What effect would it have on the lift / downforce if I smoothed off the underneath of the car with a sheet of aluminium from the front to the rear.
Would it help the flow of air under the car or would it cause it to lift. I have a front vent in the hood of the car to increase downforce if this helps.

I wouldn't do under the engine cradle... Fiero's tend to have a suction above the decklid at speeds. That suction sucks air through the decklid vents and out of the engine compartment. You still need to get air in from somewhere to have that ventalation working.

I've been thinking about this myself. I hope to one day do a frame up custom Fiero, and if I do I'd like to smooth the bottom. Trouble is I don't know if it would actually be a good idea...

Doubtfull, a plane flies in part because it takes longer for air to go over the top, creating lower pressure above the wing and thus lift. If my memory is correct at this time of night. A smmoth bottom would make the car lift more is my guess. The shape of the piece could influence the result though.

Brian

That's why I've been wondering. Would the reduced drag underneath be worth it for the increased lift?

I would think a smooth bottom would speed up the airflow under the bottom of the car because of the reduced turbulence, thus reducing lift and helping literally suck the car onto the ground, like a F1 car. Obviously any effects would be felt at high speeds only but I think you could benefit from better mileage and possibly incresed airflow to the engine bay.

Just speculating, but I know car companys do attempt to reduce turbulence under the car.

smooth is not always the thing you want to reduce drag. since you may not be able to be absolutely flat, then you can create more problems than you solve. slight valleys and hills can create dangerous lift forces that can unstabilize the car at normal speeds. Rounded stipling has shown to create less drag than a solid surface which may not be flat.there is actually not tha much under a fiero to drag air, I feel there is little to gain with that, and possibly much to lose. smothing the bottom in theory would LIFT the car not draw it to the ground, note aircraft wings are in basic form, flat on the bottom and rounded at the top, which creates lift. s550w had it right.

you may likely get a better effect from a better (true) airdam in the front of the car, more like the chin on the aero nose with a leading rubber skirt dropping to within 2-3" of the road. This will lower the pressure under the car, force more air thru the radiator, and wheels for brake cooling. it will also pull the car down to the road at higher speeds.
done with care, you can actually feel the car drop when you hit the effective speed. unfortunately it is typically 90 mph or higher, but it is noticable.
if you;re looking to reduce drag to increase mpg, then there are other areas that will offer you more. lose the wing, remove the antenna, flush mount the front signal lights. sheath the wiper blades to move air over them. change the sideview mirrors. keep the wheels behind the fender/wheel skirts. those are all the easy to fix big hits. you can do more, but then you;re talking about body modifications. The car is pretty good sitting stock tho, I don;t think you will gain alot back.

[This message has been edited by tjm4fun (edited 04-22-2006).]

quote tjm4fun said: (smoothing) the bottom in theory would LIFT the car not draw it to the ground, note aircraft wings are in basic form, flat on the bottom and rounded at the top, which creates lift.

Purpose-built race cars have underbody pans for a reason... and it's not for lift.

You should read up on ground effect aerodynamics. When something moves along the ground, you don't have just 2 surfaces to worry about... you have 3. Bernoulli's Principle applies to the air flowing between the ground and the floorpan. That's how an air diffuser works!

quote tjm4fun also said: if you;re looking to reduce drag to increase mpg, then there are other areas that will offer you more. lose the wing...

The Fiero spoiler reduces drag. It's part of the reason why the fastback Fiero has a drag coefficient of 0.340, as opposed to 0.377 for the notchback.

I agree with most everything else, though.

[This message has been edited by Blacktree (edited 04-22-2006).]

quote Originally posted by Scurvy: I would think a smooth bottom would speed up the airflow under the bottom of the car because of the reduced turbulence, thus reducing lift and helping literally suck the car onto the ground, like a F1 car.

exactly.

