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Old 01-12-2005, 11:12 AM   #1
vapore0n
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Default Need hard evidence of the function of the STI spoiler

A coworker asked the famous question. Is that thing functional?
He wants actual data, not just "yes, I read it is" type of answers.

Anyone know if ther is such data available on the internets?
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Old 01-12-2005, 11:59 AM   #2
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http://www.sti-buki.com/forums/showt...=3011#post3011

Quote:
I measured my STi wing as carefully as I could, and then used the LARC wing simulator to calculate the downforce. I assumed the following parameters:

Thickness: 25% of chord (2.0 in)
Camber: -6.5% of chord (-0.5 in)
Chord: 8 inches
Span: 4 feet
Angle of attack: -1.2 degrees
Altitude: sea level

These seem to be the best match to the STi, as well as I could do with just a tape measure. I assumed that the angle of attack was the angle of the top of the wing end plates. I measued this angle with geometry, not a level, so the angle of the car on the ground did not effect the measurement.

The calculated downforce is 60 lb at 100mph. At 150 mph, the downforce is 140 lb. These are increases in download on the rear axle of about 5% and 10%, assuming 60-40 f/r weight distribution. These are the numbers for the top wing only, not the deck lid spoiler, which will add a little more. These numbers are not insignificant.
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Old 01-12-2005, 12:01 PM   #3
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Old 01-12-2005, 12:34 PM   #4
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FINALLY! OUTSTANDING FIND!
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Old 01-12-2005, 02:28 PM   #5
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cool, i'd really like to see info on the stock wrx spoiler as well.
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Old 01-12-2005, 03:07 PM   #6
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There is a little bit of info on the wrx wing in that link too...
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Old 01-12-2005, 03:10 PM   #7
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I seem to recall Subaru using a figure of 50 lbs at 90 mph which would be pretty close to the ones above. Something is happening back there cuz the back of my car seems to always to be more dirty than the rest of the car.
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Old 01-12-2005, 03:23 PM   #8
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Wow! Very interesting read!

So...the "rice boyz" with the massive park-bench wings could be for some phenominal front lift at high speeds if they don't have anything to offset it.


Hmmm...I want info on my WRX Wagon!

Cool.
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Old 01-12-2005, 03:47 PM   #9
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I think those figures represent ideal laminar flow. Bear in mind, the wind behind our steep rear window can be a bit choppy. I think I remember seeing a smoke-trail wind tunnel shot of a 22b (or GC of some sort). It looked like laminar flow was reliably present at about a foot above the trunk lid... hence, I surmise, the current design height.
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Old 01-12-2005, 04:53 PM   #10
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I have many posts on this subject. See links below for several discussions.

http://forums.nasioc.com/forums/showthread.php?t=689502
http://forums.nasioc.com/forums/showthread.php?t=686520
http://forums.nasioc.com/forums/showthread.php?t=648828
http://forums.nasioc.com/forums/showthread.php?t=650224
http://forums.nasioc.com/forums/showthread.php?t=641162

My opinion, and I seem to be in the minority, is that the factory STi wing is not particularly effective. It *looks* like the WRC wing, but that wing has several significant differences from the factory STi wing.

In the grand scheme of things, you are looking at 60 lbs of downforce at 100mph. So 60 lbs on a car that weighs 3200 lbs. In my opinion, you won't even notice that.

I've removed my STi wing and replaced it with the WRX spoiler and am far happier. It weighs much less, and improves rearward vision 100%. I've noticed absolutely zero difference in the feel of the car even at above normal highway speeds. I don't regret the swap one bit.

-Michael
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Old 01-12-2005, 04:54 PM   #11
powerslide23
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Can someone confirm if I did see the same STi wing mounted about 6-10 inches farther out in a rally car (not from the Gravel Crew RS at Pike's Peak but that is similar) to create more downforce?

I think this photo can explain what I'm saying:

Last edited by powerslide23; 01-12-2005 at 05:10 PM. Reason: added photo
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Old 01-12-2005, 04:55 PM   #12
f4phantomii
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Quote:
Originally Posted by tee_rexx
I seem to recall Subaru using a figure of 50 lbs at 90 mph which would be pretty close to the ones above. Something is happening back there cuz the back of my car seems to always to be more dirty than the rest of the car.
Hehe...I wondered if the dirtiness of the back of the car would improve when I removed my STi wing.

I replaced it with the regular WRX spoiler...it made no difference...it is still dirtier than the rest of the car.

-Michael
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Old 01-13-2005, 04:12 PM   #13
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The predicted downforce neglects the fact that the wing material (ABS?) is too soft, so it flexes under load. I would expect this to "absorb" a lot of the predicted downforce. Plus the visible vibration of the wing seen in the rear view mirror is annoying.

Notice in the WRC picture the wing is totally different from the street STi wing. The STi wing is almost oval in cross section (not very wing shaped), while the WRC wing has a strong, high downforce wing shape (sort of bannana shaped cross section).
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Old 01-13-2005, 04:20 PM   #14
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powerslide23: yes it is mounted farther back..it's almost hanging off the trunk lid!! It could be for several reasons..being farther back it's in better air because if you are too close to the rear window the airflow might not have come back down to optimally work with the wing. Also being farther back creates a lever effect...if you push the wing farther back and push down on it..you are gonna make more downforce on the rear of the car
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Old 01-13-2005, 04:29 PM   #15
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Quote:
Originally Posted by Dr Ken
I think those figures represent ideal laminar flow. Bear in mind, the wind behind our steep rear window can be a bit choppy.
Agreed.
In addition, the few available parameters (thickness, camber, chord, span, and angle of attack) do not uniquely describe the STi wing imho. A slight variation in shape within wings of the same parameters above could result in different location of flow separation etc., causing a very different aerodynamic behavior.
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Old 01-13-2005, 05:26 PM   #16
vapore0n
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Quote:
Originally Posted by satrya
Agreed.
In addition, the few available parameters (thickness, camber, chord, span, and angle of attack) do not uniquely describe the STi wing imho. A slight variation in shape within wings of the same parameters above could result in different location of flow separation etc., causing a very different aerodynamic behavior.
I was just going to reply almost the same thing. While the answers given in the thread are good, they are still ideal mathematical theoric answers.

