Do Car Spoilers Prevent Vehicles from Taking Flight?

mark1 · Jan 5, 2004

firstly, i am not an enginneer or a physicist, so if i write something foolish, have that in mind.

i have heard that the reason why some cars have spoilers is to counter the upward lift that the air gives to the underbody of the car as it accelerates forward. this stabilizes the car at high speeds. i have three questions about this.

#1: is this correct, and if not, what is the correct explanation?

#2: if the above explanation is correct, will a normal car that needs a spoiler take flight at high speeds if it doesn't have one? (since this is how a plane works, i think, by producing more upward lift on the underbody of the wing than lift on top of the wing)

#3: if a spoiler is installed, assuming that it is installed correctly, does it in any way decrease the acceleration or speed of a car?

DarkAnt · Jan 5, 2004

All this stuff could be terribly wrong so don't quote me.

I believe the reason spoilers exist on everyday cars is just for style. You (should never) go fast enough to even have the spoiler take effect.

1. Correct

2. The car will not "take flight" but it will lose some traction and thus control.

3. Because the spoiler creates some drag it will slow down a car, but not significantly.

Again... don't quote me

NateTG · Jan 5, 2004

Spoilers are put onto cars for three reasons -
1. For looks
2. To provide downforce
3. To reduce drag

If a car 'needs' a spoiler, then removing the spoiler will limit the high speed cornering and acceleration ability of the car.

What a spoiler does depends on the type of spoiler and the speed of a car.

enigma · Jan 6, 2004

The "crane hooks" that people put on their civics do absolutely nothing, except look stupid.

Spoilers are used in race cars to provide downforce to the rear wheels, increasing traction at high speeds. Note that only works for rear wheel drive cars.

Civics, etc. are not rear wheel drive.

wimms · Jan 6, 2004

NateTG was in error on the drag part. Spoilers ADD drag, thus also increase fuel consumption. For typical streetcar usage, that's the only effect they have.

In racing, there is always compromise between downforce and drag (think of F1) that slows car down.

Enigma, I believe they work okay for fwd cars aswell. Critical event is hard deceleration, when rear end becomes awfully light and prone to loose traction. At high speed, rear spoilers add stability during braking, no matter what drive scheme. This could draw a line between stopping quickly and finding oneself in the weeds.

Many cars are very "nose-heavy" and their normal weight balance already makes rear end relatively unstable. To a degree, spoilers could help with that issue.

NateTG · Jan 6, 2004

Originally posted by wimms
NateTG was in error on the drag part. Spoilers ADD drag, thus also increase fuel consumption. For typical streetcar usage, that's the only effect they have.

Technically, F1 cars have wings, not spoilers.

A correctly designed spoiler reduces drag. A primary mechanism for drag is to shed vortices. Spoilers can prevent the formation of, or reduce the size of these vortices. At freeway speeds, a spoiler can improve the fuel efficiency of cars by more than 1%. However, if you spend $300 on the spoiler, then you'd have to spend $30,000 on gasoline -- that corresponds to about 600,000 miles in passenger cars -- in order to make it economically viable.

A popular example of a spoiler is the ridges on aerodynamic helmets worn by bycicle racer.

In racing, there is always compromise between downforce and drag (think of F1) that slows car down.

This is also incorrect. There are methods of producing downforce that do not require any drag at all, but they're illegal in car racing.

In 1970 or so Jim Hall built the Chapparal 2J which used snowmobile motors for downforce instead of wings. The increase in drag was minimal, and the car was promptly banned.

russ_watters · Jan 6, 2004

Originally posted by NateTG
A correctly designed spoiler reduces drag. A primary mechanism for drag is to shed vortices. Spoilers can prevent the formation of, or reduce the size of these vortices.

A popular example of a spoiler is the ridges on aerodynamic helmets worn by bycicle racer.

The ridges you put on helmets are vortex generators (or possibly fences or other flow control devices), not spoilers. You are right about what they do though. To elaborate, various flow control devices essentially act to keep the air where you want it - keep it attached to the proper surface. Vortex generators create small vortices on the top of a wing, making the flow turbulent (instead of laminar) in a controlled fashion, increasing stall angle of attack and (somewhat counterintuitively) keeping the flow attached to the wing. Keeping the flow better attached also reduces drag (which would be the purpose on a helmet).

