17.3 Propeller Pitch Control Flashcards
What are the two types or propellers
Pusher and pullers
What are the three ways of changing pitch if propellers
Hydraulic mechanical and electrical
What is disc braking
Propeller can be moved into a negative angle of attack (different to reverse pitch) gives more drag helping slow aircraft
What is power on braking
Making a reverse pitch with blade and increasing power creates reverse thrust force slowing the aircraft
What’s is BETA range
Pilot controls the pitch on the ground
What is reverse (negative) pitch
Used for power-on braking and manoeuvring
What is ground fine pitch
Used for engine starting and discing braking
What is ALPHA range
Also known as the constant speed range - the propeller governor controls the pitch
What is MAX fine pitch
Used for rapid acceleration during take-off, allowing a shorter take-off run
What is high (coarse) pitch
Used for high forward speed
What are the two mechanisms of pitch change
Moving piston and moving cylinder
What is a moving piston mechanism
Have a piston moving forwards and backwards powered by using oil in each chamber
What is moving cylinder mechanism
Cylinder attached to prop and oil and weight turns the cylinder moving the propeller (used on smaller aircraft)
What is a single acting propeller for single engine aircraft
Oil pressure moves blades in direction of high (coarse) and a spring moves it to low pitch
What is a single acting propeller for multi engine aircraft
Oil pressure moves blades in low (fine) pitch and springs move blades towards high (coarse) pitch
What does centrifugal force do to the pitch of a blade
Turns naturally to low (fine) pitch as a result of the distribution of the blade mass
What are double acting propellers
Able to change pitch in both directions (with pitch oil)
What does a propeller governed do
Engine RPM sensing device and oil pump, responds to change in engine RPM by directing oil to hydraulic cylinder causing blade angle change
How is the spring in the propeller governed adjusted
By pilot using propeller control lever (conditioning lever)
What can a single acting constant speed propeller control do
Turn pitch of propeller to negative using oil not CTM
How does an electrical control pitch change mechanism work
Uses electrical power to supply power to oil which moves a servo piston and moving blade pitch
What is used to change pitch angle in the modern day
Electronic control
How does the electronic control work
Use ARINC digital control to drive torque motor and change the pitch of the blades
Which electric system uses oil
Electrical system NOT electronic system
What is automatic feathering
Automatically feathers during take off and cruise. In case of engine failure the centrifugal flyweights are automatically overridden and the electric feathering pump will run
What is a second feature of the auto feather system during an engine failure
Power up engine trim to compensate for loss
When does Up trim trigger
When torque of local engine falls below 25%
What do some feathering systems have to provide reserve pressure
Accumulator
What does a centrifugal latch do
Locks piston in fine pitch position when engine is not rotating to prevent load on the starter system
What is a CSU
constant speed unit (primary propeller governer)
When does the CSU work to prevent over speed
102-103%
When does the propeller overspeed governor operate
104-106%
What is the last method of defence to prevent overspeed
Flyweights inside the main propeller governer open a bleed air link this slows fuel flow to the engine and slows propeller speed. Operates at 106-107%
