STOCKCAR AERODYNAMICS TESTING TIMES CALL FOR TOP FACILITIES Aero is fast becoming a more important factor in Sprint Cup, and teams are facing major changes in the way they work as a result SAM COLLINS

A Generation 6 being put through its paces at the Aerodyn facility Engineers working on a Generation 6 Ford in the ARC in – in Mooresville, NC – a tunnel that was purpose-built for stockcars one of only two scale model wind used regularly by Cup teams

t the 2014 Daytona team’s aero data it is hard to know of that there are a handful of especially when rule changes 500, the Hendrick- for sure but, it is certain that commercially available tunnels are introduced. Two of them – built Chevrolet SS aerodynamics are increasingly key largely dedicated to F1 testing, Aerodyn and A2 – are on the same Aof Dale Earnhardt Jr factor in top class stockcar racing. with more than 15 tunnels campus in Mooresville, NC, and was involved in a thrilling At first glance that may working on the open wheel both have been purpose-built for two-lap dash to the finish, but seem obvious, but over the designs. In comparison, in Sprint stockcars. The third – Windshear an engineer’s thoughts were years –despite substantial Cup there are only six facilities – was developed not only for inevitably drawn to a flapping bit investments in testing facilities in common use, including the stockcars, but also with IndyCar of tape on the front of the car. and technology – more effort Laurel Hill Tunnel. and Formula 1 in mind. It is the How much drag was it creating? has gone into the mechanical Now, with draconian new rules largest and fastest automotive Aerodynamic discussion performance of the cars. in Formula 1 restricting the use wind tunnel in the world. dominated the Fox Sports This is something that stacks of both wind tunnels and CFD A2 was always intended commentary of the weather- up when you look at the number clusters as well as a forthcoming to be a the little brother of interrupted race. Did the of wind tunnels in use in NASCAR cost cap, a range of new Aerodyn. It is smaller and has arrive in a higher downforce, compared to the number used technology may suddenly become fewer capabilities, but Cup higher drag trim to take advantage in F1. In grand prix racing, all available to Cup teams. It is teams do still use it on occasion. of traffic? Were the Chevy’s but two of the teams have their notable that the full-scale tunnels However, its big brother is one running very low drag to qualify own wind tunnel – and indeed currently used in NASCAR are of the most popular tunnels in well? Without access to the some teams have two. On top largely fully booked at key times, the sport. Opened in 2003, the

www.racecar-engineering.com • Stockcar Engineering 11 STOCKCAR AERODYNAMICS

Aerodyn HArPS SyStem SPecificAtion

1. Main power to the system consists of a single DC power supply rated at 250 Amps and variable 0-20 volts, located in the basement balance room 2. Main power supply is designed to control output voltage to a set point, with amperage generated as required by the load 3. A pair of 1/0 power cables and a small 24 volt control power cable are routed from the basement, up through the left front ram opening into the engine compartment, through the firewall on the passenger side, into the greenhouse, where they connect to the HARPS in-car control box 4. A total of 14 discrete channels are available via connection to the control box located in the passenger side of the greenhouse 5. Each channel has a capacity of 50 Amps, with a total available system capacity of 250 Amps 6. Each channel is provided with a 50 Amp circuit breaker, Push-To-Test switch and Power-On LED to verify proper hook-up and flow direction prior to test 7. System voltage is adjustable from 0 to 20 volts DC. The selected voltage affects all 14 channels 8. System voltage and selection of channels to be “ON” or “OFF” are controlled by the customer using an iPad and a dedicated wireless network the Windshear wind tunnel is the largest and fastest facility in the world, 9. Channels selected for “ON” may automatically start and stop in conjunction with and is used regularly by stockcar, indycar and f1 teams tunnel main fans when “AUTO” start is selected. 10. Channel status, channel amperage, total system amperage, and system voltage are simultaneously displayed in real time on the in-car control box, on the iPad, and are recorded in the data 11. For every point of every run, the customer data sheet will record: a. Channel “ON” or “OFF” status b. Channel amperage c. Total system amperage d. System voltage 12. In-car control box includes connection for a single 3in duct hose to simulate connection to media electronics packages

