Propellers Flashcards
What is meant by a slave engine with regard to propeller synchronization?
This is the engine in a multi-engine airplane whose RPMs follow those set on the master engine.
What does the pilot do to change the RPM of an engine equipped with a constant-speed propeller when it is operating within the constant-speed range?
The pilot moves the propeller pitch control. This changes the compression on the speeder spring inside the governor which moves the pilot valve. The pilot valve directs oil into or out of the propeller to change the pitch of the blades. The change in pitch changes the air load on the propeller which changes the RPM.
How is ice prevented from forming on propeller blades?
A chemical anti-icing system is used. A mixture of isopropyl alcohol and ethylene glycol is pumped into a slinger ring on the back of the propeller hub. From there centrifugal force slings it out along the blades. Ice cannot form on the resulting slick surface.
How is ice removed from propeller blades?
An electrothermal deicing system is used. Electrical heating elements are embedded in rubber boots that are bonded to the leading edges of the blades. Low-voltage DC flows from the propeller deicer control through brushes and slip rings to the heating elements. The timer sends current to one propeller for about 90 seconds and then to the other for the next 90 seconds. This allows the ice to form and then break loose and blow away.
How can you determine that the electrically heated deicer boots on the propeller blades are working as they should?
Observe the loadmeter or ammeter to see if the proper current is flowing, and follow the sequence of boot heating by feeling with your hands to see which one is heating. The boots should all have a similar heat rise in the same length of time.
How are propellers on a twin-engine airplane synchronized?
The propeller governor of the master engine is set to the desired RPM. A signal from the master engine governor is sent to the control box which sends a signal to a stepping motor. This motor adjusts the propeller governor and fuel control of the slave engine causing it to maintain exactly the same RPM as the master engine.
Where do you find a list of the lubricants that are approved for use in a constant-speed propeller?
In the maintenance manual for the propeller.
Who, or what facility, is authorized to perform major repairs to a propeller?
An FAA-approved propeller repair station that is authorized for the specific propeller.
What checks and maintenance is a mechanic with a powerplant rating allowed to make on a propeller?
Check the track of the propeller blades.
Remove small nicks and scratches from the blades.
Check the dynamic balance of a propeller.
Lubricate the propeller.
What adjustment can a mechanic with a powerplant rating make to a propeller governor?
Adjust the maximum RPM stop.
Why do some aircraft engines have a critical range of operation?
The engine and propeller combination have a resonant frequency problem in which excessive vibration can occur in a certain range of RPM. The tachometer for an aircraft with this limitation is marked with a red arc. When it is necessary to pass through this range it must be done as quickly as practical.
What is the difference between a controllable propeller and a constant-speed propeller?
Basically, it is the control system. A controllable-pitch propeller uses a manually operated oil valve to control the pitch, and a constant-speed propeller uses a governor to control the valve.
Does centrifugal twisting moment on a propeller blade tend to move the blades toward high pitch or toward low pitch?
Toward low pitch.
Do the counterweights on a propeller tend to move the blades toward high pitch or toward low pitch?
Toward high pitch.
What is adjusted inside the governor for a constant-speed propeller to change the speed at which the propeller is operating?
The compression of the speeder spring.
