17.4 Flashcards
Purpose of synchronising props?
A propeller synchronising system is used to set all propellers, installed on a multi-engine aircraft, at exactly the same RPM, thereby eliminating
beat vibration and excess noise
What phases of flight are props not synchronised?
The synchronisation system is normally used for all flight phases except take off and landing
What is the purpose of the master prop?
A master engine (normally the left hand one) is used to
establish the RPM to which all other engines (slaves) will adjust
Purpose and location of a tachometer?
These are used with each engine to generate a signal proportional to the RPM of the engine. The tachometer is usually mounted on the accessory gearbox
Purpose and location of a frequency generator?
These are used with each engine to generate a signal proportional to the RPM of the engine.
A frequency generator may be part of the propeller governor
How does the tachometer function in the system?
a tachometer is used, the signal voltage is directed to a differential motor to compare the master engine RPM and the slave engine RPM. The engine that
generates the higher voltage will determine the direction that the differential motor will rotate and adjust the governor setting of the slave engine
How does a frequency generator work?
If a frequency generator is used, the engine signals are sent to an electronic unit which compares the frequencies and sends a correcting signal to the
slave engine governor control mechanism
What is the function of the comparison unit?
The comparison unit is used to compare the RPM signal of the slave engine(s) to the RPM signal of the master engine
What is the limited range of operation for the comparison unit?
100 RPM
What can be used on a 4 engine aircraft?
A master engine selcector.
This provides an alternative engine master in
the event that the engine being used as the master becomes inoperative
What does the resynchronisation button do?
This is used by some systems to interrupt the synchronisation system operation and allow the slave governor synchronisation mechanisms to
centre, providing for full travel (100 RPM) towards the master engine RPM. This control is used if one or more slave engines are more than a 100 RPM
different from the master engine without the need to operate individual toggle switches
Why is synchronisation not used during take-off and landing?
These system is not used during take off and landing. If the system were used, failure of the master engine would result in the slave engines trying to follow the master and thereby causing a loss of power by 100 RPM
What is synchrophasing?
Synchrophasing is a refinement of synchronisation and allows the pilot to set the blades of the slave engines a number of degrees in rotation behind the
blades of the master engine
Purpose of synchrophasing?
Synchrophasing is used to further reduce the noise created by the engines. The synchrophase angle can be varied by the pilot to adjust for different flight
conditions and still achieve a minimum noise level
How does a synchrophasing system with mechanical governors work?
Through a synchrophaser the system receives a phase signal from the propellers in addition to the RPM signal through the RPM pickup or additional
pick-ups. The system then sets the slave propeller to the determined phase position. The phase position of the slave propeller is some degrees off that
of the master propeller. This offsetting is programmed in such a way that vibrations in the cabin are kept to a minimum. Thus the synchrophaser sets
the slave propeller to a constant phase displacement
