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A comment on Larry Page is pouring millions into flying cars. Parent comment

Re:Larry Page is pouring millions into flying cars by JumpCrisscross on Friday December 30, 2016 @03:57PM (#13287378)
First comment makes a good observation. When a plane loses power, it glides. When a helicopter loses power, it autorotates [1].

If a single engine on a quadcopter loses power, it crashes [2]. There is work being done on mitigating this, but I don't see why you'd go for a quad versus tri- or helicopter.

(Quadcopters are better than other aerial platforms at one thing: maneuverability. To get this agility they sacrifice speed, efficiency and payload weight.)

[1] https://en.wikipedia.org/wiki/Autorotation

[2] https://www.quora.com/Can-a-quadcopter-fly-without-one-rotor

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Re:Larry Page is pouring millions into flying cars by avar on Friday December 30, 2016 @04:06PM (#13287449)
The Ehang 184 has 8 propellers, two for each of the four quad points. I'd assume the reason is safety, that it can limp to the ground with just 7.

You're wrong about a quadcopter not being able to fly with 3 rotors, see this video: https://www.youtube.com/watch?v=bsHryqnvyYA

That looks like it would be quite a ride with a human on-board, but would probably suck less than crashing.

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Re:Larry Page is pouring millions into flying cars by woofyman on Friday December 30, 2016 @04:28PM (#13287623)
That's fine as long as all 8 have independent batteries and flight controllers.
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Re:Larry Page is pouring millions into flying cars by ambrop7 on Friday December 30, 2016 @05:11PM (#13287926)
> If a single engine on a quadcopter loses power, it crashes

If one motor fails, the quadcopter could turn off the opposite motor and reverse the direction of one of the remaining motors, so that it is left with two opposing motors spinning in opposite direction. The torque of two motors might be enough to keep it flying. Some steering would be possible with the assistance of the third working motor which could spin in either direction as needed.

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Re:Larry Page is pouring millions into flying cars by smallnamespace on Friday December 30, 2016 @06:08PM (#13288318)
> reverse the direction of one of the remaining motors

Pretty sure you won't survive that transition since your craft will be completely out of control in the seconds it takes to kill all rotational velocity and spin a rotor up again, at least for large sized rotors.

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