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Keith Tanner
Keith Tanner MegaDork
1/25/18 12:20 p.m.

Coroplast. Is there an election between now and the Challenge?

Or plywood, or street signs, or cardboard soaked in fiberglass resin...

Dusterbd13
Dusterbd13 MegaDork
1/25/18 12:27 p.m.

3/8 ply from shipping containers.  Got 3 sgeets out of the projects yesterday. 

 

I wonder what the most effective wing cross section is for autocross? 

Also, spool is a maybe. Don't know if we will or not. Depends on how much the peg leg sucks in testing. 

stafford1500
stafford1500 HalfDork
1/25/18 12:36 p.m.
Dusterbd13 said:

I wonder what the most effective wing cross section is for autocross? 

That is a question that can not be answered easily...

For simplicity and time efficiency, a very large spoiler with curvature will get you most of what you are trying to get. Think a "J" shaped spoiler bolted to the back of the car. It gives the benefit of the spoiler and also moves the higher pressure region further back for more effective leverage, plus it is simple to make with some cables to help hold the shape.

The recent autocross aero threads give me some good entertainment while I am trying to write wind tunnel test reports...

Dusterbd13
Dusterbd13 MegaDork
1/25/18 12:43 p.m.

I was thinking more along the lines of the amc wing style.  I have a visual package in my head that I'm hoping to get to what make it effective as well

stafford1500
stafford1500 HalfDork
1/25/18 12:57 p.m.
Dusterbd13 said:

I was thinking more along the lines of the amc wing style.  I have a visual package in my head that I'm hoping to get to what make it effective as well

In that case, lots of curvature, still like a "J" shape, only with a thick middle, ~1" radius on the front edge and thin back edge. Imagine if the AMC wing could have been rolled more front to back. You can do the same thing with multiple smaller/less curved wings by effectively stacking them like the picture posted earlier in this thread.

The lightest way to make what you are trying to get is glass over foam. Aluminum/ply is going to be heavy. The AMC wing was made of 0.032" sheet aluminum skin over billet ribs and weighed ~15 pounds without the supports/braces.

At autocross speed the AMC wing made about 30 pounds of downforce (less than the whole assembly weighs). But it sure looked cool.

MrJoshua
MrJoshua UltimaDork
1/25/18 1:09 p.m.

In reply to SVreX :

That wing should have weighed less than 25lbs complete, produced significant downforce, and helped the unfinished appearance at the rear of the mumpkin. I really wish I had managed to get it done.

sleepyhead
sleepyhead HalfDork
1/25/18 2:29 p.m.

this is kind of the "classical" multi-element airfoil picture...

via this site"
edit:note, this image would need to be flipped upside-down to be correct for downforce wink

although, most data for these sections is around 6million Rn... whereas any wing on an autocross is going to be operating in the 350k to 750k range... depending on the "chord", putting it square into the "Low Reynolds Number" / laminar regime... which means that things tend to not achieve the same maximum lift capability (iirc)

but, let's say you can pull off a Cl of 3, on a 5 foot long wing with a 18" chord, at 50mph (73.3 fps):  0.5*.002377*(73.3^2)*7.5*3 = 144lb of downforce

if you made a bunch of those kind of elements... most would around 6", or so... and could easily be formed out of shaping plywood, imho

JG Pasterjak
JG Pasterjak Production/Art Director
1/25/18 4:19 p.m.

I'm a firm believer in autocross aero and its effectiveness when properly applied. But even in a best-case scenario on a course the size of the Challenge, you're talking tenths, not seconds.

My first question if you wanted to go faster at the autocross would be "Are you on fresh Hoosiers?" If the answer is "no" then you're giving up a ton of time for something that wouldn't even give you a budget hit.

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