Some nice points from both camps. From what I have read on the subject I believe that if done correctly you could improve the downforce on the car.
Keep the ideas and thoughts comming please.

quote You should read up on ground effect aerodynamics. When something moves along the ground, you don't have just 2 surfaces to worry about... you have 3. Bernoulli's Principle applies to the air flowing between the ground and the floorpan. That's how an air diffuser works!

The Bernoulli Principle site is relly neat - interactive too!
Some more food for thought...
-there are several people installing hood vents to increase cooling but this would seem to increase air flow over the top of the car, thereby lowing the local air pressure in the increased airspeed zone, and in turn increasing lift on the car by way of low pressure over the car? Yet these people by in large report decreased lift on their Fiero at high speed. Hmmmm?
-the Bernoulli Principle effect on the underside of the car would depend on the existance of sideskirts to limit lateral flow of air, and a smooth bottom with a particular shape resembling a convergant - divergant nozzle
-the center of force for any Bernoulli induced downforce would be desirable to be in the center of the car's footprint, or slightly forward of it to offset tne rear weight bias of the car. The low ground clearance required to achieve this would be quite impractical for a street car.....at least where I live!
-A smooth bottom under the engine bay would reduce or eliminate the updraft through the engine bay, but what about the possible indraft through sufficiently large side vents?
-A combination of all these factors would be interesting to model mathematically prior to any implementation to gauge the likely benefit, determine the practiblity of the reduced ground clearance required to achieve any desirable effect and the required speed to notice the effect.
Any takers for this task? Its been on my back burner task list for some time now!


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Daviero - 88 N* GT

[This message has been edited by Daviero (edited 04-29-2006).]

You're right about the sideskirts. They are crucial to ground-effect aerodynamics.

The hood vents, by and large, are pressure vents. When clipping along at 100MPH+, the amount of pressure that builds up under hood is enough to push up the headlight covers. And the area above the hood (about the first foot or so from the front edge) is a low-pressure zone. This pressure difference generates lift. The hood vent helps to equalize the pressure between those 2 areas... hence less lift.

[This message has been edited by Blacktree (edited 04-22-2006).]

quote Originally posted by Daviero: -there are several people installing hood vents to increase cooling but this would seem to increase air flow over the top of the car, thereby lowing the local air pressure in the increased airspeed zone, and in turn increasing lift on the car by way of low pressure over the car? Yet these people by in large report decreased lift on their Fiero at high speed. Hmmmm?

The "boat" shape of the front pan that redirects and compresses the air under the car to aid in engine ventilation generates 120 lbs of lift at 100 mph at sea level -- secondary car aerodynamics non-withstanding. Creating the hood vents aids a little in cooling, but by and large is completely unnecessary to to that end unless you sit in traffic a lot (the air gets trapped behind the radiator without speed). The main advantage is the vents allow the air to be redirected, reducing canard lift as well as the pressures under the car. This reduces the flow through the engine compartment, but is still more than sufficient. The airflow over the rear of the car in turn excerts more force on the "bubble" created by the spoiler, making it more effective and further increasing downforce.

I've long been curious about welding on some sheet metal to smoothen the bottom of the car, but haven't experimented with it yet. But the hood vents are a definite improvement. If I recall correctly, the '89 prototype/concept included a reverse cowl-induction vent similar to the trans-am but more centralized; but don't quote me on it. I still curse Corvette to this day for killing the Fiero line just as it was getting really cool.

Editted content. Nope, no scoop on the '89 prototype. Still a beautiful car though.

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LIFE IS MADE OF OBSTACLES AND CHALLENGES — TO OVERCOME THEM IS TO PROGRESS.

DRIFTING -- IT'S NOT THE FASTEST WAY AROUND A CORNER, BUT I'LL BE DAMNED IF IT'S NOT THE MOST EXCITING.

[This message has been edited by Delphince (edited 04-24-2006).]

