Propellers

Question 1

Propeller Manufacturers

Answer 1

Mcauley
Hartsell
MTU

Question 2

Components of the Total Reaction

Answer 2

Propellor thrust

Propellor torque

Question 3

Composite Propeller

Answer 3

Preferable as much lighter than metal or wood

Difficult to repair from foreign object damage (FOD)

Question 4

Angle of Attack

Answer 4

The angle between its chord and the relative airflow

4 degrees is most efficient

Question 5

Blade Angle

Answer 5

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

Question 6

Helix Angle

Answer 6

The angle between the plane of rotation and the relative airflow

Question 7

Relationship Between RPM, TAS and AoA

Answer 7

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

Question 8

Thrust/Toque Ratio

Answer 8

Changes with the AoA

Question 9

Best Thrust/Torque Ratio

Answer 9

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

Question 10

Engine Torque

Answer 10

Acts to overcome propeller torque and enables the blades to rotate

Question 11

Engine Torque Vs Propeller Torque

Answer 11

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

Question 12

Fixed Pitch Propellers

Answer 12

Fixed blade angle

Efficient only at one TAS

Question 13

Variable Pitch Propellers

Answer 13

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)

Question 14

Increased TAS on a Variable Pitch Propeller

Answer 14

Blade angle must be increased to maintain the AoA

Question 15

Fine Pitch

Answer 15

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

Question 16

Coarse Pitch

Answer 16

Large blade angle

Suitable for high speeds (cruise at low RPM)

Question 17

Efficiency of Propellers

Answer 17

Convert BHP to THP

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

Question 18

Forces Acting on a Propeller

Answer 18

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

Question 19

Propeller Thrust

Answer 19

Acting perpendicular to the plane of rotation

No thrust with brakes on

Question 20

Propeller Torque

Answer 20

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

Question 21

Feathering

Answer 21

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

Question 22

Reverse Pitch

Answer 22

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

Question 23

Total Flow

Answer 23

Total flow = induced flow + TAS

Question 24

Slip

Answer 24

The difference between geometric pitch and effective pitch

Reduction due to the propeller working in air

Question 25

Geometric Pitch

Answer 25

= effective pitch + slip

Question 26

Constant Speed Unit (CSU) in a Single Engine

Answer 26

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

Question 27

Aerodynamics of the Blades on the Prop

Answer 27

Twisted to keep the AoA constant (may stall otherwise) | Tip of prop moves faster than at the hub

Question 28

Constant Speed Unit (CSU) in a Twin Engine

Answer 28

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

Question 29

Constant Speed Unit (CSU)

Answer 29

Maintains a constant RPM | As RPM is decreased, the prop coarsens increasing TAS in the cruise

Question 30

Counterweights

Answer 30

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

Question 31

Overspeed

Answer 31

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

Question 32

Governor Action When Overspeeding

Answer 32

``` 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 ```

Question 33

Underspeed

Answer 33

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

Question 34

Governor Actions When Underspeeding

Answer 34

``` 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 ```

Question 35

Controls For Power and RPM

Answer 35

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

Question 36

Coarse Pitch Stop

Answer 36

Max possible blade angle | Eg. A dive with power on

Question 37

Ground Operation

Answer 37

Prop in fine pitch

Question 38

Changing Power

Answer 38

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