See this thread for more information in 2012.
@Paul G.: In order to be efficient, you need a large rotor disk area. Full-size helicopters would be extremely hazardous on the ground if the rotor was not at least 7 feet high (for obvious reasons). This does make them less stable, but natural disk coning (the rotors achieving a natural equilibrium between centrifugal force and thrust pushing the tips upward - adding a little dihedral effect) restores some of this. Ultimately, however, keeping a big ship from darting off to who-knows-where is reliant upon piloting skill and far greater control responsiveness than can be achieved with a fixed-pitch multicopter.
(eh, better 2 years old than never)
Yes, but there are also other elements at play. One thing is that helicopters also have better aerodynamics that quads. They are simply less affected by the wind. Also, i think the rotor disk offers better control reactions for reasons I don't fully understand.
At the end of the day, the proof is in the pudding. Check this out:
My quad copter could barely fly in the same conditions. All I could manage was a controlled crash. After a number of attempts at landing, the best I could do was getting it momentarily level at 3 feet, and then chopping the throttle.