aerodynamics & 5th wheels
 

Hey all,

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

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

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! :)

PS- here's the primer course
http://ecomodder.com/forum/showthrea...rt-c-9287.html

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...

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!

http://ecomodder.com/imgs/knox/nasa-van-z.jpg

;)

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...

Ok, now that the forum will stop complaining about pics...

starting point:
http://i74.photobucket.com/albums/i2...801F6-orig.jpg

now they're not linked (damn rentals and what was I thinking with buying a dodge? :D) 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?

Yep, read those...

question is really do something more like this:
http://images04.olx.ca/ui/3/56/44/56045244_1.jpg
Which would be fully on the extension...

or more like:
http://www.hankstruckpictures.com/pi...rd_aeromax.jpg

or the more typical flat plate? Ala kamperbob?

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.

Oh I've got idear's ™ for boat tail later ;) but we've got 3 days to reseal the roof and play with aerodynamics, I've got materials here to extend the cab, and build a deflector (thinking 1pc unit) possibly toneau & maybe get a few quick test runs on the highway - to do some go/no go final decisions...

fully extending to the trailer - with collapsible sides, not so workable in the timeframe available.

All our spots are tight ;) dunno if you can see the truck camper in the background - its got more pinstripes from trees than I would ever be able to fix... :D We don't tend to go where other people are...

http://i74.photobucket.com/albums/i2...D5DAD-orig.jpg

Front hoop bent, going with 1/2" emt on lighter gauge steel frame, skinning with a hammered finish aluminium sheet (just happen to have a dozen or so 20x30ish pieces around...

Guess since there's no input from here, I'll bend the rear hoop with the same general profile, just 2' taller?

Andy, IMHO a gap filler is your low fruit. A wide open bed fills with separation bubble effect. Actually two bubbles. Mirror image vertical plane down center. Sides and top wash back. Up wash behind cab. Yes down wash under nose back to tailgate. Little eddies behind add a bit more flow up over the tailgate. Flows forward also on the bed bottom. It's all about flow balance and boundary condition continuity.

Note your loft nose is angled and the top edge is radiused. I wouldn't bother with a high deflector for profile effect. In plan view you have sharp sides so bow splash around both sides. You could add on to the nose instead. Make it hollow for storage with sides that open. Over the ball is a great place for extra weight stability wise. That's where I put my generator. Does both actually. Otherwise gap over pin is value lost.

Quick reply. Rough I know. Food for thought?

Quick pix of rig
 

I don't have any pix handy of my whole rig in profile in present configuration with panel up. This off-side front angle views give some idea though. Gap is sub foot scale now.

http://ecomodder.com/forum/attachmen...1&d=1345493532

http://ecomodder.com/forum/attachmen...1&d=1345493532

Camera phone quality not the greatest...

We don't need no steenkinn genset ;) have 180w of solar on the roof probably have a micro lenz2 soon (just down to building a tripod/pole) keeps us happy and not needing hookups (not that we go to places that have them)

Yeah, formed the rear hoop and went... wow that's big... it doesn't ever seem so big in sketchup... so probably just cut it down some and skin it, call it done.

Have you jacknifed the trailer hard over to determine where to place that second hoop?

Wish I could... :) 2 week old truck... (well 3 now) down for 2 weeks for a new transmission... Rental doesn't exactly have a hitch :)

Wont be crunching it with the trailer though... Shouldn't be an issue, for any real maneuvering, I've got to slide the hitch back for clearance between the bumper & jacks, that'll leave me a theoretical 8" clearance even at >90deg.

Oh that bad idear about reworking this winter? :) see att'd...

Sounds like a good plan. Keep it close for cruising, then get your fairing clearance along with your bumper clearance.

Andy, what do you know about that B&W tear drop photo?

http://ecomodder.com/forum/attachmen...3&d=1345517838

I smell a good story. :)

BTW, I wasn't pushing generator use for you or anyone else. My point was gap filler. A cubby for gear? Chairs, grill, etc...

