Airtabs

[yycwrangler]

Anyone using vortex generators or specifically Airtabs. Some claim better mileage towing but many claim less effects from passing semi trucks.

Seems like an interesting concept

Al

[JaggedEdges]

Yah, behind your flat arsed vehicle you get a pair of vacuum bubble vortexes that you're towing along. When pressurised air off the front of a semi fills the side nearest, the opposite side of the trailer suddenly makes lift and yanks you one way, then when the ass end of the semi comes by and sucks back it yanks the other way... Though just the pressure waves on the side area of a trailer will have some effect, but not quite as bad.

So shedding these large vortices in favor of small vortices both helps your stability and hopefully also your gas mileage, from all that air you're trying to pull along.

A large cargo trailer might be better off with the commercial vehicle sized ones rather than the ones they sell for cars.

However, it's possible to rig your own, foot strips of almost anything, like tall closed cell weatherstripping, or those corner sealing extrusions L shaped for bathroom, need to stand up at least half an inch but closer to an inch better. Set 'em 3" lower at the front than back (15 degree angle on foot) space them about 6" apart about 6" from the back of the trailer/vehicle...

Note, more teardrop sized vehicles, you might want more like 1/2" high, 6" long, 1.5" drop, 3" apart.

You can put them on top too, but angle them in reverse V toward front if you know what I mean.


Edit: Oh an alternative is to put a couple of vertical plates on the back, set about as half as far in as they are tall, Like 8" tall set 4" in from side, creates kind of a virtual boat tail.

[bdosborn]

Lets do the math.

Airtabs promise a 2 to 5% fuel increase. My trailer is smaller than a semi so lets assume I get a 3% increase. They recommend 3 per linear foot so I would need 50 to cover my trailer on the sides and top. That would cost $138 at $2.75 apiece. I get 14 MPG pulling the trailer with the Dodge and I drive maybe 1,000 miles a year with the trailer attached. 1,000 miles/14mpg = 71 gallons per year I use camping. At 3% better mileage I would save 2 gallons. Diesel is around $2.50 a gallon so it would save me $5 per year. $138/$5 savings/year= 27 year payback.

I'll pass.

Bruce

[dancam]

Lets do the math.

Airtabs promise a 2 to 5% fuel increase. My trailer is smaller than a semi so lets assume I get a 3% increase. They recommend 3 per linear foot so I would need 50 to cover my trailer on the sides and top. That would cost $138 at $2.75 apiece. I get 14 MPG pulling the trailer with the Dodge and I drive maybe 1,000 miles a year with the trailer attached. 1,000 miles/14mpg = 71 gallons per year I use camping. At 3% better mileage I would save 2 gallons. Diesel is around $2.50 a gallon so it would save me $5 per year. $138/$5 savings/year= 27 year payback.

I'll pass.

Bruce

27,000 miles to pay off is still a fair bit even for more serious campers.
I have never used them but am considering it. I think their for 3 types of people:
People who pull a trailer a lot, usually for buisness/work.
People who dont want the trailer to get blown around as much by crosswinds or passing vehicles.
People who care more about mpg numbers than saving money.

Im in the second group
Still looking into it though. Hoping to hear from those who have actually used them as well.

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[JaggedEdges]

I've only tested the theory with homebrew versions, on my old 80s "square" minivan and through a friend of a friend a class A RV, both seemed to gain about 5%, though on the minivan it was ~1mpg and the Class A half a mpg.

Edit: I used about $5 worth of 5/8 high weatherstrip and he used about $30 of 3/4" high truck cap weatherstrip. He went right down to Florida and back though right after and he figured it broke even that trip with some 10 gallons or so saved. He was much more impressed with how it improved the buffeting.

[aggie79]

Anyone using vortex generators or specifically Airtabs. Some claim better mileage towing but many claim less effects from passing semi trucks.

Seems like an interesting concept

Al

I agree it's interesting, but I think if they really worked you'd see them on every tractor trailer rig. With the miles these rigs drive, any efficiency gains would really affect the bottom line. I have seen other techniques used on trailers - such as skirting under the trailer, wheel discs, "trailer tail" at the rear of the trailer - that may work for cargo trailers.

[JaggedEdges]

Anyone using vortex generators or specifically Airtabs. Some claim better mileage towing but many claim less effects from passing semi trucks.

Seems like an interesting concept

Al

I agree it's interesting, but I think if they really worked you'd see them on every tractor trailer rig. With the miles these rigs drive, any efficiency gains would really affect the bottom line. I have seen other techniques used on trailers - such as skirting under the trailer, wheel discs, "trailer tail" at the rear of the trailer - that may work for cargo trailers.

Well that's the same argument as saying if hybrids worked then every vehicle sold would be a hybrid.

There would be a large proportion of the situation where the guy who pays for the gas doesn't own the trailer. I only recall seeing skirts and such where the cab and trailer were same company owned.

[flboy]

I think they would be worth the money alone if they reduced the effect of a large truck sucking the trailer in and then pushing it over as they pass.

Do they really help that?

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[aggie79]

If efficiency and handling are the goals, do you think that maybe the concentration should be on minimizing or eliminating all of the "protrusions" that disrupt laminar airflow such as vents and HVAC units, ladders, grab bars, solar panels, etc., rather than air tabs?

[JaggedEdges]

yah, build airstreams dammit.

[flboy]

If efficiency and handling are the goals, do you think that maybe the concentration should be on minimizing or eliminating all of the "protrusions" that disrupt laminar airflow such as vents and HVAC units, ladders, grab bars, solar panels, etc., rather than air tabs?

I think the large truck pulling you over and pushing you out aren't as much about the airflow around and over the trailer as much as they are about the low pressure area behind the trailer (which the vortex generators affect).. At least that is the way I understand it. I am not thinking about efficiency in this case.

Maybe someone can explain it better, but as the truck approaches from behind it is pushing air causing a higher air pressure and the low behind the trailer is attracted, the opposite when they pass by with the low pressure behind them and high in front of me..

Certainly crosswinds stability is affected by the surface area and profile, but I am think specifically of that sucking in and pushing out semi trailer and large buses create when they pass by me in the same direction of travel when I am towing the CTC

Anybody?

[bdosborn]

I agree it's interesting, but I think if they really worked you'd see them on every tractor trailer rig. With the miles these rigs drive, any efficiency gains would really affect the bottom line.

I agree. I started watching semis on the highway for airtabs several years ago. I have seen them but only a hand full of times and I would think they be all over if it worked. Somebody on the forum put them on their cargo trailer, maybe they'll chime in.

Bruce

[bdosborn]

Found it, scroll down towards the bottom:

http://tnttt.com/viewtopic.php?f=42&t=25377&start=45

Bruce

[dancam]

Found it, scroll down towards the bottom:

http://tnttt.com/viewtopic.php?f=42&t=25377&start=45

Bruce

Thats really long. I started from the end reading back, but roughly what post number? I stopped at #1740

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[bdosborn]

The link should have taken you to page 4, down the bottom of that page.