Common Misconceptions in Aerodynamics: Part 8
Rear spoilers and wings still work even if a car has front-wheel drive.
The claim: Spoilers are only for RWD cars since they make downforce at the rear.
|This myth has been around for a long time.
|I couldn't find any examples of this misconception that didn't pile on additional myths. See if you can spot them all.
The reality: This myth is just one representation of a larger misconception. Online commenters seem to be fond of making pronouncements such as this, declaring with absolute certainty that some device or other will or will not work in a certain way. Often, their comments are accompanied by simple explanations. “That rear spoiler isn’t doing anything for your car because it’s FWD.” Or, “The angle of your wing is wrong; you should have a -5 degree angle from horizontal to make the most downforce.” Or, “Your spoiler is too high because it needs to ‘reach up’ only to the Template and it will create a locked vortex over the rear window and the air will ‘skip’ over it as if there was body structure there and thus drag will be reduced” (this one’s real, shockingly). Or, “Folding your mirror in is just as good as removing it, maybe even better because the inward tapering of the mirror body toward the window will recover pressure and disrupt the flow less.”
Any time you see someone trying to explain something like
the behavior of a spoiler or wing (which have, in reality, very complex
interactions with air flow) in simple and absolute terms, run the other way.
The flow field around a car is anything but simple, as I
explained in an earlier post, and the complex interactions between various
parts and shapes of a car body mean it is only possible to generalize
the behavior of devices such as spoilers because so much depends on the actual
geometry of the specific car and device in question. The problem here is, a
statement such as “fitting that spoiler to this car may or may not reduce drag
and/or lift, we can’t say for sure what it will do and how large its effects will be without testing” is a much less satisfying
answer to someone’s question than a definitive “yes” or “no” with an
accompanying, easily-grasped explanation. This feeds into the fallacies of
predicting or intuiting flow patterns and thinking
it is possible to ascertain the effect of one shape or another on drag and lift
simply by looking at them. Neither is true.
|Uh oh! Testing a rear spoiler on a FWD Prius.