What does a spoiler do?

A little trivia, the Mitsubishi 3000 GT VR-4 is also one of the only
cars on the plant where the active aero completely changes the balance
of the car, but not the drag factor/CD.

 

(Bryan Canter) wrote in

Yes, for looks. I, for one, think the Accord ass-end looks pretty boring
without one.

 

Yes, I agree it is just for looks on the Accord. However, with race cars
and various other cars such as some Porch cars--they do have a purpose.
The air flowing over the spoiler presses the back wheels more firmly on
pavement. This effect only works when the car is going at a high rate of
speed such as over 90 miles per hour. On most cars such as Accord--the
spoiler is just for looks.

 

On most production cars you get reduction of lift. It does not necessarily
press down. There's a subtle difference.

 

In '95 I was car shopping and went to Honda for the first time. The
salesman was not very accomodating. Actually, a bit rude. I was
looking at a Civic in the showroom, but the price was more than other
cars I was looking at. I asked him why the car was so pricey, and with
a big grin on his face he said, "The spoiler!" I told him, "Well, that
spoiled the deal," and we left.

I ended up with a Subaru Impreza at the time, which I still have. Good car.

This time, however, when I went to Honda, it was quite a different
story. I don't know if corporate Honda moved in and cleaned house, but
these people were much different, very professional. I'm very happy
with my '04 Civic so far.

 

Glad you like it. I'm hoping that the first salesman you mentioned was
just joking. He should have said something about the quality of Honda
Civics compared to most other cars. I agree with Mickey--he is right--I
should have said--reduction of lift. However, the reduction of lift does
have the indirect effect of pressing down the rear portion of the car when
the vehicle is running at a high rate of speed.

 

The spoilers on Indy 5000 race cars provide 3 times the car's weight in
downforce at 200 miles per hour. So... if they wanted to, the drive
could drive upside down in a tunnel, and the downforce would make the
car "stick" to the top . Also, about front wheel drive cars, usually
they're fitted with Front spoilers, which also exist, but are less
common and noticable. I also think its funny that people put on huge
spoilers when they drag race, when accually, considering that they
don't usually have curves in drag racing, and the added air resistance
of the spoiler accually makes the car go slower....... but...... it
makes the car LOOK faster...... gay rice burners.

 

Tell that to John Force, et al.

If gay rice burners go 340 mph in under 5 seconds, I want a gay rice burner!

 

nope, not an actual wind tunnel. White smoke is used, and thus is a flat
colour. For that reason, silver tends NOT to be used as a test object
colour. Oh, and there would be no 'mood lighting' either. We can't see the
smoke if its not lit. finally, little hint - look at the radio antenna - its
not even bent. The curves are suggestive of aprox 80mph, judging by lamina
flow, and an antenna would be bent by it.

 

I did post a reply to this a good week and a bit ago, but here goes again.

All WRC class A cars are 4 wheel drive. have been since the mid-80s. The
wings you see on the focus (and the escort before it) are also standard
items on the production cosworth versions. (those are the fastest production
cars ford makes iirc) Be it the Sierra, Escort, or Focus (European versions,
of course, Americans have to make do with hugely underpowered versions, or
the ugly and slow Mustang)

Rally cars also tend to have the spoilers for slight drag, and
counterbalance purposes. Colin McRae's exit from the 2002 austrailian rally
makes this reason lain. (if you didn't know, he took one of the jumps a bit
too fast (maybe 80-90) spent too much time in the air, and the nose dropped
too far, meaning he smashed the intercoolers.

Rallying is an imprecise art. Cars have had large wings on them for attempts
at beter grip since at least the mid-70s, as I can still remember the large
wing on the back of my fathers class N Ford Maxi. Everything is about grip,
because there is so little available.

 

I don't know why this myth pervades that at 100mph, a spoiler *suddenly*
starts to work. at 50mph the effect is pretty noticable. A good number of
porches have had speed sensitive aerodynamics. Indeed, I recall reading one
case where a polieman stated in court that he knew the defendant was
speeding, as the rear spoiler was deployed, inicated he was over 50mph.

