I was sitting in my office watching planes land while we were receiving a heavy snow fall in Toronto, so I got bored and decided to write something educational. I hope you enjoy
I would just like to make a few comments about the aerodynamic improvements that a rear spoiler on a car makes. I am a pilot finishing my degree in Aeronautical science and have studied aerodynamics a bit. I own and love my 88GT and have always wondered what would happen if I added wings and a turbo-jet engine to the fiero. Hint Hint.
The way the wind and air pressure affects a car is the same as an airplane, just to a lesser degree. I have read several articles on several different sites and there seems to be a mis-conception about the benefits of a spoiler.
Unless you are doing 200 MPH there are very minimal advantages to having a rear spoiler on a car. Why do you think the wing on a 911 Carrera doesn’t come out until you hit high speeds and even then there are minimal differences. The biggest advantage to a wing is Looks. Now I do agree that spoilers can make a big improvement in the looks of most cars, but by putting your wing on 15 inch stands on the back of your car may look cool to some, it in fact can be more of a performance loser than anything. At that height the stability of the wing is very low and you just increased the amount of drag that your car creates. As the car goes faster the wing can start to shutter and vibrate and affect the streaming of the airflow.
The actual design of the spoiler on an 88 GT is a pretty good job. If you take a side view look of the spoiler, you will notice that it has the shape of an upside down airfoil or airplane wing. But, for it too work it would need a fast, clean airflow over the wing. The design of the fiero wing would create a down force on the back of the car and help add traction. Since there is not a clean airflow over the wing due to the top cab of the car and you aren’t doing 200 MPH, well some of you might, there is no real benefit.
One of the best ways to improve the streaming of your car is to flush mount everything. Do you ever see an airplane with little things sticking out? No, this creates parasitic drag and unnecessary performance loss. Clean airflow reduces drag and increases performance. Newton’s third law, for every action there is an equal and opposite reaction. Reduce drag, increase thrust or power.
You can gain more performance by keeping your car clean than by putting on a carbon fiber, double layer, 15-inch spoiler.
Know each to their own on what type of wing they want to install on their car. Everybody has different tastes. I just don’t want people to install a wing for the wrong reason. Wings can make a big improvement in the looks of a car and I think it is great when people come up with new designs, but remember it is there only for looks.
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09:40 PM
PFF
System Bot
Bradbitz11 Member
Posts: 1826 From: Kawkawlin, MI Registered: Dec 2002
This religious argument recurs from time to time. Usually, neither side persuades the other.
Basically, I'm with you: on most -- if not all -- street cars, an airfoil is entirely decorative. However, I think a spoiler is a different animal.
As I understand it, an airfoil -- a "wing" -- requires smooth, relatively high-speed airflow, and it produces lift only over the surface of the wing. Most wings on street cars are too small to produce much lift, and they operate in relatively slow-moving, turbulent air.
On the other hand, a spoiler -- an "air dam" -- operates by obstructing airflow to produce a zone of high pressure in front of the spoiler and/or low pressure behind the spoiler. A front spoiler obstructs airflow under the car, producing a low-pressure zone behind the spoiler, beneath the front bodywork. A rear spoiler obstructs flow over the deck lid, producing a high-pressure zone over the rear bodywork in advance of the spoiler. In both cases, a spoiler reduces aerodynamic lift on the car's body (at some cost in drag.) Key points here are:
> A spoiler does not need "clean" airflow; some turbulence is OK, as long as air flows in a consistent direction.
> A spoiler produces a zone of pressure differential that acts on a relatively large area of the car's bodywork, not only on the spoiler itself; therefore a spoiler can be effective at slower speeds.
Of course, I can't back-up these assertions with formal aerodynamic theory or real data; however, seat-of-the-pants instrumentation tells me that spoilers can work. My ex-wife's Capri had an industrial-strength front air dam. It made quite a difference . . . until I drove it through a deep puddle. It also made a damn fine water brake!
