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Old 03-08-2010, 01:13 PM   #21
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Would having the generators essentially under the wing make airflow go under the wing to a greater extent?

I know they will reduce vacuum right off the back of the car and thus kill the drag a bit, but I wonder if they will make for a bit less resistance to the airflow as it goes under the wing. I need to learn some more aero stuff.
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Old 03-08-2010, 01:33 PM   #22
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I would think just the opposite. If they are close enough to the wing to effect it, the vortices might slow the airflow under the wing.

I may play with some more designs. I really need some good way of visualizing the airflow. Maybe if I put this guy in the passenger seat?
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Old 03-08-2010, 01:34 PM   #23
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I like the look except for two things. First, the rivets. Couldn't you have bonded the underside reinforcement using epoxy or something? The rivets make it look too cobbled.

Second, the pins are a bit much. Something like Southco 1/4 turn fasteners would be more in keeping with the aero theme. It's not like you need to get into the trunk in a huge hurry.

the vortex generators look cool, and the weight savings are always appealing.
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Old 03-08-2010, 01:48 PM   #24
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Interesting looking test...I have been thinking about generators on the roofline (to get rid of the low pressure pocket on the rear window) but have not gone there until I can see how the air flows over the car. I am going to do a string test to map the results with a chase car. Have you thought of doing a test using fins and then comparing fins vs tabs? I wonder which would produce better vortexes...
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Old 03-08-2010, 01:50 PM   #25
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Quote:
Originally Posted by Chris Swearingen View Post
I would think just the opposite. If they are close enough to the wing to effect it, the vortices might slow the airflow under the wing.

I may play with some more designs. I really need some good way of visualizing the airflow. Maybe if I put this guy in the passenger seat?
A smoke test would be badass for sure.

Find yourself a loong straight empty highway.
Get a buddy in a camera car.
Put some smoke bombs on the front of the car.
Light smoke bombs.
Drive from 20 to 100 with buddy car off your rear quarter panel. No need to accelerate hard.
Use buddy car as a line reference, though you will probably be able to see OK.
Win.

*Sparetire is not responsible for the outcome, good or bad, of this test and the tester assumes all liability.


Or just tape some ribbons down.
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Old 03-08-2010, 01:52 PM   #26
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Here is an article by AutoSpeed on them... Has some CFD drawings as well. It is EVO specific, but same general principle.

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Old 03-08-2010, 01:56 PM   #27
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Quote:
Originally Posted by rleete View Post
I like the look except for two things. First, the rivets. Couldn't you have bonded the underside reinforcement using epoxy or something? The rivets make it look too cobbled.
this is another plus for the foam-sandwich epoxied fiberglass deal.

just run a rib (1" half round or so) of resin-compatible surfboard foam where that strip is and cover it with a lightweight fiberglass plus an inch on each side and dont make it too wet. it'll weigh the same or less that the aluminum does and provide at least as much stiffness.

then you can do more elsewhere if you find it's still too flexible.

the beauty is it's essentially air with a LITTLE compressive strength to hold the fiberglass off the underside of the lid and provide that extra "thickness" for more stiffness.
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Old 03-08-2010, 02:40 PM   #28
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Did you do any experimenting with Airtabs on the existing trunk before you made this one? Curious if it was science or instinct in adding them and deciding on placement. Gonna run some on the hard top too?
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Old 03-08-2010, 02:58 PM   #29
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Science is such a harsh word...

The shape of our rear deck is less than optimal from an aero perspective. I don't know that the air tabs are better, but I think they will be. I am changing quite a few of the aero components on the car at the moment.

Weight was the number one reason for doing the deck lid. I had wanted to try them and this was an easy way to do it. There would be some question about rules compliance if I were to have just stuck them on the deck lid, but since these are molded into the replacement deck lid they are 100% legal.

It will take quite a bit of testing to gauge their contribution to the total aero package. I may try some other versions later in the year and do some back to back evaluations. I doubt I have sophisticated enough test equipment to produce quantifiable results.

I could always buy some smoke bombs and coast through the cloud with various configurations. My engine guy would kill me if I let the engine inhale any.

Since this is an autocross car, I don't run the hardtop.

Does anyone have a CFD model of the car that could play with the various lips, spoilers, wings, and vortex generators available for our cars? That would be a great tool. It took me a long time to even find a way to model the airflow over a multi-element wing. That helped me set angles of attack, but only in theory. I never tested the improvements because I upgraded to a even more real wing for the car.

