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Thread: Anyone studied/studying aerodynamics?

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    Question Anyone studied/studying aerodynamics?

    Lo Peeps – just on the off chance that someone is/has studied aerodynamics (even better if you have access to a computer simulation)
    Im currently due to receive the race car back soon – and, as its well ‘brick shaped’, have been thinking about aerodynamics. My main concern is getting enough downforce at the back – and to this end would like to design a spoiler (probably extending from the rear boot lid) but I would also like to improve the aerodynamics of the whole car… without changing the bodyshape too much.
    So – anyone got any hints tips, cheap as possible – without having to go near a wind tunnel.
    If you have access to a computer simulation I can provide measurements as required.
    Cheers
    Iain

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    A nice halfrauds special.......... An Aluminium Stick on Fast And the Furious Spoiler

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    VTECmeous Vimeous's Avatar
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    Indeed I did study aerodynamics of cars, even if only briefly.
    The type of package you're looking for would be a CFD (Computational Fluid Dynamics) package, the one we used was called Fidap. Sadly it's a little beyond my means financially.
    The best tip I can give comes in the form of an example.

    Remember the first Audi TT's suffered tail-lift at high speed? Owners would disappear into the undergrowth backwards while doing 120mph+ round autobahn corners.
    The reason for this was the curved rear end of the car. There were no sharp edges on the rear at all and so the airflow across the car only departed as it reached the floor.
    Basically this caused a low pressure area over the car which increased as the air accelerated round the curve of the bum and caused a pressure differential between the top and undersides of the car, in turn causing lift as the differential increased. The rear wheels would go light and an arse-meets-ditch moment would occur.

    When you place a sharp edge into that airflow it causes the air to break from the car, causes an area of turbulence behind the spoiler keeping pressure above the car surface low enpugh to reduce the effects of rear-end lift.

    You'll see many modern cars with smooth rears use small but significant lip-spoilers to achieve the same effect. The latest subtle Rover 75 / MG ZT item is one example, as are many of the Hot Hatch bunch where the roof spoilers achieve the same effect.

    Now the science behind all that is far more complex and I've forgotten most of it but I'll ask around for advice on a good book to explain it in better detail.

    BTW
    Venturi tunnels are ace for sticking a car to the road. I suspect however, with bouncy tall-walled drag tyres, the effect may be wasted.

    If I think of anything else I'll get back to you.
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    Cheers,
    Im a little concerned as watching a few vids and from speaking to people, it looks like the shutdown area is where it all starts to kick off - and from seeing the aftermatch of what 'can' happen, I REALLY dont fancy haing an off at circa 130mph
    This is the sort of thing im after





    Only real difference betwen that and mine is that mines a err 4 door - and that one looks better

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    it also has a bit of a large winnet hanging off it's arse...

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    VTECmeous Vimeous's Avatar
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    The biggest thing about shutdown is that you've a huge amount of force going through the rear axle from shear grunt and downforce. As soon as you shutdown most of that force is no longer being applied.
    All the force goes through the tires. From the races I've seen on tellie most problems occur when the tyres suddenly become unloaded and respond like a spring. In the initial rebound it's quite possible for the rear wheel to leave the ground and put all the load of the car through the front axle.
    Of course at the start of a race all the load is rearwards, often leaving the front wheels in the air for a decent distance along the strip.
    On shutdown the car suddenly stops accelerating anywhere near as hard so the weight transfers forwards. Combine that with your springy rear tyres and the front end hits the deck hard putting all that load through two very skinny tyres with a tiny contact patch and which could very well be pointing in completely the wrong direction!

    In otherwords I reckon aero issues are less of a problem in the initial stages of a run IF the car shuts down. Add serious speed mid-run and it's down to driver skill to controll the front wheels.

    One thought for you though, and bear in mind I've never been to a strip.
    What are the stated rule conditions for cross-wind? With low cross-wind you could use a vertical fin (size uncertain) to provide a degree of directional stabilisation should things get a little hairy mid-run. You'd definitely need to get a techie on it (probably with some software) as it may give too much drag and such like.
    On the forthcoming Evo IX it has small roof fins on the trailing edge of the cabin. While I suspect this is more to do with body-roll reduction in high-speed cornering, it may also benefit a drag racer for longitudinal stability.

    Much research is needed!
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    Quote Originally Posted by Vimeous
    Much research is needed!
    Cheers Vimeous, a very good description of what happens there
    Ive noticed more and more american cars running vertical fins - but this is more on the 5 & 6 sec bracket (I have a way to go until I get to that stage).
    A couple of the people I will be racing against have used the wing/spoiler mentioned above and have noticed a lot more stability when shutting down, though whatever way I go it needs to be easily removeable for road use.
    Will get hold of the latest FIA book and run through the regs, thanks for your help - much appreciated
    Iain

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