| maxQ | 05-15-2006 05:26 PM |
[QUOTE=Joel Gat, 1.8L]Hello,
Yep. Except when you're talking about a car, the overall outside-to-outside dimensions don't change (usually within the bounds of the car sheetmetal) - so you "get" to use an effectively longer wing when you use "winglet" type ends.
Joel[/QUOTE]
We weren't talking about a car. But I understand that part.
Yep. Except when you're talking about a car, the overall outside-to-outside dimensions don't change (usually within the bounds of the car sheetmetal) - so you "get" to use an effectively longer wing when you use "winglet" type ends.
Joel[/QUOTE]
We weren't talking about a car. But I understand that part.
| ghschirtz | 05-15-2006 07:49 PM |
I think the impact of a spoiler must be to reduce lift and move the center of lift.
Also, remember cars like the Porsche 906 that used a spoiler to generate a "Kamm-effect" vortex aft of the car that served as a body extension and kept airflow more attached and laminar, reducing drag, but still keeping the rear end tied down.
I also believe lift and drag are not exponential with speed but a square function of speed, but I have not looked in my physics book in a long time.
I can confirm from my string test that airflow is staying more attached to the back end of the car, as SlideWRX is talking about. It has to be for the strings on the underside of the wing to lift up off the trunk and paste themselves on the underside of the wing. Further, there was a distinct lack of flutter in the strings, tending to indicate good laminar flow.
George
Also, remember cars like the Porsche 906 that used a spoiler to generate a "Kamm-effect" vortex aft of the car that served as a body extension and kept airflow more attached and laminar, reducing drag, but still keeping the rear end tied down.
I also believe lift and drag are not exponential with speed but a square function of speed, but I have not looked in my physics book in a long time.
I can confirm from my string test that airflow is staying more attached to the back end of the car, as SlideWRX is talking about. It has to be for the strings on the underside of the wing to lift up off the trunk and paste themselves on the underside of the wing. Further, there was a distinct lack of flutter in the strings, tending to indicate good laminar flow.
George
| maxQ | 05-16-2006 09:20 AM |
[QUOTE=ghschirtz] Further, there was a distinct lack of flutter in the strings, tending to indicate good laminar flow.[/QUOTE]
Good [i]attached[/i] flow. Determination of laminar flow is more complicated.
Good [i]attached[/i] flow. Determination of laminar flow is more complicated.
| ghschirtz | 05-16-2006 01:19 PM |
^Okay, I understand. Question: if the strings are not fluttering, does that not indicate smooth, non-turbulent flow (which I thought meant laminar). Curious.
Seems like attached but non-laminar flow, if I understand the concepts, would see the strings up against the underside of the wing but moving around. They were very stable.
George
Seems like attached but non-laminar flow, if I understand the concepts, would see the strings up against the underside of the wing but moving around. They were very stable.
George
| Chiketkd | 05-16-2006 01:24 PM |
[QUOTE=SlideWRX]Well I'm coming in late to the subject, but I may be able to confuse/clarify some stuff:
The spoiler on the WRX is there to re-attach laminar airflow, to reduce lift. By default, most streetcars have a certain amount of lift they produce (which is an exponential function of speed, IIRC). even the relatively brick shaped WRX produces lift. It produces it from the eddies that form on the trailing side of the car; the rear window & trunk mostly. the eddies area low pressure area versus the pressure underneath the car.
One way to keep eddies from forming as much is to keep smooth airflow over the rear of the car. The spoiler the WRX has helps the airflow re-attach to a surface at the bottom and stay relatively smooth. So the WRX spoiler by itself doesn't produce downforce, so much as eliminate some lift. It's almost just filling in the area where eddies could form, but because the currents didn't form the air generally stays 'pulled' down to the spoiler for more of the speedrange. The irony is that this is also a lower drag condition, so slightly better fuel economy. The turbulent eddy currents are a high drag & lift generating condition.
[img]http://us1.webpublications.com.au/static/images/articles/i10/1071_2lo.jpg[/img]
As for the STi wing, it still has a spoiler on it similar to the WRX spoiler, just smaller. Coincidentally this spoiler helps the actual wing on the STi by keeping the turbulent eddy currents smaller (just like the WRX one), so more smooth air flows over the wing to produce downforce. The downforce from the wing cancels out some of the lift produced by the rear window.
I'm guessing that even with the extra 'wing' added to the 2006, that there's still some turbulence, but it's probably a LOT less than previous years.[/QUOTE]
Great explanation! :cool:
The spoiler on the WRX is there to re-attach laminar airflow, to reduce lift. By default, most streetcars have a certain amount of lift they produce (which is an exponential function of speed, IIRC). even the relatively brick shaped WRX produces lift. It produces it from the eddies that form on the trailing side of the car; the rear window & trunk mostly. the eddies area low pressure area versus the pressure underneath the car.
One way to keep eddies from forming as much is to keep smooth airflow over the rear of the car. The spoiler the WRX has helps the airflow re-attach to a surface at the bottom and stay relatively smooth. So the WRX spoiler by itself doesn't produce downforce, so much as eliminate some lift. It's almost just filling in the area where eddies could form, but because the currents didn't form the air generally stays 'pulled' down to the spoiler for more of the speedrange. The irony is that this is also a lower drag condition, so slightly better fuel economy. The turbulent eddy currents are a high drag & lift generating condition.
