Jaku

what Emilio said is exactly what/how APR measure their angle of wing relative to the downforce data they provide

there is nothing wrong to use that angle of attack in this particular case

in fact, none of us can accurately measure the down force at watever angle, any reference is good to start with

f20kills

Gotta love the hard core R&C guys
I think people fail to realize not everyone "knows" everything in this forum. I know I dont

He asked if there would be a big difference, why, because he doesn't know.
Pointing people in the right direction is much better than just talking down to them, at least to me it is.

I value the posts from people (949...etc) who can provide others with useful info
Thanks

FINAL GEAR

any riser photo with the wing ?

949Racing

From the results thread for S2K Challenge #1 at Buttonwillow in January

https://www.s2ki.com/forums/index.ph...=666462&st=150

GTC200 with risers

Monster GTC300 with risers This particular wing was 67" wide instead of the standard 61"

FormulaRedline

Mike is entirely justified in his "nitpicking" in this case. The problem arises due to the fact that the APR wings have twisted cords. This means that the angle of the wing relative to the ground actually changes along the length of the wing. The idea behind this twist is to match a similiar principle in the air flow over the car. The air that flows over the roof of the car is drawn back down towards the rear deck lid so it will hit the wing at a different angle than the air coming around the side of the cockpit that catches the edges of the airfoil.

So what exactly are you referring to when you talk about the "angle of attack on this wing? The angle of the center section relative to the ground or air flow over the roof, or the angle of the end sections relative to those things?

Keep in mind even APR's CFD data, which is a good tool to use to find a starting point, is done in a free stream (not the variable angle flow it was designed for) and measures their angle of attack as 0 when the center section's leading and trailing edges are parallel to stream. This can be confusing as 0 angle of attack for the center section when mounted on the car has it pointing up, with the leading edge well above the trailing edge relative to the pavement.

This is important as according to the CFD data, the wings start stalling out over about 13 degrees angle of attack. The downforce drops while drag goes up exponentially. Almost every picture I've seen of and S2000 with an APR wing is running it stalled out.

949Racing

This is something that just adds to the confusion. The correct nomenclature from an engineers perspective does indeed describe an imaginary line drawn through the centerline of the airfoil element. Pretty tough for the average guy to determine. Even an ALMS team running a proprietary wing probably lays a straight edge across the wing element and jots down the resultant angle in a set up notebook. The engineer that drew the wing using an solid model of the entire vehicle and CFD to determine the true actual angle of attack is likely the only one that uses the term accurately.

APR, as do other 3D wing manufactures for the public, will refer to the angle as a line in the center section, with a straight edge laid across the upper most surfaces. Pretty un-scientific but it does give the layman a repeatable way to determine relative angle and in the end, that's all that matters. That the average guy has a term to describe the relative angle the wing is adjusted to. Relative angle, angle of attack, rake, whatever.

Mikes nitpicking serves to further educate the uninitiated and that's certainly appreciated but I'm not sure the tone was relevant or necessary.

My personal pet peeve is everyone, including the manufacturers, erroneously referring to anti-roll bars as "sway bars". Do I call them anti-roll bars on my website? Heck no

I'll consider this thread drift on terminology ended as its serves no particular purpose and does not aid anyone in adjusting their wings. I suggest visiting APR's website and check out their useful primer on wings

mikegarrison

I fail to see anything wrong in the one I used. Trust me, if I had intended the tone to be abusive, there would have been no doubt about it.

FormulaRedline

I think we're missing a major issue with this perspective. I'll try to simplify since I haven't communicated it correctly yet:


APR's CFD measures the angle of attack from the center section of the wing. The center section of the wing, when mounted on the car, sees an air stream that is NOT parallel to the ground. If using APR's numbers as a reference, you should probably instead set the angle of the wing based on the relative angle between the end sections of the wing and the ground.



This roughly translates into the numbers APR is using. So if the data for your wing shows that it makes less downforce after 13 degrees, that means 13 degrees between the ground and the end sections. If it says it makes XXXlbs of downforce at 5 degrees AOA, that's the angle its talking about. If we all talk in this reference frame, which APR has already established, I think we'll have a much easier time sharing setup information

Antonov

So @ say 100mph, what would you guess the angle of flow over the roof of the car is @ roof height?

Would tuft testing on the airfoil end plates give a good representation of the flow angle? Or would it be skewed due to the flow moving around the side of the car?

What AOA do you run your wing ?

-Dino

mikegarrison

No. All you would see is the tufts twirling in the tip vortex.