The principle that make a Fiero less prone to lift in the front with an opening on the hood to let the air entering the front lower dam exit by the hood, is because the surface was in a climbing angle in the direction of the motion of the car that cause the air to build an high pressure zone and resulting in a force that help to push the front of the car on the ground....at the same time, the air under the front of the car have obligatory a lesser pressure....It work exacly like wing on an F1 or IRL formula car (with less drastic result) but it's the same principle.

The same principle apply to the underside of the car...look at the car (the Fiero) like a Formula 1 (or IRL car) wing when you look at it by the side. You can just angle it, by lowering the front suspension more than the rear, to make it work like a reverse airplane wing. The air will be more prone to built a high pressure on the front of the car, result of more air passing over the car and applying more weight on the front, and under the car, a lesser quantity of air will pass. As the air goes to the rear, it will have more and more space to fill, but if you add some side skirt, not enough air will be able enter the underside to fill this area, thus making a lower pressure zone...thus forcing the car to be suck to the ground. If the underside of the car is smoothed with the addition of a panel, the air will flow with less turbulence thus improving the airflow and creating less air retention, so more effective suction and downforce. The point of a smooth underside is to have a more laminar airflow that will improve the end result of extracting the air and creating a low pressure zone under the car.

It's very simple in the end.

[This message has been edited by perry rhodan (edited 04-22-2006).]

All aerodynamics aside.........Fieros get engine cooling air from the bottom and vent it out the two top vents. The vents are placed in a low pressure area behind the vertical rear window to draw bottom air up thru. Block that flow and your engine compartment will fry....especially things like Ignition modules, coils.........Dont do it. Its already hot enough in there without getting another 100* or so hotter.

If you let the air enter by large side air dam (a la Ferrari) that are open to the engine bay this will not give you any cooling problem I think. Since the zone between the rear window and the wing its a lower pressure zone that tend to suck the air that come from the underside of the car by the engine hood opening, like you said ,it will suck the air it need by the air dam (or scoop) on the side panel of the car. Maybe I'm wrong but I think I'm near the reality of this "air dynamics"


And this will not add air under the car, and maybe it will help to accelerate the air evacuation of the underside of the car (like when you use a tube and a compressed air gun to empty a container....or the principle of a venturi/jet in a carburetor body)

[This message has been edited by perry rhodan (edited 04-22-2006).]

It would make no difference where the air came in from, under like factory, or like you say adding large ducts or scoops to the sides. As long as you get a steady, full, air flow you have no problem. The only scoop that wouldnt allow that flow is a big scoop on the engine lid (hood) The scoop and the vents would be counter productive to each other and you would just end up with a lot of turbulence in the engine bay. Side or bottom inlet would both work fine.

Although this doesn't completely apply, I figured this might be useful at least in terms of aerodynamics of the car.

When I was quite a bit less mature, and my Fiero was in significantly better condition with 80 thousand less miles on it... I would frequently drive on toll road at speeds in excess of 120 miles an hour (probably more like 130). I would basically have the gas pedal floored and allow the car to achieve it's top speed. I would simply keep it floored and the car just wouldn't accelerate anymore (with at least 800rpms left on the tach before redline).

In any case, the Fiero felt MUCH more stable at 120 miles an hour than it did at 60 or 80 miles an hour. My guess is that the aerodynamics of the car created downforce and a suction was created under the car. I think that at least for the way this car was designed a belly pan might be counterproductive.

FYI, I was 18 or 19 years old at the time. I absolutely do not drive like that anymore...

