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An Introduction To Racecar Aerodynamics & How Aero Can Improve Your Laptimes

Mark Berry's Yokohama Advan R34 GT-R Photo by Mark Pakula

So many winning teams focus so much on aero for two very simple reasons:

1. Lower drag allows you to achieve better acceleration and higher top speeds, and


2. More downforce can produce more grip, which increases cornering speeds, and improves braking performance.

Both these factors lead directly to lower laptimes.

This article explores how aero improvements can help you lower your laptimes ...

Cost Comparisons Of Aero Development Vs Other Tuning Methods

Aerodynamics is one of the areas in racecar development where significant improvements can be achieved at a relatively low cost whether the car is a road registered car that does track days, or a big horsepower racecar which has yet to have much aero tuning done on it.

In particular, the openness of aero rules and relative lack of restrictions in many categories of time attack racing mean that time attack racing is a very exciting category to be involved in, both from a driver's perspective and an aero engineering perspective.

Of particular relevance to people with track driven street cars, the speeds at which aero effects can start to kick in and be felt from the driver's seat are lower speeds that what many people realise.

The effects on stability by the addition of a properly designed rear wing on a roadcar for example can definitely be felt from the driver's seat at legal speeds on the freeway - I've noticed this many times on the road when a car is driven back to back with and without a rear wing at road legal speeds.

For highly developed racecars, the "point of diminishing returns" through traditional means of tuning and development is very familiar to a number of teams. The point of diminishing returns is where once a car reaches a particular level of development, it can cost more in dollar terms to shave a tenth of a second off the lap time than it costs to shave a tenth off the laptime in earlier stages of development. For teams who have reached the point of diminishing returns, aero improvements can potentially provide laptime improvements at a lower cost than some other tuning and development options.

So from the track driven street car, all the way to building all out time attack monster, aero development is an area where significant improvements can be had.

The Two Enemies Of Speed: Excess Drag And A Lack Of Downforce

There are two enemies of speed in racecar aerodynamics:

• excess drag
• lack of downforce or the presence of lift

Enemy 1: Drag

RAF Typhoon FGR4 (code ZJ939) on the landing run with braking parachute deployed. Photo Credit: A. Pingstone

Aerodynamic drag is an enemy of speed.

Commonly known as "wind resistance", the simplest way to visualise aero drag is to picture an imaginary parachute being towed behind your car.

Like a parasite, excess drag can reduce the effectiveness of the time and money you have spent on your engine improvements.

By reducing the amount of drag your car generates, you can reduce the size of that imaginary parachute ... and that can lead to faster laptimes.

Any object moving through air creates drag. However, through careful design and aero tuning, drag can be minimised.

You don't want your track car to move through the air like a brick. Instead you want your track car to move through the air as efficiently as possible ... while still generating downforce.

Enemy 2: Lift Or A Lack Of Downforce

The other enemy of speed in a time attack car is a lack of downforce, or in some cases the presence of lift.

Aerodynamic lift is a force that when it occurs literally tries to lift the weight of your car as you drive. In basic terms in racecar parlance, lift is the opposite of downforce.

Many people when they were a kid stuck their hand out the window of their parent's car and noticed how depending what angle they placed their hand at in the airflow, the air moving past the car could lift their hand or apply a downward force to their hand. While of course we don't recommend ever sticking your hand out of a moving vehicle, for most people that is their first experience of lift and downforce.

Some cars with stock bodywork do not create downforce when moving through air but instead generate lift, and that lift can create undesirable effects at high enough speeds, such as making the the steering feel light.

From a racing perspective, not enough downforce or the presence of lift can reduce the amount of grip your car has.

And conversely of course, adding downforce to a car can increase the level of grip, which in turn can have a very positive effect on cornering speeds and braking performance, which again can translate into faster lap times.

How Much Can Aero Changes Improve My Laptimes ?

Image Credit: Hydrargyrum - public domain image

Effective, well designed aerodynamics products can reduce your laptimes directly in two ways:

Additional downforce can increase grip.

If you have ever bogged a rear wheel drive car in mud, you'll know that adding weight over the rear wheels can increase grip at the driven wheels and help you get you out.

In a similar way, additional downforce can be used to generate effective weight that can potentially increase tyre grip.

Simon McBeath explained in an article he wrote for a Racecar Engineering Magazine ...

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Another way to evaluate how significant the aerodynamic forces are is to relate them to the vehicle's static weight.

In crude terms, the percentage of downforce over weight is the same as the extra grip obtained by virtue of that downforce at the speed at which the calculation was done.

