Expert: Mark Janus - 11/19/2010

Question
Hi,
I am bit confused on how aeroplane fly.  Some says it gets lifted caused by reaction force.  It is based on Newtom's law of motion. When it pushes air, the air pushes it.  Some say it gets lifted caused by Bernaulli's principle. Can you please explain? (No mathematics, only concept please)

Answer
Both views are correct....  If you are considering viewing from a distance, basically Newton's third law is the explanation....  If on the other hand you are examining the airflow locally very near the airplane, Bernoulli's equation (and the differences in pressure) holds...  

Basically the difference in pressure is the motive force that both pushes the air down and the airplane up....

Hope this helps,
mj