Aerodynamics?
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Hill Bill E.
Oath Keeper
So true! My last trip was to CO for 2 weeks of running the mountain passes and trails.
My buddy Dave and I, both driving XJ's with full size spares and other stuff on the roof racks, beat feet heading to Denver to meet his brother.
We ran 70-80 mph taking the freeways the entire way.
I averaged 12 mpg:snorkel:
Coming home, we took the 'two lane' roads through Wyoming and South Dakota.
There I averaged 17 mpg!:Wow1:
The XJ is a brick on wheels.:elkgrin:
I did use a THULE fairing in front of the roof rack and spare, and that helped a lot, making a 2-3 mpg difference in my daily running around (lots of freeway and expressway driving @ 65-70 mph)
I have thought about adding a curved rear 'spoiler' like you see on some busses, just don't know if the cost is worth the 'I might snag that on a tree' and rip it off thoughts in my head:snorkel:
Yep, sure would be nice to have a wind tunnel for a day or three!:sombrero:
morrisster
Adventurer
Golf ball.
Did anyone see the "mythbusters" episode where they covered a ford taurus in like 1000 pounds of modeling clay and dimpled it like a golfball? - they saw improvement from 26-29mpg (even with the weight factored in) over a non dimpled car. supposidly the small divots create micro turbulance along the surface and actually make the car more "slippery" - creating a smaller area of turbulance behind the car. basically what a boat tail does without the extra length. do you think this would work on a big rig like an expo camper? do hydroforming or something to dimple the metal like a giant golf ball...
someone give me a truck/car/van for free and i'll do the work and test it for the collective "us"
http://geometroforum.com/topic/2481401/1/ = picture of the car in the first post
Did anyone see the "mythbusters" episode where they covered a ford taurus in like 1000 pounds of modeling clay and dimpled it like a golfball? - they saw improvement from 26-29mpg (even with the weight factored in) over a non dimpled car. supposidly the small divots create micro turbulance along the surface and actually make the car more "slippery" - creating a smaller area of turbulance behind the car. basically what a boat tail does without the extra length. do you think this would work on a big rig like an expo camper? do hydroforming or something to dimple the metal like a giant golf ball...
someone give me a truck/car/van for free and i'll do the work and test it for the collective "us"
http://geometroforum.com/topic/2481401/1/ = picture of the car in the first post
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slowtwitch
Adventurer
They are dimpling top end carbon time trial bicycle rims now for the same reason. Will the clothes be next?
The Kamm tail is also being used heavily in aero frame tubes while staying within regulation and making a bike that handles better in a crosswind.
For this forum, there's probably a very long list of other easier, cheaper things to do (and not do) to save the mileage. As mentioned, slow down. Start and stop smoothly. Keep everything tuned and properly inflated. Leave the five cast iron pans at home, and opt for something lighter. Do you really need the 35" super swampers and 6" lift to drive roads a Subaru could easily handle?!
st
Hilldweller
SE Expedition Society
Overland Hadley
on a journey
Interesting product. I like the idea.
I would be interested in others peoples input.
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westyss
Explorer
In theory these should produce vortex's and reduce drag by swirling the airflow to prevent the normal sharp angle of air travel that creates the turbulence. By swirling the airflow, the flow will not naturally try to flow into the void of air that the vehicle has created but will create eddies to let it continue rearward. But,,,,,,,you still have created a low pressure system behind the vehicle that needs to be equalized, so that swirling eddy the vortex generators are creating still may be "pulled" into the void, again creating turbulence, but maybe a little less. Vortex generators for aircraft are placed near the leading edge of the wing, and create a vortex so that the air is prevented from separating from the surface of the wing when the angle of attack is increased, and thereby reducing the chances of a wing stall. I am skeptical of these things working for that fact, but would like to see a wind tunnel test of them working with a smoke trail.
All that said, these are ramblings from a guy that just woke up and is still having his first cup of coffee, so I am not sure I would listen to myself, but it sure would be nice if they worked!!
All that said, these are ramblings from a guy that just woke up and is still having his first cup of coffee, so I am not sure I would listen to myself, but it sure would be nice if they worked!!
Terrainist
Explorer
26 mpg's to 29 mpg's from dimpling is impressive. Color me doubtful though. Many of these things seem too gimmicky. The proof is in the pudding as they say, and with getting better fuel economy being a prominent concern for many people we will start to flesh these things out. The things that work will work and there won't be anymore wondering. Vortex wings, dimpling... a collapsable, short, modified boat tail and a round roof combined with strategic fairings on all prominent leading edges should see a significant increase in economy. That's the direction I would go.
As requested here is a basic sketch. The black boxy camper is the main envelope I'm going for, overlaid on that are various tapers to corners for conversation purposes. Its a little hard to see with the line weights (couldn't figure out how to get them darker on an image export quickly) and each taper in the various areas are colored different, but again its hard to see. The green box is the truck.
Summary of dims: 7'-6" long base (just noticed I only drew 7'-4"), ~7-3"wide, ~5'-0" cabover length, 13" cabover depth (I might get that down an inch or two), ~4'-8" retracted height off bed.
Summary of dims: 7'-6" long base (just noticed I only drew 7'-4"), ~7-3"wide, ~5'-0" cabover length, 13" cabover depth (I might get that down an inch or two), ~4'-8" retracted height off bed.
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ETAV8R
Founder of D.E.R.P.
Interesting thread.
My mpgs dropped 1-2 after I got the flippac. One of my bad traits is going too fast so I'm trying to curtail that habit. I wonder if a removable fairing like those of Thule would work. I can't have it up there when I deploy the flippac but it would be nice to get some better mpgs again. Heck if I did try it why not make a second piece and dimple it to see if that would be even better. One reason golf balls are dimpled is because it is a sphere and has inherent drag very different than that of an aircraft or aerodynamic vehicle.