Then, there was also the case of the Audi TT's. You do remember this, don't
you? If not, I'll recap quickly. when it was released, all was well and
good, for about a month. Then the occasional bizare accident would start
cropping up, where the driver would lose control in a moeratly fast curve.
Anyway, a general recall was put on all of the cars. Audi went, and did some
tests, and found that above 40-ish mph, the car became unstable
aerodynamically. a few more tests, and they developed a solution. That
solution was to add a spoiler onto the back. now, I dobut many of you would
recognise it as one, but that strip on the boot/trunk, about 60 inches long,
by HALF an INCH high, is the spoiler. it correctly redeflects air so as to
curb the control problem.

A similar problem was also found by owners of Lamboghini Miura (sp?) but
worse. Every time the car went over 70-80, the shape of the car meant that
enough lift was generated that the wheels would be lifted off. I believe the
fastest speed ever set in a stock miura is somethign like 120mph. Compare
that to its "on paper" max speed of 150ish

Aerodynamics is a tricky thing, almost more of an art, than a science.

 

I did not say it *suddenly* starts to work. What I meant was that the
effects of it become noticeable at 100mph+.

Well, there you go. If a car needed a spoiler, it would have been installed
at the factory. Most car makers do enough testing to see whether the car is
aerodinamically stable without one. Chances are, that aftermarket spoiler
you buy may cause more damage than good because some of those manufacturers
have mainly looks in mind when designing these accessories.

Happy Holidays!

Cheers,

Pete

 

My porches have plenty of downforce without spoilers. Not even a
hurricane could move my house. ;-)

 

GOOD FOR WIGGERS !

 

I need more grips myself! Tire! Tires! Tires! But the price for tires is
an exponential curve but the frictional gain is incremental. I was
thinking of racing with the Falken Azenis next year but decided to stick
with the Kumho Victoracers.

Anyway... I didn't realize those are all AWD's now.

The examples I brought up was merely to show that FWD vehicles benefit from
rear spoiler since someone had mentioned that many vehicles with rear
spoilers are FWD cars.

Other examples of FWD vehicles that have big rear spoilers are the Realtime
Integra/RSX Type R's, the Mazda Protege, and Sentra SE-R are all winning
vehicles in the SCCA touring car challenge.

As for my EVO - lovely car! With 320 HP at tapped - it's a clutch burning
fun! I have not messed with the upside down airfoil in the rear end but the
angle of attack adjustability is a nice thing if I ever race it someday.

For those who have studied aerodynamic you'll recognize this formula:

L=1/2pV^2SCl

L=lift
p=density
S=surface area
Cl=Coefficient of lift

Noticed that velocity is squared. Yes you'll get expotentially more lift at
100 MPH than 50 MPH but as long as you have airflow going through the
airfoil you will get lift. It has been 8 years since I was last in an
aerodynamic class so please don't quiz me on it. Notice that if you have
more surface area, you get more lift. This is why you see those AM SCCA
cars with double or triple decker spoilers that is sometime bigger than the
vehicles, it must work because they sure produce really fast time around the
track.

HAPPY NEW YEAR EVERYONE!!

 

|The examples I brought up was merely to show that FWD vehicles benefit from
|rear spoiler since someone had mentioned that many vehicles with rear
|spoilers are FWD cars.

The reason they benefit is because those spoilers are meant to "spoil" the lift
that the body shape creates at speed. They are more stable at speed with a
spoiler. Thats why Audi had to retrofit all the original TTs with an automatic
spoiler, they were found to be unstable at high speeds. Has nothing to do with
traction in that application.

|more surface area, you get more lift. This is why you see those AM SCCA
|cars with double or triple decker spoilers that is sometime bigger than the
|vehicles

They have to be that big because of the speed at which a typical Solo II is
conducted. Even an A-mod on a very open "Nationals" type course will rarely get
over 80 mph, which is about where a typical wing becomes effective.

As an interesting aside, I used to tow a Formula Coninental on an open trailer.
I noted that it sure towed hard for an 1100-lb car on a relatively lightweight
trailer. Then one day I got about 2 miles from the house and decided to stop and
take off the rear wing. What a difference! It was like I had been driving with
the emergency brake on. Made the trip to the track a lot more pleasant after
that. for all the downforce the make, they also produce a lot of drag.
Nothing's free.
Rex in Fort Worth

 

For those who have studied aerodynamic you'll recognize this formula:

Ah, but don't forget - the coefficient of drag also increases as a square of
velocity - so the faster you go, the more drag that wing is creating. The
more lift created by that wing, the slower your top speed.

