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Comment by bogdan | Hacker News Reader

Related to this, I read this article on my commute last week.

https://www.scientificamerican.com/article/no-one-can-explai...

I remember showing that article to a colleague of mine who became Very. Angry. Indeed.

They said that all the articles and explanations that are being quoted then picked apart and shown to be inadequate are, were, and always have been simplifications intended to give the non-technical person some insight into what's going on, but have never been intended to "explain flight".

My colleague went on to say that starting with each of the simplified and incorrect descriptions, one can gradually refine each, then successively combine into a bigger picture, until one ends up with a description that "feels right" and agrees with all the numerical simulations.

But they've also stopped trying to be helpful pretty much exactly because of articles like this, that take half-truths as if they are intended to be complete explanations, then debunks them.

So don't read this article from Sci.Am. and believe it uncritically.

He's wrong. All those explanations ARE intended to explain flight! They're given to professional pilots without qualifiers, presented as if they were complete explanations. (If they weren't, then the controversy would instantly evaporate.)

This situation is quite different than, say electrons of atoms. First we learn that atoms are like little solar systems ...but then also hear that this is oversimplified (wrong,) and that we'll have to learn QM and probability-clouds in order to have a correct explanation of atoms' electrons.

That's NOT done with lifting-force explanations. Pilots aren't being taught that the explanations are wrong, oversimplified, and only the professional fluids experts can attain the "bigger picture" which removes all the mistaken concepts.

Did your angry colleague supply a simple correct explanation, to replace the wrong ones in the article? "Feels right" is a cop-out. Pilots don't want hand-wavy fuzz, or some experts who insist "it's just too complicated for beginners."

How about this instead...

First we explain a hovering helicopter. It's an air pump. It pulls air inwards from all directions, then blasts it downwards. Next, shove the helicopter rapidly sideways. That's how wings actually work: they pull air in from all directions, then fling it downwards. (But this is hard to notice, since the downwash-plume of an airplane is all stretched out, and it even seems purely horizontal. It's not.)

Heh, wings are the same as VTOL jet aircraft! But the turbine-blades in the VTOL engine have broken loose and flown off alone. Yet each little blade is still acting as an air-pump, and pulling air inwards from all directions, and flinging it downwards, producing a downwash, a momentum-carrying "exhaust plume."

This feels like a motte/bailey tactic. I remember clearly being taught the equal-transit-time theory as a kid, and it was taught as actual fact, not a simplification. I was uneasy with it but couldn't vocalize why (it didn't occur to me to ask why planes can fly upside down).

If it is meant as a simplification, many HS teachers have not gotten the memo.

Substantially everything taught as fact in HS science is a simplification or a poorer approximation of a better answer though, isn't it?

In elementary school I remember hearing the planets move in CIRCLES in THE SAME PLANE around the Sun.

In an atom, electrons would also move around the nucleus like a mini-solar system.

For seven and eight years old children, it's a fair simplification, I guess.

If I taught elementary school I would explain that planets move nearly in circles and often in the same plane.

It's not that elementary school children can only handle absolutes.

Ocean waves work like this: water molecules are piled up in humps, and all the molecules slide across the ocean, while the water underneath the humps does not move. If you poured some dye into the waves, the water-humps would carry it along.

Sound works like this: vibrating objects put energy into air molecules, then the molecules zoom all the way to your ears at the speed of sound. They put the sound vibrations into your eardrum. Then they zoom all the way back to the vibrating object. Then repeat.

Uh, that's all wrong. Not oversimplified. Just wrong. (Airfoil explanations are similarly wrong. Not just oversimplified.)

> I was uneasy with it but couldn't vocalize why

I can vocalize why I am uneasy with it: why does the separated airflow need to meet back at the same point? How does the top-air know it needs to hurry to keep up with the bottom-air?

I mean, there might be a reason for that, but I would rather someone explained that instead of waving their hands. :-)

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