luxlude

This is all information I've read here and there and is written to the best of my knowledge.

Let's start with the most obvious one. WING

Wings are used to help create downforce on the rear of the car and are constructed like an upside down or inverted airplane wing.

The top illustrates how an airplane wing works as the bottom shows how a wing on an auto works. the high pressure on top of the wing pushes down on the low pressure on the bottom of the wing thus creating downforce. Now don't think if you slap on some cheap wing you'll have rear stability equivalent to that of an F-1 car. Ain't gonna happen. Most aero parts effects (especially cheap ones) cannot be felt under speeds of 80+mph. More advanced wings actually change the height and angle of the wing to accommodate the change in airflow from the air coming over the top of the roof to the air flowing from the sides of the car towards the roof seen below.

Last, most commonly found on race wings, are gurney flaps. A gurney flap is a small lip on the edge furthest to the rear of the car. More downforce is created with gurney flaps, HOWEVER, drag greatly increases with even the smallest hight increase on the gurney flap. Eg. a wing ten inches in depth with a gurney flap of 2/5th an inch increases downforce created by the wing by 25%.

Staying towards the rear let's look at ROOF DIFFUSERS

Roof diffusers are found on Evo VIII's and can be an option on Evo IX's. These roof diffusers actually create vortexes to help channel air flowing over the car to the wing at the rear. Simple. Effective. Uncommon though.

Also used more commonly at the rear of the car is the REAR DIFFUSER

Usually found at the rear of the car, emerging from in front of the rear axle to the edge or just past the rear bumper, with thin vertical walls running from the front to the rear. This helps by taking the lower pressure air that is flowing from under the car and channeling it so it flows more efficiently to the rear of the car. While you drive there is a low pressure region that is created behind your vehicle, that low pressure sucks the air from under the car out the back. These are amazing for creating downforce on a vehicle because the downforce applies to such a large area. Eg. if pressure below diffuser is 1/2 psi lower than that outside the car over a 3x6 area creates 1000lbs. of downforce at the rear. Additional diffusers are sometimes used under the center of the car, or incorporated into a front splitter to increase smooth airflow under the entire car.

In conjunction with diffusers (sometimes) FRONT SPLITTERS AND AIR DAMS


Air dams use a vertical barrier to restrict airflow going under the car by forcing air up over, and around the car. Since less air is flowing under the car it has to flow at a much faster rate. This creates suction with lower pressure under the car. Splitters use the same concept partnered with an air dam but differ because the splitter extends forward to create downforce. this is caused by using the air that is slowed by the blunt shape of the front of the car. This air is called the stagnation (sp?) point. The splitter is used to SPLIT the high pressure air flowing over the car from the low pressure air flowing quicker under the car. Sort of like a spoiler. Downforce is increased the more the splitter protrudes out the front of the car. This is another aero option that isn't REALLY felt until around 80mph and usually emerges from behind the front axles.

Now up front CANARDS

Canards help create downforce in two ways. One - The upwards sloping canard forces air upwards creating light downforce. And two - The air that flows from the canards down the sides of the car creates vortexes keeping air from flowing from the sides of the car, to underneath the car. This is caused by the slower velocity air closer to the sides of the car against the free flowing air stream around the car. Canards coupled with a low side skirt keep air from flowing under the car, keeping the pressure low, creating more downforce.

And last (for what I can think of) NACA DUCTS

NACA ducts are like good ram air ducts. The design and sharp edges over the top of the opening of the duct is used to create vortexes that allow air to flow more directly towards areas of interest. These areas include engine, brake and even the driver. EXTENSIVE testing in wind tunnels for these ducts has been done to find a happy medium between drag and flow rate increasing efficiency. Don't be fooled by cheap knockoffs with poor design and rounded edges. Those do almost nothing.

Thanks for reading. Hope I helped anyone.


Modified by luxlude at 2:27 AM 11/9/2008

Kusai.Nihonjin.Desu

wanna see some wind tunnel action.

tks for the post.

.:Made in OC:.

Johnny Mac, where are you?

Faty17

good info man!

Outrun

I thought a wing was just that, a wing. Not a spoiler.

I thought a spoiler protruded out into the air flow where the air flows over the protrusion, but not under it since there's only one air path (unlike a wing). Here are examples of what I thought were spoilers:

The black piece at the base of the windshield of the first gen Mazda MPV.


Firebird Trans Am rear spoiler.


Chin spoiler, aka lip.


The small "spine" that goes down the centerline of an Indycar from the nose to the end of the engine cover is a spoiler designed to prevent/reduce the car from becoming a lifting body...


...in a similar way to the roof ridges and flaps of a stock car. There's also a rear spoiler on this stock car.


This Camaro has a spoiler.


This Trans-Am has a wing.



Modified by Outrun at 4:52 PM 11/9/2008

luxlude

Thanks for clearing that up! I actually didn't know the word used actually made a difference. Dumb mistake.

unrealwrc

No Offense, but that actually kills your credibility. Kind of like Bad grammer or mistaken equations.

