- Aug 8, 2009
I was saving that till later but since you asked this may be a good time take a swipe at it.But on a wing the lowest pressures happen on the front half of the wing with the smallest radius. Why?
As pointed out in Post #159 the head term of the Bernoulli equation is typically omitted in aerodynamics because of the low density of air and the limited change in pressure with height.
Bernoulli was typically working with straight pipes and the assumption was made that the flow was uniform across the pipe. This is where Bernoulli's equation falls down in aerodynamics. There are other mass related terms to consider. One of those is centrifugal force or centripetal force (I see another conflict brewing) depending on the readers understanding of physics.
Bernoulli does not handle turning airflow. (That was a period!) Bernoulli theorists try to cover that up by pointing out the curvature of the wing and the equal transit time theory, etc. It is close but no joy. The Einstein airfoil discussed in Post #88 was based on that theory and did not work well. The "Vortex Theory of Lift" was invented to compliment, counter and explain that.
Bottom line, the lowest pressure happens on the front half of the wing because that is where the radius is the smallest and the forces needed for the airflow to follow the curvature are the highest. Air molecules going from zero to 150 knots in two inches require one heck of an acceleration. (Stagnation point to max speed over the airfoil versus the nose radius of the airfoil.) If the plane is doing 120 the max airspeed over the airfoil is probably 150 or more.