Cargo trailer drag estimating
 

Hello everyone.
New to the forum though I have been lurking for months learning from different posts across a wide range of subjects.
Now I realize a pre-built cargo trailer is not the most efficient shape, better if I built my own, which I may still do.
But....
Tow vehicle is a 2014 Toyota 4runner, on highway at 65 mph about 22 mpg.
In town average 19 mpg.
Both figured by pencil.
I need a small camp trailer, though a teardrop is ummm cute, not the most efficient. Thoughts are a 5' x 10' cargo trailer. Tow vehicle is 6' wide, 6' tall. Thoughts are a 5' wide, flat front (I would install a front nose cone) would stay inside the vehicle drag better than a 6'. The wheels/fenders would stick out 4" each side, about 24" tall. If I kept the trailer not over 6' tall it would "fit" better into the slipstream. But the inside height would only be about 4' 6".
Question is, is there a formula I have missed in life to look at flat front drag area? Trailer above would only "show" the wheels/fenders beyond the tow vehicle. Yes, I realize the slip stream begins to come back together behind the tow vehicle.
A better size or usable space trailer would be 6' x 10' trailer, 7' 6" tall. But then extends past the vehicle about 12+ sq. ft. exposed vs. 1 sq. ft. of the smaller trailer.

Always before I had diesel pickups, large travel trailers or gooseneck horse trailers, never worried. Now, I do not want to go from 20 mpg down to 10/12 mpg with large frontal areas. I would be comfortable dropping from 22 mpg to say 18 mpg driving 55-60 mph.

Thoughts?

A couple thoughts:

Unless you can get the gap between the truck and trailer very small, the trailer needs to be have the very best aero it can, regardless of what is in front of it.

Of course you could connect them:
Spandex connection

Other wise, a few threads come to mind:
Eco-RV thoughts

Aero car hauler

And getting that gap close will not work. Read all those stories, methods.
I have read the other two threads also.
And about radiousing the front edges, top edhes, tapering the rear top/sides (15-17*?)
Hence my question of any formula for frontal area penalty.

If you bought that small trailer, added a healthy nose cone, covered and boat tailed the wheels and built a bit of a kammback/boat tail, it probably wouldn't be too bad. I wouldn't put a ton of time into it if you have the time and skills to build a properly streamlined trailer later on.

Otherwise you'll be looking at elaborate gap filling like aerohead and BamZipPow have done- it doesn't look easy! :)

I agree that the smaller trailer with slight modifications would be more aereodynamic.
But smaller is not always practical for some people in a situation.
Hence my question of a methodology/formula for establishing the loss of or increase of aereodynamics for a given frontal area.

That's true; you're not going to be happy with a trailer that doesn't fit your needs, or one that wastes fuel. I'd say get one that you can use, then aero-mod the crap out of it! The amount of work you want to put in is up to you. Trailer aero is not well documented, so you'll have to do some designing. :)

formula
 

Hucho offered a drag table from D.M.Waters' research,presented in Proceedings of the 1st Symposium on Road Vehicle Aerodynamics,London,1969,Paper 4.
*Waters shows the drag of a flat-faced trailer,tow vehicle combination with Cd 0.82.
*By softening all the leading edges of the trailer face,the composite drag coefficient drops to a minimum when the radius used is equal to 0.39% of the square-root of the frontal area,achieving Cd 0.546.
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If you had a topper on the Tacoma that possessed a height and width equal to the height and width of the radii origins,the trailer would basically train behind the Toyota,and the radii would get the flow over the difference.
This would make for nice drafting.
http://i1271.photobucket.com/albums/...Untitled-7.jpg

The formula is Cd x A = CdA. Establishing Cd is a black art.

Maybe what you are looking for is A[sub]tow vehicle[/sub] / A[sub]towed vehicle[/sub] x [fudge factor]. I don't know about that, as long as it's greater than 1 you should be good.

For inspiration you could compare the classic Airstream to the Airstream Basecamp. It is a very utilitarian vehicle reminiscent of the Rumpler Tropfenwagen.

http://3.bp.blogspot.com/_YgYpEImCk4...airstream2.jpg

Thank you aerohead and freebeard.
Yes, I figured my question was on the edge of the black arts.
If I were to buold, it would be along the lines of the basecamp.
Ease of a cargo trailer is a factor, though curious of the factor of frontal wall 6' wide 1'6" tall sticking up above the tow vehicle.
I have given thought if I went with total 6' height, to cut/weld a lift top to increase inside height.
I do know from several conversations with people that the Chalet/Aliner trailers typically only drop mileage 2 mpg. Due to folded height way below the top of most tow vehicles though just under 7' in width. Even used ate pricey.

