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Old 12-07-2008, 03:01 PM   #1 (permalink)
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What should US Travel Trailer makers do?

I've got a challenge for the more creative people on this site...

We bought a travel trailer last year and learned quite a bit in the process of shopping for one. Like the cars on a train they are boxes on wheels to maximize interior space and utility - round the corners and it screws up something or other on the inside and pushes cabinet costs skyward. And at $15,000 on up, people won't pay for much in the way of fancy aerodynamics.

Also, it's a fairly major industry in some US states. (It's actually rather surprising that anything is still made in the US and not imported from overseas.) I imagine it's dying a horrible death right now - along with a lot of real jobs where they create real things.

Anyway, I thought I'd challenge the people on this site to come up with suggestions on what the trailer designers could do, cheaply, to improve the aerodynamics of their products and save their industry.

Just Google "images" for travel trailers and you'll see few design concessions are made by the manufacturers towards aerodynamics. (The 5th wheels are little better.)

eg - this is like the one we bought... a K-Z SPREE and I sure hope that big indentation in the front centre is a fancy aerodynamic trick - to me it sure looks like a parachute. http://forum.ecomodder.com/images/smilies/eek.gif

http://i1.imagesrv.com/1/564/i/50118...83_1037856.jpg

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Old 12-07-2008, 04:31 PM   #2 (permalink)
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The front end on that trailer is designed for adequate strength with a minimum of material, plus a window option. The recessed clearance lights are the only feature that might have been done for airflow.

Perhaps the best thing we could do for the trailer industry would be to make a kit of parts that would create a fairing to the tow vehicle. That would be better than having everyone make Airstreams. I'd start off by trying a big Coroplast box over the trailer hitch, flush with the sides, designed to support the back edge of a big cone attached near to the maximum diameter of the tow vehicle. The cone would only need a bit of bungee cord to keep it in shape, since air pressure would help hold it in position at speed. If wear ever becomes a problem, an extra skin could be stuck on.
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Old 12-08-2008, 12:23 PM   #3 (permalink)
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Welcome to Award Recreational Vehicles

Ive heard that these are some of the most aerodynamic travel trailers. I saw one for sale nearby a few years ago. It also had the frame beams drilled to reduce weight.
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Old 12-08-2008, 01:34 PM   #4 (permalink)
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Not knowing if they have the same length, weight restrictions as tractor trailers etc ... and advancement in that industry would be to adopt a system like the cruise liners. Build the interior component first then build the outside around it. That way you can still have a basic rectangle shape as a lead in price point then offer, aero add ons, like a front nose, teardrop roof line, boat tail rear, wheel skirts.

Offering these items as gas saving upgrades with data to back up fuel savings over the life of the trailer.
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Old 12-08-2008, 08:57 PM   #5 (permalink)
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The idea has been thought of before.

Bowlus Road Chief

Airstream, Inc :: Flying Cloud

Most travel trailers only travel about 500 miles a year. Unless you are one of those exceptions that travels more. the aero advantage is not worth the scarifice of cost and interior space.
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Old 12-08-2008, 10:40 PM   #6 (permalink)
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Quote:
Originally Posted by Big Dave View Post
Most travel trailers only travel about 500 miles a year. Unless you are one of those exceptions that travels more. the aero advantage is not worth the sacrifice of cost and interior space.
Beat me to it Not sure what the average is but the 1 percentile that puts many many more miles on isn't convincing enough to spend the money on R&D, implementation, etc.

