Last week when I talked about bee flight and the physics of airflow at super small scales, I just barely touched on coefficients.
And that’s not enough, quite honestly.
In aerospace, coefficients are truly fundamental to how we operate. They make our jobs a lot simpler, and expand the ways and opportunities for us to use the data we collect from tests and experimentation.
Coefficients are nondimensionalized numbers that let us describe the physical behavior of certain shapes without needing to take the exact geometry, flight conditions, and other factors into account every single time.
We call them “nondimensionalized” because these coefficients are unitless: they do not have any dimensions specified. This makes them very versatile!
To make this hopefully easier to understand, let’s talk about what these coefficients even describe. Let’s say you make a model of a long, rectangular wing for a remote-control plane you’re thinking about building, and you mount it on the roof of your car to test it. The way you mount it contains a load cell that can measure the forces that the wing experiences as you’re driving down the road, primarily lift and drag.
You take your car to the straightest, flattest long section of road you can find where you won’t get too many weird looks, and you do a few runs back and forth at a constant speed, which you make note of on your phone.
Now you have a good amount of lift and drag data for maybe one specific speed, and you can figure out how heavy of an airplane your wing can support.
But here’s the problem: your lift and drag data is only valid for the exact wing geometry you tested, at the exact speeds you drove, in the exact weather conditions you drove in.
You have data for this wing, sure, but what if you decide you want a smaller airplane? Or you want to fly faster, or slower, than you tested?
You’d have to go make more models and do more testing…if it weren’t for the magic of coefficients.