Definition
A precision measuring tool used to check the blade angle of a propeller. It is placed against the flat face of a propeller blade at a specified reference station, and a built-in level and graduated scale are used to read the angle of the blade relative to the plane of rotation.
Plain English
A handheld tool a mechanic uses to measure the exact angle of a propeller blade, to make sure each blade is set correctly.
Context Anchor
Seen in propeller maintenance, especially when checking blade angle during inspection, repair, or adjustment.
Derivation
Protractor comes from the Latin protrahere, meaning to draw out or extend. In geometry it refers to a tool for measuring angles. A propeller protractor is simply a protractor designed for measuring propeller blade angles.
Why Pilots Care
Correct blade angles are required for proper thrust, engine performance, and safe operation.
Intuition Check
A propeller protractor is not used to measure the length or diameter of the propeller. It measures the angle at which the blade is set.
Example Sentence 1
Before reinstalling the propeller, the mechanic used a propeller protractor to verify each blade was set to the correct angle.
Example Sentence 2
After the adjustment, the propeller protractor showed the pitch was within limits.