Mast bumping.

[Aviator168]

Hi all,

I am new to autogyros and been studying how the rotor work. One question. With free flapping, does the rotor bump the mast when the stick is move back and forth? It is a bit confusing to me since the rotor is supposedly rotating on its own axis.

[C. Beaty]

Imagine the rotor at the 9 & 3 o’clock position.

Moving the stick forward can only rotate the rotor about its feathering axis. The blade at the 3 o’clock position (advancing) is rotated nose down; the blade at the 9 o’clock position (retreating) is rotated nose up.

The advancing blade descends; the retreating blade rises, each reaching maximum displacement at the 12 & 6 o’clock positions.

The rotor flies aerodynamically into alignment with the rotorhead axis, no different than the swashplate controlled system of a helicopter.

And yes, what amounts to mast bumping occurs when flawed designs tumble out of the sky.

[Aviator168]

Understood. Thnx. I was thinking about that. So if the stick movement is slower than a few turns for the rotor to catch up, it should be fine or am I wrong on this regard?

[C. Beaty]

The rotor doesn’t lag the stick input by very much, a couple of revolutions to catch up depending upon its ratio of inertia to aerodynamic force.