Aerodynamics: An Introductory Rant
[ June 24th, 2008 ] By: Mark Ozimek Posted in » Ramblings
I’m going to take a brief break from the turbocharger! series to make a little segue into what I hope to by my next topic that I will take a close technical look at: Aerodynamics.
Really, we only care about two things here:
- Downforce/Lift
- Drag
Hopefully I’ll explain how these two things come about in a pretty simple fashion that explains it a little bit better than “Oh, the body pushes air out of the way.” However, before that, I have noticed some very disturbing trends among the modding community.
The most incomprehensible to me is the addition of only a rear wing to a front wheel drive car. This is really a double negative. The wing creates downforce in the rear of the car, behind the rear wheels. The wheels act as a fulcrum, and this downforce that is generated in the rear actually lifts the front of the car up at speed. Totally counter-productive, since it will decrease traction on the drive wheels, and increase the amount of understeer. Keep in mind that front wheel drive cars already tend to understeer a lot, a wing in the back will just make it worse.
The other negative of the rear wing is one you will have to deal with almost every time you try to generate downforce by pushing air up: Lots of drag. The engine has to put out a bit more power to overcome the extra drag, which increases with the square of velocity. So now we have a situation where when the wing is putting down the most downforce is when the front tires are applying the most force to the ground to propel the car forward through the air. If this downforce was applied up front, or if it was a rear wheel drive car, this would be a great thing. Since it’s not, the drag slows the car down, and increases understeer through turns even more!
The other are body kits that add ‘features’ to the body that don’t actually do anything. Some things are useful, like a front bumper that allows less air under the body of the car should reduce drag, however, many are just as counter-productive as a rear wing on a FWD car. A classic example is the intake vent on the hood and before the rear wheels on the some of the more recent generations of Mustangs. The protrusions do exactly that, protrude into the air stream. This adds extra turbulence to the airflow over the body, which is almost always a bad thing since turbulence usually increases the amount of drag on the car. It’s possible to use turbulence to your advantage, but that’s a complex topic to cover, and requires some pretty precise placement of fins to make the air go where you want it to, think F1 for an example here.
One thing that Charles said to me while we were discussing this article is that we have a pretty utilitarian view on what looks good on a car. If it improves performance somehow, we’re almost always for it. If it does nothing, is counter-productive, or just adds weight, we typically hate it and immediately reject the idea. The things that make the car ‘go fast’ also look/sound good to most people, since we associate that with performance race cars. Maybe what we should do when we get our car to modify into a rally car is mask the things that make it look fast. Sleeper race cars, ready GO!
