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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 01-13-2005, 06:37 PM   #7
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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   #8
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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   #9
amukaoen
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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 01-12-2005, 03:10 PM   #10
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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   #11
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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, 04:55 PM   #12
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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 07-20-2005, 02:00 AM   #13
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Quote:
Originally Posted by tee_rexx
Something is happening back there cuz the back of my car seems to always to be more dirty than the rest of the car.
yah so does mine...even when there was no spoiler on it....
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Old 07-20-2005, 09:23 AM   #14
vapore0n
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air tumbling behind the car.

Id like to take a ride in a 06 in the rain. See how the new mini spoiler affects air flow. In the 05 model, air is tumbling in the rear windshield/trunk area. Easy to see when there is rain.

Also, all asumptions here on how much the wing works seem to be for a solid wing. The wing we have bounces and flexes. Frequency that it flexes seems to increase as speed is increased, making the wing more stable (or at least look like it is)
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Old 07-20-2005, 09:55 AM   #15
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Quote:
Originally Posted by vapore0n
air tumbling behind the car.

Id like to take a ride in a 06 in the rain. See how the new mini spoiler affects air flow. In the 05 model, air is tumbling in the rear windshield/trunk area. Easy to see when there is rain.

Also, all asumptions here on how much the wing works seem to be for a solid wing. The wing we have bounces and flexes. Frequency that it flexes seems to increase as speed is increased, making the wing more stable (or at least look like it is)
As aircraft advanced, one reason cables were abandoned in favor of struts was the drag caused by the cables vibrating in the airflow. IIRC a vibrating cable has 3 times the drag of a 'stationary' strut the same size. If you're saying the wing is constantly vibrating (as opposed to an occasional bounce) then it is supplying increased drag. This may be part of it stabilizing effect though.

this is an interesting thread.

Carl
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Old 07-20-2005, 11:50 AM   #16
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Quote:
Originally Posted by vapore0n
air tumbling behind the car.

Id like to take a ride in a 06 in the rain. See how the new mini spoiler affects air flow. In the 05 model, air is tumbling in the rear windshield/trunk area. Easy to see when there is rain.

Also, all asumptions here on how much the wing works seem to be for a solid wing. The wing we have bounces and flexes. Frequency that it flexes seems to increase as speed is increased, making the wing more stable (or at least look like it is)
I'm curious about that too cause we all know that in the current models that the airflow does seperate about a 1/4 of the way down the rear window. It'll be interesting to see how much that diverter really does.

Like I said before, the biggest thing that interest me is how the wind is hitting the entire assembly. The wing gets the cleaner air but how much the spoiler sees would be interesting since the spoiler is making the majority of the downforce.
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Old 07-20-2005, 11:58 AM   #17
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Quote:
Originally Posted by Thumper23
I'm curious about that too cause we all know that in the current models that the airflow does seperate about a 1/4 of the way down the rear window. It'll be interesting to see how much that diverter really does.

Like I said before, the biggest thing that interest me is how the wind is hitting the entire assembly. The wing gets the cleaner air but how much the spoiler sees would be interesting since the spoiler is making the majority of the downforce.
I think there must be some consideration of any negative effects a cross wind might have on the rear 'assembly' too.

Carl
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Old 07-20-2005, 05:06 PM   #18
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Quote:
Originally Posted by vapore0n

The wing we have bounces and flexes. Frequency that it flexes seems to increase as speed is increased, making the wing more stable (or at least look like it is)
That's right but the wrong words, the wing is flappin just like a birds wings, that's why the STI will fly.
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Old 07-20-2005, 05:27 PM   #19
f4phantomii
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Quote:
Originally Posted by vapore0n
I'd like to take a ride in a 06 in the rain. See how the new mini spoiler affects air flow. In the 05 model, air is tumbling in the rear windshield/trunk area. Easy to see when there is rain.
Yep, that would be interesting.

I've noticed in my '04 STi that rain streak pattern on my rear windscreen remained the same either with the wing or without. Clearly the wing doesn't have much influence on the flowfield upstream.

I'd be very curious to know how the '06 roof spoiler affects the whole thing. Seems like channeling the flow down the rear windscreen would actually increase the lift on the car by helping the flow stay attached and less turbulent.

Based on the streaks on my rear windscreen (yeah, I know I gotta wash it, but it's cheap flow vis!), the flow over the roof flows outward as it flows down the windscreen. It leaves a very discernable pattern. Makes it look as though the downwash is wrapping up around the rear quarterpanels rather than flowing over the wing.

Another interesting observation (that has been brought up before) is that the dirt/grime that collects on the vertical portion of the trunk lid didn't really change when I swapped to the regular WRX spoiler. I would have expected some differences in the pattern between the lower portion of the STi wing and the offset WRX "whale-tail" spoiler.

-Michael
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Old 09-29-2005, 04:40 AM   #20
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Quote:
Originally Posted by f4phantomii
Yep, that would be interesting.

I've noticed in my '04 STi that rain streak pattern on my rear windscreen remained the same either with the wing or without. Clearly the wing doesn't have much influence on the flowfield upstream.

I'd be very curious to know how the '06 roof spoiler affects the whole thing. Seems like channeling the flow down the rear windscreen would actually increase the lift on the car by helping the flow stay attached and less turbulent.

Based on the streaks on my rear windscreen (yeah, I know I gotta wash it, but it's cheap flow vis!), the flow over the roof flows outward as it flows down the windscreen. It leaves a very discernable pattern. Makes it look as though the downwash is wrapping up around the rear quarterpanels rather than flowing over the wing.

Another interesting observation (that has been brought up before) is that the dirt/grime that collects on the vertical portion of the trunk lid didn't really change when I swapped to the regular WRX spoiler. I would have expected some differences in the pattern between the lower portion of the STi wing and the offset WRX "whale-tail" spoiler.

-Michael
the roof spoiler is there to stablize the air coming off the roof and direct it to the lower portion of the wing.


turbulent air has less pressure than stable air.
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Old 01-12-2005, 03:47 PM   #21
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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 01-13-2005, 04:29 PM   #22
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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   #23
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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 01-12-2005, 04:53 PM   #24
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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 01-14-2005, 10:49 AM   #25
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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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