Handout Flashcards
What is the purpose of a propeller
Convert engine power to thrust
How does a propeller produce thrust
Bernoullis principle (Blade aerofoil)
Newtons 3rd law (cold jet principle)
What is thrust in the context of propellers
Acts along the longitudinal axis of the aircraft
What is torque (propellers)
Acts at right angles to the propeller longitudinal axis
What forces are acting on a blade
centrifugal force thrust bending force torque bending force aerodynamic twisting moment centrifugal twisting moment
What is centrifugal force trying to do
Pull the blades out of the hub as it spins
What is thrust bending force
Similar to helicopter coning angle
The tips of the blade bend forward in the direction of travel
What is torque bending force
Similar to lead and lag (helicopter)
Resistance to the air bending the blade in the opposite direction of rotation
What is aerodynamic twisting moment
The aerodynamic twisting moment tries to increase the blade angle
What is centrifugal twisting moment
The centrifugal twisting moment tries to decrease the blade angle
Where is blade back and face
Blade face scoops the air, blade back is the side facing away from the pilots
How is a prop connected to the hub
The shoulders on blade shank connect to the blade hub grooves
What are blade stations
Used to specify points along the blade from their centre of rotation (the hub)
What is the difference between angle of attack and pitch or blade angle
AOA Is the angle between the aerofoils chord line and the relative airflow.
Blades are twisted, why?
The outside of the blade travels faster than the inside, blades have a twist to keep generate equal thrust along the entirety of the blade
What is geometric pitch
How far the aircraft should travel forward due to the thrust produced by one full rotation of the propeller in theory
What is effective pitch
How far the aircraft actually travels forward due to the thrust produced by one full rotation of the propeller in reality
What is slip
The difference between geometric and effective pitch
What is torque reaction
A twisting force exerted on aircraft due to the torque generated by the propeller spinning cause the aircraft to slowly roll
Similar to the torque produces by the main rotors on a helicopter
What is on speed
The most efficient desired rpm for the propellers
What is windmilling
Spinning freely in the wind
What is feathering
Making the blades straight on for the least air resistance
What is reversing the blades
Reversing the pitch to slow the A/C
What is a negative torque system
prevents the torque from turning the engine, used in descent
What is a de coupling
Disconnects prop from engine
Similar to a free wheeling unit
What is auto feathering
Auto feather the blade to take the load off the pilot during takeoff
What is a pitch lock
Safety feature that lock the propeller to provide thrust
What is a propeller brake
Similar to a rotor brake
What is the front spinner
Aerodynamic fairing
What are the 3 purposes of a barrel ASSY
Hold blades in place
Secure prop to shaft
Transfer torque from engine to thrust
What is inside the dome ASSY
The mechanism for changing blade angles
Describe the components in a propeller assy
Front spinner (fairing)
Dome (Stationary and rotating cam, piston ASSY)
Barrell ASSY (retaining nut, front + rear cone)
Rear spinner
Afterbody (upper and lower)
Control ASSY (upper and lower)
Upper is the brains (Valve housing)
Lower is the muscle (pump housing)
What components make up the barrel assy
Front and rear barrel halves
Front and rear cones (Cones expand against shaft and hold everything in place)
retention nut and snap ring
What is the purpose of blade cuffs
Improve airflow around the blade shanks
Increase the flow of cooling air to the engine nacelle
What is a fixed pitch prop
Prop can’t change
What is variable pitch blade
The blades have adjustable pitch
Achieve best performance by adjusting the blade angle
Hubs have clamp rings or bolts
What are the three types of fixed pitch propellers
Climb (Slow)
Cruise (faster)
Constant speed (works best at high speed)
What is a governor
device which automatically adjusts the angle of the aircraft propeller blade as necessary to maintain a constant engine speed under varying flight conditions.
(send fluid to the dome to move the pitch change mechanism)
What are the three purposes of a governor
Boost pressure of engine oil
Control amount of oil that flows to the propellor
Senses rotational speed of the engine
What are the three main components in a governor
Fly weights
Pilot valve
Pump
What are the two types of anti/de ice on props
Fluid and electrical heating elements
Anti is used on the low speed area and around the engine nacelle
How are props balanced
Vertically or horizontally.
If its vertically balanced it will remain vertical regardless of what blade is facing up
weights are added to balance
What are protractors used for
Used to measure blade angle
Calibrated off dome then held against blade to check it
What are 3 lethal warnings
Keep clear of the propeller arc when the GTC or APU is operating or when an external air starter is connected
Remove power IAW the relevant MM
Open (pull) circuit breakers IAW relevant MM
What are 4 safety precautions
Never walk through a Propeller Arc
Use warning signs in the cockpit
Isolate engine starter system
Isolate propeller feathering system
