Aerodynamics?

[pods8]

Query popped in my head today about our generally boxy truck campers sitting on the back of our truck that tend to be larger than the cab. That would be about whether there is much aerodynamic improvement possible to affect MPGs. I know on my rig (Dodge 1500 w/ a Hawk) I get some MPG hit just for having the camper weight there but experience most of it when driving at higher speeds. This is common for any vehicle but I'm curious if the effects of the camper are amplified more so verse the normal vehicle.

I know some folks with larger cab top to cabover gaps have installed wind fairings to try and smooth the air out. I only have a 1.5" gap so not much concern there but the front edge of a FWC is rather boxy in the vertical plane, think a rounded front design would have much effect? Also the main part of the camper is wider that most truck cabs as well (on mine its ~4-5" past on the bottom and ~10" at the top of the cab). Would a design that tapered into the cabin do much in the way of improvement?

Anyone with much aero background able to comment? I'm pondering a build, not modification to my FWC, and curious if I should try to incorporate these types of features or not make things more complicated for little return if that happens to be the case.

 

[Terrainist]

I don't have an aero background as you requested. But fuel economy is something I am very interested in and I have spent quite a bit of time looking into the things that can be done to improve the mpg's on these rigs we drive.

I just spent the last 45 minutes trying to find the most comprehensive webpage I have found to date listing the improvements that can be done and the percentage of fuel economy improvement that can be expected, but I couldn't find it. So going off of memory, the fairing you describe in the front might improve your economy somewhere in the neighborhood of .7% - 1.3%. Not much. However, I have found that the rule of thumb is - every little bit helps.

All the little improvements you can make start to add up. The most applicable research regarding aerodynamics has been done on the big rigs, the tractors and trailers.

If you start to run some queries through google images you will begin to see what is going on and get a wealth of ideas.

By far the biggest improvement you can make is to design a "boat tail" of sorts. Approx. 7%-15% improvement, nothing to sneeze at. Ultimately, a wing or tear drop shape is what is the most aerodynamic.

Ecomodder.com is a good site to look at. Check the forums too. I pulled a bunch of links while I was looking for that aforementioned mentioned page. Somewhat generic, but it will give you an idea of what is going on.

http://eideard.wordpress.com/2009/11/10/boat-tail-reduces-truck-fuel-consumption/
http://www.tudelft.nl/live/pagina.jsp?id=bdec8a2d-d269-40d5-ba27-194253d7941a&lang=en
http://www.sti.nasa.gov/tto/Spinoff2008/t_3.html
http://www.nasa.gov/centers/dryden/news/FactSheets/FS-100-DFRC.html
http://apexforums.freeforums.org/viewtopic.php?f=4&t=5325&view=next
http://www.roadtransport.com/blogs/big-lorry-blog/2008/11/nasa-man-dolphins-teardrops-la.html

If a person were to factor in, design and build all that could reasonably and practicably be done to a truck and camper design, I do not think it unreasonable to expect a 20% better jump in fuel economy. Sort of neat that you are talking about a "build", you get to start from scratch.

 

[pods8]

By far the biggest improvement you can make is to design a "boat tail" of sorts. Approx. 7%-15% improvement, nothing to sneeze at. Ultimately, a wing or tear drop shape is what is the most aerodynamic.

Thanks for the links I'll dive into them. Yeah a boat tail is good but most likely would require far to much length/tapering which for my tastes (just an assumption on my part). In my head I see a lot of lost space and more complicated build if an appreciable taper is needed.

Sort of neat that you are talking about a "build", you get to start from scratch.

and talk myself in circles in the process. :Wow1:

 

[westyss]

I am not an aerospace engineer or profess to know alot about this topic, but I do know about drag, and some common drag bits are that drag coefficient rises exponentially with speed, the other is turbulance, eliminating turb will reduce drag, a square backed truck even with a nice frontal aerodynamic shape will create drag, I believe making a fairing at the rear is called a buttress? This can reduce drag significantly, like a tear drop, any surfaces that meet at right angles or sharp angles create drag, like a wing that is joined to a fusealage, you will see most new aircraft have a bulbous fairing where the two meet. So as close to a tear drop as possible with no large gaps or sharp angles will help reduce drag. The best way to reduce drag is to slow down.