Couldn't resist the opportunity to pontificate.
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11:23 PM
Smoooooth GT Member
Posts: 8823 From: Lake Palestine, Texas Registered: Jun 2001
I was sitting in my office watching planes land while we were receiving a heavy snow fall in Toronto.
Sound's like fun to me!! Relaxing and the same time confused with all that white stuff falling like rain... ( <--ME)
quote
Originally posted by pilot: Do you ever see an airplane with little things sticking out? No, this creates parasitic drag and unnecessary performance loss.
Great... I'm screwed then!! I just hope that I can get it going down the road....
Great explaining it for some people that does'nt understand the aero-effect on car's and wing's-spoiler's!!
Smooth!!
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SmoothFieroGT@Yahoo.com Have you RATED me today?? 3.4DOHC SWAP in near future
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11:41 PM
Jan 11th, 2003
ws6fiero Member
Posts: 168 From: Montgomery, AL Registered: Oct 2002
You're right the "argument" does come up pretty regular, this time however I got off my lazy butt & got out the books ... if you will turn to page 71 of Gary Witzenburg's Fiero book you'll see that it is worth 250# down force @ 144 mph (top speed of the 2.7 sd Pace Car). The "Indy" body also knocked the cd down to 0.35 (from 0.41 - on pg70). :-)
With my Formula at lower speeds (up to 40 or so at least though) the air is flowing forward between the spoiler and trunk then looping around the front of the spoiler and back over the top. How do I know this? By looking in my rear view mirror when it's 10 below and there's a huge cloud of steam coming out of the exhaust.
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12:40 AM
hellfish87gt Member
Posts: 616 From: winnipeg manitoba canada Registered: Jan 2002
Quite a few people fail to realize it's what they can't see, that makes all the difference, related to the rear spoiler on the Fiero. The main purpose for it's design is not directly related to air flow coming off the frontal body. What it was design for was to minimize/eliminate backwash air from coming up the back of the vehicle, pushing forward over the decklid, and coming up to disturb (resistance) the air flow stream coming over the roof. Eliminating this turbulance over the back decklid contributes significantly to more streamlined airflow over the back half of the vehicle as a secondary design purpose. The combined result is a slightly lower CD and some controlled downforce (as the turbulance isn't buffeting the tail-end of the vehicle).
They don't develope the good spoilers in wind tunnels for no good reason at all. The factory wing (as most call it) and the one on my car were both developed in GM's Wind Tunnel for reasons stated above. The one on my car was very effective in bringing the Pontiac Fiero into the winners circle on campaigned race cars. Just putting my 2 cents in, if you don't believe it, do some more research, and yes it is affective on street cars.
If I remember right, the Fiero wing actually just helps clean up the airflow behind the car a little bit.. doesn't add any downforce but reduces drag a little bit.
I think the best aerodynamic upgrade would be a lip at the rear of the roof, to help get rid of the turbulance behind the window.
And a spoiler and a wing are different.. Spoilers are used on Nascars, fully attached to the bodywork. A wing is seperate from the body. at least I think that explanation makes sense
Ya, this does come up every once in a while. There all for looks period on a steet car. If you 'think' you feel a handling improvement, its all in your mind. They really have no effect under at least 150 mph. Besides looking sporty, about the only other benefit is maybe helping to keep your tail lites clean. Ever notice your car runs better after you wash it too?
The spoiler doesn't really add downforce, like some people think it does. But that's not to say it doesn't do anything. I'll try to make some diagrams tomorrow showing the airflow over a notchback, and some possibilities as to why the spoiler helps. Basically, it's there to reduce turbulence and drag coming off the rear end of the car, helping you get a few mph top speed, and somewhat better gas mileage on the highway (marginal). There probably would never be a noticable handling difference with or without the spoiler.
