Definition
The angle between the chord line of a propeller blade and the plane of rotation, measured at a specified point along the blade's length (typically at the 75% radius station).
Plain English
How much a propeller blade is tilted compared to the flat circle it spins in. A small angle means the blade is nearly flat to the spin; a large angle means it's biting more steeply into the air.
Context Anchor
Seen in propeller inspection, propeller adjustment, and discussions of fixed-pitch and controllable-pitch propellers.
Derivation
Blade comes from an old word for a flat cutting part, like the blade of a knife. Angle comes through Latin and Greek from words meaning a corner or bend. Together, blade angle means the measured setting of the propeller blade relative to the path it spins through.
Why Pilots Care
The blade angle setting determines thrust produced, engine load, and efficiency at different speeds and power settings.
Analogy
Think of a fan blade tilted slightly versus tilted steeply. A slight tilt scoops less air per spin but spins easily; a steep tilt scoops more air per spin but takes more effort to turn. A propeller works the same way.
Intuition Check
Blade angle does not mean the angle of the whole propeller on the airplane. It means the angle of a blade section compared with the flat circle the propeller makes while spinning.
Example Sentence 1
The technician checked the blade angle at the reference station to confirm it matched the propeller's specifications.
Example Sentence 2
A coarse blade angle increases engine load during takeoff and climb.