In many pieces of literature, diagrams as below are shown to explain the directional flight of Helicopter. I have the understanding that the cyclic input will only change the pitch angle of the blades and hence the amount of lift forces acting will vary around the disc. BUT the disc-plane (more specifically, the hub plane), will remain parallel (to the reference plane, for example, the skids, or the top surface of the helicopter). I mean, the disc plane shouldn't pitch down or up as shown in the diagram.

Am I correct? Also, I am finding hard to give a suitable name to the "reference frame", I tried to define above. Is there any standard name for that?

[![enter image description here](https://i.stack.imgur.com/U5ZxX.jpg)](https://i.stack.imgur.com/U5ZxX.jpg)