A spoiler, as the name implies, spoils lift. On a wing, this massively increases drag, on a street car, it only increases drag by a little (since cars aren't that aerodynamic to begin with).

The distinction between a spoiler and a wing though (as you implied) is that a spoiler acts to reduce the lift of the car and a wing creates its own lift (downward) separate from what the car body is doing. NASCAR stock cars have spoilers, Indy cars have wings.

This is also incorrect. There are methods of producing downforce that do not require any drag at all, but they're illegal in car racing.

Ground effects for example. Not illegal, but there are specific restrictions on it. In any case, a wing specifically will always produce a combination of lift and drag and a spolier will always increase drag.

And one clarification for mark1, the vast majority of lift on a wing is generated by the top surface of the wing, not the bottom. In the caption for http://www.desktopaero.com/appliedaero/airfoils1/airfoilpressures.html it says this particular wing has slightly positive overall pressure (producing lift), but some can have an overall negative pressure (sucking the wing down).

If the underbody of a car is flat, it will produce no suction or lift, but because of the small space between the underbody and the ground, there is almost always some kind of ground effect going on.

one_raven · Jan 14, 2004

https://www.physicsforums.com/showthread.php?s=&threadid=12205

Clausius2 · Jan 24, 2004

Hi folks!

I think spoiles on cars have the mission of providing more friction force between wheels and road. Then, the traction torque is less limited by adherence.

About drag and lifting:
i) I don't believe of a usual car fligthing above our heads without a spoiler (except it was a ferrari one). The lift force at 100 km/h is negligible.

ii) The drag coefficient could be increased by installing a spoiler,
but i think it depends on the height and in fact, on structure of the flow near of the spoiler. This is a very particular feature of the layout.
Anyway, it is sure that anybody who puts a spoiler on his car is thinking about the boundary layer flow, but about picking up some girls with his new toy (except in F1).

Ah! Congratulations to E.S.A. (European Space Agency), Where was the N.A.S.A when was published in all europe Mars water photos? Ja,Ja,Ja!

garagegraphyx · Jan 24, 2004

spoiler dilemma...

From where i come from, spoilers are just part of the cool design of a car... The mechanics here do not calculate the aerodynamics of spoilers. Personally i think that for the normal car-user, spoilers arent really necessary (unless you want the style which comes from using one).

The main purpose of spoilers are to reduce the drag...and unless you're prepared to invest a lot of money to make sure the spoiler really works for your car, it is not really worth the buzz and hassle. Its a totally different story for a street racer though.

However, through my own personal observations, street racers rarely put any emphasis on the aerodynamics of the spoilers but instead put a lot of energy into modifying and enhancing the engine's performance...

Are you planning on installing a spoiler yourself mark?

Andy · Jan 25, 2004

Most high performance sports cars don't have spoilers, how often do you see a ferrari with a spoiler, working for mercedes i know that none of the fast mercedes have spoilers, the SL55 AMG doesnt. But the Design of these cars provides downforce anyway because they are wedge shaped. The new Porsche carrera 4 (i think) has a spoiler that automatically raise from the boot when the car reaches a certain speed.

Have u ever seen an F1 car loose one if its wings as its going down a fast straight? The drivers are very very lucky if they can avoid smashing into a barrier, the reason F1 cars have Wings is because they are so light and powerful, the power to weight ratio is huge.

Does anybody follow the Le mans 24 hour race? I have seen one of those cars flip all the way over as it was hurtling down the long straight (cant remember what its called) at speeds in excess of 200mph, and i believe that was due to a fault with the Aerodynamics of the car, think it was the front scoopdown spoiler, air got underneath and lifted it up, very nasty.

garagegraphyx · Jan 30, 2004

high performance cars in Malaysia do...

Well,in Malaysia, there are plenty of high performance sports cars. In which i mean those which are modified and not those which are the 'original' sports car...