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03:11 AM
California Kid Member
Posts: 9541 From: Metro Detroit Area, Michigan Registered: Jul 2001
Ya, this does come up every once in a while. There all for looks period on a steet car. If you 'think' you feel a handling improvement, its all in your mind. They really have no effect under at least 150 mph. Besides looking sporty, about the only other benefit is maybe helping to keep your tail lites clean. Ever notice your car runs better after you wash it too?
Awe come on Roger, I'll bet you a beer you're wrong!
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11:09 AM
Poncho Jim Member
Posts: 869 From: Woodlands, MB, Canada Registered: Mar 2000
With my Formula at lower speeds (up to 40 or so at least though) the air is flowing forward between the spoiler and trunk then looping around the front of the spoiler and back over the top. How do I know this? By looking in my rear view mirror when it's 10 below and there's a huge cloud of steam coming out of the exhaust.
Yes.. I've seen the same thing with my spoiler at 70 Km/h or 45 Mph.. The steam from the exhaust gets sucked under the spoiler and flows over the rear hatch towards the back window. It's kind of interesting to watch
The vertical rear window causes a low pressure area to form behind it as the air flows over the roof and has to drop down to the rear deck. Notice that's where the engine vents are.. The low pressure area is supposed to suck air out of the engine bay. It also pulls air from the back of the car forward.
As far as downforce, there has to be some angle to the wing for it to work.. (Angle of attack in aviation terms).
If the wing were tilted up like this ( / ) then there would be some measure of rear downforce.. Our wings just sit flat like this ( - ) I doubt there is enough wing shape to do much to provide downforce.
Oh yea.. They do add about 10 pounds of downforce all the time... Cuz that's about what they weigh
------------------ 1988 Fiero Coupe 2.5L 1990 Trans Am GTA 5.7L
[This message has been edited by Poncho Jim (edited 01-11-2003).]
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12:31 PM
Smoooooth GT Member
Posts: 8823 From: Lake Palestine, Texas Registered: Jun 2001
By looking in my rear view mirror when it's 10 below and there's a huge cloud of steam coming out of the exhaust.
What the helll are you doing out of your house in those kind's of tempeture's..??? The house would have to be on fire for me to leave to go ANYWHERE in that kind of weather... Then again, I was raised in Houston and we only have 3 season's there... Spring(Feb-June)Summer(July-Sept) and Fall from October to January....
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SmoothFieroGT@Yahoo.com Have you RATED me today?? 3.4DOHC SWAP in near future
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01:12 PM
ws6fiero Member
Posts: 168 From: Montgomery, AL Registered: Oct 2002
I don't have any hard data, but I can give you some of my "in the field" observations regarding the Fiero wing spoiler and aerodynamics. I'll compare my 1987 SE with some aerodynamic mods to my wingless 1986 coupe.
First of all, the 1986 coupe. This car has no rear spoiler. In order to increase front downforce, I replaced the front fascia with a Formula fascia and a deeper front air dam. A few days during the winter, it will get cold enough for the exhaust to look like steam. On those days, I observe the curious "backwash" effect that's been mentioned above.
Now, the 1987 SE. This car is an aero notchback with rear spoiler. I removed the plates underneath the engine compartment gratings and boosted the spoiler so it's 7" off the decklid. Once, the engine was leaking oil onto the exhaust pipe. The oil smoke rose up through the deck vents and went straight back across the deck. No backwash effect and very little turbulence. When it's cold outside, the steamy-looking exhaust doesn't "backwash" across the decklid, either. This car also kicks up mist high enough to splatter the windshields of tractor-trailers when the road is wet (at speeds of roughly 65-70MPH). And since every action has an equal and opposite reaction, the higher rooster-tail of mist points towards increased downforce.
Whether or not the increased downforce is enough to make a difference in handling is another story entirely. I don't know for sure, because I don't drive over 70MPH much. It seems to me that both of my cars handle equally well at 70MPH. Although the upgraded suspension in the '86 coupe may be making up for the difference in downforce.
