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Discussion Starter #1 (Edited)
Thread has been updated with new video of before/after vortex generators.

This might be better in the advanced discussion but it doesn't look like it gets a lot of traffic so I'm sticking it here to either amaze, confuse or confound, your choice. This one is going to take many, many posts to complete. And I have to re-introduce myself to Mr. Bernoulli whom I have never had a mancrush on for obvious reasons, chief of which is the following:

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My brain already hurts.

NOTE: As I do more research on diffuser design, I've realized that the design of a diffuser isn't a buy it off Amazon and slap it on affair. Diffusers MUST have side plates to help accelerate the air so if you see a diffuser that doesn't have side plates, you're looking at a diffuser that does not work.

The angle, distance from the ground, side skirts, amount of air passing under the vehicle all contribute to the vortex effect of the diffuser Obviously, this will require a separate thread. This is also making me re-think my front air dam design which sits at a similar angle and height to the active aero on a 3000gt.

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There was an article published in 2001 where a Mazda RX7 was wind tunnel tested. The reason I refer to this is because the body shape is similar to the Dodge Stealth,. Not indentical but similar so we can use that data as a guide.




I suppose this is a continuation of my first aero thread

I'm installing a series of vortex generators on my Stealth, 1st gen, stock spoiler over the next few days and will go through the process here.

And I am building a rear diffuser using the same devices. I'm still studying the design of diffusers so that's my last mod.

I use a specific product that has been tested by NASA and is used in the trucking industry as well as RVs, race vehicles and other vehicles.

The vortex generators are produced by a company called Aeroserve Technologies Ltd. and they are near Ottawa, Ontario, Canada. They have a patented device call Airtab and they conduct aero vortex generation application research. The devices are designed to do two things: reduce drag and increase fuel mileage by reducing said drag.


Lockheed-Martin in Georgia did an extensive study using Airtabs on a Honda in their wind tunnel. No word on if the Honda in question has been modified for the internal missile racks or radar cross section reduction (i.e. stealth). < pun


From the report:

Introduction:

During his research, the inventor of the Airtab® wishbone vortex generator brought his concept to the Lockheed Low Speed Wind Tunnel facility in the State of Georgia USA. His aim was to confirm that the introduction of forced, arrayed, stream-wise, near-wake vorticity would serve to increase pressure at the base area of a moving vehicle thereby reducing aerodynamic drag force. He accomplished a series of unmodified (baseline) and modified (with Airtab® vortex generators) wind tunnel runs. The runs were made at a constant speed (55mph) and over a fixed range of yaw angles. The vehicle was a 1982 Honda Civic Hatchback and this particular vehicle was chosen for two reasons: The vehicle had a small enough cross sectional area to permit statistically valid, un-corrected data runs in the chosen wind tunnel without turbulent side wall interference problems and, the vehicle design offered a generous base area enabling the acceptance of an approximately 50 sensor pressure grid to measure base pressure data for each run. The vehicle was fixed with this pressure sensor grid and mounted on metric plates imbedded in a large turn table inside the wind tunnel to allow the vehicle to experience different yaw angles


The hatchback design of the Honda they used for the test has two differences from the Stealth: No deck lid and a sharper angle of slope at the rear. I'm merely showing you this to demonstrate that the effect of the device works on low speed vehicles.

I've used the Airtabs on three vehicles and each use resulted in increases in fuel economy because they increase the velocity of the airflow across the rear of the vehicle. In a simplified way, the air is going to follow the shape of the roof as much as possible, which is known as a attached flow. The airflow reaches a separation point somewhere around the end of the roof and diffuses when it moves into the area above the rear window and hatch, leaving turbulent, slow-moving air with very little fluid flow makes it smoothly down to the wing, thus rendering the wing far less effective. On my old Dakota both with a fabric and later a solid rear cover, the airflow was changed enough that over 45 mph in the winter ice would actually be drawn UP into the air stream because of the vortex created. It also created enough aero force to remove the clearcoat on the roof of the truck.

I believe that when the Stealth was designed and the questionable spoiler was designed (I mean who the hell make the front of the spoiler higher than the middle), the "turbo sail" slots make up for having the stupid thing so close to the rear window. What I have observed is that the air flow from the rear quarter window "turbo sail" directs enough air over the questionable spoiler to make it somewhat effective at speed.

My modifications with the airtabs will create a vortex that will affect the rear spoiler in such a way as to increase downforce as well as fuel mileage. I'll go ahead and generate glassy eyed screen staring: What the Airtabs do is create a disturbance in the airflow running over the end of the roof, producing a swirl of air between the high energy and low energy streams which will draw a stream of high energy air from into the boundary layer, increasing the boundary layer’s energy.
This will increase the attached airflow over the spoiler and should make the spoiler work better at various speeds. Imagine how my brain feels after writing that. Wow.

