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Old 07-10-2012, 10:01 AM   #4 (permalink)
Big Dave
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Join Date: Jan 2008
Location: Steppes of Central Indiana
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The Red Baron - '00 Ford F-350 XLT
90 day: 27.99 mpg (US)

Impala Phase Zero - '96 Chevrolet Impala SS
90 day: 21.03 mpg (US)
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Re: "...I liked that old idea you had of a Pontiac Trans Am rear window louver set..."

Big Dave says:
That was one of the things Phil & I burned some brain cells on. Porsche and Lamborghini - cars built for top speed where aerodynamic drag is a big limiting factor) use a 'stair-step" louver for cleaning up their rear windows. Those windows are small so they cannot tolerate much blocking the vision out or the driver goes blind to the rear.

I used to have a Z-28 with those louvers, but they were of equal length and paralleled the read window.

What Phil & I discussed was a set of louvers of unequal lengths set so their rear edges described the Hucho curve. For my truck (cab top is 24 inches above the top rail of the bed and the bed is 80 inches long) to very rearmost louver trailing edge should be about 8 inches above the top of the bed rail to approximate the Hucho curve. By putting three louvers on it, I get four 4 inch "steps," but they may not be equal due to the non-linearity of the Hucho curve.

I wonder what the optimum number and spacing of "steps" would be. Bondo's gold standard aerocap essentially is an infinite number of steps with an infinitesimal spacing. That's one extreme. My flat tonneau is one step of 24 inches. That's the other extreme.

A pickup may be the hardest thing to design and test for because flexibility is the very soul of the pickup truck. The utilization scenarios are numerous to say the least. Passengers, bed load and trailers all muddy the MPG waters.
2000 Ford F-350 SC 4x2 6 Speed Manual
4" Slam
3.08:1 gears and Gear Vendor Overdrive
Rubber Conveyor Belt Air Dam
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