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

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

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:

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


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


the patterns (large squares are centimeters):

https://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.

@ZugyNA, none of your pictures work.

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:

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).

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.

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.

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.

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?

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 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

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).

trebuchet03 -

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

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?)

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?

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.

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.

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

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.

Hello -

I did my magneto-airtabs :

Attachment 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 :

Attachment 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 :

Attachment 1123

Attachment 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

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?

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.

Ok, I found that thread.

I'm reading with great interest.

Thank you!!!!!

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.

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, 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?

Another link (discussion) with other links:

https://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.

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.

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.

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.

https://www.gassavers.org/garage_imag...86t3lxmwz6.jpg

Homebrew VGs
 

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.

Got any pictures?

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.

Bruce -

Blue03Civic used plastic butter dishes to make his vortex generators :

"Vortekz" generators....opinions??
CarloSW2

How much is the vacuum molding machine? lol

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.

Update
 

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.

This is a company building "vortex strakes" for trailers.
https://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.

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.