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  • OT: Trailering

    This is a bit OT but I know a lot of you guys haul stuff in enclosed trailers and have to put up with the turbulence from side winds or when a semi truck passes so you may have some knowledge on the subject.

    I just talked to a guy who is selling these things called "Airtabs" to put on trucks and trailers to supposedly cut down turbulence and increase stability and gas mileage. They are a thermoformed plastic "scoop" that is stuck onto the trailing edges of a trailer.

    It is basically a vortex generator that theoretically pulls the air into the space behind the trailer. They are kind of like the small vertical tabs they put on airplane wings to control turbulence. I checked them out on the internet and based on the testimonials they seem to do the job.

    I was wondering if anybody has used them on their enclosed trailer and has an opinion on how well they work. They cost $2.50 each and are placed on the trailing edges of semi trailers, enclosed trailers, etc, every 4 inches so it isn't cheap. I really don't want to waste the money if they are just a hoax.

    Here is their website: http://www.airtab.com/

  • #2
    One caveat: beware testimonials! They are a notoriously unreliable gauge of the effectiveness of anything.

    Of course they also don't disprove anything, either....
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.
    Don't own anything you have to feed or paint. - Hood River Blackie

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    • #3
      Have you had a problem before?

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      • #4
        I've seen those things at an RV rally and kinda figured that they're pretty much crap. Look at it this way: if they were really all that great, every semi-trailer on the road would have them.

        We pull a 28' travel trailer several thousand miles/year and are also affected by semis when they pass, but not to the point of being dangerous. Hints for stability:

        First and foremost, have a big enough "horse" in front of the trailer. Research the numbers, most importantly the Gross Combined Weight Rating. Be sure that you're not exceeding it. (see next)

        Get the rig weighed: quarry, grain elevator, truck stops, etc. all have scales. Weigh the tow vehicle alone, then weigh the entire rig. It's really best to get each wheel weighed individually, but it's not easy to find a place to do that outside a large RV rally. Weigh the tongue seperately; I use one of those Sherline scales mentioned in another thread. Be sure that all this weighing is done with the rig in a Ready to Roll condition, including your 3, 200# buddies who always ride along.

        When packing the trailer, be sure to have 10-12% of the trailer's weight on the tongue. This is VERY important, a too-light tongue will cause extreme instability.

        Return to your specs: be certain that you're not overloading ANY aspect of your rig: trailer tires, truck tires, "tow rating", GCWR, etc. Make sure your tires are at proper operating pressure.

        To minimize the effect of the semis, keep your speed down. I don't consider it too smart to drive much over 60 Mph when towing. Besides, the fuel mileage is much better. :-)

        See http://www.klenger.net/arctic-fox/weight/index.html for more details.

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        • #5
          QUOTE: "I've seen those things at an RV rally and kinda figured that they're pretty much crap. Look at it this way: if they were really all that great, every semi-trailer on the road would have them."

          Did you bother to ask the RV owners about them? No? Just skeptical? Maybe in two years all the semi truckers will have them. In fact if they really do save fuel I would BET that they will all have them. I suppose I could wait a couple of years and ask the question again when somebody really knows the answer.

          But, does anybody out there have any personal experience with this device so that they can give an opinion or answer the question now? I would like something more concrete before I risk even $2.50 for one, much less $112 for the 45 I would need for my trailer.

          Thanks, if you know the answer.

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          • #6
            Second hand from a trucker (company truck). Says the sway seems to be cut down noticibly but does not go away. Gas milage savings are there but tiny. He reported that the spray off the back wheels that blocks rearward vision did dissapear.

            His comment that if he owned the truck, he would have them for the last effect, but the rest he could take it or leave it.
            Murphy was an optimist

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            • #7
              Thanks Sparky. It sounds like they may do something anyway. I had heard that they were in use in Australia. I might buy about ten of them to put across the top of my pickup topper and see if there is any measurable effect on gas mileage. If not, then I guess I just lost $25.00! I bet the feature mentioned by the trucker of eliminating the spray kicked up by the rear tires makes it a lot harder to follow right behind a trailer truck. All of the spray would come right at you in a harder stream. Time to get out the Rain-Ex.

              Hmmm.... I wonder if the NASCAR boys know about this. Maybe it could affect their drafting technique if it really does pull the air in behind the car.

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              • #8
                Originally posted by Duct Taper
                QUOTE: "I've seen those things at an RV rally and kinda figured that they're pretty much crap. Look at it this way: if they were really all that great, every semi-trailer on the road would have them."

                Did you bother to ask the RV owners about them? No? Just skeptical? Maybe in two years all the semi truckers will have them. In fact if they really do save fuel I would BET that they will all have them. I suppose I could wait a couple of years and ask the question again when somebody really knows the answer.

