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Old 01-14-2005, 03:58 PM   #51
vz64
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Russian auto journal autoreview.ru compared Evo VII and euro STi (bug eye), prodrive version (NOT WRC!). They conducted a wind tunnel test and here is their data:



The images show front/rear downforce in Newtons at 144 km/h for

1) Evo, spoiler set to minimal angle of attack;
2) Evo, spoiler set to maximal angle of attack;
3) STi.

They praised STi shape overall and its spoiler for minimizing lift forces (unlike in Evo that was not as stable)

The article (in russian) can be found at http://www.autoreview.ru/new_site/year2002/n15/lancer_vs_subaru/2.htm
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Old 01-14-2005, 04:01 PM   #52
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Quote:
Originally Posted by Mike Wevrick
interesting ... so is the WRX wagon somehow less stable because there is no wing? (I assume that little flat thing does basically nothing) What do cars like the S4 avant use?
It's an interesting question. Does a wagon have the same properties as a fastback or a 3-box design. The more vertical rear section in a 3-box design is more aerodynamically turbulent than a fastback, and therefore causes greater drag, but gives less lift. I would guess the near vertical rear of a wagon causes even greater drag, but since the roof section is long, does not give the advantage of less lift, as a 3-box does when compared to a fastback. Kind of the worse of both worlds. I imagine the little wing at the top of the glass is there to smooth the flow off the rear and decrease turbulence, thereby decreasing drag.
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Old 01-14-2005, 04:16 PM   #53
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vz64 - nice find! Once again, I have to ask, why don't American magazines have this sort of attention to detail?
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Old 01-14-2005, 04:26 PM   #54
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I was thinking the same thing ^^
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Old 01-14-2005, 04:31 PM   #55
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Quote:
Originally Posted by Arnie
vz64 - nice find! Once again, I have to ask, why don't American magazines have this sort of attention to detail?
I was sure I will get "re-post!" replies; this article was cited before, but without references to a wind tunnel part. I hope they tested the same spoiler we are discussing here:

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Old 01-15-2005, 01:36 PM   #56
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Quote:
"Why do you assume people are thinking ballast is equivalent to aero?"
and I didn't state a lead weight specifically provides downforce. I stated "downward force", because it would do just that thanks to gravity.
No it does not. And there are no assumptions involved, except the wrong ones quoted above.

Mass does not have a property called "downward force". Gravity is not the only thing effecting mass...acceleration, deceleration and lateral acceleration are actions that effect mass and cause counter action....and not necessarily downward.
Please go here: http://www.insideracingtechnology.com/tech106force.htm
Thank you.
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Old 01-15-2005, 01:41 PM   #57
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Quote:
Originally Posted by strangerq
Mass does not have a property called "downward force". Gravity is not the only thing effecting mass...acceleration, deceleration and lateral acceleration are actions that effect mass and cause counter action....and not necessarily downward. There
Please go here: http://www.insideracingtechnology.com/tech106force.htm
Thank you.
wow you love listening to yourself don't you?
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Old 01-15-2005, 01:42 PM   #58
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No. I don't. But I dislike misinformation, especially when it is put out 'intentionally'.
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Old 01-18-2005, 02:08 PM   #59
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Default Simulated results

Best thing to do is download the wing simulator and play around with it.

http://www.grc.nasa.gov/WWW/K-12/FoilSim/index.html

Using the originally posted inputs I get this (lift shown is at 100 mph), obvious problem is wing profile looks nothing like the USDM STi wing.



Here are results with a more realistic wing profile (maintaining same span, cord, and wing area).


And finally, results with a eyeballed WRC wing profile (again maintaining same basic wing geometry).



