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  #251  
Old 11-10-2019, 11:03 PM
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Yeah - Ok I got it now...

I thinks the challenge; "... lies not in our stars, but in our "cars"..." Sorry Shakespeare

The car presents itself as an analog of a wing. So getting a high pressure over the top of the car would take some real doing. Consider the following comparison:


A vert may have more potential downforce over the center of the body - due to turbulent flow -- maybe not.

Hopefully the image shows how the shape acts like a wing and creates low pressure on the upper surface -- just like a wing.

The question might be changed from; "How do I create higher pressure on the top of the car", to; "How do I get lower pressure underneath?" It is really about the differential in pressure.

The underbody offers many "unseen" opportunities to create a low pressure area(s) and place it where you want - center of the body. You'll give up some ride height - maybe - but it would be unobtrusive and should be consistent throughout a speed range. That is to say - no pitching moments as you accelerate/slow down.

Your Pace Car style front spoiler should offer some help in the corners you mention. Additional drag through "Active Aero" would also play well for braking - but not all racing associations permit these.

Hope that info is useful.

Cheers - Jim
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Last edited by phantomjock; 11-10-2019 at 11:44 PM..
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  #252  
Old 11-11-2019, 01:00 AM
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Make new rocker moldings out of thin aluminum which are 1 to 2 inches longer. This will act as side skirts keeping flow out from underneath. Lower is always better for side skirts.

Creative use of black paint could disguise how low they are.

Also, the spare tire area is a mess, a diffuser would be too obvious for your goal, at least a smooth under belly would help.

Last edited by rtj; 11-11-2019 at 01:02 AM..
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  #253  
Old 11-11-2019, 09:48 PM
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Quote:
Originally Posted by rtj View Post
Make new rocker moldings out of thin aluminum which are 1 to 2 inches longer. This will act as side skirts keeping flow out from underneath. Lower is always better for side skirts.

Creative use of black paint could disguise how low they are.

Also, the spare tire area is a mess, a diffuser would be too obvious for your goal, at least a smooth under belly would help.
We're on similar wavelengths here. Several years ago I pulled the stock rocker panels off and made 2" lower/wider replacements with Lexan sheet, and painted them semi-gloss black. I like the looks better, and so far no one has seemed to notice the change.

I had an aluminum bellypan on the car for a year or two, but my unscientific perception of the setup convinced me that the weight (about 30#) was hurting me more than any actual aero improvement was helping.

I've also looked into doing something at the rear, but so far I can't justify the weight of a diffuser. My current direction is to reduce the slight understeer I have, and ignore the rear until it becomes the limiting factor during cornering.
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  #254  
Old 11-11-2019, 10:08 PM
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Quote:
Originally Posted by phantomjock View Post
Yeah - Ok I got it now...

I thinks the challenge; "... lies not in our stars, but in our "cars"..." Sorry Shakespeare

The car presents itself as an analog of a wing. So getting a high pressure over the top of the car would take some real doing. Consider the following comparison:


A vert may have more potential downforce over the center of the body - due to turbulent flow -- maybe not.

Hopefully the image shows how the shape acts like a wing and creates low pressure on the upper surface -- just like a wing.

The question might be changed from; "How do I create higher pressure on the top of the car", to; "How do I get lower pressure underneath?" It is really about the differential in pressure.

The underbody offers many "unseen" opportunities to create a low pressure area(s) and place it where you want - center of the body. You'll give up some ride height - maybe - but it would be unobtrusive and should be consistent throughout a speed range. That is to say - no pitching moments as you accelerate/slow down.

Your Pace Car style front spoiler should offer some help in the corners you mention. Additional drag through "Active Aero" would also play well for braking - but not all racing associations permit these.

Hope that info is useful.

Cheers - Jim
My reason for trying some aero mods at the cowl area is that it is the only spot on the upper bodywork that is shaped correctly to cause downforce/drag. Pretty much most all the rest of the forward section of a C3 is shaped to cause lift.

In addition to the PC spoiler, I've got a bellypan under it (the PC spoiler), extending back for a few feet, to reduce lift. I'm going to put a 2" air dam at the front of the spoiler to further reduce the air flow going under the car. I've also got most of the front grillwork blocked off to reduce the airflow into the engine compartment. I've also got some horizontal aluminum sheets at the bottom of the firewall area to block air trying to leave the engine compartment and going under the car. I'm trying to persuade the air to instead go out the side louvers.
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  #255  
Old 11-12-2019, 10:43 PM
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Well, keeping it looking stock makes it tough.

Convertibles supposedly have lower drag coefficient. But, that wonít help.

Maybe try messing with how the t-tops fit. Could throw a couple of layers or duct tape across the front lip of the t-tops and see if that helps at high speed.

Lower is better for skirts and spoilers. There is vinyl wall molding (floor molding) that holds up pretty good and is cheap. Hardware stores sell it in rolls, pretty wide too.
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  #256  
Old 11-13-2019, 02:20 AM
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I have been developing an interest in using surface roughness in lieu of vortex generators. It might make an interesting thesis for an up and coming student that had access to some "tunnel time." I found a study using both surface roughness and VGs on wind turbine blades. They found a decrease the lift coefficient by about 20% using surface roughness on the leading edge of the airfoil. You could sort of replicate that by using long strips of sandpaper attached with double stick tape to the hood. I think you'd want to first have some tuft studies to see if you are really tripping the airflow. The nice part you could move the "device" to get the result (if any) where you want it. Unfortunately, you'd be relying on the "Butt-Dyno" for comparative analysis. Naturally that wouldn't be really unobtrusive at first, but could maybe use some truck bed paint/liner to get the same effect.

This all goes back to a NASCAR legend when (Team Penske and Mark Donahue - as I recall in their Camaro) added a vinyl top to the car. They got a noticeable advantage, and later forced to remove it. There was some discussion at the time as to was it really an airflow device - or just hiding a lower weight roof section.

Skirts and some underbody shaping could also make useful improvements.


Cheers - Jim
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