I'll give you a few examples...the Nissan Skyline is one such car.
I went to a drag race held at an old airport strip here last year...These cars came in bunches and it was so beautifully modified!

all of them had one similarity...all had spoilers and bodykits...
obviously, they went for the style...

so i can only say them as i see them...

as for the 'original' high performance cars, who would bring a grand prix vehicle or an F1 car for a ride in the city? so once again, spoilers aren't necessary for the normal street car...but if you're thinking of joining a drag race once in a while, or bring a car into the circuit, then install one...

Porsches and Ferraris don't come with one cos they know you don't need them unless you're a serious racer. Like porsches, if you are a serious racer, then the spoilers come into action...
if not.. then, it just stays in place..

mark1 · Jan 30, 2004

Are you planning on installing a spoiler yourself mark?

nope, I am just curious about their affect

Does anybody follow the Le mans 24 hour race? I have seen one of those cars flip all the way over as it was hurtling down the long straight (cant remember what its called) at speeds in excess of 200mph, and i believe that was due to a fault with the Aerodynamics of the car, think it was the front scoopdown spoiler, air got underneath and lifted it up, very nasty.

i don't follow le manz, but i saw a clip of that on sportscenter. it was a mercedes. it was probably the scariest racing crash i ever saw.

thanks to all who replied to my questions.

russ_watters · Jan 30, 2004

Originally posted by Andy
Does anybody follow the Le mans 24 hour race? I have seen one of those cars flip all the way over as it was hurtling down the long straight (cant remember what its called) at speeds in excess of 200mph, and i believe that was due to a fault with the Aerodynamics of the car, think it was the front scoopdown spoiler, air got underneath and lifted it up, very nasty.

A similar flaw existed in NASCAR cars until a few years ago - if the car turned sideways or backwards, aerodynamic forces would push air under it, making it fly. Now if the car's attitude gets upset at all, spoiler panels pop up on the roof to keep it on the ground.

Stingray · Feb 2, 2004

First of all, nearly every street car generates lift, not downforce. There are cars which will become dangerously unstable before top speed is reached, although most modern cars undergo extensive testing to avoid this. That means less lift, not actual downforce (except in the case of the Ferrari 360).

It becomes an issue if (1) you want to race, (2) have a beefed up engine, or (3) like classic cars that had more power than they could safely deal with .

Spoilers are a simple method for reducing lift, although adding them randomly can make things worse. Aerodynamics is not a very intuitive field. A properly designed spoiler (not a wing) can decrease drag, but it will increase it if its designed more for all out downforce. Its all the engineer's choice. A wing almost always generates a lot of drag though, but it will also generate a lot more downforce.

Ferraris and such don't have big wings on them because they're ugly. End of story. You will find subtle spoilers though. Exotic car companies spend ridiculous sums of money to improve the aerodynamics of their cars while still keeping a clean look. If they didn't care what things looked like, cars with real downforce would be common. Racing versions of those cars always have wings if the rules allow it.

As a side note, 911's often have much larger spoilers than other cars because their basic shape is aerodynamically very poor. The car sells well, so Porsche keeps it around. They have to add the big spoilers as a band-aid.

Wrench · Apr 15, 2004

Yeah, sorry to dig up an old topic, but I figured that this is the best place to put this litle idea. I forget which issue of Racecar Engineering (Im not even sure if that is actualy the title); there was an editorial from someone who proposed that all aerodynamic downforce (i.e. spoilers and wings) should be banned.

I know that even your common Joe on the street would think that such a statement would be madness. "Duuh don't spoilers make the car go faster?"

However he did state an interesting scenario to illustrate his point. In a race, if the car is going near the speed in which the spoilers downforce would take effect, there is a change in tire grip. We all know that it is to be a positive effect on the traction. That very effect is what spoilers are for. However, if a racecar goes into a turn, the vehicle starts to slow down. This starts to limit the effects of the spoiler. The person in the editorial stated that when the downforce disapears, there can be a critical loss in traction. In a race where a drivers life is dependant on the traction that is available to him/her, at times the slightest change can be the diffrence between controll, or crash.

