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Adding a SPOILER! Will it help or hurt?


CiVTEC
12-12-2001, 10:16 PM
It is about time someone explains whether a spoiler will work or not. I guess I will take a crack at it.

Question: Will adding a spoiler work?

Answer: Yes and No.

A spoiler is supposed to work by generating a downward force on the car as the car moves. The force generated by a spoiler is a result of the difference in air pressure under the wing and over the wing. Think of a spoiler as an inverted wing. For a spoiler, assuming we have non turbulent air flowing through it, there is a lower pressure (higher velocity) on the bottom side of the spoiler. The top side has a higher pressure (lower velocity) which causes a downward force to be generated.
A simple analogy would be to hold a flat piece of plywood while the car is moving. Now invert the plywood downwards in the direction your car is moving and you will feel it pushing you down.
If you want to look at it mathematically, then here it is:

Cl=L / ((1/2)r(V^2)A)

where
Cl=lift coefficient
L=Lift
r=row=density of air
V=velocity
A=wing area (chord length * wing span)

Assume lift coefficient to be 1, then, L=((1/2)r(V^2)A)

This is very general but it works.

Of course the angle of attack makes a big difference in the lift force generated. The larger the angle of attack, the more force generated. However, it is at the expense of drag.

Now here is the problem. Given that we all know a spoiler will generate a lift force (I am using lift as the term for the downforce) if air flows smoothly through it, then the spoiler works. However, in the case of Hondas we drive, the air flow immediately after the roof is turbulent. The air isn't flowing in a streamline to the spoiler. Flow is now looked at in terms of large Reynolds numbers and it becomes almost unpredictable. It is possible for the air to flow backwards since there is a wake created from the stream of air separating at the end of the roof. So in this sense (for most of us), the spoiler is absolutely useless and creates a large drag on the car which SLOWS you down!

But don't despair, to get the spoiler working, we have to have it mounted above the boundary layer of flow and into a region where the air is smooth. So for all the people who have high (ricey) spoilers, they are actually using it to their benefit.

Of course there is another problem created: DRAG! In race applications where aerodynamics is key, such as Indy cars, the spoilers actually create a huge amount of drag on the vehicle. However, this drag force is negligible because of the benefits of having the car solid on the ground. In our case, the cars we drive rarely go fast enough where the negative lift force generated outweighs the drag force. With a large wing in the back, we are actually slowing our cars down (at least making it less efficient anyway). So in this sense, the spoiler is useless.

However, a spoiler adds aesthetic quality to the car (in my opinion) so it is still helpful. I have the tall stock spoiler on my civic and I can tell you it's probably useless but i'm planning on running some tests to see if it's non turbulent flow.

CiVTEC
12-12-2001, 10:26 PM
More info:

Look at the Ford Focus RS, that wing does work!
http://www.fantasycars.com/1/News/FordFocus/fordfocus.html


A front lip (airdam) is actually more helpful since it prevents a lift force being generated from beneath the car.

Actually, I'm working on designing a simple solution to creating nonturbulent flow to the rear spoilers on any car. I will have it patented and it will sell like hotcakes in the aftermarket departments...make me rich!

fritz_269
12-13-2001, 03:26 PM
Ever thought about the possibility that small, production car style spoilers and wings are not so much intended to increase downforce, but are actually mostly intended to reduce aerodynamic drag?

It's true. The idea is to cleanly slice the air away from the rear bumper so that it can mesh smoothly (more laminar) with the air from under the car. Without it, more of the air will follow the contour of the trunk and rear bumper (corbis effect) causing large vorticies, thus high velocities, thus a low pressure area directly behind the car (bernoulli), thus drag!