Curiously, the Basecamp is similar to Wally Byam's first trailer:

http://ecomodder.com/forum/member-fr...qevko1-250.jpg

Once you go expandable, the sky is the limit.

https://s-media-cache-ak0.pinimg.com...c2bb40ce46.jpg
https://www.pinterest.com/pin/279715826829704846/

" . . 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.

.

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.

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.

frontal area
 

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.
http://i1271.photobucket.com/albums/...d2/Trailer.jpg

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.
http://www.rvt.com/photos2/1964/5931964/main.jpg
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.

Bowlus Papoose?
 

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

http://ecomodder.com/forum/member-fr...17-trdrp1a.jpg

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.

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.

cutting up
 

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?

I've seen some $2000-2500 mid 60's, need floors, too long (28' or more), Airstreams on Craigslist. A rear end damaged one would be even less but normally they are front damaged. A tree or snow damaged one might work too. In a few weeks I will finally have the money to start something but I may take my time looking and planning still.

I'm not a big fan of this idea. How would you cut it up and have it come out taller and wider? I'd get a generic mid-bath, strip it down to the deck and build back up from there. I had a 1952 Silverstreak Clipper years ago and I replaced 1/2 the deck and floor joists successfully but I needed 3x8' of aluminum siding and what was sold to me was not aircraft grade material and it went all wavy because it wasn't tempered correctly for trailer siding. I lost heart and didn't keep it.

Here's someone else's [similar] Silver Streak:

http://ecomodder.com/forum/member-fr...iler-show0.png

Both ends and the top are a half-circular. Can you say Iron Man?

Nowadays I live in an off-brand (Mobile Industrial - Santa Fe Springs, CA) 35' R-license park model. It's an aluminum tube with fiberglass end caps. I believe the Argosy has steel end caps.

FWTW here's a Bowlus from the same video:

http://ecomodder.com/forum/member-fr...iler-show1.png
http://ecomodder.com/forum/member-fr...iler-show2.png

Search Youtube for the title in the upper left. There were some amazing trailers there.

I didn't mean I'd make the Airstream taller and wider, just that an Airstream is taller and wider then the Papoose.

". . 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. . . ."

One doesn't improve mpg wth this trailer type by decreasing size. Not in any significant way. Acceleration events and long grades may make increased weight more noticeable, but a properly-sized trailer is the point to the exercise of laying out trailer spec. IOW, the cost of time, labor and materials won't produce a mpg payoff. Given two identical rigs I can produce better mpg through other avenues. However, there is something to be said for better combined rig stability if aero is improved.

" . . 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.

The new EcoDiesel is rated for up to 9,200-lbs. Close enough to haul my 35' Silver Streak. Capable of 30-mpg solo highway without really trying. And with a smaller cross-section Airstream of the 1970's is seeing 18+ towing (again, without really trying) in the hands of one man I know. Careful trip planning and favorable conditions could see one at/near 20-mpg. A combined rig of around 13,000-lbs with a 28-30' er.

A full-size passenger van with a diesel engine would be worth trying to locate even if it needed a new longblock and trans. FORD and GM each made them in the past twenty years. THe first generation DURAMAX has been the only mpg competitor to the CUMMINS. But one must be aware of any problems (and avoid altogether 6.0 and 6.4L FORD). Worth investigating as solo miles predominate 60/40 or better.

The short rear overhang of a van (rear axle center to trailer hitch head) makes this type highly desirable for cargo/passenger space efficiency versus overall length AND being resistant to trailer sway.

Also, there are those us of looking at roof area on the tow vehicle for solar panel installation and a van is excellent for this. Plus the battery bank can be located in the van. A minimal battery weight for the trailer. Same for adding a BIG propane tank. A 3500-series van with a diesel is insenstive to weight additions up to around 1,000-lbs. I'd look to keep van weight at 80% of tire/wheel/axle capacity once fully loaded with passengers, gear and additions of the sort mentioned here.

Generally speaking it is better to add weight to a trailer versus the tow vehicle. But a Clipper can be pulled by a range of vehicles. I'd keep it simple if for no other reason.

But were I trying to make for all weather accommodations for six I'd stick with a 1980's Airstream, Silver Streak or Avion. In particular a tridem 34' rear bath Avion where twin beds ahead of the aft bath can be converted with overhead bunks. The front lounge with a sleeper sofa and convertible dinette can sleep an additional two, three or four people. (The triple axle keeps tongue weight low, at 10% versus 13-15% on a tandem).


