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Topic: Fifth Wheel Aerodynamics

Posted By: Bob Shaw on 04/14/09 02:02pm

Is anyone aware of any studies done on fifth wheel aerodynamics? I've where studies where done that show better aerodynamics for pick-ups running with the tailgate up than down. How does a fifth Wheel impact that? Are you better or worse with the tailgate up, or no tailgate? Do the vented tailgates make any impact?

Do the TV roof air foils really make any difference? If so, where would they have to be places and at what angle?

I did a search and couldn't find any results.

Thanks in advance for your replies.


Posted By: mkirsch on 04/14/09 02:11pm

Truck roofs are so flimsy nowadays, they won't support an air deflector. I can't even wax mine without having a suction cup on hand to pull it back out.

Since the trailer is directly behind the truck it's likely that tailgate position has little to no effect on aerodynamics.

I doubt if any studies have been done. 5th wheel towing is only a single-digit percentage, maybe less than 1% even, of the total pickup truck population. Not enough interest. There have been studies done on the aerodynamics of tractor-trailers.


2002 Chevy 3500 DRW/8.1/Allison & 2000 Palomino B1500 popup TC

-Yes, I haul a popup with a dually. No, I don't think I need a dually to haul a popup.


Posted By: bldrbuck on 04/14/09 02:13pm

I've had both a vented tailgate and a roof foil and did not see any great fifferance in fuel economy. You can find opinions both ways on an open tailgate.


93 Ford F350 Turbo Diesel, DRW, Crew Cab. PullRite Hitch. 35' King of the Road 5er, 192 Watts Solar, 2800 Watt Yamaha Generator, 1750 Watt Inverter, 2 Trogan T105 Batteries, Me, my wife and 2 maltize furkids.


Posted By: crickeydog on 04/14/09 02:45pm

I've talked with several folks over the years who've put both louvered tailgates and roof top air foil's to use; none of them have ever said they'd do it again if saving fuel was the reason for installing either. All have told me to save the money spent on the tailgate and air foil and spend it on diesel fuel. One thing I did have a guy tell me last year who had a "Taylor" wing installed on the same truck we have who said it did keep the bug's off the nose of his 5'er. Pretty pricey bug killer if you ask me.

Happy camping!!! See ya'll down the road!!!


USAF RETIRED 02/1992 "EITHER LEAD, FOLLOW, OR GET OUTTA THE WAY":
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PULL DOG:
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2004 HOLIDAY RAMBLER PRES. 5'ER


Posted By: BB_TX on 04/14/09 03:13pm

Some 5ers are pretty flat on the front generally with a slight rearward slope. Others have all sorts of contouring. The aerodynamics would vary a lot depending on the model.
And the roof air foils are located so far from the front of the 5er, I don't think they would do much good. Just my opinion.


Posted By: StoneyPgh on 04/14/09 03:49pm

I'm very happy with the V-nose design of our 5er. I wouldn't know to measure the improvement in aerodynamics, but I feel that it must be somewhat better than the rather blunt front design of most 5ers.


Peter & Nancy --- We never had a bad day camping
'03 Silverado 2500HD LS XC SB 4X4 8.1L/Ally 3.73
Reese Pro Series 15K Kwik Slide Prodigy Controller
'08 Trail Cruiser TC527RL Rear Lounge V-Series 5er


Posted By: copeland343 on 04/14/09 05:11pm

I don't know if it is aerodynamic or not but if we tow our fifth wheel with the tailgate on every thing in the bed blows out (lost some wheel chocks and other things) We now have a V-Net and every thing now stays put. So now we do not tow with the tailgate. The front is rounded and blows air both over the trailer and into the bed


Posted By: LarryJM on 04/14/09 05:46pm

Bob Shaw wrote:

Is anyone aware of any studies done on fifth wheel aerodynamics? I've where studies where done that show better aerodynamics for pick-ups running with the tailgate up than down. How does a fifth Wheel impact that? Are you better or worse with the tailgate up, or no tailgate? Do the vented tailgates make any impact?

Do the TV roof air foils really make any difference? If so, where would they have to be places and at what angle?

I did a search and couldn't find any results.

Thanks in advance for your replies.


IMHO there is no cost effective thing you can do to gain anything aerodymaically from what you have now. However you can make things worse such as removing the tailgate on a P/U towing a normal TT.

Larry


2001 standard box 7.3L E-350 PSD Van with 4.10 rear and 2007 Holiday Rambler Aluma-Lite 8306S Been RV'ing since 1974.
RAINKAP INSTALL////ETERNABOND INSTALL



Posted By: Kejsj30 on 04/14/09 06:26pm

I took my tailgate off of the last truck and 5ver combo I had and I swear I had to keep the pedal to the floor to maintain speed where with the tailgate on it was an easy cruise. It was very strange.


