What's more important? - Page 2 - Fiberglass RV


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Old 09-28-2008, 08:41 PM   #15
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I vote for cupboards.

Sure aerodynamics is important but not that much with a small trailer being pulled behind a tow vehicle which buffers the air to start with.

I doubt you save that much on gas mileage with your design change. Not enough for me any way. What's a couple of mpgs....now if it were 10 or more mpg's I'd vote for aerodynamics.

I still say the tow vehicle has a bigger dynamic on the air flow with a small trailer.
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Old 09-28-2008, 09:05 PM   #16
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I guess it would be hard to quantify the increased fuel economy by sloping the front back, but if it was significant, like 10% or more, I would surely be in to it. It would likely be different for each individual tow vehicle too.

How much upper cabinet space would you be losing anyway. If the back was to angle in by 1 foot, then you would only lose 2 feet of upper cabinet space. (One on each side)

Again, glad you are looking in to all these things, and it was great chatting on the phone. I am very excited to see what the final product looks like. I am sure it will fit our needs perfectly, way better then anything else out there.
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Old 09-28-2008, 09:08 PM   #17
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RV manufacturers could take a cue from the trucking industry on this subject. With wind tunnel tests and principles of fluid dynamics used in the design process, the aerodynamic efficiency and fuel mileage of commercial trucks has improved dramaticly over the past 20 years. It would be a good subject for an on the ball RV manufacturer to exploit. They would be better able to do the research and change the design of their vehicles than individuals are. The aerodynamic efficiency of trailers and trailer/tow vehicle combinations is a little complicated because of the variety of tow vehicles but it could be figured out. Experiments could be conducted with different trailer shapes until they came up with designs and configurations that showed improved fuel mileage. The findings could be used at an advantage to market products. The trailer manufacturer that claims it's trailers are more aerodynamicly efficient and allow better fuel mileage and can offer some kind of proof is going to get a lot of attention.

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Old 09-29-2008, 12:31 AM   #18
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I agree a windtunnel would be great if the funding was there! Hey....election coming up....maybe the govt want to chip in for a good cause!

Peter you make great points on the front and rear and I think this is where the Oxygen had a great aerodynamic design. I didn't want to go that far tho.

We are in the process of building a new 17' mold and angling the front end was something that came up after touring the local RV show this past weekend. There are some goofy looking 'stickys' trying to save fuel....but today it is something to look at.

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Old 09-29-2008, 12:56 AM   #19
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I think Peter's comments were pretty well spot on. I think for these considerations it's best to strike a happy medium between the two. You might already have that with your present Escape design with its rounded edges but less overall roundness than a Boler. And, personally, those stick builts with the slanted down front end strike me as clumsy and I wonder about their effectiveness.

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Old 09-29-2008, 06:48 AM   #20
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We are in the process of building a new 17' mold and angling the front end was something that came up after touring the local RV show this past weekend. There are some goofy looking 'stickys' trying to save fuel....but today it is something to look at.
Reace, you already have the aerodynamic shape - it is the rounding of both the side and top corners of the front that really matters. Sloping the front a bit is 'styling' - it might 'look' enough like a low-drag shape to let another manufacturer justify feel-good claims in adverts or brochures, but what matters is the corner profile.

Here in Europe, trailer manufacturers do use heavily sloped front panels - but that is to make sure the very light hitch weight percentages used here don't result in a negative hitch weight at speed - the flow over the front of a trailer makes the front end lift as speed increases, but this will be much less apparent with the higher hitch weights used in America.

If you want to make the front end perfect, aerodynamically, then using an elliptical shape on the corners would be best - a tight radius next to the front, growing to a bigger radius as it smoothes into the top. After that, attending to the drag from the rear would be the next step, as peterh says. To cut overall drag, taper the back end of the roof down, really slowly, and end in a sharp corner - contrary to some folks' instinct the rounded corners on the rear will not be doing much good at reducing drag. However this suggestion would mean giving up headroom at the back of the body, so probably isn't very 'sales-worthy'.

For a view of what a really aerodynamic trailer shape looks like, see this new British semi trailer, with a long slow taper on the rear:



Name:   trailer.jpg
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http://www.donbur.co.uk/gb/products/aerody...p_trailer.shtml

What is important to notice here is that the cross sectional area of the trailer has been [b]increased in order to enable that teardrop shape to be used - usually any increase in area means an equivalent increase in drag (it's the single biggest factor), but in this case, by tapering the roof very carefully, the reduction in drag factor (often called Cd or Cx) is greater than the increase in area. Applying this shape to a travel trailer with, say, 7 feet of headroom in the middle in exchange for having only 5 feet right at the back, might not be such an impossible idea.

Road vehicle aerodynamics (a hobby interest of mine) is a complex issue and it's easy to get wrong. Some wind tunnel time would be really useful, but it's hugely expensive - unless you have a college/university with an automotive programme somewhere near you, in which case providing them some real-world student research projects will get you welcomed with open arms.

Andrew

Edit: This old NASA paper on building full-size aerodynamic trucks is a good 'primer' on the subject:
A Reassessment of Heavy-Duty Truck Aerodynamic Design Features and ...
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Old 09-29-2008, 06:57 AM   #21
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Hi: Reace... We already know about Slope nose aerodynamics. Almost everyone who sees our 5.0 says it looks "So Sleek"!!! In a trailer where every inch counts you must strike a ballance between interior storage space and exterior aerodynamics. I thought you already had... but you can always try to squeeze out some more. Just don't ruin the "Glassic" look of your trailers to be trendy!!! My 2c worth.
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Old 09-29-2008, 11:22 AM   #22
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Applying this shape to a travel trailer with, say, 7 feet of headroom in the middle in exchange for having only 5 feet right at the back, might not be such an impossible idea.
I like that idea.
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Old 09-29-2008, 11:33 AM   #23
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Poor Reace -- he would have loved to have a nice 95% consensus, one way or the other! However, we can see two distinct camps emerging -- the first focuses on efficiency, the second on convenience.

