Cargo trailer drag estimating

[slowmover]

" . . I would be comfortable dropping from 22 mpg to say 18 mpg driving 55-60 mph. Thoughts?"

22-mpg down to 18 is 19%.

The largest U-Haul trailer (6x6x12) dropped my highway average from 24 to 18/19 mpg (loaded/empty) in two seven hundred mile roundtrips. Or, 25%. (30% is the reasonable expectation, so use for planning). This cargo trailer and pickup with bed topper were same height. THe combo, loaded, was around 13,000-lbs.

Tires were adjusted to spec and trailer was levelled using adjustable hitch head. Loading was optimized. 57/8-mph @ 1,725/50 and across the same major North American city on each of four legs. The route was Interstate, familiar, and each stop was chosen for FE compatibility. Etc. There is more to it than just the rig. Vehicle spec is major, but after controlling for climate and terrain (and then incidentals like traffic & weather) the trip plan is where the real money resides.

22-mpg down to 15+ is near 30%.

I understand folks want low RV travel costs. More can be done here than is usually realized and only part of that is fuel cost. The biggest consideration is number of nights aboard per year as that trumps putative fuel savings if the number is low. 30-nights per year times ten years is not even a full years worth of occupancy. One can, IOW, spend two-three years building something that in no way justifies the time and energy.

One can reduce total annual miles driven and then drive at a higher level of skill. Even with my 65' 18,000-lb combination I proved to myself that I could underwrite 5000 miles of annual vacation travel by being strict in discipline for annual reduced solo miles. And I was already doing well in that regard. Plannng the normal errands pays off. A 20% improvement in my case over an 1,100-mile test.

Start with the annual fuel bill (gallons and dollars). Context is everything. An existing RV platform, optimized in mechanical and safety issues, combined with a good choice of tow vehicle (that best for solo use; the vast majority of miles annually) is the way through the maze.

A VW Jetta TDI pulling one of the smaller travel trailers will stay in the 20's without a problem. As will others. Start with a clean sheet of paper for examination. Were I to use that U-HAUL trailer to mod (and it is an excellent design & build; details matter) a nosecone, bellypan, suspension/brake upgrade and a folding "trailer tail" would be more than enough work. Interior fitment requires some engineering, and ignorant choices can make a bad [dangerous] trailer.

CASITA, SCAMP, OLIVER are nice. I might go with the longest BIGFOOT were I replacing my aluminum palace (even though it isn't "aero"). This current rig currently averages 15+ for Interstate travel on non-hilly terrrain. I knew ahead of time what was needed to do this, and was already experienced [lifetime] in much of it. KamperBob has around the same mpg average with his SCAMP 5'er behind a truck not unlike yours.

The goal is to go camping. Hunting, fishing, what-have-you. I'll argue the corner that using an existing platform is the way to go. Trip plan, mechanical issues and solo driving discipline will underwrite vacation fuel bills.

Cast a wide net.

.

[freebeard]

It's always worth paying attention to what slowmover has to say.

OTOH, minimizing the mileage loss is setting your aspiration low. Although they don't mirror your situation, I can think of two examples where the mileage went up!

Boat tail project based on a single wheel trailer...

Compact camper alternative: New Beetle TDI with hard mounted pop up tent

One is a single wheeled trailer, the other a repositioned car-topper. In your case I could see a trailer that has a dual-single axle with castering wheels less than 18" apart and two clamps on the tow vehicle. The wheels could be at the end of a Tropfenwagen-style tail with a 6' high 45° edge.

Think big. The only question would be where you put the door and how high your mileage can be.

[Fourbtgait]

The 30% fuel mileage loss held true for the F150 with a topper pulling an 18' travel trailer, 8' wide, 10'6 tall at 60 mph. Frontal area killed the mileage as it was 4' higher than the tow vehicle, as did mountain roads.
Hence looking at a trailer whose frontal area does not exceed the tow vehicle, would have thought the loss would be less than 30%.
I have thought of building my own box to go on a small flatbed trailer, wheels enclosed in the body, not extending out past the body as in a cargo trailer. If I did so, design would be like the previously mentioned airstream, giving me 6' headroom inside, so then extending above the tow vehicle.

