Understanding WTAC: Aerodynamics

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The faster you are in time attack racing the bigger the role your car’s aerodynamics will play. While this is especially evident in Pro and Pro Am classes a well thought out aero mods can also have a big impact on a Clubsprint or Open Class car.

In a nutshell, aerodynamics (or “aero” for short) is a term to describe how air flows in, out and around a*car. The two main factors that affect a vehicle’s aero performance are Drag and Lift.

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Drag*is the force that acts directly opposite to the car’s direction of travel. It is created by air flowing around the car. You might have heard the term Drag Co-efficient Factor which is basically a car’s ability to cut through the air. The less drag, the faster a car can accelerate and the higher its top speed. Other factors affecting drag are*a pocket of vacuum created behind the car, usually behind the rear window and behind the boot, called “Flow Detachment”, as well as turbulence created as a result of the*detachment.

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Lift*is the force which forces the vehicle up, off the road. It is created by the difference in speed (and therefore pressure) of air flowing above and below a car. Most car shapes are prone to generating low air pressure above them hence creating Lift. Most aerodynamic aids installed on time attack cars*minimise Lift by converting it to Negative Lift.*Negative Lift*is the force which pushes the vehicle down and is more commonly known as Downforce.

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Modern CFD software allows aero designers to calculate and predict drag, turbulence, downforce and air flow through the body. This virtual testing minimises the “trial and error” period and allows for more efficient designs.

The main components of a time attack aero package are front splitters, canards, rear diffusers, rear wings and side skirts.

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While size (and therefore surface area) of a front splitter does matter, so does its*design and strength. These components need to withstand some serious down pressure!

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A wing on a race car is effectively an evil twin of the aeroplane wing. Its shape is designed to produce low pressure below it, thus forcing the air flowing above to push down on the wing.

A properly designed wing and front splitter combination can have a serious impact on a race car, greatly increasing its cornering speed. In Pro and Pro Am classes, aero is quite possibly the single most determining factor beside the driver.

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Examples of this abound. Take a closer look at the 2011 spec Cyber Evo. It certainly didn’t have the power output of Sierra Sierra but thanks to the Nakjima-san’s aero sucking it to the ground it was much faster through corners.

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All this grip came at a price though, CyberEvo’s top speed was almost 40kph down on Sierra Sierra’s. With both Tarzan and Empringham being both experienced drivers, it’s easy to see where the time was made up – through the corners.

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But aero is so much more than just canards, splitters and spoilers. Time attack cars are powered by high horsepower engines and their brakes are working overtime – meaning the path of air through the engine bay is critical. Apart from minimising drag, creating downforce, a well-designed aero package should also ensure sufficient cooling of various engine and drivetrain components.

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When American aero ace, Andrew Brilliant, designed an aero package for Nemo, he noted that the whole car has to be “an integral part of the aero package”. Nemo ushered in a new era of time attack racing with the aerodynamics playing an increasingly important role in the car’s success.

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These days we rarely hear people talking about individual aero components, if you look at the likes of Tilton, Scorch, MCA or PMQ, it’s plain to see it’s all about the entire aero “package”. An aero package that produces a massive downforce without sacrificing drag efficiency. It slices through the air at high speeds while still getting enough air through the interior to cool the engine components and brakes.

In terms of aerodynamic racing efficiency, time attack cars really are at the cutting edge of technology.

LINKS:

www.yokohama.com.au
www.worldtimeattack.com