 

Ah, but don't forget - the coefficient of drag also increases as a square of

Nope. The COEFFICIENT of drag is independent of speed. The actual DRAG
is what increases with the square of velocity.

 

Ah...yes Drag....There is a trade off between lift and drag but the drag
created by the airfoil is a small fraction of the total drag; in fact the
induced drag created by the airfoil decreases as you increase in speed (most
people don't know this, it doesn't sound intuitive but it's true). During
my naval flight school days we spent a big chunk of our time studying this
subject. The two drags that add up to the total drag on any vehicle (car or
airplane) are the parasite drag and induced drag. Parasite drag comprises
form drag, friction drag, and interference drag.

The induced drag is the drag associated with producing lift on the airfoil.
At high speeds, most of the power will be used to overcome the parasite
drag, not induced drag created by the airfoil. In fact, induced drag
"varies inversely with velocity, and directly with angle of attack". As you
speed up, the drag created by the airfoil decreases. The parasite drag on
the other hand is definitely increased at the rate of 1/2 of velocity
squared with the other items constant. That formula is so similar to the
kinetic formula.

Dt = Di+d
The formula for induced drag is: Di=(KL^2)/(pV^2b^2)
K=constant
p=air density
V=velocity
b=wing span

Parasite Drag formula:
Dp = 1/2 pV^2f
p=air density
V=velocity
f=equivalent parasite area

So... what you are saying below is true for the parasite drag, the drag
created by i.e. the surface of the vehicle itself. The drag associated with
producing the lift (or in a car's case, down force since the airfoil is
turned upside down) goes down as speed increase.

The T-34 I trained on has a stall speed of 63 knots with power at idle and
a low 41 knots with max power. It has been a long time but I believe I
would pull the nose up at about 70-80 knots... at that speed there was
enough lift created on the wings to lift off a 4000 airplane. Of course we
have a huge surface area so we didn't need a lot of speed to create so much
lift. The surface area was in the vicinity of 175 sq ft.

On my EVO, I estimate that it has 4-5 square ft of surface area on the
airfoil. This is an imprecise interpolation but at the same angle of
attack, my rear wing should produce approximately 115 pounds of down force
at about 75 mph. Is 115 pounds significant? Depending on what you're doing
I guess.

I'm guilty of this too but the term rear spoiler and rear wing is used very
loosely to mean the same thing but in an aerodynamic term, they're
completely different. I contend that most vehicles on the road don't
produce lift at high speed just based on my understanding of aerodynamic and
the shape of most vehicle on the road. As long as you have faster airflow
under the car than the top the vehicle should be producing down force.

Some have mentioned that if the vehicle needed a rear spoiler, it would come
with it. Not always true. Many manufacturer add spoilers only on their
higher trim models or as an option. My EVO is not unstable without the rear
wing, it's also not a standard part but a $750 option. I used to have an
E36 M3 and deeply admired the lightweight version, on that version, it came
with a big rear wing kit:

http://www.bmwworld.com/models/m3_ltw.htm

Sure you trade off some top speed, you now have 153 mph instead of 156 mph
but the benefit of saving time around the corner because you now can corner
a few MPH faster due to the increase traction caused by the down force, it's
a winner.

Some contend that having a rear wing is only beneficial on AWD or RWD car.
I don't agree with that. If you can get more down force, you can get higher
cornering speed. Most FWD cars tend to oversteer from the factory. I
autocross my civic and do quite well but I wish I can get some more down
force back on the rear end. Just 20 pounds of force down there makes a huge
difference. I have tried racing without my spare tire but now always race
with my spare tires back there to help control the oversteer on top of
having about 5 psi lower pressure to get more traction. I am not a
professional racer but I know enough about cars and airplanes to know that
having some force back there makes a difference. BTW: I did took our
region's championship in HS class.

Yes most people don't race. Yes most people have their big rear wing for
looks only. Yes they will lose a few mph on their top speed. Saying that
there's other added benefit for having a rear wing on a FWD car, or if it
didn't come with one from the manufacturer it doesn't need one, is not
always true.

That's my position on this subject.

 

<large post snipped>

Wow. What a clear, consise, and precise post. Well done if only more people
(such as "bill B. Johnson") could be equally more consise and thorough in
their posts.