Note WRC wing has ~10x the downforce of the street wing. It is my belief that USDM wing was designed for looks, low manufacturing cost (thus soft plastic requiring fairly thick wing), and low drag. Functional downforce was not a big consideration.
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Old 01-18-2005, 04:27 PM   #60
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Default Angle of Attack

A little problem with the calc above is the angle of attack. Without CFD or windtunnel testing, you don't know the local flow direction at the wing. This calc is highly sensitive to angle of attack and therefore even a slight variance of flow from horizontal or whatever you used as a reference would have a large effect on the downforce.
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Old 01-18-2005, 05:31 PM   #61
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Zero angle of attack is almost always the lowest drag position. Actual wing seems to have a slight positive (lift inducing) angle of attack to horizontal. I am assuming this is because of the slight downward direction of the airflow. Thus given this and the min drag assumption I used a zero angle of attack for my "realistic case".

Note - the airflow behind the rear window is turbulent/dirty, this would reduce the actual downforce compared to the ideal predicted value.
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Old 02-03-2005, 03:35 PM   #62
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i didn't like the looks of the wing at first BUT started noticing that the subaru rally team uses the same wing, it may be more designed for rally applications than track etc... but i figure if it is good enough for them then it is good enough for me, and it is finally growning on me.
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Old 02-03-2005, 03:43 PM   #63
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another source to check is the newest issue of motor trend - the evo comparison has a few wind tunnel illustrations
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Old 02-03-2005, 04:24 PM   #64
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Quote:
Originally Posted by jr4jc
i didn't like the looks of the wing at first BUT started noticing that the subaru rally team uses the same wing, it may be more designed for rally applications than track etc... but i figure if it is good enough for them then it is good enough for me, and it is finally growning on me.
Are you high? The rally car wing is totally different, the wing on a 747 is more closely related to it than the stock USDM STi wing.
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Old 02-03-2005, 09:23 PM   #65
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Quote:
Originally Posted by Grintch
Zero angle of attack is almost always the lowest drag position. Actual wing seems to have a slight positive (lift inducing) angle of attack to horizontal. I am assuming this is because of the slight downward direction of the airflow. Thus given this and the min drag assumption I used a zero angle of attack for my "realistic case".

Note - the airflow behind the rear window is turbulent/dirty, this would reduce the actual downforce compared to the ideal predicted value.
Assuming semi-smooth flow, there is a downwash coming off the top of the car, which would change the local flow angle. Thus I suspect you are right, the wing is set at a slightly leading-edge-up incidence, which, oddly enough, decreases the downforce it provides by lowering the relative angle of attack and aligning it for low drag.

Let's see..USDM STi wing provides 60 lbs downforce on a 3200 lb car...about 1.8%.
In contrast, the WRC wing provides say 500 lbs on a 2800 lb car.....about 18%

Your posts are good, and I agree with your opinion....the USDM STi wing is for asthetics only....any downforce it provides is purely coincidental. Plenty of AEM wings provide more downforce than the stock USDM STi wing.

-Michael
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Old 02-03-2005, 09:33 PM   #66
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There is no "hard evidence".
I can stick my hand out the window and depending how I angle it, I will produce downforce.
The STi wing is pure marketing.
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Old 02-04-2005, 09:09 AM   #67
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Quote:
Originally Posted by Beer:30
There is no "hard evidence".
I can stick my hand out the window and depending how I angle it, I will produce downforce.
The STi wing is pure marketing.

Dumbest thing I saw posted here yet...
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Old 02-04-2005, 10:23 AM   #68
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Quote:
Originally Posted by RumblingREX
Dumbest thing I saw posted here yet...

I was trying to make a point there swifty.
So when I stick my hand out the window angled downward there is zero down force????
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Old 02-04-2005, 11:40 AM   #69
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The STi wing isn't all about downforce. Air coming off the top of the roof will spiral as it comes over the trunk creating a vortex which causes a vacuum, in effect causing more drag on the car. Basicly the STi aero package does reduce drag.
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Old 02-04-2005, 12:22 PM   #70
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You are confusing the fuction of a wing with a spoiler (although the STi wing lower is a spoiler).

A well designed spoiler CAN reduce drag by reducing flow seperation/form drag, it can also increase drag if designed to maximazie downforce (typically small spoilers reduce drag, reduce lift; big spoilers increase drag while providing more lift reduction/downforce). Of course a poorly designed spoiler can just totally suck. A high mounted wing will not do this, it will increase drag (hopefully not a lot) while generating downforce (assuming proper angle of attack).

