Amateur Aerodynamics

Wakes are easy to observe in some media. Watch a boat moving through water and the expanding wake is readily apparent; similarly, when you've been swimming and scooped your hand through the water, you have seen the trail of bubbles following the motion. Wakes are harder to see in air—nearly impossible without rain or water spray, or smoke traces in a wind tunnel—but they exist just the same. We're all intuitively familiar with wake behavior and generally know that minimizing the wake tends to correlate with decreased fluid drag (like moving your hand palm-first versus sideways through the pool water). But just what is a wake, and why does it form? Why is wake size important? Or is it? Dragging a chopstick through a bowl of water (with food coloring added for better visibility) creates an expanding wake that looks like a "V" behind the stick. What goes on inside that wake? Wake Formation   Wakes form due to the fact that real fluids are viscous; that is, there are int...

When it comes to cars, "stability" is a loaded term because it is very imprecise. Stability could mean the car's ability to track in a straight line down the highway (which is as much a function of its alignment as anything else), or its ability to maintain its direction and rotation in a constant rate turn, or ability to maintain its composure through a slalom course, or its ability to resist changes in lift, or to not be disrupted as it moves and jostles on its suspension over a washboard road, or any number of other things.   So, to talk about "stability" in any meaningful way, we first have to narrow it down. What sort of stability? Stability with regard to what factor or input and what measurement or output? We'll see in just a minute why these fins might have been a bit misguided. Aerodynamic Stability   Since this is a blog about aerodynamics, let's consider stability as it is influenced by the movement of air around (and through) the car. He...