The popularity of the equal transit-time fallacy is a bit more complicated than a mistake spreading from a single source. It is simple, intuitively appealing (blowing over an airfoil is often invoked, along with an erroneous picture of flow lines around an asymmetric wing), and gets things done quickly. Just like the "explanation" of seasons by the Earth's changing distance to the Sun, or textbook pseudo-explanations of history, like the "crisis" over the discovery of irrationals, or Maxwell's "mathematical" reason for adding an extra term to Ampere's equation. "The truth is what works". Eastwell in Bernoulli? Perhaps, but What about Viscosity? lists the following motivations:
"• Simplified Bernoulli explanations are quick, sound logical, and make correct predictions. As Brusca (1986b) said with a sense of satisfaction, the prediction is “in complete agreement with what happens in practice” (p. 15). This would be fabulous if it wasn’t for
the fact that these explanations are also wrong!
• Statements like “as the speed of a moving fluid increases, the pressure within the fluid decreases” facilitate a misunderstanding of Bernoulli’s principle and, when used in a sweeping sense and therefore out of context, are wrong.
• Viscosity, entrainment, and the Coanda effect are not to be found in lower-level literature, despite the fact that such literature deals with phenomena that rely on these concepts.
• There appears to be a desire to have a single, best explanation for an observed behaviour when in fact a combination of factors may be “at play”"
The fallacy was likely independently reinvented by multiple textbooks authors and physics teachers. Norman Smith, who was one of the first to sound the alarm back in 1972, says the following in Bernoulli and Newton in Fluid Mechanics:
"Millions of children in science classes are being... told that Bernoulli's theorem is responsible for lift on the airplane wing and for the force that makes a spinning baseball travel in a curved path. Unfortunately, the "dynamic lift" involved in each of these items is not properly explained by Bernoulli's theorem.
[...] First, an airfoil need not have more curvature on its top than on its bottom. Airplanes can and do fly with perfectly symmetrical airfoils; that is, with airfoils that have the same curvature top and bottom. Second, even if a humped-up (cambered) shape is used, the claim that the air must traverse the curved top surface in the same time as it does the flat bottom surface (or that the molecules must meet again) is fictional. We can quote no physical law that tells us this. Third - and this is the most serious - the common textbook explanation, and the diagrams that accompany it, describe a force on the wing with no net disturbance to the airstream. This constitutes a violation of Newton's third law.
[...] The use of Bernoulli apparently began in this country some 30 years or more ago and has spread throughout school science books and popular literature to exclude virtually any mention of Newton and momentum. College-level aerodynamics textbooks generally do not use this approach, though it would not be surprising to find a few exceptions... It might be well to point out that the Bernoulli explanation is used mostly in the United States British, for example, seem to use Newton's third law in textbooks and popular literature".
Writing in 2007, Eastwell notes that things did not change much, if not gotten worse:
"Such a pressure difference is commonly justified, on the basis of Bernoulli's Principle, by statements such as “when air sweeps across a surface at high speed the pressure on that surface is lowered” (“Bernoulli Station,” 1989, p. 308) or “as the speed of a moving fluid increases, the pressure within the fluid decreases” (Mitchell, n.d., n. 1), or it is implied on this basis (e.g., Brusca, 1986b). This reasoning for the pressure difference, found not only in popular writings but also in specialist, peer-reviewed journals (e.g., see also Bauman & Schwaneberg, 1994; Holmes, 1996), is wrong."
Now that even Wikipedia has a subheading False explanation based on equal transit-time, perhaps the tide has finally turned. It is not that the use of Bernoulli's equation is entirely wrong, it is rather that it comes with a number of erroneous add-ons. As Beatty pointed out in Airfoil Lifting Force Misconception Widespread in K-6 Textbooks:
"Air-deflection and Newton's Laws explain 100% of the lifting force. Air velocity and Bernoulli's equation also explains 100% of the lift. There is no 60% of one and 40% of the other. One of them looks at pressure forces, the other looks at $F=ma$ accelerated mass. For the most part they're just two different ways of simplifying a single complicated subject. Much of the controversy arises because one side or the other insists that only their view is correct.
[...] Social psychology aside, there are also several serious mistakes usually associated with the "popular" explanation described above. Those who believe the "popular" explanation are wrongly insisting that any parcels of air divided by the wing's leading edge must meet again at the trailing edge. This is incorrect. Actually it doesn't even occur: experiments easily show that the air above a wing far outraces the air below, and parcels never meet again. (In fact, if a wing is adjusted so the parcels really do merge, this is always the zero-lift configuration!) The same people also believe that wings fly only because of pressure, and that wings don't need to deflect the oncoming air downwards. Also incorrect. These and several other mistakes commonly appear in elementary science texts, as well as in popular articles about aircraft physics. These mistakes change the popular "airfoil-shape" explanation into a system of misconceptions."
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