1980's AVION

My previous Silver Streak: A 1983 3411


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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.

Several tens of thousands made. Not "valuable" in the sense stated.

Are there wrecking lots with damaged Airstream and Argossy trailers?

Yes, COLAW in Missouri is one. Argosy is a bit rare and not worth fixating upon.

Were this my approach -- modifying an all-aluminum trailer -- the early 1950's Silver Streak Clipper freebeard shows above would be the ideal candidate as the shell itself is already a very good shape. I sincerely doubt a home-made project OR existing trailer mod would offer any significant (measurable) improvement. And let us also consider that proper weight balance is already inherent. This FAR outweighs mpg "fun". And that changes require an engineer. At what point is engineering expertise required is central. I say, stick with what is already engineered.

One will have ones hands full with re-building an antique like this (pipe frame and floor rot) so facilities to do a shell-off restoration are needed. Expect that years will be required. One man is looking at all his spare time from a career job even with outside help on occasion. There are far too may examples of this in resto threads elsewhere. Trailers are not simple taken as a whole.

(Sorry to hear of that aluminum sheet fiasco, freebeard)

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In the above pair of posts I realize I've gotten pretty far from the title of this thread. It is that I note that, for general purposes, the "thinking" about fuel economy in re travel trailers is that light weight and small size are seen as fundamental.

But the numbers are otherwise.

A turbodiesel tow vehicle and aerodynamic travel trailer (where ALL edges are radused) is the winner. Lighter weight due to materials AS WELL AS low center of gravity are also what matter, but true aero is king.

We can find dozens if not hundreds of examples where a small gasser pickup and pseudo aero trailer fail. And fail in space utilization primarily, fuel economy secondarily. What good is 15-mpg with cramped accommodations for four where the mpg is the same for six with room to spare in a far larger rig? With better on-road stability? And higher solo mpg. And that one can carry more gear for weather or hobbies as well as the ability to stay put longer once parked. Etc.

Six people is a far cry from just two. The economics of RV travel are far more than fuel cost, the other big expense is ground rent. Ten nights of full hookups at $45/night = $450. Over a month if one can cut this to four nights the savings is $270. At 16/mpg (as on mine) the distance covered at $4/gl diesel is 1,000-miles. So, how long I can park "free" on BLM land, for instance, is directly related to the trailers capacity for water, waste, food and propane.

The longer one can stay in one place without external inputs of any sort is a larger context than worrying over fuel cost (and then compounding that problem with years of time and effort).

One can play with this sort of thing quite a while. There are those who in retirement move once monthly versus once weekly to keep expenses down. $3000/monthlly is something of a bottom figure for RV travel. Those who say they can do it cheaper usually leave out considerable areas of concern (tent travellers, for example). There is a subsidization by the tow vehicle in that (very high relative miles). And lack of all weather shelter. It is possible, after all, to be sick or injured. Insects, vermin, the damp, etc, are all contraindicated in such (general purpose, in my view).

There is a ratio to be explored, here, would be the point. My starting point is two weeks of full independence as a goal for least expensive travel. Choosing where I park in order to minimize ground rent is just as important as fuel economy.

And that an RV so spec'd is also shelter for ones family when the lights go out back home. Expand the usefulness beyond being just the infrequent vacation (seen over a decade).

.

First linked resto/mod thread is by a formerly full-time sailor and his wife. Beautiful work, and a thread with literary quality. This is the size, age and "cool" factor beloved by those at vintage rallies (Franky, it is about impossible to top the cool & useful factor of this particular Airstream both in model year spec and owner modifications).

First she had to take a ride on a boat -- 1957 Caravanner

Second is a family of seven who have converted their second TT to a "bunkhouse" and with real skill, I might add. The addition of a dishwasher is worth noting. Uses less water, ha! Sold me on adding one to mine (as the "utimate" setup on mine is for two couples). This family used to use a 7.3L FORD diesel van.

Our 1986 32' Excella Rehab -- from rear bedroom to bunkhouse with two bedrooms

The quality of work, as well as material/appliance choices, is VERY high in these two threads. Cheaper is generally not better . . . and these trailers are good for another few decades without any real work.

(Joining AIR is free, and one can set page preference to 100-posts/page for easier reading).

