Pickup truck aerodynamics

[kach22i]

This looks to be the latest pickup truck thread so I'll dump this here.

https://www.ecoological.com/improved...rformance.html

[freebeard]

Needs a third brake light:

[Hersbird]

I like that idea for the benefit of having sort of a cupboard with the tailgate being a table. I don't think it's a good idea if you are adding weight for snow traction to put it behind the axle but I don't think that is the real purpose of this box anyway. Also nice to be able to take it out without climbing in to get it. Good idea overall.

[aerohead]

Originally Posted by kach22i

This looks to be the latest pickup truck thread so I'll dump this here.

https://www.ecoological.com/improved...rformance.html

It may be a mistake to make a general claim about improvements.
In the early 90s,pickups revealed a range of reactions for box modifications,and what helped one brand could hurt another.I'd ask for info. about any specific model tested.

[kach22i]

Originally Posted by aerohead

It may be a mistake to make a general claim about improvements.
In the early 90s,pickups revealed a range of reactions for box modifications,and what helped one brand could hurt another.I'd ask for info. about any specific model tested.

Can someone post that University of Texas PDF drawing showing the various improvements for pickup truck tailgate up Vs down, roof wing, partial rear half bed cover, full tonneau cover and so forth?

It's on my old computer and did several forum searches without finding it.

[freebeard]

This one?

[kach22i]

Originally Posted by freebeard

This one?

Yep, thanks...............I found it in two other places just five minutes ago.

Can never find it when I need it.

[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.

Sighard Horner's book, 'Aerodynamic Drag' is my only source for anything related.
Visualizing a 4-cup rotating anemometer:
* if the hemispherical cups are 'open' and traveling as the 'trailing' part of the cup, their Cd is 0.42.
* if the cups were filled in and 'closed' at the 'rear', their Cd is 0.37.
* a 11.9% delta-Cd between 'open' and 'closed'.
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With the tailgate closed, streamlines reaching and separating at the trailing edge of the gate will attempt to circulate around the corner, as a vortex sheet and collide with the boundary of the closed cavity, imparting some momentum.
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With the tailgate down, or removed, there's no longer a 'boundary'.
The flow separates, the vortex-sheet circulates towards the void, and collides with incompressible 'deadwater' under the tonneau, unable to impart any appreciable momentum ( punching a hand into a bowl of ball bearings ).

[aerohead]

Originally Posted by PaulB2

I'm guessing this effect is pretty miniscule, and anyway if there is a pressure differential across the tailgate, the same pressure differential exists when an intermediary form such as a box is there, and has the same effect.

The back of the vortex "sucks" the tailgate (or whatever) forward, and the front of the vortex "sucks" the front of the pickup box backward, so all that would seem to cancel too.

I'm guessing also that if you have a round vortex in a square hole, the main vortex may be streamlined but there might well be mini counter-rotating vortexes and other turbulence in the corners. If we take care that the outside of the vehicle is streamlined to avoid turbulence, maybe we should in that box too.

I'm just wondering if anyone has investigated along these lines.

Apology for another 'better late than never response.'
This is a really important question. I skimmed the old Sport Truck Magazine pickup aero article recently, and I believe that they directly address this question.
So as not to get it all wrong, I'll review it over the weekend and have something to bring next Monday.

[freebeard]

Originally Posted by PaulB2

If we take care that the outside of the vehicle is streamlined to avoid turbulence, maybe we should in that box too.

While aerhead is pondering, check out his thread from 2015, ecomodder.com/forum/showthread.php/morellis-fluid-tail-33283

Morelli was into circl[ulariz]ing the square.




Maybe he's still resentful of Photobucket watermarking his pix.