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New Methinks that ... yer physics Gots Cuth. :-)
New I could have just Googled
http://boards.straightdope.com/sdmb/showthread.php?t=728502
The rotors of a typical quad-rotor drone have very low inertia, and fixed pitch. They'll come to a stop almost immediately if the power fails.
Oh yeah, fixed pitch. I completely forgot about that.

And in more detail:
The reason quadcopters work so well using such cheap parts is the same reason they autorotate only slightly better than a brick.

The fixed pitch rotors are far cheaper and mechanically simpler than the mechanism a conventional helicopter uses. However, in order to make a fixed patch aircraft hover so well, you need to be able to respond to changes in roll/pitch/yaw extremely rapidly. So you need extremely low inertia rotor blades, relative to the inertia of the quadrocopter body and the torque from the motors.

This low inertia means if you lose power, they will slow to a speed at which they provide negligible thrust very rapidly, and the quadcopter crashes like a brick.

This is also why large quadcopters don't use longer blades, but instead become octocopters and larger.
--

Drew
     Here or sports ... - (drook) - (14)
         nice, want -NT - (boxley) - (2)
             Ooh, idea - (drook) - (1)
                 First thing I thought of reading the article. -NT - (hnick)
         Neat. -NT - (Another Scott)
         And should you be surfing sand dunes - (Ashton)
         First thing I thought of, just >>before<< I got to the complaint about limited flight times... - (CRConrad) - (8)
             Brilliant! - (drook) - (6)
                 Yeah, thought of that too. But is it needed; don't they auto-rotate like autogyros/real helicopters? - (CRConrad) - (5)
                     Doesn't that depend on the mass of the turbine? -NT - (drook) - (4)
                         "Turbine" -YM rotor? Mass - YM keeps spinning by inertia? Didn't think so; aerodynamic thing, innit? - (CRConrad) - (3)
                             Metal vs. plastic - (drook) - (2)
                                 Methinks that ... yer physics Gots Cuth. :-) -NT - (Ashton) - (1)
                                     I could have just Googled - (drook)
             You might have pissed-away a few millions of $zlotys - (Ashton)

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