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Comment by walrus01 | Hacker News Reader

the lack of ability to fly with one engine out, in a quad, is why most of the human-carrying systems proposed such as the eHang unit are what's known as an X8 configuration. Four arms, eight motors in a coaxial configuration on each arm. Can fly and land with a dead motor.

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This one can fly with just one rotor running:

https://youtu.be/gfkRCzgHGq8

Admittedly it would be a pretty terrifying ride to the ground, but preferable to plummeting. There’s a lot of rotational energy in the aircraft though.

I think there’s probably significant scope for improvement in redundancy of these systems.

But can they fly with all the motors dead? What if they loose the supply of power from the battery system? A standard config can deal with that senario.

I am not aware of any multicopter design that can autorotate. Something like this with a tilt wing approach probably has some ability to glide:

https://youtu.be/gJrKmMM7vW0

They could. They just need variable pitch (aka collective) on all the blades. And this needs to be actuated by a different power system so that it remains operational when the main power stops. Helicopters use hydraulics, or even manual power.

Autorotation is where helicopters get their speed/altitude restrictions when carrying passengers. They generally are not allowed to hover at low altitude because from there they cannot safely autorotate onto the ground. If drones want to carry people, or carry heavy things over people, then they will need to develop some sort of plan. Total engine failure should never result in the total loss of the aircraft.

Over a sufficiently long and thorough testing period, I think x8 design multirotors with eight or more motors/props will prove to have a statistical rate of motor failure much lower than the incidence of single engine failure in small to mid size internal combustion engine and turbine helicopters.

It would have to monumentally better before I'd get into one that didn't have a backup plan. The motors could be 100% reliable, but the possibility of loosing power due to maintenance or control issues remains. A perfectly good motor is useless if the cable feeding it electricity shorts out.

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