10. Propeller Systems - Sections 5-8 Flashcards
Feathering and Unfeathering
Under normal conditions, when is a propeller normally feathered
AFTER ENGINE FAILURE
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Feathering and Unfeathering
What is the main purpose to feathering a blade after an engine failure
PREVENT WINDMILLING
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Feathering and Unfeathering
Feathering a blade after engine failure prevents windmilling. What is the purpose of this
PREVENT ENGINE TURNING
If an engine failed due to catastrophic event, you do not want the engine to turn, in particular as this could pull fuel over hot system and cause a fire
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Feathering and Unfeathering
What is the simplest method for a pilot to feather a propeller
RPM LEVER
RPM lever can lift the pilot valve to the fully coarse position, bypassing the governor
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Feathering and Unfeathering
In older aircraft types that have manual feathering, what is the significant control in place to prevent feathering by accident
GATE STOP
Gate stop prevents the lever being moved into the feather position without first lifting and moving the lever into position.
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Feathering and Unfeathering
What component is used in modern aircraft to electrically operate the feathering system
ELECTRICALLY OPERATED SOLENOID VALVE
Directs pressure to the feather side of hte PCU
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Feathering and Unfeathering
What is the key requirement of all feathering systems
SUPPLY HIGH PRESSURE OIL to PCU
Pitch Control Unit
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Feathering and Unfeathering
High pressure oil is supplied by the engine typically. If the engine were to fail, this would result in high pressure oil being unavailable to supply the PCU. Subsequently, feathering systems must have what
SEPARATE OIL RESERVOIR
With sufficient oil to allow the propeller to be feathered
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Feathering and Unfeathering
In the event of engine failure, to provide sufficient oil to a PCU, feathering systems must have a separate oil resrvoir. What else will this usually include in order to provide pressure
ELECTRIC PUMP
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Feathering and Unfeathering
Large commercial aircraft will usually have what sort of feathering system
AUTO-FEATHERING
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Feathering and Unfeathering
On commercial aircraft with auto-feathering systems, what must be done before take-off
SYSTEM ARMED
System must be armed before take-off
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Feathering and Unfeathering
On commercial aircraft, when must the auto-feathering system be armed
BEFORE TAKE-OFF
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Feathering and Unfeathering
Under what conditions on a commercial aircraft will the auto-feathering system be triggered
ENGINE TORQUE BELOW 25%
for more than 3 SECONDS
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Feathering and Unfeathering
On commercial aircraft, when the auto-feathering system is triggered, what 4 things will it then do automatically
- FEATHER PROPELLER - feather on failed engine
- POWER AUX - power aux power on failed engine
- DISARM - disarm auto feather on live engine
- POWER - increase power on live engine (max take-off power)
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Feathering and Unfeathering
What is the primary reason for unfeathering a propeller on an engine whilst airborne
ENGINE RESTART
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Feathering and Unfeathering
How does unfeathering an engine in flight assist with engine-restart
WINDMILLING EFFECT
An unfeathered blade will cause airflow to move over the blades and turn the propeller through aerodynamic foces. This is called windmilling.
This will create sufficient turning in the propeller to assist with re-start, avoiding unncessary drain on the battery
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Feathering and Unfeathering
What is a method or storing oil under high pressure to allow the PCU to drive the blades away from feather
UNFEATHERING ACCUMULATOR
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Feathering and Unfeathering
How is the unfeathering accumulator isolated in the event of an engine shut down
NON RETURN VALVE
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Feathering and Unfeathering
What component opens the supply from the accumulator to the PCU when the propeller lever is moved away from the feathered position
ELECTRICALLY OPERATED SOLENOID
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Reverse Thrust
What name is given to the range of normal pitch angles for positive thrust
ALPHA RANGE
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Reverse Thrust
What name is given to the range of flight idle pitch angles of a propeller
BETA RANGE
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Reverse Thrust
What is the result to thrust if the AoA of a propeller blade falls below the 0° at higher airpseeds
THRUST GENERATED in OPPOSITE DIRECTION
relative to the aircraft movement
THrust will be generated in the opposite direction to the aircraft movement
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Reverse Thrust
What is the purpose of a fine pitch stop
MINIMUM PITCH SETTING
Prevents the propellers being put into such a fine pitch that this could cause dangerous excessive drag
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Reverse Thrust
Whatcomponents is the fine pitch stop linked to
POWER LEVER
The power lever is physically prevented from moving so far aft that excessive fine pitch would occur
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Reverse Thrust
What component is the flight idle stop linked to
WEIGHT ON WHEELS
When no weight on wheels, the power level cannot physically move into the flight idle position. Only when weight applied to wheels does this protection disengage
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As well as flight idle stop and fine pitch stop protections, what additional precaution measure can be used to prevent excessive flight idle position of the power lever
POWER LEVER GATE
Power lever has to be lifted through a gate in order to put it into a flight idle position
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Reverse Thrust
What is it important to understand regaridng the degrees of beta range
covers POSITIVE and NEGATIVE values
For example, on a Dash 8 Q 400, flight idle fine pitch stop is set from 16° and below
Reverse Thrust
What sort of drag is produced in large amounts when a blade is moved into the negative pitch angle
TORQUE DRAG
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Reverse Thrust
To move the blade into the negative angle beta range, it produces reverse thrust. From the pilots perspective, they will want to retard the power. What is the problem from the engines perspective in regards to the power lever
WANTS TO WORK IN REVERSE
More power needed to produce reverse thrust to overcome torque drag
When the blade is at a negative angle, it is producing a lot of torque drag.
