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Old 09-22-2018, 12:46 PM   #5 (permalink)
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cab wing

Originally Posted by hat_man View Post
Hello again everyone.

I am enjoying reading my new book (Aerodynamics of Road Vehicles) and found the chart we have all seen on the aerodynamics of pickup trucks. I currently have a Ford Ranger with a soft full tonneau. According to the chart, there is a large gain (reduction in drag) to be had from adding a cab spoiler/wing as long as it attempts to fit the template. It only shows this with a half tonneau.

Does a spoiler/wing work just as well with a full tonneau (and didn't need to be drawn on the chart) or is the half tonneau the only want to see that amount of drag reduction? How does the extra cavity behind the cab from a half tonneau affect air flow as opposed to a full tonneau? Does it draw the flow downward to more approximate the template?

I would like to keep my full soft tonneau as it comes in rather handy and it's much better than the open bed.

The other question I have is regarding the type of spoiler/wing on the chart and how it may compare to something like a full aero cap cut in half. Something like this but shaped to better fit the template. For me it would allow better rearward visibility without having to engineer a weatherproof window to keep things dry. And if designed right I could still keep my soft tonneau.
In the original 1988 SAE Paper by Texas Tech,they listed the lowest drag lengths and angles for the cab-wing,depending on whether the truck was a short bed or long bed.
And to my knowledge,they were only tested with the half-tonneau.
I believe that this data is in the 'Seminars' on page-1 of the aero forum.
The theory behind the 1/2 cover,is that the low pressure from the swirling core of the vortex captured by the 1/2 cover,is communicated under the cover to the inner face of the tailgate,creating a high pressure differential across the gate,giving a forward 'thrust' if you will.
As to half of an aeroshell,AeroStealth and I tested a half-tonneau with the last half of an aeroshell installed on top,and realized an 8% improvement in HWY mpg.
We never tested the 'forward' half.
You might cobble something together with cardboard and duct tape,strong enough for testing.If you like the result,then make a permanent version.
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