Airtabs, 14% MPG gain and (mostly) eliminates trucks pushing you around

[Jim Jacobs]

We installed Airtabs (Airtab | Aerodynamic Fuel Savers | Welcome) on our Jayco travel trailer in 2014 as a way to control how much trucks pushed us off the road when being passed at high speed. They worked really well, in fact, so well, we could hardly believe it, and our tow car mileage went from 9 mpg to 12 mpg, so when we traded up to our 2012 Thor ACE 29.2 last fall, we thought we should put Airtabs on it as well.

Initially, we drove from Ohio (where we had purchased the MH) back to Virginia and then from Virginia to Florida and back again. That gave us a "baseline" without the Airtabs. Going through the mountains coming back from Ohio we got 6 mpg, and a steady 7 mpg @ 65 mph to and from Florida.

We had hoped the size of our MH relative to the trucks would keep us from being blown to the side of the road, but alas, while better, it still wasn't as good as we had experienced with the Airtabs on our Jayco.

So, I measured the Thor and bought the tabs. They are $2.75 each. I bought 110 black and 70 white. Those are the only colors. If you want to match your exterior, you can paint them with Rust-Oleum plastic paint. All together with shipping, the cost was $518 which included some extras for mistakes. That might seem like a lot, but as I shall show shortly, it's not really.

These are small pieces of plastic in the shape of a "wishbone" with the back side filled in. The large opening faces the front of the vehicle, with the narrow point at the rear. Wind going through the device tends to swirl in a "vortex" pattern causing a slipstream to form behind the vehicle, rather than having the air stream curve around into the low pressure "vacuum" behind the vehicle. This reduces drag and aids fuel economy, but most importantly, it stabilizes the air currents so that passing trucks have minimal effect.

The back side of the air tabs has a very sticky, permanent adhesive. For installation, you take the protective paper off and apply the Airtab to the surface. You only get 1 try as the adhesive is so aggressive, that you don't want to make a mistake and think you can reposition it - you can't!

However, I worked out a simple technique for placement which did allow for positioning and then final placement. It turns out that if you peel the adhesive backing off a little more than 1/2 way and fold it back on itself so that it's sticking out just a little bit from the wide edge, you can place the Airtab and get the alignment very close to perfect. Then, because only the adhesive on the small end is actually touching the MH surface, you can rotate the Airtab making a small adjustment up or down. Once perfect, you hold the Airtab steady while pulling the rest of the backing out from underneath the Airtab, allowing it to then stick in place.

I used "easy off" masking tape to make straight lines for the forward edge and a small block of wood to make sure they were 4" apart. You can also turn one of the Airtabs around and without taking the backing off, use it as a spacer. It's remarkably simple and easy to do. Preparation for an aesthetically pleasing alignment takes longer than actually installing the Airtabs.

The Airtabs are placed 3 per linear foot, i.e. every 4 inches. I installed the black ones on both rear side edges as well as behind the wheel wells. On the roof, I used the white ones on the rear edge and along the sides of various skylight hoods, etc. I also put white ones on our Toad (a 2010 White Scion xB). The entire job took an afternoon.

Do they work? The answer is yes. I have 3 lines of evidence.

First, is the fact that we are no longer blown off the road as much as we were before the Airtabs. Do we know a truck is passing at high speed? Yes, but the push/pull on steering is very mild. However, we also installed a Roadmaster steering stabilizer, and that also helps with better handling so I can't entirely chalk up the improvement to the Airtabs. But they certainly feel like they help.

Second, is the fact that our model is built on a Ford F-53 chassis with a 5 speed automatic transmission. In cruise control, at 65 mph, we normally run just about 2100 rpm on a flat road. Before the Airtabs, at the slightest hint of a hill, our transmission would downshift. If the "hill" was particularly steep, it might downshift 2 gears and send the engine RPM revving into very high, nerve racking ranges. Now, after installing the Airtabs, we've noticed it doesn't downshift nearly as much anymore, particularly on highway overpasses. The engine increases RPM slightly and just labors up the incline, suggesting we have less wind resistance than we used to have. This downshifting problem, by the way, apparently has been corrected in the Ford models built after 2015? where they went to a 6 speed transmission, so if you're thinking about getting a newer MH and it's on a Ford F-53 chassis, go for the 6 speed transmission.

