2 ms·

What do you mean, symmetric wings generate no lift? There are plenty of lift-generating symmetric airfoils out there. Your link indicates that Einstein fell vi

What 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.

cryptonector 9y ago
Symmetric wings generate no lift at a neutral angle of attack. At a positive angle of attack they do generate lift, naturally, but the point is that you have entrainment with NO Bernoulli effect pressure difference.
- mikeash 9y ago
  If they’re generating lift, there’s a pressure difference. If there’s a pressure difference, it’s coming from a speed difference. When you say there’s entrainment with no Bernoulli effect pressure difference, are you talking about zero angle of attack, or non-zero? At zero I don’t see the relevance, and at non-zero it’s just wrong.
  - cryptonector 9y ago
    "there is a force" != "it's the Bernoulli effect" Here are a few pages that explain that the Bernoulli effect isn't the full explanation https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html https://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html https://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html https://www.newscientist.com/blogs/nstv/2012/01/physics-in-a-minute-how-wings-really-create-lift.html https://www.newscientist.com/blogs/nstv/2012/01/physics-in-a... Here's a page saying it ain't the Coanda effect, but ultimately that the Bernoulli effect is only a small part of lift: https://www.quora.com/What-are-the-differences-between-Bernoullis-Principle-and-the-Coanda-effect-when-we-apply-them-on-aircraft-wings-1 https://www.quora.com/What-are-the-differences-between-Berno... But perhaps the best resource I've seen so far is John Denker's page on this topic: http://www.av8n.com/how/htm/airfoils.html http://www.av8n.com/how/htm/airfoils.html You'll trivially find lots of other pages that say it is the Bernoulli effect, but near as I can tell, they are wrong.
    - mikeash 9y ago
      From your last link: > We have seen that several physical principles are involved in producing lift. Each of the following statements is correct as far as it goes: > * The wing produces lift “because” it is flying at an angle of attack. > * The wing produces lift “because” of circulation. > * The wing produces lift “because” of Bernoulli’s principle. > * The wing produces lift “because” of Newton’s law of action and reaction. > We now examine the relationship between these physical principles. Do we get a little bit of lift because of Bernoulli, and a little bit more because of Newton? No, the laws of physics are not cumulative in this way. > There is only one lift-producing process. Each of the explanations itemized above concentrates on a different aspect of this one process. The wing produces circulation in proportion to its angle of attack (and its airspeed). This circulation means the air above the wing is moving faster. This in turn produces low pressure in accordance with Bernoulli’s principle. The low pressure pulls up on the wing and pulls down on the air in accordance with all of Newton’s laws. In other words, it is the Bernoulli effect. It is also circulation, and the rest. That does not mean it is partially Bernoulli and partially other things. Each separate explanation individually explains 100% of lift, they're just different ways of explaining it. It's like calculating the speed of an object dropped from a height by integrating gravitational acceleration over time versus calculating changes in potential and kinetic energy. Does acceleration account for some part of the final speed, and energy accounts for another part? No, each one is individually responsible for 100% of the result. They're just different ways of looking at it.
      - cryptonector 9y ago
        Ay, I hadn't reread his page, and only (mis)remembered it. I'll have to reread it. It's still the case though that that NASA page says it's not about the air above going faster than the air below. It's at least the case that there is disagreement.
        mikeash 9y ago
        The NASA page says it’s not about the air going faster above due to a requirement to traverse the airfoil in the same amount of time as the air below. The popular misconception of airfoils states that the upper path is longer than the lower path. This means the air taking the upper path must move faster in order to meet the air taking the lower path. Faster means lower pressure means lift. This is incorrect. But it’s very important to understand why it’s incorrect. It’s true that air moves faster over the top, that this produces lower pressure on top, and that this produces lift. The incorrect part is thinking that this all happens because the air on top takes a longer path faster in order to meet up with its friends from below. In fact, the air moves over the top much faster than this idea would indicate. Unfortunately, a lot of people have learned about this fallacy and taken away the wrong lesson, that lift is mostly unrelated to air moving faster over the top of the wing, or to lower pressure on top of the wing. When you’re thinking that way, it’s easy to misread sources debunking the “equal time” theory.

