Ordered Airtabs today!

[jeffreymccoy]

I ordered my set of black airtabs today http://www.airtab.com/

Im planning to install them as seen here to start:

http://www.airtab.com/Images/gallery/Paulst/2.JPG

http://www.airtab.com/Images/gallery/Paulst/3.JPG

Exerpt of his experience with these....
We've increased our fuel mileage by about 9mpg on a full load, from 11-12 MPG to 20-21 mpg. We pull fast, heavy and long most of the time. With the Airtabs as installed, wind noise is reduced and the trailer stability is phenomenal. Evidence the Airtabs are working is most noted in rainy weather, in cross winds and meeting larger semi-trailers on two lane highways. The unloaded truck will get 25 mpg but with Airtabs fitted as per our pictures, we are getting 32-34 mpg. The Airtabs on the top rear of the cab eliminate 80% of the bugs on the front of the trailer. If you watch the bugs, they tell you where the air is going. The Airtabs on the hood of the truck keeps the windshield cleaner and reduces wind noise with the windows open.

There are 67 Airtabs on the truck and 95 on the trailer. A small investment for this kind of fuel economy and stability, not to mention the extra horsepower. It seems with Airtabs we aren't bucking wind, but directing it. This outfit gets a lot of curious looks but these results prove the Airtabs usefulness. The savings on a 1000 mile trip fully loaded would be approximately 35 gallons of fuel. At $3.00 per gallon, that's $105.

Ill post back installation pics and eventually MPG data once available for anyone interested in how these do. This could be a good front wheel skirt replacement option for just about any car possibly and maybe a front windshield deflector? For me, Im hoping it does that as well as also help around the back of the cab and bed maybe... anyway - I have them coming, will see how they do.

-Jeff

[trebuchet03]

He Jeff, when you get them... Can you possible take some detailed pictures of them (preferably with a ruler or some sort of scale for dimensions) before they are installed?

I'd like to model them and do some CFD on their specific design (or as close as I can get) for application on a human powered vehicle... It'll probably be useful to others too. I have to do research anyway, so it seems like a good idea to start with a commercial product :p


Out of curiosity -- how did that gentleman find the separation points on his truck?

[jeffreymccoy]

Separation points? meaning how far apart to space them is what I think your asking. If so, Im not sure how he did it, but the airtabs themselves come with 2 spacing templates, fill them both up, then move the first template beyond the 2nd (becoming the 3rd) and so on - like leapfrog. I will be using this method as closely as possible. I expect something to hinder complete compliance, but it will be close.

I will be glad to get some close up pictures with a ruler. It will be late next week at the earliest.

[trebuchet03]

Separation points?


So air tabs add energy to the boundary layer much like the tabs on airplane wings or dimples on a golf ball do (in fact, exactly like they do). Separation is a fluid (in this case air) interaction where the flow that is attached to the skin of the vehicle (boundary layer) just lets go. It was discovered that if you give this layer a little bit of energy slightly BEFORE this separation occurs - you effectively move the separation point further back. In the case of a plane wing - you create more lift and thus lower the stall speed.

The easiest way to see what I'm talking about....
http://www.gassavers.org/attachment.php?attachmentid=997&stc=1&d=1192830726

Notice how the red dye just lets go :)

Mitsubishi posted a paper on this - showing a reduction in cD by 6 points (.006) when they placed their vortex generators (basically, air tabs) 100mm in front of the separation point.

The trick is, and the focus of research, is how tall to make them. Optimal height is equal to the height of the boundary layer. But, the height of the layer increases with velocity. Make them too tall, and all you do is create turbulence -- make them too short, and they don't add much/enough energy to be effective :/


I will be glad to get some close up pictures with a ruler. It will be late next week at the earliest.

Thanks :thumbup: Much appreciated :) I guess it would be beneficial to mention that a top, side and front is the most helpful :)

[Red]

FWIW I am running AirTabs on my hard top and I haven't noticed any quantifiable increase on FE. YMMV

http://lostleagues.com/wp-content/uploads/2006/12/at_lines_2.gif

[lovemysan]

9mpg improvement just from airtabs sounds like a stretch to me. I've spent a lot of time on the road towing a lot of equipment, box trailers, backhoes, etc. There just wasn't that much difference. Pulling the backhoe mileage went down only 2-3mpg.

That said it doesn't mean that I don't want to try them. I'm seriously considering getting some to try on my saturn. I just don't know if there the right size for my application.

[lovemysan]

FWIW I am running AirTabs on my hard top and I haven't noticed any quantifiable increase on FE. YMMV

http://lostleagues.com/wp-content/uploads/2006/12/at_lines_2.gif

Red, my guess would be that the airflow has not reattached to the roof before it hits the air tab. I've looked at the jeeps before and there quite possibly one of the most unaerodynamic vehicles out there. I imagine that they would work better on the sides of the jeep. D

[Danronian]

I'd be interested to see a documented increase in MPG related to installing this product. To me it seems like a miracle product for anything other than sustained driving at a highways speed, but I'm quite the skeptic.

[Red]

Red, my guess would be that the airflow has not reattached to the roof before it hits the air tab. I've looked at the jeeps before and there quite possibly one of the most unaerodynamic vehicles out there. I imagine that they would work better on the sides of the jeep. D

And mar a perfectly vertical surface? :D Always worth a shot

[trebuchet03]

I'd be interested to see a documented increase in MPG related to installing this product. To me it seems like a miracle product for anything other than sustained driving at a highways speed, but I'm quite the skeptic.

Ask and you shall receive :p Okay, so it's not mpg increase - it's decrease in cD. It's also not for this specific product, it's for Mitsubishi's design (which is a basic delta wing foil).

Let me know if that link is dead ;)
http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf

The juicy images

Left with - Right without
http://www.primitiveengineering.com/blog/img/vortex_gen_cfd.jpg
^^ Notice the Blue low pressure zone on the windscreen is larger without the VG's.
Left with - Right without
http://www.primitiveengineering.com/blog/img/vg_pressure.JPG
Despite the lower pressure just behind the VG's (deeper blues), Mitsubishi got a decrease in cD - notice how the larger green area behind the VG's compared to without.

Here's Mitsu's Design
http://www.primitiveengineering.com/blog/img/vortex_top.jpg

Here's what you might find on a plane
http://www.primitiveengineering.com/blog/img/vg_wing.jpg

I too was skeptical until reading that paper -- I had thought the velocities needed to have an effect needed to be much higher...

Oh, I also forgot to mention -- you can also find VG's under aircraft flaps - for increased stability at lower speeds ;)
http://www.nasa.gov/centers/langley/news/factsheets/Micro-VG.html

I feel it also necessary to state that this is in no way an endorsement for the Airtab product. Flow control does work, intelligently designed - anyone can make something look cool - but that doesn't mean it works. Claiming to lower mpg is ballsy in my opinion - the much safer (and likely more accurate) claim is that it can reduce cD when properly installed.

[Danronian]

Great article. But I still hold that I am skeptical to see what actual results will be seen in MPG with these.

From what I understood, these airtabs should speed up the airflow and smooth it to lower the CD. So would these work on any part of the vehicle that doesn't flow as well as it could such as the wheels, or even on the back of a hatchback civic? I would assume it would given the principle of how they work, but I would guess there would also need to be flow testing done to prove there effectiveness (and to make sure they don't do more harm than good) to be sure of it.

[ZugyNA]

A hidden thread:

http://www.gassavers.org/showthread.php?t=1482

The 1st PDF shows research on how high to make them, angle to use, and where to put them. This testing was done at highway speeds.

[jeffreymccoy]

Thanks for that ZugyNA - I'll read through it all sometime this week. I decided to purchase the product instead of attempting to make them for 2 reasons:

1. It seems that the shape and angles need to be just right, and Im not that patient or precise...
2. Multiply #1 by 75 VGs that would have to be produced and you'd have one frustrated F150 owner.

Im looking forward to posting actual driving test data for the board.

[jeffreymccoy]

on my truck. I imagine it has a greater impact on the shape of a truck / van than it would on an already much more aero car.

First - the scale pics, as requested:

http://www.doodlebuckets.com/epnc/IMG_2283.JPG

http://www.doodlebuckets.com/epnc/IMG_2284.JPG

http://www.doodlebuckets.com/epnc/IMG_2285.JPG

http://www.doodlebuckets.com/epnc/IMG_2286.JPG

http://www.doodlebuckets.com/epnc/IMG_2287.JPG

http://www.doodlebuckets.com/epnc/IMG_2288.JPG

http://www.doodlebuckets.com/epnc/IMG_2289.JPG



Then - pics of them installed on the F150 (I may take the time to paint them red later - but most likely not.)

http://www.doodlebuckets.com/epnc/IMG_2290.JPG

http://www.doodlebuckets.com/epnc/IMG_2291.JPG

http://www.doodlebuckets.com/epnc/IMG_2292.JPG

http://www.doodlebuckets.com/epnc/IMG_2293.JPG

http://www.doodlebuckets.com/epnc/IMG_2294.JPG


Finally the stats on the test route...that being a 45/55 mph bypass stretch with stoplights out, a 65 mph interstate out, 65 mph interstate back, and 45/55 mph bypass back.

