Wind deflectors and Aero mods for fuel economy.

[JeffWright]

I was debating trying to find a solar panel to use as a deflector. The 100 watt Renogy survived a rollover accident and still works so I can’t imagine why it wouldn’t work as a deflector.

 

[ckent323]

The bugs that splat and collect on it will effectively shade the cells cutting down on its power output.

A small amount of shade over a panel can seriously degrade its power production.

The other challenge will be to keep it from flexing in the high wind environment and eventually cracking the cells. If you do this I recommend mounting it to a stiff piece of metal plate or equivalent that will preclude flexing.

If you do this please post pictures and give us an update how it is holding up after it has been in use awhile. It is always helpful to read about the results of new ideas that are implemented. Critics are often proven wrong. ;-)

 

[JeffWright]

Good advice!! I’m not super worried about the bug splatters. I think it will be much easier to clean than the one on my roof. And I’d imagine I’ll just clean it when I clean my windshield at the gas station. I think it will be easier to keep the snow off of it in the winter and I suppose I can angle the rig south and pick up a little more sun when it’s low on the horizon in the winter. I’ll keep you guys posted!

 

[ntsqd]

I wonder if a wind deflector at the back of the camper would help. Deflect air flow down to the back surface of the camper to reduce the pressure drop back there. The back side of our campers has an awfully large surface area. Some semi-trucks have fold out panels that basically do the same thing.

This is an often over-looked very large factor.

Think about the typical shape of a falling water drop. Water droplets can assume any shape that you can conceive of, but that is their actual shape when free-falling. Why is that? Aerodynamic drag "pulls" that tapered "tail" out from the main body of the droplet.

The flat rear of a camper is very much not an aerodynamic shape.

I had a 1966 Econoline long body van a number of years ago. 300 cubic inch straight 6 engine. Gobs of torque, super smooth to drive, got 10 mpg. It got 10 pulling the Grapevine at 80 mph, it got 10 coasting ~40 mph down CA33 into Ojai, it just got 10 mpg. UNLESS I was flat towing my fiberglass dune buggy behind it. Then it got 11 mpg doing any and all of those things. As "ugly" aerodynamically as the dune buggy was, that very thing filled that vacuum behind the very flat rear of the van and made the combo more aerodynamic. The buggy became the "tail" of the water droplet.

 

[Machinebuilder]

I have just learned about a product that looks very interesting. I may give it a try If I can figure out where to buy it.

https://seeiiairfoils.com/

I am as interested in the ability to keep the back of the camper cleaner, any Fuel economy would just be an additional benefit.

 

[BlueSky]

Found this, Airtabs... https://www.airtab.com/application-rv.htm

I think I will give them a try. Not terribly expensive, and I can probably use VHB tape to try them out.

 

[Bosque Bill]

Found this, Airtabs... https://www.airtab.com/application-rv.htm

I think I will give them a try. Not terribly expensive, and I can probably use VHB tape to try them out.

Hmmm. Seems counter-intuitive when aircraft engineers go to great lengths to minimize vortexes with wingtip airfoils, etc. to improve efficiency. Admittedly a wing is slightly different from the square boxes we push down the road.

Please keep is posted on your results.

 

[ckent323]

I flew on a large specially modified aircraft (say no more) that had a sliding door in the side that opened in flight (at altitude) to allow a large optical system onboard to look out of it. The leading edge of the door has a raised wing like structure with numerous holes in it to create a smooth (laminar) flow across the open port. It worked. It was a perforated air foil.

The multi blade airfoils (look a bit like a louvered window shade) also can work.

I have also seen dimpled air foils used on the trailing edges of big trucks to break up the low pressure area created behind the big box of the truck.

The perforated airfoil was similar to this image although the holes extended the entire length

 

[ntsqd]

ckent, if that was one particular DC-8 then I think they later gave those optics their own special windows so they didn't have to open a hole in the aircraft.

Who remembers these usually stainless steel side pillar mounted deflectors?

Eventually the OEMs offered similar features:

And they're still offering them on some models:

I recall seeing an experimental F-16 that had tiny holes in the top skin of it's wing. Had an APU fitted that pulled a vacuum thru those holes. The idea being to keep the air laminar regardless of attack angle. To the best of my understanding that "5th Gen fighter" in the latest Top Gun movie is using something similar.

