Improving MPG

[Donna D.]

... there's an interesting thread going on over on the Casita Forum: http://www.casitaforum.com/invboard/...improving-mpg/

for those of you that can't see it, they're discussing this mod... note the Casita info about half-way down the page. Aerodynamic truck, trailer, RV add on for fuel saving, stability, safety

[Thomas G.]

I like the pizza pan wheel covers.

[Donna D.]

I did too Tom. Big disks, kinda old skool. Remind me of rodded Mercs.

[Thomas G.]

Originally Posted by Donna D.

I did too Tom. Big disks, kinda old skool. Remind me of rodded Mercs.

Exactly - influenced by salt flats cars.

[carlkeigley]

$220.00

Products to Improve Gas Mileage and Improve Engine Performance

[Thomas G.]

Originally Posted by carlkeigley

$220.00

Products to Improve Gas Mileage and Improve Engine Performance

I wonder if you could just glue on some dust pans from the dollar store?

[MC1]

Just buy an Airstream...

There are some real deals out there if you don't mind a fix-r-upper...

[Bob Miller]

The AirTabs show up about every 2-3 years on several motorhome sites I am on and, so far, other than posts(?) by those wanting to justify their $200+ investment, about all I see that's valid is an Egg owner that claims they keep the back window cleaner.

Wouldn't one think that if even a .1 MPG increase was possible that every OTR truck in America would have these things by now and that at least a few coach builders would install them at the factory to hype better handling and economy????

I might have been born at night, but it wasn't last night.....

[Donna D.]

Snake oil then? I thought someone like Mike who tows his LilHauley for a living might find it of value and it does keep the back end cleaner which is were his door is. I know I wouldn't put something like that on my trailer if it blocks the windows.... I'll just drive slower

[brian m.]

Hrumpff ...

Here's the details from their website. Note the phrase "but the theory" and "results may vary" ...

Airtabs™ are patented, unique wishbone shaped vortex generators designed to increase vehicle aerodynamic performance and fuel economy by reducing aerodynamic pressure drag at two key locations; the tractor-trailer gap and the rear facing surface (the base area) of any commercial or private square backed vehicle or trailer that routinely attains highway speeds. Drag reduction and fuel economy benefits from Airtab® application is not limited to commercial trucking operations. Airtabs™ enhance aerodynamic performance equally well on cube vans, straight trucks, expeditors, SUVs, RVs, buses, horse, toy and utility trailers, faired "bob tail" tractors, flat beds and tankers. The results may vary somewhat with vehicle type but the aerodynamic theory and principles are the same for all.

[Mike Magee]

Nope, I am pretty skeptical of the airtabs.

[Donna D.]

Well, I tried I'm still going to follow the CasitaForum thread....

[Westcliffe01]

These are the real deal
Vortex generator - Wikipedia, the free encyclopedia





Commercial ones



Real VG's have sharp edges since they are intended to create turbulent wakes. Rounded off edges and such weaken that effect. But the RV owners probably complain about getting their hands cut on them while washing the RV.

I think the claims made on the website are pretty outrageous.

[floyd]

Originally Posted by Donna D.

Snake oil then? I thought someone like Mike who tows his LilHauley for a living might find it of value and it does keep the back end cleaner which is were his door is. I know I wouldn't put something like that on my trailer if it blocks the windows.... I'll just drive slower

Sounds strange to me, my Scamp gets plenty dirty on the front due to TV tires,but the trailer stays clean at the rear.

[SRD]

Washing and waxing nightmare + no $ savings = not a good idea.

[cpaharley2008]

I think one of those large airfoil wings on your tow, the same you see on big trucks may help, but these little things seem worthless

[peterh]

As Westcliffe01 pointed out, vortex generators are pretty common in the aircraft industry. You see them on the top edges of the main wings, just aft of the point where the wing's curve really starts to flatten out.

Look carefully at the water's edge in a glass. It's not flat; the water kind of creeps up the walls of the glass at the edges. That's surface tension.

Air, like water, creates surface tension and clings to surfaces when its molecules are collected and moving (or staying put) together. This is a great thing when it's cold outside, because you get a thin layer of air that warms and clings to your skin. On an aircraft wing, however, it's like having a layer of molasses sticking to the wings and creating unneeded drag. The vortex generators perterb the air, get the molecules to run in opposing spirals down the wing's surface to break the surface tension, increasing both the amount of lift the wing generates and increasing the speed and fuel efficiency of the craft.

Will it work on an RV or trailer. Absolutely . . . but.

RVs aren't like wings. They already have lots of little things sticking out, like vent covers, window trim, roof vents, air conditioners, solar panels. All these things hit the air as the trailer moves through it, kicking it up into a turbulent, non-cohesive mess. I guess it's conceivable that the turbulence might subside somewhat by the time it gets to the back of the RV, but the abrupt, non-tapered end of the RV would tend to do that anyway. I doubt this product does much in terms of drag reduction or improving gas mileage..

[stevebaz]

My Nissan Pathfinder gets an easy 21 MPH on the highway but when towing the 13 foot Scamp I fight between 15/16 MPH. My Pathfinder has a wing on the rear put on by the factory which keeps the rear window clean and may have a stability function too. But I do know when towing the 13 foot trailer the truck isnt working hard to tow it but I can hear the buffeting on the front of the trailer. I can hear the window cover slapping the front window with any change in pressure. The Nissan is probably blocking about 80% of the frontal area of the trailer I always thought of a wing mounted to the roof rack to bypass the factory wing when towing and maybe help streamline the trailer when towing. But most of my tows have been relatively short making any gains hard to track. I wanted to stick on a bunch of yarn tuffts and record the action with and without the wing using my Go Pro to see the effects if any but I have been too lazy.
Anyone have a cheap source of yarn tuffts about 3 inches long? I an scareed of sticking something on then taking a month to clean up the mess.

[Carol H]

Originally Posted by stevebaz

I always thought of a wing mounted to the roof rack to bypass the factory wing when towing and maybe help streamline the trailer when towing.

I have a wing mounted on the front cross bar of my factory roof mounted bike rake. Have done some pretty long trips without the bike portion of the rack on and with it as well as without the bikes and with the bikes. Only thing I actually notice with having the wing on the rack is if I have the sun roof open it does cut down on the rack noise from over head - only a bit though. No differences in MPG at least not noticable any which way.

[Brian B-P]

Originally Posted by cpaharley2008

I think one of those large airfoil wings on your tow, the same you see on big trucks may help, but these little things seem worthless

The aerodynamic purpose and function of a cab-top deflector and the vortex generators are completely different; each is sized for its purpose. The deflector smoothly moves the air around the front of the trailer (so a rounded deflector has he frontal area matching the exposed trailer front, and the wing type is nearly as big); the vortex generator just break up air flow in the thin boundary layer against the trailer walls or roof, just before the air gets to the rear corners.

Originally Posted by Carol H

I have a wing mounted on the front cross bar of my factory roof mounted bike rake...
No differences in MPG at least not noticable any which way.

I doubt this deflector would make much difference to trailer drag in any location, but I suspect that way up there (where it should be to protect the bikes) is too far from the trailer for it to matter.