4 ms·

In that case the 2nd theory must be correct but they say its incorrect for some reason. Which doesnt make sense to me at all. They say it's incorrect because i

In that case the 2nd theory must be correct but they say its incorrect for some reason. Which doesnt make sense to me at all. They say it's incorrect because it doesnt account for the airflow on the top. Well the flow on the top doesnt strike the wing (except its forward facing part, the wing is pitched 'up' slightly) so it doesnt push it down. But the bottom flow does push it up (it strikes the whole surface of the wing). Really cant see whats wrong with this simple explanation.

ColinWright 5y ago
The top surface does cause the air to move down. Unless stalled, the air "clings to the top surface" and is pulled down by the shape of the foil. But the simple explanation is wrong because when you actually do the sums the numbers don't add up ... there is more going on.
- gear54rus 5y ago
  OK well we can add that to the simple explanation. If the top airflow is diverted down when it wants to go straight, it would still want to go straight therefore pulling the top surface up, right?.
  - ColinWright 5y ago
    The numbers still don't add up, you still need to account for the pressure difference (lower on top, higher underneath) due to Bernoulli. The "downwash theory" doesn't give enough lift on it's own. So it's more complicated than that.
    - mansoor_ 5y ago
      I think you have a misunderstanding here. You are right that downwash accounts for a tiny proportion of the overall lift, in fact it only become significant close to the wing tips. Downwash (in the context of lift generating wings) refers to the downwards motions of air generated by tip vortices (look-up "induced drag" for more details). This is not the same as the net downwards motion of the air in the wake, relative to the free-stream air. Take for example, an infinite wing (or a 2D wing). Here, there is no downwash but we still generate lift and have a net downwards motion of the air in the wake. You can see this with online fluid simulators for airfoil sections, many of them are 2D.
wbeaty 5y ago
It's wrong because the force on the lower airfoil surface is far smaller than the total lifting force. The flow above the airfoil "sticks" to the airfoil. Since the upper flow is being forced downwards by the curved upper surface, it forces the airfoil to move upwards. What happens if the upper flow doesn't curve downwards? Simple. That's called "stall," and your airplane drops out of the sky. "Stall" is when the upper flow becomes detached, and goes straight back, rather than following the curved upper surface. (The force on the bottom of the airfoil is far too small to keep the plane in the air. Most of the lift is created by the upper surface! That's why "stall" is such a huge deal.)

ColinWright 5y ago

The top surface does cause the air to move down. Unless stalled, the air "clings to the top surface" and is pulled down by the shape of the foil. But the simple explanation is wrong because when you actually do the sums the numbers don't add up ... there is more going on.

gear54rus 5y ago
OK well we can add that to the simple explanation. If the top airflow is diverted down when it wants to go straight, it would still want to go straight therefore pulling the top surface up, right?.
- ColinWright 5y ago
  The numbers still don't add up, you still need to account for the pressure difference (lower on top, higher underneath) due to Bernoulli. The "downwash theory" doesn't give enough lift on it's own. So it's more complicated than that.
  - mansoor_ 5y ago
    I think you have a misunderstanding here. You are right that downwash accounts for a tiny proportion of the overall lift, in fact it only become significant close to the wing tips. Downwash (in the context of lift generating wings) refers to the downwards motions of air generated by tip vortices (look-up "induced drag" for more details). This is not the same as the net downwards motion of the air in the wake, relative to the free-stream air. Take for example, an infinite wing (or a 2D wing). Here, there is no downwash but we still generate lift and have a net downwards motion of the air in the wake. You can see this with online fluid simulators for airfoil sections, many of them are 2D.

wbeaty 5y ago

It's wrong because the force on the lower airfoil surface is far smaller than the total lifting force. The flow above the airfoil "sticks" to the airfoil. Since the upper flow is being forced downwards by the curved upper surface, it forces the airfoil to move upwards. What happens if the upper flow doesn't curve downwards? Simple. That's called "stall," and your airplane drops out of the sky. "Stall" is when the upper flow becomes detached, and goes straight back, rather than following the curved upper surface. (The force on the bottom of the airfoil is far too small to keep the plane in the air. Most of the lift is created by the upper surface! That's why "stall" is such a huge deal.)