Before (all current mods except Airtabs), according to SGII
23.6 / 22.6 / 20.6 / 23.7

After airtabs installed, according to SGII
25.7 / 24.3 / 22.0 / 25.6

Appears to be a solid 2 mpg gain (7-9% increase).... It was also pretty cool to "see" them working. I drove under a falling leaf. It would normally have hit my windshield and bounced over. Today, I saw it falling and then get rushed up over the windshield without ever hitting it, so it would appear that the tabs on the hood are indeed directing airflow over the windshield to some extent. Granted, this was one lousy leaf... it will be interesting to see if this trend continues (lots of falling leaves this time of year), and if I have the same experience noted by the other guy - a cleaner windshield...:thumbup:

Cheers
-Jeff

[SVOboy]

Damn, you ordered a buttload of them things...

Any chance you'd be interested in doing a string test and filming while driving before and after?

I have to think about making some for my crx now...zugy NA's write up is pretty good, dunno how I never saw it before, :p

[jeffreymccoy]

I think that would be difficult to do for three reasons...

1st - the tabs are stuck on pretty good, I "could' get them off, but I'd be afraid of them not reattaching as well once they were pried off. This would disappoint me greatly and cost me more money (in the way of new adhesive of some sort).

2nd - I dunno how to do a string test, but Im sure someone could describe the proper method. I would be willing to do it if Im able on the existing setup. Perhaps windtunnel test results could be found on google somewhere for a stock F150 (I can try to find that). If not, here is a stock dodge that provides some evidence of a before - albeit not my exact truck.

http://web.archive.org/web/20030414234348/mars.acnet.wnec.edu/~ehaffner/Tonneau.htm

3rd - I dont own a camera, and would need to get someone to assist me that does. I assume that the filming also needs to be done by a chase car? So I just need to find the right assistant (someone with a camera who is willing to help me out)

Let me know how to do the testing, and if this would provide any value to folks, and Ill see about pursuing it.

[SVOboy]

Eh, don't worry about it. I'm sure treb will mock one up and run it through his water machine a school in a few days time anyway, :)

[2TonJellyBean]

Just use someone else's fee-zoh (f150) for the control string test...

[trebuchet03]

Thanks for those pictures - thanks for the extra measurements too - I can make a spline to get pretty close to that curvy shape :) They help a whole lot :)

Eh, don't worry about it. I'm sure treb will mock one up and run it through his water machine a school in a few days time anyway :)

I wish, I don't have direct access to the water tunnel anymore :/ Perhaps within a few months, I can see about using it though (when it's filled for other classes) :D

[SVOboy]

Oh, poo...I wish all my friends weren't crappy econ majors and mehbe I could make them do something like that...

[Red]

Maybe I just didn't use enough of em on the Heep.....

Jeff, any noticeable increase/decrease of wind noise? Stability changes? Anything blowing around?

[jeffreymccoy]

I dont know that I have noticed any stability changes, but Ill get a better feel for that after a long hwy 95 trip tomorrow. It may seem a little more stable, but I may just be thinking that based on what Ive read - the power of suggestion you know. Really hard to say. I havnt noticed any less wind noise either - but the radio is usually on too. I will listen for it on said hwy 95 trip.

[SVOboy]

Where do you live on 95?

[jeffreymccoy]

Raleigh, NC area...traveling up to Baltimore

[SVOboy]

Ah, you're way down from me then, I'm from jersey.

[jeffreymccoy]

yup, opposite ends, maybe we'll cross paths one day

[DarbyWalters]

Man, I put 5, just 5 white ones on a white Jeep Liberty, and couldn't bite the bullet and mount them everywhere...I have to applaud you for diving in like that.

[Danronian]

Wow! Great results for the ford truck!

Hopefully your results continue to show an increase in MPG to show this is more than a one-time event. Good luck with your better MPG quest!

Maybe I'll look into some of these for the VX. I'm sure they can't hurt!

[jeffreymccoy]

I often travel the bypass portion of my test route. Two more trips out and back along this stretch showed 25.x mpg. So it has been repeated a few times. Ill update the group with more after the road trip.

[ZugyNA]

Before (all current mods except Airtabs), according to SGII
23.6 / 22.6 / 20.6 / 23.7

After airtabs installed, according to SGII
25.7 / 24.3 / 22.0 / 25.6

Appears to be a solid 2 mpg gain (7-9% increase).... It was also pretty cool to "see" them working. I drove under a falling leaf. It would normally have hit my windshield and bounced over. Today, I saw it falling and then get rushed up over the windshield without ever hitting it, so it would appear that the tabs on the hood are indeed directing airflow over the windshield to some extent. Granted, this was one lousy leaf... it will be interesting to see if this trend continues (lots of falling leaves this time of year), and if I have the same experience noted by the other guy - a cleaner windshield...:thumbup:

Cheers
-Jeff

Now that's what I call just diving in! Wondering where you got the idea for using the tabs on the hood?

[jeffreymccoy]

From the airtab display gallery...

http://www.airtab.com/Images/photogallery/gallery1.htm

http://www.airtab.com/Images/gallery/Paulst/2.JPG

http://www.airtab.com/Images/gallery/Paulst/3.JPG

[csrmel]

the price is a ripoff.
you could make airtabs for 20 cents a piece with a vacuum molding machine. my friend had one in his garage. you put a part on the plate and a sheet of 1/8th inch plastic is heated up untill it almost melts. the its placed on the plate and a vacuum opens and sucks the hot plastic sheet down onto the airtab so it follows its contours. when the plastic cools you pull the sheet off, cut around the part and you have an exact copy for 20 cents.
if you guys are serious about airtabs, just buy one and take it to someone who does vacuum molding. have them make you 50 or 100 or heck 5000 and sell the extras on ebay.

[jeffreymccoy]

Just arrived from the 333 mile trip from Raleigh to Baltimore.

Previously, this tri yielded a 22.3 MPG hwy run...arriving with just over 1/4 tank left.

Today, with airtabs and wheel covers, it increased to 26.7 MPG...arriving with about 1/2 tank left!

Very exciting gains. I will update you guys with the leg home info if you want. Then I'll drop it.... they work, at least on my truck. Take care all.

[cfg83]

jeffreymccoy -

Just arrived from the 333 mile trip from Raleigh to Baltimore.

Previously, this tri yielded a 22.3 MPG hwy run...arriving with just over 1/4 tank left.

Today, with airtabs and wheel covers, it increased to 26.7 MPG...arriving with about 1/2 tank left!

Very exciting gains. I will update you guys with the leg home info if you want. Then I'll drop it.... they work, at least on my truck. Take care all.

Wow! Yes, more info please.

CarloSW2

[lovemysan]

CFG83 you need these on your wagon. the .36cd is screaming for them. I'm just not sure if they'll help me.

[SVOboy]

Just arrived from the 333 mile trip from Raleigh to Baltimore.

Previously, this tri yielded a 22.3 MPG hwy run...arriving with just over 1/4 tank left.

Today, with airtabs and wheel covers, it increased to 26.7 MPG...arriving with about 1/2 tank left!

Very exciting gains. I will update you guys with the leg home info if you want. Then I'll drop it.... they work, at least on my truck. Take care all.
Interesting results. Can you dig up a weather comparison between the two trips for us?

:thumbup:

[dogncatboy]

if you guys are serious about airtabs, just buy one and take it to someone who does vacuum molding. have them make you 50 or 100 or heck 5000 and sell the extras on ebay.

Yeah, you could do that but you'd probably be violating the copyright on their design and it certainly is morally questionable at best. The price might seem steep to you, but I'm sure that significant R&D went into developing the product and they are trying to recoup their investment. How'd you like it if you developed a product and some punk stole your design? People develop products to make $$$. Take that away from them and the good ideas will stop coming, period. Do something productive with your life, don't spin your wheels thinking up ways to rip off legit businesses. I own a small business so I know what its like to try to make a buck. Its hard enough without people like you dreaming up ways to steal an idea that (a.) you would never have thought of and (b.) probably don't even understand. If you don't like the price, don't buy the product.

[thisisntjared]

Interesting results. Can you dig up a weather comparison between the two trips for us?

:thumbup:

i am curious too, especially with the winter summer blend mix ups as a possibility. :/

[dogncatboy]

Just arrived from the 333 mile trip from Raleigh to Baltimore.

Previously, this tri yielded a 22.3 MPG hwy run...arriving with just over 1/4 tank left.

Today, with airtabs and wheel covers, it increased to 26.7 MPG...arriving with about 1/2 tank left!

Very exciting gains. I will update you guys with the leg home info if you want. Then I'll drop it.... they work, at least on my truck. Take care all.

How much do you think was the wheel covers? It'd be interesting to know.