“We can prep a car and get through four or five cars a shift –

A ford in the Aerodyn tunnel, a facility which boasts 22 fans compared to that’s ideal for cataloguing” one big fan found in many other wind tunnels, speeding testing up

tunnel has been in a state of Aerodyn, but with rule changes There will be one noticeable ‘With so few days allocated constant evolution, and has many in both Cup and Trucks, there change in wind tunnel availability to testing, development time is interesting design features that will be some more development. this year in , and it a valuable resource. To get the make it perfect for the work that Currently, while in a static period is all due to the 2014 Formula 1 maximum from it, we pre-fit every Cup teams do. of rules, there is more cataloguing sporting regulations. In recent new part we’re looking to test to ‘We have 22 fans on this tunnel according to the teams. years, grand prix teams have been make sure it can be changed over whereas most tunnels have one One new addition to the strictly limited on aerodynamic quickly. We left a certain amount big fan,’ says Chris Osetek, one of Aerodyn tunnel is the HARPS (high testing, with few straight-line of kit at the facility in America the engineers at Aerodyn. ‘The amperage remote power supply) testing days allowed and even last time, so the crew has already problem with one big fan is the system. It is a fully-automated fewer tests allowed at full-scale. been out there this week to deceleration time and acceleration control system designed to provide The only wind tunnel in the world make sure everything still works, time, but with these small fans it’s control and power to on-car fans able to really deliver the airspeed that our software is compatible much faster. One data point takes including in-line duct, radiator or at full-scale required by F1 teams with theirs, and so on. This is us 50 seconds, but we have an both. It allows the team using is Windshear. important to make sure that when active ride height control in here the tunnel to connect all fans to ‘The Windshear test falls we arrive we can hit the ground which means that if a team was a central connection point, and to under the designated amount of running straight away.’ doing an aero map, they can keep control everything remotely from testing we’re allowed to do during However, the new rules for running. We can prep a car and get the control room using an iPad app. the course of a year,’ said Lotus 2014 have completely banned through four or five cars a shift, so ‘There is a high amp power F1 team manager Paul Seaby last full-scale aerodynamic testing, that’s ideal for cataloguing.’ system, a big box that is mounted year. ‘The rules allow four days of partly due to an accident during Cataloguing is the process in the car, and there is a 200 Amp on-track aero testing, which can an airfield test session in England where teams compare a number power supply that comes up from be exchanged for wind tunnel that eventually proved to be fatal, of their cars to work out which the bottom of the tunnel and the testing. We chose to swap all of and partly due to the fear of the one to use at particular venues, teams hook up all of their duct our allotted on-track aero testing costs associated with flying cars and to see if any are too draggy to fans and things like that,’ says for one big hit of wind tunnel from Europe to North Carolina to use without further work. Osetek. ‘If they want them to testing. We have done this in test. This will almost certainly The teams do both come on during the test, they just previous years and found it to be leave some free time available at cataloguing and development at use the iPad to control it.’ of significant benefit. the Concord facility.

www.racecar-engineering.com • Stockcar Engineering 11

STOCKCAR SUPERMODIFIEDS A HIGHLY MODIFIED KIND OF RACECAR The refuge of frustrated engineers that crave a bit more freedom than other classes provide, supermodified racers have a character all of their own SAM COLLINS

