Part 2 - The relative wind

by Ihab Awad, Founder of Airball.aero

If you missed it: Part 1 - Simple beginnings.

As I learned to fly, I started reading Stick and Rudder, by Wolfgang Langeweische. In it, he describes the relative wind as:

As pilots, we are taught to think of three quantities: Angle of attack, angle of yaw, and airspeed. But these are just the "numbers" that describe the relative wind vector. Langeweische spent a lot of time in his book trying to get us to visualize it, using imaginary arrows and windsocks on cartoon airplanes:

The stakes are high. As Langewische's illustrations show, where the wind is coming from is not where the nose is pointed relative to the ground. Whether it's the airliner that crashed in San Francisco, or the Cirrus SR20 that crashed in Houston Hobby Airport in 2016, or any of a number of such accidents, pilots time and time again, in perfect weather, lose awareness of the relative wind, with fatal results.

We can describe the relative wind by three numbers. The indicated airspeed gives us the strength of the relative wind. The angle of sideslip gives us its direction to the left or to the right. And the angle of attack gives us its direction above or below the nose. We are accustomed to the first two quantities in most aircraft from the ASI and the turn and slip "ball". Glider pilots, wanting a more sensitive yaw signal, measure it directly using a "yaw string" taped to the canopy. And (all too infrequently), we have the angle of attack represented on yet another instrument.

But we are working too hard! The relative wind is a vector quantity. A vector is just a quantity and a direction. We are getting mired in the numbers we used to describe the vector and forgetting that it is all really quite simple. Where is the wind coming from? No numbers -- just point in that direction! And how hard is it blowing? Again, no numbers -- is it big or little?

Can it be that simple? We believe it can! Stay tuned to hear more!

Next time: Part 3 - Measuring the relative wind.