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If rotor has 0 friction mounting then sure, no constant torque. Otherwise small constant torque that depends on friction.



See, in physics, you can assume there is no friction. Engineers often forget this one weird trick.


>"See, in physics, you can assume..."

In theoretical model of ideal XXX. Not when asked to actually calculate something practical unless the ideal model is good enough for constraints.

I am not an engineer. Actually MS in physics however ancient ;)


It's an old engineering jibe, of course :)

I suspect that the engineer in the GP's story might not remember the equations for angular acceleration, but has an intuitive sense that if a spinning something is in contact with a non-spinning something, you need a good reason for why some of the energy won't get transferred from the former to the latter.


Which is balanced by the torque applied by the working fluid that's being shoved through the rotor to keep it spinning.


Friction with the helicopter doesn't matter, friction with the air does.




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