Pitch angle changes during rotational motion of the blade. Pitch angle of main blades of helicopter is a function of swahplate.
This animation shows the relation between pitch angle of two opposite blades as function of swashplate position. When the blade passes azimut 0 that means it passes above a tailboom of the helicopter. azimut 180 means nose of helicopter.
![](https://i.ytimg.com/vi/bj6fDrRT7Ag/maxresdefault.jpg)