problem Special Issue |
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This is a brave move. To believe that we can stumble across the solution that has evaded the FIA for the last three years, or even more, is somewhat arrogant, very ambitious, and probably unrealistic. On the other hand our ignorance may well allow us to see a solution that the experts can’t. Judging from the quality of responses that we have had from our readers a lot of you are very passionate F1 followers and are dismayed by the almost total lack of overtaking opportunity in F1 today. Many of you have a good understanding of the formula and I am sure that if we allow ideas to flow freely we will come up with a few suggestions worthy of bringing to the attention of the FIA. This issue summarises the problem as I see it. Aerodynamics that close to the ground is a very complex issue. Environmental factors in a Formula One car (proximity to the ground, angle to wind changes in corners etc.) make the aerodynamic design far more complex that that of all but few highly specialised aircraft. An aircraft only has to deal with airflow. It is suspended in the air and uses aerodynamics to change direction or slow down. It even relies on air to accelerate or brake A Formula One car, like most other cars, relies on its wheels for propulsion, steering and braking even though aerodynamics apply the greatest force to the chassis. I am going to simplify all of these, very complex, issues as much as possible, but please bear with me if it gets confusing. Also remember that, as I am not privy to any of the data that the teams have, all of what follows is an approximation based on observation. The theory should not be invalid but most facts are guessed at and will not necessarily be totally accurate. But then I do not think it matters. Whether the turbulence behind today’s F1 car trails for six or twenty car lengths, it is there and it makes overtaking impossible. Downforce. There are four aerodynamic devices on a F1 car: The front wing, the rear wing/s, the body and the diffuser. Lets deal with the wings first:
Figure 1 Figure 1 depicts a simple wing or foil, similar to a sail on a boat. I did not complicate it by varying the cross section (or thickness) for those of you who have a better understanding of aerodynamics than I have. Downforce is caused by a lower pressure being created in the red area (as a result of the air under the wing being forced to move faster than the air above the wing). So, although there is some pressure from above the wing most of the downforce is created by the low pressure area below the wing and it is literally "sucked down". Turbulence really screws this up. For any wing to perform well it needs still air and although it can cope with some distortion it really stops functioning if the air it encounters does not conform to expected flow. (A bit like trying to steer a small boat through the wash of the propeller of a large ocean liner). On a Formula 1 car the front wings are in front of the wheels and therefore clear of the turbulence created by the wheels and the rear wings are above most of the turbulence of the body and wheels. Both work well providing that the air encountered is reasonably stable. Aerodynamics also play a huge role in the design of the body of the car. All special visual effects are now relegated to the paintwork as the luxury of an aesthetic shape can no longer be afforded. The body of the car is designed as an integral part of the aerodynamic package and with that much surface area it has to be used to maximise downforce. The 4th and last aerodynamic device is the diffuser. This is that multi element device behind and under the engine, between the back wheels. The purpose of the diffuser is to extract the air from under the car and it does this by employing a venturi effect. This serves two purposes: One it creates a low pressure area under the car, which adds to the downforce and two, it removes air turbulence under the car, created by rolling the air between the bottom of the car and the road, which works against downforce as well as adding some drag. The front wing also helps to eliminate the amount of air that would pass under the car by scooping it up and over the car (at top speed the car squats down and the front wing is virtually in touch with the road). Turbulence: We already know that the current F1 car deals badly with turbulence so let us have a look at where it comes from. Well, primarily, it is caused by a car disturbing the air as it passes through. The shape and speed of the car determines the severity of the turbulence. A F1 car creates huge turbulence because of its speed and shape. Wings certainly leave a lot of turbulence behind but the diffuser does its fair share too, and that is close to the ground where a following car’s front wing is severely affected. Wheels also create a lot of turbulence. We have all experienced the effect of turbulence behind large vehicles on an expressway. Regardless of the shape most of the turbulence is created by the flow to fill the hole the vehicle punches through the air. The severity of the turbulence increases dramatically as the speed of the vehicle is increased. Another thing to realise is that turbulence doesn’t move. The air (with the exception of any wind) is stationary and apart from a small movement in the direction of the car that passed through it, it just gets all mixed up right where it is, waiting to stuff up the aerodynamics of the next car that comes along.