[jeffreymccoy]

On 8/8/2007:
http://www.wunderground.com/history/airport/KRDU/2007/10/8/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA

Temperature:
Mean Temperature 79 °F / 26 °C 63 °F / 17 °C
Max Temperature 93 °F / 33 °C 74 °F / 23 °C 87 °F / 30 °C (1990)
Min Temperature 65 °F / 18 °C 51 °F / 10 °C 35 °F / 1 °C (1964)
Degree Days:
Heating Degree Days 0 4
Month to date heating degree days 0 28
Since 1 July heating degree days 3 49
Cooling Degree Days 14 2
Month to date cooling degree days 77 22
Year to date cooling degree days 2035 1496
Growing Degree Days 28 (Base 50)
Moisture:
Dew Point 65 °F / 18 °C
Average Humidity 66
Maximum Humidity 93
Minimum Humidity 38
Precipitation:
Precipitation 0.00 in / 0.00 cm 0.11 in / 0.28 cm 2.54 in / 6.45 cm (1996)
Month to date precipitation 0.13 0.94
Year to date precipitation 26.35 34.80
Snow:
Snow 0.00 in / 0.00 cm - - ()
Since 1 July snowfall 0.0
Snow Depth 0.00 in / 0.00 cm
Sea Level Pressure:
Sea Level Pressure 30.03 in / 1017 hPa
Wind:
Wind Speed 2 mph / 3 km/h (SSE)
Max Wind Speed 8 mph / 13 km/h
Max Gust Speed 13 mph / 21 km/h
Visibility 10 miles / 16 kilometers
Events Fog



Today, 8/22/2007:
http://www.wunderground.com/history/airport/KRDU/2007/10/22/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA

Actual: Average : Record :
Temperature:
Mean Temperature 70 °F / 20 °C 58 °F / 14 °C
Max Temperature 83 °F / 28 °C 70 °F / 21 °C 86 °F / 30 °C (1947)
Min Temperature 56 °F / 13 °C 46 °F / 7 °C 26 °F / -3 °C (1974)
Degree Days:
Heating Degree Days 0 8
Month to date heating degree days 23 114
Since 1 July heating degree days 26 135
Cooling Degree Days 4 0
Month to date cooling degree days 133 39
Year to date cooling degree days 2091 1513
Growing Degree Days 20 (Base 50)
Moisture:
Dew Point 54 °F / 11 °C
Average Humidity 63
Maximum Humidity 83
Minimum Humidity 41
Precipitation:
Precipitation 0.00 in / 0.0 cm 0.09 in / 0.23 cm 0.62 in / 1.57 cm (1958)
Month to date precipitation 0.30 2.35
Year to date precipitation 26.52 36.21
Snow:
Snow 0.00 in / 0.00 cm - - ()
Since 1 July snowfall 0.0
Snow Depth 0.00 in / 0.00 cm
Sea Level Pressure:
Sea Level Pressure 30.23 in / 1025 hPa
Wind:
Wind Speed 3 mph / 6 km/h ()
Max Wind Speed 15 mph / 24 km/h
Max Gust Speed 17 mph / 27 km/h
Visibility 10.0 miles / 16.1 kilometers



Little cooler this week than 2 weeks ago, and slightly less humidity. Pretty close to the same, even avg wind was close 3 vs 2, although gusts were a little different. Overall, similary conditions between the 2 days, nice sunny fall days....

[SVOboy]

Pretty cool, nice bonus that is was cooler...interesting stuff.

[jeffreymccoy]

How much do you think was the wheel covers? It'd be interesting to know.

I gained 4.4 MPG or so on the run this week. Based on previous test route evaluation, I think that I gained 2MPG with the wheel covers / well covers, and then another 2 with the airtabs...

this is based on the following

before well & wheel covers:
21.5 / 22.5 / 20.5 / 21.5


After covers / Before Airtabs, according to SGII
23.6 / 22.6 / 20.6 / 23.7

After airtabs installed, according to SGII
25.7 / 24.3 / 22.0 / 25.6

Hope this helps.

[omgwtfbyobbq]

Any chance you could post up your route?

[cfg83]

lovemysan -

CFG83 you need these on your wagon. the .36cd is screaming for them. I'm just not sure if they'll help me.

I was thinking the same. My car is white, so I could have white air tabs. I am conflicted because they aren't my aesthetic. I should copy the wheel covers first and see what happens.

I think the one thing that's kept me from doing a mod like this is the reversibility. I know I can reverse it with some good old-fashioned elbow grease, but I avoid mods that could effect the paint. That's not a cool excuse :(, but I can't help it.

jeffreymccoy -

Thanks for the weather information. That is a detail that is always in the back of my mind.

CarloSW2

[jeffreymccoy]

Sure:
From Apex, NC
US1 N
440 Beltline
64 E
95 N
295 Richmond bypass
95 N
495 beltline
95N
MD-100
Snowden River Parkway Marriott Hotel

See it here...map is slightly off, due to the fact that I took the Richmond bypass for example. I dont know how to tell google to map that way..but here is the general route. My directions above are accurate. My mileage read 333 miles when I filled up in Columbia...

I dont have my ftp user credentials on my travel laptop, so I cant post the map pic right now, but use this link to see the route...

Google Maps Route (http://maps.google.com/maps?saddr=Apex,+NC&geocode=&dirflg=&daddr=100,+columbia,+md&f=d&sll=35.752921,-78.85334&sspn=0.125101,0.2314&ie=UTF8&ll=37.579413,-76.673584&spn=3.908798,7.404785&z=7&om=1)

[JanGeo]

Actually if you really wanted to make some airtabs then make them in a strip of plastic already properly spaced as one piece and apply the entire tab strip to teh top and sides of the car. Man I am thinking if it can help an F150 with that kind of mileage it should really make a difference in my xB.

[jeffreymccoy]

I saw an xB flying down the road today and thought the same thing - could be a big deal on the back of that square box.... I am going to apply them to the family chevy express van next. I think they do what they say they do... depends on the shape of the car as to how effective they are.

[DarbyWalters]

It inspired me to add three air tabs to each side of my Jeep Liberty...they don't look out of place at all...maybe because there aren't so many. I do have to say that I was in a wicked crosswind with gusts up to ~30+ and the Jeep felt stable.

[lunarhighway]

seems like i have to look into these things again.

one things that i find puzleing is some people place them in FRONT of wheelwells.
while their overall results show an improvement i wonder what's the benefit of placing them there?

as to me it would seem like they would actually cause more air to enter the opening... wouldn't they be better placed BEHIND the wells? so that they reattacht the air that's messed up by the cavity ahead?

perhaps dirt accumulation could give a partial clue as to what goes on aerodynamically either way.

[ZugyNA]

the price is a ripoff. you could make airtabs for 20 cents a piece with a vacuum molding machine.

You could duplicate them in sheet metal or plastic...though they claim their design flows better and is more efficient.

Like this:

............/\-/\-/\-/\-/\-/\-/\-/\.................

flow from below...spaced 3 Vs per foot?

[jeffreymccoy]

one things that i find puzleing is some people place them in FRONT of wheelwells.
while their overall results show an improvement i wonder what's the benefit of placing them there?

as to me it would seem like they would actually cause more air to enter the opening... wouldn't they be better placed BEHIND the wells? so that they reattacht the air that's messed up by the cavity ahead?


If the air is entering the front wells, the idea of placing these in front of them is that air will be directed around them, rather than into them. They would do nothing to help the well airflow if you put them behind the well. They dont cause the air to re-attach to anything, they cause air to be smoothed around an otherwise turbulent separation point.

I think I have basically created a virtual boat-tail with the way these are positioned around the cab and and bed of the truck... you think?

[jeffreymccoy]

the price is a ripoff.

You could duplicate them in sheet metal or plastic

To me it was worth the 2.50 each price. I put 80 of these on my truck. For me to create 80 identical pieces out of sheet metal or plastic would have been mind-numbingly tedious. I am not even sure that I could have done it. So for me, not a rip off at all, (in fact I thought they were very fairly priced)...and not something I could duplicate successfully in my opinion. I have to think that there is something specific to the curves and angles of the tabs, which is not something I could have perfected - certainly not 80 times in a row.

[Danronian]

This is some interesting results, but sadly, I agree that I don't like mods that affect the paint... I think it's because I always have the resale value of my car in mind, and every time you mod it, it just keeps going lower and lower.

Hopefully I can figure out a way to use these and spare my paint.

Great results with that f150! I'll be interested to see them keep working consistently.

[jeffreymccoy]

This is some interesting results, but sadly, I agree that I don't like mods that affect the paint... I think it's because I always have the resale value of my car in mind, and every time you mod it, it just keeps going lower and lower.


I agree completely with this point of view. I dont think they will damage the paint at all. I put them on and then relocated 2 of them the next day (the top front wheel well tab was became the bottom well tab). No issues with paint, it came off with some hard pulling, but then re-attached nicely to the new spot. I need to relocate some on the right side of the hood too, they are not lined up just right. Im more concerned about them resticking as strong than I am about the paint. I really dont think it will be a problem.