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Todd,
2006 Pontiac Solstice
2004 Volkswagen Beetle Convertible (Wife's Car)
2002 Ford Crown Victoria LX
1987 Pontiac Fiero SE / V6 5-Speed
1987 Pontiac Fiero SE / V6 (3.2L) Auto
1984 Pontiac Fiero 2m4 SE
1981 Pontiac TransAm (Olds 455BB)
1973 Volkswagen Type-2 Transporter

Guys, I don't want to go off on a side issue which might constitute a thread-jack, but Bernoulli's Theorem does not play the major role in lift of an airfoil. It is the aggregate physical effect of of air molecules striking the underside of the wing at speed when the wing is presented at an angle to the direction of movement of the wing. This is what people have intuitively thought was the reason before they were mis-taught that stuff about Bernoulli's. Little molecules smacking the bottom of the wing - that's the major cause of lift.

quote Originally posted by rogergarrison: The only scoop that wouldnt allow that flow is a big scoop on the engine lid (hood) The scoop and the vents would be counter productive to each other and you would just end up with a lot of turbulence in the engine bay.

I hate seeing those kits. In the words of Carlos Mencia: DEE DEE-DEEEE!

Box-sealing the intake to one of those does work well as a ram-air intake, but few go through the extra effort.

quote Originally posted by Blacktree: The Fiero spoiler reduces drag. It's part of the reason why the fastback Fiero has a drag coefficient of 0.340, as opposed to 0.377 for the notchback. I agree with most everything else, though.

ok, that wikipedia quote and your suggestion of the effects of the bernoulli effect. first you are compressing the air that is forced under the car, which increases it's velocity relative to the air over the top of the car. this creates lift. read your link on airfoils. he is talking about a sheet of metal, not a computer designed airfoil to properly channel the airflow. the bournoulli effect is why cars float off the road at high speed.
If the object is to reduce under car drag, then some smoothing of hanging objects could help. Smooth panned racing cars have many other associated factors to assist them in working, the smooth pan without the airfoil systems would make the cars float more easily.
As I mentioned, an airdam will reduce the air volume entering the underside of the car. I did forget to mention side skirts, but they are not always necessary. One issue is loss of cooling to the engine compartment, but leaving off the sideskirts and proper airdam in the front will reduce the air pressure under the front 1/3 of the car, thus pulling the nose down slightly. more high speed stability. Air will still enter thru the sides to be drawn up thru the engine vents, which should not hurt the cooling. The angle of the car will also help there, eg dropping the high nose of the 88gt changes the air profile allowing less air under the car, and better tracking at speed. Having spent alot of time under the fiero lately,(drun NE salt/rust) there is not alot "hangin out " in the breeze under there. possible some light smoothing on a few brackets would help as much as a smooth pan.
REalize tho, the gains from even a full flat pan on a normal driven car at legal speeds will be negligble. I've driven cars with fully functional aero effects, and they don;t really start to come into play till 90+mph, and when they "grab" you feel it. Even installed a decent inplementation on a car I drove daily, and at 92mph consistnely, you would feel the car drop and lock in. a very unsettling feeling till you understand what just happened.

BTW, I'd love to see the link with the tunnel tests on the wing issue, last time I looked at it, all the cars tested showed either no effects from the wings, or most showed an increase on drag. I can;t recall reading if the fiero was tested in that group, it may have been post discontinuance of the car. Most pre 90's cars only had aero effects for show, they in reality hurt mor than helped! (not that I'd ever take my wing off, sometimes it is about looks! )

Is it possible to relocate the battery and put a functional scoop on the passenger side? I've never looked to see if it's possible but has anyone tried?

My Raptor with v8, had scoops similar to C4 corvette on both sides. Just cut panel out, still left battery there. Any additional air going in is good.

quote Originally posted by Blacktree: The Fiero spoiler reduces drag. It's part of the reason why the fastback Fiero has a drag coefficient of 0.340, as opposed to 0.377 for the notchback.

From The Enthusiasts Guide to the Pontiac Fiero:
84-85 cpe/sport cpe/se 0.377
85 gt 0.350
86 cpe/sport cpe 0.377
86-87 se 0.350
86-88 gt 0.365
87-88 cpe/sport cpe/formula 0.357

It didn't state with or without spoiler.

