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Old 01-16-2011, 04:29 PM   #503 (permalink)
basjoos
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Join Date: Dec 2007
Location: Upstate SC
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Aerocivic - '92 Honda Civic CX
Last 3: 70.54 mpg (US)

AerocivicLB - '92 Honda Civic CX
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The boundary layer doesn't have a distinct demarcation line to it, but is a velocity gradient that becomes thinner with increasing speed. The air down right next to surface (where the loose sand grains would lie) has zero velocity relative to the surface. As you get farther from the surface you encounter faster moving air until at the edge of the boundary layer the air is moving at the velocity of the vehicle. At lower speeds (30 mph) the boundary layer can be up to 1/8" thick, but it gets thinner as the airspeed increases. Those sand grains would be blown off at 130 mph and at 250mph you would want to have a wax smooth surface for minimum drag. Yarn tufts work because the tufts stick up high enough into the moving air to be influenced by it even if they are still partially within the boundary layer at low speed. If you tufted using fine nylon thread you would not see them streaming with the air flow until you reached a much higher air speed than with the much thicker yarn.

The Lexan fogs up about as easily as glass. You can't use Rain-ex on it, but rather one of the Lexan compatible defoggers that Motorcylists use such as Rain Magic.

The two vents at the back of the cabin exit into the small low pressure pocket produced at the back of my boat tail (because it ends in a flat area with the license plate instead of a point). This low pressure exhausts air from the back of my cabin.
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