Its a '35 airstream torpedo, plan built airstream that just has a really sweet shape. :) the original plans have been posted in a few places now, although I'm not sure one would want to build them that way anymore...

http://1.bp.blogspot.com/_VfqCl4nEg8...-Truck-654.jpg

This is my 2nd favorite trailer design :)

Kamperbob - yup :) following the theory, just have to pull out the cheech "we don't need no steeeeenkin" every now and then lol - other than a cooler I can't think of anything I'd want to put up there...

holman_norman [Tin Can Tourists Wiki]

There's the rest of the story about that picture - crap I can practically hear paul Harvey reading it...

Its a damn good thing I'm not a professional tin basher...

Kinda grumpy with sore hands now... Pneumatic riveter puked on the third rivet- so by hand from that point on... thought I had set the front hoops angle so as to keep it within an inch of the cab... guess I knocked it and shifted things at some point...

Doesn't look too bad, did decide to run as a 12" deflector.
http://i74.photobucket.com/albums/i2...Untitled-2.jpg

So here's what I have to fix:
http://i74.photobucket.com/albums/i2...Untitled-1.jpg

I gotta see if I have some pool noodles around, those were good for a gap on the old truck camper...

Looks good!!

I'm still not quite happy with it... got a bunch of finishing to do, and this gap is driving me nutty, or should I say the 45° off the cab into a gap is making my head hurt... its close to 6" to span in places... duct tape isn't a solution I accept...

Thanks!

It's interesting that today's Basecamp model looks a LOT like a truncated version of the "original" teardrop. T@B came and went recently (and may rise again) with some noteworthy modernizations. But they got the nose wrong IMHO. Plan curvature was more useful inside with better aero outside. If only they Kammed the back and radiused edges for smooth recombination (instead of Vortex antagonisms) it would've been perfect. Still dang good, best in class, and far ahead of its time.

As for nose storage over the pin with a nose extension think stuff that folding chairs, dutch oven, BBQ grill & fuel, leveling blocks, wheel chocks, jack, tire iron, the spare tire maybe even, camp rake, small shovel, axe, bow saw, etc. It depends how you intend to use the trailer of course.

That should help with aero. I haven't been ABA religious about mine I data correlation agrees with qualitative perception and theoretical basis.

Will the back side of your gap cap be open or closed? If open, swirl from separation bubble eddies reach inside as deep as they can. If you drive through rain it won't stay dry unless closed up. Closed requires engineering convenient access. It'll be interesting to see your solution and learn from your experience. :)

The basecamp was supposed to be a throwback to the original, but I still like the original better... nevermind that the interior is pretty useless... its funny - every time I want something cool - I'm headed back to the 30s for inspiration.

I was planning to leave open, but it wouldn't be hard to slap a piece of poly carbonate on the back side - on a piano hinge for access...

Contemplating my way through a foam / fiberglass seal, want to grab so,e foam today for a drop in tonneau solution to test before we hit the road, but I have to go see if my RV roof reseal stood up to last nights thunderboomer first.

Playing with flow illustrator and windtunnel 2d now... Seeing if there's anything else that can be tested...

Deflector definitely is better than a gap filler, at least in the theoretical world of CFD in 2D...

Been playing with a wing design - see if one of those oldschool wings like we used to have on vans & hatchbacks in the 80s makes a difference (kick some air down behind the RV) but looks like for it to be effective it'd have to be 16" over the back to catch some clean air...

Interesting pressure zones between truck & 5th, not sure if this is 2D effect or real...

Interesting pressure zones between truck & 5th, not sure if this is 2D effect or real...

The "big truck rule" (as per KENWORTH) is that gaps between tractor and trailer of over 30" overcome aero aids such as spoilers. A closed gap -- preferably no more than 24" -- is where this "crosswind" begins to abate (and why I have a problem with the idea that a pickup pulling a conventional trailer is helped by a spoiler when the gap is generally four feet or more).