Here are a couple of interesting tests on a Fiero.

https://www.fiero.nl/forum/Archives/Archive-000002/HTML/20041015-1-041694.html

https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20060206-2-064636.html

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quote Originally posted by Gokart Mozart: From The Enthusiasts Guide to the Pontiac Fiero: 84-85 cpe/sport cpe/se 0.377 85 gt 0.350 86 cpe/sport cpe 0.377 86-87 se 0.350 86-88 gt 0.365 87-88 cpe/sport cpe/formula 0.357 It didn't state with or without spoiler.

Isn't memory a wonderful thing? I should've said 0.377 for the bumperpad notchie and 0.350 for the aero notchie. (source)

quote Originally posted by tjm4fun: ok, that wikipedia quote and your suggestion of the effects of the bernoulli effect...

So you're refuting a credible source (wikipedia) with no credible source of your own? Google something up. Then we can talk.

[This message has been edited by Blacktree (edited 04-23-2006).]

quote Originally posted by tjm4fun: ok, that wikipedia quote and your suggestion of the effects of the bernoulli effect. first you are compressing the air that is forced under the car, which increases it's velocity relative to the air over the top of the car. this creates lift. read your link on airfoils. he is talking about a sheet of metal, not a computer designed airfoil to properly channel the airflow. the bournoulli effect is why cars float off the road at high speed.

increased velocity creates lift?

Increased velocity underneath the car creates a LOW pressure area, which would cause the car to get "sucked" to the road.

The underside of a car is exactly like a convergent-divergent delaval nozzle. The convergent (high pressure) zone is from the nose of the car to the radiator air dam. From there to the back of the car is pretty much the throat. If you had a diffuser, it would allow the transition from low pressure to high pressure air at the back of the car, and would give you needed downforce.

All of this is assuming no rake.

Ryan you're absolutly right.

Also the benefit of an "extractor" at the back is that you will be able to keep the weigh balance ratio of the car, that will not be the case if you drop the front and jack the rear of the car to obtain the same kind of effect under the car like I mentionned earlier.

I wonder , if you install some kind of fan under each of the deck lid opening that extract the air from the engine bay (thus the underside of the car) and propel it outside ....if you manage to extract enough volume of air at any given speed, this will maybe help suck the car to the floor....side skirt will help greatly in this case I think and the air flow in the engine bay will be greater and thus taking away engine compartment cooling problem.

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My Chrome Yellow Fiero GT 86 1/2 ...for now

quote Originally posted by Blacktree: So you're refuting a credible source (wikipedia) with no credible source of your own? Google something up. Then we can talk.

I don't need to quote a source when you are applying a law out of it's context, like you are doing.
those links and the effects of the bournoulli principle are being quoted and taken completely out of context.
you are assuming the car is stationary, the ground is stationary and the air is forced under the car. BIG mistake.
in fact the ground is stationary, the air can be assumed to be stationary, and one surface is moving. those formula's and descriptions do not cover that scenario at all, in fact, not even close.
First off the airflow is not smooth and straight. the ground has texture. the underside has texture. the leading edge of the vehicle, no matter the car, compresses the air as it moves under it, creating turbulance. Now you have eddy forces. the pressure under the car increases as you drag the air under the car onto the stationary air in front of the car.
By your application of the theory, all cars would suck to the ground the faster they go. since this is not the case, your statements are already proven false.
finding a site, and quoting it;s facts as proof of a concept they had no relation to doesn't make it right. detemining proper design and effects of air movement requires complex equations and modeling, not a simple application of the laws of gases thru a tube.
Once you change one condition involved, the theorum and formula become inaccurate until corrected.
why do you think they use super computers to figure this stuff out?
According to you, they should drop that and apply a simply theory of gas thru a tube. nice. I'm sure the auto mfg's will be thrilled at the savings.
Oh, and wiki pedia is not the end all of reliable information, it may state formulas and facts, but they are built by contribution, not
exact definiton of a given situation, they are constantly be corrected and updated.
Mis-application of information is worse than no application at all.

