6 ms·
Even a nautil.us article is not spared from making this classic mistake: > Spinning in vortices, air could travel more quickly now above the long narrow wing
by 21 9y ago
Even a nautil.us article is not spared from making this classic mistake:
> Spinning in vortices, air could travel more quickly now above the long narrow wing than below it, creating the pressure difference that would lift them into the skies.
- mikeash 9y agoWhat mistake? The classic mistake is to assume air travels faster over the top than the bottom because the top path is longer and they must take equal time. In fact air does travel faster over the top, quite a bit faster than the equal time fallacy would indicate.
- jordanb 9y agoI wonder if there's a word for this; where people learn that one bit of common knowledge is a fallacy and then "overcorrect" by assuming related things are also wrong. Perhaps "meta fallacy?"
- mannykannot 9y agoI do not know if there is a name for it, but it comes from not fully understanding why the original fallacy is fallacious.
- ithkuil 9y agoCargo cult fallacy?
- theophrastus 9y agoThe legal term, which presupposes the fallacy, is: Falsus in uno, Falsus in omnibus[1] [1] https://en.m.wikipedia.org/wiki/Falsus_in_uno,_falsus_in_omnibus https://en.m.wikipedia.org/wiki/Falsus_in_uno,_falsus_in_omn...
- 21 9y agoThe mistake would be that this is what provides the lift force, as stated in the quote. If this was so, birds wouldn't need to flap, which is the actual lift generator (pushing air down).
- mikeash 9y agoThe pressure difference pushes air down. It does provide the lift force. Birds flap to create thrust, not lift. Surely you’ve seen birds flying without flapping?
- 21 9y ago> Surely you’ve seen birds flying without flapping? Isn't that when they just "ride" the winds? The wind pushing against the back of their wings which is hold angled thus pushing it higher (like a boat sail).
- mikeash 9y agoSorry, I don’t really understand what you’re saying here. Birds and airplanes work on the same principles. Airflow over the wings produces lift. That airflow also produces drag, which must be counteracted with thrust to maintain altitude. The only difference is that birds produce thrust by flapping, and airplanes produce thrust with engines. A non-flapping bird is equivalent to an airplane with the engines shut off.
- 21 9y agoI was referring to this theory, which NASA calls wrong: https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html Most interestingly, NASA also calls wrong what you seem to defend, or maybe there are some subtleties that I'm missing: https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html
- mikeash 9y ago
- cryptonector 9y agoAir going over the top of a wing more quickly than the air below is NOT what causes lift. What causes lift is "entrainment" plus the wing shape redirecting entrained air downwards at the trailing edge. By Newton's third law of motion, the acceleration of air downwards by the wing implies the acceleration of the wing upwards (and with the wing, the airplane).
- dilyevsky 9y agoFalse. Both Bernoulli Principle and Newton's 3rd Law explanations are correct - https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html https://www.grc.nasa.gov/www/k-12/airplane/bernnew.html
- cryptonector 9y agoCorrect, but the biggest factor is the entrained air.
- mikeash 9y agoYou can’t redirect air downward without a pressure differential. You can’t have a pressure differential without a speed differential. “Air goes faster on the top of the wing,” “pressure is lower on top of the wing,” and “air is pushed downward” are physically equivalent statements.
- cryptonector 9y agoThat's not how it works. It's almost all entrainment and very little Bernoulli effect. The proof lies in symmetric wings, which generate no lift but still entrain air. Einstein famously designed what he thought should be a very good wing based on the Bernoulli principle, and it turned out to not work, and if you look at it[0] you'll see why... [0] https://www.google.com/search?&q=einstein+wing+design https://www.google.com/search?&q=einstein+wing+design
- mikeash 9y agoWhat do you mean, symmetric wings generate no lift? There are plenty of lift-generating symmetric airfoils out there. Your link indicates that Einstein fell victim to the equal time fallacy. While the equal time fallacy supposes that lift is generated because air moves faster and generates a pressure differential, air moving faster to generate a pressure differential does not necessarily imply the equal time fallacy.