Thus far, I have placed some of the Airtabs on the roofline where they'll be attached so you all can see what I'm talking about. I still have to prep the surface and probably some slight mods to the tabs themselves. BTW, The center one right over the rear sprayer should make an excellent "James Bond spray on the tailgater" device.

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Discussion Starter #2
Well, these new medications are kicking my ass and I am not qualified to drive right now in as I keep fainting so it's time for me to set up old garage wind tunnel, aka the massive electric industrial blower. I measured the airflow with my anemometer - which came from the University of Michigan wind tunnel where it was used for the original NASA shuttle wing studies - at 40 miles an hour.

I did the tuft method of checking the air flow over the rear wing without the vortex generators and with. At low speeds, the difference with vortex generation and without isn't super obvious but it's there. Without being able to generate smoke to visualize the airflow you'd be correct in thinking that this is a rather subjective test.

In the video, the lower left window is with the Airtab vortex generators, upper right is without. What I'm seeing is that the test with the vortex generation has a more stable air flow over it - the yarn wiggles around less, becomes more what is called laminar. This creates a more steady airflow over the spoiler of the vehicle.

Next, I'll be mounting the generators onto the roof of the car. Since there's a slight curvature to the roof and the generators are flat, I might have to do some modifications but we'll see how it goes. I've bought enough generators (22 of them) to do both the hood and diffuser with some left over for some other ideas rolling around in my elderly head.

You can see that without the generators, the tufts are bouncing up and down. With the generators, they point steadily in the direction of the air flow. Anyways, here's the video that I shot.


 

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Discussion Starter #3
I realized I missed uploading the photos of the anemometer. It's kind of cool owning a little bit of history. It has the original conversion table that one of the engineers wrote up to determine the mph of the wind.

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I don't really know what to say, but I gotta say this is taking your randomness that no one ever asked for to a whole new level. I love it. I hope you keep producing these near-scientific bored "old man" type experiments. Convince the wife you need to light a fire in the garage for strangers on the internet.
 

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Discussion Starter #5
How does a 50,000 BTU propane heater sound? That thing rocks the garage. A few years ago I decided to do the body work and paint my truck so I took off the week between Christmas and New Years to do the work. Laid in the fiberglass, sanders, paint, body filler, the whole thing. Set record cold that week. I had every space heater we have including the propane monster just to get it up to 50 degrees. What a PITA that was.

I'm hoping that I can drive today so I can toss a camera in the back and tape the yarn at 55 and above. There ain't no randomness - that's just to fool Chevy owners. At some point, I'd like to crack the 25 mph mark and the vortex generators will be a big step in that direction. I've finally found that 73 MPH is the best mileage speed.

I actually had a dream last night about building a diffuser.
 

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so, is it correct that you are trying to use the vortex things to get more clean/stable air flowing across the stealth banana? if so, i'm all for that :)
or is my understanding wrong?
I think I said before that I was doing some 70mph (?) on the highway when I drove through a rain storm and the rear window and banana on my car stayed dry.
 

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Discussion Starter #8 (Edited)
I watched the video and I gotta be honest, they look the exact same to me lol.
I should have recorded from the side. It was easier to see the difference from that angle. Maybe I'll reshoot it later. Watch the trailing edge yarn - the difference is small but you'd expect that at the low velocity of the wind I can produce. I was standing there watching it and once I saw the video I was like "There's no difference" but there is. I'm hoping to get my act together later today and go on the road with it without the generators and get a higher speed baseline.
 

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Discussion Starter #9
so, is it correct that you are trying to use the vortex things to get more clean/stable air flowing across the stealth banana? if so, i'm all for that :)
or is my understanding wrong?
I think I said before that I was doing some 70mph (?) on the highway when I drove through a rain storm and the rear window and banana on my car stayed dry.
You are correct. I know from past experience that the generators do work. The ice on the bed cover on the truck rose up into the air. In the rain it was amazing watching the water bounce around back there on a fiberglass cover.

I don't see any road racing or any more top end finding in my future but I'd like to be able to get the car planted better on the highway because I do go over 100 fairly frequently and honestly, the car feels light when it gets to high speeds.

Here's a photo from the 2005 Pike's Peak race of a truck with the airtabs. It's a pretty visual picture of their effect.

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I thought about one of those stupid roof wings to direct the air down towards the banana but I suspect the lift caused by that would negate any effect on down-force.

My question is will they affect the spoiler on the Stealth. I know from my highway driving in the rain that you can barely see any mist over the wing. I think that minimal amount mixed with the speed of the air dries any moisture that you'd see otherwise.

