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Old 12-18-2012, 03:13 PM   #43
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I think a flat cover on a open pickup bed actually increases fuel milage, both while towing and running empty. I could see a very heavy, large cap on a light truck maybe adding enough weight to lower milage.
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Old 12-18-2012, 06:19 PM   #44
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In the past couple of years, skirts have been installed underneath some semi-trailers to cut air turbulence under the box and between the tractor wheels and rear trailer axles. I wonder if some kind of skirt between the pickup bed and the front of the Airstream would improve fuel economy...
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Old 12-18-2012, 06:27 PM   #45
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Aero treatment of each vehicle is the simple optimum. The "Aerolid" shown above hasn't reached production, but takes that gasser 1/2T to 25-mpg. A half-tonneau cover is the next best as the open area just behind the cab induces a vortex across the bed that "equalizes" pressure on both sides of the tailgate. A full tonneau cover is about the same or bit better than a close-fitting, cab height bed topper. Any of these are better than an open bed.

The gap between TV & TT is a major hurdle. There are some indications that roof deflectors may work, but we lack the genuine evidence thereof (non-anecdotal A-B-B-A testing, etc). This is where Andy's recommendation of an airspeed indicator will show problems (reversing winds). One can feel them as they hit this gap. Air is then flowing not only longitudinally, but latitudinally. Hairy stuff considering the wind speeds encountered.

As in my earliest post, the mechanical baseline (pressures, align, drag) are the places to focus attention on past travel speed of below 60-mph. Reduction of acceleration & braking events, plus fewer steering wheel inputs are all good for safety, economy, and stress reduction.

Final drive ratio gearing would be the last thing on the list. For a given TV-TT combination that isn't altered much in weight from trip to trip (all trips: to Alaska or to the local lake) could be dialled in just so for all conditions encountered. This assumes an overpowered TV (as most are).

And, Bob, cover the bow opening to your boat and affix to Sub roof (as well as cover the rest). You'd see an FE change.

.
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Old 12-18-2012, 06:29 PM   #46
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In the past couple of years, skirts have been installed underneath some semi-trailers to cut air turbulence under the box and between the tractor wheels and rear trailer axles. I wonder if some kind of skirt between the pickup bed and the front of the Airstream would improve fuel economy...
I have wondered the same thing.

Besides underneath, some semis now have a deflector on the back of the trailer.

I suspect you would have to put on the same kind of mileage the semis do to see a justifiable savings. I have not heard of anyone who has tried it on an RV level

We need an aeronautical engineer to chime in here.
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Old 12-18-2012, 06:34 PM   #47
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I have wondered the same thing.

Besides underneath, some semis now have a deflector on the back of the trailer.

I suspect you would have to put on the same kind of mileage the semis due to see a justifiable savings. I have not heard of anyone who has tried it on an RV level

We need an aeronautical engineer to chime in here.
There has been some work done over on Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com where the knowledgeable reside (Phil Knox).

Best TT would be "bullet nose" with a "boat tail" (likely truncated).



Section these in half to give a barely rounded underside and completely enclose wheels.
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Old 12-18-2012, 06:58 PM   #48
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Old 12-18-2012, 07:05 PM   #49
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But the edges need to be radiused. Not optional. Those square edges kill the other advantages. Radius should be from 12-degrees to around 22.

The roof sloping up, and then down, is also crucial. (No more flat roof)
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Old 12-18-2012, 07:07 PM   #50
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Vehicle highway mileage

Here in the UK the manufacturer's published highway fuel consumption figures are based on a steady 56 mph in accordance with law. Not surprisingly, vehicle designers will optimise vehicle economy around that speed so as to impress buyers with advertised fuel mileage figures. Certainly this is the case with my UK 1990 Land Rover 200tdi Discovery. At around 56mph I can average over 30 mpg, and the engine is remarkably smooth at that speed.
My superficial research indicates that in the USA the highway mileage is calculated at an average of 48 mph, and never exceeding 60 mph throughout the test:
Detailed Test Information
When I'm in the USA, my Dodge Ram Cummins 3/4 ton achieves 22mpg solo when driven at a steady 55 mph, and again the engine seems very smooth at those revs.
It would be interesting (to me, at least!) to know how these legal standards affect the design of, for example, camshaft profiles and fuel injection patterns.
Wind resistance is king, but perhaps this is another influence.
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Old 12-18-2012, 07:12 PM   #51
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I also have a CTD. Max pulling power, smoothly, is within the 56-66 mph range on an all-stock 3/4T truck. I think the OEMs expect that these heavier pickups will actually do work instead of acting solely as commuters (1/2T pickups) where gearing/tuning "may" slightly favor higher speeds.
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Old 12-18-2012, 07:16 PM   #52
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or this
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Old 12-18-2012, 07:29 PM   #53
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Dymaxion car , 1933

Gotta love those things. I would very much like to see one in the flesh, where I could actually get into it, and see the future through Buckminster Fuller's eyes.

I don't think it would make much of a tow vehicle though, what with the rear steering it used.

But wow, it WOULD make a great toad!

http://en.wikipedia.org/wiki/Dymaxion_car
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Old 12-18-2012, 07:37 PM   #54
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Wow! Look at that Reese Dual Cam hanging on the tongue of that thing. That tells you how old THAT technology is.
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Old 12-18-2012, 07:49 PM   #55
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Gotta love those things. I would very much like to see one in the flesh, where I could actually get into it, and see the future through Buckminster Fuller's eyes.

I don't think it would make much of a tow vehicle though, what with the rear steering it used.

But wow, it WOULD make a great toad!

Dymaxion car - Wikipedia, the free encyclopedia
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Old 12-18-2012, 09:47 PM   #56
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Surprising Fuel Savings at 55 mph

Quote:
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Wow! Look at that Reese Dual Cam hanging on the tongue of that thing. That tells you how old THAT technology is.
The photo is of Dr. and Mrs. Norman Holman and was taken in either the late 1960s or early 1970s. Dr. Holman built the "Liner" in 1936 utilizing plans published by Wally Byam and sold through either Mechanixs Illustrated or Popular Mechanics. The trailer and its owners were regular participants at WBCCI International Rallys up through the death of Dr. Norman Holman, Jr. near the conclusion of the International Rally near Sedalia, MO in 2012. Dr. Norman Holman, Sr., and later, his son Dr. Norman Holman, Jr. made regular presentations at International Rallys regarding the building and subsequent modifications to the trailer over the years. Dr. Norman Holman, Sr. was a gentleman of innovation and applied many innovations to his trailer throughout the years, and I suspect he was among the first adopters of the Reese Dual Cam Sway Control system when it became available. I count myself as being very fortunate in having the opportunity to hear Dr. Norman Holman, Sr.'s discussion about his "Liner" more than once as well as Dr. Homan, Jr.'s presentation "My Father's Trailer" on more than one occassion. The trailer can be easily recognized today by its WBCCI membership number -- 1936.

Kevin
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