So, my querry is this; do you think that the person is exagerating? Or do you think that he raises a valid point?

I personaly am not that sure. I think that it would depend on other variables, and balances in the design of the car. Also, a drivers job is to know his car. A driver, idealy should know the mannerisms of the vehicle that they drive. On the other hand, if the total downforce effect is unreliable enough, or just plain unnecisary, then that should be considered as well.

I am no where in the league of the proffesionals. However I would like to know the opinions of those who post here. What do you all think?

Cliff_J · Apr 16, 2004

While the downforce will drop significantly with a drop in speed, the job of the racecar driver is to know and understand their car. Only an extreme event (like happened to Aryton Senna in 1994 when a suspension link broke) would put the driver in a situation where they would have a sudden drop in traction that could be critical.

Leaving racing aside, why does the new Enzo Ferrari have no wing on a car designed to go 200MPH+? Because the underbody of the car is the downforce generator and it generates enough downforce that it is actively controlled to roll back the downforce generated at high-speeds so the car can be setup with a softer more street-worthy suspension and avoid some of the drag penalty at those high speeds. So if you do away with wings and spoilers, how do you regulate the underbody of a car?

As Smokey Yunick used to say, "...it ain't cheating if you don't ge caught..." and that is why there are some many rules to control the level of competition. If you compare just Indy/CART/F1 for open wheel racing, the Indy/CART camp have desiginated manufacturers and the teams buy from them, and in Formula 1 you have all the manufacturers complying with rules regarding dimensions and equipment. In both, assuming you ignore Ferrari's recent domination in F1, the racing ends up quite closely matched even though very different approaches have been used to make the competitive field near equal.

For real downforce, look at F1's history with fans used to create active downforce, and the exclusive McLaren F1 road car used this same technology during its short production run. Those wouldn't drop off with speed. :) But lack of ability to regulate and to reduce costs through reduced complexity such devices were banned along with active suspension and other electronic gadgets.

Besides that sounds like an editorial from a NASCAR fan who is bitter from the late 60's competition called the Aero-Wars between the Torino Talladega/Cyclone Spoiler and the Superbird/Charger Daytona and the safety issues that arose. Most of those issues had to due with the increase in speed and inability of the tires to support such speeds, not with shifting downforce levels causing lack of control.

While we're at it, why don't we ban the flaps on the roof of the current crop of NASCAR cars. You know, the ones that lift up to spoil the lift when a car is going sideways? If we're going to ban all devices, we might as well take out the ones for safety too so we can see spectacular flips and crashes.

IMHO anyways.

Cliff

kurious · Apr 16, 2004

Downforce could also be created on cars by having a curved tube whose intake is
horizontal relative to the ground but with an exhaust end that points skywards.
As a car turns on a bend in the road it would open a flap which allows air to rush into the tube and shoot up vertically.The reaction to this movement of air would push the car harder onto the road surface.Would make a hell of a noise though!

Wrench · Apr 17, 2004

Just in case anyone wanted to know, the article was in "Racecar Engineering" magazine. It was November '03 Volume 13, No. 11. Its a U.K. Magazine and I got it in Barnes & Noble.

www.racecar-engineering.com

The article in question is called "Drag act" and the author is Paul Van Valkenburgh. Ironicaly enough Cliff J, this guy was one of the people that exploited aerodynamic downforce back in the 60s. However like I stated before, he proposes that the life of a driver is based on the predictability of traction. He also says that in a superspeedway situation, drafting (following the car in front of you so that you gain acceleration from their car blocking the wind) can be dangerous because the rear downforce is affected. Most drivers avoid this trick on "Gentlemen's agreement" and avoid doing so. I have to work on some math homework, and Ill go over anything I left out later on. But once again, he brings up an interesting idea.

Cliff_J · Apr 19, 2004

Yeah I did a little more research into this as well, mostly NASCAR stuff with the 'pack' effect and how to split up the field for spectators and safety.

I follow F1 and CART mostly, only sometimes the old-school <80's NASCAR or them on a road course (I like to see drivers drive, not run circles) so my current knowledge of their issues is a bit rusty.