There is way more science that could be applied to our cars than anyone to my knowledge is doing. Maybe it is happening and thing aren't finding their way into the public domain.

I am always open to learning from others if they care to share.
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Old 03-09-2010, 01:15 AM   #30
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so wait a minute you are doing all this aero **** and not running the hardtop or running with the top down am i the only one who thinks that is kind of counter productive? How much lighter is this than the gutted one the rmcelwee did to save 7.5 lbs Red Beast - Lightweight Miata
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Old 03-09-2010, 09:00 AM   #31
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Quote:
Originally Posted by magnamx-5 View Post
so wait a minute you are doing all this aero **** and not running the hardtop or running with the top down am i the only one who thinks that is kind of counter productive? How much lighter is this than the gutted one the rmcelwee did to save 7.5 lbs Red Beast - Lightweight Miata
Reading all the way back to post number #1
Quote:
Originally Posted by Chris Swearingen View Post
My decklid with the bracing for the wing weighed 19 lbs. The hinges were another 4 lbs. I didn't weigh the latch mechanism, but I am going to claim it is a direct offset to the weight of the aluminum hood pins.

The deck lid that was vacuum formed for me weighs 5 lbs. That is including the inch and a half by 1/8th aluminum I used to make the front edge a little stiffer.

Total weight savings 18 lbs.
So 18-7.5 = 11.5 lbs

Again we are back to that science word. When I eventually put a cage in the car, it will wear the hardtop when it's on track. In order to do that I have to really do some major work on the seat mounting. My head hits the hardtop without a helmet on now. With some surgery to the rear seat corners and some creative mounts I can probably move the seat down almost the two inches I need if I also move it back about the same amount. Sometime during the summer I am going to get to that project on the list. Moving ~10% of the cars weight back and down two inches can't be a bad thing.

The Spec Miata guys all run the hardtop, but they are for the most part a momentum class. While momentum is important in autocross as well, it often comes down to acceleration. If you look around at National level events, you don't see any of the top cars running a top. Granted most of them aren't in SSM and don't have the horsepower I do, but neither do the Spec Miatas.

At some point after the seat mounts, I can probably do some testing, but if someone beats me to it I wouldn't mind.
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Old 03-09-2010, 09:21 AM   #32
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Quote:
Originally Posted by Chris Swearingen View Post
Based on the number of times I have been asked that question, I sold it way to cheap.
It was worth a shot I only ask because I finally picked up a GT-II wing for like $100...more or less got the uprights and endplates I need...the foil is a 5.5" flat foil and I called APR to see if I could order ANY foils (carbon or alum) and they don't have any such parts anymore. This leaves me on the hunt for 2 7.5" cambered foils. I tried that contact you mentioned but never heard anything back :(

On a side note, APR says their working on a new version of the "flat wing" (GT-I/GT-II) wings.
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Old 03-09-2010, 09:48 AM   #33
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I thought only Hustler stored young men in his trunk?

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Old 05-07-2010, 10:47 PM   #34
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Bumping this because I am curious as to whats going on with the lid and the airtabs.
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Old 05-08-2010, 11:49 AM   #35
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I have not driven the car in anger since I started this thread. I have been traveling way too much for work.

This weekend should see the wing mounted up. If I don't get hung up on something else the first event should be the 15th.
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Old 05-09-2010, 04:10 AM   #36
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Subscribed just for the shear coolness factor of this.
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Old 05-15-2010, 07:12 PM   #37
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Full updates in a few days, but here are some more shots.





And the hardtop for those of you who are going to harass me. The car will get a cage after this years SCCA National Championships in September.
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Old 05-15-2010, 07:23 PM   #38
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Dude, you need to get a smoke machine, get some tygon tubing (or similar), make that **** work in your car, put some dye into the mix and do some tests. I am thinking about doing it...just a matter of getting my hands on a cheep machine...
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Old 05-20-2010, 07:23 PM   #39
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Quote:
Originally Posted by Chris Swearingen View Post
Full updates in a few days, but here are some more shots.
Hows is the staggered 13"f/15"r setup working out for you?
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Old 05-20-2010, 08:41 PM   #40
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How many Thanksgivings did it take you to save all them wishbones for the vortex generators?
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