The upper yellow line, and lower red line in your last image is a bit of a distraction in my opinion.
Just compare top of bed to bottom of bed and keep things simple.
Splitting hairs or doing something half-way serves no purpose.
Quote:
Originally Posted by hat_man
Also, if you put it at the level of the red line does this create an area above the tonneau that helps direct air flow rearward and keeps it from spilling out randomly over the sides?
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I will comment on the mid-position (red line) in passing, I suspect the little bit of the tailgate sticking up would act as a Gurney flap / Wickerbill. This could produce a tube-like vortex of swirling air that may pull airflow over it and lower drag while providing a little down-force........... as the rear spoiler on my pickup truck does (
link in signature below). Mind you that your bed has to be long enough, and the top edge high enough to fill out the Aero-Template or close enough to start talking about air-flow.
I have not tested this next theory, but would like to one day.
I suspect the cab sail panels do more than a roof wing. The Texas U diagram did not test cab side sail panels as I recall.
The reason for this theory is after having watched many wind-tunnel videos, it looks to me that if the smoke wand in front is even a little bit left or right of dead center the smoke air flow veers off to the sides by rolling diagonally across the windshield then travels along the sides of the vehicle.
My conclusion; more air is flowing off to the sides than up and over the top.
What if anything does this say about "air pressure"?
There is higher velocity air traveling a longer path over the centerline top of the vehicle as in an airplane wing - causing lift.
Higher velocity air has lower pressure than slower moving air.
There is lower pressure at the sides therefore the airflow meanders in that direction in an attempt to equalize.
The air does not want to be accelerated at all, it takes energy to do this, so it will always attempt to be restored to a resting state.
I know what you are probably thinking, that none of this air is actually moving, it is the vehicle that is moving. I know, I know, I just cannot get my brain to work at that advanced level - I've tried, I'm just too stupid and untrained.
