Definition
The internal assembly within a constant-speed propeller hub that rotates each blade about its long axis to change blade angle (pitch). In most light aircraft, it uses oil pressure from the governor acting on a piston, opposed by spring force and counterweights, to twist the blades to a higher or lower angle as commanded.
Plain English
The parts inside the propeller hub that physically twist the blades to a flatter or steeper angle while the engine is running.
Context Anchor
Seen in constant-speed propeller operation, especially when explaining how the propeller changes blade angle to help maintain the selected engine speed.
Why Pilots Care
It keeps the engine running at its most efficient speed during climb, cruise, and descent, protecting the engine and improving performance.
Analogy
Like shifting gears on a bicycle so your legs keep pedaling at a comfortable rate even as the hill gets steeper or flatter.
Grounding Statement
When the airplane needs a different propeller blade angle, this mechanism is what physically moves the blades.
Intuition Check
Do not picture the pilot directly twisting the propeller blades. The pilot selects a setting, and the propeller system uses this mechanism to move the blades.
Example Sentence 1
When the pilot pulled the propeller control back, the governor directed oil to the blade changing mechanism, which rotated the blades to a coarser pitch.
Example Sentence 2
If hydraulic pressure is lost, the blade changing mechanism uses counterweights to move the blades to a high-pitch position.