[This message has been edited by tjm4fun (edited 04-23-2006).]

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Norm Vandermee

SCHWEEEEEEEEEEEET! Nice job there. I'd love to do that, but I'd remove it everytime I went up my driveway.

quote Originally posted by normsf:

Ive known several guys who put fans in the grills. It does keep the bay cooler in traffic, but actually restricts flow at higher speed according to their tests.

Interesting. Explain for me then how an airfoil (oh, let's say an NACA 23012) can produce a Cl of .1 at an angle of attack of 0°. If you look at the profile of a 23012 you'll see there is a lot more frontal area on the TOP of the airfoil for the air to "smack" than there is the bottom at a 0° AOA.

John Stricker

quote Originally posted by ICouldaBeenAV8: Guys, I don't want to go off on a side issue which might constitute a thread-jack, but Bernoulli's Theorem does not play the major role in lift of an airfoil. It is the aggregate physical effect of of air molecules striking the underside of the wing at speed when the wing is presented at an angle to the direction of movement of the wing. This is what people have intuitively thought was the reason before they were mis-taught that stuff about Bernoulli's. Little molecules smacking the bottom of the wing - that's the major cause of lift.

quote Originally posted by perry rhodan: I wonder , if you install some kind of fan under each of the deck lid opening that extract the air from the engine bay (thus the underside of the car) and propel it outside ....if you manage to extract enough volume of air at any given speed, this will maybe help suck the car to the floor....

I don't mean to be rude, but what?!

The only way you could significantly exceed the stock level of airflow at speed would be to install hovercraft-grade turbines, and the horsepower required to spool them would prevent you from ever leaving second gear! The Fiero is designed as much around engine ventilation as the A10 Warthog is designed around its main gun.

I'm not sure why Ryan's stating what he is up there, but read the Fiero's design theory. The car is designed to have a >1 bar pressure zone under the chassis from the radiator to the rear firewall. It's one of the two structural designs that work in concert, with the second being the car's notchback design. (Note: ALL Fieros are notchbacks, the fastback model is for impression only and is technically not a true fastback.) The 90-degree angle the rear window holds against the deck creates a low pressure zone when travelling at any significant speed, for the sole purpose of drawing air up through the vents. The MR2 and Lotus Elise use nearly identical designs. The draw through the vents is assisted by the already-moving air expanding upwards from the bottom of the bay after being compacted under the car by the ram behind the radiator, insuring ample supply to the engine compartment. The two systems assist each other to create a very effective flow of air around the engine, and if you've ever blown a ring and your PCV system isn't perfect, you'll get a good idea just how much air is being moved. Attempting to suppliment the flow with fans would only interfer with the airflow and make it harder to escape the bay, as only an elaborate (and extreme horsepower-sapping) engine-driven turbine system would be able to exceed the normal flow rate above a few dozen miles per hour. Fans would be helpful for idling park situations like a traffic jam, but they would get in the way the rest of the time.

Reducing the air pressure under the car by installing vents in the hood would reduce the airflow, but shouldn't cause any ill effects as the system is more efficient than it needs to be. Taping up your exhaust manifolds, y-pipe, and a good length of the exhaust is always a good idea too. As I mentioned earlier, hood vents have the secondary benefit of helping in traffic conditions, as allowing air to rise from the radiator directly back to the atmosphere eliminates the problem of hot air being trapped behind it under the hood in stand-still conditions.

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LIFE IS MADE OF OBSTACLES AND CHALLENGES — TO OVERCOME THEM IS TO PROGRESS.

DRIFTING -- IT'S NOT THE FASTEST WAY AROUND A CORNER, BUT I'LL BE DAMNED IF IT'S NOT THE MOST EXCITING.

