Busting an aerodynamic myth -- Planes don't fly due to Bernoulli Effect

[Quazar]

Originally Posted by winkosmosis

Read the NASA article. The Bernoulli Effect is not what makes the plane fly. The air flows faster over the top of the wing, yes, because of the angle and the downward curve at the rear-- airflow on the bottom is compressed because it hits the underside and slows down relative to the plane. But the air speed difference is a tiny tiny contributor. It's not the majority or even a major portion of lift.

Redirection of flow is what creates lift.

If you know of a plane that can fly at 0 degrees wing pitch, post it.

My statement is that the Burnulli principal come into play, it is the principal that creates the upwash.

I think you are confuning the Bernoulli effect with the longer path effect. Bernoulli states that the faster it moves (air or water for example) the less pressure it has.

Even in the article it states-
"

{The upper flow is faster and from Bernoulli's equation the pressure is lower. The difference in pressure across the airfoil produces the lift.} As we have seen in Experiment #1, this part of the theory is correct. In fact, this theory is very appealing because many parts of the theory are correct

"

When in effect the Bernoulli effect causes, among other things:
The air is bent around the top of the wing, it pulls on the air above it accelerating that air down, otherwise there would be voids in the air left above the wing. Air is pulled from above to prevent voids. This pulling causes the pressure to become lower above the wing. It is the acceleration of the air above the wing in the downward direction that gives lift.

You are confuning the "equal transit" theory with Bernoulli, Equal transit used the Bernulli principal, but when that was found to be false, what they found was the principal still held true, just in a different way.

[winkosmosis]

No, I understand that part. That's what I said in my original post.

My point is that it's the pulling of air downward and the resulting low pressure at the top that creates lift, not the speed difference itself.

I'm emailing the NASA guy listed at the bottom, because I think section 3 of that article is unclear. In section 1 he specifically states that it's the turning of flow that creates lift, then he says you can explain lift with the air speed difference. How can it be both exclusively? You should have to add those two together.

[winkosmosis]

Originally Posted by dcb

I'm not quite ready to discount the bernoulli principle as being a significant contributor to lift.

One of my favorite RC sailplanes in my little fleet uses a SD7037 airfoil (pictured below). It is fast and has good penetration upwind (important when you don't have a motor), but it doesn't like slow very much.

But what I want to point out is that here it is drawn in normalized position, the leading and trailing edges are on the 0.00 line. So that when the air splits at the leading edge at this angle of attack, it should "rejoin" at the same exact height at the trailing edge. If there were no bernoulli, this would not create lift.

But it is creating quite a bit of lift. The zero lift angle of attack for the SD7037 is actually -3.29 degrees, meaning you have to lower the leading edge to get this to stop making lift.

I'm not sure the normalized position based on the leading edge and trailing edge makes sense. We know that aerodynamics at the rear is more important than the front right? So why can't the rear-facing slope of the wing be more important than the front-facing slope? That is the part where flow gets pulled downward to meet the wing, which I think is how most lift gets created.

In order to reach zero lift, you have to angle that rear-facing slope so that it's balanced by downforce on the rear-facing bottom surface.

[gone-ot]

Originally Posted by Piwoslaw

If gravity can be explained by Intelligent Falling, then lift could be the effect of Intelligent Ascending, right?

...does that make bouyancy the "toilet neutrality"?

[dcb]

I'm a little confused. You specifically asked for 0 degrees here:

Originally Posted by winkosmosis

If you know of a plane that can fly at 0 degrees wing pitch, post it.

then you say that position doesn't make sense...

Originally Posted by winkosmosis

I'm not sure the normalized position based on the leading edge and trailing edge makes sense.

My point is that this, and most asymmetrical airfoils, make lift at 0 degrees, so it is simply a matter of going fast enough and/or being light enough before you have a plane that can fly at 0 degrees wing pitch.

What do you think is redirecting the air on top of the wing?

[winkosmosis]

Originally Posted by dcb

I'm a little confused. You specifically asked for 0 degrees here:



then you say that position doesn't make sense...



My point is that this, and most asymmetrical airfoils, make lift at 0 degrees, so it is simply a matter of going fast enough and/or being light enough before you have a plane that can fly at 0 degrees wing pitch.

What do you think is redirecting the air on top of the wing?

The Coanda effect is redirecting air, and as I understand that is related to the Bernoulli effect. But it's not the Bernoulli effect itself that is creating the lift. If airflow left the back of the wing at 0 degrees, you could attribute lift to Bernoulli, but lift requires airflow leaving the wing at a downward angle.

That's why the 0 degree plane you use doesn't apply IMO. Because what matters are the angles at the rear of the wing.


You said zero lift happens around -3 degrees. Would that happen to be the angle at which the top and bottom trailing edges are equal angles from horizontal?

[winkosmosis]

[dcb]

Originally Posted by winkosmosis

You said zero lift happens around -3 degrees. Would that happen to be the angle at which the top and bottom trailing edges are equal angles from horizontal?

No, that is the definition of zero degrees angle of attack. The same amount of air is going over the top as the bottom (more or less)

[dcb]

Originally Posted by winkosmosis

yes, that is (about) the zero lift angle of attack for that airfoil.

[skyking]

you need to get your terms straight. His diagram shows a wing with a line through it. This is the chord line and that is what is used to define angles of attack and angles of incidence.
By definition that wing produces lift at a 0 degree angle of attack.
Many sailplane wings will fly at 0 and slight negative angles of attack.
The angle of attack is the angle formed by the chord line and relative wind.
The angle of incidence if formed by the the chord line and the longitudinal axis of the fuselage.