All of that aside. I've been collecting a set of "Aero Rules" - here's a few that apply... I haven't really edited these - so pardon any goofy language Names in the curly brackets are the source/author

Front Corners shall not have a radius to vehicle width ratio (r/W) no less than .045 {PAWLOWSKI}

Winshield angle from vertical shall be biased towards 90 degrees to reduce cD {G.W. CARR} but, the reduction is not as much as assumed. After beyond 60 degrees, there is almost no further reduction and may result in optical refraction and cabin heat issues {R. BUCHHEM, et. al.}

Lower Stagnation Point is better {R. BUCHHEM, et. al.}

Optimal roof camber ratio (a_r/l_r): .065 Where a_r is height above "flat" roofline and l_r is the length of "flat" roofline. Assumes FA remains constant. delta cD = -0.02 {R. BUCHHEM, et. al.}

Optimal taper angle is highly dependent on the "history" of flow. {HUCHO}

With increasing length, positive effect of tapering become weaker. "Bob-tailing" or truncating thet taper results in little loss in drag reduction {D.J. MAULL, W. KAMM}

Rear diffusers: For a given area ratio (outlet area/inlet area), long diffusers are better. The same drag reduction can be had with a smaller angle rather than a shorter diffuser). Small angle = 2 degrees {J. POTTHOFF}



-----
What does all that mean?
1. You don't need much corner rounding to make a significant impact
2. Both top and side profiles should bell outward in the center (camber)
3. For long objects - resisting resistance is futile...


I think it'd be cool to see these things made like large fiberglass boats. Prefab the "hull" - drop in the prefabbed innards... Glue on a "deck." That as opposed to the prefab wall on chassis method. If precise enough (and composite tooling can), a non square cabinet can be made a "standard" (routed wood or blanked/compressed composite) and allow for fast assembly that fits well.

-------
Now what should they do - aero aside?

Optimize material selection, manufacturing process and feature selection. Put cost, quality and innovative features as top priorities. Other factors should be secondary or tertiary considerations only if one of the three will benefit.
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Old 12-08-2008, 11:49 PM   #7 (permalink)
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We're still looking to buy a fullsize trailer next spring, but not 100% still. Size and weight is a concern of course.

I've yet to drag my tent trailer project into the garage for work yet. We're looking forward to trying this out next spring whether we get a fullsize or not. The tent trailer is small and light enough to be pulled by my Grand Cherokee. And our F150 hardly notices it. I know a couple folks that traded from fullsize trailers down to tent trailers that also carry ATVs. Size, weight, wind resistance had as much to do with their decisions as pulling only one trailer (Utah allows double tows without CDL) to save fuel.
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Old 12-10-2008, 04:47 PM   #8 (permalink)
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What?

The members have pretty much covered the physics of what could be done.Perhaps the manufacturing companies could present some "concept" trailers at their traveling RV shows around the country and see if they get laughed off the premises,or if people queue up to place orders. "Virtual" tours in autocad would allow the potential" market" to view and experience "virtual" trailers at relatively little cost (compared to experimental full-scale prototypes). Either way,if there is no public interest,"good business-practice" will dictate that they do nothing until forced.---------------- Preston Tucker established a business practice like the mobile home industry,marketing a product which did not yet exist.Color graphics by Alex Tremulis were enough to launch a car company based expressly on consumer expectations.Perhaps it is a propitious time for the RV industry.------------------- With accounts-receivable,in the way of deposits,venture capitalists will usually "smell" money and release startup money for a product launch.You just have to steer clear of Michigan State Senators!
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Old 12-11-2008, 07:31 AM   #9 (permalink)
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I think Airstream is the best going right now.

I had a 34 foot HitchHicker 5th wheel with a wing attached to the top of my pickup. It help with the wind, but was a trial and error on the wing angle. I think a lot has to do with the tow vehicle and how it channels air around the trailer - then up to the trailer to exit the air smoothly. You see some big rigs set up for something like this - let me find a pic somewhere...

Here is an example to get things brainstorming...maybe RV manufacturers could offer aero kits for the tow rigs to match the RV aerodynamics?



Lonestar:



Aero RV stuff:



Titanium:



Maybe a modified "hi-lo" would be a good base to start out with then improve from there?

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Old 12-11-2008, 07:32 AM   #10 (permalink)
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PS I sold my HitchHiker and now just plan on throwing my tent in the Metro - how aero is that?

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