[This message has been edited by Delphince (edited 04-24-2006).]

quote Originally posted by jstricker: You're also making a lot of bad assumptions. The air is NOT stationary. The instant the car moves through the air, the air moves as well. The energy imparted to the air as the body passes through it is, in fact, very significant to what's going on. If this were my design exercise I would first put a chin spoiler on the car, as low as practical with whatever roads you're driving on. Perhaps even a splitter style similar to the DPG cars. I'd then smooth up the bottom of the car. Ideally, I'd put air inlets on each side of the nose to feed the radiator and fill and smooth the center of the nose. The idea on this would be to draw as much air away from the point of the car where you're not going to be able to have it pass smoothly beneath it and that area is at the tires. On the bottom, I'd smooth it but leave a shallow tunnel in the center, from the radiator back along the bottom of the fuel tank, then divergent at about the rear cradle mounts exiting out and as wide as the inside of the rear tires. Ventilation of the engine compartment would be troublesome (to put it mildly) but I think it could be done. Perhaps reverse NACA scoops in the rear fenders somewhere with an inlet over the car body (narrow and moderately wide, perhaps). A whole lot of trial and error would be involved in lieu of getting some wind tunnel time. Supercomputers are used, but not necessary. The SR71 was designed almost completely without computer as was the P51 and other aircraft that are still held up as some of the finest aerodynamic models ever made. When computers really became necessary was in dealing with super high reynolds numbers and supersonic shock waves. John Stricker

the previous arguments on the air using the bornoulli's principle is based on the air moving. To examine the effect on the car it is not a valid assumption that the air is moving, it is NOT moving in accordance to the theory. the ground is stationary. the air is stationary. car comes along.
ground stays put. (well maybe not in ca in an earthquake) air wants to stay still, but it is dragged along by many many factors, but relative to the car , it is not the same speed. there will be air pressurized by compression of the front nose, forced up into it by the small air dam, then down after the radiator, there is leakage under the airdam. 2 different speed air masses meet, turbulance builds, but relative to the car will move to the back as a pressure factor. it is not moving relative to the ground as fast as the car is moving relative to the ground. so you are correct that it is moving, but not in the fashion that bournoulli's equations are designed for. I just haven;t been wording this properly.
what my point was that blindly taking a principle like that and trying to paste it into something it is not designed for is wrong.

And yes the sr71 was not designed by a computer, but by some genius level people who understand and spent their careers designing aircraft,and using practical knowledge to guide them.

As I had said earlier, I agree with you whole heartedly on the front chin/airdam. I have done this to cars, and I have driven said car at speeds in excess of 150 mph, and seen the differrence it makes when you start to get over the 90 mph speed.
In the case of a fiero, requiring the air movement to aid in cooling the engine compartment, I feel that leaving the true side skirts off will allow enough air to be drawn in mid car to then be sucked out the vents. keep in mind with the chin/airdam, you are eliminating some fo the air, but there is still a bit being passed thru the radiator and back down under to also add air supply. not sure what I would do with the pan in the area of the engine compartment tho. that is tricky due to the low pressure at the vents being the draw, if not done correctly, you could create draw under the car and negate the vents, making for one real hot engine. the side scoops could be an answer, or possibly an undercar scoop to force air up into the engine. time to get out the ol manometer and tape tubes to the car! always a fun way to determine where your pressure points are!

There is no difference, aerodynamically, if the air is moving and the body stationary or if the body is moving and the air is stationary. If there was, an airplane would never fly as that is a case of the body moving through a relatively stationary mass of air. Keeping that in mind, I still don't see what you're trying to say. The instant you pass a body through a fluid (air, in this case) things happen and force is imparted. If you want to argue terms like Bernoulli's theory, fine, but I don't think that's what the discussion is about. The discussion is about what happens if you smooth the bottom of the car.

Normally, smooth is better when it comes to drag reduction. Occasionally you want surface imperfections for boundary layer control and other issues, but in general, the smoother the better. If you have a chin spoiler that is LOWER than the smooth pan of the car, it will most likely reduce drag but don't expect any dramatic downforce from it. OTOH, the Fiero is made so that it would be possible to play with a diffuser tunnel down the middle of the car if someone were so inclined and that most certainly COULD help increas down force.