.

Spent the day beating my head against an aluminium roof ;) leak is still there, I just wish I could figure out where its coming from... water can't travel uphill can it? :)

I needs me a wind tunnel... this theory stuff sucks, I could be printing models on the reprap and be testing... all I'd need is a pressure sensor , anemometer and some humidity/pressure data...

In other words, my head hurts from trying to translate class 8 to RV ;)

you might try a v shaped or wedge between the 5th wheel and the tailgate, close to the bumper. attach it to the camper and include a bottom panel and tight to the underside of the overhang to throw the air to the side in that area. Might help

Kinda pondering that, there's actually a bunch of stuff I'd like to try out, but full scale testing gets expensive... so, I have a feeling, I'm about to start some scale model testing in the near future... got a 1:24 ram printing on the reprap now, working on a rough model of the 5th in sketchup - time for some wind tunnel testing...

And now have more Fab time, truck won't be ready until next week now... fml

bulbous
 

Pat Nixon,who ruled Texas Tech's Aero Lab fiefdom,put a VHS video together for me in 1990 from their pickup/trailer studies.
The best of all configurations was always the bulbous nose on the trailer.Kust like KamperBob has on his rig.

Has that ever been published? I'd love to see it :)

published
 

General Motors staff published an SAE Paper on it in 1963 I believe it was.They used the Guggenheim Aero Lab at Cal Tech to do model studies.
I believe that paper is mentioned over at the full-boat-tail-trailer thread.
With Texas Tech's video footage you can just observe what the smoke does,given different leading edge add-on devices.
In elevation profile,the bulbous nose wins.And from data also at the above mentioned thread,the bulbous nose wins in crosswind hands down.
All this is in Hucho's books also.

Well some real world testing in... 32km highway round trip (3 secondary highways), with some blustery weather... Secondary highways, so wasn't fighting traffic, tried to keep accel/decel rates the same, cruise to keep the drift down...

Working off the dashboard lie-o-meter, here's the numbers:

Truck - no 5th, 13.2L/100
Truck & 5th - 21L/100
Truck w/ deflector & fifth 18.7L/100
Truck w/ deflector (duct tape to fill cab to deflector gap) & fifth 18.4L/100

Ran 2 tests of each configuration (except the duct tape - it only got a single test) was +/- 0.1L/100 on restest

I'll leave the duct tape off :) 5L of fuel on this upcoming week's run - isn't worth having to look at duct tape.

Truck w/ deflector (duct tape to fill cab to deflector gap) & fifth 18.4L/100

Glad you're on the way. A gasser has some problems to overcome versus a few of the early 2000's turbodiesel 1T trucks. Pulling all-aluminum aerodynamic travel trailers from 28' to 34' (8k to 12k weight), a fairly common number is 14.7L/100 on level Interstate (these are 55' to 63' combination rigs).

The best I've seen is reports in the low/mid 10's for Airstream trailers below 23' pulled by Euro TD SUV's.

You and KamperBob and Skyking are all up to some good work. The potential for a 5'er is definitely high, and, [my guess] that will eventually pull away on the lowest fuel burn numbers.

.

12% better FE from your short cap is a nice win.

Found a nice pic on several forums of a slick two-piece "wing", but could not find any more information:

Here, at TurboDieselRegister

EDIT: Tried to find more information about this, but came away only with:

AIR FLOW
PH# 1-877-655-3244
WEB SITE= Wind-Tunnel-Designs.com
e-mail save @2wtd.com



.

Not to be rude, but I'm just going around telling everyone that designing your own vortex generators without an engineering degree is a bad idea. Pretty much ANYTHING other than VG's in the aero mods section I think is viable for amateur ecomodders, but after studying vortices, there's no way anyone without access to CFD, extensive wind tunnel hours, or time to get a mechanical/aerospace degree is going to be able to reliably design their own effective VG's. If you want to try go right ahead, but chances are you'll hurt more than you'll help, especially if you're just eyeballing it.