If you take a peek at almost any modern car, even if there is no sizeable spoiler or wing, there is a dimple or crease in the trailing edge of the trunk, and a sharp angle from the horizontal to the vertical plane of the trunk lid. In essence, it's a mini-spoiler; but it's for drag, not downforce. :)


Here's another question - at what speed do you have to be moving for a rear wing to provide enough downforce to increase your lateral-g cornering ability? What if you're in a FWD car that exibits understeer characteristics (like most Hondas)?
:smoker2:

sparq
12-13-2001, 05:58 PM
Originally posted by fritz_269
Here's another question - at what speed do you have to be moving for a rear wing to provide enough downforce to increase your lateral-g cornering ability? What if you're in a FWD car that exibits understeer characteristics (like most Hondas)?
:smoker2:

Depends on the car, the wing, etc... but a good shot in the dark is around 80-90... and if you are taking a corner at this speed in a honda guess what? :flipa:

texan
12-13-2001, 08:56 PM
Aerodynamics start to take effect around 45 mph, wings and spoilers start to really show their effects at around 70 mph (depending upon design). And to clarify the difference between a wing and a spoiler, a wing is any airfoil with airflow over two sides, a spoiler only has airflow over one.

LjasonL
12-15-2001, 02:37 AM
theres also the fact that 99.9% of spoilers, wings, or whatever u wanna call them were only made for looks and very little regard was given to whether or not they actually do anything good to your car. theres a joke i heard about roughly 95% of the spoilers out there produce maybe 2 pounds of downforce at 180 miles per hour. of course thats a big exaggeration but it illustrates my point.

texan
12-15-2001, 02:42 AM
Originally posted by ldelaysionl
theres also the fact that 99.9% of spoilers, wings, or whatever u wanna call them were only made for looks and very little regard was given to whether or not they actually do anything good to your car. theres a joke i heard about roughly 95% of the spoilers out there produce maybe 2 pounds of downforce at 180 miles per hour. of course thats a big exaggeration but it illustrates my point.

But that's an opinion, not a fact. Last time I checked, automotive egineers still earned a living, which is why the state of automotive art continues to move forward little by little, even after 100+ years of r&d. Aerodynamics in particular is no different... form follws function and Cd levels, among other things, fall a little more every model year. It might look good, but that doesn't mean it won't work.

LjasonL
12-15-2001, 03:27 AM
i wasnt exactly referring to stock spoilers when i made that comment i was referring to the ricer spoilers that are getting way too common. u cant tell me if u look in an advertisment for spoilers and u see theyre all more of a round bar than a flat or curved plane, and have this wierd bend in the middle, and then another one on top of that but that ones straight so the 2 planes are less than an inch apart in the middle but 3 or 4 inches apart on the sides, u cant say u think that actually does anything do u? of course i have no proof.

texan
12-15-2001, 08:14 AM
Originally posted by ldelaysionl
i wasnt exactly referring to stock spoilers when i made that comment i was referring to the ricer spoilers that are getting way too common. u cant tell me if u look in an advertisment for spoilers and u see theyre all more of a round bar than a flat or curved plane, and have this wierd bend in the middle, and then another one on top of that but that ones straight so the 2 planes are less than an inch apart in the middle but 3 or 4 inches apart on the sides, u cant say u think that actually does anything do u? of course i have no proof.

Sure I'll agree with you, but your description is hardly 99.9% of the designs out there, more like .1%. The fact is most spoilers and wings are either factory made parts or modeled after factory made parts, and you'd be surprised at how many were designed for a function beyond their looks.

Someguy
12-18-2001, 12:37 AM
The other "real" question is how many cars would see any overall benifit from a after market spoiler or wing. Very few.

