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Old 07-03-2015, 06:39 PM   #21
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Originally Posted by blw2 View Post
yes, interesting indeed. I'm skeptical though, that your avg MPG will improve that much. There are way too many variables... including subtle even sub conscience driving habits, such as accelerating just a wee bit easier, even if you think you're not.

I'm betting on some improvement though.....
Are you concerned possible confirmation bias affects testing?

It's a valid concern. My mother is a participant in a clinical drug trial and it's being done double-blind so that she doesn't know whether she is getting the medicine or a placebo. The researcher that documents her feedback also doesn't know so her own bias doesn't affect the results. As humans we often have a difficult time remaining objective when we have competing interests.

I know what you mention about altering one's behavior can occur. An engineer I worked with a long time ago confirmed in his own personal car that attaching a magnet to his fuel line somehow affected the gasoline and made his car get 1/2 MPG higher. As I recall his experience wasn't uncommon back then.

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Old 07-05-2015, 08:09 PM   #22
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Incredibly, on today's return trip, I averaged 9.6mpg.

I was careful to drive normally, and used the speed control whenever I could. I am getting the mpg reading from the ScanGauge.

Today's temperature and wind conditions were pretty similar to Friday's. But I think the only real difference is the return trip was a bit more "downhill" from the trip on Fri.

One other oddity is late last year, I swapped out the Garmin Ecoboost for the Scanguage, as it started acting flakey. But until that time, it had been registering around 9mpg. The Scangauge has never registered above 8.5mpg, either late last year, or before I put the tabs on this year. I put about 8 trips on the scangauge before installing the Air Tabs.

One thing I think might be causing this is the GPS shows about 2MPH faster than the Scangauge at highway speeds. I did a timed run between mile-markers on the freeway several times, and the GPS always read correctly - so the Scangauge reads a bit low MPH wise.

This might cause the descrepancy in the MPG readings between the Garmin Ecoboost and Scangauge, as of course, MPG is dependant on distance travelled and fuel burned. As the distance travelled in the Scangauge is likely different than the GPS, that is probably the thing causing the discrepancy.

However, even if the MPG rate has a small error between instruments, if I use one instrument for all of the testing, I should obtain reasonable accuracy as I am then measuring the difference the gauge is reading with or without Air Tabs, rather than an absolute value.

I did hesitate a bit to mention this because someone will say using two instruments is where the difference comes from, but that is not what I am doing. I am seeing the difference in the Scangauge by itself with/without Air Tabs, not between the Garmin and Scangauge instruments.

At any rate, I am very encouraged by all of this, and while I may not be able to keep my observation from having any bias, I am trying to control the environment as much as possible.

However, since vortex generators is sound science, I think I can safely say at this point that there is some improvement in using Air Tabs.
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Old 07-05-2015, 09:17 PM   #23
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Ambient temperature can make a significant and measurable difference too. If by late last year you mean during cooler weather than now, that could account for some variation in readings.
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Old 07-05-2015, 09:42 PM   #24
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I don't think so. I am not seeing any pattern emerge that would suggest seasonal temperature changes are effecting the gas mileage.

On one hand, denser air would suggest more air drag (less MPG), but colder air might mean better combustion. Do these offset each other somewhat? I have no idea.

However, since I saw a drastic and immediate difference in the ScanGauge reading after installing Air Tabs, that pretty much rules out seasonal temperature changes.

I believe that the shape of the rear of the RV matters. Perhaps not as much as the front, but it has to contribute to the drag of the box going down the road, and that affects fuel mileage. Whether or not the Air Tabs sufficiently change the shape will reveal itself especially during longer term testing.
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Old 07-05-2015, 10:28 PM   #25
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...cut....

On one hand, denser air would suggest more air drag (less MPG), but colder air might mean better combustion. Do these offset each other somewhat?

...cut....
No. Not really. Not in a significant way.

Increased air density due to colder air leading to greater aerodynamic drag is an accepted fact.

Colder air can increase an engines maximum power output at full throttle because the air is more dense, but since most gasoline RVs don't operate at full throttle, then this in itself doesn't affect efficiency significantly.

In theory the thermal cycle of an internal combustion engine is improved with colder intake, but the difference is very minor. Certainly less than you could measure.