2008 Chevy Silverado 2500HD
2008 Keystone Raptor 3712TS


Posted By: amxpress on 04/14/09 06:46pm

I witnessed the effects of aerodynamics between my TT and fiver.
I actually get better MPG when towing my fiver, even though it is 5000# heavier than my TT. Pulling the TT was like a box, where the fiver has a much more aerodynamic nose and curved roof.


2007 Dodge RAM 2500 Quad Cab w/6.7 Cummins
2013 Palomino Columbus 320RS
Reese 15K Pro Series manual slide
Prodigy
Firestone Air Bags
Champion 3500 genny
M.I.L denied parole! Yeah!



Posted By: Bob Shaw on 04/17/09 10:02am

Wow, I would love to see a wind tunnel test of these things. I'm sure the Titanium folds have had to do one, otherwise, how would they come-up with their over-the-cab design.

I know there are some mighty fierce winds in the bed of my pick-up when towing my 5'er, and it will blow stuff out over the tail gate, if I'm not careful. I was justg hoping there had been some research on the subject that would help us 5'er owners get the most out of our rigs, and be as efficient as possible.


Posted By: BenK on 04/17/09 01:20pm

One of my startups was in WindGenerators and hired two Aerodynamicsts (sp?) who
had retired from NASA Ames (Mountain View, the largest wind tunnel in the world
at that time...early 80's). Did lots of work on our towers, blades and heads
working side by side with these two.

Am researching my next trailer for my next career and have these links on file.

Basicly the reasoning behind Titanium's design philosophy is to reduce the 'gap'
between the TV and trailer *AND* to keep the leading air flow from ever dropping
back into the 'gap' between the TV cab & bed. There is little to none of that,
so there are next to no vortices between the TV & trailer. Think of how a hood
edge bug deflector works. In this case the air deflected goes up and over and
doesn't come back down to create a vacuum behind the TV cab.

Every time there are vortices, there is increased drag when it 're-touches' any
portion of any part of either the TV or trailer.

Semi's try to reduce the 'gap' between the tractor & trailer & trailer. Even
the air flowing beneath creates vortices that create drag.

Some of these links has great diagrams showing what those vortices are and do.
Both drag and pure high pressure area (think of a sail or parachute).

Notice that some semi-trailers have a tail cone that tries to keep the air flow
laminar and finally dumping it off to form vortices that will *NOT* touch any
thing on the tractor or trailers.


http://www.rvtrailers.ca/titanium/



http://www.donbur.co.uk/gb/products/aerodynamic_teardrop_trailer.shtml



http://www.heavydutytrucking.com/2006/03/072a0603.asp

http://www.freightwing.com/

http://airmansystems.com/



http://www.johnbridge.com/TravelTrailerAerodynamics2.htm



http://www.slipstreemaero.com/


http://www.atdynamics.com/products.htm


Moderator edit to re-size image to to fit page and to correct URL.

* This post was edited 04/17/09 04:21pm by an administrator/moderator *


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...


Posted By: wittmeba on 04/18/09 07:02am

My thoughts are what sophisticated equipment and how was the test performed to evaluate the mileage? I dont think the average PU truck owner would have such. Far too many factors that would affect the outcome.

I personally wouldnt believe the mfg of things like spoilers, deflectors or other addons either. A neutral study would be far more convincing for me.

Tailgate up or down:
http://www.dailyfueleconomytip.com/aerod......../fuel-economy-tip-keep-your-tailgate-up/

More comments here:
http://www.dallasnews.com/sharedcontent/........_0923liv.ART.State.Edition1.1c9f215.html

I read on another link where once you pass approx 50 mph, the decrease in mileage is very significant and expotentially decrease with speed.

But I did get some Super-Slippery Wax and my mileage did increase by 1.7 mpg


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Posted By: Gunpilot77 on 04/18/09 08:25am

As a transporter I have pulled hundreds of trailers, all shapes and sizes. Regardless of weight I pull them at the same speed to maximize mpg. The best mileage comes from fiberglass 5ers with rounded front and rear caps. I get the same mpg pulling a 35 ft Cedar Creek or Alpenlite as I get with a 30 foot enclosed empty bumper pull cargo trailer. The worst mileage comes from aluminum sided bumper pull toyhaulers. Because of the square, flat, oversize rear door all toyhaulers are aerodynamic disasters. I recently pulled a 36 ft fiberglas sided, 4 slide 5er from TX to Canada and even bucking headwinds the whole way got as good mpg as I get with the aforementioned TT toyhauler in light wind conditions.

