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ATPL Instruments > Engine Instruments / Fuel > Flashcards

Engine Instruments / Fuel Flashcards

1
Q

What are the 2 categories of gas turbine indicators

A

Performance indicators

Condition indicators

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2
Q

What is the SI symbol for rotation speed

A

N

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3
Q

What is the first sign of a engine starting in a 3 spool engine

A

Rotation in N3

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4
Q

What is the first sign of starting in a 2 spool engine

A

Rotation in N2

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5
Q

What does the N1 gauge show

A

% of max rotational speed of low pressure (LP) shaft (fan)

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6
Q

What is EPR

A

Engine pressure ration

P7/p1

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7
Q

What is P1

A

Compressor inlet pressure

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8
Q

What is P7

A

Exhaust outlet pressure

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9
Q

What happens to EPR if P1 probe is blocked

A

EPR will overread

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10
Q

What must be done to the EPR on takeoff

A

Set to a forward speed due to an apparent decrease in pressure at P1

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11
Q

What does the N2 gauge show

A

High speed shaft (engine core) speed = shown as % of max value

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12
Q

What does the P7 probe show

A

Situated at rear of engine gives exhaust pressure displayed at direct psi or %

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13
Q

What are condition indicators

A 
Oil temp / pressure 
Fuel temp / pressure 
Fuel flow 
Exhaust gas temperature (EGT)
Vibration
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14
Q

How does the mechanical tachometer work

A
  • flexible drive taken from rear of engine
  • fed to rear of instrument where it drives a magnet within an aluminium drag cup
  • rotating magnet sets up eddy currents
  • turning force is restricted by hairspring

In engine close to cockpit and fairly low revving

Max length of drive = 2m

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15
Q

How does a DC tachogenerator (electrical) work

A

Essentially a voltmeter

Output voltage varies with engine speed

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16
Q

What is the 2 disadvantages of a DC tachogenerator (electrical)

A

Requires a commutator and carbon brushes = leads to wear = electrical sparking can cause radio interference

Voltage loss in transmission = indication error

17
Q

What is a single phase AC tachogenerator (electrical)

A

Same as a Dc tachogenerator except used AC and then rectifies it to Dc

Voltage is proportional to rpm

Still has indication errors caused by voltage losses in transmission

18
Q

What is a three phase AC tachogenerator (electrical)

A

3 phase ac current

Frequency varies with RPM

magnets designed to rotate at the same frequency as the generator = ‘asynchronous’ or ‘squirrel-cage’

19
Q

What is a squirrel- cage motor in the three phase AC tachogenerator

A

Rotates slightly slower than ac generator = rotor slip

Motor turns magnet on aluminium ‘drag-cup’

Drag cup turns against hairspring to move indicator needle

20
Q

What does a gas turbine need for the three phase Ac tachogenerator

A

Step- down gearing because of faster rpm

21
Q

Advantages of a three phase AC tachogenerator

A

Because frequency is senses not voltage then losses in transmission are negligible

22
Q

Disadvantages of a three phase AC tachogenerator

A

Because of extra wiring = heavier

23
Q

What is a induction tachometer (speed probe) ‘electronic’

A

For engine spoils that do not drive a gearbox

Probe adjacent to either a toothed wheel or the fan

Creates magnetic field as wheel turns

Charges induced are proportional to the rpm detected

24
Q

How is the signal for the induction tachometer processed

A

1) in older air craft = transformed to create high voltage / low current

signal loses little strengths in transmission over long cable runs

2) modern aircraft square off into digital signals

Not affected by voltage loss in transmission = suitable for engine management computer

Disadvantage is it required power

25
Q

How is engine vibration measured

A

Accelerometer or piezo electric element

Number given in cockpit has no units

26
Q

What is a mechanical fuel quantity measure

A

Measured valine

Affected by aircraft attitude

May require power if sensor if variable resistance and for instrument light

27
Q

What is a capacitance type fuel quantity gauge

A

Dielectric property of fuel is 2 x that if air

The charge the capacitor can hold is doubled in fuel

Works by measuring the capacitance or the capacitor

28
Q

What do you do if the fuel quantity doesn’t quite match up

A

Use a drip stick

29
Q

What is a reference capacitor

A

Used for reference or the fuel in a capacitance type fuel quantity gauge

Always submerged

30
Q

Is a capacitance fuel quantity gauge affected by attitude

A

Nope

31
Q

Fuel flow mechanical (vane) type

A

Measured volume

Used with piston engines

Ltr / hr

32
Q

Impeller type fuel flow system

A

F= ma

Measured mass flow

Kg/ hr

Totaliser = fuel flow x time

How much fuel has been used

33
Q

What is a synchro scope

A

To synchronise propeller RPM Tor mep

Master sets reference of other engine(s)

Can use voltage from alternator as measure

Synchronise rpm for to reduce vibration and noise

Doesn’t improve fuel burn

34
Q

What is synchrophase

A

Same as synchroscope

Also adjusts prop position

Further noise reduction

ATPL Instruments (18 decks)

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