Chris Osetek’s supermodified being put through its paces in the A2 wind tunnel

hat is the fastest governing them are few and dimensions – but then it’s really ‘Short stroke, long stroke – you car on a short track? the fans that follow them are as open. It’s an open wheel class with can do what you like, but we run NASCAR Sprint Cup at knowledgable and passionate as huge tyres, huge motors, and the in the 900bhp range whatever,’ WBristol? Sprint cars? the drivers are brave.’ cars weigh in at 1850lbs. All four he adds. ‘I have my motor rotated BriSCA F1? Actually it’s none of It sounds like an excessive tyres are different sizes, with the by seven degrees, but some them. The fastest thing on the amount of hyperbole on the right rear at 18 or 19 inches. We people run them as much as 24 short tracks is a Formula little part of the promoter, but in get one race out of the tyres, and degrees, which can lower the seen outside of a few areas of reality it is not. Supermodifieds they cost $850 a set. ‘ CG height by about a quarter the USA. Supermodified racing have become something of a The engines in supermodifieds inch. But when you factor in the started up in the New York State refuge for engineers frustrated are immediately noticeable, not exhaust installation it ends up area and is still popular there, by restrictions in other classes for their design particularly, but being almost neutral.’ where it is sometimes called the of racing. One of them is Chris for their installation alongside the The cars have no transmission Indy of the East. Osetek, who by day is an engineer driver. ‘The motor is often offset or gearbox – the engines drive the One of the promoters of at the Aerodyn wind tunnel in on these cars and we run 68 per rear wheels directly, meaning that supermodified racing, Bob Mooresville, NC. He has designed cent max left side weight,’ says the cars require a push start. If a Gangwer, describes the cars as and built a number of cars for Osetek. ‘Back in the 1980s there driver spins, his race is over. Many ‘the king of the asphalt’. himself and others. were guys doing rear-engined cars currently racing use universal ‘You have to realise that ‘The reason I drive up and down cars and four-wheel drive cars, joints, but Osetek runs a CV joint, this open wheel racecar is very between North Carolina and New then the engine ended up on something he believes is worth lightweight, and produces copious York all summer long is because the left and that kind of stuck. up to 10bhp at the wheels. amounts of gut-wrenching torque it is a class of racing still open The rules say that the engines The chassis rules are evidently and horsepower. They are rare to innovation,’ he enthuses. ‘The must be steel block, normally quite open, but there are some, and exotic beyond imagination. rulebook is very small – a engine aspirated, run on methanol and as Osetek explains. ‘It must have No two are alike, the rules capacity rule and some basic be no bigger than 468ci. a roll cage, but after that it’s

www.racecar-engineering.com • Stockcar Engineering 11 WILLIAM J TAYLOR The cars feature no transmission or gearbox, and the engines drive the rear There are two classes of supermodified – wing and no wing. However, wheels directly. If a driver spins, that spells the end of their race the no wing cars still feature large aerofoils front and rear kind of open. A friend of mine wing class they feature a aerodynamic package as an says Osetek. ‘When you go to the did a full aluminium honeycomb 24 square foot moveable wing after-hours project in the A2 wind first race of the year you get to monocoque – that did really well. on the top of the car. The wings tunnel. ‘In aero terms it’s pretty see all the new things people are My car has a stressed skin on a are not meant to be driver free. We are at the track, and say trying. That’s the problem – with tubular chassis, with aluminium adjustable, but they are passive we win a race, they weigh us an open rulebook things can get bulkheads. Over the years they adjustable so you can design it to and check the engine capacity – expensive, but we still get 34 have tried to keep carbon fibre flatten out on the straightaway but that’s about it. So unless you cars per race. But a car less motor out because of the cost, but you and pop up in the corners. are doing anything crazy, then will sell for $40,000-$70,000 can get round it as the rule says Within the 24 square feet it’s probably allowed. In aero with people then putting another something like “carbon fibre can anything goes, so it’s pretty terms you have boxes to work $30,000-$40,000 on the motor.’ only be used for driver safety”, huge downforce. Some people inside, front and rear wings If supermodifieds ever which is an easy argument to win.’ use that top wing almost like a are open, so are side panels. did become more widespread There are actually two classes drag brake, as we are no longer There is quite a bit of downforce then the costs would almost of supermodified car – wing and limited by the aero. In fact we are as you can imagine.’ certainly rise even further, which no wing. That said, the ‘no wing’ limited by the tyres which after An open rules class such as could spoil the formula. cars still feature fairly substantial a point drop off in performance if this is an engineer’s dream, but So it’s likely to remain the aerofoils front and rear. Both the load is too high.’ it must be wondered why it has refuge for any engineers classes have substantial Osetek is reluctant to reveal not become more popular over working in NASCAR who want downforce, increasing the exact downforce figures, but the years. ‘None of the cars are a bit more design freedom, and cornering further. ‘In the he has developed his car’s the same – that’s the cool thing,’ long may it last! u “The rules say that the engines must be steel block, normally aspirated, run on methanol and be no bigger than 468ci”