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So in other words, adding downforce adds effective weight to the contact patches where your tyres meet the track, (ie the weight your tyre's contact patches "see") thereby potentially creating additional tyre grip.

However (crudely speaking) the beauty of downforce and effective weight at the contact patches vs actual weight is that downforce increases the effective weight on the contact patches, but without adding actual mass to your car which your car's engine would have to lug around the track (as additional actual mass would reduce acceleration, braking and cornering performance).

This ignores of course the actual weight of the aero devices themselves such as wings, splitters, diffusers, canards etc, however because most high quality aero parts are made from carbon fibre and have low weight, the additional weight of the aero parts themselves is relatively insignificant when the amount of downforce they can create is considered. In this case, relatively light weight parts can make big differences in the total downforce a car makes.

As shown above, the Project S14A time attack car project sponsored by The Tuners Group has been designed with not one but two wings - a rear wing and a front wing.

With more grip you can potentially corner at higher speeds and brake faster and later.

How much faster do you think you could get around a circuit with more grip created by more downforce ?

The answer is that it depends on a few factors ... including how effectively you generate that additional downforce while minimising the amount of drag you create.

The key is to generate usable downforce, without creating so much drag that your car goes slower instead of faster ...

Minimising Drag

The second way that well designed aerodynamics products can reduce your laptimes is by minimising drag.

If the aero parts on your car are not correctly designed, they can definitely produce unwanted excess drag.

We've even seen some cars at the track running their rear wing at an angle so aggressive that the point at which maximum downforce is created has been passed, so all they are doing is generating additional drag ... and wondering why their car is not going faster with their "super aggressive" wing angle.

Given the amount of money and time that racers invest in improving engine performance, lightening their cars, suspension and braking upgrades etc, to then let some of that additional performance be taken away from you by the enemy of drag is a tragedy.

The good news is that by identifying sources of excess drag on your car, you can claim back that power lost to drag.

Applying More Downforce & Minimising Drag At The Track

If you can increase your exit speed from key corners on the track, such as the final turn before a main straight, you can also potentially increase your top speed as you reach the end of the straight, and cover the distance of that straight faster.

If you can then increase your speed through the corner at the end of the straight (by having more grip because you have more downforce), then your speed through that corner is higher too and you can cover the distance round that corner faster.

Eastern Creek International Raceway. Image Credit: Will Pittenger. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Think about turn 12 at Eastern Creek International Raceway (home of the World Time Attack Challenge).

If you can maximise your exit speed out of turn 12, you have a headstart in building up speed down the main straight, which can help you achieve a higher top speed on the main straight and help you cover the length of the main straight faster.

If you can then maximise your exit speed from turn one, potentially you can also maximise your speed down the straight between turn one and turn two.

Via lower drag and increased grip via greater downforce, it is potentially possible to add incremental increases in speed through each corner, exiting each corner and on each straight, and those incremental improvements through individual sections of the track can add up to a significantly lower lap time.

Rear wing, wheelwell vents and rear diffuser on the Panspeed RX-7 at 2010 World Time Attack Challenge

The effects that carefully designed aero and higher cornering speeds and straightline speeds can have on laptimes were very clearly demonstrated by the top cars at Superlap 2010 / World Time Attack Challenge.

The top teams all definitely understand the importance of aero, and the photos that were published in the lead up to Superlap of the Cyber Evo in a wind tunnel in Japan attests to how seriously the overseas teams take their aero development.

The aero development done on cars like Mark Berry's R34 which we sponsor in the leadup to Superlap 2010 shows that some leading local teams also understand that aero is an area which can definitely help them go significantly faster and are applying aero changes to their cars to help them go faster.

It is important of course to use properly designed aero parts that are tested and proven to work - parts that create additional downforce without creating excessive additional drag.

The key is to create additional downforce without creating excessive additional drag. And that is one of the key areas that the science of racecar aerodynamics is all about.

Balancing Front Downforce & Rear Downforce, As Well As Applications For Front Wheel Drive Cars

Some people claim on various internet forums that a rear wing is of no use on a front wheel drive car.

That is not correct.

It's important to remember on a front wheel drive car that though the front wheels are the driven wheels and simultaneously put power to the ground as well as steering, the cornering load is shared between the front wheels and the rear wheels.

So it is possible to increase the rear grip by adding rear downforce, which can potentially help cornering speeds.

However, whenever adding downforce to a car, it is very important to get the balance of front downforce and rear downforce right.

Under braking the weight balance of the car that the tyres see tends to shift to the front wheels of course, so additional rear downforce can have an effect on how much grip the rear wheels have under braking.