And lastly is gas mileage. We know from several long distance tests (1000+ miles) on the same interstate that before installing the Airtabs, we were getting 7 mpg on the mostly flat terrain between Virginia and Florida towing our Scion at 65 mph using cruise control. After Airtab installation, on the same run, same speed, we were averaging 8 mpg. Big deal, you say. 1 mpg increase!

But looking at in another way, that's a 14% increase in mileage. This summer we plan to drive some 7,000 miles as it's a long way from the East Coast to the West Coast and back again. In the "pre-Airtabs" era, we could have expected to use about 1,000 gallons of gas. With the Airtabs, we can expect to use 7000 / 8 = 875 gallons. If regular gas costs an average of $3.00/gallon (which many people are forecasting might be the case this summer), that will amount to a savings of 125 gallons x $3 = $375. Further, our Scion, which we drive for daily commuting around town gets 28.1 mpg and we're not trying to conserve. This is up from the 26 mpg before installing the Airtabs.

Suddenly, my cost is only $518 - $375 = $143, and that's just for 1 year. Since we will likely do this again in future years, I'm guessing the "payback" is about 2 years. Or put another way, if I hadn't put the Airtabs on, I'd be spending the money (for gasoline) anyway and not have the other benefits of a smoother ride, less nerve racking gear changes, and staying put on the road when trucks, in their great need to hurry, pass us by.

[Bob Denman]

http://www.thorforums.com/forums/att...1&d=1523829996

[TyCreek]

One little tiny note: increasing from 7mpg to 8mpg after a few 1000mi is very common with new rigs. ... Just something to think about when jumping to fact conclusions

[JamieGeek]

Yeah the V-10 is notorious for gaining a mpg or two in the first 5k or 10k miles--without doing a thing.

[Jim Jacobs]

Good to know about mileage increases for a new rig.

Ours, however, isn't new. It's a 2012 model and came with 25,000 miles on it.

[blw2]

I'm wondering about your sample sizes for the MPG data.....was that 1 MPG jump based on one trip of 1,000 miles, or multiple trips on the same route
I mean, the 7 MPG was based on multiple runs....I'd assume in both directions round-trip, over several different days right?

Was the 8 MPG based on one trip one way, one round-trip, one day or multiple days?

The reason I ask is to better understand the value in the data. Weather, relative wind, traffic conditions, and on an on all could affect 1 MPG average over a 1 direction a day drive. Cruise control does dampen out much of the traffic condition variable, but not all of it. 1,000 miles is what, maybe 2 tanks of gas... could even be a little bit of filling error in that.

I think to really know for sure, you would need many trips of that length over several different days, and they would need to be round trips, some North and some South, all with very careful attention to that cruise control setting.... my gut tells me I wouldn't be convinced fully with fewer than maybe 6-12 trips each with and without the airtabs.... there are just so many variables to dampen out and the 1 MPG difference is a lot, but not so much that couldn't be caused by a combination of many of these other variables, or even just one of them

Please don't take this wrong..... I'm not intending to poo-poo your report. On the contrary I'm extremely interested in it. I appreciate your post. I remember reading one other report that anecdotally indicated a similar result with these things. I've had it in the back of my mind for a while now....

As a side note... I'm an aviation buff and private pilot.... and a mechanical engineer by schooling. Back in college I did a research paper on vortex generators used in general aviation. Specifically micro VG's (https://microaero.com/). definitely an interest of mine.....

[Chance]

Originally Posted by blw2

....cut....

