Doppelgänger

iTrader: (12)

So, next year I plan on running a wing for autoX. I've been reading the rules for mounting such a rice device, and they are as follows...

-May be no more than 8 sq/ft
-May not hang further back thatn the rear most part of the rear bumper
-May not be wider than the body of the car
-May be NO higher than 6" above the highest point of the car (windshield frame)
-Must mount no further than the center point of the rear axle.
-No part of the wing can exceed 6" forward of the rear axle line.

So with that layed out, I got to wondering, I know everyone tends to mount wings to the most rearward position. Also, we know the Miatas profile isn't very friendly to aerodynamics...and in my case, I don't have a hard top. So I'm wondering about mounting a wing to the forward most possible position (within the rules allowed). My reasoning to seek insight is based partly on the old Chaparral race cars that had the wings mounted in middle of the car and on the idea of catching air right as is expands/sinks off the rear roof line to restrict airflow under the wing but not sit it right up against the top.

Attached is my quick rendering of the restrictions.

What do you guys think would be the effects of mounting a wing like this?

Oscar

iTrader: (2)

placing it there should expose it to clean air and generate downforce at a relatively low AOA and reduce drag. Going to build one yourself or use an of the shelf solution?

Savington

iTrader: (31)

The further back you mount it, the more leverage you get on the rear tires. Put the element wherever you want, but make sure it mounts as far back as possible.

gospeed81

iTrader: (51)

Placing it forward will also apply the downforce right on the rear axle, as opposed to creating a moment about the rear axle which (slightly) unloads the front tires.

It would be a very small difference, and is surely offset balance-wise by the weight of the turbo kit, and placing it further back applies the force behind the rear wheels without adding pendulum-like weight back there.

crashnscar

iTrader: (9)

This is what you want for auto-x.

gospeed81

iTrader: (51)

^^^holy ****! lol

Doppelgänger

iTrader: (12)

Funny thing about CSP...

They are allowed to add an element to the rear of the car, but it cannot act as a wing....so they're running those spoilers. I've often wondered how much difference in benefit there is between a large spoiler and a large wing like Chris Swearingen's car...

Chris Swearingen

iTrader: (1)

You might notice in that picture there is a spoiler and a wing. I believe that to be a legal configuration, but have never run it at a "big" event, so I don't know how it would hold up to protest.

I did a quick cut and past to show the comparison of mounting locations for you. I don't know that the forward location will get as clean an airflow as the rear section will. If you add a diffuser as part of the rear valance, the further back will help improve the performance of the diffuser.

Edit: I added my proposed splitter/air dam and canard changes as well

thagr81 us

iTrader: (5)

This is quoted for the truth... The further the point of applied pressure (wing) is from the fulcrum point (rear axle) the greater the torque (downforce) will be applied to the system. It's Physics baby!!!

sbrian2

iTrader: (12)

Yep, you want a wing, not a spoiler like shown on the black car above. This is what we run on the car I am driving.
It is an APR piece. If you tell them you are an SCCA member, they give you a nice discount too.

thagr81 us

iTrader: (5)

Chris Swearingen

iTrader: (1)

When you talk to them (APR) you want the 55" GT-II wing, but you want both elements to be the 7.5" high camber wings. You will wind up building your own end plates (14x14 inches to take full advantage of the allowance) and adding a Gurney flap to the upper element. Talk to them about custom mount spacing as well if you want to mount at the edges of the trunk lid.

y8s

iTrader: (8)

sav's description seems slightly incorrect, but thagr81's clears it up to make me happy.

center of pressure * distance from pivot (wheels and/or CG) = rearward downforce moment. further back = more rear downforce.

Faeflora

iTrader: (2)

I think you are going down the wrong direction. For big aerodynamics it would best to take the body off your car and weld a boxfish shaped sheetmetal to your frame.



Boxfish.



See what I'm getting at?

9671111

iTrader: (10)

You should probably worry about your own welding endeavors for now.

thagr81 us

iTrader: (5)

Glad I could bring some science to the conversation... I am a chemist afterall. Haha

Faeflora

iTrader: (2)

Oh shut up. I am being a little silly with the boxfish thing but it's true:

See:

The bionic car - MSN Autos

Faeflora

iTrader: (2)

My thoughts are that you should get a magazine feature before messing up the profile of your car. You have one of the best looking Miatas ever. Seriously..

Doppelgänger

iTrader: (12)

faeflora-Don't worry, I have a spare trunk lid that i'll be using to affix any aerodynamic aids to...and will be keepinf the one that is currently on the car nice and cherry
I wish I knew someone who could help me get the car into a mag. SCC was going to do it, but they folded right in the middle of our discussions.

Chris- Don't worry, I have no forgotten a single thing you have discussed with me about aerodynamics I was just contemplating and take all information in. I wish we could run diffusers in SSM :(

thagr- I knows, about wing placement and how the rear axel acts as a fulcrum point. I am curious as to what might be the effects of putting the weight straight down on the wheels.

Faeflora

iTrader: (2)

Why not try for a feature in a good import/car blog?