What is the function of the accumulator used with some McCauley feathering propellers?

• A. Stores fuel to increase range.
• B. The accumulator stores oil under pressure when the engine is operating normally. This oil is used to help the propeller blades move toward low pitch when the propeller is being unfeathered.
• C. Stores hydraulic fluid for anti-ice.
• D. Acts as a coolant reservoir.

Answer: (B)

Feathering propellers are driven by hydraulic pressure to move the blades to the desired pitch, and an accumulator provides a ready source of that pressure to act quickly during unfeathering. The accumulator stores oil under pressure while the engine is running, so when unfeathering is commanded, the pressurized oil in the accumulator assists the mechanism by pushing the piston that moves the blades toward low pitch. This quick hydraulic burst helps overcome inertia and any momentary loss of pump pressure, letting the propeller return to efficient, low pitch promptly. It’s not a fuel, anti-ice fluid, or coolant reservoir.