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Old 08-01-2008, 02:14 PM   #131 (permalink)
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vortex generation

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Originally Posted by 95badbird View Post
so what exactly is causing a vortex?
As the air moves rearward along the cap,the air atop, and aside the cap are moving at different velocities, and at different pressures,mingling only at the top intersection,and held in place by the positive pressure gradient ahead of,and around the truck.When the air reaches the back,there's no longer any surface left to support the flow,and pressure differential will cause the slower,higher pressure side- flow,to head for the faster,lower pressure top- flow,spiraling into the vortex as the two dissimilar flow fields attempt to mingle and blend.------------------------------------ From Hucho's research at Volkswagen, a backlite angle of 28-degrees produces the most violent vortex,and this kinetic energy of the "spin" cannot be converted back to static pressure,for perhaps hundreds of feet behind the vehicle,where viscous attrition from colliding with surrounding air,finally brings the vortex to rest.I think this is what MetroMPG and Bicycle Bob are referring to.-------------------------------- 28-degrees is big trouble!

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Old 08-01-2008, 04:15 PM   #132 (permalink)
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Quote:
Originally Posted by aerohead View Post
As the air moves rearward along the cap,the air atop, and aside the cap are moving at different velocities, and at different pressures,mingling only at the top intersection,and held in place by the positive pressure gradient ahead of,and around the truck.When the air reaches the back,there's no longer any surface left to support the flow,and pressure differential will cause the slower,higher pressure side- flow,to head for the faster,lower pressure top- flow,spiraling into the vortex as the two dissimilar flow fields attempt to mingle and blend.------------------------------------ From Hucho's research at Volkswagen, a backlite angle of 28-degrees produces the most violent vortex,and this kinetic energy of the "spin" cannot be converted back to static pressure,for perhaps hundreds of feet behind the vehicle,where viscous attrition from colliding with surrounding air,finally brings the vortex to rest.I think this is what MetroMPG and Bicycle Bob are referring to.-------------------------------- 28-degrees is big trouble!
so, is what I have hurting me more than an open bed?
or worse then a tanuea cover?
or a regular camper shell?

I have gone from 13 mpg to 17 just changing my driving habbits.


I'm guessing this vortex is bad.
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Old 08-01-2008, 05:34 PM   #133 (permalink)
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You'd have to conduct back-to-back tests,with and without the cap to really isolate it's performance.I can't imagine that it would "hurt" your highway economy.I think the consensus is that its less than ideal,but still way out ahead of nothing.I'd keep it.Shooting from the hip,I'd say its good for 5% mpg gain.
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Old 08-01-2008, 05:39 PM   #134 (permalink)
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A flat tonneau would be better. When used a flat tonneau, it was good for 1.5 MPG over the open bed with tail gate up.
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Old 08-18-2008, 05:32 AM   #135 (permalink)
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I stumbled on this thread from another site. I noticed that no one has posted since the 1st of Aug. Where is everyone? Bondo, are you still out there making it happen?
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Old 08-27-2008, 08:44 AM   #136 (permalink)
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I realize that this thread is dead or dying, but I just returned from a trip to Italy. When there, I saw a Nissan Navara pickup truck with a hard bed cap on it that looked unbelievable to the one that bondo made for the F150. It looked like this.




In all, I saw 3 of the pickups and all had the bed cap on it. There is a cap like the one shown that is available through Nissan that cost 2.614,80!!!!! But there are other makers of the hard caps like the one above that look the same. Do a google images search on Nissan Navara Hard Top and you will see all the suppliers of the cap.
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Old 08-27-2008, 04:05 PM   #137 (permalink)
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Oh, torr, I wish you hadn't posted that. I have a Frontier that REALLY needs that cap now! I was going to build one over the winter, but have decided to do an electric car instead, and having a pre-fab cap would have been great.

Emailed the mfgr about North American distributors...
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Old 08-27-2008, 09:22 PM   #138 (permalink)
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wow, that thing flows with the truck like crazy!!!! mite be a factory option?
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Old 08-28-2008, 02:52 PM   #139 (permalink)
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Quote:
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wow, that thing flows with the truck like crazy!!!! mite be a factory option?
If I would get off my butt, and take some pics of my setup, you would think mine is a factory piece...
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Old 08-29-2008, 02:12 AM   #140 (permalink)
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95badbird- Do you have any recent pics of your set up? other than the one you posted on
7-29-2008.

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