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Old 08-19-2012, 02:11 PM   #1 (permalink)
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aerodynamics & 5th wheels

Hey all,

OK, so came here looking for VG designs, now have way more questions...

I'm starting with a 2012 ram 1500 (quad cab, 140.5" wb), towing a 19' frontier 5th (3000lbs - just a baby not a monster 5'er) I'd love to post pics of the pair, but... well I'll leave that alone for now manufacturing defect hopefully get it back later this week)

Any who, wanted VGs for stability - as we spend our vacations running the rogers and crowsnest passes - side winds and passing trucks are a major issue, but researching placement etc, realized that's not my biggest issue... leaning towards a couple strakes on the roof + VGs on the sides. But now, what to do about the mess that'll be created between the cab and 5th...

Roof line of the 5th is only about 2' taller than the truck, deflector can be added easily, but with my 1 tow with the pair - I literally had tool boxes flying in the bed (yes with tailgate up) 5th has a v shaped nose, so I'm guessing its pushing a fair bit of air down into the bed of the truck...

Shot of the 5th:
<snip - guess I need more posts first>

Any thoughts on how to make the pair a little more fuel efficient?

Thanks in advance!

Andy

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Old 08-19-2012, 03:08 PM   #2 (permalink)
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The consensus here is that VG's are useless for fuel economy, and sometimes detrimental because they sap energy to generate vortexes. You'll want to research boat tails, belly pans and gap fillers. The deflector is only the beginning!

Boat tail:
http://ecomodder.com/forum/showthrea...d-e-18151.html

Gap fillers:
http://ecomodder.com/forum/showthrea...ta-t-7839.html

Design:
http://ecomodder.com/forum/showthrea...ign-18585.html

Smooth belly pan:
http://ecomodder.com/forum/showthrea...n-s-18427.html

Start reading!

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http://ecomodder.com/forum/showthrea...rt-c-9287.html
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Old 08-19-2012, 03:17 PM   #3 (permalink)
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Like I said - VGs are for stability, ran them on my truck camper and in side winds in the pass - they made an incredible change in handling... so we'll be starting there again.

But now I am pondering what can be done with the whole cab to 5th / bed area - its ugly when you throw it into the 2d wind tunnels, and I'm not sure the deflector is the fix, it makes it look worse...
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Old 08-19-2012, 04:00 PM   #4 (permalink)
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VG's may going to hurt your MPG either way so you may have to make up for it in other ways if you want a net gain in FE. I understand the need for stability, though. Do what you need to.

A deflector should help you in the FE department, but gap fillers would add to that- make it more effective. If you really want to get some MPG go for the low-hanging fruit of the boat tail. It's well documented that boat tails on cars can improve aero by 20-30% and MPG, respectively, by 10-15%. A 5th wheel has a lot more to gain, so with a fully streamlined setup you might see better than that on flat ground.

(For gap fillers, check out Aerohead's posts about his streamlined trailer behind the T-100. The posts may be spread out in several threads but the info is there.)

I haven't streamlined a trailer though, so go by what you read in the links. If one of those approaches suits you, go for it!
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Old 08-19-2012, 04:07 PM   #5 (permalink)
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Old 08-19-2012, 04:22 PM   #6 (permalink)
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I don't think boat tail is happening this year - though I'm contemplating a winter rebuild, to make some structural adjustments and re-skin... so perhaps the boat tail can be examined then.

Reading here, tonneau cover on the rear 1/3rd and something like a razor back - extending the cab roof line/ gap filler + deflector are probably my 'low hanging' Fruit?

The underside of the trailer is pretty clean already, save for the axle and tank drains. Thanks to a previous owner who was fond of sheet insulation...
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Old 08-19-2012, 10:27 PM   #7 (permalink)
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Ok, now that the forum will stop complaining about pics...

starting point:


now they're not linked (damn rentals and what was I thinking with buying a dodge? ) so angles are off, but spacing is pretty close...

so, what I need to work on, is adding about 2' to the cab profile, and adding a deflector? Should I worry about doing a tonneau setup on the bed at all? Or would that be counter productive? Like I said, my one tow with this setup had a plastic toolbox with my electrical tools (5ish lbs) literally getting airborne by the buffeting it was getting on a flat smooth road... had to stop and relocate it into the cab, so it didn't go missing (and with my luck - take out tires)

Extension/deflector, if I build like a 18wheelers daycab, peak about where the RV roofline is? Stick to truck width tapering as it goes up and back?
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Old 08-19-2012, 11:59 PM   #8 (permalink)
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Old 08-20-2012, 12:25 AM   #9 (permalink)
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Yep, read those...

question is really do something more like this:

Which would be fully on the extension...

or more like:


or the more typical flat plate? Ala kamperbob?
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Old 08-20-2012, 12:33 AM   #10 (permalink)
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Hello!
That tornado in the bed is a real drag, no pun intended. My thought was to build a system that got really close to the trailer face, that would move out of the way when turning sharply.
As far as boat tails go, thing about some simple brackets on the rear of the trailer, and removable or foldable panels like the new commercial trucks have. This is better than anything permanently mounted, if you ever intend to camp in tight spots. No need to re-skin anything.

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