The majority of the braking is done by the front wheels of course, but when you bear in mind that all four wheels can provide braking force, if you can increase the rear grip without reducing the front grip it is possible to increase the overall grip under braking of the car as a whole.

If a car is running an aftermarket front splitter for example without a rear wing, the addition of a rear wing can then produce downforce at the rear, helping to address the front downforce to rear downforce balance, but that balance requires you to look at front downforce and rear downforce simultaneously of course.

The Importance Of Balancing Front And Rear Downforce

It is also very important to balance the front and rear downforce, because if a car has significantly more downforce at the rear than at the front, or has lift at the front, the front of the car can feel light under certain situations on the track.

That lightness in the front of the car can lead to understeer, simply because the front wheels are lacking grip relative to rear grip. If you've ever towed a trailer with a front wheel drive car, you'll be familiar with how the additional weight of the trailer on the rear wheels relative to the weight on the front wheels can influence the front grip and handling.

So in many cases whether the car is rear wheel drive, four wheel drive or front wheel drive, adding a rear wing should also include adding downforce at the front of the car to keep the front to rear downforce balanced.

As an example of adding front and rear aero simultaneously, when Porsche developed the rear ducktail spoiler for the Carrera RS they also added a modified front spoiler / bumper assembly.

There is a very interesting diagram in a book about the Carrera RS where the car was tested without both spoilers, with only the front spoiler, with only the rear spoiler, and with both the front and rear spoiler.

Using the car with front and rear spoilers removed as the baseline, the results were:

• Front and rear spoilers removed: baseline
• With rear spoiler only: speed increased by 0.5 km/h over baseline
• With front spoiler only: speed increased by 2 km/h over baseline
• With front and rear spoilers fitted: speed increased by 4.5 km/h over baseline

So with both spoilers fitted, the speed increased.

Generally speaking, a lot depends on if a car has balanced front and rear downforce before a wing is added, or if the car has more front downforce than rear downforce before a rear wing is added.

If a car is already making front downforce but not generating enough rear downforce (or generating rear lift), then the addition of a rear wing can balance the front and rear downforce numbers.

Just like on a rear wheel drive car or four wheel drive car, on a front wheel drive car if you can increase the grip available to the tyres by adding downforce, without adding excessive drag, you can potentialy improve laptimes.

The key of course is to get the balance of front downforce and rear downforce correct.

So on many track cars where you are trying to increase downforce, what you are trying to achieve is an increase in front downforce and an increase in rear downforce, while keeping the balance of front downforce to rear downforce correct to avoid introducing any undesirable handling or grip issues by getting that balance wrong.

Putting Technology To Work For You - Computational Fluid Dynamics (CFD), Supercomputer Clusters, and Virtual Wind Tunnels

Computational fluid dynamic (CFD) image of the Hyper - X at the Mach 7 test condition with the engine operating. Image Credit: Dryden Flight Research Center - NASA Columbia, the new (2004) supercomputer, built of 20 SGI Altix clusters, a total of 10240 CPU. Original caption: "Birds-eye view of the 10,240-processor SGI Altix supercomputer housed at the NASA Advanced Supercomputing facility. Image Credit: NASA

Modern supercomputer clusters offer exciting ways to improve a cars aero performance via branch of engineering known as computational fluid dynamics (CFD).

Basically speaking CFD is all about using computers to simulate, measure and visualise the flow of a fluid - in the case of a racecar the fluid we are looking at is air, and how it flows around a racecar.

By using CFD software and supercomputers, it is possible to produce a virtual wind tunnel system in which aero parts, aero changes and even full cars can be tested aerodynamically.

The use of virtual wind tunnels will become more and more prevalent in the future.

NASA recently stated ...

CFD has taken the place of wind tunnels for many evaluations of aircraft and, as computing power increases and computer models become more sophisticated, CFD will largely replace wind tunnels.

In fact the advancements in CFD has resulted in some very exciting developments, to the point where this year's Virgin Racing Formula One car reportedly had it's aero testing and development done only in CFD, without the use of a large scale physical wind tunnel.

Cost benefits of using CFD & Virtual Wind Tunnel Systems

Just as the advances of moving from analog to digital editing in the music, film and television industries has revolutionised what is possible, CFD and virtual wind tunnels are the racing equivalent of that process.

The Traditional Way Of Designing And Testing Aero Parts

Fan blades of Langley Research Center's 16 foot transonic wind tunnel - Photo Credit: NASA

In the past, designing aero parts and finding the shapes and profiles that worked was largely a trial and error process.

