Definition
A type of feathering propeller design in which engine oil pressure, directed through the propeller governor, is used to drive the blades toward higher (coarser) pitch, while springs and counterweights move the blades toward lower (finer) pitch and, if oil pressure is lost, toward the feathered position.
Plain English
A propeller setup where oil pressure pushes the blades to a flatter angle into the wind (coarser pitch), and springs and weights pull them back the other way. If oil pressure fails, the springs and weights take over and turn the blades edge-on to the wind, which is the feathered position.
Context Anchor
Seen in multiengine airplane systems, especially when learning how a feathering propeller changes blade angle after an engine failure.
Derivation
The phrase is descriptive: oil pressure is the force that 'increases pitch,' meaning it rotates the blades to a coarser angle. Naming the system by what oil pressure does makes it easy to predict what happens when oil pressure is lost — the opposite.
Why Pilots Care
Knowing the direction oil pressure moves the blades helps a pilot predict what happens during an oil-system failure or when selecting feather.
Analogy
Think of oil pressure like hydraulic force pushing a part into position. In this system, that push turns the blades toward a steeper angle instead of letting them go there by spring force alone.
Intuition Check
Pitch does not mean sound here. It means the angle of the propeller blade; increasing pitch means turning the blade to take a bigger bite of air.
Example Sentence 1
On airplanes with an oil-pressure-to-increase-pitch propeller, a loss of oil pressure causes the blades to move toward the feathered position automatically.
Example Sentence 2
With an oil-pressure-to-increase-pitch design, loss of oil pressure prevents the pilot from moving the blades toward feather.