A - Engine instruments (06/11-06-18)

Question 1

What are the 2 categories of indications on an engine?

Answer 1

Performance

condition

Question 2

What do performance indicators measure?

Answer 2

They measure power from pressure ratios or speed indications or temperature indications

Question 3

What is an engine pressure ratio (EPR)?

Answer 3

the ratio of pressures between the compressor inlet and the turbine outlet/exhaust

Question 4

What happens to EPR with a speed increase?

Answer 4

it decreases slightly

Question 5

At what speed is the EPR usually set by?

Answer 5

60kts and not changed during TO unless there is an emergency

Question 6

What is the function of the P1 probe with regards to engines?

Answer 6

Measures compressor inlet pressure

Question 7

What happens to the indication of a blockage in the P1 probe?

Answer 7

it over indicates

causing EPR to increase,

causing fuel flow to decrease

causing less thrust

Question 8

What happens to the indication of a leak in the exhaust probe of an engine?

Answer 8

EPR decreases

fuel flow increases

therefore higher thrust

Question 9

What are the condition indicators in an engine?

Answer 9

Fuel pressure

Fuel temperature

Oil pressure

Oil temperature

Vibration

Question 10

What can be measured to indicate power in a turboprop?

Answer 10

Torque

Question 11

How is torque measured in a turbo prop with a hydraulic system?

Answer 11

axial load produced on helical gears is hydraulically measured when a torque is being transmitted to the prop

This pulls/pushes pistons which allow oil to flow easier or harder

more flow means higher pressure which means more power

Question 12

How is torque measured in a turbo prop with an electric torquemeter?

Answer 12

2 exciter wheels, one reference one on the prop shaft, are mounted on the shafts which interact with magnetic pickups

when thrust is changed the exciter wheels become out of phase and this phase shift is measured as torque.

Question 13

How is engine RPM measured on an engine?

Answer 13

electronically or mechanically by tachometer

Question 14

What are the 3 types of tachometer?

Answer 14

mechanical (drag)

tacho-generator (electrical)

Induction probe (electronic)

Question 15

How does a tacho generator measure RPM?

Answer 15

the engine turns the generator which creates a voltage

This voltage is sent to the instrument to be converted to an RPM measurement

Question 16

How does an induction probe tachometer work?

Answer 16

a speed probe is mounted on the compressor casing near a fan blade/notched phonic wheel.

as notches/fan blades pass it a disturbance is measured by the probe and are counted to give RPM

Question 17

How does a mechanical drag tachometer work?

Answer 17

A cable its rotated in a tube which is linked to a magnet

This rotates a drag cup on a spring which turns a needle

Question 18

Why are engine indicator needles designed to point the same direction under normal operation?

Answer 18

to allow the pilot to easily see if there are any issues

Question 19

What is a synchroscope?

Answer 19

A device that indicated if any engines are rotating at a slightly different speed to the master engine

thus allowing the pilot to make sure they are spinning at the same RPM

Question 20

How is engine vibration indicated?

Answer 20

relative to a normal level of vibration.

Question 21

What is the max pressure to be measured by a bourdon tube, its accuracy and where would one be used in an engine?

Answer 21

800psi

+/- 0.5 - 3%

engine and oil pressures

Question 22

What is the temperature measurement range of a thermistor?

Answer 22

25 - 300degC

Question 23

What is the max measurable temperature and +ve & -ve wire materials of thermocouples?

Answer 23

+ve wire, -ve wire, max Temp (application)

Copper, Constantan, 300degC (CHT)

Iron, Constantan, 410degC (CHT)

Chromel, Alumel, 1000degC (EGT)

Platinum, Rhodium-platinum, 1400degC

Question 24

What is a pyrometer?

Answer 24

An instrument that measures EM waves emitted by an object to measure its temperature

Question 25

How does a float fuel gauge work?

Answer 25

The float ball is attached to a variable resistor via a pivot

As the float rises the pivot changes the contact point on the variable resistor and thus reads a fuel volume.

Question 26

How does a flat plate capacitance fuel gauge work?

Answer 26

The capacitance across the plates where the fuel is has a relative permittivity of 2 whereas that with air is 1.

Thus a measure of capacitance can be measured to provide a fuel level.

the plates are actually tubes and there’s many in a tank.

Question 27

What is the equation for capacitance?

Answer 27

Capacitance = relative permittivity x area of plates / distance between plates

Question 28

What are fuel flow sensors used for?

Answer 28

checking for fuel system leaks

estimate A/C/engine performance

compare fuel used with fuel remaining

Question 29

What are the 3 types of fuel flow sensor?

Answer 29

Mechanical - fuel flow turns an impeller and rotation is measured as fuel flow

Electrical analogue - swirl from a motored impeller turns a torque reaction turbine. This torque is measured as fuel flow

Electronic - uses chemical make up of fuel

Question 30

What does a fuel flow sensor require to measure mass flow from volume flow?

Answer 30

SG

Question 31

What may excessive fuel flow indicate?

Answer 31

a fuel leak

Question 32

Where is flow rate usually measured in an engine?

Answer 32

in the low pressure fuel supply

Question 33

What is the schedule for engine maintenance based on?

Answer 33

Engine cycles

Hours of operation

Calendar intervals