I make mods knowing that if it needs to be sold, they all come off and the truck is back to original state. I think that will be the case, even withthese tabs. Even if some glue is left behind, some goof-off (or other glue remover) will likely take care of any residue.

[theclencher]

yule hit 50 mpg in no time

[thisisntjared]

nah, guys, most adhesives don't damage the paint. my buddy put a lip on the trunk of his audi and it was there for a couple months, then he moved it and the paint was still fine, so if he were to sell his s4 he could just pull it off with no issues.

its not like its gorilla glue or anything like that, or even scotch tape, most paint safe adhesives usually stay kinda gel-like.

i mean havent you guys ever taken off stickers from your car? even the most stubborn ones just require a little goo-gone and the paint underneath is in better shape than the surrounding paint.

[2000mc]

one example i've seen a few times of adhesive damaging paint is vent visors / wind deflectors for windows. i've only seen it on trucks that were 5+ yrs old that probly had them put on when they were new, something happens to one of em somewhere along the way, but the dealer i work for isnt going to be seeling something with a damaged vent visor, or 1 or 3 vent visors. so the remaining vent visors are removed. problem is, the clear coat is gone where the adhesive was at.

[jeffreymccoy]

finished the leg home this evening. 392 miles. I only achieved 23.1 mpg average on the way home. this includes 25 miles of city driving, but that's not a big deal. I think the big factors in todays mileage were the rain and temp differences. still 23.1 is my 2nd best tank avg.

on the way up my IAT was reading at 100 - 110. today it was 80 - 85. it rained the whole trip.

correct me if you think I'm wrong, but I think both of these had negative impact on FE because:
1. harder to push through water than air
2. harder for tired to roll on wet suface than dry surface - higher rolling resistance
3. lower iat means more dense oxygen input. requiring proportionatly more fuel to maintian programmed air/fuel ratio

this sound right to you guys?

[SVOboy]

Sounds about right!

[cfg83]

jeffreymccoy -

finished the leg home this evening. 392 miles. I only achieved 23.1 mpg average on the way home. this includes 25 miles of city driving, but that's not a big deal. I think the big factors in todays mileage were the rain and temp differences. still 23.1 is my 2nd best tank avg.

on the way up my IAT was reading at 100 - 110. today it was 80 - 85. it rained the whole trip.

correct me if you think I'm wrong, but I think both of these had negative impact on FE because:
1. harder to push through water than air
2. harder for tired to roll on wet suface than dry surface - higher rolling resistance
3. lower iat means more dense oxygen input. requiring proportionatly more fuel to maintian programmed air/fuel ratio

this sound right to you guys?

That sounds right to me. The IAT seems to be a big factor in the ScanGauge algorithm. Obviously in the rain, the air is a lot more humid.

When you were driving through the rain, did the raindrop pattern look different? The next time it's raining, you might want to have someone drive your truck while you watch it/film it from another car.

CarloSW2

[SVOboy]

re: #3 but then ya just use less throttle to do yer speed.
Which increases resistance past the throttle plate, :p

[cfg83]

2000mc -

one example i've seen a few times of adhesive damaging paint is vent visors / wind deflectors for windows. i've only seen it on trucks that were 5+ yrs old that probly had them put on when they were new, something happens to one of em somewhere along the way, but the dealer i work for isnt going to be seeling something with a damaged vent visor, or 1 or 3 vent visors. so the remaining vent visors are removed. problem is, the clear coat is gone where the adhesive was at.

Well, I think I've figured out a compromise for me. I can get the magnetic sheet that is used for car signs and use that as a base for the airtab. That way, I could move the airtabs anywhere I want on the metal part of the car. For my Saturn, that means the hood and roof. What would be interesting about this is that I could test them in the hood location that jeffreymccoy is using, *or* test them up against the windshield as a windshield wiper turbulence deflector.

To make them more secure, I can also use the interior volume of the airtab to add a stronger magnet (or magnets).

Here is an example of a use for magnetic sheet that gave me the idea :

MAGNETIC CAR BRA for 1999-2002 SATURN SL
http://cgi.ebay.com/ebaymotors/MAGNETIC-CAR-BRA-for-1999-2002-SATURN-SL_W0QQcmdZViewItemQQcategoryZ50457QQihZ013QQitemZ 230024699982QQrdZ1QQsspagenameZWD1V
1001

CarloSW2

[2TonJellyBean]

Carlo, if I ever see your car with the "mag-tabs", it's gonna make it far too easy for me to ummm "borrow" them for my own experiments, :D

[cfg83]

2TonJellyBean -

Carlo, if I ever see your car with the "mag-tabs", it's gonna make it far too easy for me to ummm "borrow" them for my own experiments, :D

Ooof, now I'll have to take them off when I park somewhere :D !

Hrrmmm, maybe I'll RFID 'em, heh heh heh.

CarloSW2

[jeffreymccoy]

When you were driving through the rain, did the raindrop pattern look different? The next time it's raining, you might want to have someone drive your truck while you watch it/film it from another car.

The drop pattern did not look all that different on the front windshield. It was really hard to tell what the spray behind the truck looked like from my side and rear view mirrors. I saw all kinds of spray coming off every other car, but it was really hard to see mine at all, and when I did, it didnt seem to be as dramatic as other trucks that were on the road.

Without being in a chase car, its really really hard to tell though

[SteadFastStylee]

does anyone know if it'd make a difference if you just sat around smacking the body with a rubber mallet for awhile? I might be buying a pretty crappy looking CRX HF that wouldn't loose much "sex appeal" from a few hundred smacks with a mallet.

[Gearshredder]

does this have nething to do with a golf ball?

[cfg83]

SteadFastStylee -

does anyone know if it'd make a difference if you just sat around smacking the body with a rubber mallet for awhile? I might be buying a pretty crappy looking CRX HF that wouldn't loose much "sex appeal" from a few hundred smacks with a mallet.

Ahhhhh, the golf-ball dimple theory. Here are some similar threads on this :

dimple tape?
http://www.gassavers.org/showthread.php?t=1508

Aerodynamic grooves/ridges?
http://www.gassavers.org/showthread.php?t=3267

Winglets and bumpy paint?
http://www.gassavers.org/showthread.php?t=3478

CarloSW2

[SteadFastStylee]

I had read quite a few threads on it, but obviosly others have been taking ALOT of interest in this....sadly I'm not sure where my opinion lies now.

In one sense it almost seemed as if to create an improvement similar to the golf ball thing you would need to do it on a correct scale(larger dimples) and near the rear of the vehicle....then in other ways it seems sensible that using bumps instead of depressions more towards the front would help(the whole reason why drafting works)...then in Mitsubishi's tests it seems that bumps near the rear are the answer......

I'm glad I'm learning something either way! :D

[trebuchet03]

In one sense it almost seemed as if to create an improvement similar to the golf ball thing you would need to do it on a correct scale(larger dimples) and near the rear of the vehicle....

Speaking intuitively... Take a look at nature :)

Sharks have dermal denticles (I think that's the right term) - which makes their skin sand paper like; I think on a shark it's called a placiod scale (if you care to search). The shape varies from specie to specie (I'm fairly certain it's a way to identify different species) - but one purpose is that they create small vorticies to reduce drag. They are very small - you really can't see individual ones at all :)

-----
Now, speaking from something I saw at the San Francisco Maker Faire....

Look at the tail end dimples ;)
http://blog.scifi.com/tech/pics/nmg_yellow.jpg

I can't say if they help or not though... but it sure looks cool :p


-------

Oh, and I forgot to mention in my water tunnel picture post earlier.... I don't have a picture (batteries died)... But, tennis ball fuzz has a very similar purpose to golf ball dimples... While not as effective, there was a clear benefit over a "fuzzless" ball ;)

Anyone up for covering their car in some low pile carpet? :p

[SteadFastStylee]

That's gotta be the funkiest 3 wheeler I ever seen HAHA...My dad owned an old three wheeled milk truck for quite a number of years. Two wheels in back, one in the front..we named it the "Blue Moon". One of our favorite things to do in her was to find long curved well paved side roads and get up to just the right speed to travel along on two wheels.....ahh the good 'ol days LOL

[ZugyNA]

on the way up my IAT was reading at 100 - 110. today it was 80 - 85. it rained the whole trip.

3. lower iat means more dense oxygen input. requiring proportionatly more fuel to maintian programmed air/fuel ratio

Maybe set up a warm air intake for winter? ...of course in winter you almost have to max out any heat you can find to see much gain.

[ZugyNA]

How to apply airtabs to a hood and why:

http://www.airtab.com/bugs.htm

[73challenger]

Do these work on normal cars or only on semis and trucks?

[JanGeo]

Get a single AirTab and fill it with Bondo and add the Bondo molded AirTab to the body - repeat - prime - paint!

