Pickup truck aerodynamics

[freebeard]

kach22i -- When the white pickup passes it's just like the ending of the movie Vanishing Point.

I think the half-tonneau question is explained by this, the augmented coanda nozzle:



The cavity is about as long as it is tall, and contains a bubble of air about the size of a hay bale that is spinning. If the bottom was half-rounded instead of filled with batteries or whatever it would be optimized.

Edit: Xist -- Possibly Twerks=T-100. Compound curved?

[aerohead]

I think it was Sport Truck Magazine that interviewed the industry aero gurus around early 90s.
The operation of the 1/2-tonneau was explained as :
*the low pressure of the locked-vortex is telegraphed under the cover to the inner face of the tailgate.
*The delta-P across the gate is more favorable than with a closed,100% tonneau.
*It's this delta-P which gives the aero advantage.
*it's half the weight
*it allows access into the bed

[freebeard]

The would be an interesting test for someone with a pickup truck:
• No mid-wall
• Flat mid-wall
• Curved mid-wall

[aerohead]

Originally Posted by freebeard

The would be an interesting test for someone with a pickup truck:
• No mid-wall
• Flat mid-wall
• Curved mid-wall

Anyone with an OBD-II pickup could do a set of quick and dirty back-to-back runs and establish an MPG pattern with the three configurations.Volunteers?

[slowmover]

Somewhere on this forum is the comment that a half-tonneau bed cover "equalizes" the pressure fore & aft of the tailgate.

[craveman85]

I'm tempted to screw a piece of plywood to my truck bed now. I wonder how much bed length has to do with the CD measurements. Is an 8' optimal over a 6'? I'm assuming the longer the better ( at least with bullets longer heavier bullets have a higher ballistic coefficient or CD).

[craveman85]

What's the mid wall? From the front half of the tonneau to the bed? What if its left open there?

[aerohead]

Originally Posted by craveman85

I'm tempted to screw a piece of plywood to my truck bed now. I wonder how much bed length has to do with the CD measurements. Is an 8' optimal over a 6'? I'm assuming the longer the better ( at least with bullets longer heavier bullets have a higher ballistic coefficient or CD).

The longer bed provides the (rearwards facing step) geometry which better supports flow re-attachment and vortex capture without reversed flow entering from behind.

[aerohead]

Originally Posted by craveman85

What's the mid wall? From the front half of the tonneau to the bed? What if its left open there?

The mid wall is as you imagine,projecting down to the box floor from the front edge of the 1/2-tonneau.
The patent reflects a free opening underneath to the inner gate face.It's performance is predicated upon this feature.
Someone has done a CFD analysis with the mid wall.It's posted somewhere at this forum.Don't know where.

[Oceanic815]

Details of the half-tonneau patent:Analytics for US Patent No. 4,573,730, Drag reducing partial tonneau for pickup truck by Gondert, Theodore R;MacDonald, Richard A