Anyways, I think their lack of updated safety regarding track design, car design, and safety testing has put them in a more delicate situation than aerodynamics. How many 18-19 year old kids died of basilar skull fracture before Earnhardt without any safety updates that would have ironically saved his life?

And their aerodynamic problem isn't so much a speed differential, its the giant 3000lb race car messing up the air. How much lead time is given to each aircraft for takeoff at a runway based on tonage (a bunch as dictated by the FAA) and yet wasn't it 2-3 years ago that an Airbus plane went down on Long Island after the tail broke off and the initial likely culprit was turbulence from the preceding plane?

Personally I think they should change it to be a stock car race again if they want it competitive. Cars that would look like a real street car like the Speed Channel challenge with factory sheet metal over a full cage and not 45 Ford Taruses with only stickers to tell you what brand of car it is suppossed to be. Earnhardt Jr out there with a FWD V6 and 7 inch wide tires isn't going to be able to go too fast to be unsafe! IMO anyways. :)

Cliff

hitssquad · Apr 20, 2004

The hydraulically actuated rear wing of the Enzo Ferrari

Cliff_J said:

Leaving racing aside, why does the new Enzo Ferrari have no wing on a car designed to go 200MPH+?

http://www.roadandtrack.com/article.asp?section_id=3&article_id=627&page_number=2&preview= improve airflow, there is a pair of countersunk air channels that start just aft of the radiator outlet up front, wrap smoothly around the greenhouse and then gently open up again toward the back. This ensures that undisturbed air can be directed to help clean up the turbulent flow aft of the greenhouse, and also to make the small, low-mounted rear wing work effectively.

http://www.roadandtrack.com/article.asp?section_id=3&article_id=627&page_number=3&preview= 37 mph and 159 mph, the rear wing will extend fully, and the 1-foot-wide flaps hidden underneath the two split radiators up front stow flush with the car's underside. As speed increases, the wing will retract gradually as the front flaps are deployed. This ensures as little change as possible to the ride height and handling stability. Ferrari tells us that at 124 mph, the Enzo can generate 758 lb. of downforce. The aerodynamic load tops out at 1709 lb. at 185 mph, then decreases to 1290 lb. for less drag so the car can reach its maximum estimated speed of 218 mph.

Cliff_J · Apr 20, 2004

Its still not a visible wing like the F40 had out back. :-)

Cliff

ken · May 25, 2004

Hi

By spoiler, I assume you mean the inverted wing placed across the back of a street car. So how effective are they?

L = 1/2 p V^2 S Cl

where L = Lift, what we want to find
p = density of air 1.225 Kg/M^2
V = velocity say 28 m/s (around 100kmph or 60mph)
S = Plan surface area say 1.8m^2 (around 1.2m by .15m or 4 foot by 6 inches)
Cl = lift coefficient say 1.5 which is a good high value for this size and speed

L = .5*1.225*28^2*1.8*1.5

1296 Newtons or around 132Kg force if the wing is well designed an aligned in the airstream and I think I have been generous with the size of the thing.
Placement of these things is very important, most are low over the back of the car
behind the cab where airspeed is reduced. Note that aerodynamic forces are roughly proportional the the square of the airspeed. That means at 1/2 the speed, you get 1/4 of the force.

You could take the extra drag of the wing to be around .05 to .1 of the lift.

Integral · May 26, 2004

I have a "spolier wing" on the back of my '94 Probe. The way I drive the only purpose I can see for it is to serve as a convient handle to open the hatch. I have also used it to wrap a bungee cord around when hauling lumber.

ken · May 26, 2004

OOPS

The area above should have been 0.18m^2 not 1.8.
I thought the above was way too much. Just goes to show I can't do 2 things at once.
Think and type.

Answer is max load at 100kmph is 128.6N or 13Kg force.
Given the usual placement of these things, I think your right. They are more useful as a handle to open the boot.

Regards,
Ken

enigma · May 26, 2004

ken said:

Given the usual placement of these things, I think your right. They are more useful as a handle to open the boot.

Especially on a front wheel drive car.

