aero effectiveness of roof fins on the evo8
06-01-2005, 12:36 PM
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aero effectiveness of roof fins on the evo8
Originally Posted by platypus
Originally Posted by dsilver668
On a side note EvoWorks makes a set of vertical fins that sit on the rear of the roof. They help channel the air back over the wing to provide even better down force. I haven't seen this for the STi yet, but according to the technical manager at work's it really does help.
In the right setting I can definately see the strakes smoothing the airflow to the rear wing, but only if there was a sufficiently attached laminar airflow at that point on the car (which there probably is, but i want data dangit).
</hijack>
If the roof fins on the evo8 help with rear downforce, how do they shape the airflow to achieve this?
I can only guess that the fins must create vortices which direct more air towards the wing, which gives it more of an opportunity to create downforce, but I'm not at all sure.
dangit we need a wind tunnel that we can put our cars into (and nasa ames is all booked up)
06-01-2005, 12:44 PM
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ahh, the wonders of google
now to go get some carbon and make a set for the rally car.
The MR introduces various other extra-equipment features, some of them quite useful and others falling squarely into the mildly functional engineering geekdom category. Speaking of the latter, eight small "vortex generator" fins have been added to the back edge of the roof. At first glance, you wouldn't think they have anything to do with aerodynamics, but they actually increase the functionality of the rear wind spoiler and add downforce. A Mitsubishi engineer from Japan said the effective downforce of the system's flow, combined with the rear wing, helps to effectively reducing lift by 35 percent at 160 mph, which is the Evo's approximate top speed.
06-01-2005, 12:54 PM
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Originally Posted by porkchop
no need.. it doesn't go fast enough... =P
06-01-2005, 01:15 PM
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looks like it would probably serve the same purpose, air redirection not so much generating downforce on it's own. besides I would initially suspect that the fins would result in lower drag.
06-01-2005, 01:19 PM
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Aren't they called canards?
As I understand it it, they breakup the airflow mass, causing vortices (as you said), pulling in additional volumes of air beyond the boundary layer, and allow for a greater pressure differential above & below the wing (i.e. more downforce). I think it along the lines of "controlled turbulence". Me thinks.
As I understand it it, they breakup the airflow mass, causing vortices (as you said), pulling in additional volumes of air beyond the boundary layer, and allow for a greater pressure differential above & below the wing (i.e. more downforce). I think it along the lines of "controlled turbulence". Me thinks.
Last edited by stevedood; 06-01-2005 at 01:21 PM.
06-01-2005, 01:59 PM
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the term "canard" appears to refer to nose-mounted wings on an airplane (i think it's actually the flaps being mounted forward of the main wing), so I don't think the roof fins would fall into that category. They're more accurately called strakes, i think, but anyway terms are less important than the effects of the device.
06-01-2005, 02:07 PM
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The STi design seems like it would work better. That top rear window spoiler would direct the air flow down over the rear window and under the trunk spoiler. It seems like that would be more functional at lower speeds than the evo design.
06-01-2005, 02:34 PM
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Originally Posted by mbquarts
The STi design seems like it would work better. That top rear window spoiler would direct the air flow down over the rear window and under the trunk spoiler. It seems like that would be more functional at lower speeds than the evo design.
</bench racer>
06-01-2005, 02:46 PM
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spoller and fins.
Yup I thnink you will also be fighting a drag coefficiant once you hit a certain speed but at normal highway speeds it would funnle all that air straight to the rear wing.
This is why the fins only work at higher speeds. They need enough air flow to creat that channled flow. The fins look like those of a rocket. They are curved on both sides, so at high speed it would compress the air heading down the back wind shield like a ram jet.
Of course since we all drive the speed limit this is all kinda a mute point anyway right? :P
This is why the fins only work at higher speeds. They need enough air flow to creat that channled flow. The fins look like those of a rocket. They are curved on both sides, so at high speed it would compress the air heading down the back wind shield like a ram jet.
Of course since we all drive the speed limit this is all kinda a mute point anyway right? :P
06-01-2005, 03:02 PM
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I went out trying to look up info on the fins, or even the wings of the evo or STi and didn't find anything. Anyone have a friend at NASA Aims. I could donait my car for the test..
06-01-2005, 04:46 PM
#15
Originally Posted by mbquarts
The STi design seems like it would work better. That top rear window spoiler would direct the air flow down over the rear window and under the trunk spoiler. It seems like that would be more functional at lower speeds than the evo design.