If your tabs are indeed the only variable and therefore responsible for almost 10% improvement, then I'd be extremely happy with those results.
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Old 07-05-2015, 10:46 PM   #26
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I'll admit I am pretty surprised by the results, which I did not expect. I am hoping that longer term testing will rule out any variables that might skew the results.
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Old 07-14-2015, 08:44 AM   #27
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After 500 miles, I have noticed some pretty interesting results. I drove in various conditions, rain, sunshine, cool, and warm temperatures, secondary highways and freeways.

First, there is a phenomenon called "Station Wagon Effect" which is essentially a low pressure that is present at the rear of "boxy" vehicles, such as SUVs, motorhomes, and semi trailers. This low pressure is detrimental to fuel mileage, and is what Air Tabs aim to remedy.

I noticed on a rainy day that the rear-view camera was much cleaner. Previously, the camera got all dirty and water spots on it, so much so that it was not useable in the rain. This time though, I did notice the camera was much more viewable. In fact, it was interesting that I could see the vortexes coming off the ends of the vehicle by observing the visible water vapor in the air while raining. I never noticed this before, because... for one thing, the camera would always get water spots on it in the rain.

I cannot make any conclusion to this other than it was interesting to watch.

Over the 500 miles, I noticed that my combined fuel mileage (city + highway) increased by around 6%. This was observed by the Scangauge as well as confirmed by calculating fuel used vs. miles driven at fuel stops.

Of course, I filled the tank to the brim each time. Still, there could be variations here, so the more I repeat this, the more accurate results I will have.

At highway speeds (55~60mph), the mileage increased 12~15%, and I consistently saw over 10MPG average. This makes sense as the air tabs are only effective at speeds above 45mph or so, and when averaged over the overall driving pattern, the tabs won't change the lower speed fuel mileage at all, so the only fuel savings is at higher speeds.

I also noticed that at highway speeds, my tachometer dropped about 100RPM from before. I was seeing around 2,150RPM at 60MPH (reading from the ScanGauge).

I also purposely drove as close (safely) to the center line as I could on secondary (2 lane) highways so I could feel the effect of semis passing. I felt some push at times, but nothing scary. The push felt about like it does when in a passenger car.

The RV definitely handled much better in winds. Yesterday we drove through a thunderstorm, and the winds were pretty strong at times. I was able to maintain 55~60mph with a bit of steering correction, but not bad at all. I was even passing other RVs during this time.

Previously, this would have been a white-knuckle experience.

Now, a month before adding the Air Tabs, I added aftermarket Hellwig sway bars, so I am not sure which of these additions was the most help to remedy this, or if they both helped. Regardless, the handling is so much better.

While it may be a stretch, the break-up of low pressure in the back could - and I mean could - be causing more weight to remain on the front axles, improving steering. I cannot quantify this in any form, so call it speculation, but it could be happening. If indeed there is less suction in the rear, it makes sense.

So while I am going to do some more testing, I feel pretty confident that I am observing a 5% increase in overall (combined) fuel economy (it would be more if the air tabs were effective at low speed), up to 1MPG increased economy at highway speeds, improved handling in certain situations, and perhaps a bit less grime on the back.

A cleaner camera is encouraging, but I won't know for sure until I tow the toad in the rain.

I'll have to admit though that we had our bicycles attached to a hitch-mounted bicycle carrier (we didn't take the toad on this trip). They seemed dirtier after driving through the rain, which was surprising.

The only conclusion I can make is I also tied streamers to the back of the RV (not on the rainy day though), and again, from the rear-view camera - I saw that the streamers on the bicycles at the center of the RV were horizontally pointed to the left/right of the coach, while the streamers on the ends were going straight back.

This kind of suggests airflow from the center towards the outer edges on the back of the RV, and perhaps that was happening with the gunk on the bikes. The more air flow, the dirtier they became I suppose.

In all honesty, I am not sure why, as the camera was cleaner (but it is a lot higher too). I am not sure what to make of it, and it could either be further evidence of loss of low pressure in the back, or something else. One thing for sure, the bikes never got that dirty before.