Cliff_J · May 26, 2004

Shhhhh, there's lot of guys in the last few years with wings on the back of their FWD cars...

I thought 132Kg sounded really high for 60MPH but I'm too lazy to do the math...lol I wonder how much 'clean' airflow is available anyways. One time in a rental car with a 'wing' on the trunk (when I didn't latch it properly) the lid actually lifted up a little bit going down the road but closed at stops!

Cliff

krab · Jun 4, 2004

ken said:

S = Plan surface area say 1.8m^2 (around 1.2m by .15m or 4 foot by 6 inches)

There's the error: It's actually 0.18m^2. So the lift is 13kg or 30 pounds force. Sounds right to me. Consider: the amount of power needed to go a steady 60mph in a typical car is 20hp. So the total drag force is (P/v=) 125 pounds.

Sorry Ken: I see you already corrected it.

DM · Jun 20, 2004

i have heard that the reason why some cars have spoilers is to counter the upward lift that the air gives to the underbody of the car as it accelerates forward. this stabilizes the car at high speeds.

That's right. Cars reaching extreme speeds can actually take off from the ground. Spoilers spoil lift and drag but mostly lift, that's why planes use spoilers when landing.

#2: if the above explanation is correct, will a normal car that needs a spoiler take flight at high speeds if it doesn't have one? (since this is how a plane works, i think, by producing more upward lift on the underbody of the wing than lift on top of the wing)

Yes. Besides spoilers reducing lift, they also reduce speed immensely.

#3: if a spoiler is installed, assuming that it is installed correctly, does it in any way decrease the acceleration or speed of a car?

There's a major cut down in acceleration.

In addition and even though cars exceed speeds and end up lifting from the ground, a nasty crash would occur as I presume you understand. There are no wings installed on the car and even if they were, a crash would still occur.

Lift on a car very much depends on its weight. Light cars reaching top end speeds would lift and actually roll in the air.

ken · Jun 23, 2004

Re: the post about removing wings etc from race cars.

If the wings are effectively able to load the car to sufficient traction for a corner, that
corner can be taken at any speed you like. Sounds crazy but read on.

Aerodynamic forces are proportional to to velocity squared (V^2).
See L = 1/2 p v^2 S Cl

That means that at 1/2 the speed, you get 1/4 of the load.
That applies more to lift than to drag because coefficients change a little with reynolds number an Cdf in more prone to this than Cl.

Now if we look at centrpetal force: Fc = M * V^2 / R
We see that centrapetal force is also proportional to V^2.

So if the wing is large enough that the reaction vector of lift and centrapetal force,
ignoring the weight of the car resolve so as not to exceed the tires grip, the car will not slide at any speed. The weight of the car being a traction bonus.

Roll can be countered by an aerodynamic aleron effect.

This would require large wings so there is a drag issue. If the wings angle of attack (AOA) was driven by tilt vectors (pendulum), then the wing AOA could be set for min drag in a straight but inclined near Cl max in a hard corner. Now you might say that
you still have a large wing producing nothing but drag in the straight but this drag is
very small because drag is comprised of 3 basic types( form drag, induced drag and parasitic drag) in the straight you would have only form and parasitic drag but no induced drag because induced drag is proportional to Cl^2 and the AOA of the wing would be set to Cl = 0. In a hard corner, the AOA would be increased to something like CL = 1.5 and induced drag would be by far and I mean really far the major drag component the othe 2 being insignificant by comparison. If you still think the straight line drag too high, there are variable geometry options as well like sweep and telescopic wings which are a functional reality in some applications.

Of course all this ignores rules and rules place limits on the engineering.
The above is only intended to demonstrate the relative importance of
some of the forces involved.

Regards,
Ken

Proko · Aug 29, 2004

According to the Bernoulli's Effect "The pressure in a fluid decreases with increased velocity of the fluid. (The faster the liquid moves, the lesser is the pressure in that liquid.)"
So the air must travel faster across the top of the car, decreasing the pressure, causing the car to have more lift from the less dense air. there is no kind of new upward pressure toward the bottom of the car.
Yes there is upward pressure on the bottom of the car, but it does not increase.

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