How to improve fuel economy with a tonneau cover

[aerohead]

Originally Posted by sc2dave

I don't see nothing done in the "basic redesign" graph and that has the most effect.what am i missing here?

This research was conducted at the time when GM was introducing its all-new pickup design in 1986.The new pickups drag coefficient was around 20% lower than the former design.

[PaleMelanesian]

Originally Posted by brucepick

The "simple wing" seems to get decent results as shown, but...

I think the "simple wing" could be improved a bit by angling it down slightly towards the tailgate's top edge. The ideal would be a rounded transition going to maybe a 10-12º angle downwards. But even a straight line panel, about 10-12º downwards, should be better than the straight wing.

And of course combine it with the bed cover for a nice improvement.

That's basically what they've done with the cab on the new F150. It angles down (probably 10-12º) for a few inches at the back edge.

[sc2dave]

What if the tailgate was lowered halfway down,to a 45* angle?

[TX_Dj]

Seems to me, that would be even worse- because you would be keeping less of that "pressure pocket" in the bed, AND have a big inefficient spoiler... Seems it would be worse than having the tailgate all the way down, but what do I know.

I used to be one of those tailgate down/off/net in its place guys until I tried some semi-scientific stuff of my own, and found that I had a marginal improvement over all else with the tailgate up *in that specific truck*... It only got about 8 mpg (83 F250) and anything other than gate-up configuration would drop it below 8 mpg a hair. Each config measured over several fill ups (and it had about 55 gallons on board).

[aerohead]

Originally Posted by sc2dave

What if the tailgate was lowered halfway down,to a 45* angle?

Texas Tech's wind tunnel research demonstrated that the lowest drag was achieved with the tailgate all the way up.It prevents air flowing into the bed backwards from behind,and sequesters a locked-vortex which has a rear terminus closer to the curvilinear path of lowest drag.
The air above the vortex skips over as if the vortex were a solid structure.
You'll notice that current day pickups have a proto-spoiler incorporated into the tailgate.The 'spoiler' performs no function other than help remind the owner to keep the gate up.

[sc2dave]

According to this video,it shows less turbulence with the tailgate halfway down as i mentioned.

http://www.youtube.com/watch?v=ncHDI...eature=related

[kach22i]

I don't know what to really make of that last video.

Air with the tail gate all the way up is trapped in a pocket of turbulent flow, which flowing air travels over like a bubble.

Letting the tail gate down half way (45 degrees) releases this trapped pocket of air so that the tufts lay flat, but what of the main flow going over the truck? It is sucked downward, therefore reducing the overall drag?

[PaleMelanesian]

All it shows is there's less turbulence on that side of the tailgate. What about the whole rest of the truck?

[TX_Dj]

+1 - There's no way to tuft-test this, IMHO, needs smoke in a tunnel...

[radioranger]

I'm thinking about putting a sheet of plywood across the rear half of my 6 ft bed ranger and letting a foot or so hang over the gate , any comments or make it flush with the gate, if i let it hang over 1 ft I would be covering 3 ft of the 6 ft bed and one foot overhang , or should I cover 4 ft since that's around 66 % of the bed as per the testing, great advice so far, very promising,