kane2k
01-04-2002, 04:36 PM
Simple fact is that a rear wing by itself is not a benefit to a front wheel drive car. The good news is that you would need a wing far beyond the standard ricer wing to get any real downforce benefit. The bad news is that any downforce produced exclusively by a rear wing serves to destabilize an FWD car. The reason for this is pretty simple physics. If you need a visualization take a Hot Wheels car and press down on its rear deck. How does this effect help a car that depends on its front wheels for the vast majority of all power inputs ( accel, braking, steering). Rear wings can be useful at high speeds and with an aerodynamically tuned car. First off to go back to the math lift is dependant on V^2.. drag follows the exact same equation but with Cd instead of Cl ( subscript would be really helpful right now ). Unfortunately Cl and Cd are also dependant on each other in a polynomial relation of angle of attack for a given wing. This means that if you want Cl to be high ( i.e. downforce at low speed ) Cd will also be high for any wing. So assuming you can get up to speeds where this is useful then you hit the next important concept.. centre of pressure. In a standard passenger car the centre of pressure is located in the approximate middle of the car.. which is perfect.. unfortunately that standard centre of pressure is where the lift acts.. not downforce. Adding a rear wing to this will cause the hot wheels effect discussed earlier. But then you ask, why do FWD race cars have rear wings. The answer is that the rear wing is the sticker on the side of your car that says "aerodynamic" instead of Greddy. Sure anybody can put the sticker on.. but you cant see whether or not the car actually is unless you look under the car.. as you would normally look under the hood for a turbo. An FWD racecar is quite an achievement because the front end and the bottom of the car have to be completely reshaped to turn that car's aerodynamics upside down. If the front end can cause air to move more quickly under the car and the underside of the car can cause this air to decompress while its under there.. then downforce is born. Once you have this very important effect... which by the way... is not a fibreglass front bumper you can slap on... then you can go ahead and add the rear wing. The rear wing then creates downforce which, by itself, moves the centre of pressure further back.. but also collaborates to strengthen the underbody downforce by reducing the base pressure at the back of the car.. thus speeding up the air under the car and further reducing pressure, and increasing total downforce which is properly centred. Wow that was long winded. Anyway long story short... if you have a wing on your FWD car without having redone the underbody of your car then I see you as a Ricer because you bought the sticker without buying the part.

Moppie
01-04-2002, 08:31 PM
Nice Rant, but maybe you should go explain it to VW.
The new FWD Turbo Beattle has a small wing on the back of the hatch that opens at speeds above 60mph to help with high speed stablity. i.e. when doing 100mph+ down the Autobahn. It's sole purpose is to increase down force at the back of the car.

The Audi TT (shares the beattle platform and is most commonly FWD) also has a functional rear wing, in fact with out it the car becomes very dangerous at high open road speeds. (also why they added a great big hunk of lead to the rear bumber)

If your theory is totaly correct then both these cars, which dont make use of extensive areodynamic undertrays would suffer from instablity at high speed. However they both completly contridict what you have claimed.

:cool:

CornerCarver
01-05-2002, 12:51 AM
The problem with the Beetle and TT is that they were designed with so much "style" in mind and so little "function", that areodynamically they are the worst possible shapes you could conceivably make a car. Their shapes were so bad that aerodynamics caused the rear of both of these cars to lift at high speeds, causing instability and uncontrollable oversteer while careening down the autobahn. Thus, the wings and added weight in the back ends.

But I think the bottom line is that street driven FWD cars do not need rear wings. Add one if you like, but don't try to tell me it's for function... :P

JasonAccord98LX
01-05-2002, 01:26 AM
perhaps you fellas mentioned this already--i may have missed it--but some newer porches and i think a model of the vw new beetle, have spoilers that come up whenever you reach a certain speed. And in the case of the porches, some of them actually automatically change the angles of their spoilers as you drive. e.g. the faster you go, the greater the spoiler angle, which increases downforce.

Veetec
01-05-2002, 10:12 AM
Originally posted by CornerCarver
But I think the bottom line is that street driven FWD cars do not need rear wings. Add one if you like, but don't try to tell me it's for function... :P Iīm not sure about this because I donīt like most of the aftermarket spoilers and wings and personally I would never buy one => I never cared or thought about that! But somebody told me that the wing of an ITR for example will help you while cornering because of the additional pressure on the rear tires! I can see his point but I dunno why a daily driver should be equipped with one because IMO itīs really unnecessary. Like most of the other aftermarket parts.

texan
01-05-2002, 02:36 PM
Originally posted by Veetec
Iīm not sure about this because I donīt like most of the aftermarket spoilers and wings and personally I would never buy one => I never cared or thought about that! But somebody told me that the wing of an ITR for example will help you while cornering because of the additional pressure on the rear tires! I can see his point but I dunno why a daily driver should be equipped with one because IMO itīs really unnecessary. Like most of the other aftermarket parts.