cryptonector 9y ago

Symmetric wings generate no lift at a neutral angle of attack. At a positive angle of attack they do generate lift, naturally, but the point is that you have entrainment with NO Bernoulli effect pressure difference.

mikeash 9y ago
If they’re generating lift, there’s a pressure difference. If there’s a pressure difference, it’s coming from a speed difference. When you say there’s entrainment with no Bernoulli effect pressure difference, are you talking about zero angle of attack, or non-zero? At zero I don’t see the relevance, and at non-zero it’s just wrong.
- cryptonector 9y ago
  "there is a force" != "it's the Bernoulli effect" Here are a few pages that explain that the Bernoulli effect isn't the full explanation https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html https://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html https://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html https://www.newscientist.com/blogs/nstv/2012/01/physics-in-a-minute-how-wings-really-create-lift.html https://www.newscientist.com/blogs/nstv/2012/01/physics-in-a... Here's a page saying it ain't the Coanda effect, but ultimately that the Bernoulli effect is only a small part of lift: https://www.quora.com/What-are-the-differences-between-Bernoullis-Principle-and-the-Coanda-effect-when-we-apply-them-on-aircraft-wings-1 https://www.quora.com/What-are-the-differences-between-Berno... But perhaps the best resource I've seen so far is John Denker's page on this topic: http://www.av8n.com/how/htm/airfoils.html http://www.av8n.com/how/htm/airfoils.html You'll trivially find lots of other pages that say it is the Bernoulli effect, but near as I can tell, they are wrong.
  - mikeash 9y ago
    From your last link: > We have seen that several physical principles are involved in producing lift. Each of the following statements is correct as far as it goes: > * The wing produces lift “because” it is flying at an angle of attack. > * The wing produces lift “because” of circulation. > * The wing produces lift “because” of Bernoulli’s principle. > * The wing produces lift “because” of Newton’s law of action and reaction. > We now examine the relationship between these physical principles. Do we get a little bit of lift because of Bernoulli, and a little bit more because of Newton? No, the laws of physics are not cumulative in this way. > There is only one lift-producing process. Each of the explanations itemized above concentrates on a different aspect of this one process. The wing produces circulation in proportion to its angle of attack (and its airspeed). This circulation means the air above the wing is moving faster. This in turn produces low pressure in accordance with Bernoulli’s principle. The low pressure pulls up on the wing and pulls down on the air in accordance with all of Newton’s laws. In other words, it is the Bernoulli effect. It is also circulation, and the rest. That does not mean it is partially Bernoulli and partially other things. Each separate explanation individually explains 100% of lift, they're just different ways of explaining it. It's like calculating the speed of an object dropped from a height by integrating gravitational acceleration over time versus calculating changes in potential and kinetic energy. Does acceleration account for some part of the final speed, and energy accounts for another part? No, each one is individually responsible for 100% of the result. They're just different ways of looking at it.
    - cryptonector 9y ago
      Ay, I hadn't reread his page, and only (mis)remembered it. I'll have to reread it. It's still the case though that that NASA page says it's not about the air above going faster than the air below. It's at least the case that there is disagreement.
      - mikeash 9y ago
        The NASA page says it’s not about the air going faster above due to a requirement to traverse the airfoil in the same amount of time as the air below. The popular misconception of airfoils states that the upper path is longer than the lower path. This means the air taking the upper path must move faster in order to meet the air taking the lower path. Faster means lower pressure means lift. This is incorrect. But it’s very important to understand why it’s incorrect. It’s true that air moves faster over the top, that this produces lower pressure on top, and that this produces lift. The incorrect part is thinking that this all happens because the air on top takes a longer path faster in order to meet up with its friends from below. In fact, the air moves over the top much faster than this idea would indicate. Unfortunately, a lot of people have learned about this fallacy and taken away the wrong lesson, that lift is mostly unrelated to air moving faster over the top of the wing, or to lower pressure on top of the wing. When you’re thinking that way, it’s easy to misread sources debunking the “equal time” theory.