I'm not trying to argue so please don't take offense, but I'm not trying to fill out the template. Like I said, we all know that the template is the Holy Grail but that's not what I'm after. What I am trying to learn about is relating to this from Aerohead:
Quote:
Originally Posted by aerohead
*Without the tonneau cover,there's nothing but turbulence back there.All the kinetic energy is lost forever,and there's no chance for any re-attachment.A lot of drag and a lot of lift.
*The tonneau provides a surface of re-attachment for the separated flow,allowing for a much smaller wake,and it kills most of the rear lift.
*The half-tonneau is a peculiar animal.It allows a locked-vortex to be captured behind the rearward facing step of the cab.
*The inviscid (streamline flow) follows over the vortex as if it were more a solid body,strikes the tail end's upper surface,really killing lift.
*The extremely low pressure of the 'eye' of the vortex is transferred to the inner face of the tailgate.This inner face is at a lower pressure than behind the gate,creating a pressure differential which 'pushes' the gate forwards,something which doesn't happen with a full tonneau.....
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What I was curious about was how the "extremely low pressure eye of the vortex" being transferred to the inner face of the tailgate is affected by the size of the area (volume) of the space under the cover.
Let's throw some numbers at it. If I cover the back half of a 6' bed of a Ranger it makes a covered area of about 19 sq. ft. that is open to the front portion of the bed. Air moving at 55 mph over the cab creates a low pressure vortex behind the cab that is transferred to the inner face of the tail gate. Let's quantify this pressure as (X). This would be like the red cover without the Ridgeline rails.
If the Ridgeline rails were added and the red cover was used again at the same 55 mph, the only difference I can see is that some of the air flow over the cab might be slightly "captured" and better directed over the half cover rather than being allowed to freely spill outwards like it would with the red cover and NO rails. Unless (?) the air flowing down the sides of the truck (doors and bedsides) creates a barrier that keeps the air flowing over the cab from spilling outwards. That I don't know. The question in this instance is....Is this new pressure (Y) with the red cover and Ridgeline rails greater than/less than/or equal to pressure (X) with the red cover and no rails? I'm thinking maybe greater than, but only very slightly.
The other question would concern the yellow cover. If you added the Ridgeline rails to a Ranger and used the yellow cover (on top of the Ridgeline rails which are slightly sloped) it would create an area of about 24 sq. ft. under the cover yet still open to the front portion of the bed. Nearly 5 sq. ft. larger than the red cover area. So the same 55 mph now creates a low pressure vortex behind the cab that interacts with a larger volume of air to create a new pressure at the tailgate we could call (Z) Given the same low pressure vortex and the new larger volume of air, is (Z) greater than/less than/or equal to (X)?
I wasn't worried about filling out the template so much, and maybe it was a little misleading me mentioning it in relation to the Ridgeline rails. In my mind I was seeing the sloped rails creating a sloped cover that might be more beneficial than the flat red cover on the plain Ranger bed.