Powerplant Chapter 12 Flashcards
Propellers
What is the difference between a fixed pitch propeller and a controllable pitch propeller?
A fixed pitch propeller is one that has a built-in blade angle that cannot be changed by the pilot. These propellers can have the blade angle changed by the manufacturer or an approved repair station to optimize performance. A controllable pitch propeller is one that can be changed by the pilot and is usually controlled by a governor that maintains a constant speed. Some controllable propellers also provide reverse pitch and feathering.
What is the function of a propeller?
The propeller blades create thrust to pull or push an airplane through the air.
How are some wooden propeller blades protected from wear and damage?
By metal tipping fastened to the leading edge and tip.
What happens to the blade angle of a constant speed propeller during a constant power dive?
The blade angle increases to prevent an overspeed.
What are the functions of a constant speed propeller governor?
It boosts engine oil pressure before it enters the propeller hub, it senses rotational speed of the propeller, and then adjusts the oil flow to the propeller hub to change pitch and, therefore, speed of the propeller.
What is the purpose of propeller counterweights?
Centrifugal force acting on the counterweights causes the blade angle to increase.
What is meant when a propeller governor is in an “on-speed” condition?
The governor is not accelerating or decelerating and the speeder spring and flyweight forces are in balance.
How is a constant speed feathering propeller feathered?
By releasing oil pressure in the governor, the counterweights and feathering spring move the propeller into feather. This happens automatically if the governor oil pressure drops to zero (following an engine failure in most turboprops), or can be manually controlled by the pilot by moving the propeller control into the feathering detent.
What is an unfeathering accumulator?
It is an oil accumulator used to provide oil pressure to unfeather a propeller.
What is “alpha range” and “beta range” and where are they found?
The alpha and beta ranges pertain to the operating modes of the turboprop reversible-pitch propellers. In the alpha range, the propeller is operating in the standard, constant speed mode, which is usually in flight. In the beta range, the propeller is operating in the zero or minimum thrust range and negative thrust or reverse thrust mode, which is usually on the ground.
What systems are commonly used for propeller ice control?
Fluid (alcohol) and electrical heat applied to the propeller blade root.
What propeller repairs can be performed by a certified mechanic with a powerplant rating?
Only minor repairs and alterations can be performed by a certified mechanic with a powerplant rating. Major repairs must be performed by the manufacturer or a certified repair station. The propeller manufacturer’s maintenance manual outlines the scope of repairs.
How are wooden propellers generally cleaned?
With a brush or cloth and warm water with mild soap.
Where would you find the correct method and technique for cleaning an aluminum propeller and hub?
The propeller manufacturer’s maintenance instructions.
What type of non-destructive testing should be accomplished to a propeller after blending?
The procedures recommended by the manufacturer.
