Aerodynamics, anyone?

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Nigel
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Aerodynamics, anyone?

Post by Nigel » Fri Jun 11, 2004 10:00 pm

Serious question for the engineer/pilot/aerodynamicists out there. Rear deck spoilers, wings, air foils, whatever you want to call them, have been on cars for years. Because of the import tuner/Fast and the Furious crowd, the bigger spoilers/wings are even more popular. My question is this: For a street car, what's the real effect of these wings? I see many different styles, some with endplates, some without. (for street cars) are they really that important? I know for race cars they are, since I watch Champ Cars, and they're needed to keep the cars on the ground. And for race cars, as well as planes, I know the principles involved. But I'm talking about a grocery getter car, your normal every day Honda. Are they really effective at aerodynamics? Or are they on the car because they just look cool?

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Post by Goshawk » Sun Jun 13, 2004 6:50 pm

Boy, I'd sure like to know this, too. I'm currently driving a Ford Focus, a Grocery-Getter Car if there ever was one, and I feel a little silly tooling around town to Kroger and Wal-Mart and the mall at 35 mph with my rad-lookin' spoiler on the back. I've often wondered whether it actually does any good, or whether it's just to make Hubby feel like he got something special for his money.

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Post by Nigel » Sun Jun 13, 2004 7:17 pm

I did see a discussion on about this topic at I think Snopes. But there were several different opinions as to whether spoilers on street cars made a difference. It's not just do they make a difference in airflow (I'm certain they do), but why so many different styles? There are short spoilers with ends that bend toward the ground, and one piece spoilers, and of course the high wings. I'll bet there's someone on here engineer enough to know. May take a while though. If this thread falls, I'll bump it until get an answer. Dammit.

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Post by Abdul Alhazred » Sun Jun 13, 2004 11:20 pm

Goshawk wrote:Boy, I'd sure like to know this, too. I'm currently driving a Ford Focus, a Grocery-Getter Car if there ever was one, and I feel a little silly tooling around town to Kroger and Wal-Mart and the mall at 35 mph with my rad-lookin' spoiler on the back. I've often wondered whether it actually does any good, or whether it's just to make Hubby feel like he got something special for his money.
I'm not an engineer or a pilot, but I know cars.

On your Focus the spoiler is just for pretty, like the
decorative phoney spare tire on a Lincoln, or the tail
fins of the 1950s.
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Post by Bearguin » Mon Jun 14, 2004 2:16 pm

For hogher speed cars (like F1 stuff) the wings produce downforce to keep the rear tires on the road.

On my wife's Malibu, it looks better (in Her opinion) then without the spoiler and she has an easier time backing up using the spoiler as a reference.

Rice rockets are somewhere in between. I really think it is more image than usefullness.

I'm going to bolt a 2x4 on the back of my truck for a true redneck spoiler.

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Post by MRC_Hans » Mon Jun 14, 2004 2:26 pm

Abdul Alhazred wrote:
Goshawk wrote:Boy, I'd sure like to know this, too. I'm currently driving a Ford Focus, a Grocery-Getter Car if there ever was one, and I feel a little silly tooling around town to Kroger and Wal-Mart and the mall at 35 mph with my rad-lookin' spoiler on the back. I've often wondered whether it actually does any good, or whether it's just to make Hubby feel like he got something special for his money.
I'm not an engineer or a pilot, but I know cars.

On your Focus the spoiler is just for pretty, like the
decorative phoney spare tire on a Lincoln, or the tail
fins of the 1950s.
First of all, spoilers on street cars have no meaning holding the car down, like on a race car. They are too small for that, and the speeds at which such a small spoiler could give any useful negative lift, would be above the capabilities of the ordinary family car (not to mention the law). Also, the shapes are usually inefficient.

Some sports cars (Porche 911 comes to mind) feature huge spoilers that might have some effect at high speeds.

Some of the standard spoiler arrangements you see have some purpose for improving aerodynamics. For low air resistance, it is important that the rear edge of the car has a clear cut, to let off the slipstream with as little turbulence as possible. Especially small edge-like spoilers on the rear-end of the cabin roof have some effect here.

Most spoilers are purely ornamental, however. Especially those placed on the boot of saloon cars. If you can see your spoiler through your rear window, it will be down in the turbulent lee of the roof of the car and entirely worthless, aerodynamically.