 

[ckent323]

ntsqd it was not a DC-8 it was an RC-135. It never had a window. It has been decommissioned and repurposed. I was a civilian crewmember and flew on it many times I also helped engineer, install and operate parts of the system.

I have seen semi rigs with side baffles similar to those you show but variously with holes in them or dimples on them.

https://www.globalsecurity.org/intell/systems/cobra_eye.htm

 

[DavidGraves]

Howdy

I always assumed those station wagon wind deflectors were to help keep rear widow cleaner.

Many vehicle body shapes seem to carry a negative pressure at the trailing edge....witness the dirt on rear window after driving a dusty road.

Who'd have thunk ?

DG

 

[rubberlegs]

It’s fun playing around with an app like Wind Tunnel. I need to try a better drawing though!

 

[DavidinPhx]

You may want to nerd out to this:
https://ntrs.nasa.gov/api/citations/20120000497/downloads/20120000497.pdf
It’s NASA’s report on their research into truck aerodynamics …. I kid you not.

Also this: scroll down to post 248 for some real interesting graphics illustrating drag coefficients for various shapes and vehicle combinations. Searching this forum brings up some more real interesting stuff.
https://ecomodder.com/forum/showthread.php/full-boat-tail-trailer-gap-fillers-toyota-t-7839-25.html

 

[ntsqd]

You may want to nerd out to this:
https://ntrs.nasa.gov/api/citations/20120000497/downloads/20120000497.pdf
It’s NASA’s report on their research into truck aerodynamics …. I kid you not.

Also this: scroll down to post 248 for some real interesting graphics illustrating drag coefficients for various shapes and vehicle combinations. Searching this forum brings up some more real interesting stuff.
https://ecomodder.com/forum/showthread.php/full-boat-tail-trailer-gap-fillers-toyota-t-7839-25.html

Page 66 of the above link has a paragraph about the vortex generators. Excellent link, thank you!

 

[kmcintyre]

Wow.... a lot of info/reading, etc. Interesting too that they patented it. I wasn't able to read all of it and went to the end to the "results". I'll have to go back when I have more time and read it more closely but still not exactly sure what the final, best solution would be for our campers. I've eliminated most of the gap between the cab and camper which I think helps but I'm sure there's more I can do.

You may want to nerd out to this:
https://ntrs.nasa.gov/api/citations/20120000497/downloads/20120000497.pdf
It’s NASA’s report on their research into truck aerodynamics …. I kid you not.

Also this: scroll down to post 248 for some real interesting graphics illustrating drag coefficients for various shapes and vehicle combinations. Searching this forum brings up some more real interesting stuff.
https://ecomodder.com/forum/showthread.php/full-boat-tail-trailer-gap-fillers-toyota-t-7839-25.html

 

[buckland]

I made mine out of 1/8" aluminum. 4" high.

 

[JaSAn]

I made mine out of 1/8" aluminum. 4" high.

What improvement did you see?

 

[buckland]

quieter less buffeting, rear slide cab window airflow less noise and volume. I figure about a mile per gallon improvement. As I have 2 gallon Pax fuel (3) also in the space behind ...less turbulence.

 

[DavidinPhx]

[Page 66 of the above link has a paragraph about the vortex generators. Excellent link, thank you!

Your welcome.

FWIW, I put a row of AirTabs across the back of the roof of my Ovrlnd Camper as a cheap experiment. Didn't expect any MPG increase, but hoped for better dust control on my rear barn doors. Don’t think I got either dust or MPG improvement, but its so hard to say what works with all the variables. I did the AirTabs around the time I also regeared from 4.30s to 4.88s (on 21 Tundra). My mileage has definitely improved 1 to 1.5 mpg, but I attribute that almost completely to the regear.

I may put the AirTabs down the sides of the camper to get better dust control, but dont love the look of either color (B or W) on the anodized aluminum skin of the camper. I’m sure they do a little something, but its not enough to overcome the giant square hole we’re all punching in the air!

 

[BlueSky]

Thanks for the report on the AirTabs. I was going to try them but there is not a lot of room to put them on the sides. Recently I did a trip with a paddle board on the roof (Yakima racks) with the fins up (rocker curve down). The back of the paddle board was about at the edge of the rear of the camper. I got really good gas mileage on that trip. Maybe it was the way the air was channeled under the paddle board and directed downward at the rear of the camper. Perhaps a sheet of plastic at the rear Yakima crossbar angled down and ending just past the rear edge of the camper would do it. It will be an inexpensive experiment.