The desire is for a lot of thrust to be produced in the opposite direction of aircraft movement.
To overcome torque drag, more power is required.
From the engines perspective pulling back on the power lever would mean it wants more power to be produced, not less.
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Reverse Thrust
What is the purpose of an under-speed governor
SCHEDULES MORE FUEL in REVERSE THRUST
Pilot selects reverse thrust using the power level. Torque drag increases, RPM drops.
The under-speed governor activates and schedules more fuel to the engine to increase power output
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Reverse Thrust
When a pilot selects reverse thrust on a commercial propeller aircraft, torque drag INCREASES or DECREASES, and RPM INCREASES or DECREASES.
What component is then activiated to supply more fuel to the engine
UNDER-SPEED GOVERNOR
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Cabin noise and synchrophasing
What causes high level noise in the cabin on multi engine propeller aircraft
PRESSURE WAVES
Propellers in line with teh cabin rather than forward of the nose
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Cabin noise and synchrophasing
What is the term used for the number of times the blade of a multi engine aircraft passes the body of the aircraft, causing high levels of noise
BLADE PASS FREQUENCY
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Cabin noise and synchrophasing
If an aircraft has 2 or more propellers, when the blade frequencies are combined, what does this create
BEAT FREQUENCY
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Cabin noise and synchrophasing
What is a beat frequency
2 or more propellers combined blade pass frequency
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Cabin noise and synchrophasing
Very uncomfortable noise levels can be experienced in a multi engine aircraft when the beat frequency coincides with what
NATURAL RESONANT FREQUENCY
of the cabin structure
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Cabin noise and synchrophasing
When propellers are rotating at slightly different speads, what can this cause
Slow rise and fall beat frequency
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Cabin noise and synchrophasing
How can rhythmic noise pattern be cured
SYNCHRONISING PROPELLERS
Synchronising propellers so that they are totating at exact same RPM
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Cabin noise and synchrophasing
What does a synchronising unit do
SYNCHRONISES PROPELLERS
Makes propellers rotate at exact same RPM
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Cabin noise and synchrophasing
If there are 2 or more engines, in order to synchronise, what roles are assumed by the engines
1 x MASTER ENGINE
REST are SLAVES
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Cabin noise and synchrophasing
How does the syncrhonising unit use the relationship between the master engine and the slave(s)
COMPARES RPM of SLAVES to MASTER
Adjusts accordingly so slaves rotate same as master
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Cabin noise and synchrophasing
The synchronising unit can eliminate RHYTHMIC CHANGES or BEAT FREQUENCY
RHYTHMIC CHANGES
It does not effect beat frequency at all
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Cabin noise and synchrophasing
What does the synchrophasing unit do
ensure BEAT FREQUENCY
does not match
RESONANT FREQUENCIES
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Cabin noise and synchrophasing
What is the difference between a synchronising unit and a synchrophasing unit
Synchronising unit
Remedies RHYTHMIC CHANGES
Sychrophasing unit
Remedies BEAT FREQUENCIES
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Cabin noise and synchrophasing
How many decibles can good synchrophasing reduce cabin noise by
10dB
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Control, Indication and Operation
In each engine type, what gauge is used to indicate power;
1. Simple single engine
2. Constant Speed Propeller System
3. Turboprop engine
- RPM gauge
- MAP gauge
- TORQUE gauge
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Control, Indication and Operation
On a turboprop aircraft, a torque gauge is an indicator of power. What 2 methods can this be sensed
- ELECTRONICALLY
- MECHANICALLY
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Control, Indication and Operation
On the most common types types of piston and turboprop units, what are the 2 levers used for controll engine power
- RPM (gearbox)
- THROTTLE (power)
For the RPM lever, think that it is an infinite gearbox, with fully forward being similar to 1st gear or “fully fine”.
The further you retard the RPM lever, the “higher” the gear (coarser the blade)
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Control, Indication and Operation
Typically, what coloud is the RPM lever used for adjusting the propeller angle
BLUE
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Control, Indication and Operation
Fully fine setting on the RPM lever makes the propeller fine and minimises torque drag. What 3 phases of aircraft movement/flight is this important for
- TAXING
- TAKE-OFF
- GO AROUND
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Control, Indication and Operation
Essential pre-takeoff and pre-aldning checks should ensure that the RPM lever is set in what position
FULLY FINE
(MAX RPM)
Same as 1st gear. Ensure that prop is fully fine to reduce torque drag so that in the event of go around, response from increasing throttle is quick
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Control, Indication and Operation
What type of supercharged engine is particularly at risk of overboosting
TURBOCHARGER
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Control, Indication and Operation
Commercial turboprop modern aircraft have a condition lever per engine. What is the purpose of this
SHUT OFF FUEL
and
SET OPERATING MODE
There are several operating modes normally. For example, take off, climbe, cruis. The condition lever can be set to a mode and the engine will be governed accordingly
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