# How much effect does the Bernoulli effect have on lift?

I understand that the Bernoulli effect is a flawed explanation for the cause of lift, and does not cause much at all, but how much?

Is there any experimental data on the force caused by the Bernoulli effect? Maybe implicitly through data of the pressure difference between the top and underside of an aeroplane's wings. After that, I assume I could (crudely approximating the pressure to be acting perpendicularly to the flight direction) use $\Delta P A$ to work out the net force on the plane.

Perhaps there is another way to quantitatively analyse the extent to which the Bernoulli effect causes lift.

Edit: see this short cartoon (content similar to Mike Dunlavey's answer).

-
Yeah, that video is pretty good. The only question is it refers to the Coanda effect above the wing. Denker explains why that's not right. –  Mike Dunlavey Jun 21 '13 at 12:39
–  Ben Crowell Jun 21 '13 at 13:26

There's no problem with the Bernoulli effect, only with the way it's understood and explained. It's usually explained with mistakes, like the need for asymmetrical airfoil and equal flow time above and below, and without mentioning the need to deflect the direction of airflow.

Here's the best light-math explanation I've seen. Also study this section that directly answers your question.

EDIT: It is easy to find wrong pictures like this:

as opposed to a correct one like this (from the link above):

So the answer to your question is: All of the lift depends on the Bernoulli principle, because speed and pressure are in trade-off, but the physics need to be correctly understood.

-
It is equally true that all the lift depends on the change in airflow direction. You have to calculate one or the other but not both. –  Marty Green Jan 18 '13 at 17:53
@mike Thanks Mike. I'm not used to people agreeing with me. –  Marty Green Jan 18 '13 at 18:46
@Alyosha: There really isn't a larger thing. If you really want basics, you can go back to Newton's laws. Bernoulli's principle is just a consequence of Newton's laws. –  Mike Dunlavey Jan 18 '13 at 19:47
@Alyosha: Pretend you're a wing. You can only be lifting if the pressure underneath exceeds the pressure above. Then pretend you're a slug of air. This wing comes along, cuts you in half, then pulls/pushes you downward. Same thing. –  Mike Dunlavey Jan 18 '13 at 22:05
+1 Very good answer. I've seen many comments/answers on this site that unnecessarily bash Bernoulli because the author equates Bernoulli with the incorrect "equal time" explanation. Glad to see someone else trying to set the record straight. –  OSE Jan 27 at 20:17