Hopefully, somebody found that interesting.
Pilot: Also, keep in mind that aerodynamics as applied to automobiles and aerodynamics as applied to aircraft are two completely different animals. The basic concepts are the same, but the applications are very different. Automobiles rely almost completely on ground-effect aerodynamics, whereas aircraft only utilize it for take-offs and landings.
[This message has been edited by Blacktree (edited 01-11-2003).]
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05:51 PM
pilot Member
Posts: 82 From: Ontario, Canada Registered: May 2002
1- My town just got hit with a major snow storm. When I walked out of the house the snow was above my knee (14 inches in one night) and I could not see my fiero.I wish I had a digital. So yes I did stay in my house.
2- The swirling effect that a few people mentioned is called a vortice. All objects that are hit with a relative airflow produce this swirling effect. It also produces induced drag and this is bad. Yes, the wing is there to help break up the turbulence and reduce the drag. Do you remember that tragic accident in New Jersey that downed that aircraft into a neighbourhood? A Boeing 747 took off approx. 2 miles ahead of it and the accident was blamed on the vortices of the 747's wings ripping of the vertical stabilizer of the fallen plane. If you look at a 747-400 or Airbus 330, 340 you will see something at the end of the wing called winglets. Very similar to a wing. There to break up the vortices and reduce induced drag. They look kind of like this \______Wing___________. Same effect as you see at the back of the fiero with the smoke or steam or snow. These vortices increase the amount of induced drag and rob the performance of the fiero. But, the faster you travel through the relative airflow, the more the induced drag is reduced. Hence there is more effect of the rear wing when you travel at high speeds. I used 200 MPH as a reference. There could be an advantage at 140 MPH but probably not too much lower than that. Again, depends on the body style of the car.
3- When comparing different types of fieros you have to remember that they all have different body styles and small differences. These differences change the way the car is affected by relative airflow, so every car will react differently to high speeds. Some cars will flow better than others. In a car low pressure is better than high pressure. Low pressure keeps the car from rising. This is opposite of an aircraft wing. I do believe that the wing of the fiero was tested in a wind tunnel and that is why it looks like it is mounted upside down compared to an aircraft wing.
4- A front spoiler or wing will work a lot better than a rear wing due to the fact that there is more of a clean airflow than a rear wing. Remember the Lamborghini with the front spoiler. The main thing that is stopping the rear wing from being an advantage is the cab of the car (No clean relative airflow) and yes the angle of attack of the wing does make a difference. You should notice that a chop top would be better at lower speeds than a regular fiero. More of the clean airflow will come in contact with the wing. I believe if you increased the height of the wing by two or three inches on a chop top, you will notice a big improvement at high speeds.
I am going to go and try to find my car now.
Pilot
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08:12 PM
PFF
System Bot
Jan 12th, 2003
Poncho Jim Member
Posts: 869 From: Woodlands, MB, Canada Registered: Mar 2000
Poncho Jim That's part of the cd drop as far as angle of attack it is 1 1/8 over 11 1/2 inches
Wow, that's the first time I've seen that article on the Pace car. Very interesting. Thanks for posting it.. Actual printed articles are much better than raw speculation.
I'm still a -little- skeptical.. 250 Lbs of downforce.. That sure would be hard on our little plastic hatches.. Of course most of us can only dream of 140 so there isn't much to worry about
Where did the article come from ?
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07:04 AM
MrPBody Member
Posts: 1787 From: Decatur, GA, USA Registered: Oct 2000
I'll believe it when I see data. I don't mean a reporter's third-hand rehash of a GM press release, but hard numeric data from a series of aerodynamic tests, showing significant increase in downforce or decrease in drag resulting only from addition of a stock wing.
Relaxing and the same time confused with all that white stuff falling like rain... ( 
<--ME) 
Great... I'm screwed then!! I just hope that I can get it going down the road....