Engineers would design a part, then a prototype would be made.

Often a mold would have to be manufactured using CNC, and then the prototype part made in that mold.

The prototype would then either be fitted to a full scale car for testing, or some teams had scale models used for aero testing.

If your team had access to a physical wind tunnel, you then need to add the cost of testing that part in the physical wind tunnel.

However, the effectiveness of a particular part could only be evaluated by building that physical prototype and testing it on the car or scale model. And of course building full size physical prototype parts or scale models of each part carries with it a significant fabrication and testing cost.

If the prototype part did not achieve the desired result, then it was binned. Then you go back to the drawing board and try again.

Obviously that kind of trail and error approach to aero parts design was particularly costly.

An interview with Virgin Formula One team's technical director Nick Wirth with sportinglife.com where he talks about the cost benefits of CFD and how much money was spent in the past using a physical prototype testing approach reads ...

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Wirth claims £20,000 per day was spent on parts in tunnel testing prior to the all-CFD approach with Acura, of which £18,000 worth was binned given a success rate of just one in 10.

"It was just a criminal waste of money, time and resources, and that wasn't even F1," added Wirth.

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The Process Of Designing & Testing Aero Parts With CFD And Virtual Wind Tunnel Systems

By contrast, with CFD / virtual wind tunnels, you can take a CAD drawing of a part, test it in the CFD / Virtual Wind Tunnel system, and get your CFD results ... all without having built a physical prototype.

If the part does not work as hoped, then you don't have to bin a physical part and you don't have to bin the mold, and additionally you have saved the labour costs of making the mold and making the physical prototype.

With CFD you quickly get an indication of if the direction you are heading in aero-wise is working or not, and once you find a shape that provides improvements, you can then refine and optimise that part's shape and dimensions in the CFD / virtual wind tunnel system - again without having to build a physical prototype.

So with CFD, you do a great deal of your testing and optimisation digitally, find the shapes that work best and optimise them as much possible digitally.

Once you have done all that digitally, only then do you make your physical part.

How much can that save ?

In the article with sportinglife.com, talking about the cost savings with CFD Wirth said ...

"I would say the way we are going about things is a fifth of the cost."

That represents a cost reduction of approximately 80%.

Part of a 2011 article published on Joe Saward's site here about the 2011 Virgin MVR-02 Formula One Car reads...

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"This is the team’s second car to be designed entirely without any wind tunnel work, using only computational fluid dynamics. ...

The team says that the new car is an improvement in all areas. ...

“We were extremely pleased to have demonstrated that it is possible to compete at the highest level of motor sport with a car designed wholly in computer simulation,” said technical director Nick Wirth. ...

“In terms of sheer CFD throughput, the number of configurations that our new processes have allowed us to test for the MVR-02 is a giant step forward from the VR-01, and we are looking forward to further improvements here as we finally begin to benefit from the new supercomputer that our partners CSC have provided for 2011.

I am confident that we have made real progress with the MVR-02, producing a car with considerably more aerodynamic efficiency than the VR-01 despite the regulation changes, and having made significant gains in terms of overall quality.

It provides a good basis for development over the course of the season, and I’m very sure we’ll be able to keep up the impressive rate of aero development that we’ve had since the beginning of the MVR-02 project.”"

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The Tuners Group's Inhouse Virtual Wind Tunnel Supercomputer Cluster

The dual element rear wing arrangement run on the Mark Berry Yokohama Advan R34 at 2010 World Time Attack Challenge (Photo credit: Kory Leung Photography)

At The Tuners Group we have our own supercomputer cluster inhouse to be used as a virtual wind tunnel system to model and analyze airflow around a car.

This allows us to model and test potential aero parts designs on the supercomputer before building physical prototypes, and rapidly speeds the development process.

It can also help us understand on a relatively detailed level what particular aero challenges a particular car presents.

Practical Questions For Racers That CFD Can Answer

Do you want to know what height and angle you should run your rear wing at to maximise downforce or minimise drag ?

Front bumper and splitter assembly of the Sun Cyber Evo - Winner of the 2010 World Time Attack Challenge

Want to know which rear wing from the huge range of wings on the market is the one you should be running on your car, and how much downforce a given wing actually makes ?

Want to know which front splitter design or diffuser design will be most effective on your car ?

Want to add an additional element to your rear wing to increase downforce but don't know which additional element profile will work best on your car or how it should be positioned relative to the main element ?

Want to know which combination of fenders, bumpers, splitter, diffuser, and rear wing will give your car the maximum downforce or minimum drag ?

