P Propeller Principles and Systems

Question 1

What is the blade AoA?

Answer 1

The angle between the blade chord line and the RAF

Question 2

What are the 2 component forces acting on a propeller blade?

Answer 2

Thrust and torque

Question 3

How does TAS effect AoA on a fixed pitch propeller?

Answer 3

Higher TAS = lower AoA

Question 4

How does RPM effect AoA on a fixed pitch propeller?

Answer 4

Higher RPM = Higher AoA

Question 5

What can happen at low RPM and high TAS on a fixed pitch propeller?

Answer 5

Negative AoA

Question 6

What is blade twist?

Answer 6

Twisting the shape of a propeller blade to maintain more efficient AoA along the span of the blade

Question 7

On an efficiency/TAS curve for a fixed pitch propeller where is maximum efficiency?

Answer 7

At a single point, designed to occur when in the cruise

Question 8

What is a fully fine blade pitch?

Answer 8

0 degrees

Question 9

What is a coarse blade pitch?

Answer 9

A greater blade angle towards 90 degrees

Question 10

What is a 90 degrees blade angle called?

Answer 10

Feathered

Question 11

What does feathering do?

Answer 11

Sets the blade to fully coarse, considerably reduces drag from a failed propeller

Question 12

What are the characteristics of an efficiency/TAS curve for a variable pitch propeller blade?

Answer 12

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

Question 13

What is a threat to the spinner?

Answer 13

Ice accretion

Question 14

How does a constant speed drive maintain constant RPM?

Answer 14

Balances engine torque and propeller torque using a reduction gearbox

Question 15

What is the centrifugal twisting moment?

Answer 15

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

Question 16

What is the aerodynamic twisting moment?

Answer 16

When the blade CP is ahead of the pitch change axis, this drives the propeller towards coarse

Question 17

What do centrifugal latches/low pitch stops do?

Answer 17

Prevent blades from entering a feathered condition on engine shut down

Question 18

What is a Hamilton Standard CSU?

Answer 18

• 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

Question 19

What is CSU on speed?

Answer 19

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

Question 20

What’s happens in CSU overspeed?

Answer 20

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

Question 21

What happens in CSU under speed?

Answer 21

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

Question 22

What is an un-feathering system?

Answer 22

Using an accumulator to drive the blades away from feather

Question 23

How do propellers generate noise in the aircraft?

Answer 23

Pressure waves impact the fuselage

Question 24

What is a method of noise reduction?

Answer 24

Synchro-phased propellers

Question 25

What is a master engine?

Answer 25

The engine to which all others are synchronised to