I’ve always loved to teach. That love has led me to multiple places within the realm of aviation and aerospace, starting with being the nerdy kid standing in front of his high school government class with his models of Gemini and Apollo spacecraft, to being a NATOPS instructor in the F-14, an astronaut trainer at NASA’s Johnson Space Center for a decade, and a Light Sport Flight Instructor and blogger (writer) today. Through it all, I’ve always strived to make difficult technical subjects accurate and understandable to my audiences.
I’ve also seen and experienced the other end of the scale, i.e., instructors who made technical content more complex that it needed to be in an apparent scheme to demonstrate their mental superiority to students, and instructors who “simplified” the material to the point it became technically inaccurate. Both approaches are a form of arrogance or ignorance; take your pick.
I’m a personal fan of Einstein’s admonition that “everything should be as simple as it can be, but no simpler”. About two weeks ago, I was in Edward Tufte’s class on presenting technical data where he stated that “dumbing down is pandering”. How true! The assumption behind any “dumbing down” is that the audience is not smart enough to understand the technical material but the presenters are. This is often not the case. As a good friend of mine used to say: “You can’t give away what you don’t have”; and that applies to the understanding of a subject as well as other things.
The latest unfortunate example of something dumbed down to the point of being technically incorrect is the current iteration of AOPA’s “Essential Aerodynamics” presentation. Frankly, there is nothing essential at all about it; I do, in fact, steer my students away from it. You know something is dreadfully wrong with their approach when they state that the “wing pushes down on the air”, something that simply does not happen. I say that as an aerospace engineer who, as a student, plotted the pressure distributions about a subsonic wing section in a wind tunnel. Once you see the large low pressure area above the wing which grossly outclasses the high pressure areas underneath, you can intuitively tell that the most accurate explanation for what is happening is that the wing is sucked up from above.
So where did AOPA get the idea that the wing pushes down on the air? I don’t know, but it could have been from someone taught by a teacher who bought into a poorly thought out push by the American Association of Physics Teachers (AAPT) in the early 2000’s to replace Bernoulli’s law, which does a good job explaining how a wing generates lift, with Newton’s laws. The best rebuke to that approach was written and published in their magazine, “The Physics Teacher, Volume 40 in 2002 by aerodynamicist Charles N. Eastlake and entitled “An Aerodynamicist’s View of Lift, Bernoulli, and Newton”. (Ask Google to find it.) In it, he explains how both sets of principles apply and then goes through a technical explanation of the airfoil and how lift is created. He emphasizes that the choice of which set of use depends on which one is simpler to use. Indeed, we did use both approaches (i.e., Bernoulli’s and Newton’s) in various aerodynamic problems to find the answers. But since most kids and many pilots are not going to know how to use calculus, I personally believe that using Bernoulli’s explanation is not only correct but intuitively easier to understand. Additionally, you can use it in a classroom with very simple models (i.e., wing sections and simple wind tunnels) and do the calculations to show the forces involved, something that is difficult to do when using Newton’s laws to calculate the change in momentum of the airflow. When you talk to most people about Newton’s laws, and especially about Newton’s third, they intuitively understand it when talking about the application of thrust, since that’s what we’re nearly all familiar with. But start trying to relate that to the change in momentum of the total airflow field (the Newtonian approach), and they’ll scratch their heads or come up with some off-the-wall and technically incorrect explanation that the wing on a fixed wing aircraft pushes down on the air. Using Newton is a more intuitively easier approach to use and understand when talking about how propellers, jet engines, or rotor blades create force (thrust or lift), even though Bernoulli’s principle is alive and well and at work in them, too.
The AOPA presentation also decides that explaining aerodynamics using a wing is too hard, so they use a surfboard generating “lift” as it races through the water as their example. This is truly baffling, since it ignores one of the major rules of communication (common symbols and experiences between the transmitter and receiver) and totally fails to account for the force of buoyancy, which airplanes other than seaplanes don’t have for long if they land in the water. There simply was no reason for it; it did nothing to simplify the explanations of relative wind or angle of attack and brought the confusing environment of the water in the picture. (Daddy, how come an airplane doesn’t float in the air? My surfboard does.)
The presentation excuses its approach by telling viewers they don’t need to use the common approaches used for a century to explain aerodynamics because they were used for designing airplanes and it only needs to educate pilots (i.e., pilots are not smart enough to understand it). I didn’t think anything of that at first, until I saw where they were going. After that, I felt it was a red flag that it was all about to go off the track. True enough, pilots don’t need to know how to use calculus and integrals or the power and drag required values to calculate what to do next. But they do need to have a proper understanding of how a wing works and that needs to tie intuitively with what’s going on in the cockpit. I can use Bernoulli’s and angle of attack to make it clear what a stall is and that reducing the angle of attack to break the stall is all that counts; I’m not even sure how you could approach it when trying to explain it using Newton’s laws using change of momentum. In fact, I could easily see how someone not grasping it might think you need to use the wing to throw more air at the ground and pull the stick back HARDER. (The same action can result by teaching someone to believe in “impact lift”, which is not lift at all but drag acting in a vertical or near vertical direction.)
I did contact AOPA about this and forwarded them a copy of Eastlake’s article. In response, I got some mealy mouthed excuses about the difficulty of presenting complex technical material. The lesson has remained unchanged. Additionally, a few months after I set my response, “Flight Training” magazine, when promoting this presentation asked its readers “Newton or Bernoulli?”, stepping into the same nonsensical environment the AAPT had created. It’s not an either or choice, except when you’re trying to explain it. To do that correctly, you need to know what you’re talking about. And better care.
There’s a reason why NASA websites and the FAA’s “Handbook of Aeronautical Knowledge” uses Bernoulli for their basic explanation of aerodynamics. Too bad you don’t get WINGS credit for going there; you should.