[ZugyNA]

You could make a mold and make them yourself....IF you could find a material to cast with that didn't cost so much...have you priced Bondo lately?

Maybe adobe mud might be cost effective?

I've made and applied some alum vgs (airtab distant cousins) and will post pics and the patterns when I'm done.

[MetroMPG]

Do these work on normal cars or only on semis and trucks?

You'll be hard pressed to find empirical evidence showing fuel saving capabilities on passenger vehicles.

You will find lots of anectodal claims based on non-scientific observations made by people who have already paid money for them.

[MetroMPG]

Now, speaking from something I saw at the San Francisco Maker Faire....

Look at the tail end dimples ;)
http://blog.scifi.com/tech/pics/nmg_yellow.jpg



Agreed - looks neat.

But look at the aft side of the front wheel arch. They've got dimples there too, where they would be utterly useless.

So they're either (a) blindly throwing aerodynamic darts, hoping some of them work; or, (b) doing it for the "neat-o" factor.

[trebuchet03]

So they're either (a) blindly throwing aerodynamic darts, hoping some of them work; or, (b) doing it for the "neat-o" factor.

I'm betting on the "neat-o" factor...

You'll be hard pressed to find empirical evidence showing fuel saving capabilities on passenger vehicles.

I tend to agree.... But I stand by my previous comments - that the concept is sound. The implementation, of course, is where things become questionable - so far, we can be certain nature is the closest to a good implementation :p I will hopefully have some CFD in the next few weeks to bring some non real world data to the table :p

[MetroMPG]

I'm of the same opinion.

I've said before: I've got a box of Airtabs myself. I CAN say conclusively they do NOT save any fuel sitting in the basement :D

I decided they were worth investigating more last year, and had intended to to test them to the best of my abilities in the real world this summer ... but got pre-occupied by the ForkenSwift.

So they're still on the list.

[charlesB]

But, tennis ball fuzz has a very similar purpose to golf ball dimples... While not as effective, there was a clear benefit over a "fuzzless" ball ;)

Anyone up for covering their car in some low pile carpet? :p

http://www.retroclobber.co.uk/movie-t-shirts/images/tshirts/dumb-and-dumber-dog-van-t-shirt-logo.gif

^^Maybe they weren't so dumb afterall?

[theclencher]

Agreed - looks neat.

But look at the aft side of the front wheel arch. They've got dimples there too, where they would be utterly useless.

So they're either (a) blindly throwing aerodynamic darts, hoping some of them work; or, (b) doing it for the "neat-o" factor.

The main thing to keep in mind when dissecting Sparrows is these things weren't made by engineers, they were made by tinkerers. Not saying tinkering is bad, but it does result in mis-applied theories. Don't put too much stock in what you see on them.

I've seen em and sat in one. It appears to me that, among other things, the weight and balance of the thing is way wrong, and accident reports seem to back that up.

[trebuchet03]

I've seen em and sat in one. It appears to me that, among other things, the weight and balance of the thing is way wrong, and accident reports seem to back that up.

I agree... I've sat in a Pizza Butt version...

I've said before: I've got a box of Airtabs myself. I CAN say conclusively they do NOT save any fuel sitting in the basement

I decided they were worth investigating more last year, and had intended to to test them to the best of my abilities in the real world this summer ... but got pre-occupied by the ForkenSwift.

Something tells me that leaving them in the basement to work on the forkenswift yielded better FE :thumbup:

[ZugyNA]

I rolled my own...or maybe bent them:

Decided that I couldn't be left behind in the vg race...so I made some out of ~.011" alum flashing material. A better material might be alum siding which tends to be ~ .022" thick. This stuff can be cut with regular scissors...but don't use your mommy's sewing scissors.

My analysis of the airtab:

The airtabs is around 5" long, but the "effective" area is only 3" and is angled at 30*. There is a straight "intro" area and an "exit" area that are likely shaped to "condition" the air flow to avoid any extra disruption of the air flow over the tab. The "exit" area probably helps to cause the vortexes to pull towards the centerline of the vehicle slightly? At any rate the complex shape probably makes them more efficient (cleaner vortexes with less drag) than a simple vane type vg.

I made two versions of vg...a smaller one that is just two straight vanes both angled at 20*...and a larger more complex one with the same 20* angle.

With the smaller vg the surface area of each vane is maybe 30 % greater than the airtab, but they are angled at 20* rather than 30*. The NASA research shows that too sharp an angle can cause the vortexes to break up with a straight vane type vg. With this vg it is easier to find a relatively flat place to install them.

The larger vg has a different design and is made to try to use streamlined shapes to cause less disruption of the air flow. The cross section of each vane is maybe 30% more than the smaller vg, but are also angled and not vertical.

The larger vg could be used on a van or on the hood of most vehicles. (pay no attention to those people in the other lane that are laughing about something)

* paste url into address bar and hit ENTER??

the vgs:

http://www.nonags.org/members/nijqk/vg-a.jpg


http://www.nonags.org/members/nijqk/vg-b.jpg


the patterns (large squares are centimeters):

http://www.nonags.org/members/nijqk/vg-patterns2.jpg


Can you get away with it?

Last time I had some on the side of a car...I had two cruisers...probably with their video going came up behind me...I was just about to hit the afterburner and flare switches...when they veered off.

This material...espec the .011" stuff is pretty flimsy...I sanded the edges, painted them, and used about 3 dabs of silicone caulk to stick them on...along with a level to get them straight. They should be placed less than 10" from the back edge and spaced maybe 4" to 5" apart on center.

They probably shouldn't project out much farther than the greatest width of your vehicle.

Cost?

Depending on whether you have the materials laying around...$0 to maybe $10. Your social standing might have to be defended. Buy a ray gun.

[boofighter]

@ZugyNA, none of your pictures work.

[8307c4]

I think I might spring for it sometime next year when money improves, but what I question is... Does one somehow drive better after installing these, and is this the actual factor that contributes to the increase?

Because on my 3/4 tons, on my '86 removing the tailgate increased mpg, but on my '95 it did not... The 86 has since been sold, but that was my first truck I removed the tailgate on, and then and now I wonder, did it make me drive better since I was already hoping I would get better mpg, and if so, is this what actually did it?

One figures by the time I got to fooling with the '95 it didn't affect my actual driving anymore, but there is a marked difference between the styling of the two (the 95 is far curvier than the 86 was). Oddly enough, the '86 got way better mpg than the 95 does, even thou the later model has a bigger engine it's also MPI (vs. carb'ed).

It can't hurt, the way I see things is I'm breaking up the flow of air before the rear of the car has a chance to suck it in. What I question is, why not let the air flow as it should in the first place, doesn't the airtab itself create just that amount of drag it in turn saves?

It strikes me like one of those vortex impeller tornado things one supposedly sticks in the intake to 'atomize' fuel or what have you...

Stranger still, this Audi race car uses a similar type of flaring near the fenders...
Although it appears to simply be for down force:

[trebuchet03]

Zugy, what criteria did you use to pick location?

Don't take this the wrong way - just offering my advice based on research I've done :)

The best way to figure out the location is with CFD and a wind tunnel. Find the separation point and place whatever flow control method you're going to use slightly before that point.

A not so perfect, but acceptable method is to do a rolling tunnel wool tuft test. Basically tape a whole bunch of strings to your car (a bright easy to see color) and take a bunch of pictures while at cruising speed. Watch for tufts pointing in a direction not parallel to air flow. Then place your flow control just in front of that....

As for the height -- the height should be only slightly thicker than the boundary layer. Remember that the goal is to bring a little bit of higher energy flow into a weakened boundary layer (weak because over a distance, it slows down and becomes thicker until separation).

The trickiest part of all of that.... the separation point changes with air speed.... So you have to pick a compromise...

Does one somehow drive better after installing these, and is this the actual factor that contributes to the increase?

The concept itself is sound... but the devil is in the details of application ;) Mitsubishi has a technical paper showing a reduction in cD by 6 points, many aircraft wings have them (not necessarily this product, but something of the same idea). Even power lines etc. use flow control (but for a very different reason :p).

[ZugyNA]

@ZugyNA, none of your pictures work.

* right click and click view pic....or paste url into address bar and hit ENTER??

[ZugyNA]

Zugy, what criteria did you use to pick location?

Don't take this the wrong way - just offering my advice based on research I've done :)

The best way to figure out the location is with CFD and a wind tunnel. Find the separation point and place whatever flow control method you're going to use slightly before that point.

A not so perfect, but acceptable method is to do a rolling tunnel wool tuft test. Basically tape a whole bunch of strings to your car (a bright easy to see color) and take a bunch of pictures while at cruising speed. Watch for tufts pointing in a direction not parallel to air flow. Then place your flow control just in front of that....

As for the height -- the height should be only slightly thicker than the boundary layer. Remember that the goal is to bring a little bit of higher energy flow into a weakened boundary layer (weak because over a distance, it slows down and becomes thicker until separation).

The trickiest part of all of that.... the separation point changes with air speed.... So you have to pick a compromise...