As a comparison, the 2015 25' Airstream highly optioned is around $130,000. And a BOWLUS at $110,000 (one buys these not as a car but as a second house under terms of mortgage: low monthly payments over 20-years or more). A post-1996 Airstream is the best buy for least amount of work, and a 1980's model and later avoids some of the failings of earlier years. The 1950-1963 years are highly coveted and expensive to buy, repair and operate despite "ideal" size and shape.

There are a number of well-known shops specializing in Airstream resto, but it is $$$$ work. An excellent condition candidate (let them locate and buy it for you) is priority one in keeping costs down. Otherwise expect that, with the decision to buy or build your own -- starting today -- one is around five years out from using it to travel full time.

DIY has huge setbacks not usually well-examined. But the Internet has made possible reasonable comparisons. Two years for a good one bought today needing limited work (can be used in the interim, but full resto over a longer period) is a good approach.

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Do we know the drag coeffcient of a typical (any?) Airstream trailer? Google hasn't yielded one for me yet.

A little better than a sphere (≈0.47) maybe? Worse due to awnings, A/C, and other stuff?

FWIW, I bought both trailer and truck in my sig for just under $30k, but expect to spend more than double that amount over time (this is my home, after all).

So lets look at a vacation for two or more people where access to a major national park is the point. Spend the time there in various activities. And a bit of other driving around for fishing.

From South Texas to Rocky Mountain National Park is 1,200-miles. If I stay two weeks at one location (paying the premium this area requires) and my daily fuel consumption is divided out by the number of days of the entire trip (or, say 2,500-miles to be conservative) as against ground rent we can come to a daily rate of fixed expenditure.

Who among us wouldn't want to spend two weeks in the Rockies during the summer? And to see the reasons our great-grandfathers chose such a spot for a national park.

I can easily carry three weeks worth of food for two as well as have enough water + propane before setting out. Call this zero daily travel expense. Quality food bought and frozen, etc. Wine, beer and spirits on sale. Like the trailer and tow vehicle it is not trip dependent. (my propane capacity for a trip like this almost isn't relevant even using the furnace nightly and cooking twice daily; an advantage of "big").

$3.25/gl diesel at Denver as of today. Same here at home.
2,000 miles at 15-mpg = 133/gls. $430.
200 miles at 9-mpg for summertime mountain traffic; $72.
300-miles of solo at 18/mpg = $54; or,
$560 at an overall trip fuel burn of 172/gls = 14.5 mpg.
21-days = 8/gls diesel/day, or, $26

At $4/g diesel, $690 or $33/day fuel cost for the trip.

At one of the RV parks closer in to RMNP: $600 for two weeks of full hookups.

$33/day for diesel, and $45/day ground rent.

$78/day over 21-days to go on vacation

Overnights en route -- sans utility hookups -- at truck stops, rest areas, WalMart or other is zero daily expense. And I still take a hot shower, cook meals and have electricity for general purposes. Stream a movie, read a book, you-name it. (This also applies to boondocking in the main).

With full utility hookups: two 15k BTU A/C, run the microwave/convection oven, dishwasher, hairdryer, espresso machine, home theater w/ surround sound, WiFi hotspot, satellite radio & television plus amateur two-way radio and clothing washer/dryer, etc. Mine really is a rolling condominium. But not a 7-mpg Class A motorhome or obese fifth wheel.

The adherents of this sort of travel call it "glamping" [glamorous]. With a separate genset I could do both. There are now hybrid solar/gensets that can keep both to a smaller footprint & weight and can run an RV most impressively. Using these other devices is a choice, not a requirement. (I don't have all the above, but could and likely will as the goal is comfort for two couples. Not all places are shirt sleeve weather and one can have the need to hunker down somewhere for an extended period).

So, $1100 to $1200 for a three week trip to cover fuel and ground rent. Short of fees for access to park amenities one can see that ground rent can be fully half or more the cost of a trip. 50-cpm in fixed expense plus food, propane and other.

Fuel cost isn't the problem given good vehicle spec at the outset. Figures above are conservative as I believe I could actually do better than this. A different trip to other locations in Colorado off season would still be about the same given the occasional need to replenish and refresh at an RV park, plus the mountain driving would cause a drop in towed mpg. Call it five days of hookups at $50/day. Or, $250 + fuel.

$1200 is a good number, IOW. Increasing mpg by a small percentage isn't going to change this trip. KamperBob does a more minimalist type of travel, and I recommend his blog, not just his advice (which is very good).

