Just a couple of thoughts.

Redo the rear wing airflow test with two "high flow" deck lid vents. Will the air flowing under the wing be lessened of turbulance better? Since the amount of low pressure may be lessened with the greater deck lid updraft.

I wonder if the whale tail affects vent performance.

Compromise vents: remove leaf catcher and replace with mesh. That way the vents looks mostly stock.

Anybody remember the vortex generators on the rear of either the WRX STi or The Evo of a few years ago? Can't remember which one had it. It was to improve the aerodynamics by minimizing the air tumbling down the rear glass. These vortexes (sp) would swirl like mini tornados toward the back of the car. I read somewhere that air can only follow a 7 degree curve, if i remember correctly.

Thoughts?

P.S, Way to go Blacktree. You actually are testing ideas. The rest of us just sit back an wait in anticipation. + for you.

quote Originally posted by Knight: I own a page! My first without starting a post! ....... And now back to our regulary scheduled Posting. (And back on topic.)

One too late I'm afraid

!

No, I looks like Knight got it. He's the first two posts on this page.

I wonder how stock '84 and later year Dukes of the same body style would compare in these experiements. As the only difference would be side vents vs. center vent. I really like how the center vent looks on my '84.

-Michael

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"A guy know's he's in love when he loses interest in his car for a few days." -Tim Allen

He who dies with the most toys... still dies.


Check out my restoration!

Still have spare vents you can have if you want them. Harry

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87 GT Maroon 3800SC & White Formula

I'll keep that in mind.

OK, here's a much-needed update.

Today, I had some downtime. So I strapped the camera mount to the roof and took it for a spin. First, I drove around without the camera in it. I wanted to be sure it wouldn't fall apart, come off the car, etc before trusting my camera to it. It survived the ordeal unscathed.

So I then installed the camera and drove around some more. This time, I wanted to film it so I could see if the setup is stable enough to get a decent picture. It's kind of jittery, but should suffice. Below is a short clip taken from the film test. During this clip, I sped up to 65 MPH and then stopped for a red light.



For the next test, I'll put tufts of yarn on the hood, to determine the airflow patterns.

[This message has been edited by Blacktree (edited 02-12-2009).]

Its going to be one funny looking fiero when you have that roof mount and yarn all over your car

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Yeah, you should've seen all the "WTF?!" looks I got today.

haha all in the name of science

as for the headlights up effect, its crazy. think of snowdrifts around trees, where the snow is blown away in a parabolic pattern and an area directly behind is left mostly unaffected. thats what headlight motors do to snow when my headlights r up and theres snow on the hood.

I have a pretty good idea what the headlights will do to the airflow when they pop up.

Actually, I took some video of that today. But unfortunately, I had some technical difficulties. So I'll have to do a re-shoot sometime this weekend.

Alright, we have video!

I was able to reduce the camera wobble by stuffing foam rubber into the enclosure. So the video isn't so jittery.

My headlights are the slim pop-ups using the brackets from Fiero1Fan and Hella 90mm lamps. So they don't pop up as far as the stock ones. The effect on airflow was still pretty crazy. This is what it looks like at 60 MPH:



Notice how the tufts behind the headlights flare out when the headlights are popped up. That appears to be the twin-vortex affect... the same thing that causes the big swirls in the tire smoke when airplanes land.

I also noticed how turbulent the air was in the center of the hood, behind the hood vent. I assumed the hood vent was causing it. It looked like the air passing by the sides of the hood vent was being curled inward toward the center. That lead me to believe that the hood vent didn't flow enough air to match the airspeed of the surrounding air. This prompted me to conduct experiment #6.

In experiment #6, I wanted to see if turning on the radiator fan would break up the turbulence behind the hood vent. I figured the extra airflow would help fill the low-pressure area behind the hood vent, and reduce the swirling.



Apparently, I was mistaken. I turned on the radiator fan right after making the first lane change, and turned it off just after making the second one. I couldn't tell any difference. If you watch closely, you'll notice that the radiator fan was spinning before I turned it on. The airflow through the radiator was strong enough to spin it.

I now believe that I inadvertently caused the swirling airflow pattern when I made the curved rear edge of the hood vent. It makes the ends of the vent bigger than the middle, which probably causes the air to flow at different speeds. This in itself can cause the air to swirl.

