Tonneau Cover Range Improvement numbers

[Pitbull2o08]

I just took my hard cover off last week to move a treadmill. I was lazy on putting it back on immediately. Guess what, my efficiency was the same as it always was. No perceivably drop and no perceivable gain when I put it back on.

I mean, the science is sound. But what do i know about fluid dynamics? Im just an anesthesia provider who also flies airplanes.

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[Pitbull2o08]

I mean...I think he was more or less agreeing with you...

I’m affirming his comment.

 

[NW Ontario Ford Lightning]

It keeps snow out of the bed.
That's reason enough for me.

 

[ZeusDriver]

Writing as someone who used to fly and used to develop courses for both transition training and recurrent training for airline pilots, I can say that being a pilot does not automatically mean that you know nothing about aerodynamics, but it also does not mean you know much about it either. Nor does driving an over-the-road truck full-time mean that you know a lot about the truck's aerodynamics. You may take it on faith that cameras instead of mirrors help, or that the various tail treatments help, or that side skirts help, but chances are good that you were not in the wind tunnel when the tests were done. I'd flown for decades (and had been a certificated ground school instructor for a decade or so) before seeking out aero mentors at Cornell and Sanford who were able to show me the numerous errors of my ways.

When I took high school physics and later read the "Principals of Flight" that was the basis for private pilot ground school, the equal transit time explanation of lift generation was used in both cases. Obviously wrong, but it's what many (most, at that time) pilots believed.

I have a boxy boat with a lot of frontal area. I can see that when I tow it, my range is halved. Most drivers can detect differences of that magnitude, and few aero people would challenge them. But the vast majority of drivers cannot detect any difference from smaller mirrors, rolled down or rolled up windows, inactive or active front air dam, tonneau cover or lack of tonneau cover, tailgate up or tailgate down, or even an Aero X bed cover, which gives the appearance of being streamlined, but is probably no more effective than using the air bubble that normally forms to guide the airflow when no cover is present.

Wind tunnel tests, on the other hand, can detect differences for each of those devices and conditions, reliably and repeatably. Taking a large number of small changes together (each of which can be measured in a wind tunnel, or with expensive versions of CFD -- but not on the road) is what leads from the .40 Cd of an old Jaguar XKE to the .19 of an old GM EV1: both look pretty streamlined -- one is one is not.

Over at the Ford Maverick forum, you can find this claim:
>> A lot of independent testing has been done and the number that seems consistent is 7, 7% improvement in mpg over no cover. That's a 2 mpg gain on my Maverick not to mention the other benefits.<<

This is on a truck with an even shorter bed than the F150. Seems improbable that there is a 7% consistent reduction in drag. But even if there were, that would not translate into the 7% increase in mileage claimed. The increase would depend upon speed, but even at high speed, the MPG improvement would not be 7%, because there are other sources of energy consumption. It is not all aero.

You can ask your favorite AI: "Are there still CFD skeptics? " the answer will be yes, and some AI will elaborate at length. So even now, the wind tunnel is the real deal despite the considerable time it takes to go through design iterations and making real rather than virtual models.

A wind tunnel, unlike "real world" (necessarily casual) tests, can measure the effect of all the items (mirrors, covers, etc) I listed above, reliably and repeatably. Nothing else works. Do I have strong reason to believe that Brad Richards' claim that tonneau covers always reduce drag are bogus? No. Is it plausible that the "landing" point that Richards refers to is too far back to matter with a 5.5 foot bed? Could be, but the only way to know is in a wind tunnel with smoke and with, of course, a balance. Do I believe that on-the-road tests can measure the difference. No, of course not. An on-the-road test cannot make any conclusion, either way. You don't measure a machined bearing housing with a ruler. Does that mean that there is no difference? No.

Can an on-the-road test measure the cumulative effect of the 100 differences between a Jag XKE and a GM EV 1? Yes. Can it measure the effect of any group of 5 or 6 differences? Unlikely.

There is some value in science and metrology.

 

[MM in SouthTX]

Popping back onto this forum after selling my Lightning about 2 years ago. I now drive a PowerBoost. I wanted to report my mileage on a recent 250 mile trip that usually yields 18-19 mpg with the wind conditions that I had. On this trip, I had two tractor tires in the bed. I have a FlowTarp, which basically is a soft bed cover with 3 anchor points per side along the top of the bed. In this case, the tarp was angled from the tires, so that it looked a little like a CyberTruck in profile. I got almost 21 mpg.

This might be helpful for someone who suffers from poor highway range like I did. Perhaps something like this. Dorky looking, but...

 

[Pitbull2o08]

Popping back onto this forum after selling my Lightning about 2 years ago. I now drive a PowerBoost. I wanted to report my mileage on a recent 250 mile trip that usually yields 18-19 mpg with the wind conditions that I had. On this trip, I had two tractor tires in the bed. I have a FlowTarp, which basically is a soft bed cover with 3 anchor points per side along the top of the bed. In this case, the tarp was angled from the tires, so that it looked a little like a CyberTruck in profile. I got almost 21 mpg.

This might be helpful for someone who suffers from poor highway range like I did. Perhaps something like this. Dorky looking, but...

That’s because the tear drop is the most aerodynamic shape an engineer can work towards. If we weren’t talking about enclosing a flat space that is already subject to high pressure, then I’d succeed to the hatch back look. But we are simply talking about a flat cover.

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