[aerohead]

This telescoping-roof unit would be an option to the tilt-roof.
It introduces its own packaging challenges,however it really deals with the frontal area beast.

[Fourbtgait]

Ive thought of the trailer lifting as your example. Actually have given it a lot of thought. Several items though keep me away from it. The lifting mechanism would not be bad, body/body seal not bad. Split door/hinginge could be a problem. It is kind of like the aframe pop ups, that to make a quick lunch break, one has to "assemble" it. I would rather have an aframe than lifting top.
Tent style though great ideas, beautiful designs at times, I hesitate due to wife and trips to yellowstone, glacier and such.
Ive spent a lot of time on the tntt website, am surprised that no one seems to want a "perfect" design. They want simplicity of construction. I want it all, but designing, building compound curves is not that difficult. I have built several small boats, which take a little thought. Bead and cove strips, thin veneers laminated together, etc. a trailer in a way is just an upside down boat.

[Hersbird]

Originally Posted by Fourbtgait

Ive thought of the trailer lifting as your example. Actually have given it a lot of thought. Several items though keep me away from it. The lifting mechanism would not be bad, body/body seal not bad. Split door/hinginge could be a problem. It is kind of like the aframe pop ups, that to make a quick lunch break, one has to "assemble" it. I would rather have an aframe than lifting top.
Tent style though great ideas, beautiful designs at times, I hesitate due to wife and trips to yellowstone, glacier and such.
Ive spent a lot of time on the tntt website, am surprised that no one seems to want a "perfect" design. They want simplicity of construction. I want it all, but designing, building compound curves is not that difficult. I have built several small boats, which take a little thought. Bead and cove strips, thin veneers laminated together, etc. a trailer in a way is just an upside down boat.

I'm just down the road from you in Missoula. I have been looking at the exact same thing for the last year, going over every factory built option and not really wanting a popup. There are a few promising looking new trailers out there, I like this one but wish the AC was in the wall and it was a little lower.

Then the issue is the cost, it seems I could build something like that but more how I want it for much less then the $16k they want for it. I've also though about tapering/boattailing a long airstream. Those older long airstreams are better priced than the shorter ones, I figure why not just shorten a long one and improve the trailing end while I'm at it. I'm also trying to decide on a tow vehicle. I kind of want 6 passengers plus 2 dogs and a 6000# rating or so. Ultimate would be a new Ram ecodiesel but more likely will be 98ish conversion van which means I'm starting under 20 mpg without towing.

[aerohead]

A home-built Pappose would give standing room with minimized frontal area,nice drag characteristics and hard sides (Grizzly bears at Yellowstone).
http://cdn.c.photoshelter.com/img-ge...mm0062mod4.jpg

[freebeard]

Sort of an invert Bowlus. Door in a rear truncation so you don't have to climb over the hitch, and minimal gores that run vertical instead of horizontally.

Tandem 12" wheels for reduced frontal area need the Bowlus fenders.

[Hersbird]

Originally Posted by aerohead

A home-built Pappose would give standing room with minimized frontal area,nice drag characteristics and hard sides (Grizzly bears at Yellowstone).
http://cdn.c.photoshelter.com/img-ge...mm0062mod4.jpg

That was the idea I was thinking with cutting up an Airstream, just overall a little taller, wider, with the front part being stock Airstream and then boattail the back like on that Papoose. It would need to be a mid-bath airstream and then put the bed into the V like a V-berth on a boat.

[aerohead]

Originally Posted by Hersbird

That was the idea I was thinking with cutting up an Airstream, just overall a little taller, wider, with the front part being stock Airstream and then boattail the back like on that Papoose. It would need to be a mid-bath airstream and then put the bed into the V like a V-berth on a boat.

In a perfect world we'd have drag data for both the Papoose and Airstream,and we could predict with certainty,the outcome of such a modification.
The Airstreams are so valuable that you'd want to have a high confidence of the outcome before you took an air nibbler to that beautiful sheet aluminum.
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If you had a plaster cast of the Airstream forebody,you could layup a composite nose and then fabricate the new aft-body from there.
Sell the Airstream intact to finance the materials for the rest of the project materials.
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Are there wrecking lots with damaged Airstream and Argossy trailers?