His whole point was that fwd cars are traction limited at the front, not the rear. There's no point in increases rear end traction on these cars, all you are doing is increasing aerodynamic drag (very few aero parts have a positive side effect to drag).

Veetec
01-05-2002, 06:49 PM
Originally posted by texan


His whole point was that fwd cars are traction limited at the front, not the rear. There's no point in increases rear end traction on these cars, all you are doing is increasing aerodynamic drag (very few aero parts have a positive side effect to drag). Yea, I know! I know what the point in here was. I`m talking about the guy who told me the thing with the ITR and he wasnīt talking about traction on the front. Of course a wing doesnīt help the traction of a ff car.

CornerCarver
01-07-2002, 10:08 AM
Originally posted by Veetec
Yea, I know! I know what the point in here was. I`m talking about the guy who told me the thing with the ITR and he wasnīt talking about traction on the front. Of course a wing doesnīt help the traction of a ff car.

The ITR is front wheel drive.

LjasonL
01-17-2002, 06:17 PM
if u watch fwd touring cars, those cars have rear wings, it is to keep the rear planted during high speed cornering, so there IS a purpose to a wing on an fwd car, but the car must be cornering VERY fast, and the suspension must be tweaked. a standard fwd car has loads of understeer, and a rear wing will only complicate this problem.

VTEC_boi
01-17-2002, 07:02 PM
Originally posted by ldelaysionl
if u watch fwd touring cars, those cars have rear wings, it is to keep the rear planted during high speed cornering, so there IS a purpose to a wing on an fwd car, but the car must be cornering VERY fast, and the suspension must be tweaked. a standard fwd car has loads of understeer, and a rear wing will only complicate this problem.

I was under the impression that FWD cars have OVERsteer problems?

Am i wrong?

texan
01-17-2002, 07:04 PM
Originally posted by VTEC_boi


I was under the impression that FWD cars have OVERsteer problems?

Am i wrong?

Understeer = Front end traction is lower than the rear, causing the front end to swing wide during cornering.

Which is exactly the problem you naturally run into on a front heavy, front wheel drive car (especially on corner exit with throttle applicaton).

VTEC_boi
01-17-2002, 07:06 PM
Oh..alright

thanks Texan!

Sorry ldelaysionl!!

peace
boi

pushVTEC
01-19-2002, 02:27 PM
When you are getting a spoiler the last thing you should be worried about is it's "downforce" capabilities. You are driving a FWD car... therefore the downforce created on the back of the car wont do anything since all your power is coming from your front wheels. With a spoiler you're looking for style not functionality :D

911GT2
11-22-2002, 10:46 PM
Originally posted by CiVTEC
More info:

Look at the Ford Focus RS, that wing does work!
http://www.fantasycars.com/1/News/FordFocus/fordfocus.html


A front lip (airdam) is actually more helpful since it prevents a lift force being generated from beneath the car.

Actually, I'm working on designing a simple solution to creating nonturbulent flow to the rear spoilers on any car. I will have it patented and it will sell like hotcakes in the aftermarket departments...make me rich!

The large majority of wing buyers are riceboys. Riceboys don't care about performance and will therefore not even consider your product no matter how good it is. And a flattened wing (which most aftermarkets are) will not give you downforce one way or the other.

And putting downforce on the rear of a FWD car will give you horrible high speed stability.

pushVTEC
11-23-2002, 01:54 AM
Talk about bringing back a post from the dead lol :D

Flycyhm
12-03-2002, 02:10 PM
Wow, am I sorry I missed this one! Go for a few weeks with out the internet, and look what I miss!

So is this all settled now or what? Personally, I think the guy who mentioned the point about the rear spoiler or wing (both do it) increasing the laminar flow characteristics of the air leaving the trunk and reducing drag (also reducing the dirt on the back of the trunk due to the vortices circulating dirt and debris against the car) had a good argument, and no one seemed to acknowledge it.

That is really what all the factory ones are for, with the exception of some very expensive high end sports cars. The rest are just for looks.

Damn, sorry I missed this. I just did a lot of aerodynamic modifications to my aircraft (I'm an Aeronautical Engineer and Pilot), and I love a good debate.

