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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Sun, Apr-04-2010, 05:08:28 AM   #21
PurduinaM3
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Quote:
Originally Posted by TomS2 View Post
i asked the question about three times and each time people on this forum posted that there was nothing needed, or nothing done to the front of the car to counter the downforce. so yu are correct that i've never seen the LTWs undertray, and in fact, based on statements made by some self proclaimed experts here did not know one existed.

now that I know, i know i will not but one of those fugly gigunco ltw spoilers on my car without also putting the undertray on.

thanks for setting the record straight.
http://www.m3forum.net/m3forum/showthread.php?t=266721
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Old Sun, Apr-04-2010, 03:05:14 PM   #22
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Originally Posted by M3Works4Me View Post
Well the understanding I had on the topic was from previous discussions I've had with people who also claimed to be educated on the topic, but I can make no such claims..

I do however notice that Wikipedia supports what I posted, but I suppose the accuracy of Wikipedia can be called into question.

The article I read and the comments I've had in person from people who have done a track test on the spoiler vs no spoiler in the e36 M3 are true though, so I expect the truth lies somewhere in the middle.

I still believe the spoiler is generally not for downforce on most production cars, and that it has more to do with changing the airflow over the car - that just makes sense to me. I don't doubt your education, but I would very much like to hear from someone who designs the spoilers and is privy to the wind tunnel / airflow measuring that went on when this was being done.
I just skimmed over this topic so forgive me if I missed something but yes, spoilers (which is not a wing) can "spoil" up force. This is obviously not as good as creating down force but can be helpful to the aerodynamics of some vehicles. On the other hand ones which don't have a significant problem don't need this ( it should always be "balanced" in the front as posted above). in our case it seems to me and seems to be the general consensus over the years is that the OEM spoilers do little to nothing in this (or any) aerodynamic regard.

Laminar airflow (as far as I know, not really my area of expertise) can occur below the roof line, that's really more the nature of the car and/or other modifications done to it.

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Originally Posted by slickfast View Post
That's fine about the roof spoiler, I wasn't disagreeing; rather I was just explaining why that occurs. As for the CSL bumper, you're absolutely right... it doesn't effectively add downforce; it's an aesthetic piece. I don't know what you mean by "cleaning up airflow", since a spoiler by it's very nature creates turbulence.
This is the nature of every spoiler? I think most spoilers are detrimental because they are put on "sports" car for the hell of it or for the look, but as far as I am aware it can certainly reduce turbulence, right? Isn't that the very nature of a boundary layer? Or you could even have vortex generators on spoilers ect. (I guess I don't know if they would still be considered a spoiler)

EDIT: actually in some cases I could see a spoiler being used to spoil too much down force. I remember on top gear that new Jag had instability issues after 150 mph because the rear brake light was forced into a poor position due to legalities. This creating too much down force in the rear and/or not enough in the front. There are many ways to solve this, perhaps more in the front, but couldn't a spoiler disrupt the flow over the brake light? Creating an effective aerodynamic piece?
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Old Sun, Apr-04-2010, 04:33:41 PM   #23
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Originally Posted by M3Works4Me View Post
Well the understanding I had on the topic was from previous discussions I've had with people who also claimed to be educated on the topic, but I can make no such claims..

I do however notice that Wikipedia supports what I posted, but I suppose the accuracy of Wikipedia can be called into question.

The article I read and the comments I've had in person from people who have done a track test on the spoiler vs no spoiler in the e36 M3 are true though, so I expect the truth lies somewhere in the middle.

I still believe the spoiler is generally not for downforce on most production cars, and that it has more to do with changing the airflow over the car - that just makes sense to me. I don't doubt your education, but I would very much like to hear from someone who designs the spoilers and is privy to the wind tunnel / airflow measuring that went on when this was being done.
I work in the aeronautics industry, have performed wind tunnel/hand calculations/CFD on all sorts of objects, wings, and obstructions to measure their aerodynamic effects on aircraft in a professional environment for a major aircraft company. Not trying to say those other people aren't educated, but if what they told you agrees with what you have said, I really would like to get in touch with them to try and understand their thinking. Let me know if you'd like to do that.

Something to clarify: the intent of a spoiler is one thing, the intent of a spoiler on a production car is completely another. One thing to keep in mind is that to create lift, one must deal with the price of drag, as you can't have one without the other. Production cars (even sports cars) are made to be attractive to a customer. Unless it is intended as a track only car, being attractive to a customer means it must be efficient. It is for that reason that even though customers think they're getting a spoiler, they really are receiving a mostly aesthetic piece that doesn't compromise drag (and therefore fuel economy).

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Originally Posted by I3MW View Post
I just skimmed over this topic so forgive me if I missed something but yes, spoilers (which is not a wing) can "spoil" up force. This is obviously not as good as creating down force but can be helpful to the aerodynamics of some vehicles. On the other hand ones which don't have a significant problem don't need this ( it should always be "balanced" in the front as posted above). in our case it seems to me and seems to be the general consensus over the years is that the OEM spoilers do little to nothing in this (or any) aerodynamic regard.

