Where did the false "equal transit-time" explanation of lift originate from?
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Where did the false "equal transit-time" explanation of lift originate from?
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Re: Where did the false "equal transit-time" explanation of lift originate from?
#2No idea why you would provide the equal transit time theorem to students, it makes such a low amount of sense that you're inevitably going to get your students extremely confused if they are paying any attention at all.
"Why does the air have to transit in the same time period?"
"But _why_ is the air moving over the top faster? Weren't you going to tell me how a wing works?" Etc etc etc
It is the worst kind of lie-to-children (and adults) in my opinion, it's not a simplified true answer it's a whole cloth fabrication that vaguely gestures in the right direction, partially, if you are being generous.
The idea that people get tested on regurgitating it for a pilots license is crazy.
It's up there with those ridiculous tounge maps with taste regions on them.
Re: Where did the false "equal transit-time" explanation of lift originate from?
#3I recently encountered this in a sailing class when the teacher was explaining how "pull-mode" works in sailing, where the wind is coming from ahead of the vessel and pulls the sails rather than pushing them. I knew this theory to be debunked and yet couldn't work out the answer from non-debunked physics (and certainly didn't want to disrupt the class by arguing physics with someone who's been sailing for 50+ years - if it worked for him, it'll probably work for me, even if debunked).
Modern sailing vessels always sail into the wind, because they're always going faster than the wind blows. I do find the physics of this fascinating.
Re: Where did the false "equal transit-time" explanation of lift originate from?
#4Glad to see this posted more!
I was asking about this 9 months ago and it started quite a thread [1]. I remember learning about this in grade school, finding it pretty confusing, and wondering why a simple "newton's third law" wouldn't suffice. That's incomplete but at least not wrong.
Re: Where did the false "equal transit-time" explanation of lift originate from?
#5“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.”
Love it! Anyone have any others?
Re: Where did the false "equal transit-time" explanation of lift originate from?
#6“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.” Love it! Anyone have any others?
Simplified explanations of how electrical current flows in conductors comes to mind. Water analogies, for example.
Re: Where did the false "equal transit-time" explanation of lift originate from?
#7I recently encountered this in a sailing class when the teacher was explaining how "pull-mode" works in sailing, where the wind is coming from ahead of the vessel and pulls the sails rather than pushing them. I knew this theory to be debunked and yet couldn't work out the answer from non-debunked physics (and certainly didn't want to disrupt the class by arguing physics with someone who's been sailing for 50+ years -…
For the physics of sailing see http://gentrysailing.com/pdf-theory/A-Review-of-Modern-Sail-...
Re: Where did the false "equal transit-time" explanation of lift originate from?
#8Fluid mechanics has always seemed so complex that scientists joke
about it. Supposedly [0] Werner Heisenberg and/or Horace Lamb quipped
that when they died they'd ask God about relativity, quantum
electrodynamics and turbulence... and they didn't expect he would have
an answer for the last.
[0] https://boards.straightdope.com/t/did-heisenberg-really-say-...
Re: Where did the false "equal transit-time" explanation of lift originate from?
#9Handy video showing relative speed above and below the curved wing surface, and non-equal times :
Re: Where did the false "equal transit-time" explanation of lift originate from?
#10Glad to see this posted more! I was asking about this 9 months ago and it started quite a thread [1]. I remember learning about this in grade school, finding it pretty confusing, and wondering why a simple "newton's third law" wouldn't suffice. That's incomplete but at least not wrong. [1]: https://news.ycombinator.com/item?id=40835223
Newton's third law (as in, thinking of air molecules hitting the wing underside, disregarding any interactions between air molecules) would work for something like a spacecraft in the initial process of reentry, where one may assume that the atmosphere is so thin that air molecules don't interact much with each other. Lower down that assumption is no longer valid, and then applying Newton's laws to a continuum of interacting particles gives you fluid mechanics (Navier-Stokes etc).