How do helicopters fly?

Question: How do helicopters fly?

Asked by batman to Douglas, Antonia, Matt, Hugh, Tom on 22 Jun 2010 in Categories: General.
- Matthew Hurley answered on 21 Jun 2010:
  
  The rotors are slightly angled so that as the rotors rotate they push air downwards (a down draught). When this force is enough, the helicopter flies!
- Douglas Blane answered on 22 Jun 2010:
  
  Each helicopter blade is at a slight angle. So as it’s whizzing round the air pushes up on it, just as the air rushing past an aeroplane wing pushes up on it.
  
  That push is called the lift force. The big difference between a helicopter and an aeroplane is that the plane’s wing produces a lift force without the engines running, just because the air is rushing past it. So a plane will glide for quite a long way with no power.
  
  But if a helicopter engine fails the blades stop moving and there’s no lift force. A helicopter glides through the air about as well as your teacher does.
  
  That’s why helicopters are much more dangerous than aeroplanes. A helicopter produces no lift force if the engine fails. It just falls out of the sky.

Question: How do helicopters fly?