Vortex Generators on my Lancer
 

I know this is a topic that won't die :D but it caught my attention, so here goes... After spending a few quality hours reading up on the topic, here's what I gathered:

Despite some amazing efforts to test it out (props to everyone doing the work!!), no one really knows if it's effective. However from the little data that I came across and the anecdotal evidence I saw, it seems to me that hatchbacks (or any rather boxy shaped tailend for that matter) do not profit from VGs and may even lose FE. On the other hand, cars with a tail-end that is just a bit to steep to keep the flow attached - such as a lot of sedans - can benefit from the right kind/type of VG.

In evaluating the case for/against VGs on my Lancer, the Mitsubishi reserach was of course a tremendous help as they were basically doing their research on 'my car' with only the rear spoiler being a significant difference.

At the end I decided to go ahead and order a set of Vortekz for my Lancer. Here's my reasoning:

• As the Mitsubishi research showed, there can be a drag reduction.
• The Evo wing that was in use in their testing is meant to increase downforce (which it did, as the testing showed increased downforce from the smoother flow). The spoiler on my OZ however is an optical gimmick, not a working wing, thus smoother airflow around it shouldn't increase drag.
• Even if they don't work, they don't do any FE harm either, at least I have not seen anything that would indicate that.
• At the very least I will have better visibility during rain as I have no rear wiper. Worst case scenario, I will see a small advantage even if they don't do anything for FE. And I rather like the look :cool:

I did have one question:
Vortekz.com recommends installing some of the VGs at an angle, can anyone fathom why? I could not find any good information on this topic and from the Mitsu reserach it seems to me that the ideal VG is a delta shape parallel to the airflow :confused: (I did e-mail them about that but have no answer yet)

On another note, I would love to do some A-B-A testing if I can find the time, however I do not know of any flat and straight highways in the Baltimore/Washington area that would lend themselves to do the testing. So if anyone familiar with the area can recommend a spot (within a reasonable driving distance) I would be very grateful.

Perhaps they think slightly angles out towards the back is the direction of the airflow? Either way, before you install, I would tuft test your roof to see what direction the flow is actually going in.

They actually just got back to me, here was there answer:

"Hi Ben, it has something to do with the side draft of a car I think. The placement we suggest follows the placement on the Lancer Evolution 8 and they did some extensive wind tunnel testing.

Matt Dawson"

Mitsubishi must have done some more testing than just that one report that we've seen. Hopefully over the weekend I'll have the time to do the tuft testing that you recommend.

Hmmm. I naively followed the vortekz recommendations for placing the VGs at decreasing angles starting from the vehicle center line on my own Jetta. I think there is some logic to placing the delta wing at an angle to the prevailing air flow. If you look at the "airtabs" style VGs, they force air to either funnel down through the rear opening or spill up over the top angled edge. I think the spill over may help to enhance the VG effect. It would certainly enhance local turbulence, which is essentially the purpose of the VG, to disrupt and trip the boundary layer.

Unfortunately it probably also adds drag, so I might reposition mine. I have seen people claim good results with the VGs parallel to flow. so it might not be necessary. It seems clear that the folks over at vortekz know absolutely nothing about aerodynamics though...

Current position:
http://i287.photobucket.com/albums/l...z/IMG_1754.jpg

As their e-mail response to my question clearly illustrates, you are absoluetly right.

If I can find some time, I'll do the tuft test, if not I'll go with the recommendations in the Mitsubishi paper.

As you surely know, for vortex generators to be beneficial, they need to be positioned just right on the chord. There is always a tradeoff between vg chord placement and additional frontal area, even if you see attached flow all the way. IMHO, your money could be better spend elsewhere.

I've added about 45 vortex generators to the back of my 88 Dodge RV conversion van. They are the delta wing shape at a 20 degree angle I read were the most effecient. No I'm not about to do ABA testing as it would ruin the DB sticky tape which was the most expensive part of this project. Yes it did help, I thinking .1-.3 mpg. But then this 5800# box only got 14 mpg it's first trip, with the help of this site and others it gets 17 mpg now. That's a 22% increase. It has a 2' raised roof extension (not in EPA ratings) so just getting it back to the 17 mpg EPA rating is all I might expect for now.

I will refer you to my second to last and last point in my original post:

And as I have just done the passenger mirror delete, a clear rear window during rain will actually be a big advantage :D



Yeah the more i think about doing the ABA testing the on this project the more it seems like it is not the ideal project to do it if one has never done it before! However even if I end up doing the tests, I don't expect any FE gains that would be outside of the margin of error to begin with.



Seems like my initial judgment of the situation was about right: installing VGs to increase FE is an act of faith :thumbup: So I'll have to be happy with the better view out the back. Thanks for the feedback everyone

Luxbg,

There are many roads with longish straight sections on the Eastern Shore.
Whether this is a "reasonable driving distance" is a personal thing. :p

I'm thinking of Rte 50 in Maryland, and Rtes 13 and 113 in Delaware. The
farther south you go, the flatter they get. However, the roads have long, low
rises and declines, so aren't truly flat. Below Salisbury, and especially in Virginia, things really flatten out.

Haha yeah, I was hoping for something a little closer but if I ever have a free weekend, I might consider doing a whole day's worth of ABA testing at once and getting as many mods as possible out of the way. Thanks for the tips though!