Hopefully someone else will come in and stir the pot too! :)


Flycyhm

DGooden
12-04-2002, 10:51 PM
I think adding will be cool. It'll look cool and worth the money IMO

Chris
12-06-2002, 11:51 AM
well, I posted this a long time ago, i feel it is a good explanation:

A spoiler can add drag (porsche 911 turbo, the 'whale tail' years).
A spoiler works on the Coanda effect. That is, air (or any gas or liquid) flows along like the surface it was on. Therefor, on a car, it goes DOWN the back, meeting the air from the bottom. This increses drag, but the air moving that way kinda (a little bit) decreases lift. Now, as far as I understand it, a spoiler causes the air to go up momentarily, flowing STRAIGT behind the car, not as much going down. This decreases drag. Now, the air UNDERNEATH the car has to come UP to the rear of the car, increasing the distance it has to travel, and therfor increasing speed and decreasing pressure going up (lift).
Now you see how it works. (they are in capitals just to highlight important stuff, not trying to make you look dumb. I have done that unintenially in the past )

That is a spoiler, the small 'lip' thing on the back of a car. It has nothing to do with aviation (actually, it does, but not for this reletively simple stuff)
A wing is a device that is an upside down airfoil. It decreases lift, but increases drag. If it is small enough, the drag will be slight. Sometimes it can actually decrease drag by letting the air out quicker and more efficiently. This all depends on a gazillion factors that are hard to understand.

Most magazines call small wings spoilers, which they are not.

Heres another example. On the 911 Turbo, it has a spoiler at first. Then it rises up into uninterupted air, in effect a wing. A true definition is hard to come by, as most people us the terms when they shouldn't.


Also, ALL cars now have spoilers. Look at the back of any car, I did today. From Fireflys to Minivans to corvettes to Ferrari 550's, all cars have them, because they work. Most aren't very defined though, but then they don't need to be.


I find wings to be useless for almost all street cars. Especially on front wheel drivers. The last thing you want is downforce on the rear, unless you commensurately increase the downforce on the front. And you wont need that extra downforce on your average honda. It will just cost money, increase noise, increase air resistance (slower), etc....

texan
12-06-2002, 07:56 PM
Originally posted by Chris
A true definition is hard to come by, as most people us the terms when they shouldn't.

Good post BTW, not that many people know about Coanda (ever see the Cobra Daytona Coanda rearend?). But regarding the above qoute, I'll qoute myself from much earlier in this post... "And to clarify the difference between a wing and a spoiler, a wing is any airfoil with airflow over two sides, a spoiler only has airflow over one."

Chris
12-06-2002, 08:31 PM
I alwayss get excited when the server works, and I can do something, so I didnt read the whole thread.
Thanks for the compliment, tho:)
And in a R&T recently, they had an article by one the head designers of the Cobra Daytona. He took most of his ideas from an obscure German guy of about 30-40 years earlier. No one his Cobra design would work, but it did.

And regarding surface area increasing drag; a good general rule, but almost never true. F1 cars have a very small cross-section (area if it were a rectangle), but they produce much much more drag than the largest SUV. THis increase downforce for due to way they are setup, but this is just an example.

If you take an aerodynamic course in University, you will learn that there is no definite formula to determine air resistance, it is done experimentally in wind tunnels (now, CFD is taking over, tho). Still, it is a very interesting area, which often involves a little bit of black magic.

integra818
12-08-2002, 02:06 AM
My dad spun out at 90 mph on a road course with his 91 crx because he didnt have a wing in the rear, he was taking a BIG turn, the back went out and he didnt countersteer fast enough, and he ended up in the dirt, the next race, we went equiped with a big alluminum wing, the thing helped alot, the rear was planted to the ground after putting that wing, it proved that wings on fwd cars really do help.

integra818
12-08-2002, 02:06 AM
My dad spun out at 90 mph on a road course with his 91 crx because he didnt have a wing in the rear, he was taking a BIG turn, the back went out and he didnt countersteer fast enough, and he ended up in the dirt, the next race, we went equiped with a big alluminum wing, the thing helped alot, the rear was planted to the ground after putting that wing, it proved that wings on fwd cars really do help.