Good post though. something like this with a little more information should be "stickied" for those wanting to find out more about aero and get into tuning for the track.

luxlude

Well I've always just said spoiler or wing. I knew people referred to lips as lip spoilers but didnt know a spoiler was used how outrun said, I would have just said wing or spoiler. You didn't have to be a dick about it. I know i should have clarified that now and I took it in stride.

essex

This is Honda-Tech, we just got 8 extra smilies this year.

welcome

luxlude

haha thanks.

kb58

These deviced don't "just work" by bolting them on. The airflow surrounding them makes all the difference between producing actual downforce or, far more likely, being a passive but expensive piece of bling to make the driver feel good. The rear diffuser does little good if it's fed dirty air due to all the crap hanging down in front it of. A rear wing does nothing if the airflow off the roof is turbulant. A front spoiler doesn't work if it's too high - or too low. I highly suggest reading the Katz book, "Race Car Aerodynamics".

Almost all this stuff is useless when applied to a typical commuter car since ride height is typically too high to allow the parts to work as well as claimed. A beautifully fabricated carbon wing/splitter/undertray has nothing to do with good engineering - so many people confuse the two. That's what wind tunnels are for, to develope real, actual working aero devices for a specific car.

Generic bolt-on parts, if they work at all, will apply to only one model car, the one used in the R&D part of its developement - if it was done at at. Beware, there's all sorts of people happy to take your money in exchange for pretty - but useless - aero devices.


Modified by kb58 at 6:50 AM 11/10/2008

Johnny Mac

Gurney flaps do help most wings generate more maximum downforce by effectively increasing camber for a given wing. Of course this is great, but what if I wanted to use the wing in say the middle of its downforce range? Will there be more drag for a wing w/o GF operating at say a lift coefficient of -1.2 (max being around -2.0 for example)? The answer is that many wings with a Gurney flap operating at a medium level of downforce also operate at a lower drag coefficient. So the benefit of a GF is twofold: a wing can be used for more max downforce or it can be used more efficiently at a lower downforce than the same wing with no GF.

Johnny Mac

These are not diffusers, rather, they are called vortex generators. They are used to help keep air attached to the downward sloping rear window that would otherwise separate. This is done for two reasons: Firstly, a separated flow is generally of a significantly lower pressure than is attached flow, which generates more drag than if the flow stayed attached. Secondly, the wake region in a separated flow extend higher above the decklid than attached flow which would make a lower mounted wing less effective since it would be operating in turbulent air which has large and small eddies (swirling vortices) and moves at lower bulk velocity towards the wing. If these eddies are allowed to impinge upon the wing, then the wing will not operate correctly since there may be some localized separation on the wing in addition to the slower moving bulk air going over the wing. All in all, you want the wing mounted above the separation wake so that it operates more efficiently.


Modified by Johnny Mac at 3:01 PM 11/10/2008

TunerN00b

Speaking of roof mounted vortex generators, any opinions on these?
http://www.vortekz.com/generators.htm

Johnny Mac

Vortex generators come in many shapes and sizes from "delta" wings to cambered airfoil stubs to angles and channels. Each of these shapes can produce vortex cores that serve to keep the air's boundary layer attached to the surface it is moving over, especially in what is known as an adverse pressure gradient where the boundary layer is very susceptible to separating. The adverse pressure gradient occurs where the flow slows down due usually to the shape of the body it is moving over - such as the rear window in an auto or the rear section of a wing. In an adverse pressure gradient, the thick boundary layer - which becomes much thicker than a flow over a surface with no pressure gradient - lacks sufficient kinetic energy to stay attached to the body. By placing a vortex generator upstream of where the flow would ordinarily separate, an infusion of high energy (the vortex core) energizes the boundary layer so that separation is either avoided or at least delayed somewhat.

Vortex generators generate their own drag in mostly in the form of induced drag, but if the vortex generator's shape, size, and orientation are optimized, this VG drag will be smaller than the drag that is reduced by delaying the separation. Improper specification or mounting of the VG's can actually create more drag than the car had prior to their installation. In other words, if a little is good and maybe more is better, than too much can be much worse. Every car will have it's own VG requirements based on many factors including the boundary layer thickness where the VG is installed, the air speed, the car's rear window geometry, and even whether or not a wing is installed.

This is one more example of the difficulty in understanding how aerodynamics works on complex shapes like a car body.


Modified by Johnny Mac at 12:36 AM 11/11/2008

Chronicsinners

grammar

luxlude

WOW I'm glad I posted this on here and people with more knowledge are contributing to this. Thanks to everyone who's supplied input. I never said I knew everything about aero but I think I had a decent general knowledge of it lol.

unrealwrc

velocecrat

Don't know whether this has already been posted, but here's the technical paper by those two Mitsubishi engineers on the Evo's vortex generators:

http://www.mitsubishi-motors.com/cor...004/16E_03.pdf

drewbie

this thread makes me wonder is the mazdaspeed front splitter does any good on the miatas 90-94 as seen here



There is nothing behind the splitter. It is shaped like a ' C ' with an empty void behind the front.

NTCustoms

i don't see a splitter in that pic. all i see is a lip.