Again, the one definite conclusion - things have changed, but the what and why is not fully determined.
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Old 07-14-2015, 10:04 AM   #28
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Get a beer and sit under the awning and relax! You guys are way too serious.
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Old 07-14-2015, 10:14 AM   #29
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I like that idea.
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Old 07-14-2015, 12:54 PM   #30
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....cut....

I also noticed that at highway speeds, my tachometer dropped about 100RPM from before. I was seeing around 2,150RPM at 60MPH (reading from the ScanGauge).

.....cut......
Any idea how the air tabs would affect RPMs at same speed?
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Old 07-14-2015, 01:52 PM   #31
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I will wait for the test results before deciding if they are garbage or not. That being said, I really do not see myself ever purchasing them. Good luck in the trials!
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Old 07-14-2015, 03:10 PM   #32
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I actually find it fascinating.
Being a pilot and aviation bug, I've thought and studied a fair bit of aerodynamics.... & I've seen vortex generators many times. I have no doubt they have merit, but just how much???....I'm glad to see your report! It's very encouraging.

I look forward to seeing more data after a dozen or so tanks of gas!....hopefully you have that much "before data" to compare it to!
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Old 07-14-2015, 03:20 PM   #33
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Fw28z, Really appreciate, respect and anticipate your research, facts and assumptions. Please pursue further and keep us posted.
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Old 04-28-2016, 01:34 AM   #34
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Airtabs

Last year...I see there was a discussion regarding Airtabs...
I had no idea what they were...so I went to the site.
Airtab | Aerodynamic Fuel Savers | Application
Now, We know what they are...an aerodynamic aid which stabilizes Tractor Trailers, Horse Trailers, RV's and just about anything else which moves down the road.
I read 10-12 reviews,and found no poor results.
This application can, also, aid in fuel consumption...appears nothing significant on RV's.
Click image for larger version

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I printed the instructions...application must be precise, everyone sez it is not difficult.

Has anyone used this application on a Vegas/Axis or larger coach ?

Interesting !

K
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Old 04-28-2016, 02:45 AM   #35
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Give it to the myth busters....
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Old 04-28-2016, 02:46 AM   #36
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Get a beer and sit under the awning and relax! You guys are way too serious.
I am with you...
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Old 04-28-2016, 03:03 PM   #37
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Air Tabs, like other "performance improving" technologies are one of those things that one either swears by - or laughs at.

Like calculating orbits for more than three bodies, the equation for the gas mileage one sees consists of so may variables that it is virtually impossible for a layman (one of us) to properly test the effect of such devices. Any observed change less than multiple miles per gallon is simply too small to reliably attribute to any single variable.

Try 'em if you want. If you think they work for you great! But lacking specific testing by the likes of NASA or the JPL please, pay no attention to the "evidence" you find on the web - no matter how well-intentioned or apparently thorough.

By the way, the improvement reported by FW28Z is not "statistically significant" - (yes, I did run the numbers - I'm one of "them" ). It is too small to be the result of any specific change and results from normal random variation in the myriad variables that affect gas mileage.

Regards,

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Old 04-28-2016, 03:16 PM   #38
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Also note that FW28Z no longer has that motorhome and is thus no longer recording any data.
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Old 04-28-2016, 05:37 PM   #39
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That paragraph reads like an executive summary. It documents that they have been "shown effective", which would imply that data does exist. I consider "could" in this context to be scientific extrapolation of data.... not smoke and mirrors marketing and not false claims.
How grounded the extrapolation is to reality, well.... that's another question.

As has been discussed already, there are likely too many variables for anyone outside of a wind tunnel test lab to really verify performance....
But I for one am interested in reading FW28Z's observations.
Aerodynamic add-ons reduce fuel consumption of semi trucks by 7-12%

This is a DOE super computer study that indicates that some things work. Wish they would do one on Air Tabs and similar devices. It's only about $200 to buy them for an Axis, but I can just hear "that's ugly" comments... Gas is cheaper.
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Old 04-28-2016, 07:40 PM   #40
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Please don't take my comments to say anything about whether they work or not. I truly don't know!

I do know that it's damn hard to test without a lot of miles and the ability to control or account for all of the other variables.

And yep, they be ugly!

Regards,

Randy
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