It looks like I'll be redesigning my hood. When it's done, I'll get some video of it in action.

Ok, I didn't read every response, so this may been asked/said: A lot folks and I have moved the rear wing aft 4" or so for looks. I suspect that 4" may change the results a lot. Still, the wings are probably 99% looks and one% function add in the few pounds of one and it's kind of a moot device. Also with the engine where it is in a Fiero, do we really need more down force back there? Just my 2 cents

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[IMG]




trueleo.com
RSpiderII@aol.com

quote Originally posted by Francis T:...Still, the wings are probably 99% looks and one% function add in the few pounds of one and it's kind of a moot device. Also with the engine where it is in a Fiero, do we really need more down force back there?...

I don't believe that down force had much to do with the design of the wing at any speeds remotely close to legal highway speed. It contributed more to the reduction in drag.

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RickN
White 88GT 5spd
White 85GT Auto
White 99 F250SD 7.3PSD 6spd
1956 Ford 860 Tractor w/ Freeman Loader

quote Originally posted by Blacktree: It looks like I'll be redesigning my hood. When it's done, I'll get some video of it in action.

I'd like to see a pic of it from the side. I can't tell if it's just a hole or has an indention behind it.
I would also like to see this with a stock hood, & of course if you know anyone that has one of my vents I'd like to see that too.
~ Paul
aka "Tha Driver"

quote Originally posted by RickN: I don't believe that down force had much to do with the design of the wing at any speeds remotely close to legal highway speed. It contributed more to the reduction in drag.

Correct. The drag coefficient was lowered by the OEM Fiero Spoilers...

quote Originally posted by FieroFanatic13: Correct. The drag coefficient was lowered by the OEM Fiero Spoilers...

X2
The reason is because it's a spoiler and not a wing.
The difference is the wing creates downforce much like an inverted airfoil would, and the spoiler decreases the downward angle that the trailing airflow 'sees', making it less turbulent, thereby reducing drag.

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Journal of a concept: http://southeastfieros.com >>> Build Thread >>> Parts thread (for project funding)

quote Originally posted by Tha Driver: I'd like to see a pic of it from the side. I can't tell if it's just a hole or has an indention behind it.

The hood vent is raised in front, and recessed in the rear. This build thread should give you a better picture of its shape.

I also plan to run the same tests on a stock hood. So we'll have our control group in the near future.

First off, Kudos to you Blacktree for actually testing and trying to learn what the airflow is doing. It is the only way to know for sure.

There has been so much written on aerodynamics in the last couple of pages which is just plain wrong I hardly know where to start but I'll try to clear up some of the misconceptions.

There is no free lunch. When you hang things in the wind they make drag, that is a given. The question is can you hang things in the wind that give you enough of what you're looking for in the form of lift or downforce to be able to have an acceptable amount of drag. It's always a tradeoff. In the case of aircraft, the holy grail is the most lift for least drag and that is actually plotted on the airfoil graphs as L/D ration, or Lift to Drag ratio. The lower that number, and assuming you can get the aircraft to cruise at that angle of attack, is where you want to be.

Angle of incidence means nothing as far as if a wing will produce lift. Angle of attack is everything. Angle of incidence is fixed and will not change in 99.999% or more of the aircraft at least in reference to the main wing (and not discussing the stabilator). The angle of incidence is really an angle determined on how the wing is fixed to the fuselage of an aircraft. IOW, an imaginary fixed line that is determined. On airplanes, that can be determined a number of ways, but most of the time it's fixed on a line in the engineering prints.

What can, and does, change is the angle of attack. That means the angle the wing hits the flow of air. Just because the angle of attack changes does not mean the angle of incidence has changed.

An airplane does not need a laminar flow wing for it to fly inverted. I can give you any number of airfoils that are not laminar flow when, if the angle of attack reaches a certain point, will develop negative lift, or downforce. If you turn that upside down, as in inverted flight, you will have positive lift. Heck, a barn door will do it given the proper angle of attack.

There's nothing wrong with the wing of the GT Fiero. It could certainly generate downforce, or negative lift if and only if it had sufficient airflow. What the OP's tests are showing is there is little or no airflow in that area of the car so it's not making any downforce to speak of. The drag reduction, IMHO, that's reported is due to it keeping the turbulence actually behind the car lower than it is on the non-wing equipped cars.

