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Old 12-14-2020, 06:16 PM   #15
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Shaped like a brick or shaped like a turd, fuel mileage will be the just about the same. What they build today seems to sell just fine.
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Old 12-15-2020, 05:21 AM   #16
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It's easier (cheaper) to build square cabinets, and you get more storage space in those cabinets ...
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Old 12-15-2020, 06:19 AM   #17
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Here you go if you need reading material - https://pdf.sciencedirectassets.com/...qa&type=client

Hard to make a House Streamlined - - so you can drive it down the Road -
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Old 12-15-2020, 06:58 AM   #18
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Here you go if you need reading material - https://pdf.sciencedirectassets.com/...qa&type=client

Hard to make a House Streamlined - - so you can drive it down the Road -
Interesting result in that paper in that Configuration B (pp 203 and 205), which only has the gap between the tractor and the trailer filled completely, is just a shade less slippery at 25.5% drag reduction than Configuration F at 26.1% drag reduction. Config. F has full skirting over the entire trailer.

As far as an RV goes, given the shape which is similar to a TT with cab/trailer gap fill, it's probably about as slippery as it's going to get.

No configuration included Airtabs or TrailerTails, which would have been interesting, and may be applicable to an RV.

Strange paper, though - full of typos, too.
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Old 12-15-2020, 08:24 AM   #19
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Different Goals

At 40 mph, a brick and a turd may have similar performance. At 85 mph the difference becomes obvious. Those of us who travel the high speed highways of the western US may have different goals than those who use the low speed eastern or western seaboard highways.

I choose to drive at 60 mph because I have a fetish for fuel economy and the difference between 55 and 65 mph is dramatic. If my TT were streamlined like an Airstream I would choose to drive faster. I would greatly appreciate that even though the economics and life style don't justify.
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Old 12-15-2020, 10:09 AM   #20
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This looks pretty slippery in the wind, too.
A slippery wiener is always better...
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Old 12-26-2020, 12:10 PM   #21
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The is no significant benefit to streamlining. Most major builders use cfd software like star-ccm plus, and the benefits are minimal
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Old 12-26-2020, 02:07 PM   #22
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I had a conversion van I put many aerodynamics on. Mpg improved from 12 to almost 15. Next was a 05 Fleetwood Fiesta. Added many too. Mpg went from 8 to 9+. Had a 20 degree sloping windshield. It helped. Then a boxy Bounder. Never got 8 mph.
Now a 32k lbs Discovery DP gets 8.8
It's got many protrusions. Flat front and rear. It's too nice to add aerodynamics.
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Old 12-26-2020, 04:05 PM   #23
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Interesting.

At highway speeds, most of the noise that our MB Class C RV makes is wind noise. A close second is tire/road noise and then last the MB diesel engine. Traveling into versus down wind is quite a dramatic difference though. I can only imagine the bow wave and wind noise of a Class A brick going 60 mph.

There were some cool & more daring designs in the past that were probably a bit more aerodynamic/fuel efficient. The Monaco Vesta comes to mind. A really unusual one was the 2002 Newmar New Aire 2802 Classic. The roof line on that coach was really something different.

From this article on tractor/trailer fuel consumption/economy : https://www.fleetowner.com/running-g...el-economy-101
"Aerodynamic drag (wind resistance) accounts for most truck energy losses at highway speeds"

The addition of roof deflectors, side fairings, rear "wings" etc..are not for nothing.

The 2021 Winnebago Journey tucks the awnings into the roof line. The Navion does as well. It's a start.
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Old 12-26-2020, 05:02 PM   #24
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I have to agree that wind noise is the loudest thing we hear while driving at 60 mph.

Our old Airstream was much quieter at speed, but it was also much more aerodynamic. Also lower over-all height by 18 inches, even without any AC's on our roof now.
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Old 12-26-2020, 08:00 PM   #25
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The major drags on anything moving through the are frontal area and the negative pressure (vacuum) behind the vehicle. As to the vortex generators you see on the side of some trucks I'm thinking they don't work too well otherwise you'd see a lot more of them. In fact, the winglets on the end of airplane wings are there to prevent a vortex from forming. Probably the best advice I have ever heard for increasing gas mileage is "Anyone in favor of saving fuel raise your right foot". This is an interesting discussion.
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Old 12-27-2020, 08:26 AM   #26
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Yes, to really get the benefit in terms of aerodynamics, you have to streamline both the front and back end, not just the front. (Like AirStream trailers, or the fiberglass egg trailers.) Nothing sucks like a vacuum.
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Old 12-27-2020, 09:16 AM   #27
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Agree this is an interesting discussion. One difference in comparing motorhomes to over-the-highway trucks is that trucks may drive a hundred thousand miles each year, so a very small improvement adds up to being cost effective. I don't see very many vortex generators but more folding "Trailer Tails", and even more of the (California mandated?) long baffles under the 18 wheel trailers. Also, note how many newer trucks have aerodynamic features. These cost money and wouldn't exist if there wasn't some benefit.

On the issue of whether the new, goofy styled motorhome fronts are aerodynamic; I can personally say that looking at some of these things make my eyes hurt so they are a safety issue and should be turned in to the NHTSA (Off topic: this applies to some of the new cars too. as Bob Lutz said "Why does a new car have to look like an angry kitchen appliance"



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The major drags on anything moving through the are frontal area and the negative pressure (vacuum) behind the vehicle. As to the vortex generators you see on the side of some trucks I'm thinking they don't work too well otherwise you'd see a lot more of them. In fact, the winglets on the end of airplane wings are there to prevent a vortex from forming. Probably the best advice I have ever heard for increasing gas mileage is "Anyone in favor of saving fuel raise your right foot". This is an interesting discussion.
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