John Stricker

quote Originally posted by tjm4fun: the previous arguments on the air using the bornoulli's principle is based on the air moving. To examine the effect on the car it is not a valid assumption that the air is moving, it is NOT moving in accordance to the theory. the ground is stationary. the air is stationary. car comes along. ground stays put. (well maybe not in ca in an earthquake) air wants to stay still, but it is dragged along by many many factors, but relative to the car , it is not the same speed. there will be air pressurized by compression of the front nose, forced up into it by the small air dam, then down after the radiator, there is leakage under the airdam. 2 different speed air masses meet, turbulance builds, but relative to the car will move to the back as a pressure factor. it is not moving relative to the ground as fast as the car is moving relative to the ground. so you are correct that it is moving, but not in the fashion that bournoulli's equations are designed for. I just haven;t been wording this properly. what my point was that blindly taking a principle like that and trying to paste it into something it is not designed for is wrong. And yes the sr71 was not designed by a computer, but by some genius level people who understand and spent their careers designing aircraft,and using practical knowledge to guide them. As I had said earlier, I agree with you whole heartedly on the front chin/airdam. I have done this to cars, and I have driven said car at speeds in excess of 150 mph, and seen the differrence it makes when you start to get over the 90 mph speed. In the case of a fiero, requiring the air movement to aid in cooling the engine compartment, I feel that leaving the true side skirts off will allow enough air to be drawn in mid car to then be sucked out the vents. keep in mind with the chin/airdam, you are eliminating some fo the air, but there is still a bit being passed thru the radiator and back down under to also add air supply. not sure what I would do with the pan in the area of the engine compartment tho. that is tricky due to the low pressure at the vents being the draw, if not done correctly, you could create draw under the car and negate the vents, making for one real hot engine. the side scoops could be an answer, or possibly an undercar scoop to force air up into the engine. time to get out the ol manometer and tape tubes to the car! always a fun way to determine where your pressure points are!

You guys are all obviously more versed in this than me....

But when I crawl under the car, I can plainly see several areas that could benefit from small pans without having any adverse affect on the designed air flow. For instance, just covering the center tunnel with aluminum sheet should reduce drag without affecting the amount of air flow underneath. Also the sides/rockers with the cooling pipes look like they could be covered with aluminum sheet as well, again without interrupting any of the normal flow - just decreasing drag. Also, I believe a front air-dam has a major benefit of directing flow around the front tires. As pointed out by the numbers above, the tires are a major source of drag and directing flow around them will reduce drag. The open mouth air dams look like they would do a good job of directing a lot of airflow away from the wheels while still allowing sufficient(normal?) amounts of air under the vehicle.

The discussion of how much a full belly pan would help/hurt could go on forever, but I have no doubt that some strategicly placed components would help a lot.

Jstricker "If you want to argue terms like Bernoulli's theory, fine, but I don't think that's what the discussion is about. The discussion is about what happens if you smooth the bottom of the car."

I started this thread to debate the feasibility of creating a smooth underbody would have on the aerodynamic and handeling of the car, while it`s nice to see everyone has different ideas on what this would / wouldn`t achieve it seems silly to start a flame war over it.
Having read through everything if I sheeted off the entire underbody of the car with an inverted scoop on the underside drawing air in to the engine along with some side scoops, is there a chance that this might be benificial

Not being a structural or aerodynamics engineer, IF you do some ducting for air flow INTO the engine bay near the bottom, you could put a pan across the bottom. You would have to have a way to also extract the hot radiator air out from under the front. You might have some benefits if all the above are met, but any improvement, in my opinion, would be so slight, it wouldnt be worth the effort. For example youve smoothed the air underneath, but youve 'dirtied' up the outside by adding drag (scoops). It would be like spending $5,000 to gain 2 horsepower....could be done but why.