The concept itself is sound... but the devil is in the details of application ;) Mitsubishi has a technical paper showing a reduction in cD by 6 points, many aircraft wings have them (not necessarily this product, but something of the same idea). Even power lines etc. use flow control (but for a very different reason :p).

I'm using a combination of the NASA research and the airtab instructions.

These are supposed to be "clones" of the airtabs so I use the less than 10" away from the back edge (close as possible) and 4-5" spacing.

The NASA research was based on a 1" height for the larger vgs. Since with a car you will have a good bit of roughness to the surface in most cases...I go with the 1" high vgs to get above the disruptions.

The vortexes deteriorate over a short distance...thus the use of the 1" high vgs....they last longer.

Where I place them is based on...is there a flat surface?...is this place likely to do what I want...as in create a strong vortexed flow to either get the air past a wheel opening or to attempt to create the same type flow near the back in order to avoid the creation of the large disruptive vortexes?

If you hold your hand on the door surface when driving you can get a feel for the wind dynamics as you drive...there is usually a dead space where the flow has separated...with fast air above it. Put your hand behind the mirror and get an idea in miniature of the disrupted flow behind your car.

I think it's fairly easy to visualize what the flow is doing. Flow direction might surprise you some if tested though?

If you have a surface angled into the air flow you have higher pressure.

If you have a surface parallel with the airflow it might start to separate especially if there are variations in the surface.

If you have a surface angled away from the airflow...you have separation and lower pressures.

Look at the picture of the apple?

When you have separation...your vehicle is then dragging the large vortexes of disrupted air along with it...because they are at a lower pressure and tend to stick to the car.

I've got 22 small vgs on my car and hope to see maybe 1-2 mpg gain...but maybe not. The side of this car is fairly rough...with the windows set in some....not to mention the mirrors. Also can't put vgs on the roof due to a rack that is on the car. The placement decisions were fairly easy...at the back they need to be close to the trailing edge. In front of the wheel openings I needed a flat surface and a high pressure area (good flow).

[theclencher]

http://forums.tdiclub.com/showthread.php?t=147718&page=4

[ZugyNA]

http://forums.tdiclub.com/showthread.php?t=147718&page=4

Interesting discussion, but when I hear too many scientific terms and formulas mentioned as to WHY something won't work...it impresses me about as much as another RIDICULE FEST. A lot of the talk is really just people trying to impress themselves and others with how clever they are...and they are doing a disservice to the truth...in order to inflate their own egos.

Some of the technical links and info are good sources though.

The difference between myself and others on this forum is that I am actively looking for ways to increase mpg (as a hobby) and too many others are just talking about it.

Bottom line is you have to TEST an idea vs real world mpg. I can understand most of the scientific mumbo jumbo...and I use the research as a guide.

As I find techniques that work....I will eventually put together a vehicle as a "system" that uses the various techniques.

[ZugyNA]

I've got 22 small vgs on my car and hope to see maybe 1-2 mpg gain...but maybe not. The side of this car is fairly rough...with the windows set in some....not to mention the mirrors. Also can't put vgs on the roof due to a rack that is on the car. The placement decisions were fairly easy...at the back they need to be close to the trailing edge. In front of the wheel openings I needed a flat surface and a high pressure area (good flow).

Might have gained a little mileage...but sure didn't lose any. Hard to say...only 1 tank and using winter fuel. Car seemed more stable in a crosswind. Will be testing another aero idea next tank.

Did buy some airtabs for 1/2 price on Ebay.

[DarbyWalters]

I had five on the roof...didn't notice that much but wasn't doing any highway travel...added 3 to each rear side and subjectively the Jeep felt more stable (and I am lifted). I got my best mileage of 30+ on the highway for a distance of 226 miles. Some of the gain could have been from the "HyperTank" competition but I'll take it.

[mattW]

Ok here is my theory on why they sometimes work and sometimes don't. This is purely speculation, based on the Evo paper, people's air-tabs test results and the air tab website but i think it fits the data. The air tabs form a little vortex which acts like a bridge for the air immediately after it so imagine a small (probably a foot long?) bridge on the car that allows the air to jump over places where it would become more tripped up (wheel wells, gaps on trucks, bad windscreen designs and rear windows on 3 box cars). While the air tabs themselves actually INCREASE drag (increasing effective frontal area and adding energy to the air) they are a good way to avoid areas which would have increased the drag by more anyway. The summary of this is that air tabs can hurt! if your car is already quite slippery there is nothing for the vortexes to jump over- all they will do is increase drag. This is especially true on smooth sides and roofs. I am assuming this is why they are marketed specifically at trucks- they have big gaps that need jumping because they aren't designed all that well. On the other side of the coin if you have a relatively box-like car/truck with areas of turbulent flow or harsh angles for air to bounce off then using air tabs placed ahead of these points in areas of attached flow would allow the air to avoid the problem areas thus increasing you cars slipperyness.

The reason I think they work on the back of the car (i.e. the evo) is that the vortex stirs up the air which makes it easier to suck down so it can reattach to the car. I would be surprised if using them right at the back of a hatchback would make a difference because the air that is being sucked (vortex) is already turbulent- off the back of the car that would more or less the same as the wake was anyway. It would be possible that in certain situations the air tab vortex would reduce the size of the wake but it could also just as easily increase it. And I don't think we as hobbyists have the resources to test this accurately enough for it to be worth the risk. On the body of the car wool tuft testing would be a must to make sure the air tabs are doing their job (both before and after) but you can't do wool tuft testing behind the car. I am not saying that air tabs won't decrease your wake, but I am saying that unless they are done well they will possibly increase your wake.

In Summary: If you have an already aerodynamic vehicle then I think air tabs are more likely to do harm than good. If you insist on using them then I would try in front of wheel wells and under the car in front of anything that sticks out (unless you have wheel fairings/ a belly pan). If you are driving a car that has sticky out bits and lots of turbulence then air tabs would be a very good investment, but make sure if you are going to do it then do it well. Learn how to do air tuft testing, work out where there is turbulence and put the air tabs ahead of where it trips so they are still in the attached flow bit. Remember if you just stick them on willy nilly you are risk increasing drag.

It might help to think of air tabs as directing visitors past the dirty rooms in your house so they won't be unimpressed. If the rooms are already clean (aerodynamically) then you might as well show them in (no air tabs) and let be impressed by its cleanliness. Avoiding clean rooms would probably give them a worse impression of the house (more drag).

Feel free to rip this theory apart, I'm only trying to be helpful and like I said its purely speculation. What do you think?

[trebuchet03]

The air tabs form a little vortex which acts like a bridge for the air immediately after it so imagine a small (probably a foot long?) bridge on the car that allows the air to jump over places where it would become more tripped up (wheel wells, gaps on trucks, bad windscreen designs and rear windows on 3 box cars).

Matt, I have yet to come across any study that shows VG's effectiveness at bridging a physical gap (such as wheel openings, etc.) of filling the low pressure zone of a wake.

It's not that they create vortices to "jump" - it's that they put faster moving flow into a boundary layer that is fizzling out as the boundary layer gets thicker and slows down over a length of a body. By moving some higher energy (faster) flow into a unenthused BL, you can decrease the effects separation.

The summary of this is that air tabs can hurt! if your car is already quite slippery

The slippery conditions necessary are streamlined conditions (most drag comes as a result of pressure drag - not the wake) - of which, most cars are not. Even so, really long streamlined bodies can benefit too ;)

Most cars, unfortunately, are bluff bodies - where most losses are a result of wake formation. So it's quite beneficial to slightly increase pressure drag for a reduction in wake.

And as always, the devils in the details of application. They work when applied slightly in front of separation caused by low energy boundary layer. As far as decreasing wake effects due to a physical void (wheel arch, end of car, etc.) - it's an open book to be written by the person that does the analysis and scrutinized by everyone else :p

Feel free to rip this theory apart, I'm only trying to be helpful and like I said its purely speculation. What do you think?

Not ripping :p The conclusions you drew from your assumptions weren't too far in the outfield :p But the initial assumptions were a little off :D


The interesting thing about the EVO VG's is that they are very different to the air tab design... and very different to other designs :p The air tab design is almost like a spoon scoop whereas the EVO's is a delta V (a shape with a whole of engineering background).

[cfg83]

trebuchet03 -

...

The interesting thing about the EVO VG's is that they are very different to the air tab design... and very different to other designs :p The air tab design is almost like a spoon scoop whereas the EVO's is a delta V (a shape with a whole of engineering background).

They are a scoop, but aren't they also forming the opposite shape when used in unison to the other airtabs? If two of them have a 4 inch centerline application, isn't there a complimentary shape that could be effecting aerodynamics also?

CarloSW2

[ZugyNA]

It's not that they create vortices to "jump" - it's that they put faster moving flow into a boundary layer that is fizzling out as the boundary layer gets thicker and slows down over a length of a body. By moving some higher energy (faster) flow into a unenthused BL, you can decrease the effects separation.

