12.72 Propellers

12.72.2 With respect to propeller terminology, define the meaning of the following:

(a) blade section;

A blade section is the cross-sectional shape of a propeller blade at any point along its length, taken perpendicular to the blade span.

Each blade section is shaped like an aerofoil, with:

• A leading edge
• A trailing edge
• An upper (cambered) surface
• A lower surface

As the propeller rotates, each blade section produces an aerodynamic force in the same way a wing produces lift. The forward component of this force becomes thrust.

The shape of the blade section is designed to provide efficient airflow, lift, and thrust production.

Summary:
A blade section is the aerofoil-shaped cross-section of a propeller blade, which produces the aerodynamic force that creates thrust.

(b) blade angle;

Blade angle is the angle between the chord line of the propeller blade and the plane of rotation of the propeller.

• The chord line is an imaginary straight line joining the leading edge to the trailing edge of the blade section.
• The plane of rotation is the circular path swept by the rotating propeller.