 

[The Swiss]

When I had my Maggiolina RTT on my Jeep, I spent a lot of time trying to make my brickwall more aerodynamic. I slid it more to the front, more to the rear, increased the gap between roof and RTT, mounted it as close to the roof as possible, with fairing, without fairing. I'd love to have a wind tunnel to my disposal for a day . Whatever I did, increase or decrease of mpg was marginal. I did gain almost 2 mpg though by moving the RTT on the trailer and leaving the trailer at home :elkgrin:

 

[westyss]

When I had my Maggiolina RTT on my Jeep, I spent a lot of time trying to make my brickwall more aerodynamic. I slid it more to the front, more to the rear, increased the gap between roof and RTT, mounted it as close to the roof as possible, with fairing, without fairing. I'd love to have a wind tunnel to my disposal for a day . Whatever I did, increase or decrease of mpg was marginal. I did gain almost 2 mpg though by moving the RTT on the trailer and leaving the trailer at home :elkgrin:

Ha! see, its going real slow in your driveway and not producing drag.

 

[pods8]

I am not an aerospace engineer or profess to know alot about this topic, but I do know about drag, and some common drag bits are that drag coefficient rises exponentially with speed, the other is turbulance, eliminating turb will reduce drag, a square backed truck even with a nice frontal aerodynamic shape will create drag, I believe making a fairing at the rear is called a buttress? This can reduce drag significantly, like a tear drop, any surfaces that meet at right angles or sharp angles create drag, like a wing that is joined to a fusealage, you will see most new aircraft have a bulbous fairing where the two meet. So as close to a tear drop as possible with no large gaps or sharp angles will help reduce drag. The best way to reduce drag is to slow down.

What fun is that? :wings:

Yeah the rear is an obvious detractor but other than doing a little corner rounding and such I don't see a whole lot being practical on a truck camper without compromising and space/length.

 

[AmericaOverland]

The best way to reduce drag is to slow down.

And take your time on the trip. It's about relaxation, isn't it? Though I do have to admit that I drive fast on the longer trips, as it turns out that the faster I go, the better the gas mileage, and besides, that CRV rides real smooth beyond 80 if I don't watch my speed, which is why I like to set the cruise control and enjoy the old view.

Element owners have a saying at the online club - "Screw aerodynamics." I agree with them. If you want all those curves, why not become an astronaut and go on some of the first moon/Mars missions?

I have to admit that the boxier a vehicle is, like the older vehicles, the better it looks and the better it functions (if you keep it simple). However, (I don't understand the twist on this myself), I think that the FSJ style looks better than any style since in its line, except maybe the JK series (I wish these didn't have all the electronics on them, though).

So, cough up the extra money and enjoy these classic-looking trucks!

 

[Overland Hadley]

When I had my Maggiolina RTT on my Jeep, I spent a lot of time trying to make my brickwall more aerodynamic. I slid it more to the front, more to the rear, increased the gap between roof and RTT, mounted it as close to the roof as possible, with fairing, without fairing. I'd love to have a wind tunnel to my disposal for a day . Whatever I did, increase or decrease of mpg was marginal. I did gain almost 2 mpg though by moving the RTT on the trailer and leaving the trailer at home :elkgrin:

That is hilarious! I needed a good laugh.

 

[Overland Hadley]

The best way to reduce drag is to slow down.

Yes. Staying under 60-65 mph really helps.

Drive a full tank at a max of 45 mph and prepare to be amazed.

 

[pods8]

And take your time on the trip. It's about relaxation, isn't it?

If I had infinite time you bet. But when limited and I've got hundred of miles or expressway to cover to the place I actually want to slow down and explore then the gas gets pressed.

 

[Deleted member 9101]

If I had infinite time you bet. But when limited and I've got hundred of miles or expressway to cover to the place I actually want to slow down and explore then the gas gets pressed.

X2 I have been knows to do 80-85 pulling my jumping jack just to beat the rain to a camp ground....lol. I am a big fan of aerodynamics, but I cant complain too much,,11.9 MPG doing 80 with kayaks on top of the trailer.

 

[slowtwitch]

A Kamm tail oriented vertically would lend it self to the rear of a shell better than a full 'teardrop' shape and work at least as well if not better, all things considered. You can basically cut off the thinner part of the teardrop, and the wind will still flow around it as it it were there, yet be superior in crosswinds. Think outline of a Prius body... nice flat rear.


st

 

[pods8]

A Kamm tail oriented vertically would lend it self to the rear of a shell better than a full 'teardrop' shape and work at least as well if not better, all things considered. You can basically cut off the thinner part of the teardrop, and the wind will still flow around it as it it were there, yet be superior in crosswinds. Think outline of a Prius body... nice flat rear.


st

So basically tapper the roof to the rear a bit and make sure there is a decent radius on the back vertical corners? Any clue how long/deep of an arc the rear taper would be on something of this size?

 

[Terrainist]

You might come up with some sketches and have people take a gander at them. So difficult to do something like this through text messages. And the people to let have at it would be the peeps at Ecomodder.com, just from preliminary observations. I would think those guys would be all over this since you are going from scratch to try to nail down a/some designs. They live and breathe this stuff.