My mpgs dropped 1-2 after I got the flippac. One of my bad traits is going too fast so I'm trying to curtail that habit. I wonder if a removable fairing like those of Thule would work. I can't have it up there when I deploy the flippac but it would be nice to get some better mpgs again. Heck if I did try it why not make a second piece and dimple it to see if that would be even better. One reason golf balls are dimpled is because it is a sphere and has inherent drag very different than that of an aircraft or aerodynamic vehicle.
Terrainist
Explorer
1. One of the biggest things you can do is to make sure that the camper portion that goes over the truck cab follows the slope of the windshield. Or that it does not stick out beyond the front of the cab over the front windshield and that a fairing can be added to create the same angle up as the slope of the windshield. So many campers have the over cab extension that go beyond the front of the windshield, talk about an air dam. Might as well deploy a parachute and drag that around. So if you (a) leave room for a fairing to match the windshield slope or (b) design the slope into your camper - you are way ahead. I would say that would be about 20%-30% of your optimum achievable aerodynamic design. If you have that overhang, you are just about screwed.
2. Make that roof convex. Akin to this camper pictured here. http://xtrv.smugmug.com/gallery/8908475_XhKRb#591112274_qNHwE If you don't design it convex, then plan on designing a round roofed rack perhaps. What would amount to a bolt on rounded roof rack 'fairing' making the roof round.
3. design a short, easily collapsable boat tail. Something that can be bolted on and might take 15 seconds or less to get out of your way when you need to access the back or get into your camper. Akin to this http://www.roadtransport.com/blogs/big-lorry-blog/2010/06/post-15.html
Almost any camper design can be made into an aerodynamic shape after it is built as long as you take into account that you will be adding fairings to make it so afterwards. But not if you have that forward overhang above the windshield, nothing can be done about that once it is there.
Point being, that you can build your camper and then make it aerodynamic afterwards with proper design planning now.
Even the vertical protrusions behind the cab above the bed on both sides can have short collapsable fairings installed.
And what sort of truck will this camper be going on? I can't reload the thread right now for some reason to see if you mentioned it. If you are starting with a truck that gets super bad fuel mileage already, then you most likely will not be happy with any results you get.
2. Make that roof convex. Akin to this camper pictured here. http://xtrv.smugmug.com/gallery/8908475_XhKRb#591112274_qNHwE If you don't design it convex, then plan on designing a round roofed rack perhaps. What would amount to a bolt on rounded roof rack 'fairing' making the roof round.
3. design a short, easily collapsable boat tail. Something that can be bolted on and might take 15 seconds or less to get out of your way when you need to access the back or get into your camper. Akin to this http://www.roadtransport.com/blogs/big-lorry-blog/2010/06/post-15.html
Almost any camper design can be made into an aerodynamic shape after it is built as long as you take into account that you will be adding fairings to make it so afterwards. But not if you have that forward overhang above the windshield, nothing can be done about that once it is there.
Point being, that you can build your camper and then make it aerodynamic afterwards with proper design planning now.
Even the vertical protrusions behind the cab above the bed on both sides can have short collapsable fairings installed.
And what sort of truck will this camper be going on? I can't reload the thread right now for some reason to see if you mentioned it. If you are starting with a truck that gets super bad fuel mileage already, then you most likely will not be happy with any results you get.
Terrainist
Explorer
Addendum - I see you have a Dodge 1500. I'm going to guess you get maybe 12 city, 15 highway on the good days. If you were able to get 20 mpg highway if your beginning number is 15 mpg, then that would be a large % increase. However, as you can see it's still not great fuel mileage.
What kind of fuel mileage do you get now with camper on and what kind of mileage are you hoping to achieve?
What kind of fuel mileage do you get now with camper on and what kind of mileage are you hoping to achieve?
Good call. Didn't even think of that, I'll definitely have to pull some measurements and perhaps adjust the amount the bed area goes into the camper if required.
Do you think I need to go full convex or could I angle up over top of the cabover (with a flat panel), then go flat for a bit and then angle back down? I was also thinking of angling to the sides as well. This would in effect have one flat spot on the top (figured solar there) and then all sides sloping away to shed snow/water easier. Rational on the flat panel angels is just a bit easier to build.
I'm thinking I'll design this for my quad cab dodge but also make sure it'll accommodate an extended cab ford if feasible. I'm interested to see where ford goes with the direct injection stuff over the years.
I don't have a target MPG, I just don't want to leave anything at the table if some easy design modifications can bring them into play. Right now my mpgs vary by 15-20% based on speed. Cruising highways around 45-65mph I'll get high 13s almost 14. Cranking down the highways at 80-85mph I drop to around 11.5mpg. I don't have a ton of unloaded data but the 45-65mph highway speeds can get around 16pmg unloaded.
So as noted above the higher speeds (and more drag) really attack the mpgs quick but I don't know how much of that would be improved by aerodynamic improvements on the camper verse it just being a lot of truck to move in general.
chnlisle
Adventurer
http://autospeed.com/cms/A_3061/article.html
The test car in this case was a Honda Insight.
Five AirTab vortex generators were placed across the trailing edge of the rear hatch.
After fitting the vortex generators, the measured trip fuel consumption immediately rose to 3.0 - 3.1 litres/100 km, a 3-7 per cent increase over the 2.9 litres/100km average. No change in the feel of the car could be felt - there was no apparent improvement in stability, reduction in wake noise or any other positives. Simply put, the vortex generators made things worse.
On the basis of the scientific evidence that is available, and the results of this test, we very much doubt whether vortex generators fitted to the trailing edges of vehicles will reduce drag. That said, it is well worth closely reading the testimonials page for AirTabs at www.airtab.com.