As a side note... I'm an aviation buff and private pilot.... and a mechanical engineer by schooling. Back in college I did a research paper on vortex generators used in general aviation. Specifically micro VG's (https://microaero.com/). definitely an interest of mine.....

Interesting that in FAQ section, it states tabs do not affect top speed, other than a 1% reduction at full throttle at 12,000 ft.

In order for a motorhome to improve fuel economy from 7 to 8 MPG, everything else being equal, the aerodynamic drag would have to be lowered by something like 20% or more. If that were the case (for a motorhome that is), the top speed would definerely go up considerably.

Not suggesting to do a MH top speed test to confirm effect of tabs, but airplane data suggest to me that either MH fuel-economy data isn’t accurate, or that the technology isn’t comparable between airplanes and motorhomes in a significant manner.

A 20% or greater Cd reduction would be nice, but I would think that if it were that easy, every truck on the road would already have them.

[Jim Jacobs]

The initial "pre-installation" test was a trip to and from Florida on Rt. 95 which is mostly flat. December conditions were dry both ways, i.e. no rain. We tried to be careful with filling the gas tank all the way to the "top", and getting exact measurements, but as you noted, it's difficult. We used "regular" gas at Pilot/Flying J because of the 5 cents discount through Good Sam, and were thankful for the small savings. Filling an 80 gallon tank can be faint inducing. I shudder to think of the cost coming up this summer.

The mileage wasn't exactly 7 mpg, more like 7.07 mpg, and the "after installation" was more like 8.05 mpg. That's still pretty close to the 1 mpg we're suggesting, but we could be wrong for some of the reasons you pointed out.

"Wind" is a huge factor and it is our sense that the trip "south" to Florida met more head wind than the return trip coming "north". However, we didn't keep track of the difference, just the overall mileage for the whole trip.

The second trip was to Florida and back in February, as well as another up to Washington, DC and back, both coming in at just (barely) above 8 mpg. At least the results were consistent even though the conditions were not identical.

However, the Washington journey was done at 60 mph, not 65 mph, so that alone could account for the difference. That said, the terrain is much more hilly, and that's what impressed (and surprised) us most, i.e. that the transmission didn't downshift nearly as much going up inclines, something we were not anticipating. I'm pretty sure that if (when) we upgrade to a newer model someday, if we stay with a gas engine, we'll get the 6 speed transmission which has not only better gear ratios, but apparently stops the insane down shifting through numerous gears when in cruise control at the slightest hint of a hill.

On our Jayco travel trailer, we didn't install Airtabs with the hopes of better mileage (although that is something the company touts, and we were happy enough to accept). We were looking for a way to keep from being blown off the road every time a truck passed us by, which can be quite nerve racking. Airtabs worked much better than we expected for that. The difference was instantly noticeable.

It was mostly, then, for the purpose of steering control that we installed the Airtabs on our "new" (actually used, 2012) MH. Any increases in mileage are incidental, although, much appreciated if true.

We will know more after this summer's long trip to the West Coast and back again. Conditions will range from hilly to flat, valleys to mountains, cool to very hot. Unfortunately, we won't have any "before installation" data to compare with, but I'll update this post along the way. Our current plan is to drive 60 mph under cruise control, but the West is a very big place and we may have to up that to 65 mph just to make it between RV parks where we already have reservations. That small increase in speed could make the entire trip much more costly. Here's hoping Airtabs show some quantifiable benefit.

[wredman]

Originally Posted by Chance

A 20% or greater Cd reduction would be nice, but I would think that if it were that easy, every truck on the road would already have them.

I would think that every car maker would incorporate something like it into their moldlines.

I wonder if this is less beneficial if the basic shape of the body already has a "boattail"

Lots of wind tunnel tests would be helpful.

[Thehobe1]

I suspect that your speed and traffic patterns have more to do with the MPG. In a previous forum discussion it has been noted that the difference in mpg at 75 mph and 60 mph can be easily 20% and maybe 30% different. Traveling across the country from Wisconsin to California late last Summer, I was traveling at speed from 65 to 80 mph and got terrible gas mileage compared to other identical RVs. The experiences ranged from my 8 mpg to 12 mpg for very conservative drivers. Maybe I should have used the miracle plastics. My RV engine was brand new as well and not broken in.