Did prodrive test the STI wing? I know they tested their version of the prodrive kit.
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Old 01-13-2005, 06:34 PM   #17
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But in practice, I note no difference in gas mileage, stability, or air noise between having the STi wing on and not having it on.

Aerodynamics aside...I think the factory STi wing is purely for show.

-Michael
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Old 01-13-2005, 06:37 PM   #18
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Quote:
Originally Posted by 911-3.2
There is a little bit of info on the wrx wing in that link too...
I couldn't find this info. What did they say? I've always assumed the WRX spoiler doesn't provide any downforce.
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Old 01-13-2005, 07:09 PM   #19
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Quote:
Originally Posted by porque
I couldn't find this info. What did they say? I've always assumed the WRX spoiler doesn't provide any downforce.
It does something, although not very significant imho. Here's a thread linking to an even older thread (for the bugeye model), see post#11:
http://forums.nasioc.com/forums/show...ighlight=uk300
Quote:
Originally posted by Simon Lines
Hi Guys

The following (long) post is (some) of the mira report we commissioned.
...
MIRA Full size wind tunnel
16 OCTOBER 2000
...
The standard WRX has a drag power requirement of 60.5 bhp at 100 mph, front lift is 59.2 lbs. rear 75 lbs.
...
The addition of the low WRX wing has no effect on drag but reduces rear lift by 19.3 lbs. and adds 12.2 lbs. of lift to the front.
...
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Old 01-14-2005, 12:28 AM   #20
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Default what about the rival's wing?

STi wing is just for show... its basically just made to look like the WRC car's spoiler. its plastic and pretty worthless.. but i love it :] I think it makes my car look a lot better, without it, it seems a bit naked...

with that aside...


anyone know if the EVO wing is actually functional.. cause that one actually looks like it is, and with the MR's vortex generators... im sure it makes a lot more downforce as the STi's spoiler.. maybe 2x as much? but thats just a guess.. overall im sure it still makes no real differnce.. Id love to know for sure though.
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Old 01-14-2005, 04:44 AM   #21
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This was for the Evo7, but gives you a rough idea.



This is from a German magazine called Sport Auto. THIS is how you test cars! None if this "0-60, 1/4 mile, skid pad, 60-0 brake" and that is all the testing we do. This magzine actually does windtunnel testing as well as the usual measured tests. I think I have a longterm test of the GC8 (Impreza Turbo) as well as Audi RS4 in one of their issues.

Last edited by Arnie; 01-14-2005 at 04:50 AM.
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Old 01-14-2005, 10:13 AM   #22
f4phantomii
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Cool picture.

Hmm...wonder if it would stay so laminar with a weeks worth of road dirt on it.

It would be interesting to see the same picture of the STi. Wonder if it would show the large area of circulation behind the car...you know, the eddies that throw dirt on the back of our cars so they get dirty faster than the rest of it.

-Michael
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Old 01-14-2005, 10:49 AM   #23
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Quote:
Originally Posted by f4phantomii
the grand scheme of things, you are looking at 60 lbs of downforce at 100mph. So 60 lbs on a car that weighs 3200 lbs. In my opinion, you won't even notice that.

-Michael
I think you are rationalizing because you hate the way the wing looks, and wanted to get rid of it.

60 pounds of 'downforce' on the back of a car which by design at high speeds is subject to 'lift', thereby unloading the rear and causing the car to fishtail....is significant. Downforce is not analogous to sitting a lead weight on the back of the car! It is more akin to attaching a magnet to the back of a train gluing it to the track.

As an aside: I owned a wrx before my STI and the STI is much more stable at high speeds in cross winds.

If you hate the wing...get rid of it, but don't claim it doesn't work just because you don't like the way it looks.

We had someone make the same argument about the 'far uglier imho' hood scoop.

Sure...get rid of the hood scoop....and void your warranty. It's up to you.

Last edited by strangerq; 01-14-2005 at 10:58 AM.
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Old 01-14-2005, 11:58 AM   #24
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Splitting hairs here!

{cheap shot}
The wing may not be the WRC wing with all the proclaimed downforce yadda yadda, but you are an idiot if you think it does nothing at all!
{Fuel}
Bashing the wing for looks is one thing and totally personal opinion. Bashing the wing because you "think" it does nothing is just plain stupid. I have driven WRX's with and without the spoiler, and over 90mph the wingless get twitchy. For daily commute and legal speeds I 100% agree, it does not add to the driving experience. The STi wing does vibrates at legal speeds, proving it is in the wind stream and providing some downforce.
{Match}
These wing threads or annoying the living crap out of the engineer in me. They are purely opinions stated to prove why the wing needs to go to justify a certain member dislike of the "look or visual limitations" of the wing. Just say what you want say "I Hate The Look Of The Wing!" Don't make engineering judgement to back up your opinions!
{Flame suit on and run!}
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Old 01-14-2005, 11:59 AM   #25
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[quote=strangerq]I think you are rationalizing because you hate the way the wing looks, and wanted to get rid of it.
[quote]

I write so slow......
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