Expert: Mark Janus - 6/28/2010

Question
There is a concept which I think should be simple, however I cannot understand it. What would be the difference between the lift created by a helicopter propeller and the lift created by a jet engine turned on its end so that the air was flowing towards the ground?

Answer
When the dust all settles (no pun intended), both methods do the same thing....   they both push the air down to hold the craft up...  in general a helicopter pushes more air slower than a jet which pushes less air faster, to accomplish the same thing....  recall Newtons second law...  

F (force) = M (mass) x A acceleration  

F is the force equal to the weight of the craft, M is the mass of air moving through the machine, and A is how much that air has been accelerated...

That's the basics of what's going on...

Thanx,
mj