Thursday, April 09, 2015

How Do Airplanes Fly?

I get asked this often, strangely enough. So it is nice to have a quick illustration via a video on how it works.



Douglas Natelson said...

I'm glad they mentioned angle of attack! Freshman physics texts sometimes imply that the Bernoulli equation (which actually has some serious restrictions in its applicability) is solely responsible, and if that were so then airplanes could never fly upside-down.

John Palkovic said...

My two-cent explanation: "A wing throws air down." The reaction force from the downward-bending airstream is lift.

Much of the lift of an airfoil is generated by the flow over the top curving downward. The video is good for a layman's explanation. The wikipedia article on lift is also good. It has a nice animated gif that illustrates how much faster the air moves over the upper surface of the wing.

The fallacy in the freshman physics texts is called the "transit time fallacy." The erroneous explanation involves some hand-waving about packets of air separating at the leading edge of the airfoil and then taking equal time to transit the upper and lower surface of the wing, which is just plain wrong. Ih also fails to explain how aerobatic planes can fly upside-down. They have symmetric airfoils, like jet fighters do.