I'd love to see additional accurate testing procedures done to convince me to plant a few hundred on these wishbones on my RV.

Airplanes have certainly seen some benefit on their wingtips or they would not have gone to the trouble.

[Jim Jacobs]

Good question. I wonder if the Airtabs company has wind tunnel tests on RVs, especially ones like our ACE which has a very flat front face? Our rear end isn't a "boattail" either, though I was hoping that adding the Airtabs to the side of the "toad" would help direct the air around the both of us, treating us like a single unit, though no one would call a Scion xB aerodynamic.

[JamieGeek]

Did anyone do any searching before discussing this?

There was a lengthy discussion about Airtabs before, which also delved into boat tails on RVs.

You can read that here: http://www.thorforums.com/forums/f27/airtabs-1776.html
(Yeah you'll recognize a lot of the same users as in this discussion ! LOL)

[Thehobe1]

I think I will get some and mount them backwards and then report the decrease in fuel economy.

I think mounting them backwards would increase the amount of laughter generated (LPM = laughs/mile)

What a waste of time and money!

[Tom Bowe]

With the AirTabs installed are you seeing less accumulation of “crud” on the back of the motorhome when traveling on wet roads? You’d expect to see that if the low pressure behind the coach is being broken up, or so I’d surmise.

[blw2]

Originally Posted by Chance

Interesting that in FAQ section, it states tabs do not affect top speed, other than a 1% reduction at full throttle at 12,000 ft.

In order for a motorhome to improve fuel economy from 7 to 8 MPG, everything else being equal, the aerodynamic drag would have to be lowered by something like 20% or more. If that were the case (for a motorhome that is), the top speed would definerely go up considerably.

Not suggesting to do a MH top speed test to confirm effect of tabs, but airplane data suggest to me that either MH fuel-economy data isn’t accurate, or that the technology isn’t comparable between airplanes and motorhomes in a significant manner.

A 20% or greater Cd reduction would be nice, but I would think that if it were that easy, every truck on the road would already have them.

This might have something to do with the application and design intent. On the aircraft application, notice they are installed close to the leading edge, where on the RV they are at the trailing edge? For the airfoil, they are installed so at to add energy to the boundary layer, so that high angles of attack the air takes longer to separate from the wing. At high speeds they are virtually out of play.... the wing is at a flatter angle to the relative wind so the VG's are down further to the 'front'...so they basically don't do much of anything.
At the trailing edge of the RV, they are most likely adding the energy so that the air flow stays more streamlined (think teardrop shape) extending well behind the RV, as opposed to rolling straight around behind the RV

[Jim Jacobs]

I am quite sure they work for reducing the effect of a truck passing and blowing our MH right toward the side of the road. I am also quite sure our MH no longer downshifts when going up modest inclines as frequently as it did before applying the Airtabs.

Whether they increase gas mileage or not I don't know as the discussion about Airtabs has caused me to question our test conditions.

It's entirely possible the apparent 1 mpg increase is not real. There may have been less head wind, or more tail wind, or we spent more time in the slipstream of a truck, or any number of other possibilities.

To try to better gauge the effects on gas mileage, since I have a long upcoming trip and since I've been meaning to do so anyway, I decided to buy an EEZ Tire Pressure Monitor, model T515 with 10 sensors (6 for the MH and 4 for the toad).

Setup was straight forward, but I did have one sensor not register, no matter what I did. A call to the factory suggested I disassemble the sensor and test the battery. It's supposed to be 3.1V or 3.2V with a minimum of 2.9V. That sensor was 2.8V. Once replaced, it worked fine.

I bought the ones with the anti-theft covers, but they were such a pain to put on and take off, I removed the outer shell and just used the sensor "as is". This means, of course, they will be subject to theft, but that's a risk I'll just have to take.

