FAA Aviation Mechanic Powerplant (AMP)PropellersHard
A technician is comparing pitch-change mechanisms of different constant-speed propeller designs. In a Hamilton Standard hydromatic propeller, how is blade pitch changed in BOTH directions?
- AGovernor oil pressure is used to move blades toward both increase and decrease pitch, without reliance on counterweights
- BSprings alone move the blades toward decrease pitch; oil pressure only increases pitch
- CGovernor oil pressure increases pitch; counterweights and centrifugal twisting moment decrease pitch
- DCounterweights alone control both increase and decrease pitch with no oil pressure involved
Show answer & explanationAnswer & explanation
Correct answer: A. Governor oil pressure is used to move blades toward both increase and decrease pitch, without reliance on counterweights
The hydromatic propeller is a double-acting design in which engine oil, boosted by a pump, is directed to either side of the piston within the propeller dome to move blades toward increase or decrease pitch, unlike counterweight-type propellers which rely on counterweights or springs for one direction of movement.
Why the other options are wrong
- B. Springs alone are not the mechanism used in hydromatic propellers.
- C. This describes a counterweight-type propeller, not a hydromatic design.
- D. Hydromatic propellers rely on oil pressure, not counterweights alone.
Hydromatic Propeller (Double-Acting)
A constant-speed propeller design using engine oil pressure boosted by a pump to move blades toward both increase and decrease pitch, without relying on counterweights.
- Double-acting: oil used for both pitch directions
- Counterweight-type: oil for one direction, counterweights/springs for the other
- Hydromatic uses a piston within the propeller dome
Memory trick: Hydromatic = oil does double duty both ways