I think they do cause the air flow to "jump" some openings....i.e....not get into gaps such as wheel wells where more turbulent flow is created.

In theory what they do at the rear of a car/truck is to reduce the "amount" of low pressure area formed at the back.

If the shape is "blunt" then large "cells" of roiling low pressure air are formed that affect stability and cause tire wear. Semi trucks.

With a more streamlined shape like a car probably not so much of this...but still some low pressure area that might be "filled" some. The idea here would be to design a vg that would not only create a vortex or a some kind of high pressure stream, but would also deflect the flow a few degrees toward the centerline of the vehicle..reducing the area of low pressure that is formed? I think the airtabs attempt to do this.

Saw a school bus with a large wind deflector at the top in back...not sure if it was for keeping the back free of dust or for mpg. (both?)

[ZugyNA]

In Summary: If you have an already aerodynamic vehicle then I think air tabs are more likely to do harm than good.

I would call the two pickups that have shown "results" with the airtabs rather high on the aero scale...though the shapes are pretty complex and not ideally aero for sure...at least no uneeded sharp corners?

[JanGeo]

Sounds like you all need to get a fan and a cardboard box and mount a scale on the box to measure air drag forces then add air tabs to it and see if drag is reduced. You can also run the yarn air flow telltails on the box and see the effects right in front of you.

[DarbyWalters]

Have 11 AirTabs on my Jeep Liberty...and the taillights are also shaped like an AirTab from the side (by accident I am sure). I did not do a test with only the AirTabs as the change...so I can not give any empirical data. I will say that the rear window does stay a bit cleaner in the rain, the Jeep feels a bit more stable at highway speeds and in turbulent air and fuel mileage did go up but other things probably contributed to that also. I think with a SUV type shape, you do get results that are most likley measurable because there is such a large area to improve upon.

The good thing is that the AirTabs are cheap to buy and/or similiar vortex tabs are easy enuff to make that there is no real harm. I think the trick is not to go overboard and create some kind of "Armadillo Skin" on a vehicle. Put them in the areas where the air leaves the vehicle in the rear...most likely benefit.

[ZugyNA]

Sounds like you all need to get a fan and a cardboard box and mount a scale on the box to measure air drag forces then add air tabs to it and see if drag is reduced. You can also run the yarn air flow telltails on the box and see the effects right in front of you.

I live about 75 miles from where the Wright Brothers original air tunnel is located...maybe I could borrow it?

[SD26]

Good information on this thread.

I'm new. Thanks for having me.

As a racer, I have a couple things I think about. One, I'd like to go faster, and, two, I'd like to do it cheaper. My travel costs are kind of high with a shuttle bus and an enclosed trailer.

I will agree, yeah, if the aerodynamics are good already, it's going to be hard to get dramatic improvements. But if you've got a brick, well, you might be able to polish the piece up and get something for a gain.

I teach six schools were I have to drive 650 miles one way to do it. So, if I could improve my FE from 11 to 12 MPG at $3.50 a gallon of diesel, I'll have got the cost of some of the Airtabs back, depending upon how many I use. If there's some stability to be gained, I'd like that too.

Looking forward to hearing more. I won't be making any changes myself until later toward spring when it gets warm out here in Wisconsin.

[cfg83]

Hello -

I did my magneto-airtabs :

1121

On the website, I thought that I wouldn't like them aesthetically. But, they have already grown on me. They haven't fallen off at 65 MPH, so I think I am ok with the magent solution for the roof (and the hood).

For side, non-magnetic applications (gravity and plastic body panels), I think I will install more of them as follows :

1122

The one problem is that they are designed for flat surfaces, so they have limited applications on curved passenger car surfaces. The gooves on my roof limited my application. That made me ask this question. Would they still work if I attached them like so :

1123

1124

Assuming for the moment that there is no vibration, would this be a better application, or would the lack of a surface underneath the end of the tabs sabotage the positive aero effect?

CarloSW2

[ZugyNA]

I teach six schools were I have to drive 650 miles one way to do it. So, if I could improve my FE from 11 to 12 MPG at $3.50 a gallon of diesel, I'll have got the cost of some of the Airtabs back, depending upon how many I use. If there's some stability to be gained, I'd like that too.

Besides the airtabs...try this?

www.oilcrusher.5u.com

ListerEngine forum:

"I had a horse trader cowboy from west Okla., call me one night… He was not a farmer, nor had time to press seeds. He had 3 Duramax Chevys pulling horses all over the USA. He said the $3.00 fuel was killing his profits. “What can I do he pleaded”. Well off the top of my head ,, I told him to go to the store and buy a cheap gallon of cooking oil.. Take it home and mix it with 2 gallons of gas and add that mixture to his 40 gallon pu tank.. Well he called me several days later, wanting to pay me for my help. He said his pu went from 12mpg to 18mpg on his first tank."

50% gains are hard to come by?

[SD26]

Hmm... Interesting.

50% gain? Kind of like that guy with the gain from the Airtabs being 100%, I'd be skeptical. Might give it try though. Put it on my list.

You have a link for that statement?

Currently, I collect all my used engine oil from our cars, the race bikes, and the bus, I run it all through some thing to clean it up a bit, then put it in the diesel fuel tank. Used engine oil has more BTU's than diesel, 135k-140k per gallon compared to petrol diesel at under 129k. I don't know if I'd use that in a 6.0 Power Stroke, but the 7.3's would probably run on dirt and water if you mixed it right.

I love the magneto Airtabs. That's really a great idea. Unforunately, my trailer has full fiberglass walls and the bus has an aluminum skin. Even the hood of most Ford vans are composite. I might use the idea for our Ford Focus though.

[SD26]

Besides the airtabs...try this?

www.oilcrusher.5u.com

ListerEngine forum:

"I had a horse trader cowboy from west Okla., call me one night… He was not a farmer, nor had time to press seeds. He had 3 Duramax Chevys pulling horses all over the USA. He said the $3.00 fuel was killing his profits. “What can I do he pleaded”. Well off the top of my head ,, I told him to go to the store and buy a cheap gallon of cooking oil.. Take it home and mix it with 2 gallons of gas and add that mixture to his 40 gallon pu tank.. Well he called me several days later, wanting to pay me for my help. He said his pu went from 12mpg to 18mpg on his first tank."

50% gains are hard to come by?
Ok, I found that thread.

I'm reading with great interest.

Thank you!!!!!

[Big Dave]

There are whole websites (www.veggievan.org) and major forums in big truck websites (www.thedieselstop) dedicated to the use of homebrew bio-diesel and waste vegetable oil (the call it WVO) in diesels. Herr Doktor Diesel's original engine ran on peanut oil. Google will result in an avalanche of links.

Not recommended for cold weather as you might imagine. Many WVO trucks start on dino-diesel and warm up the engine and WVO system then switch over. Before you shut down you switch back to dino-diesel for the next startup.

I've never bothered with it because:
a) There isn't that much free WVO around to be had
b) I despised chemstry labs
c) My injectors are $400 a pop to overhaul and I have eight

Back on topic, there a lot of measures that work OK on egregiously bad shapes (a Jeep) that aren't worth the effort on a fairly slick shape. As always, valid experimental data gets the last word although I simply don't believe they will make a gas pickup get 30 MPG.

[SD26]

Yeah, manufacturing my own biodiesel doesn't trip my trigger. That would be a constant process of work, and, like most people, I have tasks to do. Additionally, I'm not going to carry all my fuel on board during a long trip. It's not practical.

If I can make improvements to the overall shape of the vehicle that would enhance air flow, etc. that would reap continued dividends, regardless of the fuel source.

Big Dave, you have the conveyor belt air dam, right? I find that very, very interesting. I've been doing a lot of thinking about the underside of my bus, pictures of the bus and my previous, smaller trailer (http://visionsportsridingschools.com/headlights.html), and even the underside of the trailer.

Again, anything I can do aerodynamically reaps dividends each time I go out. Maybe the trailer would benefit from an air dam?

[ZugyNA]

Ok, I found that thread.

I'm reading with great interest.

Thank you!!!!!


Another link (discussion) with other links:

http://listerengine.com/smf/index.php?topic=1734.0

Some are also trying 8 to 16 oz biodiesel or straight veggie oil from the grocery in gas engines.

[SD26]

Yeah, after the quote you posted up about the guy increasing mileage so much pulling horse trailers, I came upon that thread. Thank you!

The gentleman that is harvesting the sunflower oil brings up a great point about how fuel has changed in that a lot of the older "good stuff" is no longer in fuels. I know that in the early 90's, a racing fuel manufacturer we were working with was making some additives for use if we wanted to run pump gas, but now that additive doesn't do much anymore because everything is pretty much garbage anymore.

Certainly, this made the initial sound of adding something like acetone to fuels interesting to me, but I don't think it's been completely exciting as of yet.