fritz_269
12-11-2002, 07:13 PM
Originally posted by texan
Good post BTW, not that many people know about Coanda (ever see the Cobra Daytona Coanda rearend?).
http://www.autodrome-cannes.com/cobra_daytona.jpg

Sometimes things just work out cool. :)

integra818 -
Let me guess, your dad's car has stiffer springs and a sizeable rear sway bar. In a corner, rear downforce won't help a car that naturally understeers (almost every production car made today) - it will just enhance that tendency to plow. But a car specifically set up for racing will be close to neutral or mild oversteer, and a carefully designed wing certainly may help cornering speed.
:cool:

2cm
08-21-2003, 06:13 PM
Depends on the car, the wing, etc... but a good shot in the dark is around 80-90... and if you are taking a corner at this speed in a honda guess what? :flipa:


what would happen exactly? :eek7:
:sly:

goatnipples2002
10-15-2003, 09:25 PM
I plan on putting an H22a type S in my 95 civic 4dr dx.

From what I hear it will be front heavy so wouldn't a rear wing help balance out the weight at highway speeds.

Also I was gonna get a low spoiler on my trunk until I read that post.

after reading the forum I was wondering if a front roof spoiler help or a rear roof spoiler (the front one would look weird, probably).

texan
10-15-2003, 09:38 PM
You've got the dynamics backwards. The heavier the front end of your car becomes, the more it will tend to understeer. Adding aerodynamic downforce aids to the rear of the car will only worsen this condition because it increases rear end grip, something you already have more of than front end grip. You most definitely don't need to add any type of downforce at the rear of a Civic with an H22 in the nose, what you need is to figure out how to get the front end to bite.

goatnipples2002
10-16-2003, 10:39 AM
I don't know what exactly understeer is? Is it when you turn the steering wheel and it doesn't turn as much as it should? I have a front sway bar and I hear that's what causes understeering.


Braces and bars won't help keep my car on the ground when I get my h22a?

What do most people do to fix understeer?

Oh yeah (unrelated)
Since honda engines are hi rev'n would it hurt to put my car in 3rd at about 50-60 mph? I put it in 4th alot to get some get up and go. When that's not enough I drop it in 3rd. With my AEM cai and greddy exhaust it doesn't sound bad at all. Is this bad?

Buzz1167
10-16-2003, 03:02 PM
Understeer is what happens in about all cars that are fwd, do this, try a u turn and floor it while you turn. The front end will stop turning even though the steering wheel is cranked, that becuase you lost grip on the front end: mostly becuase there is alot of mass to move, and most of it is the engine, the tires just cant do it. Really, the way you "fix" understeer is a big problem, you have to get the front end as light as possible (you really want everything as light as possible if your racing, but thats beyond the point), and you need the car stiff as possible, structure-wise. With some decent tires and new suspention it will get better, but I doubt if it will go away unless you really got modifying like what integra818's dad did, whitch was modify a car to be a real racer, not a ricer.

Anyway, wings wont help the most of us unless its in the front (whitch I have yet to see). What you really want to do is change the center of mass, you want it as low as posible, and in the middle of the car. But since its got a horridly off center CG (as in most front wheel drive cars) its gonna take some work. This is also the reason that mid engine cars like the Toyota mr2 can be made into track racers, becuase they are already well balanced front to back, about 55-65 or something, so little has to be done. But look up the balance for a civic (if you can find it) and I bet its more like 70-30 or worse. Moving 20% of the engine to the back is a hard feat.

Buzz1167
Jon N

wutitbelikewodey
02-02-2004, 01:14 PM
Oh yeah (unrelated)
Since honda engines are hi rev'n would it hurt to put my car in 3rd at about 50-60 mph? I put it in 4th alot to get some get up and go. When that's not enough I drop it in 3rd. With my AEM cai and greddy exhaust it doesn't sound bad at all. Is this bad?

I'm not completley sure, but I have a 99 prelude that I just bought, and I downshift to 3rd at about that speed all the time, and it should pull pretty well.

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