Laminar airflow (as far as I know, not really my area of expertise) can occur below the roof line, that's really more the nature of the car and/or other modifications done to it.

This is the nature of every spoiler? I think most spoilers are detrimental because they are put on "sports" car for the hell of it or for the look, but as far as I am aware it can certainly reduce turbulence, right? Isn't that the very nature of a boundary layer? Or you could even have vortex generators on spoilers ect. (I guess I don't know if they would still be considered a spoiler)

EDIT: actually in some cases I could see a spoiler being used to spoil too much down force. I remember on top gear that new Jag had instability issues after 150 mph because the rear brake light was forced into a poor position due to legalities. This creating too much down force in the rear and/or not enough in the front. There are many ways to solve this, perhaps more in the front, but couldn't a spoiler disrupt the flow over the brake light? Creating an effective aerodynamic piece?
I love how when something like this comes up everyone is instantly becomes an aeronautical engineer. The intent of a spoiler is very simple: to create lift (lift being towards the ground in this case). The same exact airfoils present on low-speed aircraft can be applied to a car's spoiler.

As for airflow than can occur below the roofline, you are absolutely correct. It is completely dependent on the shape of the vehicle, as in everything in aerodynamics. However, it is very generally a pretty good rule of thumb to say that air below the roofline is not very useable.

One very important thing that you guys need to understand that seems to keep popping up: spoilers do NOT get rid of or reduce turbulence. They don't necessarily create it, but they DO NOT reduce it.

I think I've devoted enough time to this thread, and it's becoming a bit of a back and forth debate. I don't usually pipe up unless I am confident that I know what I'm talking about, and this is one of those times. I go to school for this, and deal with aerodynamics all day, everyday. If I couldn't answer a couple questions here about spoilers, I don't deserve to be in the field. Take what you will from what I've said, but I'm pretty confident in the above; and that comes from a guy not confident about much.
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Old Sun, Apr-04-2010, 04:42:31 PM   #24
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Apparently the drag coefficient of the e36 M3 coupe is .32, while the sedan is .33, so even the minor differences in shape can make a difference to drag.

The sedan is only 12mm narrower and 30mm taller than the coupe, same length, yet the Cd number is slightly greater. Knowing the effect on the variation of the shape of these two cars, it stands to reason that adding a wing would have a significant effect on airflow at higher speeds.

In scouring the vast reaches of internet-ia, it seems there's a common theme in the discussions about the effect of an airfoil, spoiler, wing etc on the turbulence off the roof and back of the car.

It appears that a rear window slope of less than 20 degrees allows the airflow to follow the roof and slope of the rear window. If this is more than 20 degrees, we get turbulence off the roof over the rear window area, which increases drag.

It appears that the net purpose of this appendage is a reduction in lift, drag and an increase in high speed stability. Almost every discussion I found on the topic supports this, which may not make it true, but it is nonetheless very compelling.

For those who can't be bothered to look into what a BMW designed wing does and why it has a specific shape for air to flow over AND under it, you can safely assume that somewhere sometime, this has been developed and tested in the BMW wind tunnel and they found a justifiable use for it.

Perhaps someone can find a better explanation, but here is one page that has diagrams to help explain this theory.

Aerodynamic aid: Drag & lift - COD - rear spoiler effect - Smooth undertray etc.
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Old Sun, Apr-04-2010, 05:07:02 PM   #25
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I agree wholeheartedly with nearly everything above except for this:

Quote:
Originally Posted by M3Works4Me View Post
It appears that the net purpose of this appendage is a reduction in lift, drag and an increase in high speed stability. Almost every discussion I found on the topic supports this, which may not make it true, but it is nonetheless very compelling.
The purpose of the wing is to create lift pointed towards the ground, as you have basically said (reduction in lift = lift with a downward vector; remember, lift does not always have to be straight up), however this lift WILL come at a price of INCREASED drag. It is a simple fact of lift, as pointed out by D'Alembert's paradox to aero guru's. As a result of all of this, increased downforce creates a more stable feeling at high speeds.
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Old Sun, Apr-04-2010, 05:23:28 PM   #26
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Quote:
Originally Posted by M3Works4Me View Post
Apparently the drag coefficient of the e36 M3 coupe is .32, while the sedan is .33, so even the minor differences in shape can make a difference to drag.

The sedan is only 12mm narrower and 30mm taller than the coupe, same length, yet the Cd number is slightly greater. Knowing the effect on the variation of the shape of these two cars, it stands to reason that adding a wing would have a significant effect on airflow at higher speeds.
ONLY if the wing is in clean air. In turbulent air it does hardly anything.

Quote:
Originally Posted by M3Works4Me View Post
In scouring the vast reaches of internet-ia, it seems there's a common theme in the discussions about the effect of an airfoil, spoiler, wing etc on the turbulence off the roof and back of the car.

It appears that a rear window slope of less than 20 degrees allows the airflow to follow the roof and slope of the rear window. If this is more than 20 degrees, we get turbulence off the roof over the rear window area, which increases drag.
Not true in all cases, but as a general rule of thumb, sure. Turbulence always happens though....

