17.3 - Propeller Pitch Control - 4q Flashcards
How are ground adjustable propellers adjusted on the ground?
By mechanically loosening the blade changing the pitch and then locking them again
What type of propeller is used on a modern aircraft?
Constant speed propeller
(propeller blade pitch is varied by the action of a governor to maintain a constant speed system RPM.)
List the cockpit controls associated with a pitch control mechanism?
Condition lever (Propeller speed lever)
Which control presses down on the speeder spring in a governor?
propeller speed lever (Condition lever)
How is the pitch control oil pressurised?
By the governor which uses a boost pump
What effect does moving the power lever forward have on blade angle?
The power lever controls fuel flow and only blade angle in beta mode
BETA MODE = 65% to 95% of system rated operation (ground operation)
???
What effect does moving the condition/speed lever forward have on blade angle?
The propeller condition lever controls propeller RPM in alpha mode (95 - 100% engine RPM)(flight mode)
Makes it more fine?
What is the primary purpose of feathering a propeller? (2)
Feathering is a procedure where the propeller blade pitch is put into a very coarse angle. i.e. +88 degrees using the condition lever.
- In flight shut down, prevents windmilling of dead propeller which yaws aircraft
- after shutdown, upon next start up will not load engine
Explain the purpose of a feathering pump?
Feathering double acting propellers need oil pressure in order to feather the propeller. This oil pressure is usually supplied by a feathering pump
What is a hydromatic propeller?
Propellers that change their pitch using oil only are called “Hydromatic Propellers’’
(Double acting Propeller system = Hydromatic propeller system)
A hydromatic propeller does not use any springs or counterweights
What happens to the governor flyweights as propeller speed increases?
'’over and out’’
They move out due to the higher centrifugal force acting on the propeller due to its higher speed
How far or if they move out will depend on speeder spring tension which is set by pilot through propeller speed lever or condition lever
What happens to the pilot valve as propeller speed increases?
Fly weights move out due to increased centrifugal force, this pushes pilot valve up.
Oil flows in to increases blade angle which increases bite, more load on engine which lowers RPM
Explain on-speed condition?
The speed condition in which the engine is turning at, the RPM for which the propeller governor is set
or
The centrifugal force acting on the governor flyweights is equal to the tension on the speeder spring
What is windmilling?
A propeller that is rotated by air flowing over the blades rather than powered by the engine.
Will create alot of drag, causing undesirable yawing of aircraft
Some feathering propellers use an accumulator to speed up the _______ (feathering or unfeathering) action
unfeathering
