Pictures are worth million words... so I give you zillions of words instead. Watch this video from NightFlyyer on YouTube

http://www.youtube.com/watch?v=buMlFzMhcKc&feature=sub

Single balded props ARE the most efficient. The problem is the impracticality of manufacture, particularly w.r.t. balancing.

Great video and idea.

Even tho the single prop may fly as long the prop is balanced that is not a big.. thing, the concern is the out put if you see compared to the input is less means this is less efficient plus more power loss whatever the power source it may be battery, glow, gas. This is my experience of what i think of a single prop.

I think its entirely different... the thrust should be more, as there is no turbulence... no?

As said earlier by Sushil, single blade is better than twin, twin is better than three and so on so forth..