With the World Time Attack challenge rapidly approaching we thought we would give our fans an insight into one of the “key areas” that has really become the hot topic in recent years and that is AERO.
In most classes of racing aero is one of the areas that is most often restricted as the performance gains can be enormous and in these “rule driven” categories, such as F1, the top teams will often spend a large slice of their total yearly budget trying to find the aerodynamic edge over their opposition.
Today we present an Introduction to “Race Car Aerodynamics” written by Scott Beeton. Scott is a former Williams F1 Aerodynamicist and now offers consulting services around the world specialising in race car design and aerodynamic development through his Australian based company Aero Design Pty Ltd . He can be contacted at email@example.com, by phone on+61410 103 254, or via the website www.aerodesign.com.au
Race car development in Australia has always been primarily based on engine and suspension modifications. The onset of time attack racing in Australia has led to rapid development in the area of aerodynamics as profound performance benefits are available when the appropriate modifications are made. As this is a relatively unknown topic for most people, we will build up your knowledge base with a few articles on this important area in the lead up to the 2012 WTAC.
In this article we discuss the importance of aerodynamics, and show you why it can result in such performance gains especially for a time attack vehicle. We must first appreciate the fact that all loads generated by a racecar whist accelerating, braking and cornering are transmitted through 4 very small contact patches between the tyres and the ground. Everybody knows this already, but it is important to point out at this stage as it is the interaction between the tyre and the ground and the resultant forces that are transmitted through these four interfaces that can really show us the immediate advantages of increasing the aerodynamic performance of your vehicle.
Tyres build their lateral load capacity (cornering potential) as the slip angle increases. There is a point where the cornering load is at its maximum, and then the cornering power tends to slightly taper off after this as the slip angle further increases. A graph of this can be seen below. We can see for the blue data that the maximum cornering load is developed at about 6 degrees, so we aim to have the tyres run at these levels of slip angle in cornering conditions.
The slip angle of the tyre is controlled by suspension adjustment, such as static toe in or out and also dynamic toe with camber change or bump steer. The point of this particular graph is to illustrate that with suspension adjustments, we can really only move the maximum cornering capacity along this particular blue curve and that anywhere between 4.5 to 7.5 degrees we will have a similar result.
A major part of the suspension setup is optimising these slip angles so that maximum cornering forces are achieved and this also will result in better tyre wear, heat distribution, and lap times if the driver can drive the car as close to the optimum slip angles as possible. If you have a vehicle that has a good base setup and you are aware that you are around optimum toe and camber settings, then the only method for increasing the cornering potential is to add more downforce to the vehicle.
Now, with the addition of more vertical load, we introduce the red curve. This illustrates an increase in the vertical load on the tyre of 300 pounds (136kgs), which should be easily obtained on a previously unmodified vehicle. It becomes quite obvious that at all slip angles there is greater cornering potential. Even if the car is not running in the optimum area of slip angles around the maximum, we will still achieve decent performance gains which will improve cornering speeds and hence reduce laptimes.
The Cyber Evo undertray shows the length that winning teams go to. Photo: Speedhunters.com
With the above information in mind, it now makes sense why such emphasis is placed on aerodynamics in the top levels of motorsport around the world. I should note that every single team in world championship level motorsport is doing it, and that performance is generally awarded to the teams that can test the most design variations to optimise their design. This will also hold true in all other levels of motorsport, as the more you develop and test a vehicle, the more potential for performance improvement against its competition. World Time Attack is an excellent category for aerodynamic development and this can be seen by the extensive development that is being undertaken by all of the Pro Class teams.
There are two main factors that dictate a vehicles aero performance and these are termed Lift and Drag. The Lift force describes the force on a vehicle which tries to lift the vehicle off the road (which is less than ideal in a racing scenario), and so we are interested in negative lift, commonly referred to as Downforce. As we described above, downforce will result in an increase in the vertical load on the tyres and increase the vehicle’s maximum cornering potential.
One crude way to increase the vertical load at the tyres is to add mass to the vehicle, but this has implications as you then need to accelerate and brake this additional mass around the track, which will slow you down. By adding this aerodynamic downforce, which increases the vertical load at the tyres, we will increase the vehicles cornering performance with minimal impact on other areas of the cars performance. When aero development started in F1, the engineers at Lotus did not explain their findings and development path to the press, but simply stated that they had “found something for nothing”.
Now this isn’t strictly true. There is a by-product of this downforce and this is known as Drag. the drag force is the aerodynamic force opposing the direction of travel which is created by the pressure in and around the vehicle. Drag affects the acceleration of the vehicle and also its top speed. Fortunately for a car that has to negotiate corners, unlike a drag racer, we can develop a considerable amount of downforce with a limited drag penalty.
A key point to note at this stage is that in terms of lap time, adding downforce increases our speed in corners, and a drag reduction will help our acceleration and top speed. Hence on a tight and twisty racetrack, downforce will have the biggest contribution to performance, and on a track with long straights, drag will be the main contributor to performance.
To increase the aerodynamic efficiency of a vehicle we either need to increase the downforce, or decrease the drag of the vehicle.
In the images below of the flow around a Nissan R35 GTR, the high pressure is red, low pressure is blue, and green is neutral. Ideally, we want high pressure regions on the upper surface and low pressure regions on the underside of the vehicle, thus increasing the vertical load on the tyres, and allowing for greater cornering forces to be generated and faster lap times.
Pressure at Central Slice Plane of GTR
Pressure at Central Slice Plane and on GTR Body
To modify the aerodynamic performance we need to change the pressure distribution around the vehicle. If we can increase the pressure on the top of the vehicle then this will result in additional downforce. If we can decrease the pressure on the underside of the vehicle then again, we can increase the downforce. The aim is to do this in the most efficient way possible so that we add as much downforce as possible, with as little gain in drag as we can manage, thus increasing the overall aerodynamic efficiency of the vehicle.
Although there are a number of ways of achieving this and the design of such systems is unique to each vehicle, the main additions are Front Splitters, Canards, Rear Diffusers, Rear Wings etc. These are all added to the vehicle in the quest to reduce lap times and can be seen in the images below.
In the following articles we will look at how we can modify these pressure regions to our advantage to gain downforce and/or reduce drag on a racing vehicle. We will discuss some of the common methods used in time attack today.
Copyright Scott Beeton 2012.