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dumb aero question

 
Old 03-17-2008, 11:56 PM
  #16  
C.J. Ichiban
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an aside from my ghetto aero theory: the more front-end downforce you can generate should help your turn-in a bit, since it's pushing down the front end. Any increase of rear wing/ rear downforce surely stabilizes you at higher speeds...also, the downforce generated from the front end takes effect at lower speeds than rear end downforce.

as far as the "boat" shaped front end...you mean like the Ford GT?

sunday driver- how many sections on your car can you calculate downforce for? I've always wondered that.
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Old 03-18-2008, 12:46 AM
  #17  
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Originally Posted by JackOlsen View Post
Yes. You'll see benefits up to about 5 inches.
Don't most sanctioning bodies require the splitter to stay withing the boundaries of the body, or very close to it? A 5" splitter looks like it would stick out 4+" on that car. Plus, it looks like a splitter like shape is built in to the bumper.
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Old 03-18-2008, 12:47 AM
  #18  
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good observation and take on the situation.

In fact, there are "bottomless" wings, proving the importance of the topside of a wing, (airplane) compared to the bottom, that can be totally open! the drag effects are not as desirable as the closed bottom versions, (nor is the strength), but it shows that the lift is provided by the increased air flow on top vs the bottom, creating the lower pressure zone, where the lower pressure bottom end, now pushes the wing upwards.

Mk

Originally Posted by stownsen914 View Post
Mark,

I'll have to dig out my Joseph Katz racecar aero book, but I am quite sure that he addresses how cars with "dirty" undersides (basically anything other than a flat-bottom) cause slowing of air that passes under the car. Granted, the car is moving, not the air, so let's just think of it as movement of air relative to the car. This is compared to, say, air passing over the top of the car, which does not slow all that much over most newer Porsches, anyway, since they are well-designed aerodynamically. So a car travelling at 100 mph would have air flowing over the top at something close to that speed relative to the car, while the air underneath the car would travel at somewhat lower speed relative to the car. Essentially some of the air under the car is getting dragged along for the ride by all the little protrusions under the car. In summary, the slowing of the air under a non-flat-bottomed car can have a tendency to create drag and (I thought) some meaurable lift.

You are certainly correct that most aero lift on a car comes from the shape of the topside of the car. Getting rid of any drag and/or lift caused by dirty airflow under a car is desirable, but arguably would not have as much impact as having good flow over the topside of the car (possibly one of the reasons most manufacturers emphasize topside aero and largely ignore underside aero).

Scott
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Old 03-18-2008, 12:56 AM
  #19  
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all that work for a nice new bumper and all the air that hits it will just roll off the front, and go under the car. you could cut big holes in it and route the air through the front hood, about mid way! Otherwise, the spitter will guide the air around the sides to reduce lift. with a 911 light front end, this becomes a way to help the pushy handling. it doesnt take much to help handling in the medium to fast speed corners, and surprisingly enough, many of the club guys are doing a lot of this!

mk

Originally Posted by kurt M View Post
Just an internet opinion but I would as there is little down side to it. You are already have a blunt faced air dam and pay for it with increased drag. You might as well keep more air from under the car and produce some down force to boot.
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Old 03-18-2008, 08:38 AM
  #20  
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Originally Posted by C.J. Ichiban View Post
sunday driver- how many sections on your car can you calculate downforce for? I've always wondered that.
I measure downforce through math channels based on ride height. By smoothing the ride height, any changes from static height down the straights are due to downforce (except where you get a hill). So I get front downforce, rear downforce, total downforce and the location of the center of pressure. You can clearly see the effect of a degree change on the wing, changing dive planes, etc. Not as good as using strain gauges, but it is good enough for my use.
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Old 03-18-2008, 11:10 AM
  #21  
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I'll probably mount something in front of the cooler face and blend it into the brake ducting area to channel air onto the lower portion of the bumper and around the car. Thinking about it more, I don't think I need a full width splitter with this bumper.
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Old 03-18-2008, 11:46 AM
  #22  
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Originally Posted by chrisp View Post
Would you add a splitter to this front bumper?
NO!
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Old 03-18-2008, 11:56 AM
  #23  
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Originally Posted by JackOlsen View Post
Smoothing out the underbelly of my car with a sheet of ABS plastic made a noticeable difference in my laptimes.
Jack, would you have some pictures of this you could post? I would also be interested to hear how you mounted the sheets and the thickness used. I have a 951 that I am having a hard time finding stock engine trays for and have been considering fabricating something like this up.
Thanks.
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Old 03-18-2008, 11:57 AM
  #24  
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Fred, why not?
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Old 03-18-2008, 12:02 PM
  #25  
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Originally Posted by constaf View Post
NO!
Why not? I would mount a single piece splitter that extends out a few inches and back as far as the rules allow (which is the centerline of the front axle in BMW CCA racing). I would do the same thing on your car as well to help prevent all of the air below the silver portion of your bumper from dumping under your car and under your front tires. There's almost no downside if the rules allow it.
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Old 03-18-2008, 02:38 PM
  #26  
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"NO!" was potentially too strong an answer. Let me just say that it will not improve the handling or performance of the car. The upside of putting it on is negated by the downside of putting it on. My 85 Carrera with Ruf bumper had one and my current car does not. Doesn't make a difference. Besides, your front bumper already has a built in splitter of sort. And I am a fan of drag reduction as you can tell by the tape that I put on the hood of my car... Lastly, need I see more than Mark Hupfer does not wear one... ?

my 2 cents.
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Old 03-18-2008, 02:44 PM
  #27  
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That car definitely has proven itself to not need one that's for sure! I may bolt something up just to test the idea. I'm probably not fast enough to really tell though.
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Old 03-18-2008, 02:47 PM
  #28  
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While we're talking about all things aero has anyone tried those louvers you see over the front wheels of many race cars?

Do you then take out the plastic wheel well?

Does it only help if you're doing 150+??

Inquiring minds want to know...
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Old 03-18-2008, 02:49 PM
  #29  
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Originally Posted by chrisp View Post
I'm probably not fast enough to really tell though.
It is not you, it is the car. I spoke about this very subject of D/E stock SC airflow optimization with Mark Hupfer at Road America last Fall. I am a big fan of his. He dreams up the slightest adjustments to make our cars go faster... he is all about drag reduction. And if you have not raced with him, let me say that he is in a class of his own when you consider SCs.
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Old 03-18-2008, 03:07 PM
  #30  
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Originally Posted by smlporsche View Post
While we're talking about all things aero has anyone tried those louvers you see over the front wheels of many race cars?

Do you then take out the plastic wheel well?

Does it only help if you're doing 150+??

Inquiring minds want to know...
I can only imagine Ray Newman's (PCA scrutineer) face when I show up with my louvered front fenders.
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