Definition
The flat or nearly flat surface of a propeller blade that faces aft, toward the pilot, when the propeller is mounted on the aircraft. It is the rear side of the blade, opposite the curved cambered side that faces forward into the airflow.
Plain English
The back side of a propeller blade — the side you see when you stand behind the propeller and look at it. It is the flatter side, while the front side (which faces away from the pilot) is curved.
Context Anchor
You will see this term in propeller descriptions and during preflight inspection of propeller blades.
Derivation
‘Face’ here uses the older sense of ‘the flat or principal surface of an object,’ the same sense used in ‘face of a hammer’ or ‘face of a clock.’ It marks the flat reference side of the blade, in contrast to the curved back.
Why Pilots Care
Knowing which side is the blade face helps pilots understand how propeller angle of attack and thrust are created.
Intuition Check
Do not read “face” as just the side you happen to be looking at. In propeller terminology, the blade face is a specific side of the blade: the flatter pressure side.
Example Sentence 1
During preflight, the pilot ran a hand along the blade face of each propeller blade, checking for nicks or corrosion.
Example Sentence 2
Increasing blade angle changes how the blade face meets the oncoming air.