OTOH, I took up the challenge from Diesel Dave to try and see if my solo city-only mpg could be increased from 18-mpg. Over an 1100-mile test I averaged 23-mpg. That, alone, pays for around 5,000-miles of Interstate towing. Free fuel, boys & girls, if my then annual average miles savings were applied to vacation fuel costs. Just cutting annual miles by combined trips will do this without any hyper driving.

Focusing on the trailer isn't the payoff some expect it to be. A turbodiesel tow vehicle is where the money is. The right aero TT is the economical choice because it tows so well and lasts so long. Terms of independence from outside supply is the key, here, since trailer size is a negligible fuel cost given proper design, not low weight or short length.

Combine the two in a smaller package than mine (SUV or sedan + 23' TT) and fuel costs are better on average by 4-mpg -- for the trip above -- to 135/gls. Call it forty gallons ($160) or $7.50/day. A meal at McDonalds. But it may be easier to park somewhere (and at home) and has a lower utility cost overall, but at the expense of payload and water/propane capacities. Trade-offs abound. Etc.

60,000 miles is about the lifespan over ten years of a conventional plastic box RV. 25-years and 250,000 miles for an Airstream type TT . . . and then you rebuild it instead of tow it to the landfill. Run the fuel economy numbers against this time/miles framework.

An OLIVER as mentioned previously, is going to have most of the same benefits. Over 20' for a regular bed and good bath size is a minimum for extended travel in my opinion (and that of many others). I also prefer a tandem axle trailer as they pull so much better.

Make the SUV in the pic below a 3L DODGE EcoDiesel. For a new rig without the cost of an Airstream (the Oliver ain't cheap, though) long term ownership and operational costs would be near to best as could be. 20-mpg highway should be do-able given attention to lash-up details (a PRO PRIDE hitch).

http://olivertraveltrailers.com/wp-c...-trailer-2.jpg

Okay, Bubbas & Bubbettes, more than you want to spend. I get it. But see where the money actually goes. Don't overemphasize one aspect at the cost of others. Ain't nothing cheap to buy in vacation areas. Not to mention the time to track down inferior goods that takes away from being away. That'll kill any putative savings in fuel if more fuel and time is necessary to keep going when supplies run out.

Find out what is state of the art, now, and make good choices per your time as against being able to travel today. Five extra mpg five years from now doesn't seem so smart to me. KB's SCAMP 5'er does 15-mpg behind his small Toyo gasser pickup. It is of a size with decent capacities. And purchase price had to be low, lower than my low purchase cost I'd wager. As well, the ongoing cost of ownership on both vehicles (repairs and maintenance) will be lower as well. But not the fuel cost as it is barely $100 less for the same trip using conservative numbers. (I could re-arrange the type and number of miles to meet or beat his rig with mine as solo is higher for me). See?

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The Clipper has that optimal shape (on the outside, inside there is less overhead storage), but the construction is an outer skin of aluminum, aluminum C-channel ribs and the inner skin in steel. The additional weight isn't a problem as much as the combination is galvanicly active.

They all have floor rot. That's why I like shipping containers.

I'm over it. If I'd made that work, I would never have lived in the geodesic dome. That was good as it ever got, for me. :thumbup:

Glad you brought up those points before someone searches one out. Trailers that age demand a high level of skill. Aerowood for skills guru on AIR.

By the mid 1960's this is not quite so given a trailer stored under cover. 1983 and later is fairly conventional in all respects with fewer frame problems (being able to use standard RV suppliers past Airstream-only minor items); 1996 and later for the "wide body" thus new in A/S terms .

There are those rigs at 20+mpg with the latest (and not the smallest) Airstreams behind TD SUVs.

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I think we tried an estimate earlier. Search posts by aerohead and Airstream.

The gap between tow vehicle and trailer is more to the point. And, that crosswinds do not pile up and push against the trailer so much as that they flow over the radiused edges and exert a "pull". Much easier to live with and definitely has less of an affect at the steering wheel.

THe Airstream supplied figure is that it takes 20% less fuel to pull one.

HI-LO is another brand to look at.

http://www.rvweb.com/rvimgs/hi_lo_tr...d_exterior.jpg

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I'm in favor of hard-sided trailers, but a black bear -- god forbid a grizzly -- can tear open the much tougher sheet metal of a truck. Bring the lever-action .358 Winchester along.

My TT is considerably taller and wider than my pickup. Yet 16-mpg was not hard to achieve with the last one that was one foot shorter and no lighter than the present one (see link in revised signature; pic of rig about post #25. Pic can be expanded several times). Turbodiesel is the answer to trailer towing mpg. 30% doesn't hurt in this instance. And these smaller vehicles (light duty trucks) can comfortably tow TT's with power to spare.

