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  #166  
Old September 23rd 2011, 22:53
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Hi

Very good results, I wonder if anybody with a roof type deflector could do a test, its very clear from your test that the tufts get sucked down without the spoiler so that part of the test wouldn't need to be repeated.

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  #167  
Old October 12th 2011, 11:47
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Originally Posted by Humble View Post
I think everyone's seen my aero by now, hard to miss...



Large vents in the front fenders seem to help a bit but I won't know for sure until I take it to a race track. The rear wing is almost necessary above 120, and can be felt as low as 50-60mph. I've also trimmed up the rear fenders to help them air out a bit as well.
How did you decide to put the vents there, vs. like along the rear near the bottom of the fender, or the middle or ? Just wondering if you did some pressure readings in the fender beforehand or if this is a known trapped area of air along the inside near where the fender bolts to the body.

I ordered a punch and flare tool to do some holes on the fenders on my bug (autocross car).
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  #168  
Old October 14th 2011, 12:08
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Also, has anyone considered doing a mod. like this to the front hood? A lot of the 911 guys do it to vent the oil cooler up front up through the hood as well as create more downforce on the front end. I see this on Nobles and some other cars as well. Not quite sure how it works though, creates an air pocket to disrupt the high pressure zone on the front half of the hood vs. low pressure on the back half?

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  #169  
Old October 14th 2011, 14:11
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I think its a great idea, but maybe less practicle to realise on a Vee-dub body-wise?
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  #170  
Old October 14th 2011, 20:22
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Did some testing with the car just a little while ago. No one could help me film the outside of the car so I just stuck my arm out the window to video the left front part of the car. This is all in anticipation of drilling some holes along the back of the fender. So, thoughts?






Where should I drill the holes, would it help aero flow or not matter? This racer from a few pages ago has holes along the bottom back of the front fenders. I also plan on running some fender flares to match the fender edge with the tires better.

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  #171  
Old October 15th 2011, 03:10
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Great testing! Kudo's to you!

I would make some vertical slots in the front fenders as near to the body as possible. Might do some to mine.
The overpressure on the inside of the fenders will not show with the wool on the outside though. Still, you'd think that the flared fenders will grab more air then original ones.
For some reason my car seems to have huge drag at speed. Part might be the air grabbing fenders (and wide tires) is my reasoning.
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  #172  
Old October 15th 2011, 07:32
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Nice test work Jadewombat!

Like Wally said, you're talking about two different things. Your tests show how the aiflow is over the fender.
The slots in de fenders are for relieving air "pressure" in the wheel wells.

BTW, the airflow shouldn't be attached all the way to the bottom of the fender. Turbulence behind the fender is good, that means the airflow is de-attached from the fender. The angle of the rear of the fender is too steap for good airflow.

I think you could improve the aerodynamics of your beetle by installing wheels that fall inside the fender. Or install wider fenders. Your wheels stick out a couple of cm's, that can't be good for aerodynamics.

Again, nice work on the wool tuft test! I hope more people do this!
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  #173  
Old October 15th 2011, 16:47
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Are you using running boards? If not try them.

Otherwise the air flow as it passes under the rear edge of the wing might create a turbulent area as seen in the photos. Also the wheels out in the air flow also tends to create turbulence and drag.
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  #174  
Old October 15th 2011, 22:06
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Will try both of those things, thanks. Also been experimenting with a CF cover I fitted to the front underside with quick release pins, mounted just in front of the sway bar where the factory A/C would be normally. Did some tests on it yesterday with and without. Definitely some change but I need to do more tests moving the tube to the top of the bulkhead to see what through the vents and over the cover.

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  #175  
Old October 16th 2011, 02:19
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Jadewombat

What do you think about this solution? Beautiful, but it works?

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  #176  
Old October 16th 2011, 03:50
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I think ^^ would work about just as well: air from the fender lip get guided out the holes thtough the side openings of the holes, but rain and mud from the tires is still held off. Very subtle!
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  #177  
Old October 17th 2011, 09:00
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Looks great, thanks for the photo. Great idea.
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  #178  
Old October 18th 2011, 08:09
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Quote:
Originally Posted by Jadewombat View Post
Also, has anyone considered doing a mod. like this to the front hood? A lot of the 911 guys do it to vent the oil cooler up front up through the hood as well as create more downforce on the front end. I see this on Nobles and some other cars as well. Not quite sure how it works though, creates an air pocket to disrupt the high pressure zone on the front half of the hood vs. low pressure on the back half?

The Clan Crusader is often modified with this type of duct but it has an adverse effect in that the downfoce at the front is excessive and although the rear is designed for downforce and Kamm rear the imbalance is noticeable and thus ought to have a full rear wing, that in some instances the rules will not allow.
As Wally says the bugs bodyshape doesn't lend itself to this kind of ducting. To get it to fit would result in the outlet being close to the high pressure area at the base of the windscreen reducing the effectiveness of the duct and causing turbulance that will disrupt wiper and vent function. Given this it would seem better to vent the cooler into the wheel arch (fender) and then vent this away down the side of the car. Holes at the base of the arch or better still a louvre section onto the top would create suction to assist.

Clive
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  #179  
Old October 18th 2011, 12:16
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Would this excessive downforce from ducting the front end and the inverted scoop create more drag? That's one thing I can't afford to add a lot on my car, I don't have a lot of hp. I think I understand the theory of it though, the air passing up through the middle or bottom of the front end passes up and over the hood essentially grabbing the front end pushing it down more. Pretty common now on cars with radiators or external oil coolers:



Another thought about running boards, because the bottom side of VW running boards is curved (like the inside of a fender), doesn't this create a vortex in this space for the air to swirl around in and create more lift of the whole car? Meaning, you want as much of the bottomside of the car as flat as possible like the pan, correct? After looking at this highly modified autocross Elise, it looks this gradual taper along the side they have with the fender edges smoothed to the doors work pretty well if applied to a bug:



Those flaps along the back of the front fenders have got me curious as well. A picture of my car attached. Thinking maybe I could do something similar to this Elise, smooth out the area where the running boards would normally attach to the car (circled in purple) so it's flush with the door lines and some small strips of material to smooth out the transition between the fender corners and the pan (circled in red).
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  #180  
Old October 18th 2011, 14:05
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Regarding my front fenders, I kept the wholes large and close to the body to fill the void behind the fender. The fender is curved like the body and is is a high pressure area, both good cause for lift. After venting the front fenders I had to add a little more angle on the rear wing for high speed cornering stability. If I did it again I would (and still might) create a larger vent, same vertical size but a little wider and closer to the body.

For the running boards, I've mentioned somewhere before creating a wedge shape much like the ones on the Jeffery's race bug. Sizing them right takes some work and you can be more aggressive on a track car vs. a street car, but ideally they should be as close to the road as possible. Its common practice to use sheet metal or fiberglass moldings and rivet a rubber curtain to it.
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