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Post by Agammamon » Mon Jun 14, 2004 5:09 pm

My car has a spoiler built into the design which is fairly small and unobtrusive (realy just a slight upturning of the back end of the trunk [boot for those non-American speakers] and the Boxster has a spoiler that only comes out in the 70+ MPH regime - basically illegal speeds throughout most of the US.
If these cars (which are designed from the get go to go fast) don't use spoilers at low speeds then I would be willing to bet that a four-banger won't make much use of the off-track (even if it does have a huge exhaust pipe).
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Post by Nigel » Mon Jun 14, 2004 5:19 pm

MRC_Hans wrote:
Abdul Alhazred wrote:
Goshawk wrote:Boy, I'd sure like to know this, too. I'm currently driving a Ford Focus, a Grocery-Getter Car if there ever was one, and I feel a little silly tooling around town to Kroger and Wal-Mart and the mall at 35 mph with my rad-lookin' spoiler on the back. I've often wondered whether it actually does any good, or whether it's just to make Hubby feel like he got something special for his money.
I'm not an engineer or a pilot, but I know cars.

On your Focus the spoiler is just for pretty, like the
decorative phoney spare tire on a Lincoln, or the tail
fins of the 1950s.
First of all, spoilers on street cars have no meaning holding the car down, like on a race car. They are too small for that, and the speeds at which such a small spoiler could give any useful negative lift, would be above the capabilities of the ordinary family car (not to mention the law). Also, the shapes are usually inefficient.

Some sports cars (Porche 911 comes to mind) feature huge spoilers that might have some effect at high speeds.

Some of the standard spoiler arrangements you see have some purpose for improving aerodynamics. For low air resistance, it is important that the rear edge of the car has a clear cut, to let off the slipstream with as little turbulence as possible. Especially small edge-like spoilers on the rear-end of the cabin roof have some effect here.

Most spoilers are purely ornamental, however. Especially those placed on the boot of saloon cars. If you can see your spoiler through your rear window, it will be down in the turbulent lee of the roof of the car and entirely worthless, aerodynamically.

Hans
Thanks Hans. That pretty well confirms what I thought. I'd known the effect on racecars (most open wheel racecars have enough downforce to stick to the roof of a tunnel at 100 mph, and sustain 4 lateral Gs). That, of course, is function. For street cars, your average family car, it's image. Which sells, of course.

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Post by exarch » Wed Jun 16, 2004 1:50 pm

Nigel wrote:I'd known the effect on racecars (most open wheel racecars have enough downforce to stick to the roof of a tunnel at 100 mph, and sustain 4 lateral Gs). That, of course, is function.
Hey, someone should actually try that one :D
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Post by Kilted_Canuck » Wed Jun 16, 2004 8:50 pm

Yeah, our ford focus has one, and with most new model cars the size of the spoiler would not make any difference anyway. The spoiler is on the rear, yet almost all new cars are FRONT wheel drive.*





*I saw some highschooler from across the city driving a new-model Saturn, with a 7 inch long, 3 foot wide racing type spoiler on his trunk. He wasn't pleased when we pointed out that no matter what size the spoiler, it wouldn't matter unless you were driving a RWD car anyway.

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Post by Sorgoth » Wed Jun 16, 2004 9:00 pm

Kilted_Canuck wrote:Yeah, our ford focus has one, and with most new model cars the size of the spoiler would not make any difference anyway. The spoiler is on the rear, yet almost all new cars are FRONT wheel drive.*



*I saw some highschooler from across the city driving a new-model Saturn, with a 7 inch long, 3 foot wide racing type spoiler on his trunk. He wasn't pleased when we pointed out that no matter what size the spoiler, it wouldn't matter unless you were driving a RWD car anyway.
Uh...could you explain this? Why would it make a difference?

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Post by jr » Wed Jun 16, 2004 9:19 pm

I think the Kilted Canucks reasoning would be that generating downforce over the driven wheels would be more advantagous than generating it over non-driven wheels.
I would say that getting a front/rear balance regardless of the driven wheels would be more advantagous. But I agree that sticking a big spoiler will do nothing to help your handling. If anything it will just add drag.