The IMSA air dams are made to create downforce by pulling air in from the sides as well as doing a little straight over the decklid. Not much over the decklid, because there's not much air to work with there, but a little. In the front of the car I don't believe by looking that the aero nose is much, if any, better than the bumper pad nose. The gains would come in putting an airdam or a chin spoiler on the car to keep as much air as possible from getting under the car. The lower the dam or spoiler is to the ground, the better off you're going to be. The shape of either nose is such that if you can keep air from underneath, air pressure on the front hood and nose will provide a little (emphasis on the LITTLE) downforce, but more importantly if you can keep the air out from under the car it will help in preventing the nose from lifting.

John Stricker

quote Originally posted by Francis T: Ok, I didn't read every response, so this may been asked/said: A lot folks and I have moved the rear wing aft 4" or so for looks. I suspect that 4" may change the results a lot. Still, the wings are probably 99% looks and one% function add in the few pounds of one and it's kind of a moot device. Also with the engine where it is in a Fiero, do we really need more down force back there? Just my 2 cents

Moving the wing back will not put it into the air stream. It will accent the amount of air being collected from the air moving up the back bumper and over the deck.

The only way to make the wing work like a wing is to raise it up. I figure raising it level with the top of the cabin probably is a good starting point. However, it would look a little ricey IMHO.

Arn

Now we have some video of the decklid, with three different spoiler setups. This is the video footage that I was anticipating the most.

The first setup is the control group, i.e. no spoiler. See photo below.



The next test was with my modified spoiler installed. The custom brackets move it back about 5-6" from the stock location. It sits about 1.5" above the rear deck.



And for the third test, I installed a strip of plastic under the spoiler, to block the airflow underneath. The idea here was that if I blocked the airflow underneath the spoiler, it would reduce the "backwash" effect, and reduce the turbulence on the rear deck.



In all three test runs, I accelerated to about 60-65 MPH. Here's the video.



In the first segment (no spoiler), almost the entire decklid is experiencing forward airflow. Only at the very edges, which are probably in the side air stream, do we see air flowing in the proper direction. So the idea that air flows forward across the deck is not a myth. And like the saying goes, "for every action there is an equal and opposite reaction". Which means all that air being accelerated forward is likewise accelerating the car rearward. In other words, it's a lot of drag.

In the second segment (spoiler installed), the picture is a little different. We still have some air flowing forward in the center of the decklid. But there is more front-to-back airflow on the outer edges. The zone of turbulent air has been reduced in size. And that means less drag. Also notice that the rear part of the spoiler is also experiencing front-to-back airflow. This would suggest that the airstream from the roof is hitting the spoiler near the back edge. This is a good thing, because it also means less drag.

In the third segment, I have installed an air dam of sorts under the spoiler. It prevents air from flowing underneath the center section of the spoiler. The idea here is to block the air behind the car from flowing forward onto the decklid. I don't know about you, but I can't see any noticeable difference between this and the previous segment. Unfortunately, it may take more sophisticated equipment to measure the difference. So the jury is still out on that one. It's disappointing, because I was hoping that plastic strip would make a noticeable difference.

I'd like to make one final statement about this video, and the aerodynamics of the Fiero's rear end in general. And that is this: unless you put a hatchback on the Fiero, there will always be some amount of forward-flowing air on the decklid. That's because the vertical rear window causes a zone of turbulent air behind it. Friction between this air mass and the air stream flowing over the roof causes it to spin. The top of the air mass moves to the rear, and the bottom moves forward. That's why the air flows forward across the rear deck. The important part is to keep this turbulent air mass as small as possible, and to keep it under control. Less energy spent moving air means less parasitic power loss, i.e. less drag. Plus, if you keep this air mass contained, you can create an air bubble that acts as a sort of "virtual hatchback" to help keep the roof airstream flowing smoothly.

Ironically, this is similar to the aerodynamics of a pickup truck bed. On a pickup truck, the tailgate separates the air in the truck bed from the air behind the truck, causing in an air bubble to form in the truck bed. The air bubble allows the airstream above it to flow past with relatively little fuss. While the air bubble is not as efficient as a solid top, it's better than nothing.

