downforce

[mr2 mkII 1993]

i am going to go wingless with my mr2 is this going to create downforce problems at higher speeds??

[mr2ace]

how fast do you plan on going?

[mr2 mkII 1993]

well i dont plan on going faster than 100 but wouldnt it with the MR setup make the car "light" or "float"

[butter nuts]

I don't think the stock spoilers do anything at all. For a spoiler to have any real effect on handling, it has to be taller than the roof.

[mr2ace]

Originally Posted by butter nuts

I don't think the stock spoilers do anything at all. For a spoiler to have any real effect on handling, it has to be taller than the roof.

I do not think that is true...
The wing needs to be in the airstream which goes over the car. The wing on the Porsche 911 creates downforce and is functional. It is not taller than the roof. But still, you need to be going pretty darn fast in order to actually require downforce, and you need a spoiler that is designed with that intention. I doubt the one on the MR2 was designed for anything more than aesthetics.

[3sgtepower]

Ive read in the aerodynamics part of the forums, that the area behind the cabin is a low pressure zone and therefore the stock spoilers offer little to no benefit without being in the main airstream and would thusly need to be atleast as tall as the roof line is.

Madpsi.net makes a neat little lip you can add to your roof line that they claim offers some downforce benefit, without having to put a huge tacky wing on your car.

[mr2 mkII 1993]

i know ive been debating about buying that

[MX450248]

Originally Posted by 3sgtepower

Ive read in the aerodynamics part of the forums, that the area behind the cabin is a low pressure zone and therefore the stock spoilers offer little to no benefit without being in the main airstream and would thusly need to be atleast as tall as the roof line is.

Its the same concept as the bed of a pickup truck. the space in the bed is a low pressure area also because the wind stream from the roof passes over it and shoots down behind the tailgate. The same applies to the MR2 back half section, the wind goes over the roof and passes over the engine lid section, but that is where the low preasure area would stop. It would be disrupted when the engine lid section shrouding stopped. I would say that the spoiler does come into effect. See below:

[MX450248]

Originally Posted by butter nuts

I don't think the stock spoilers do anything at all. For a spoiler to have any real effect on handling, it has to be taller than the roof.

The evolution spoiler creates a good amount of downforce and its not above the roofline.

[chicagoisonfire]

Originally Posted by mr2ace

I do not think that is true...
The wing needs to be in the airstream which goes over the car. The wing on the Porsche 911 creates downforce and is functional. It is not taller than the roof. But still, you need to be going pretty darn fast in order to actually require downforce, and you need a spoiler that is designed with that intention. I doubt the one on the MR2 was designed for anything more than aesthetics.

The 911 spoilers aren't so much creating down-force as they are counteracting Bernoulli's principal. The way the 911 is shaped it creates lift at high speed (much like an airplane wing) and by adding the spoiler it breaks up the line of the car eliminating (fr the most part) the lift generated. If you look at a carrera, they have the pop out spoiler at 60mph+ that is pretty much just to get rid of lift. The turbos, however; do create some downforce, but that isnt their primary purpose.

[Gairloch]

Originally Posted by chicagoisonfire

The 911 spoilers aren't so much creating down-force as they are counteracting Bernoulli's principal. The way the 911 is shaped it creates lift at high speed (much like an airplane wing) and by adding the spoiler it breaks up the line of the car eliminating (fr the most part) the lift generated. If you look at a carrera, they have the pop out spoiler at 60mph+ that is pretty much just to get rid of lift. The turbos, however; do create some downforce, but that isnt their primary purpose.

QFT

The purpose of the stock spoiler on the MR2, 91-93 at least, isn't about creating downforce so much as it is about preventing lift.

[Sylvan]

At the moment I'm running wingless while I am doing some body work, then I plan on putting the 94 wing on. I have to say, the car looks kinda weird with no wing. I'm not a huge fan of the look.

[MX450248]

I would have to agree^

[Louis]

I have some experience with mechanical engineering and aerodynamics is like a hobby to me. I call it like MX says about the low pressure zone; but high downforce can still be produced from low pressure air. It's not as good as high pressure, but still can work. Another important aspect is the direction the air is travelling when it hits the wing. If it is going down when it hits the wing that will create more downforce. If it is going up, well,the wing would be nuetral. It is obvious that after the roof the air will go downwards, but, the big question is, how much will it go down? Will it pass over the wing, or will it curve down enough and hit the entire wing and produce downforce. In all my experience, I say it will produce some downforce; the best way to tell would be a wind tunnel, but who has access to one of those? I think the best wing would be one a little higher than stock, just to get into some more free flowing air. But I don't think going all the way to the roof is nesesary.