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Originally Posted by M3Works4Me View Post
It appears that the net purpose of this appendage is a reduction in lift, drag and an increase in high speed stability. Almost every discussion I found on the topic supports this, which may not make it true, but it is nonetheless very compelling.
I can discuss economics until my eyes are red and voice hoarse, but that doesn't make me an expert. Slickfast is. I'm an engineer with a good bit of aero and fluids knowledge (not nearly as much as Slickfast...ME not AE), but internet wisdom is just that-- "wisdom." Just because someone looks like they know what they're talking about doesn't mean they do.....which applies to 99% of internet discussions (especially when it comes to suspension design, that's a fun one to read "expert" idiocy).

The purpose of the spoiler is aesthetics. It provides zero benefit, adds drag, and maybe a negligible ten pounds of downforce.

Quote:
Originally Posted by M3Works4Me View Post
For those who can't be bothered to look into what a BMW designed wing does and why it has a specific shape for air to flow over AND under it, you can safely assume that somewhere sometime, this has been developed and tested in the BMW wind tunnel and they found a justifiable use for it.

Perhaps someone can find a better explanation, but here is one page that has diagrams to help explain this theory.

Aerodynamic aid: Drag & lift - COD - rear spoiler effect - Smooth undertray etc.
I worked at BMW engineering last year.....you'd be surprised how much was made in the name of style and form rather than function. So no, I highly doubt anything was designed other than market research to see if people wanted a spoiler to make the car look sporty.

The LTW wing functions decently well because it is tall enough to likely get some clean air and to direct the turbulent air. It's not nearly as functional as the PTG wing or a proper wing like Bimmerworld's.
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Old Sun, Apr-04-2010, 06:40:07 PM   #27
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I agree wholeheartedly with nearly everything above except for this:



The purpose of the wing is to create lift pointed towards the ground, as you have basically said (reduction in lift = lift with a downward vector; remember, lift does not always have to be straight up), however this lift WILL come at a price of INCREASED drag. It is a simple fact of lift, as pointed out by D'Alembert's paradox to aero guru's. As a result of all of this, increased downforce creates a more stable feeling at high speeds.
OK, so yes, if it creates negative lift, the benefits of that should include stability, correct? EDIT - You already said this, sorry….

Does turbulence also create drag? If so, alleviating it seems logical.

Well, from this discussion, which does seem to draw out a lot of opinion and unsubstantiated comments from people, I can say that I appreciate your input, and I think we're actually in agreement on most of it now.

I guess that is why I'm here, to take advantage of someone who knows more than I do about certain things and is willing to share their knowledge.
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Old Sun, Apr-04-2010, 09:44:05 PM   #28
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The purpose of the spoiler is aesthetics. It provides zero benefit, adds drag, and maybe a negligible ten pounds of downforce.

I worked at BMW engineering last year.....you'd be surprised how much was made in the name of style and form rather than function. So no, I highly doubt anything was designed other than market research to see if people wanted a spoiler to make the car look sporty.

The LTW wing functions decently well because it is tall enough to likely get some clean air and to direct the turbulent air. It's not nearly as functional as the PTG wing or a proper wing like Bimmerworld's.
This, especially the first part about the spoiler.

Not surprised at all about BMW making form over function decisions... it's not a friggin aircraft after all. On aircraft there is little to no compromise for form over function, as its all seat cost per mile.

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Originally Posted by M3Works4Me View Post
OK, so yes, if it creates negative lift, the benefits of that should include stability, correct? EDIT - You already said this, sorry….

Does turbulence also create drag? If so, alleviating it seems logical.

Well, from this discussion, which does seem to draw out a lot of opinion and unsubstantiated comments from people, I can say that I appreciate your input, and I think we're actually in agreement on most of it now.

I guess that is why I'm here, to take advantage of someone who knows more than I do about certain things and is willing to share their knowledge.
anytime man, that's why I took the time to explain.

To answer that last question you had, turbulence can sometimes increase drag, it really depends on how rough the surface is. Sometimes, such as a golf ball, having a high surface roughness can actually increase drag. For the most part though, a laminar airflow is always preferable, though it is pretty hard to do as the surface has to be extremely smooth (we're talking bugs being stuck on the windshield here). Often though, there isn't a straight answer to things like that, which I think is what makes it such an elusive subject to try to grab hold of for any casual people that are interested. It's kind of one of those things where you have to be either fully educated or not know much at all.
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Old Sun, Apr-04-2010, 10:01:53 PM   #29
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Just because something looks like it does something [good], does not mean a thing. Most of what has been discovered by science contradicts a person's first instinct.
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Old Mon, Apr-05-2010, 04:45:58 AM   #30
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OK, well BMW certainly takes aerodynamics seriously these days with the largest rolling road wind tunnel in the world.

See it here.

And here.

Hopefully they use it well..
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Discussing Admiring BMW's aerodynamics (question inside) in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)