When I was teaching at Comair several years ago, a couple of my well-read colleagues decided to leave the approved syllabus and explain to their students the real story of dynamic lift, that magic that makes an airplane fly. Unfortunately, the restrictions of a Part 141 curriculum mandated that they teach what was approved, not necessarily correct, and they were ordered by management to cease and desist and return to what the FAA allowed them to say, even if it was wrong.
If you are a pilot, you have heard that lift is created because when the relative wind meets the leading edge, the airflow over the top has to move faster over the curved, longer-distance top of the airfoil to meet the same air molecules at the back of the wing. Even as an early student, this was illogical to me- why would the air have to match up again?
Recently, an article in the November AOPA magazine reminded me of that puzzle. The author, Catherine Cavagnaro, wrote of a filmed series by German aerodynamicist Alexander Lippisch. Made in 1955, this series is now available on-line, and yes, it is black and white and absent the slick production values of videos made today, but it is also stupid simple. There are several episodes but I really wanted to see the one about dynamic lift.
Using a wind tunnel with smoke streams, Dr. Lippisch demonstrates many different aerodynamic principles, and one of the ones he puts to rest is what is called the “equal transit” theory- that is, that two air particles separated at the leading edge of the wing are reunited at the trailing edge. He shows this is wrong and you can see it clearly in the video- the air moving over the top of the wing moves faster because it is compressed, and it clearly does not meet eventually at the end of the journey because it’s, you know, faster.
I am including a link to this video here but there are 7 segments total, each around 30 minutes long. The old-school production values and heavy accent may be distracting, but his work is fascinating if you have any interest in flight dynamics.