P Propeller Principles and Systems Flashcards
What is the blade AoA?
The angle between the blade chord line and the RAF
What are the 2 component forces acting on a propeller blade?
Thrust and torque
How does TAS effect AoA on a fixed pitch propeller?
Higher TAS = lower AoA
How does RPM effect AoA on a fixed pitch propeller?
Higher RPM = Higher AoA
What can happen at low RPM and high TAS on a fixed pitch propeller?
Negative AoA
What is blade twist?
Twisting the shape of a propeller blade to maintain more efficient AoA along the span of the blade
On an efficiency/TAS curve for a fixed pitch propeller where is maximum efficiency?
At a single point, designed to occur when in the cruise
What is a fully fine blade pitch?
0 degrees
What is a coarse blade pitch?
A greater blade angle towards 90 degrees
What is a 90 degrees blade angle called?
Feathered
What does feathering do?
Sets the blade to fully coarse, considerably reduces drag from a failed propeller
What are the characteristics of an efficiency/TAS curve for a variable pitch propeller blade?
Each bade angle has its own maximum efficiency, so by altering blade angle a variable pitch propeller can maintain high efficiency over a wide speed range
What is a threat to the spinner?
Ice accretion
How does a constant speed drive maintain constant RPM?
Balances engine torque and propeller torque using a reduction gearbox
What is the centrifugal twisting moment?
The leading edge and trailing edge of the prop blade have a force to move outwards, this causes the blade to have a tendency to fine off
What is the aerodynamic twisting moment?
When the blade CP is ahead of the pitch change axis, this drives the propeller towards coarse
What do centrifugal latches/low pitch stops do?
Prevent blades from entering a feathered condition on engine shut down
What is a Hamilton Standard CSU?
- A rotating governor is driven by the engine
- Landed valve attached to the governor
- A regulating spring which opposes the movements of the governor flyweights movs the landed valve
- The valve moving opens different channels which either fine or coarse the pitch
What is CSU on speed?
When engine torque and propeller torque match the landed valve shuts off supply of high pressure oil. This creates a hydraulic lock holds the propeller at the selected pitch
What’s happens in CSU overspeed?
As the flyweights move further upwards, the spring compresses and pulls the landed valve up, this opens the valve for the blade to coarse, therefore reducing RPM
What happens in CSU under speed?
As the flyweights move further downwards, the spring contracts and pushes the landed valve down, this opens the valve for the blade to fine, therefore reducing RPM
What is an un-feathering system?
Using an accumulator to drive the blades away from feather
How do propellers generate noise in the aircraft?
Pressure waves impact the fuselage
What is a method of noise reduction?
Synchro-phased propellers
What is a master engine?
The engine to which all others are synchronised to
