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Old 09-08-2010, 07:04 PM   #2 (permalink)
aerohead
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Quote:
Originally Posted by dmac257 View Post
OK .. I have been looking for recommendations for placement of air dam, belly pan, side skirts, wheel spats, wheel boat tails with respect to ground height.

The only thing I found for air dam is "as low as the lowest under belly part .. or lower" However I have seen several vehicles with air dams almost touching the ground. Is there an ideal ground clearance as far as aerodynamics is concerned?

Belly Pans also nothing about an ideal height and I could not find anything about the contour of the pan itself (ie can it curve from the bottom of the door panel under the vehicle to the other side or is it better to be parallel to the road) .. but I found a suggestion that if full belly pan .. higher is better than lower.

If both air dam and belly pan the air dam doesn't need to go below the pan as everything behind the dam is smoothed by the pan?

Side skirts along the side between the front and rear wheel. Would these extend down below the center of the wheels and if so how far down? Also same question for front of wheel spats and behind wheel boat tails. Is the goal to part the air in front of the front wheel .. guide it past on both sides with the skirt to the rear wheel .. then recombine behind the rear wheel.

Would the ideal shape of the underside of the vehicle be a smooth tunnel parallel to the road that begins to rise up towards the rear bumper just before recombination behind rear end (small turbulant wake).

I am thinking to do as much as I can .. and would like to know how these all fit together for end product so I can plan how to proceed

Don
Don,The Society of Automotive Engineers have some minimum criteria for ground clearance for 'fixed' suspension cars.
Ahead of the front wheels they recommend nothing below a line projecting forwards and up at a 16-degree angle.
Behind the front tires and in front rear tires they say to respect a 10-degree angle.
And behind the car,also a 10-degree angle.
Anything hanging lower is at risk of being scrunched at the nearest driveway ramp.
Many states have laws forbidding any portion of the car to be below the bottom of the wheel rim bottom.If say,you made wheel fairings which were lower,the first pot-hole might rip them right off.
The belly pan should maintain the highest allowable ground clearance.
The diffuser portion at its rear will be determined by where it begins.
I will be able to tell you more about the airdam/bellpan question in a few weeks.On my Civic,even with a smooth belly,the car got better mpg with an airdam blocking air from underneath the car.All the lowest-drag,highest mpg concept cars block the underside even with perfect bellypans.
Side skirts should be even with the belly.
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