Partial Tonneau cover on pickup (plus cab extension - cab wing)

[Concrete]

Originally Posted by cmroseberry

...Tim Maxwell and Walt Oler are still at Tech and probably have photos of prototype devices installed on pickups.

If you could post pictures that would be terrific
even more of the original content of the report would help

I have been struggling with this concept since summer
the best I have managed is to breaking even on drag

Picture is worth a thousand words
picture of my second generation cab extension
what am I doing wrong?

the third generation cab extension looks better but still a loser
any inspiration would be appreciated
Thanks

[cmroseberry]

Phil, I believe we actually met briefly. I remember your boat-tailed crx parked in front of the Industrial Engineering Building. It had a nice cooling inlet right under the front bumper in that it projected frontal area (instead of being a bottom breather). I actually can't take any credit for the aeroshell. I remember seeing the aeroshell model add-on sitting around, so I think some other senior design class tested it a semester or two earlier.
I don't know where Pat is now, he would have had to stay at Tech a long time to still be there. In addition, I was really disappointed to find out that TTU ME converted their big tow tank to lab space, but I understand if it was just sitting idle it would be hard to justify maintaining it. It makes me feel old since that tow tank had just been finished when I got my MSME.

Concrete: just looking at the photo, I would give you an A+. I don't see any problems with the contour of the surfaces. The Tech prototype just had a fiberglass surface on top (that why it was referred to as a "wing") and some exposed square tube framework on the sides. The cab extension and the partial bed cover were not conceived simultaneously. I believe the cab extension appeared first. One of the partial bed cover prototypes was just a sheet of plywood. It was a surprise that the two devices worked synergistically (like adding 2 and 2 and getting 5). Some Tech students would drive the modified pick-ups on the highway that circled Lubbock to look for milage changes. I believe I heard that they had trouble controlling the test drives enough to see clear results.

[Christ]

Originally Posted by aerohead

Kevin,I wish your paper was available at dealer showrooms! The automakers have been installing faux spoilers on tailgates for a few years now,in hopes that it will promote"tailgate-up" driving.Unfortunately,many truck owners apparently do not "get it",and continue to drive with the gate "down," clinging to intuitive concepts about how the air "must" behave.Some remove the gate altogether,thinking the combined :weight-savings and drag reduction" will save them fuel.Hope you sleep okay knowing what you know.It drives me nuts!

LOL I used to drive with my tailgate down... but for a diff reason - I was hiding my license plate. In PA, you can put a car plate on a truck as a temp... until you get the real truck plate. I got pulled over in NY state (used to live on the border) at LEAST 15 times in one month, b/c they'd never seen anyone do it.

After all that hassle, I drove around w/ the tailgate down so the plate wasn't as noticeable.

On that same note, though, I always had a lop of plywood bolted to the rear half of the bed, as well.

[mobilerik]

That's pretty cool, Concrete.

Eventually I'd like to start playing with foam and fiberglass to make some more pro-looking stuff. Not to mention lighter. My new tonneau-top/giant-spoiler/proton-torpedo-launcher thing is kinda heavy given the two layers of hardboard. Not heavy as in affecting-fuel-efficiency, but heavy as in slightly-uncomfortable-to-lift. And my cab extension looks great in the cell pix, but up close.... it needs some help. Anyone who hasn't seen my latest concoctions should check out my '03 Tacoma Prerunner thread. I got all my ideas for these mods from this (Ben's) thread here, as well as your pizza wheel thread. Eventually I'll post more detail of how I made all this stuff, including the original half-tonneau, which is attached in a neat way.

I can't figure out from your photo, Concrete... are you doing a tuft test in your garage? I don't see a fan, so I'm confused about that.

[cmroseberry]

Concrete: Maybe the trouble you are experiencing in improving your mileage has to do with your engine being lightly loaded. The drag decrease would have decreased the engine load further. I am looking at page 90 of my old Hucho book at Specific Fuel Consumption map (fig. 3.7) that has driving resistance curves plotted on it. The figure shows how it is possible for a drag reduction to take the engine operating point further away from the region of best engine efficiency. The book suggests changing gear ratios. At this point, I am getting out of my own territory of knowledge and experience, so I will leave it to the engine and transmission experts to give you further guidance on this issue if it is indeed the problem.

[Concrete]

Originally Posted by cmroseberry

Concrete: Maybe the trouble you are experiencing in improving your mileage has to do with your engine being lightly loaded...

I have considered that - but it shows up in the throttle position too
so it is driving a heavier load on the truck
I did get it adjusted from -2 mpg to zero loss
the best I can figure is that the air is not rolling happily behind it

akashic,
I have been following your build thread
good work, it has been enjoyable reading
tuffs were for on the high way - like Bennelson/MetroMPG style test
sorry a little jittery
BTW this is the -2 mpg configuration

http://www.youtube.com/watch?v=nmZdPy1wqBg

[mobilerik]

Originally Posted by Concrete

I have considered that - but it shows up in the throttle position too
so it is driving a heavier load on the truck
I did get it adjusted from -2 mpg to zero loss
the best I can figure is that the air is not rolling happily behind it

Neat vid. I don't know what to think, so I'll just throw out some ideas:

• Maybe the shoulders want to be more rounded at the rear of the extension.
• Maybe the base of the extension should be flush with the side of the truck and twist upwards to meet the top.
• The extension changes the interaction with the tonneau and whatever "bubble" was created before. Maybe you accidentally added drag by removing a helpful section of the bubble.

I'd like to suggest trying a set of comparisons between cab extensions but without the tonneau, and maybe with a partial tonneau. I have a suspicion that the reason a partial tonneau can outperform a full tonneau is that a full tonneau eliminates the "box" that would otherwise support the stationary vortex, i.e. "bubble". Maybe messing with that bubble will get you the results that have mysteriously evaded you. Worth a try?

[Concrete]

Originally Posted by akashic

I'd like to suggest trying a set of comparisons between cab extensions but without the tonneau, and maybe with a partial tonneau. I have a suspicion that the reason a partial tonneau can outperform a full tonneau is that a full tonneau eliminates the "box" that would otherwise support the stationary vortex, i.e. "bubble". Maybe messing with that bubble will get you the results that have mysteriously evaded you. Worth a try?

Thanks for the advice
I agree - the tonneau is part of the problem somehow
but my temp setup uses the tonneau for support - note sand bags to hold the foam down
and I really like the covered bed - I may just have to make a full aero shell

I may make the third generation into something more like what you have
the second gen worked better when I cut it shorter

[aerohead]

I lament hearing of the loss of the TTU ME tow-tank.I understand that the $60,000-plus 1/3 -scale Taurus model proved invaluable for underhood,engine bay aero investigation.Last I heard,the tank was being used for some Defense Dept. parachute R&D.------ Quite a loss!!!!!!!!!!!!!!!!!

[hypermiler01]