www.racecar-engineering.com • Stockcar Engineering 11 STOCKCAR PRODUCTS Moment of inertia test rigs

The Centroid rig’s location next to the Aerodyn tunnel allows teams to run an MOI test before or after any wind tunnel test, saving multiple trips

he rise of simulation assume a symmetry through the reaction force at one end – you can ‘The aerodynamicists always technology in motor car. Certain vehicles like Formula 1 then get two values: the centre of want to put things higher too. The racing, both multibody cars are very evenly balanced, so gravity height and also any offset chassis has raised at the front over Tand driver-in-the-loop, has with them it is usually within 2mm from the x or y direction.’ the years as they want to get air placed ever-increasing importance of the vehicle centre line, and on Force India’s head of vehicle under the nose. In the past there on understanding a car’s real road cars it can be up to 10mm off.’ science James Knapton is in also tended to be a lot of winglets moment of inertia and centre of The rig is linked to a computer charge of the team’s usage of the on the top of the bodywork and gravity. The first test rig to be which logs only three channels of Cranfield rig, and for him one of we had to assess whether the revealed that is specifically-built data, including the timing pattern the results it puts out is clearly the gain outweighed the losses from for this task was revealed in 2012 and a force via a load cell. But the most important when developing a raising the centre of gravity height. at Cranfield University in England. results are just what is required by new model such as the VJM05. But if the rules don’t change, you The rig itself looks deceptively racing teams’ vehicle dynamists. ‘We go there once a year to target it to be reduced, and for us simple, like a scaled-down version ‘There is no point in just carry out a centre of gravity test it has between 2010 and 2012. It of a child’s seesaw. Mounted on an measuring the moment of inertia and an inertia test,’ he explains. is usually between 200-250mm air bed which supports the vehicle, on its own though,’ Dr Watson ‘We primarily look at the centre of above the bottom of the car, which there is an arrangement of steel adds. ‘That would be meaningless gravity height, which is massively is fairly low. We could make it arms with two long ones running – we have to reference it back to important in F1. If you change it lower still, but we would have to the length (or width) of the vehicle. the centre of gravity. You can get by 10mm you go about two tenths compromise the aerodynamics, The rig is capable of being aligned that in the x and y planes very of a second faster. Over time you by lowering the radiators and for testing in pitch, roll and yaw, easily on a flat patch with corner may expect the centre of gravity sidepods – things like that.‘ and all three are used by F1 teams weights, but by using the rig for to go down as each new model Beyond understanding the like Force India for its calculations. a supplementary test you can is completed, but actually it has car’s centre of gravity height, ‘We can also calculate the principal measure the height of the centre often gone up which can scare the the inertia of the car is also very moment of inertia and find out of gravity – you simply measure management. It can be heavily important to the team. ‘The inertia which axis the object would like the reaction force in a pitch influenced by regulation changes. of the car, how much it resists to rotate about,’ Dr James Watson orientation and a roll orientation. When the car safety was improved turning round a corner, is of course points out. ‘The centre of gravity That is simply a case of tilting with side panels for driver the primary function of this rig,’ is not always on the car’s centre the vehicle for a set number protection and bigger headrests Knapton continues. ‘Over the years line, in either x or y planes, but we of degrees and measuring the the height raised, for example. it stayed roughly the same with