So it's no coincidence that the wrap-around IMSA spoiler looks kind of like the back end of a pickup truck bed. After all, it performs a similar function.

In my next video, I'll examine the rear airflow from a different angle. That should give us more insight into the "air bubble" concept that I mentioned.

[This message has been edited by Blacktree (edited 02-18-2009).]

i've been through this thread once a while ago, but wow Blacktree your research and presentation of your results are awsome! + for you

So what you're trying to say is that I did the right thing by installing an IMSA wing?

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Very, very interesting !!!. The data and responses get somewhat"'esoteric"..but here is a experience I had with 2 Fieros. I sold a 84SE that had a "scoop" from damper and was always "true" driving in some wind, were as my 85GT would " wander or dance" in the wind. Tried this experiment at the same speeds, on the same day over the same road back and forth. The tire pressures, suspension et al was the same. When I see GT-1 cars, Can Am cars I notice the BIG differences as to what is used for down force or cooling. Gotta remember, Fieros ain't Ferraris..just interesting small sport cars NOT HIGHLY REFINED !!!

Thanks for posting, great experiment.

quote Originally posted by doublec4: So what you're trying to say is that I did the right thing by installing an IMSA wing?

Yep.

I've been thinking of getting one, too. I haven't made up my mind yet, though.

Interesting. Anyone ever seen pics of the red GTA that GM did a "Kammback" to? Like the world's sportiest station wagon. Ever. Anyway, same as turning a ford Ranger into a Bronco II. So, if we extended the Fiero's roof on back equal with the rearmost part of the bumper...? How about the extended roof, but this time taper it at the rear like a raindrop, then remove the Fiero's sail panels, and run clear plastic vertically down to the decklid? Still some drag, but probably alot less lift.
If noone else tries it, I will. I'm already working on an airdam like the one on Hot Rod Magazine's '78-'81 camaro Bonneville Salt Flats car. I hate how most factory ground effects are closer to the ground just ahead of the front tires than farther forward. It's obvious why this should be for real world use, but the only alternative is a shorter front overhang, and I for one am not about to put a '95 RX7 nose on my Fiero. I'd rather do a Countach front wing.

Be really cool if you take a video from the side and then could set a smoke bomb off low on the roof. Be interesting to see if that would show the bubble over the rear...
If you had a couple smoke bombs from the 4th and could set them off in a tin can to protect the car body but let the smoke roll over the rear. Would have to be quick or have a helper to light them... or get a couple model rocket igniter's so that you could set them off with a battery while you drive...

Would also get some really good looks from anyone around...

[This message has been edited by Dodgerunner (edited 02-24-2009).]

quote Originally posted by Dodgerunner: Would also get some really good looks from anyone around...

"Oh look honey, it's another Fiero on fire!"
-Paul

huh... can anyone think of any good ways to manipulate the airflow to get it into the deck vents? watching these videos it seems to me that there has to be some way to make the air do what you want, as long as the air is gonna create drag why not make it do it in a usefull way? i dont know if this is possible, i dont know enough about this stuff (yet) so just asking the people who know wat they are talking about.

A lot of comments / opinions of drag co-efficient in this thread.
Here's a directly quoted paragraph from Road & Track November 1984 issue on the 1985 GT.
That car has the aero nose, ground effects and spoiler like Blacktree's 1987 S/E (although I'm not sure what wheel / tire combo Ron is using...)

"For those aerophiles among our readers, the following will be of more than passing interest. The original Fiero with 13-in. wheels and tires has a Cx of 0.377; add 14-in. wheels and tires and that figure climbs to 0.406. With the pace car nose and 14-in. wheels and tires the coefficient of drag drops to 0.372 and falls still further to 0.350 with the addition of the rocker panel extensions and the rear wing."

They made no reference on where they obtained the data, but presumably from GM when they were designing the aero package vs. the bumper pad car.
You guys have got me wondering what my Cx is on the stretch hatchback
Ryan

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Indy Northstar-Stretch ~ LT1-NOS Roadster

Bump. more research must be done =)

Unfortunately, the Fiero's engine gave out. After the new engine is installed, testing will resume.

quote Nohbdy:... can anyone think of any good ways to manipulate the airflow to get it into the deck vents? ...

Yes, several have BTDT. hint: scoops.

[This message has been edited by 30+mpg (edited 04-26-2009).]