CFD can answer all these questions.

Importantly CFD can:

• help reduce the cost of development
• help you avoid wasting valuable track and testing time on parts that don't improve your car's performance
• help you ensure that the parts you choose for your car are actually improving the aero performance of your car and not simply generating more drag
• help you get the very most performance out of the aero parts on your car.

Just as when you purchase engine components, you know that buying the components themselves is one part of the process, and getting the most out of those components is down to the skill of your engine builder and your dyno tuner, getting the most out of your car's aero package is also all about careful parts selection and design, figuring out what actually works on your car as a whole, and then tuning your cars aero performance using tools like CFD and virtual wind tunnel systems.

CFD and virtual wind tunnels are very cost effective and exciting technology, and we're definitely looking forward to helping teams improve their cars' aero packages with the help of CFD, our inhouse virtual wind tunnel supercomputer cluster, and the huge experience of the two aerodynamics experts on our Racecar Engineering & Development Team.

Want some help making your car faster ?

A DJ rear wing being wind tunnel tested on the RLR Msport Ligier in the MIRA Full Scale Wind Tunnel

The Tuners Group is based in Sydney and in addition to being the exclusive Australian distributors for Works Bell and Gibson Racing Wheels, is also one of only 8 authorised overseas distributors for ARC listed on the ARC website.

We are also the exclusive national representatives for world renowned UK based manufacturer DJ Engineering, a leading name in the design and production of motorsport composite components.

DJ supply a range of wind tunnel tested pre-preg carbon fibre aerofoils and wings, to teams from sprint racing to Historic F1 and international level GT racing. They are also used on a range of hillclimb cars and rally cars. More info on these wings is below.

We sponsor a number of leading cars like Mark Berry's R34 GT-R, the Kakavas Racing WRX, the Tomaszewski R35 GT-R, and the Pilatus R35 GT-R and attend a number of test days to dial in the aero performance.

The Tuners Group also operates a Racecar Engineering and Development Team with two highly experienced aerodynamics experts on the team, as well as having a CFD virtual wind tunnel supercomputer cluster inhouse in Sydney.

We can also attend various wind tunnels with your team for full scale wind tunnel testing. With aero experts on our Racecar Engineering & Development team in Australia, Europe and the USA, our experts can attend a number of wind tunnels with your team, including the Monash Wind Tunnel in Australia, the MIRA Full Scale Wind Tunnel in the UK, and a number of US based wind tunnels.

For more info about how we can help you improve the aero performance of your car, and for advice on selecting the right aero parts for your car, get in contact with us via our Contact Us page.

Our range of aero products

A DJ Racecars rear wing being tested in the MIRA full size wind tunnel on the Paragon Porsche 997 ALMS GT2. Image credit: S. McBeath / sm-aerotechniques

We are also the exclusive national representatives for DJ Engineering.

DJ Engineering manufactures a range of wind tunnel tested pre-preg carbon fibre high downforce wings and high efficiency wings, designed by world renowned wing designer and highly respected aerodynamics and racing author, Simon McBeath.

DJ supply a range of wind tunnel tested pre-preg carbon fibre aerofoils and wings, to teams from sprint racing to Historic F1 and international level GT racing, to hillclimb cars and rally cars.

DJ's wing customers include ...

• Lotus Motorsport (the Lotus factory motorsport department) with their Exige GT3
• Lotus Cars track spec 2-11 (again the Lotus factory)
• Prodrive (US based Prodrive Aston Martins)
• Paragon Porsche 997 American Le Mans Series GT2
• Matech (Ford GT FIA GT Racecar. Matech were the FIA GT3 Champions in 2008 and FIA GT3 Championship Runners Up in 2009)
• RLR Msport Ligier JS49 LMP3
• Riley Technologies MkXXII
• Arrows A4 Historic F1 car, run by G-Cat Racing
• Juno (DJ wings are standard fitment on all Juno's)

Click here for more info on our range of DJ Engineering wings ...

http://www.tunersgroup.com/Products/wings.html

More information about our Racecar Engineering & Development Team can be found here ...

http://www.tunersgroup.com/engineering/

You can browse our product range and order products online in our online store here ...

http://www.tunersgroup.com/Online_Store/

You can view our product range listed by manufacturer here ...

http://www.tunersgroup.com/Products/

To be notified when new aero articles are published on our website you can sign up to our free award winning TunerWire Live email newsletter here ...

http://www.tunersgroup.com/TunerWire_Live/

created on 2010-08-31 17:43:50 by adamr