What is an Aero Map?
Aero maps are crucial to optimise racecar set-up. But what actually is an aero map and how do you build one for your own racecar?
What is an Aero Map?
A map is a way of visualising the relationship between different parameters. For example, a geographical map can show altitude as a function of longitude and latitude. In the case of a racecar the aerodynamic lift, drag and balance can be shown as a function of car set-up such as front and rear ride height or rear wing angle. So, an aero map effectively visualises the relationship between the geometrical properties and the aerodynamic properties of a racecar.
How do you use an aero map?
Aero maps are one of the many tools that help engineers to build a model of a racecar. These models are then used to predict the behaviour of the car to different set-up changes. Being able to investigate and quickly understand the effect of different set-up changes is essential when the driver, track and conditions change which is why modelling has become such a critical part of motorsport engineering.
So if you wanted to find how the aero balance (percentage of total downforce on the front axle), would change if you lowered the front ride height by 3mm, how would you use an aero map? Firstly, let’s look at an example of an aero map. For a range of front and rear ride heights, the amount of downforce can be visualised by different colours with red being high and blue being low. Separate aero maps can then be used to visualise front, rear and total downforce as well as drag.
Now let’s look at ride height. As the car makes its way around a track, the amount of downforce acting on the car is constantly changing which in turn varies both the front and rear ride heights. Taking the example of a single seater aero-dominated racecar: the amount of downforce increases with the cars speed. So during straight line acceleration, where vehicle speed is high, there is more force pushing down on the car, which is why both front and rear ride heights decrease as shown on the ride height envelope below.
As the car slows down under braking, downforce gradually comes off the car and therefore the front and rear ride height increases. This is illustrated by the hypothetical ride height envelope for formula cars.
This ride height envelope can then be overlayed on an aero map to analyse different set-ups as illustrated below. We can see that by extending the ride height envelope (pink) the car will benefit from slightly more downforce at the front (as indicated by the yellow area). While on the rear it will move the maximum downforce (red area) into the middle of the ride height envelope which is more desirable for stability.
How do you make your own aero map?
Sometimes, manufacturers supply aero maps, but often these are either not shared or not entirely accurate. A budget-friendly way to build an aero map yourself, without testing in the wind tunnel is to run CFD simulations on various set-ups.
Step 1. Obtain a 3D model
It is unlikely that you can get this from your manufacturer, but luckily there are plenty of professional modellers that provide high-quality 3D models of racecars at relatively low cost (e.g. Hum3D, Turbosquid or CGTrader). These can either be used in their raw form or you can digitally add modifications to match the real car. Furthermore, usually these models, which are primarily renderings, feature gaps and holes which can crash CFD simulations and take a long time to resolve. However, by using a platform such as AirShaper, you can run simulations directly on these type of 3D models, without having to spend weeks cleaning up the CAD geometry.
Step 2. Run the simulations
Let’s take an example. The ride height of a public model of the 2016 Audi R8 LMS was increased by 20mm in two steps. The ride height could not be lowered due to the minimum ride height regulations.
Step 3. Map the results
Once the simulations have been completed, you can then analyse the drag, downforce and aero balance.
Drag and downforce
From the graph below we can see that increasing the ride height did not have a significant effect on the aerodynamic drag much but it did reduce the downforce greatly. This is because the front splitter and rear diffuser help to accelerate the air underneath the car. This reduces the pressure (the Bernoulli effect), which then creates a downward suction effect. When ride height is increased, this channel effect is reduced and therefore crucial downforce is lost.
Unsurprisingly, increasing the ride height also impacted the aero balance of the car by shifting more downforce to the rear wheels in this case. To counter this, you may need to play with the front splitter, the angle of attack of the rear wing, or the rake of the car, depending on whether the regulations allow this.
So for your next race, be sure to have your aero map ready when the driver is complaining about understeer or oversteer – a few tweaks during a pit stop could be the difference between winning and losing.
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