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Old 12-13-2007, 06:04 AM   #111
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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.
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Old 12-14-2007, 05:27 AM   #112
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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?
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Old 12-14-2007, 09:25 AM   #113
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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.
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Old 12-14-2007, 04:12 PM   #114
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Bruce -

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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??
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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.
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Old 12-19-2007, 08:52 PM   #115
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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
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Old 12-20-2007, 05:16 AM   #116
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Quote:
Originally Posted by Bruce View Post
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.
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Old 12-31-2007, 11:58 AM   #117
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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.
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Old 12-31-2007, 01:27 PM   #118
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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.
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Old 01-01-2008, 04:54 AM   #119
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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.
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Old 01-19-2008, 04:13 PM   #120
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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.
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