Don Terrill’s Speed-Talk

When setting the "angle of attack" of a rear wing (on a RED) do you measure relative to the chassis or to the ground? My car is slightly "nose down" on a level surface, about 2 degrees. The wing is currently just about parallel to the chassis and therefore 2 degrees down relative to the ground.

I guess it may not matter in the sense that if I want more down force I can always angle it further down, but I am curious about the concept. It seems to me that the setting is relative to the chassis, but am not sure. Anyone have any input?

to the ground, ... which may not be easy. any tire or suspension changes may alter the car angle thence the wing
what about using one of those little digital angle meters, or an app for your pad ? Set the car then lay the device on the exact same spot on the wing each time you want to check the angle. In fact then you can check the angle across the wing as well

lada ok wrote:to the ground, ... which may not be easy. any tire or suspension changes may alter the car angle thence the wing
what about using one of those little digital angle meters, or an app for your pad ? Set the car then lay the device on the exact same spot on the wing each time you want to check the angle. In fact then you can check the angle across the wing as well

well does anyone else agree ?

I agree.



Think of the wing itself as it moves through the air?
The wing doesn't know what angle the chassis is?

If the chassis flexes enough at whatever speed you want the wing to work at, need to adjust for that angle?
(like on TF dragster that bows up in the middle changing the wing struts angle)

John Wallace wrote:I agree.



Think of the wing itself as it moves through the air?
The wing doesn't know what angle the chassis is?

If the chassis flexes enough at whatever speed you want the wing to work at, need to adjust for that angle?
(like on TF dragster that bows up in the middle changing the wing struts angle)

Thanks john, I just like to know if I'm wrong !
I thought it was a very good question.

Just like John said, the wing only knows of the air it's passing through, nothing else. You could run up a 45º hill and your wing angle is still relative to the ground.

Also, if you are testing, make sure to try 0º angle of attack too. Proper wings work when flat. That's how our Altered wing is set, although admittedly the wing is way too big for what the car needs. Looks cool though.

Depending on the position of the wing, the air may not all be flowing horizontally. E.g., over the rear deck, the air may diverge down the slope so that a wing set a zero degrees to the earth is actually operating in the central area at 10° or more incidence. This is the reason for 'twisted' profile wings that reduce the incidence in the middle to prevent local stalling.

2X re downforce at zero degrees. The (non-twisted) wing on our road race car doesn't reach zero DF until ~ minus 4°

Bill, he's in a rear engine dragster, so the assumption is he's got the wing up in relatively clean air.

Here's a picture of mine on our altered just for kicks:

Oops! Missed the RED reference...

The angle of attack is measured using the ground as a reference point compared to a line along the chord of the wing.

The chord line is an imaginary line that goes from the leading most edge to the trailing most edge of the wing (not by using an angle finder referenced on the top of the wing).

99% of all aerofoils are in a database maintained by NACA and can be found on the internet.

If the manufacturer of the wing will give you the NACA I.D. number, you can calculate with pretty good accuracy the down force at each angle of attack.

Unless your wing is really low, as compared to most RED, it will be in free stream air and unaffected by turbulence coming off of the rest of the dragster.

Does NACA also maintain data of how wicker bills and spill plates effect each aerofoil design?

My guess is no, in which case there are some very good automotive aerodynamics books that delve into those subjects in depth. Two particularly readable and knowledgeable authors you could Google are Simon McBeath and Joeseph Katz.