Aerodynamics of a bug

[graham]

Hi very interesting thread here.I would like some peoples views on the best way to dissperse air out under the car once its been through the front grill and through the rads.I do have a box section made up to cover the rads but I am sure that this could be better designed to creat downforce instead of lift and also channel air better under the floorpan.I have also been tinkering with some designs for the rear wings, apron and bumper set up I will post some sketches when I get time thanks.
[IMG]~original[/IMG]

[IMG]~original[/IMG]

[aircured]

Originally Posted by Gerrelt

I've grown quite fond of the elefants feet rear taillights. They have a really nice functional look.
I only wished they were a bit better build.

+1 al kaholic...
I don't like the look of the new beetle style rear lights either.

[Wally]

Thanks for the link Gerrelt!.Think they are those.
Mystery solved!

Nice car Graham! I like some more ideas for backside front fender vents. I think you could make them so that the escaping 'high pressure' air adds a little in downforce.

[graham]

Nice car Graham! I like some more ideas for backside front fender vents. I think you could make them so that the escaping 'high pressure' air adds a little in downforce.[/QUOTE]

Thanks for that Wally it means a lot coming from someone who owns a car like yours.

I will try and upload some pics of my sketches to show the ideas

[judgie]

the aim is to get the air to flow quickly under the car, thus reduceing its presure. so as flat, leval and clean a underside as you can get will help. also deeper running boards to stop the air under the car spilling out at the sides.
the other option is to stop as much air as possable getting under the car but this can cause a lot of turbolance at the rear of the car creating a lot of drag.

[graham]

Originally Posted by judgie

the aim is to get the air to flow quickly under the car, thus reduceing its presure. so as flat, leval and clean a underside as you can get will help. also deeper running boards to stop the air under the car spilling out at the sides.
the other option is to stop as much air as possable getting under the car but this can cause a lot of turbolance at the rear of the car creating a lot of drag.

Thanks judgie I was trying to find time to call you today as I would like to talk to you about setting my cars suspension up properly, are you about tomorrow for a chin wag ?

[ricola]

Couple of aero basics for you:

To get downforce the rear exits would have to be channelled to point upwards, the downforce is a result of a reaction force.

The air over the top of the car would be detached from the surface way before the engine cover, typically at the top part of the rear window.

Downforce is mostly a result of STATIC pressure and the difference of this between top and bottom surfaces of a body. Target is to get higher pressure at the top surface which will result in overall DOWNforce. According to Bernoulli's equation: faster fluid flow results in lower static pressure. Using this, you want to get the air under the car flowing as fast as possible to get the static pressure as low as possible giving any increase in pressure over the body a chance to create the downforce.

[spannermanager]

Graham, well done so far, a very nice side step to the usual copy cat builds, but do you want all that venting on a road car? i have exactly that type of venting on my race car, but its not subtle. with a water cooled road car, why not work towards a diffusor and flat bottom it up to the bumper line? this was a factor in my water cooled engine choice, together with diminishing DB control thresholds at the races, i'm now 3/4 db quieter over aircooled with water cooling alone. you will need to move the lower shock mounts to make a worthwhile flat bottom workable, and the exhaust needs attention with any engine to get it out of the way. Just my view, but i think a road car, or a race car come to that, should be as understated as possible, its easy to get carried away and the KIS rule always applies. but well done so far anyway.

[judgie]

i'm in work next week so give me a call.
this is the sort of thing you wnat under the car

[Jadewombat]

Of all the aero. tricks I've tried so far, venting the fenders made the most difference I could feel right away. Took the car out on the highway the next day and it felt much more planted to the road than before. I used a punch and flare tool on mine to make the holes. The turbulent air of the spinning wheels causes the fenders to act like wings and give the car some 'lift' at speed. If you look at new(er) cars they have a fender liner to minimize this distance between the tires and the inside of the wheel well.



Made a cheapo. roof spoiler out of garden edging recently. Just couldn't bring myself to spend $200 on a little piece of carbon fiber strip. Seems to help, car scoots off the line a hair quicker, could be my imagination too as I'm not being very scientific here but it definitely doesn't feel likes it's creating any drag.

[Gerrelt]

I just found this interesting youtube vid & facebook item and thought I had to share it here.

See: Youtube video VW bug in a wind tunnel

And there was a poll on the face book page, see the top red box. The answer is in the bottom red box:


(click on it to get to the entire facebook page, I couldn't link directly to this item)

The beetle has 6% less drag when going backward.
I think it's because of attached flow staying attached to the rear window, which creates drag. Going backwards, there's nothing to attach to after the windscreen point. So the airflow can form itself like a teardrop.

[Wally]

Thats very interesting and sad at the same time. Shows us also here's a lot to gain with aero improvements.
We're probably on the right path Gerrelt

[Gerrelt]

Yep!!

[spannermanager]

Here is my underbody at its present stage. the rear ARB need moving to finalize the airflow, and is next for the chop saw, its going inside a tube running through the cars rear wheel boxes, bugs are hard work aero wise, the exhaust is particularly difficult to package away from everything in order to fit streamlining panels that wont be ripped off in the first race, my car already bottoms on the spring plate bolt heads and its not low enough yet, ideally the torsion tube needs raising and the horns chopping out.

[graham]

My car has been hibernating whilst I am waiting to finish a large building project before work begins again on it. I am still looking at the builds here and seeing peoples ideas and views.

Spanner, it's interesting that you mention raising the torsion tube and chopping out the frame horns .Thats got me thinking.

Part of the next stage of mods on my car will involve cutting the torsion tube in the centre and replacing the frame horns to aid the g50 gearbox fitment.Do you think raising the torsion tube or removing it completely may be worth considering whilst I am at it ????

What are peoples views/ideas on the best possible rear end set up to accommodate the g50 minus a torsion tube.I will be using one of Alex's uniball set up's.I am now thinking of a gearbox cradle/frame horn combo to tie into the cage and hold the uniball kit at the same time raising the top shock mounts.Here's the car as it is at the moment.[IMG]~original[/IMG]