h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Please kill me for being pedantic or stupid, but does the rotorblades of the helicopter generate forces by moving through the air? And not as written by moving the air?

Short answer, I don't know!
This is one of those things that has been discussed for a long time and I have never seen a satisfactory solution to the argument.
The rotors produce lift by their movement through the air, this is what actually lifts the helicopter up. However, there is a school of thought which suggests that the lift is actually due to the reaction to the air that is displaced downwards,
So it's not a stupid question!
My own belief, and the one that I was taught, is that lift is produced by the rotors movement and that the displacement of the air is a by-product.

This was a long time ago, however!

The rotor blade of a helicopter is the same shape as an aeroplane wing. It is an airfoil. The blade is shaped such that the upper surface is curved and the lower one flat. As the blade cuts throught the air, the air above the blade has to travel further and faster over the surface than the air below the wing, and therefore has to travel faster. This causes a pressure differential with a lower pressure above the wing than below, causing lift.

For more information search for Bernoulli's Principle at all good search engines, or take a look here http://www.allstar.fiu.edu/aero/fltmidfly.htm
http://encarta.msn.com/find/concise.asp?ti=021cb000

fogot to say that the downwash is just a by product of the motion of the blades through the air and only assists the lift at ground level.

Fatman
Ex Air Cadet of 9 years.

Thats pretty well what I was taught many years ago.
I suspect that the argument is a hangover from prop driven aircraft, where the commonly held opinion was that it is the mass of air being moved backwards that does the trick. However, as a propellor is an aerofoil it can be proved that it develops lift on its forward facing surface. Indeed, in wind tunnel tests the efficiency of a prop can be obtained measuring this lift and applying elements of Bernouilli's theorems.


I am now quite happy to leave all these arguments to those who have the facilities to test their ideas!