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Post by Nigel » Thu Jun 17, 2004 1:44 am

exarch wrote:
Nigel wrote:I'd known the effect on racecars (most open wheel racecars have enough downforce to stick to the roof of a tunnel at 100 mph, and sustain 4 lateral Gs). That, of course, is function.
Hey, someone should actually try that one :D
You might talk to Chip Ganassi, Michael Andretti, or Roger Penske, all team owners in the IRL. Their cars go flying often enough. (Racing joke)

Seriously, it can cost an open wheel team somewhere in the neighborhood of $6million per season per car to race for something like Champ Cars, and in F1, Ferrari is rumoured to spend as much as $500 million per season on their 2 car team. So it'd be pretty unlikely to convince someone to part with their car for the demonstration. Though ChampCars (CART then) did show they have better acceleration than an F-18 on the ground.
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Post by Nigel » Thu Jun 17, 2004 2:38 am

Right. On race cars, the wings act as upside down airplane wings, keeping the cars glued onto the track. Obviously a big advantage when you're driving a missile at close to 240 mph. My question was do they act the same way on your regular passenger car, and if so, why do they vary in design so much? Just this morning, I saw 2 cars on the interstate - 2 different wing styles. One was connected only on the ends, so it looked like a stretched out upsidedown U. The other had three supports, one on each end, and one in the middle. The tips were not touching the car, though, while on the other, they were connected by the tips. Which, if either, would be advantageous, and why?

I think the answer we've come up with is neither - on a street car, they're for looks, and don't do much functionally, because in a street car, you don't really go fast enough to make it worth it. Plus, and no one else has brought this up, but what about all the other drag components of the car? You have a tremendous amount of weight, relative to a race car (Champ Cars weigh about 1500 pounds, give or take, F1 cars some 200-400 pounds less). Exterior antennae must have some sort of drag effect, plus are the wheels designed for aerodynamics, what about driving with the windows open or closed? That has an effect, I'm sure. The bottom line is a street car is designed for the street - a race car is purpose-built, and as such, wings play a pivotal role. Wings on street cars make people feel like their part of the racing community - an old race slogan - "Win on Sunday, sell on Monday."

Wings on street cars are fake.
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Post by Abdul Alhazred » Thu Jun 17, 2004 2:51 am

Nigel wrote: Wings on street cars are fake.
Fake is the wrong word. They are decorations that owe
something to something that was once functional.

The spare tire shape on a Lincoln's trunk and the curly things
behind the back window on a Cadillac Brougham are of the
same order.

I saw a VW Beetle (new variety) today that had a "spoiler".
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Post by exarch » Thu Jun 17, 2004 10:37 am

Nigel wrote:Wings on street cars are fake.
Well, their purpose as downforce providing apendages is fake, although the car will look faster. They may still serve a real "spoiler" function, reducing turbulence at the side and rear of the car, and as such reduce the drag by controlling the airflow.

But driving with the window open, or hanging a ribbon on your antenna will probably cause more drag than the spoiler can solve. Even little details like trimmings and door edges cause lots of airflow disturbance ...
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Post by MRC_Hans » Thu Jun 17, 2004 10:44 am

exarch wrote:
Nigel wrote:Wings on street cars are fake.
Well, their purpose as downforce providing apendages is fake, although the car will look faster. They may still serve a real "spoiler" function, reducing turbulence at the side and rear of the car, and as such reduce the drag by controlling the airflow.

But driving with the window open, or hanging a ribbon on your antenna will probably cause more drag than the spoiler can solve. Even little details like trimmings and door edges cause lots of airflow disturbance ...
I think spoilers are an effect of the al-pevading functionalism during the second half of the 20th century. If you look at artefacts from the 19th century and before, they are often ornamented. Those ornaments were pure ornaments with only periferal reference to shape and function of the artefact.

During the 20th century the functionalistic style became all-pervading, and generally still is, so when we want to add ornaments, we will disguise them as functional details. So we add ornamental spoilers to cars, instead of gargoyles or something like that.

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Post by exarch » Thu Jun 17, 2004 2:02 pm

MRC_Hans wrote:... instead of gargoyles or something like that.
Shhh! You'll give some crazy Americans ideas :|
Like cars covered in bells, or bottlecaps, or grass :shock:
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Post by Loon » Fri Jun 18, 2004 4:48 am

MRC_Hans wrote:So we add ornamental spoilers to cars, instead of gargoyles or something like that.
I sooooo want gargoyles on my car.
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