[Zeffrin]

MX450248's diagram is close but probably not quite correct, however Louis is correct.

While the air pressure striking the top side of the spoiler may be lower than that which is striking the wind shield it will still be higher than that which is passing below the spoiler.

Therefore some down force is generated, the higher the speed the more pronounced the effect.

Now... while the air behind the rear window will tend to form a static air pocket the air passing over the top of said pocket will induce Bernoulli's observed behaviour (the faster moving air being of a lower pressure) and wish to move toward it... this effect is noticed across the entire length of the car meaning that certainly some air does move from said air pocket up into the main stream but also out across the spoiler, creating some down force.

Now a significant difference is noticed in that the shape of the wind shield roof and speed will determine the curve of the low air pressure stream as it passes over the car. If the car did not have a boot at all and instead had a flat back behind the engine then that would create a large static air pocket behind the car resulting in more drag.. now this part is not really clear to me but the static air pocket the car "drags" around with it causes the car itself need to pull harder to "drag" said air pocket.

The boot reduces the air pocket behind the car by providing a moving surface to continue "cutting" through the air. Then the air pocket is reduced being the height of the back of the car and length well, dependant on speed but certainly smaller than the height of the cabin. Now the spoiler has an interesting effect... it increases that drag behind the car but it also raises the position of the back of the car so that at increased speed the air is intercepted by the spoiler and thus the top side catches that stream flowing off the roof. Ironically the faster one goes the more the air stream will confirm to the shape of the vehicle due to the increased velocity and thus attraction to high pressure air within the air pocket to move out into the stream of "cut" air.

Basically... a spoiler will create downforce even though it's not as tall as the roof... the greater the speed the more pronounced effect which is nice since the greater the speed the more intertia once must overcome in order to change speed/direction of the vehicle.

To see all this visually watch Mythbusters Golf Ball Dimpling test but also the Tailgating reduces fuel consumption myth... in both cases they use a water tank with dye to visualize the aerodynamic effect of vehicles. Pay particular attention to the swirling dye behind the vehicle, this is the static air pocket area.

In the end, if you're not driving at any great speed, the additional downforce created by the spoiler may not make a difference to stopping/cornerning, and the reduced profile may even decrease drag and therefore improve acceleration.

For street users obeying speed limits. I doubt it matters.

[jasenklems]

there is a wind tunnel program that I have seen on line I dont know where to find it but you can search for it and then see who is correct and let all of us know. But I will give my thoughts on this in the picture that was photo shopped you are about right on the point of low pressure but dont forget about the turbulence that is going to be created I should think that the wing will smooth the airflow again and that is about it. If you raise the wing to high you will not smooth that airflow anymore and that will disrupt any downforce that you are trying to make. Now I am more than likely wrong but that is how I see it and I try to look at thinks as simply and as practically as possible

[Zeffrin]

Originally Posted by jasenklems

there is a wind tunnel program that I have seen on line I dont know where to find it but you can search for it and then see who is correct and let all of us know. But I will give my thoughts on this in the picture that was photo shopped you are about right on the point of low pressure but dont forget about the turbulence that is going to be created I should think that the wing will smooth the airflow again and that is about it. If you raise the wing to high you will not smooth that airflow anymore and that will disrupt any downforce that you are trying to make. Now I am more than likely wrong but that is how I see it and I try to look at thinks as simply and as practically as possible

it's not a matter of someone being not correct, they're both onto the right idea. I was just saying the diagram is pretty close but I think not 100%... I actually think the turbulence behind the rear wind shield would be larger but anyhow

The wing will not smooth out turbulance... there will be turbulance behind the wing where the air flowing under and over meet and probably have different pressures.

Wings add a little more drag but also add noticeably more downforce making the trade off worth while at high speeds and with powerful cars.

[328FTW]

I need to build a full solidworks model of an mr2 and then do some fluid dynamics tests on it aerodynamic threads come up a lot. Would be good to have a test model to mess around with I can never be bothered though.

[MR JAS]

Originally Posted by 328FTW

I need to build a full solidworks model of an mr2 and then do some fluid dynamics tests on it aerodynamic threads come up a lot. Would be good to have a test model to mess around with I can never be bothered though.

its Sunday shouldn't you be sleeping

also i removed mine and didnt notice any difference

if anything i would say it would get taily in a high speed slalom or such but how often do you do that kind of driving

[MR JAS]

correction its already monday

as you were