DIY Hillbilly Truck Bed Cover (Tonneau) for 2019/20 Ford Ranger.

Floyd

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Hi Andy,

Actually a tonneau cover increases drag. I spent 10 hours in the Lockheed wind tunnel on several occasions trying to improve Race Truck aerodynamics and the tonneau was top on my list of things to try. Results was a significant increase to the tune of about 10% in aero drag for a tonneau cover. Ditto for tail gate removal... Best increase was a 6" strip across the box at the tailgate. Doing the smoke test you could see why this worked when other items did not work....Air flow is not intuitive and you cannot see its flow. For the cab the air rolls and spirals in such a fashion that this 6" strip alters the spiraling. It was amazing that the Ford Aerodynamist with me could envision such things working...
So I wish to debunk this theory that tonneau covers on pickup trucks decrease aero drag, Tonneau covers increase drag...

Best,
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co. Retired
Thanks for the experience,
I do think it varies from truck to truck, or when towing the effect may be different.
On my former Ranger, we did an unscientific experiment.
With no cover, I placed a paper cup inside the box next to the tailgate, at around 60MPH the cup would suddenly slam into the front of the box from the air coming over the cab and dropping into the box right about the tailgate and causing a low pressure area behind the cab.
When I raised my sunroof (about3") the cup would stay calmly at the tailgate all the way to the truck's rev limiter.
I don't know if there is more or less turbulence with the box cover installed and the sun roof down,but I do know that the sunroof pushed the air beyond the box when it was up. That would then seem to mean a zero effect good or bad for the box cover in those particular conditions.
I just installed a box cover for an upcoming trip which also includes a travel trailer so I was curious about the effect.
I doubt that the difference will be significant enough to be easily measurable, especially since the box will be full of boxes and gear either way.
As you say, it is not all it seems, My 1976 Econoline had a drag coefficient of .33 whereas the average bicyclist is about a 1.0.
I have also found that bicycles in an open trailer produce notably better fuel economy for the tow vehicle than bicycles on the roof without a trailer.
Most all of this is anecdotal and the purpose of a box cover is to secure cargo and keep it safe,dry, and out of sight



 
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P. A. Schilke

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Thanks for the experience,
I do think it varies from truck to truck, or when towing the effect may be different.
On my former Ranger, we did an unscientific experiment.
With no cover, I placed a paper cup inside the box next to the tailgate, at around 60MPH the cup would suddenly slam into the front of the box from the air coming over the cab and dropping into the box right about the tailgate.
When I raised my sunroof (about3") the cup would stay calmly at the tailgate all the way to the truck's rev limiter.
I don't know if there is more or less turbulence with the box cover installed and the sun roof down,but I do know that the sunroof pushed the air beyond the box when it was up. That would then seem to mean a zero effect good or bad for the box cover in those particular conditions.
I just installed a box cover for an upcoming trip which also includes a travel trailer so I was curious about the effect.
I doubt that the difference will be significant enough to be easily measurable, especially since the box will be full of boxes and gear either way.
Hi Floyd,

Yes, the effect is likely as we used to say "like picking fly shit out of the pepper". It takes very accurate equipment to measure the change in aero horsepower. That is why Andy attempting to do this on the street is likely to deliver very mixed results as there are so many variables on the road that cannot be accounted for in such a non scientific manor. What we found was a 6" wide strip at the back resulted in a decrease in aero horsepower but the drag of the air rolling off the cab onto the tonneau cover increased aero horsepower required to maintain 90mph. What the testing told us was to keep the tailgate up (Big Ford Oval on the tailgate for the TV cameras) and allow the box to fill with a cushion of air as opposed to drop the tailgate or use a net etc. The sanctioning body would not allow the 6" strip as they suspected some sort of trickery from Ford (read directed at ME!) Your sunroof deflector certainly redirected the air over the tailgate.

A bit of a backstory that I may have mentioned in another thread...CRS here! We did get around the sanctioning body with a composite pick up box used on the electric Ranger. When they found out our pick up boxes were composite (saved about 150lbs) they were absolutely furious. I got called to their trailer. I calmly reminded them of the rule in their rule box that any Manufacturer part could be used if it has a manufacturer production part number, of which the composite box had a valid part number. Shut them down almost instantly...thus we were able to run composite pickup boxes with their reluctant blessing. Protests by the other manufacturers were dismissed.... I love beating the sanctioning at their own game! :LOL:

Best,
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co. Retired
 

MyLittleRanger19

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they mention the 6 inch strip next to the tailgate here. this is with an f150 in fords tunnel and a ford engineer.
maybe things have changed since the 80s?
 
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DIYAndy

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At 1:37, in the above video, "Tonneau cover are more efficient" :question:When something is more efficient then you "might" get more MPG;)
BTW - This summer vacation I will definitely check for any noticeable MPG differences with my DIY truck bed cover on/off;)
 
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svache

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Oh who should we believe.. The retired engineer with nothing to gain by sharing his knowledge, or companies who want to make a buck or two.... :rolleyes:
 
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DIYAndy

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Oh who should we believe.. The retired engineer with nothing to gain by sharing his knowledge, or companies who want to make a buck or two.... :rolleyes:
Correct me if I am wrong, but it seems we have two Ford engineers (one working and the other retired) saying two different/opposite things about the efficiency of a Tonneau cover.;)
 

svache

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Correct me if I am wrong, but it seems we have two Ford engineers (one working and the other retired) saying two different/opposite things about the efficiency of a Tonneau cover.;)
There's Phil, who I know tested this. Who is the other one?

For what it's worth, I don't recall noticing a decrease or increase of my mileage after installing the cover. A cover looks better IMHO, it keeps my stuff dry, but when it comes to mileage, who gives a hoot lol. If people wanted a fuel efficient car, they shouldn't be driving a truck ;)
 
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DIYAndy

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who I know tested this. Who is the other one?
From the video above Ref. #48 - Brad Richards - Design Manager, Ford Motor Company;)
 
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jsphlynch

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Hillbillies don't file or get patents they just do it to get the job done;)
@DIYAndy do you think this will get the job done? I changed your design quite a bit and have almost got my version finished. Pic is of a test fit before adding anchors for final mounting.
20200216_173521.jpg
 
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DIYAndy

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do you think this will get the job done? I changed your design quite a bit and have almost got my version finished. Pic is of a test fit before adding anchors for final mounting.
Yep, and you must had spent some time on the sleek edge contours of your truck bed cover (Tonneau):thumbsup:
Just curious, approximate cost?;)
 

I_smell_like_diesel

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@DIYAndy do you think this will get the job done? I changed your design quite a bit and have almost got my version finished. Pic is of a test fit before adding anchors for final mounting.
20200216_173521.jpg
Looks sharp for a home brew bed cover. Like that quite a bit!
 

jsphlynch

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Yep, and you must had spent some time on the sleek edge contours of your truck bed cover (Tonneau):thumbsup:
Just curious, approximate cost?;)
Yeah, I spent more time than I should have trying to make inconsequential things look sleeker. I guess that makes mine more of the "city slicker" version than the "hillbilly" version.

I'll do a full write-up in the next few days including actual cost, but I think it's in the range of $130-140 before taxes.
 
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DIYAndy

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jsphlynch

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I take it, from the cost, that you designed a "soft cover";)
Nope, it's solid. I think I may have used a lower grade of plywood than you, plus I skipped out on all the steel braces you used (which I'm sure added up). Hopefully I don't regret either of those changes...
 











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