Propellers Flashcards
What 3 parts make up a propeller
Blades
Spinner
Hub
What is the chord reference point for a propeller
75% of the blade hub> tip
What is the helix angle
Angle between the raf and axis of rotation
What is geometric pitch
How far the blade would travel if put through a solid material
What is effective pitch
Geometric pitch - slip
What does torque do
The opposite of what the engine wants
What happens to blade AOA with TAS and RPM
TAS up = blade AOA down
Rpm up = blade AOA up
What should you do if engine failure on propeller aircraft
Stop propeller from windmilling
Feather
What is the efficiency of a fixed pitch propeller throughout its flight envelope
Low efficiency at low speed
Good efficiency at cruise speed
What are high aspect ratio blades good for
Efficiency
What are low aspect ratio blades good for
Best force
What are short dumpy blades good for
Acceleration
What are long blades good for
Efficiency
What happens if a blade is noisy
Less efficient
What happens if there is too many blades
Turbulent air = less efficient
What is blade solidity
How much of propeller disk has something solid in it
How does blade solidity affect force
Solidity increase = Torque absorption increase (better able to convert power to thrust) = More force
What’s the max number of blades per hub
Around 6 at present
What are contra rotating propellers
2 sets of blades rotating in opposite directions
What is torque reaction
Blades rotate to right
Aircraft wants to rotate to left
On ground what effect does torque reaction have
Wheels on side torque is trying to turn plane have more weight
What effect does the slipstream from propellers have on yaw
Sideslip on rudder = yaw left (if right hand turning propeller)
What is asymmetric blade effect (p-factor)
When propeller disk is included (at a higher AOA)
Downgoing blade = fast than upgoing blade = more thrust = thrust line moves to the right = yaw to left
What is the pitch difference for asymmetric blade effect (p- factor)
Downgoing blade = travels further (greater pitch)
Upgoing blade = travels less = less pitch
What is the gyroscopic effect
Resulting force 90° to the imput
Nazi symbol
When is asymmetric flight at its worst
Slow speeds
Why is propeller engine failure / asymmetric thrust worse
No prob wash from dead engine = less lift on wing
Yaw due to asymmetric thrust = less lift on lost engine wing
+
Drag from prop
What is the benefit of the wing down method for asymmetric flight
More streamlined
What is the drawbacks of the wingdown method for asymmetric flight
Subjected to somatogyral illusion
Benefits of wings level method
All horizons align
What happens to Vx for a jet engine with critical engine failure
Slower
What happens to Vx for a propeller aircraft during critical engine failure
Faster
What is the critical engine
The engine opposite to direction of rotation (for propellers)
Or for jet / counter / contra rotating propellers
Engine on the windward side
What is Vmc (A)
Velocity minimum control in a given configuration usually take off
When the critical engine fails
What is Vmcl
Velocity minimum control landing
In landing configuration
When the critical engine fails
What is Vmcg
Velocity minimum control ground
When on the ground of in (ground effect during take off only)
When critical engine failed
How does cg affect vmc speeds
Rear cg = higher Vmc speeds
How is Vmc (a) determined
Max available take off thrust Worst cg position Trimmed for take off Max sea lever take off mass Most critical take off configuration (with gear up) No more than 5°bank towards live engine Out of ground effect Propeller windmilling or (if autofreather is fitted)
How is Vmcl determined
Go around power Worst cg position Trimmed for approach Heaviest weight Critical landing configuration
Also need to roll control = faster speed
How is Vmcg determined
If critical engine fail you need to maintain control with rudder only without deviating more than 30ft laterally from centre line
Max take off thrust Worst cg Trimmed for take off Heaviest mass Critical take off config
What is the order (fastest to slowest) of the Vmc speeds
1) Vmcg
2) Vmcl
3) Vmc (a)
How does a temperature affect Vmc speeds
Not day = Vmc speeds slower
Because eng produces less thrust = less rudder needed to counter
How does altitude affect Vmc speeds
Slower = less engine thrust = less rudder needed to counter
