Anyone use those AirTabs to decrease drag?? - Page 2 - Fiberglass RV
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Old 08-21-2017, 09:03 AM   #21
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My wife wants to know if they will fit on the back of my belt. She thinks I need some sort of deflector.
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Old 08-21-2017, 09:50 AM   #22
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My wife wants to know if they will fit on the back of my belt. She thinks I need some sort of deflector.
Ha! Thare's an idea. Maybe it will make walking easier. Less turbulence around the mid-section. Maybe you're on to something.
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Old 08-21-2017, 10:23 AM   #23
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Originally Posted by Neto View Post
My wife wants to know if they will fit on the back of my belt. She thinks I need some sort of deflector.
Ha! Thare's an idea. Maybe it will make walking easier. Less turbulence around the mid-section. Maybe you're on to something.

Or could it be the train whistle and the gas that comes along with it that has her concern.
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Old 08-21-2017, 12:32 PM   #24
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Huh, and here I thought that - with how many 18-wheelers I have seen with those air-tabs on the top of their truck cab (plus the wing-type deflectors many truckers attach to the very back of the cargo compartment) - they must have SOME actual benefit, such as reduced drag.

However, from what the majority seem to be indicating, the only way to really reduce drag is to drive slower. Guess the old "Drive 55" is the key here.
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Old 08-21-2017, 12:43 PM   #25
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I don't think anyone is questioning whether large deflectors such as this, deflect air around a semi trailer.
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Old 08-21-2017, 12:46 PM   #26
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Some of those big wind deflectors I see sticking up on top of trucks look to me like they increase drag. Just a big barn door sticking up with a big vacuum and lots of turbulence behind it behind it.
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Old 08-21-2017, 12:47 PM   #27
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The difference between the large deflectors used by trucks, and these things, is large enough to drive a you know what through.

Do you think that major truck lines haven't tested big air deflectors on part of their fleets before adopting them?

http://s89686473.onlinehome.us/fit-airtabs6.jpg
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Old 08-21-2017, 01:09 PM   #28
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They look great

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Old 08-26-2017, 10:25 AM   #29
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Why would you put yet another item that causes disruption of airflow onto the surface

"the fuel efficiency improvement is considered statistically significant."

Of trucks and dogs, reports from vortex generator (aka air tabs) testing down-under... (apparently semi-trailers are "dogs" in Australia!)

Mind you, these tests don't involve little rounded fiberglass eggs, but the trials on large truck and trailer combinations indicate that vortex generators do reduce fuel consumption.

2015 report:

http://airflowdeflector.com/wp-conte...Generators.pdf

2016 newsletter:

http://www.rms.nsw.gov.au/documents/...e-2-201606.pdf

2017 case study:

http://www.rms.nsw.gov.au/documents/...oad-trains.pdf
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Old 08-26-2017, 10:26 PM   #30
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Not what I found in study

A previous post offered links to Australian studies of air foils with this quote:

"the fuel efficiency improvement is considered statistically significant."

So I clicked the third link: 2017 case study (link below).

Near the beginning is a Summary. It says
No Change . . . No Change . . .No Change



Thinking I may have missed something, I scrolled down pages to Section 4. Results. They were:
"The results of the first statistical test showed that, for validated fuel consumption data, on average there was less than one per cent fuel efficiency difference between the baseline and trial periods as shown in Figure 6 (located under Conclusion). Assessed separately for heavy load groupings and light load groupings, the difference was closer to two per cent."

Next:
The test for the null hypothesis showed there was a 30 per cent chance that this was simply a result of “noise”. For comparison, a common convention is to consider five per cent or less as “statistically significant”. In other words, it is likely that the small difference in fuel consumption was just random. For heavy and light load groupings, this was 1.2 per cent and 7.2 per cent respectively – meaning the heavy loads had a significant result, but the result for the light loads was not statistically significant.

and then:
On the basis of the whole dataset, the change in total fuel efficiency was found to be less than one per cent. Heavy and light load groupings showed 2.7 per cent and 2.3 per cent difference respectively.

5 Conclusion
The findings of this trial suggest that in this road train application, vortex generators provide no fuel efficiency benefit, no economic benefit, and no greenhouse gas (GHG)
benefit.

http://www.rms.nsw.gov.au/documents/...oad-trains.pdf
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Old 08-27-2017, 02:59 PM   #31
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Tom,

I'm glad to see that someone is reading rather than just writing!

I failed to add a link. In fact, this is the one that I lifted the quote from (refer page six).

Another 2017 Case Study:

http://www.rms.nsw.gov.au/documents/...i-trailers.pdf

The third study entailed fitting "side-tipping trailers", which I believe were run without tarps if the illustrations in the report are any guide. The other three studies did indicate fuel savings. It appears the studies are all sponsored by the same organization.

I think it's a good illustration that devices will often provide different results in different applications and under different circumstances.

Many products are over-sold. In turn, I think some things are at times too broadly condemned.
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Old 08-27-2017, 03:35 PM   #32
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I skimmed Mike's latest study and it appears legit.

In a study involving a semi-trailer they claimed a 2.7 to 4.1% gain. They conclude that a semi using the tabs could expect a 3-4% increase in fuel economy. I did not check the cost to implement, and payback period, but if someone is operating full-time, adding that much to profits would be an easy decision.

For some reason, those were very different results. I see no reason a fleet owner wouldn't consider trying them on part of the fleet.

In lighter weight vehicles used casually, let's just say, your mileage may vary.
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Old 08-27-2017, 08:13 PM   #33
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Quote:
Originally Posted by Tom 72 View Post
For some reason, those were very different results.
It's rumored that the trucks in one test were hauling apples, and the other, oranges.
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