17.4 Propeller Synchronisation

Question 1

What is a propeller synchronising system?

Answer 1

A system used to set all propellers on a multi-engine aircraft at the same RPM, eliminating beat vibration and excess noise.

Question 2

How does a propeller synchronising system achieve RPM synchronisation?

Answer 2

By adjusting the propeller governors, which can be either mechanical or electrical.

Question 3

When is the synchronisation system normally used?

Answer 3

For all flight phases except take off and landing.

Question 4

What is the role of the master engine in a synchronisation system?

Answer 4

The master engine establishes the RPM to which all other engines (slaves) adjust.

Question 5

What is the function of a tachometer or frequency generator?

Answer 5

To generate a signal proportional to the RPM of each engine.

Question 6

Where is the tachometer usually mounted?

Answer 6

On the accessory gearbox.

Question 7

How does a tachometer signal work in the synchronisation system?

Answer 7

The signal voltage is directed to a differential motor to compare master and slave engine RPM.

Question 8

What does the comparison unit do?

Answer 8

It compares the RPM signal of the slave engine(s) to the RPM signal of the master engine.

Question 9

What is required for synchronisation to occur?

Answer 9

Slave engines must be within approximately 100 RPM of the master engine RPM.

Question 10

What is the purpose of the master engine selector?

Answer 10

To allow the pilot to select the master engine on some 4-engined aircraft.

Question 11

What does the resynchronisation button do?

Answer 11

It interrupts the synchronisation system to allow slave governors to centre for full travel towards the master engine RPM.

Question 12

When is the synchronisation system not used?

Answer 12

During take off and landing.

Question 13

What happens if the master engine fails during synchronisation?

Answer 13

The slave engines would try to follow the master, causing a loss of power by 100 RPM.

Question 14

What occurs during normal operation of the synchronisation system?

Answer 14

Slave engines adjust to the same RPM as the master engine when the system is switched on.

Question 15

What is the function of a master control system in relation to synchronisation?

Answer 15

It can be used at any time to adjust the RPM of all engines.

Question 16

What is synchrophasing?

Answer 16

A refinement of synchronisation that allows the pilot to set the blades of slave engines a number of degrees behind the master engine.

Question 17

What is the purpose of synchrophasing?

Answer 17

To further reduce the noise created by the engines.

Question 18

How is the phase position of the slave propeller determined in a mechanical governing system?

Answer 18

By receiving a phase signal from the propellers in addition to the RPM signal.

Question 19

What is the role of the electronic governing system in synchrophasing?

Answer 19

It governs the RPM of the propeller very exactly, allowing for minimal RPM differences during synchrophasing.

Question 20

What activates the synchrophasing function?

Answer 20

It is automatically activated to reduce propeller noise under certain conditions.

Question 21

What does the Magnetic Pickup Unit (MPU) do?

Answer 21

It provides the PEC with a Power Turbine speed indication and determines the phase of the propeller.

Question 22

How is the phase and speed detected in the MPU?

Answer 22

By 6 of the 7 targets located on the de-icing slip-ring.