Pickup truck aerodynamics

[PaulB2]

This differential has been attributed to some of the drag reduction which is not present when a bulkhead is placed between the gate and leading edge of the tonneau.

Who says it is not present? Even assuming the drag goes up (how much?) with a bulkhead, that might be the effect of other things, such as the shape the vortex is forced into assuming. With another truck, with different height and width of the box and shape of the wing, a bulkhead might make the drag go down. From my reading so far I get the impression this bulkhead effect is not a settled thing.

Let's imagine a sealed box was bolted to the front surface of the tailgate. If there was a pressure differential without it, then there must be one with it. It doesn't matter what pressure is inside the box, since it is sealed.

If it is not sealed, then the low pressure in front of the box is simply translated through the box to the front of the tailgate.

Indeed, the tailgate is itself a box. It has a front and rear surface.

Personally I don't buy this pressure differential doing anything, since it has the reverse effect at the front of the pickup box. Instead I think what happens is that the vortex simply transfers (more or less efficiently, depending on configuration) the air over the opening to the half-tonneau. Your adding the blister just helped this along by providing a surface for the airflow to easily attach to.

I'm getting the impression nobody has tried to give the vortex a cylindrical space to rotate in.

[aerohead]

Originally Posted by TheTestPilot

That poses the question of, what are the results of tailgate down or removed with a hard tonneau.
I would like to try this but my 4y hilux ate no. 4 sparkplug at 556000kms , I think it's dead.
Alas poor Hilux.

Member,Sepp,in Belgium,reported that he experienced lower performance when the gate was removed.

[aerohead]

Originally Posted by PaulB2

Who says it is not present? Even assuming the drag goes up (how much?) with a bulkhead, that might be the effect of other things, such as the shape the vortex is forced into assuming. With another truck, with different height and width of the box and shape of the wing, a bulkhead might make the drag go down. From my reading so far I get the impression this bulkhead effect is not a settled thing.

Let's imagine a sealed box was bolted to the front surface of the tailgate. If there was a pressure differential without it, then there must be one with it. It doesn't matter what pressure is inside the box, since it is sealed.

If it is not sealed, then the low pressure in front of the box is simply translated through the box to the front of the tailgate.

Indeed, the tailgate is itself a box. It has a front and rear surface.

Personally I don't buy this pressure differential doing anything, since it has the reverse effect at the front of the pickup box. Instead I think what happens is that the vortex simply transfers (more or less efficiently, depending on configuration) the air over the opening to the half-tonneau. Your adding the blister just helped this along by providing a surface for the airflow to easily attach to.

I'm getting the impression nobody has tried to give the vortex a cylindrical space to rotate in.

If you can find the patent illustration for GM half-tonneau you'll have your answer.

[freebeard]

Originally Posted by PaulB2

I'm getting the impression nobody has tried to give the vortex a cylindrical space to rotate in.

I've suggested it, but I don't have a pickup truck.



Here's an augmented Coanda nozzle that demonstrates the principle. And here's a pickup truck that applies the nozzle to the side stacks instead of the half-tonneau:

[aerohead]

"A half-tonneau - one that covers the back half of the bed (GM' US Patent 4,573,730 ) - was more effective in reducing drag than the full tonneau.It did so by relieving even more pressure on the front of the tailgate."
---------------------------------------------------------------------------
*1/2-tonneau drag reduction------------------ delta-Cd 0.044
*1/2-tonneau with bulkhead ------------------ delta-Cd 0.039
*Drag penalty due to bulkhead ---------------- 12.8%

[aerohead]

here's a link to the HILUX concept
http://carsmelon.com/wp-content/uplo...ux-concept.jpg

[aerohead]

http://www.caradvice.com.au/wp-conte...-concept-2.jpg
SORRY! It's Mitsubishi GR-HEV

[Xist]

Originally Posted by aerohead

http://www.caradvice.com.au/wp-conte...-concept-2.jpg
SORRY! It's Mitsubishi GR-HEV

[freebeard]

It took a while to figure out they weren't the same vehicle. Navara wins because the Ferrari-style grab-handles.

[slime]

Just an FYI, the Chevrolet truck in the very first post is an 88 model (First year of that body style change) I currently have a 1996 3/4 ton, extra cab, long bed, 2WD with a fiberglass topper. My last highway trip averaged 16 mpg at 70 mph plus. That is about the same as my daily commute to work but it's only 15 miles each way. It's big and heavy and I've been daily driving it while I replaced everything in the cooling system on my Mazda MX-6 GT...