You probably think that a wing lifts an aeroplane because the airflow moving over the top has a longer distance to travel and “needs to go faster to have the same transit time as the air travelling along the lower, flat surface”. Well, you are wrong.
University of Cambridge’s Professor Holger Babinsky was so frustrated that everyone seems to believe this that he thought he should demonstrate that it is absolutely wrong:
I don’t know when the explanation first surfaced but it’s been around for decades. You find it taught in textbooks, explained on television and even described in aircraft manuals for pilots. In the worst case, it can lead to a fundamental misunderstanding of some of the most important principles of aerodynamics.
So he created this one-minute video that actually shows what happens to the air as it travels the wing. It’s a quite simple and clever demonstration of how air actually goes around the wing.
What actually causes lift is introducing a shape into the airflow, which curves the streamlines and introduces pressure changes — lower pressure on the upper surface and higher pressure on the lower surface. This is why a flat surface like a sail is able to cause lift — here the distance on each side is the same but it is slightly curved when it is rigged and so it acts as an aerofoil. In other words, it’s the curvature that creates lift, not the distance.
There you have it. It’s the curvature, not the distance. He hopes the video will debunk that stupid myth once and for all.
RooBoy
Wednesday, January 25, 2012 at 8:10 AMI was under the belief that this was already well understood? Any one I know who flys knows this principle throughly, its what keeps you in the air after all… The science behind wind stall is not new, but this is a good video demo of the affect.
RooBoy
Wednesday, January 25, 2012 at 8:11 AMwind = wing.. sorry typo
Sam D
Wednesday, January 25, 2012 at 8:26 AMI actually had a secondary school physics teacher try to explain something different again (which was very wrong).
z3d
Wednesday, January 25, 2012 at 8:50 AMwhat i don’t like about this video is that the basic concept of a wing is that it is flat at the bottom and curved on the upper side. by putting it in the wind tunnel at a such an angle demonstrates drag more than lift. if you’re going to demonstrate to people airflow over a wing, you need to start with level wing. you introduce angle of attack with wings to generate more lift for a given wing size, but also significantly more drag with every degree of angle…. but that’s a different subject altogether.
Rod
Wednesday, January 25, 2012 at 10:01 AMIt’s not just the Bernoulli principle at work (where higher speed air creates lower pressure), it’s also the Coanda Effect, which is the air above the wing wanting to follow the surface and cause a change in direction of the airflow.
Telextial
Wednesday, January 25, 2012 at 10:11 AMI’ve never heard of of the supposed myth. Then again, educational “games” in my childhood may have had something to do with it.
Dave
Wednesday, January 25, 2012 at 2:15 PMwould like to see the same thing but with a sail
Hunter
Thursday, January 26, 2012 at 4:22 AMIt would be interesting to see the demonstration with symmetrical and asymmetrical airfoils, highly cambered airfoils, and flat plates. I have made many balsa gliders and paper airplanes that fly marvelously well with flat-plate wings. Clearly, “curvature” of the airfoil is not an absolute necessity for generating lift. I also agree that seeing the progression of changes in airflow from chord parallel to airflow up to stall would be instructive.