[dan_hawkins]

> No. What causes lift is the differential in pressure between the top and the bottom surface of the wing.

How do you explain airplanes that can fly with wing with symmetrical cross-section profile?

How do you explain airplanes flying upside-down?

[fransje26]

To create lift with a symmetrical airfoil, you are going to need a non-zero angle of attack. You can see the effect of a varying angle of attack on a symmetric NACA 0012 airfoil here [0].

The following plot shows the pressure distribution over a wing at 3 different angles of attack [1]. As you can see from the first plot, some lift is created at -8 degrees AOA, but clearly a lot less than the +10 AOA example, as that airfoil is optimized for positive angles of attack.

[0] https://www.youtube.com/watch?v=8uMlDL9HiaY

[1] http://avstop.com/AC/FlightTraingHandbook/imagese0.jpg

[dan_hawkins]

Explanation based on Bernoulli effect requires longer path of air taking on top than on the bottom of the airfoil to create speed/pressure difference. With symmetrical airfoil both paths are the same regardless of the angle of attack. So when you mention AoA you implicitly lead to the explanation that lift, in majority, is not based on the Bernoulli effect.

I've read excellent article debunking the Bernoulli effect and lift many years ago, I'm not sure I can find it again...

[fransje26]

Explanations based on the Bernoulli effect are trying to explain a speed differential by pretending that two particles that were separated on the leading-edge of an airfoil, to then travel one above the airfoil, one below, would then rejoin at the trailing edge of the airfoil. And so, if you were to change the upper-camber of the airfoil, the flow on the upper part would need to accelerate to be able to join the trailing edge at the same time. And that would create a lower pressure, therefore lift.

The nonsensical part of this model is that a particle on an upper streamline has anything to do with a particle on a lower streamline and that it is trying to keep up with it. Not so of course.

But the lift created by a pressure difference due to a locally faster flow still holds.

> So when you mention AoA you implicitly lead to the explanation that lift, in majority, is not based on the Bernoulli effect.

For a NACA 0012, you'll need an AoA, to have a faster flow on the upper part of your airfoil, as it it symmetric. Other airfoils are perfectly fine creating lift at 0 AoA.

[bdamm]

The Bernoulli effect only contributes to making wings more efficient. It isn’t fundamentally why lift occurs.

You can make almost anything fly if you have enough power and a tail. But how efficient will it be? Not as efficient as an airfoil that takes advantage of all the fluid motion properties.

[dan_hawkins]

I think you wanted to respond to the parent comment. My questions have been a lead to debunk myth that the major contributor to the lift is the Bernoulli effect.

[bbojan]

> How do you explain airplanes that can fly with wing with symmetrical cross-section profile?

> How do you explain airplanes flying upside-down?

Angle of attack is what causes lift. If you have a surface angled against the relative wind, it will produce lift.

[dan_hawkins]

I know all of that. I wanted to provoke parent commenter to let them see that the Bernoulli effect doesn't explain my two examples.