As to building ones own, having the trailer wheels outside the body means lower ground clearance and wider stance in re roll center. Much better stability. UHaul does this for this/these reason. Torsion axle is the way to go, not leaf spring.

My trailer has interior headroom of 6'4'. Exterior clearance with A/C on roof is 9'8". Width is 96". Height is the killer, not overall frontal area. I would much, MUCH rather have a trailer six feet longer than one foot taller.

Look to pics/spec of 1960's Streamline Duke for dimensions.

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http://ecomodder.com/forum/showthread.php/side-mirror-drag-effect-fuel-economy-quantified-95.html#post936

This suggested 40% improvement, but over what? 0.50 ==> 0.30, or 1.0 ==> 0.60?

The problem with a modern airstream and a modern diesel to pull it is you will never, ever, save enough on gas to offset the price compared to a $8000 10 year old common Chevy 5.3 Tahoe or pickup and a new $15,000 Jayco mid 20 footer. The first 250,000 miles is basically free. Personally I think the $15,000 Jayco charges is robbery compared to what you get let alone a $80,000+ airstream. Why I figure I will just build one. And if you are going to build one you might as well improve the shape a bit.
I get what you are saying about size and weight, but to me 30 feet is just wayyy more then we want. With all the mountains and curvy roads around here the weight does kill mileage. No matter how you try to drive you will be burning energy with the brakes. The reason I was talking about cutting down a big airstream was because and old 20' is still to much money while and old 30' is pretty reasonable. I also don't really care about, "man that looks amazing inside, like a fine yacht!" I just want warm and dry with a place you can sleep and stand upright in, a place to heat up some soup, and a place for my wife and daughter to pee in the middle of the night. Otherwise we aren't hardly in the thing from 9am to 9 pm. Our last setup was a big 12' lance slide in in a duramax crew cab. We could get 11-14 mpg (although with diesel $.70/gal more here not much better then a 454 getting 8-10 mpg) and also take our pontoon boat but the pontoon needed a new outboard and the truck sat in the yard all but 3 weeks out of the year and a couple weekends so we sold it all, about a $20,000 total. That $20,000 is what I want to keep the new setup (camper and puller) under but get the 14ish mpg on less expensive unleaded.

I say go for it. Salvage a trailer frame and construct the shell out of rolled 5x10' sheets. Two sheets per 5' of length and a single seam down the middle of the top. 20' needs 8 sheets, so at $125/sheet you have a single-layered shell for $1000.

http://ecomodder.com/forum/member-fr...17-trdrp1a.jpg

Airstream Cd
 

I've never seen numbers published for Airstream.Hucho shows a few caravan Cds from the late 1950s in his first book.
Since the tow vehicle/trailer combination is what we're after,we'd have to have numbers normalized to some specific reference tow vehicle.And the composite Cd is based on the trailers frontal area.
For a clue about the Airstream,look at the radiused bus body of Cd 0.314,and then think about that Cd being lower,as it is partially shielded while drafting the tow vehicle.
http://i1271.photobucket.com/albums/...ead2/Scan1.jpg
The gap affects Cd
http://i1271.photobucket.com/albums/...Untitled-6.jpg
And if the tow vehicle is sufficiently large,the trailer drag can be cut in half.
http://i1271.photobucket.com/albums/...head2/Gaps.jpg
It's complicated

Since the closest fit is at 0.314 Cd, it appears that the tapered Airstream might have 0.263/0.314 or 84% the drag of the donor vehicle. Replacing the back window with a door would create about the right amount of taper.

I never intended to keep re-posting that manila folder and masking tape model. It was based on a 4x12' sheet of plywood with 4', 3' and 5' bottom edges.

I shall revise it into a 20'er with 4ea 5' bays. The first a wedge, the 2nd a straight barrel section, a third with the [single-axle] wheelwell and taper in plan but not elevation, and the 4th as a transition to a Gothic arch.

aeerohead can confirm I'm heavily into Gothic arches.

Something in that series of "buses" doesn't add up.

.88 Cd to .36 by just rounding the front? That doesn't agree with other known Cd's I've seen (NASA and others).

I think the claims of an Airstream being about 30% better than a "normal" trailer are probably close, some from a better Cd, and some from a smaller frontal area. Which is also in the same ballpark as one of the NASA studies where they rounded the front of a boxtruck. 30% better than .88 is .62, way off .36.

Which is all just speculation. No real wind tunnel tests = no real number. Seems like there isn't one out there.