“We can calculate the principal moment of inertia and find out which axis the object would like to rotate about“

www.racecar-engineering.com • Stockcar Engineering 11 STOCKCAR PRODUCTS “It’s important that we have the correct centre of gravity height and inertial properties in our model – it must behave like the real thing”

Force India use the Cranfield facility once a year to carry out centre of gravity and inertia tests

our cars, but in 2009 we started height and inertial properties in to know the rate of deceleration feeds into other models which to make the car longer for stability our vehicle model,’ says Knapton. and the centre of gravity height. give us the maximum loads for the and aerodynamic reasons, and ‘It must behave like the real thing. Another way we use the data is suspension. It’s especially critical in 2010 the refuelling ban made We use that data in dynamic if we do stability calculations on as we don’t use very high safety them longer still, and that changed models like our driver-in-the-loop the car, and try to work out the factors, perhaps 25-50 per cent.’ it a lot. There is not a lot we can simulator – getting the data right yaw moment making the car turn. This facility in the rolling do about yaw inertia because means that it feels like the real car The front tyres will try to make fields of England seems a world the parts of the car pretty much for the driver. We had an incident the car go round the corner while away from the equally rolling have to be where they are, and we recently where we got the roll the rear tyres try to stop the car countryside of North Carolina, have regulatory limits on weight inertia wrong, and the drivers were going round the corner looking at but in an anonymous building distribution, which further limits complaining that the car was very that yaw rate sensor of the car. alongside the Aerodyn wind tunnel where we can place things. The strange to drive. We didn’t believe Differentiating that from yaw is ‘Centroid’. This is former Hendrick yaw inertia is usually dominated them, but later realised that it was acceleration we can then divide engineer Gary Eaker’s equivalent of by things like the front wings and out by a factor of 100, due to a that by the yaw inertia – and we the Cranfield facility, but it seems front tyres which are right out at user error. The car was oscillating get the moment acting on the car. far more capable. The team behind the corners. Our yaw inertia has and the drivers picked it up.’ We can then use that yaw moment it are still a little cagey about its gone up quite a bit recently, but The data also can be used to asses the stability of a change exact specification, though it strangely the drivers don’t notice in real-world car development, we make to the car. has been specifically developed it. You’d imagine they would get something Force India technical ‘The data from the VJM05 with Sprint Cup cars in mind. As out and say it feels very sluggish director Andrew Green has placed and the forthcoming VJM06 will is the case with most of Eaker’s and unresponsive, but they don’t an emphasis on. be fed back to the design team projects, the technology used really pick it up.’ ‘We work out the aerodynamic to allow them to optimise other in the Centroid rig is all in-house In the age of digital simulation, loading on the car via load cells parts of the car. and some of it is very innovative it seems strange that such a on the pushrods. If we change ‘We use this when we are indeed – and according to Eaker, simple looking tool is so critical, an aero component, we look at designing the suspension ‘pretty difficult to copy’. but what CAD packages output is those outings to see if there is any elements. We need to accurately Its location next to the Aerodyn no comparison to the real world. change, but when the car brakes calculate the load that goes tunnel allows teams to run a MOI But the data is crucial to improving you get a huge weight transfer through them. If a wishbone fails rig test just before or after any the team’s digital version of forward putting load on the front. at high speed, it is bad – as you wind tunnel session, saving teams reality. ‘We use a lot of the data If you look at the data it looks probably realise. The data from making multiple trips. from this rig in our simulation like there is a massive load on the the centre of gravity height helps The full story on the Centroid models, it’s very important that we front. So, we need to compensate us to accurately predict the car’s rig will appear in the next issue of have the correct centre of gravity that out and to do that we need contact patch loads, and that Stockcar Engineering.

www.racecar-engineering.com • Stockcar Engineering 11