10. Propeller Systems - Sections 5-8 Flashcards by C MC

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 ## Footnote 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 Pg 254

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 ## Footnote Power lever has to be lifted through a gate in order to put it into a flight idle position Pg 254

# Reverse Thrust What is it important to understand regaridng the degrees of *beta range*

covers POSITIVE and NEGATIVE values ## Footnote 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 ## Footnote Pg 256

# 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 ## Footnote 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. Pg 256

# Reverse Thrust What is the purpose of an *under-speed governor*

SCHEDULES MORE FUEL in REVERSE THRUST ## Footnote 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 Pg 257

# 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 ## Footnote Pg 257

# 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 ## Footnote Pg 258

# 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 ## Footnote Pg 258

# Cabin noise and synchrophasing If an aircraft has 2 or more propellers, when the *blade frequencies* are combined, what does this create

BEAT FREQUENCY ## Footnote Pd 259

# Cabin noise and synchrophasing What is a *beat frequency*

2 or more propellers combined blade pass frequency ## Footnote Pg 259

# 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 ## Footnote Pg 259

# Cabin noise and synchrophasing When propellers are rotating at slightly different speads, what can this cause

Slow rise and fall beat frequency ## Footnote Pg 259

# Cabin noise and synchrophasing How can *rhythmic noise pattern* be cured

SYNCHRONISING PROPELLERS ## Footnote Synchronising propellers so that they are totating at exact same RPM Pg 259

# Cabin noise and synchrophasing What does a *synchronising unit* do

SYNCHRONISES PROPELLERS | Makes propellers rotate at exact same RPM ## Footnote Pg 259

# 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 ## Footnote Pg 259

# 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 ## Footnote Pg 259

# Cabin noise and synchrophasing The *synchronising unit* can eliminate *RHYTHMIC CHANGES* or *BEAT FREQUENCY*

RHYTHMIC CHANGES | It does not effect beat frequency at all ## Footnote Pg 260

# Cabin noise and synchrophasing What does the *synchrophasing unit* do

ensure BEAT FREQUENCY does _not_ match RESONANT FREQUENCIES ## Footnote Pg 260

# 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 ## Footnote Pg 260

# Cabin noise and synchrophasing How many decibles can good *synchrophasing* reduce cabin noise by

10dB ## Footnote Pg 261

# 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

1. RPM gauge 2. MAP gauge 3. TORQUE gauge ## Footnote Pg 263

# Control, Indication and Operation On a *turboprop* aircraft, a torque gauge is an indicator of power. What 2 methods can this be sensed

1. ELECTRONICALLY 2. MECHANICALLY ## Footnote Pg 263

# 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

1. RPM (gearbox) 2. THROTTLE (power) ## Footnote 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) Pg 264

# Control, Indication and Operation Typically, what coloud is the *RPM lever* used for adjusting the propeller angle

BLUE ## Footnote Pg 264

# 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

1. TAXING 2. TAKE-OFF 3. GO AROUND ## Footnote Pg 264

# 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) ## Footnote 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 Pg 264

# Control, Indication and Operation What type of supercharged engine is particularly at risk of *overboosting*

TURBOCHARGER ## Footnote Pg 266

# 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 ## Footnote 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 Pg 268