Vortexes are often good for flow, as they can delay flow seperation and reduce form drag (they do not CREATE a vacume). Look at the (admitedly dumb looking) vortex generators on the EVO MR. Different types are also widely used on formula and sports racing cars. Don't base your aerodynamic knoledge on what you see on "Tuner Transformation" or in "Super Street" Magazine.

Grintch
Also class of '96 (but Auburn University)
Currently working at Marshall Space Flight Center

Last edited by Grintch; 02-04-2005 at 02:44 PM.
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Old 02-04-2005, 01:44 PM   #71
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Old 02-04-2005, 02:49 PM   #72
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Quote:
Originally Posted by Grintch
You are confusing the fuction of a wing with a spoiler (although the STi wing lower is a spoiler).

A well designed spoiler CAN reduce drag by reducing flow seperation/form drag, it can also increase drag if designed to maximazie downforce (typically small spoilers reduce drag, reduce lift; big spoilers increase drag while providing more lift reduction/downforce). Of course a poorly designed spoiler can just totally suck.

Vortexes are often good for flow, as they can delay flow seperation and reduce form drag (they do not CREATE a vacume). Look at the (admitedly dumb looking) vortex generators on the EVO MR. Different types are also widely used on formula and sports racing cars. Don't base your aerodynamic knoledge on what you see on "Tuner Transformation" or in "Super Street" Magazine.

Grintch
Also class of '96 (but Auburn University)
Currently working at Marshall Space Flight Center

There was a picture floating around here showing an STi in a windtunnel, showing the difference between one with a wing and without it. And the one without the wing showed that when the air came off the roof it would tumble instead of flowing of the back the car. The wing interupted this tumbling allowing it to flow cleanly ou the back of the car. Its the extreme stepdown of the rear glass. Cars like the Porsche 911 don't really suffer from it.
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Old 02-04-2005, 04:19 PM   #73
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Well....I'll chime in here again.

If the STi wing was actually a drag reducing appendage, in theory, I should have had a drop in gas mileage when I removed mine and replaced it with the WRX spoiler.

In fact, looking back at my records now (I keep track every time I buy gas), I note average mpg with the STi wing is actually 0.12 mpg *lower* than what I'm averaging without the wing. The increase in gas mileage is probably due to the lower weight of the WRX spoiler!

I notice *zero* difference in the way the car feels or handles, even at highway speeds. On rare occasions I've had it up to 100mph trying desparately to not get crushed by merging semi's. It drives exactly the same, and my rearward vision is dramatically improved.

-Michael
Currently working at Gulfstream Aerospace
but working with NASA-Dryden on a supersonic flight experiment
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Old 02-04-2005, 04:56 PM   #74
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Mike, you probably have been in more wind tunnels than me, but if I am in a tunnel (even assuming the wing discussed above was a USDM wing and not a ProDrive wing, rally, or JGTC wing [some people seem to think all big blue wings are the same]), can't moving the smoke generator (for the streamline) an inch or two change visably turbulant flow into smooth flow simply because you moved it out of the boundry flow region?

I personally wouldn't put much stock in a photo as proving aerodynamic efficiency. There are tons of things going on that effect the flow that won't show up or could be actively hidden/faked in a photo. One of these days I am going to do a real coast down test.
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Old 02-04-2005, 05:36 PM   #75
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IF I had an STi, I would keep my wing on.
How would you know if you're not getting down force? Can you ACTUALLY FEEL anything if someone was sitting on your rear bumper? How DOES 10hp feel?

Can you actually feel lift?

DO YOU THINK THAT THE CUSCO IMPREZA's HUGE REAR CARBON GT WING ADDS DOWNFORCE or is it just for looks? Do you notice how HIGH it sits? The height is because of the rear window. The wing can get a better attack of the air when placed higher on the rear of a car like the Impreza, which has a steep slope rear window.
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