I have seen hundreds of fellow transporters over the years. Every now and then I'll see one with a wing or deflector on the roof of the pickup. I spoke to one in Oregon who told me he was given the wing and he used it only because it decreased the amount of bugs he had to wash off the front before delivery (a requirement for new trailers). If they really helped mileage the word would be out and we would all have them. Full tme transporters drive over 120,000 miles a year (at least we used to). If the mileage gains advertised were true, having one would have saved me $1500 last year alone.

Long story short, if you are worried about mileage, get an Airstream, a pop-up or drive a Honda and stay in motels.


Fifth wheel pulled with a pick-up


Posted By: Bob Shaw on 04/18/09 09:53am

BenK, Thanks for the response. This was on the line with what I was looking for. I'm sure Titanium has done some of the wind tunnel tests. I just wish they were available.

* This post was edited 04/18/09 01:55pm by Bob Shaw *


Posted By: Gunpilot77 on 04/18/09 08:10pm

Gee, I guess real world experience without a wind tunnel doesn't count as a valid study. I'm sorry I wasted my time answering.


Posted By: LAdams on 04/18/09 10:45pm

Gunpilot,

You didn't waste your time answering... I found your actual experience to be of great value - you can't beat unbiased answers and yours was great because you make your living doing it... I'm sure if there were a answer for better mileage (other than slowing down), you would know about it

Les


2000 Ford F-250SD, XLT, 4X4 Off Road, SuperCab
w/ 6.8L (415 C.I.) V-10/3:73LS/4R100
Banks Power Pack w/Trans Command & OttoMind
Sold Trailer - not RV'ing at this point in time



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Posted By: Gunpilot77 on 04/19/09 07:17am

Thanks fo the kind words Les.


Posted By: Bob Shaw on 04/19/09 09:12am

Gunpilot77 wrote:

Gee, I guess real world experience without a wind tunnel doesn't count as a valid study. I'm sorry I wasted my time answering.


No, no, sorry, I really liked your reponse, and found it very helpful. Still, I was hoping for some wind tunnel test results. I knew about the pick-up wind tunnel test that showed that runnign with the tailgate up was better than running with it down and was wondering how a fifth wheel impacted that, better with a tailgate or without, and by how much?

Your response validates that buying a 5th wheel was a good decision. By the way, you say you always tow at a certain speed. What is that speed? I generally tow at about 62 mph, based on my GPS. That puts me at about 2,000 - 2,100 rpms on my 8.1 GMC. I notice that if I go faster, my mpg's drop pretty quickly.

Thanks again for your response.


Posted By: BenK on 04/19/09 09:28am

Gunpilot...I also enjoy and like your real world experiences.

It is a balance between empirical data and simulation. I still place
more weighting on long term empirical data (dependent on the person)
than pure simulation.

We coined that 'green/red light' designers when was at SunLabs. The
kids today tend to place all on simulations than real world testing.

We are now the OEMs test mules for most designs. No more are there
hundreds of vehicles racking up millions of mile out on the test track
and streets.

All of these trailers are compromises, not optimally designed for any
'ONE' vehicle, but for the majority if not all of them. Your real world
testing and observation has way more combo's in this matrix of setups.

Thanks for sharing!


Posted By: Gunpilot77 on 04/19/09 07:05pm

Well it is nice to know I wasn't being ignored. I drive at 60 which is 1900 rpm in my Dodge (Cummins 5 speed manual, 3.5 diff). Because of a few engine mods that is the lower end of my TQ curve. Stock it was 1700. If I have to drive 55 while towing I have to drop down to 4th gear and mileage goes down.


Posted By: 67Airstreamer on 04/20/09 04:11am

I have found that a wind wing on the rear of the cap of my F250 does increase the mileage a bit when towing my travel trailer, in the range of a half to one mpg.

(I also use AirTabs on the rear of the trailer, so possibly part of the savings is due to them, although I could not document savings with them. I got the AirTabs for increased stability, which they do provide.)

The wing keeps most bugs off of the top-front of the trailer, and I have to assume it is because the wind is being diverted up and over the trailer, carring the bugs along.

The wing is set at about a 35-degree angle. Setting the angle of the wing is a bit of black magic, because if too shallow, the wind is not diverted enough. If set too steep, the wing can create more wind resistance than it provides help.

I may be able to increase the efficiency of the wing with a different angle setting, but that would take too much testing for me. I did a bit of testing when I first got the wing several years ago, but it got the the point that I could not or would not finesse the process any more for maximum confirmed benefit. A wind tunnel would be nice.

I would not expect gigantic gains from a wind wing, but in my case, the approximate 4% to 7% fuel savings was good enough to keep. I begain using the wing because I lost some efficiency when towing a less aerodynamic trailer than compared with my Airstream, and the wing basically brought the efficiency back to the Airstream level.


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