No one knows how airplanes fly
scientificamerican.comNot a very good article at all. I'm beginning to consider calling it the 'Non-Scientific American' magazine.
So tell me what causes lift when there is a zero angle-of-attack? If it's not Bernoulli's Principle?
There are TWO causes of lift: both Bernoulli's Principle AND a (limited) Angle of Attack. These combine arithmetically to produce lift. Engine power (thrust) produces speed of the wing through the air.
NOTE: Angle of Attack is measured against the relative air-flow. It has nothing to do with the angle of the wing relative to the ground.*
If the countering weight plus drag elements are less than the lift plus thrust elements the wing will fly. If the weight plus drag elements are greater than the lift plus thrust elements, the wing won't fly.
* Assume a powerful jet plane with engine-thrust greater than its own weight. That will allow it to climb vertically at 90 degrees to the ground. Assume the wings on that plane are fixed at zero degrees angle to the longitudinal axis of the plane.
Q: If the plane is climbing vertically (90 degrees), what is the angle of attack of the wings of that plane?
A: Zero degrees.
How I hate that article. Poor John D. Anderson will forever be associated with this ridiculous claim that no one knows why aircraft fly. Also note, that he does not say that at all:
“What Anderson said, however, is that there is actually no agreement on what generates the aerodynamic force known as lift. “There is no simple one-liner answer to this,” he told the Times.
Not only does he not say that no one understands lift, he also doesn’t say that there is no agreement. What he says is that there is no simple answer. That means something completely differently.
Edit: there are two fundamental ways to describe lift: as the resulting force from integrating pressure over the surface of the wing (here discussed in a distorted way as ‘Bernoulli’), and a control volume way of Newton’s 3rd axiom, where air is pushed downwards by the wing and the wing in turn experienced a force in the opposite direction.
There is no mystery. Both views are equivalent. What is hard is to predict the exact force, as one would have to predict the flow field around the wing.
Well, there is at least a third way to produce lift, although maybe I shouldn’t call it lift.
The engines themselves can also produce a lifting action by their sheer power. Technically that is thrust, but insofar as that force has a vertical component, it contributes to lift
That’s also Newton’s 3rd.
Flight Without Formulae by A.C. Kermode and Thrust for Flight by W. Thomson are two of my favorite books on flight mechanics and propulsion. Books that I thoroughly recommend for anyone to read before reading Anderson. Both are in the same vein: no formulae. I wish we had a book for software like that. Software without code.
Two different theories are commonly proposed to explain lift, and advocates on both sides argue their viewpoints in articles, in books and online.
Can we also say that no one knows how fish swim?