[JanGeo]

Back in my college days when gas was 25 cents a gallon a professor said to try some home heating oil in the gas and when I did in my old Rambler American it helps a little but on colder days it would smoke a lot until it warmed up and on warm days it had trouble shutting off - kept on running ha ha. Basically if you are adding oil to the gas you provide some upper cylinder lube and some more energy to the fuel to burn. What you want to watch out for is fouling the cat and O2 sensors.

[DarbyWalters]

Hello -

I did my magneto-airtabs :

1121

On the website, I thought that I wouldn't like them aesthetically. But, they have already grown on me. They haven't fallen off at 65 MPH, so I think I am ok with the magent solution for the roof (and the hood).

For side, non-magnetic applications (gravity and plastic body panels), I think I will install more of them as follows :

1122

The one problem is that they are designed for flat surfaces, so they have limited applications on curved passenger car surfaces. The gooves on my roof limited my application. That made me ask this question. Would they still work if I attached them like so :

1123

1124

Assuming for the moment that there is no vibration, would this be a better application, or would the lack of a surface underneath the end of the tabs sabotage the positive aero effect?

CarloSW2

You usually want to keep them away from the very edge. They are supposed to be located like you did on the roof to stop the separation...so you would put them on the side windows themselves. I too grew used to mine and don't even notice them much anymore...had them on just the roof like you...finally stuck three on each side near the rear.

http://www.gassavers.org/garage_images/t3nnlp9ouj86t3lxmwz6.jpg

[Bruce]

I've been eyeing vortex generators since reading the Mitsubishi paper. Last night, I finally took some thick aluminum flashing I had laying around, applied some Scotch VHB tape to it and cut it up into 10 tabs of the recommended profile with tinsnips - a triangle 20mm high, 40mm long with the peak ~35mm behind the trailing edge sticking up, with a 40mm long x 1" wide rectangular base with the tape applied. I bent up the triangles at a right angle with the vise for my drill press, flattened out the bases and chamfered the point of the tringles.

I then applied a piece of masking tape across the roofline about 4" from the rear window and applied the tabs using the angles recommended by Vortekz and Mitsubishi in roughly 4-1/4" increments. This is wider than the 100mm recommended by Mitsubishi, but I had to avoid the rain channels in the roof.

I had also calculated the expected improvement. Mitsubishi had determined the VGs lowered the Cd by roughly .006; my car has a base Cd of .31, so that'd be a 2% reduction in drag, which would be expected to improve FE by roughly 1% at highway speeds. My base mileage is around 40 MPG this time of year and only about half of my commute is on the expressway, so the improvement should be around .3 MPG -- far less than the day-to-day variation of my commute.

I couldn't tell the difference on the drive in. Coasting times were about the same. I managed 39.8 MPG for my 15-mile commute at 25°F, which I suppose was pretty decent considering the traffic -- two cars backed out in front of me, another left-turning vehicle necessitated acceleration from a stop facing uphill and a raging driver forced me to accelerate to pulse too much after a merge. Normally, I have relatively minimal interference.

A few glitches:

- I realized after mounting the tabs that our safety inspection has a prohibition against jagged metal edges, and these almost certainly qualify. So, they can only stay on in their current form until next August. I will probably purchase some clear acrylic angle stock from a home improvement store and use that instead.

- I bent all the tabs in the same direction, so the bases are not symmetrical with respect to the centerline of the car. This is primarily an aesthetic problem, although symmetrical bases would allow symmetrical positioning closer to the rain channels.

- Also, when viewing the front of the car from a distance, the VGs are obscured by the dome in the roofline. They'll need to be further forward to be more effective.

But, all in all, it was a fun project and the results look fairly decent.

[ZugyNA]

A few glitches:

- I realized after mounting the tabs that our safety inspection has a prohibition against jagged metal edges, and these almost certainly qualify. So, they can only stay on in their current form until next August. I will probably purchase some clear acrylic angle stock from a home improvement store and use that instead.

- I bent all the tabs in the same direction, so the bases are not symmetrical with respect to the centerline of the car. This is primarily an aesthetic problem, although symmetrical bases would allow symmetrical positioning closer to the rain channels.

- Also, when viewing the front of the car from a distance, the VGs are obscured by the dome in the roofline. They'll need to be further forward to be more effective.

But, all in all, it was a fun project and the results look fairly decent.

Got any pictures?

[Bruce]

No, and I guess there won't be any...I knocked 4 of them off the car and flattened a few more in the process of clearing snow last night. :( I guess that would explain why they aren't used in OEM applications very much.

I may still try plastic, but I'll need to use stronger adhesive. I'm thinking of using silicone RTV, since it'll remain flexible but can still be removed without screwing up the paint.

[cfg83]

Bruce -

No, and I guess there won't be any...I knocked 4 of them off the car and flattened a few more in the process of clearing snow last night. :( I guess that would explain why they aren't used in OEM applications very much.

I may still try plastic, but I'll need to use stronger adhesive. I'm thinking of using silicone RTV, since it'll remain flexible but can still be removed without screwing up the paint.

Blue03Civic used plastic butter dishes to make his vortex generators :

"Vortekz" generators....opinions??
Considering they are probably identical to the VGs on the Mitsubishi Evo and the stuff (images, numbers) they have on their site is from Mitsubishi's research, which can be found in pdf form quite easily, I'd say they probably work quite well.

However, I spent a mere $4 for all 8 of my VGs, which are made out of a plastic butter tray I picked up at Target and cut to pieces with a hobby knife and stuck on with 3m double-side adhesive... They are modeled after the VGs on the Cessna 182 a friend of mine owns and just based on watching the dew dry off my back window, in triangular patterns extending from the positions that my VGs are placed on, I'd say they work. I will probably be tuft-testing to see in better detail the effect they have soon.

CarloSW2

[caveatipse]

the price is a ripoff.
you could make airtabs for 20 cents a piece with a vacuum molding machine. my friend had one in his garage. you put a part on the plate and a sheet of 1/8th inch plastic is heated up untill it almost melts. the its placed on the plate and a vacuum opens and sucks the hot plastic sheet down onto the airtab so it follows its contours. when the plastic cools you pull the sheet off, cut around the part and you have an exact copy for 20 cents.
if you guys are serious about airtabs, just buy one and take it to someone who does vacuum molding. have them make you 50 or 100 or heck 5000 and sell the extras on ebay.

How much is the vacuum molding machine? lol

[ZugyNA]

No, and I guess there won't be any...I knocked 4 of them off the car and flattened a few more in the process of clearing snow last night. :( I guess that would explain why they aren't used in OEM applications very much.

I may still try plastic, but I'll need to use stronger adhesive. I'm thinking of using silicone RTV, since it'll remain flexible but can still be removed without screwing up the paint.

There must be something wrong with your snow clearing technique. I managed to remember mine were on there and just cleared around them.

Silicone caulk works best...and is removable espec if you have factory paint.

[Bruce]

I bought a 4' length of 3/4" (~17mm) edge protector -- essentially clear acrylic angle stock -- from Home Depot on the 18th, cut it up into the Mitsu recommended shapes and stuck it on with the VHB tape about 12" from the rear window at the recommended angles and spacing. I was driving back and forth to our other facility that week (~90 mi RT); mileage appeared to go up ~1 MPG despite colder temperatures and wet roads.

They didn't snap or fall off during snow removal this time and they've been on for a couple of weeks at this point, so I guess they're staying. I think they look pretty decent.

I'll upload some pics when I get a chance.

[SD26]

This is a company building "vortex strakes" for trailers.
http://www.solusinc.com/vortexstrakes.html

Just an idea on the edge protector. I was thinking of using 1" pieces of aluminum angle.

[ZugyNA]

This is a company building "vortex strakes" for trailers.
http://www.solusinc.com/vortexstrakes.html

Just an idea on the edge protector. I was thinking of using 1" pieces of aluminum angle.

Probably what I will use on the back of a camper.

[SD26]

Ordered some Airtabs the other day. Just ten of them. I might have a couple places that I'll use them on the bike, actually. Just want to have them and think about what to do with them. Would like to do the corn starch thing on the cars, but the weather isn't helping here much.

[johnf36]

Hi All, have a neither source for VG's that work better on smaller cars.
http://www.vortekz.com/
I still have the roof to do but I now have 3 on each c pillar and have picked up 2 mpg

[YakiMini]

I'm on here b/c of Johnf36 and so far the boot on my Mini is Cleaner via the VG's mentioned and I'm recording MPG to see if there is a change?

[SL8Brick]

Hi All, have a neither source for VG's that work better on smaller cars.
http://www.vortekz.com/
I still have the roof to do but I now have 3 on each c pillar and have picked up 2 mpg

Interesting how you mounted them on the sides. I know Vortekz doesn't recommend it. I'd think they'd act as mini-canards mounted that way, but I suppose they could still generate vortices.

[curv872]

I'm on here b/c of Johnf36 and so far the boot on my Mini is Cleaner via the VG's mentioned and I'm recording MPG to see if there is a change?

Curious on your results? Any change in MPG?