why aren’t there human-piloted quad-rotors?
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* Safety: You have four rotors. Two rotate clockwise and two anticlockwise; this controls the way the whole vehicle rotates. If you lose just one rotor then, to avoid spinning, you have to power down the diagonally opposite rotor to balance the spin. So a quadcopter has to be powerful enough to maintain altitude on only half its rotors … which is hard.
* The square-cube law: If you just scale up a toy quad-copter by a factor of 10 then its weight will go up by a factor of 1000 (because you’re multiplying length, width and height each by 10). But the strength only goes up by a factor of 100, so it’s now very fragile. The propeller area also goes up by a factor of 100 so you’d need to scale up the rotor speed by 10. Small, fast rotors are very inefficient; conventional helicopters use the largest practical rotors to keep the down-draft slow. Basically, you can’t scale 3D objects much and expect them to work the same way.
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