The efficiency group probably already leaves behind the things they don't need, because un-needed items add the other gas-mileage killer - weight. This group can generally make do just fine in whatever storage space happens to be there, and the loss of just one or two cubic feet of storage won't negatively impact them.

The other group places a higher priority on convenience, and will pack any and every available storage space with items that add to the comfort or peace-of-mind. The loss of even one cubic foot of storage is a significant set-back to the enjoyment of their camping style.

It is interesting, too, that the cabinet in question is a FRONT cabinet, which translates into pure tongue weight. This translates directly into tow-vehicle capacity, and therefore, to some degree, economy. For instance, my tow vehicle (which isn't Escape-class) is rated for 1500# of trailer, and for 150# tongue weight. However, the suspension can't really carry that much tongue, so front cabinets are a major negative to me in whatever I tow. My tongue capacity keeps my towing capacity down to about #1200, based on the 10% rule.
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Old 09-29-2008, 12:03 PM   #24
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I agree a windtunnel would be great if the funding was there! Hey....election coming up....maybe the govt want to chip in for a good cause!

Peter you make great points on the front and rear and I think this is where the Oxygen had a great aerodynamic design. I didn't want to go that far tho.

We are in the process of building a new 17' mold and angling the front end was something that came up after touring the local RV show this past weekend. There are some goofy looking 'stickys' trying to save fuel....but today it is something to look at.

Reace
Reace dont do a sharp angle front , this is ugly ,"sticky" hit the air like a wall! They have the Cx of a 40' contener! Your Escape is perfect like it is....Maybe one complain...Give us a bigger battery box! G...I wish you give anough space to carry 2 T-105 6Volt in your new 19' because we need them! Old time is gone we are in futur and we carry more power ungry luxury Item, Radio/TV/DVD Sat receiver and solar system just to name a fiew. We need power!

May the force be with you
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Old 09-30-2008, 03:12 AM   #25
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Aerodynamics
The complexity of this topic is massive, and altogether exciting to look at. The simple solution that you have come up with, will in all likeliness not improve anything.
You guys need to watch some Bill Nye!

But in all seriousness... (from my understanding), Most of drag that makes trucks and campers so inefficient is the back of the vehicle. As you are running down the road, you are displacing air, that you are running into (at the speed limit I hope). The issue is that the air has to be replaced (you are in effect creating a vacuum behind your vehicle), and air has to be filled/replaced into your wake. This replacement in your wake, is what slows you down, and it actually pulls you back. It also makes your engine work harder to overcome. Slowing down actually improves your aerodynamic efficiency...

Enter the teardrop shape. As you may know this shape is very aerodynamically efficient. The reason is, it allows the air to be replaced in the rear more effectively, and removes a lot of turbulence.

EDIT: Also consider the "cool" wing that many vans/cars use on the back of their vehicle. The idea has a scientific basis. The purpose is to redirect a stream of air behind your car, filling the void/vacuum that you are creating...

At any rate, I hope that I have added a little knowledge to your base...

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Old 09-30-2008, 10:13 AM   #26
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As always.... a wealth of information here!

Thank you all for your contributions....I will leave the design alone. I would the change the front in an effort to reduce drag and lose storage if there would be some gain over fuel economy.

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Old 09-30-2008, 10:28 AM   #27
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As always.... a wealth of information here!

Thank you all for your contributions....I will leave the design alone. I would the change the front in an effort to reduce drag and lose storage [b]if there would be some gain over fuel economy.

Reace
How about considering something with a pop up roof? It would fit into a garage, not get charged overheight on ferries, but allow plenty of headroom when camping.
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Old 09-30-2008, 10:59 AM   #28
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Close to 30 years ago my parents drove coast to coast with a 19’ stick built towed with a Ford Fairlane station wagon sporting a small V8. When they started out the rig would not go faster than 55 mph flat out on a level road with no wind. Somewhere mid country they stopped at a home center and purchased some plywood and made a simple air deflector for the roof of the station wagon. Now they could easily cruise at 65 or better.

I believe that rounding the corners of the trailer, as we have with our molded fiberglass units, would help some but the major drag reduction was to form a virtual smooth(er) shape, keeping the air form sucking back in at the back of the car (causing drag) only to hit the front of the trailer (causing more drag).

About 20 years ago I drove from SE Pennsylvania to Montana and back with 4 adults and one 18 month old in a Ford Taurus station wagon towing a small pop-up. The fuel economy averaged about 32 mpg if I am remembering correctly. This is better than I ever experienced with the car by itself. Similar but not as dramatic experience with the same pop-up towed with a full-size van. The pop-up seems to have created a much smoother transition for the air to fill in the air hole thereby greatly reducing the drag.

Reace, a roof mounted air deflector might be a very useful accessory product. A little more unusual but a removable fold up tail cone for the trailer might also reduce drag quite a bit. Just might realize significantly reduced fuel burn, good for both the wallet and ecology.

Don't give up on doing some experimenting. Many universities have small wind tunnels and are looking for student projects. You can also do some very meaningful model testing on your own.

Craig T.
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