                But, does anybody out there have any personal experience with this device so that they can give an opinion or answer the question now? I would like something more concrete before I risk even $2.50 for one, much less $112 for the 45 I would need for my trailer.

                Thanks, if you know the answer.
                What? That is only 40 gals of diesel! 112 dollars. Buy the damn things and then tell us what fools we are for not getting in early before the price went up.

                Seriously, If they worked as advertised you would have your money back soon enough. If they don't well.......
                Jim, By the river enjoying life...

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                • #9
                  It is highly unlikely that such small devices will do much. They do have some effect and similar techniques are used on aircraft using small turbulators to keep airflow attached to the wing surface but the velocities are far higher and the energy of a moving stream of air goes up as the cube of the velocity. For low velocities such as a moving vehicle you need large surfaces to have a noticable effect.

                  This isn't exactly a new field of study. To see what is needed to make a significant difference just look at the wings on race cars.

                  There have been tests done on tractor trailer units in the past and a similar idea can work. To produce a measurable and worthwhile effect it requires two panels, one on each side placed vertically on the back of the trailer on each side for the full height. The panels are about two feet by whatever the height is. They are provided with an adjusting system to change the angle, in or out toward the sides like a door sticking out from each rear vertical side corner, usually tucked in a bit. I seem to recall that they can save several percent or a bit more in fuel mileage.

                  Downsides are they extend the length of the vehicle and that poses regulatory problems as well as increased expenses when length matters which is often, as licences, ferry fees, parking etc may depend on vehicle length. Also, they are a problem with loading docks and can get in the way of the van doors.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    IIRC, Mr. Penske back in '69 or so, showed up at a TransAm race with two Camaros which had been fitted with a herringbone patterned material glued to the roof surfaces of his cars, ala: landau roof?

                    The two cars were successful that day: (Same Penske who won at Indy yesterday). At the next race for the Camaros, more than one competitor showed up with some kind of fabric material covering the roof of their racecar. Everyone figured Penske was on to something.

                    As it turns out, the roofs of the two Camaros had been drastically acidized to remove weight. So drastically, that they were very thin and had become visibly wrinkled. According to Penske, the roofs were so unsightly, it was easier to cover them with a material, than to replace them.

                    Evan probably has a good idea of the advantage of flush top rivets versus crowned rivets, on the effects of air moving over the skin of an aircraft.

                    G

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                    • #11
                      I was talking about intentionally increasing turbulence on an aircraft wing. Many aircraft have some sort of mechanical device(s) installed on the wing near the trailing 1/3 area to increase turbulence. This adds energy to the boundary layer of air flow and tends to keep it attached to the wing surface. On sailplanes this is often in the form of a line of rough surface tape. On the Cessna Citation business jet for instance there is a line of small vertical "teeth" that stick up on the inboard half of the wing in front of the flaps.

                      None of this sort of thing will have much effect at ordinary highway speeds as the airflow just isn't energetic enough to matter much. It does make a slight difference but not enough to notice unless the devices are sufficiently large such as the ones I described above.

                      Your best bet when trailering is to just slow down. I have driven thousands of miles towing my fifth wheel through the US and Canada and slowing down makes a huge difference to handling and economy. I tow my 18.5' fifth wheel with my 2.9 liter V6 Ford Ranger and it works great. You wouldn't even know it is there except for acceleration and braking (and mileage!). The trailer is a special 7' wide light weight model and is one of the best trailers I have ever pulled.

                      It doesn't even twitch when passing or being passed by large trucks and my Ranger has no problem towing it. The only mod I did on the Ranger was to build an engine oil cooler that patches into the oil filter attachment point and passes the oil through a rad I built. The oil rad is installed on the front of the regular rad. It has a valve to switch off the oil cooling when not needed. Oil cooling the engine makes a huge difference to how hot the engine runs and I have towed that trailer through the central valley of California and Oregon in summer with no problems with overheating.

                      My trailer

                      It's for sale these days as I no longer have five weeks off each year like I did when I worked for the big X.
                      Last edited by Evan; 06-29-2006, 03:57 PM.
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                      • #12
                        I have had the chance to try a couple of modern motorcycle helmets that have some shapes molded into them to create a similar effect.

                        Not as drastic a shape as those.

                        However the difference is noticable.

                        Even at 60 mph you can feel the change compared to a smooth helmet.

                        Especially in a head wind the buffeting is noticably reduced.
                        Gene

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                        • #13
                          This post is to work around the date stamp problem and will throw the post off the top of the list.
                          Free software for calculating bolt circles and similar: Click Here

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