Some blade characteristics or output are refered to as being in-plane or out-of-plane. These refers to planes that are characteristic of a blade and its movement around the main shaft.

When talking about in-plane at the blade root, we refer to the plane that contains the pitch axis and is perpendicular to the Out-of-plane plane at the root. When talking about in-plane for a Blade aerodynamical station (for example at the tip of the blade), we refer to the plane that contains the elastic center of that station and that is parallel to the in-plane plane at the root.

The figure below illustrates this concept: the in-plane plane at the root for the vertical blade is highlighted in yellow.

Note:  in the figure above, the cone and the tilt have unrealistically high values to show that the in-plane plane is not generally the same for all blades of a rotor.

This plane is used mainly for two outputs:

In-plane deflections
This output can be found in the Blade [Time] sensor and the Blade aerodynamical station sensor
The in-plane deflection is the deflection along the line defined by the Airfoil plane and the in-plane plane.

In-plane moments
This output can be found in the Blade [Time] sensor
The in-plane moment is the bending moment that is perpendicular to the in-plane plane (i.e. that corresponds to a deflection in the in-plane plane).

The figure below illustrates a positive in-plane deflections, which results in a positive in-plane bending moment at the root of the blade.