Cambridge University
3 HN mentions · mentioned in 3 months, 2021–2025
1:14 · 609K views · Jan 20, 2012
A one-minute clip from Cambridge's Prof. Holger Babinsky that debunks the equal transit time explanation of lift. It shows how air actually flows over a wing.
Linked in lift-theory arguments as a clear demonstration that air over the top of a wing does not need to catch up with air underneath.
3 comments from Hacker News
You're right- there isn't, and it doesn't. In fact a parcel of air moving over the top of the wing will beat its counterpart moving below it to the trailing edge. This[1] video has a very good demonstration of this. (Relevant part begins around 0:25.) So saying that air on top of the wing moves faster, creating a pressure differential and thus lift, is absolutely correct. The problem begins when some people try to come up with an intuitive explanation for _why_ the air would need to speed up. "Because this is the lowest energy state that conserves energy, momentum, and mass" isn't a very satisfying answer; neither is "because this system of PDEs say so"; so they came up with the "equal transit time" explanation, which is simple, intuitive, and completely wrong. Hopefully aeronautical engineers at P&W didn't actually believe that last bit? [1] this video
Funnily enough, there's another web page on the NASA domain that outlines the "longer path" or "equal transit" theories as the correct cause of lift on an aircraft wing: [LINK] When I was studying for my PPL, they taught us using the equal transit theory, though the instructor couldn't help himself from telling us that it was a simplification. This video from Cambridge University illustrates what happens to the airflow over an aerofoil: this video
> right, the other is that if you remove every incorrect statement from the AI "explanation", the answer it would have given is "airplane wings generate lift because they are shaped to generate lift". ...only if you omit the parts where it talks about pressure differentials, caused by airspeed differences, create lift? Both of these points are true. You have to be motivated to ignore them. this video