[img]http://us1.webpublications.com.au/static/images/articles/i10/1071_2lo.jpg[/img]
As for the STi wing, it still has a spoiler on it similar to the WRX spoiler, just smaller. Coincidentally this spoiler helps the actual wing on the STi by keeping the turbulent eddy currents smaller (just like the WRX one), so more smooth air flows over the wing to produce downforce. The downforce from the wing cancels out some of the lift produced by the rear window.
I'm guessing that even with the extra 'wing' added to the 2006, that there's still some turbulence, but it's probably a LOT less than previous years.[/QUOTE]
Great explanation! :cool:
| maxQ | 05-16-2006 05:28 PM |
[QUOTE=ghschirtz]^Okay, I understand. Question: if the strings are not fluttering, does that not indicate smooth, non-turbulent flow (which I thought meant laminar). Curious.
Seems like attached but non-laminar flow, if I understand the concepts, would see the strings up against the underside of the wing but moving around. They were very stable.
George[/QUOTE]
In the large majority of cases, attached turbulent vs. laminar flow isn't really visual. It doesn't affect lift hardly at all but has a large effect on drag.
The only time you will see fluttering of the size string you used (I'm betting it's rather large household string) is when the flow is separated from the surface (stalled).
Based upon the roughness and poor airfoil design of the STi wing and the incredibly messy flow along the back window, I'm 98% sure the flow is turbulent from the leading edge to the trailing edge of the wing.
(in other applications, there will be a transition point at which the flow becomes turbulent at some point along the surface)
Seems like attached but non-laminar flow, if I understand the concepts, would see the strings up against the underside of the wing but moving around. They were very stable.
George[/QUOTE]
In the large majority of cases, attached turbulent vs. laminar flow isn't really visual. It doesn't affect lift hardly at all but has a large effect on drag.
The only time you will see fluttering of the size string you used (I'm betting it's rather large household string) is when the flow is separated from the surface (stalled).
Based upon the roughness and poor airfoil design of the STi wing and the incredibly messy flow along the back window, I'm 98% sure the flow is turbulent from the leading edge to the trailing edge of the wing.
(in other applications, there will be a transition point at which the flow becomes turbulent at some point along the surface)
| ghschirtz | 05-16-2006 11:14 PM |
^Thanks, Max.
Cheers,
George
Cheers,
George
| sonny2 | 08-07-2006 05:35 AM |
OK. So we know from George's experiment the STi wing does something (thanks George!!!) However, how much of a something is not quantifiable by his test. But it does [i]something[/i]. Now back to the original poster's question -- what about the WRX wing? Does that do anything like the STi wing?
I'm very interested in this question b/c I plan on taking my STi to the track. (My 220HP turbocharged Mazda Miata tracktoy needs a new head gasket.) Presently, I've got the WRX wing on but have my original STi wing sitting in the basement.
I might have to take BOTH trunks/wings to the track & try them out for myself. I might even get some video of the different wings with attached yarn as an addition to George's test.
I'm very interested in this question b/c I plan on taking my STi to the track. (My 220HP turbocharged Mazda Miata tracktoy needs a new head gasket.) Presently, I've got the WRX wing on but have my original STi wing sitting in the basement.
I might have to take BOTH trunks/wings to the track & try them out for myself. I might even get some video of the different wings with attached yarn as an addition to George's test.
| ghschirtz | 08-07-2006 09:46 AM |
^^^Hey Sonny,
Video would be way cool. My own guess is the STi wing is higher up and probably in smoother air, so it may be more effective, but it has a shorter chord, I think, so the downforce generated might not change that much. Eitherway, I would love to hear what you find out. Seems like the consensus is the wings help. I think I mentioned that I had no problems at all at CA Speedway, running into the banked corner at 125. Speed would scrub down to 115 on exit, but the car did nothing funny. To make sure, I have the low wing, not the high STi one.
Look forward to hearing what you find out. Thanks for working on it.
Cheers,
George
Video would be way cool. My own guess is the STi wing is higher up and probably in smoother air, so it may be more effective, but it has a shorter chord, I think, so the downforce generated might not change that much. Eitherway, I would love to hear what you find out. Seems like the consensus is the wings help. I think I mentioned that I had no problems at all at CA Speedway, running into the banked corner at 125. Speed would scrub down to 115 on exit, but the car did nothing funny. To make sure, I have the low wing, not the high STi one.
Look forward to hearing what you find out. Thanks for working on it.
Cheers,
George
| cdvma | 08-07-2006 10:00 AM |
[QUOTE=BlackSnake]Anyone know if the WRX wing Creates any downforce? Like a Nice 2lbs? :lol:[/QUOTE]
Several years back IIRC Prodrive quoted 20 lbs @ 80 mph in a tunnel test.
Several years back IIRC Prodrive quoted 20 lbs @ 80 mph in a tunnel test.
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