Propellers Flashcards

1
Q

Propeller Manufacturers

A

Mcauley
Hartsell
MTU

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2
Q

Components of the Total Reaction

A

Propellor thrust

Propellor torque

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3
Q

Composite Propeller

A

Preferable as much lighter than metal or wood

Difficult to repair from foreign object damage (FOD)

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4
Q

Angle of Attack

A

The angle between its chord and the relative airflow

4 degrees is most efficient

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5
Q

Blade Angle

A

The angle between the chord line of the propeller and the plane of rotation
Blade angle = helix angle + angle of attack

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6
Q

Helix Angle

A

The angle between the plane of rotation and the relative airflow

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7
Q

Relationship Between RPM, TAS and AoA

A

Fixed pitch (blade angle remains constant):
For a given RPM, increased TAS will reduce the angle of attach and vice versa
For a given TAS, increased RPM increases the angle of attack and vice versa
Any angle of attack can be achieved with combinations of TAS and RPM
One RPM value will only have one TAS to achieve a certain AoA
As AoA decreases, thrust decreases as TAS increases

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8
Q

Thrust/Toque Ratio

A

Changes with the AoA

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9
Q

Best Thrust/Torque Ratio

A

Achieved using the most efficient AoA
Gives the greatest amount of propeller thrust for the smallest amount of propeller torque
Best value for money

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10
Q

Engine Torque

A

Acts to overcome propeller torque and enables the blades to rotate

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11
Q

Engine Torque Vs Propeller Torque

A

ET = PT: the blades rotate at a constant RPM (RPM constant)
ET > PT: RPM increases
ET < PT: RPM reduces

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12
Q

Fixed Pitch Propellers

A

Fixed blade angle

Efficient only at one TAS

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13
Q

Variable Pitch Propellers

A

Varies the blade angle to maintain an efficient angle of attack over a wide range of RPM and TAS
Also known as constant speed units (CSU)

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14
Q

Increased TAS on a Variable Pitch Propeller

A

Blade angle must be increased to maintain the AoA

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15
Q

Fine Pitch

A

Small blade angle
Good for acceleration (high RPM)
Suitable for takeoff and slow flight

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16
Q

Coarse Pitch

A

Large blade angle

Suitable for high speeds (cruise at low RPM)

17
Q

Efficiency of Propellers

A

Convert BHP to THP

80 - 90% efficient due to working in the fluid air (slip)

18
Q

Forces Acting on a Propeller

A

Centrifugal Forces: work to pull blades apart from the hub
Tangential Component (centrifugal twisting): Which wants to turn the blades to fine the pitch
Aerodynamic Twisting: Tries to turn the blades in the opposite direction

19
Q

Propeller Thrust

A

Acting perpendicular to the plane of rotation

No thrust with brakes on

20
Q

Propeller Torque

A
Acting in the plane of rotation
Opposes rotation
Opposed by engine torque (turning force)
Can overrev when the propeller begins to turn the engine (eg. in a steep dive)
Increases with RPM
21
Q

Feathering

A

Propeller must feather (become extremely coarse) in an engine failure to ensure it does not create drag and twist the aeroplane
A position of 0 torque

22
Q

Reverse Pitch

A

Acts as a braking mechanism and enables aircraft to be reversed
Creates a relatively large negative angle of attack by allowing the blades to turn past the fine pitch limit

23
Q

Total Flow

A

Total flow = induced flow + TAS

24
Q

Slip

A

The difference between geometric pitch and effective pitch

Reduction due to the propeller working in air

25
Q

Geometric Pitch

A

= effective pitch + slip

26
Q

Constant Speed Unit (CSU) in a Single Engine

A

When speed is increased, fly waits are flung outwards, lifting the oil valve and pushing oil to coarsen the prop to maintain RPM
When speed decreases, fly waits go in, lowering the valve and pushing away to fine the prop to maintain RPM

27
Q

Aerodynamics of the Blades on the Prop

A

Twisted to keep the AoA constant (may stall otherwise)

Tip of prop moves faster than at the hub

28
Q

Constant Speed Unit (CSU) in a Twin Engine

A

When speed is increased, fly waits are flung outwards, lifting the oil valve and pushing oil away to coarsen the prop to maintain RPM
When speed decreases, fly waits go in, lowering the valve and pushing oil in to fine the prop to maintain RPM
If oil pressure is lost the propeller feathers

29
Q

Constant Speed Unit (CSU)

A

Maintains a constant RPM

As RPM is decreased, the prop coarsens increasing TAS in the cruise

30
Q

Counterweights

A

Only in multi-engine
Used to coarsen the pitch
Oil pressure reduces pitch

31
Q

Overspeed

A

Engine torque > Prop torque
Prop tries to speed up
CSU coarsens pitch
PQ increases to match EQ

32
Q

Governor Action When Overspeeding

A
Prop RPM starts to increase
Flyweights spin faster and are flung outwards
Pilot valve rises
Oil Flows:
- To the hub (single)
- Away from the hub (multi)
Blades move to a coarser pitch
Extra prop torque stops the RPM from increasing
33
Q

Underspeed

A

Engine torque < prop torque
Prop tries to slow down
CSU drives prop to fine pitch

34
Q

Governor Actions When Underspeeding

A
RPM starts to reduce
Flyweights slow down and are flung inwards
Speeder spring wins
Pilot valve moves down
Oil flows:
- From the hub (single)
- To the hub (multi)
Blades move to a finer pitch
Less prop torque, stops the RPM from reducing
35
Q

Controls For Power and RPM

A

Throttle controls MAP (The primary power gauge)
Pitch lever controls RPM
- Increased RPM creates a fine pitch

36
Q

Coarse Pitch Stop

A

Max possible blade angle

Eg. A dive with power on

37
Q

Ground Operation

A

Prop in fine pitch

38
Q

Changing Power

A

Avoid high MAP with low RPM die to the risk of detonation
High MAP: lots of mixture entering cylinders
Low RPM: valves open for longer, allowing more mixture to enter the cylinders