The touring car aero study is here at last!
This is going to be a multi-part series with a couple prologues. This is Part 1.
First, let’s get a base knowledge on how a race car’s wings work.
As you can see above, a wing is formed by having one flat surface mated to a curved surface. Airflow along the flat side remains at constant pressure while air passing along the curved surface is forced to speed up because of its longer path. The faster air travels, the lower it’s pressure is.
Note how I labeled the sketch: When viewed in this orientation, the wing profile is producing downforce because the curved side is on the bottom, but when rotated 180 degrees the profile becomes an aircraft wing producing lift.
Also note: In science and engineering “downforce” is technically known as “negative lift” much like “centrifugal force” doesn’t exist - it’s actually “tangential force”.
Now, lets get more specific about airflow as it nears the trailing edge of the airfoil:
Notice how my flow lines at the top surface of the wing rapidly dip down as they clear the surface tip. This is because the air under the wing is at a lower pressure and therefore sucking the higher pressure top-surface air into the low pressure stream. Because of the significant pressure differential a vortex is created by the high-pressure bending into that low-pressure and it continues to swirl sometimes hundreds of feet behind the car (depending on speed and wing size, chord, pitch, etc. which I’ll address later) and many miles behind a large aircraft.
The vertical arrows I’ve drawn are the force lines showing what kind of forces are acting on the wing in the vertical axis. The top side has uniform pressure pushing down on it - this is purely the weight of the air molecules acting on the surface when the wing is at 0 degrees like this. (Be aware that 0 degrees is never “neutral” for a wing - more in Part 2)
You may be wondering why my force lines on the underside begin with upward pressure. Logic tells us that air encountering a downward-sloping surface is deflected along that surface and forcing the surface in the opposite direction (equal and opposite reaction, etc.) meaning the air is actively pushing the leading edge of the airfoil upward until the air is bent back the other direction by the curve (more about this in Part 2).
Oh, and yes, I did do this on a napkin at a restaurant with my waitress’ pen.
This concludes Part 1. Do feel free to inbox me or reblog the post with questions you have. And reblog away just to share knowledge. Cuz, ya know, that’s what I’m here for!