Also, I've noticed in the rain because of the coating on the paint and the RainX on the windows that the droplets, when they go past the mirrors go UP to the roof of the car making those side sail things questionable in their effect.

An interesting story. When I had my first Stealth, I was a the gas station one night and a police car rolled in. It looked weird so I checked it out. It was a Ford Aspire (?!). I got to talking with the driver who was wearing Ford coveralls and it turns out that Ford was shoving 5.0 liters in some of them to see if they'd make good law enforcement cars. Well, there was a plexiglass shield in front of the light bar. He tells me that was because the first one they tested spun around at 130 miles an hour because the light bar created so much lift it dragged the ass end of the car off the ground. The car was totaled but the driver walked away. That pretty much killed the whole idea but they messed with it for a while longer.
 

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my guess is that you need to know the required location (eg height) of the banana so that it gets some clean stable air at high speed. we know from wind tunnels that the 3000gt spoiler catches wind :)
 

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Discussion Starter #11
my guess is that you need to know the required location (eg height) of the banana so that it gets some clean stable air at high speed. we know from wind tunnels that the 3000gt spoiler catches wind :)
Actually raising the banana was in the future plans but I would posit that a gurney flap will do the trick.


I believe this is what you speak of, the world famous Russian wind tunnel tests with no documentation and tiny photos.

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I wonder if your VG needs to be on the top leading edge of the glass, not the trailing edge of the roof
 

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Discussion Starter #13
I wonder if your VG needs to be on the top leading edge of the glass, not the trailing edge of the roof
On the tail end of the roof just before the sprayer so it catches as much air as possible. Putting them on the glass puts them out of the stream of air.

Anyways, here's a on the road test with the tufts. Of course when I was going 50 mph, the damned reflection ruined the clear view. As you can clearly see, even as slow as 25 mph, there is airflow over the banana.

 

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Discussion Starter #14
Well, the generators have been installed. I'll be doing the yarn test once more tomorrow morning. It's supposed to rain as well so I might take my retired carcass out to actually observe the vortex generation.

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you almost get a vortex shape between each vortex
 

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Discussion Starter #16
So it was raining and like a dummy I was driving around in it. But it does come in hand when visualizing airflow. I had stripped the wax off the roof so when I parked it didn't come beading off.
I'll do another yarn test video tomorrow. However, I can also say that when driving over 40 mph, the rear window is totally dry except for the very driver/passenger strips where there are no generators.

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Discussion Starter #17 (Edited)
I was able to get on the road without rain soaking the yarn. The video shows the difference with and without the vortex generators. The flow appears more stable with the generators - i.e. the yarn doesn't wave around as much.

What's really surprised me (and I don't know why nobody has ever done this) is that over the years I've heard time and time again that the banana spoiler is a useless piece of garbage that only sits there and embarasses the average Stealth owner, etc, etc, yada, yada.

I think I've finally laid that to rest. The Stealth spoiler does in fact work at basically any speed over 25 mph. Of course, just because air moves over it doesn't mean it does anything other than dry out wet yarn. The next step with the spoiler is to install the Gurney flap on the tail edge of the spoiler. And don't be fooled by that foam crap you see on Amazon or the gentle bending so called Gurney flaps you see on some cars. An actual gurney flap is a 90 degree piece in various heights to create various stages of downforce.

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I'll be using a lot more yarn on the spoiler, end to end, front to back to determine exactly how the airflow goes over the spoiler with the sails (that's what I keep seeing the vents behind the rear 1/4 window called). I'm also wondering if and additional panel on the sails themselves would direct more air onto the spoiler at highway speeds.


Addressing the elephant in the room, exactly how much downforce does the spoiler create, is something that will be harder to determine. The only real way to do it correctly is with a series of sensors on the rear struts to take exact measurements which will cost more than I'm willing to throw at the issue. Another method I've seen at a Ferrari forum is to use an electronic (and sensitive) level mounted in the car and see how many degrees of bubble you get at X speed. Perfect excuse for a 100 + mph run. "Well, officer, you see it's like this. There's this one guy named Bob in Ohio who's old like me that wants to know how much my bubble moves over 100 mph."
 

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Hahahahaha.

That's right, blame Bob, lol.

Bob. ;)
 

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Hahahahaha.

That's right, blame Bob, lol.

Bob. ;)
Heh, wait'll I bring Dan Gurney into it and why I have all that yarn hanging off the spoiler. Either I'll get an escort as I test or they'll call my wife to see if she knows what I'm up to.

True story - I had a case of the wife's beer on the front seat and she refused to go and get it for fear she's scratch something.
 

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the ECS equipped cars have gforce sensors. I've never seen the information that the gforce sensor sends to the ECS computer but maybe it shows changes in downforce.
 
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