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Comment by hyperpallium | Hacker News Reader

Why not autorotation? https://wikipedia.org/wiki/Autorotation

Is it less mass and therefore momentum in the rotor/drivechain?

That needs forward flight to work. A quad copter does not have a glide ratio high enough that it would be able to start up the rotors to spin fast enough to get some lift out of them. A quad copter is best modeled as a brick with a magic anti gravity device attached, if the anti gravity device fails it is a suspended brick and gravity will soon assert itself.

A real helicopter (or an auto-gyro) is best modeled as a rotating wing, as long as the blades rotate you can control the craft to greater or lesser extent. It still won't be pretty in a proper helicopter but at least you have a chance.

Additionally, you need "collective pitch" control, i.e. the ability to angle the rotor blades for windmilling and then for hover flight right before touchdown. Multicopters just have fixed-pitch rotors and rely on differential torque/thrust for attitude control and ascend.

>A quad copter is best modeled as a brick with a magic anti gravity device attached, if the anti gravity device fails it is a suspended brick and gravity will soon assert itself.

Very nice definition.

There isn't AFAIK such a neat distincion in English, in Italian the iron (the device you use for ironing, maybe flatiron?) has a specific name "ferro da stiro" so it is common to use it as a term of comparison for such a behaviour.

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