Upon firing up the system, I discovered that the pressure in all 4 rear MH tires was quite a bit lower than expected. They were about 74 psi, with one as low as 70 psi. I'm pretty sure they weren't that low when running "before and after" tests with the Airtabs, but now I can't say for sure.

So the test I plan is to fill up as full as I can get the MH, drive 300 miles or so, towing our Scion toad, on an interstate using the cruise control and monitoring tire pressure which is presently set to the Thor recommended 85 psi. I'll record the gas used and miles driven. Then, after a short stay overnight, take the same route back home, again noting gas used and miles driven. I plan to stay out of the slipstream of trucks as much as possible and go a steady 65 mph (where allowed). Head and tail wind will be variables I can't control for. Driving will be during the day, hopefully without rain. If I have to run the generator or use the AC, I'll try to do so for the same amount of time both ways. Feel free to chime in with other conditions to try to control for.

By the way, this isn't being done just to try to answer the Airtabs question. I have to make this initial test run anyway on account of all the new gear we've installed. We have to make sure everything is in good working order before heading off for trade shows later this summer, which is our primary use of the MH, i.e. for business travel.

I'll let you know what I find.

[Chance]

Originally Posted by blw2

....cut..... At the trailing edge of the RV, they are most likely adding the energy so that the air flow stays more streamlined (think teardrop shape) extending well behind the RV, as opposed to rolling straight around behind the RV

I can see how a teardrop shape, like those of small teardrop trailers that resemble an airplane wing, could benefit from controlling the air flow. However, at the back of a truncated motorhome body, I personally can’t see how air tabs can make much of a difference. As a motorhome travels down the road at 60+ MPH, the squared-off body at rear will leave a large low-pressure zone (like a partial vacuum). Controlling air flow with air tabs to make it either more or less turbulent isn’t going to suddenly make the air flow want to make a 90 degree turn at back of motorhome. Hence negative pressure should remain about the same at rear of motorhome.

[Bob Denman]

Originally Posted by Tom Bowe

With the AirTabs installed are you seeing less accumulation of “crud” on the back of the motorhome when traveling on wet roads? You’d expect to see that if the low pressure behind the coach is being broken up, or so I’d surmise.

I was wondering the same thing.
But I'd never insult you, by saying that "Great minds think alike!"

[TyCreek]

Originally Posted by Jim Jacobs

We installed Airtabs on our Jayco travel trailer in 2014 as a way to control how much trucks pushed us off the road when being passed at high speed. They worked really well, in fact, so well, we could hardly believe it, and our tow car mileage went from 9 mpg to 12 mpg, so when we traded up to our 2012 Thor ACE 29.2 last fall, we thought we should put Airtabs on it as well.

Until now, I've never heard of somebody doing this twice ... so ok, who knows ... after all these years ... I'm still open to convincing logic ... however there's a lot of data stacked against this "idea"...

Make no bones about it ... I call'em snake oil!

FWIW... I make it a point to strike up conversation with the owners of rigs with these and while not scientific, my consensus is those that have had them for a short time ... try to believe. Those that have had them a long time not so much

Many a campfire chat where Air-Tabs were the brunt of jokes and stories of folly. We all fall pray to gimmicks that we've justified one way or another. Hell I remember a day long ago when they just about got stuck to one of my rigs!

[JamieGeek]

Originally Posted by Jim Jacobs

...
To try to better gauge the effects on gas mileage, since I have a long upcoming trip and since I've been meaning to do so anyway, I decided to buy an EEZ Tire Pressure Monitor, model T515 with 10 sensors (6 for the MH and 4 for the toad).
...

The thing here is that: If you have to be this precise on the experiments to measure an affect beyond "noise" there must not be that much of an affect at all.

In our experience the mpg difference between bringing a toad along or not gets lost in the "noise". I would suspect that the airtabs would have a smaller affect than an extra two tons or not.