Figure 2 Fortunately the air settles down very quickly (less than one second) but it means that each car leaves a wake behind it as depicted in Figure 2. Again we do not know how long this is but it seems to be around 10 to 15 car lengths and could be as wide as two cars at its widest. Immediately behind the car it is very bad and eases off as it widens and the further we get behind the car. As it weakens it fans out, much like a shock wave, and soon is ineffective. How dependent is the car on this downforce? Well, we have seen how they perform if they lose a wing. Any broken wing renders the car totally uncompetitive and although it can still be driven, it is way, way off the pace. But we can be a little more scientific than that. The average family car has a drag coefficient of around 0.3. Drag coefficient (D.C.) is the measurement of drag or air resistance of a particular shape (in other words what resistance it encounters as it is pushed through the air). A F1 car has a drag coefficient of between 0.7 and 1.1 depending on the circuit (as a result of the size, curve and angle of the wings to generate the required downforce). If we assume that the body of a F1 car should have a lower coefficient of drag than dad’s old sedan, it follows that the extra drag is due to the wings (and the open wheels – but I feel that the wheels could still be accounted for within the CD of an average family car). Although it does not necessarily follow that this additional drag is directly transformed into downforce it does follow that the only reason why a formula one car has a D.C. of three to four times that of a family car is purely to create grip. How much of every horsepower used to overcome the additional drag is converted to downforce would be hard to determine with the information we are allowed. So, if the wings and other aerodynamic devices increase the drag from 0.3 to 1.1 it means that at maximum speed roughly 70% of the power of the car is being converted into downforce, which is around 600hp. Sure, I know that there is some mechanical friction and drag that has to be overcome so maybe we are out by 20% say 500hp in round figures. Not all of that will be directly converted into downforce (see figure 1) as the resultant force from the wing is not perpendicular. Some of the force will be pulling the car back but more than half would force it down on the road. That is a lot of squeeze! Mechanical grip uses the weight of the car to create adhesion to the road, aerodynamic grip is created by the wings. There is around 750 kg of mass in the F1 car to achieve mechanical grip but no less than two tonnes of downforce when the car is up to speed. The wings on the car would not be optimised for maximum speed (possibly with the exception of Monza) as it is safe to assume that at maximum speed cars should be running in a straight line, or pretty close to it. Wings will be optimised to improve grip on the greatest number of corners on each circuit and these will be significantly less than maximum speed. The slower the corner the bigger the wing to gain the same downforce. As the size of wings are strictly controlled, more downforce can also be created by changing the angle and curve of the wing. Either way, it means that on most circuits downforce accounts for 75% of the grip. Most relate this downforce only to the cars cornering adhesion or ability but this is not the only place it counts. It is needed to brake (and it is interesting that most braking is achieved with the back wheels), corner and accelerate. All of these are crucial in the typical overtaking manoeuvre. Not all downforce is lost in the turbulence of another car. If this were true most cars would just run off the road as soon as they catch up with another car and back markers would become an insurmountable problem regardless of the size of the blue flags. On the other hand, the loss is more than enough to make overtaking impossible. Mechanical grip is also affected as it depends on the amount of travel, or "give" in the suspension allowing the wheels to stay firmly in touch with the road. On the family car this is roughly 4 to 6 inches but as the F1 car is around two inches off the ground it has to be less than that. 1 ½ ‘ is sufficient travel to maximise mechanical grip but when you are expecting the same suspension that is managing a mass of 750kg around the very slow corners to also cope with an additional 2000kg once aerodynamics kick in, it will be in a total "bottomed out" state most of the time. With the introduction of "the plank", a flat board fixed under the body of the car that has a minimum specified thickness (measured at the end of every race) teams can’t afford to totally bottom out too frequently. There is no point in winning a race only to get disqualified for too much wear of the plank after the race, so at its lower end the "give" in the suspension is very limited. The only compromise is to use some of the travel at low speeds for mechanical grip and stiffen up fast so that there is still some mechanical grip left at high speed. Whichever way you look at it Aerodynamic grip becomes more important and at high speed dominates the roadholding of the car. Proposed regulations. Some three weeks ago now, just as we were coming to the conclusion that the FIA has to do something – they did! They changed the technical regulations. In 2001 the front wings will be 50mm (2") higher. If nothing else changes that will reduce the effect of the front wings. As they will be further away from the road the "ground effect" will be reduced (similar to a venturi effect that uses the expansion of the gap to the road to accelerate air flow and therefore downforce) as well as allowing more air under the car which also counters downforce. Because the front wings will provide less downforce an equivalent reduction in rear wing downforce will have to be effected by the teams to maintain the balance of the car. A higher front wing should also be less sensitive to turbulence. Do I believe that will eliminate the problem? No. It will be a matter of time (very little time, I believe) before this is countered in the wind tunnel and the same downforce, with possibly more turbulence is achieved. Today teams are using as much downforce as they can afford ,not all that they can generate, and I suspect that they will all go back to the wind tunnel to figure out how to achieve the same effect with a wing that is two inches higher. Click here to read the suggestions made by the Heretic and our readers Please submit any comments you have on this
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