flight instruments

Question 1

how is the magnetic needle attached to the floating compass card

Answer 1

liquid, usually alcohol, supports weight of the bar magnet and reduces friction and helps to dampen compass movement

Question 2

what is compass dip error

Answer 2

when aircraft is banked, needle of compass will attempt to follow earths magnetic field in vertical plane - the compass swings and points towards the centre

Question 3

how do you compensate for compass dip error?

Answer 3

UNOS - undershoot north, overshoot south

Question 4

what is compass acceleration error (acceleration)

Answer 4

on an easterly heading and aircraft accelerates -> compass will swing towards us and indicates a turn to the north

Question 5

what is compass acceleration error (deceleration)

Answer 5

on an easterly heading and aircraft decelerates, compass swings away and indicates a turn to the south

Question 6

how do you compensate for compass acceleration error

Answer 6

ANDS - accelerate north, decelerate south

Question 7

what is a gyroscope

Answer 7

a rotating mass that becomes rigid in space

Question 8

what does rigidity depend on

Answer 8

rotational speed, mass, radius of mass from centre

Question 9

what is gyroscopic precession

Answer 9

when a force is applied to a gyroscope, the resultant force acts in a direction that is perpendicular to the applied force

Question 10

power for gyro instruments comes from…

Answer 10

electrical power and suction pump

Question 11

how is electrical power supplied to gyro instruments

Answer 11

• some instruments have their have their gyros sped up by electrical power
• within the gyro, an electric motor is attached to the gyro axis in order to rotate the gyro at correct speed

Question 12

what does red flag on turn co-ordinator mean

Answer 12

gyro not running

Question 13

how does the suction pump provide power for the gyro

Answer 13

• some instruments have their gyros powered by air flowing over small buckets in outer edge of gyro wheel
• flow of air caused by suction pump attached to the engine, which draws air through gyro instruments

Question 14

what instruments does the suction pump power

Answer 14

attitude indicator and direction indicator

Question 15

what is an alternative to the suction pump

Answer 15

an external venturi tube

Question 16

where is the venturi tube

Answer 16

the fuselage side

Question 17

how does the external venturi provide power to the gyro

Answer 17

• a hole in the device is connected to the air powered instruments
• since the hole is in the low pressure area of the venturi, the other end of suction tube is open to atmospheric pressure = air is drawn through gyro devices and out into the venturi tube

Question 18

what are the disadvantages of using a venturi tube to power the gyro

Answer 18

• instruments do not start working immediately (gyro must meet operating speed)
• suction feed from venturi is only produced after the aircraft reaches a certain airspeed

Question 19

attitude indicators can topple for pitch angles of … and bank angles of …

Answer 19

pitch angles of more than 70 degrees

bank angles of more than 100 degrees

Question 20

what kind of gyro is the attitude indicator?

Answer 20

an earth gyro - gyro rotating in horizontal plane about the vertical axis (shaft)

Question 21

how does the direction indicator work

Answer 21

provides a stable gyro platform that is referenced to compass

Question 22

the direction indicator topples at pitch angles of … and bank angles of …

Answer 22

pitch angles of more than 55 degrees

bank angles of more than 90 degrees

Question 23

what are some errors that can happen to a direction indicator

Answer 23

real wander
transport wander
apparent drift

Question 24

what is real wander

Answer 24

friction causes gyro to wander

Question 25

what is transport wander

Answer 25

- rigidity in space causes gyro to maintain orientation - appears to the pilot that gyro heading wanders

Question 26

how to calculate transport wander

Answer 26

change of longitude x sin(mean latitude)

Question 27

what is apparent drift caused by

Answer 27

caused by earth's rotation - since gyro is fixed in space, earth rotates but gyro remains pointing to same direction - at pole, after 6 hours, the earth would have rotated 90 degrees = so gyro DI shows a heading error of 90 degrees - amount of precession caused by earth's rotation depends on earths latitude

Question 28

how to calculate precession per hour

Answer 28

15 degrees x sin(lat)

Question 29

how to reduce apparent drift

Answer 29

using a latitude nut - forces gyro to precess at a rate opposite to earth rate

Question 30

what does the turn indicator indicate

Answer 30

provides indication of rate of turn (rate of change of heading)

Question 31

how does the turn indicator indicate a rate of change of heading

Answer 31

gyro tries to remain still in space, so as aircraft turns, gyro exerts a force trying to maintain position = force is indicated to pilot via needle *not bank angle

Question 32

what does a turn indicator show

Answer 32

provides indicates of rate of turn

Question 33

what is a gimbal

Answer 33

a pivoted support that uses motors and sensors to stabilise a camera or device

Question 34

how much is the gimbal raised by at the front of the turn coordinator

Answer 34

30 degrees

Question 35

which is indicated first on the turn coordinator - roll or heading?

Answer 35

roll

Question 36

what is a rate 1 turn

Answer 36

a change of heading of 360 degrees in 2 mins

Question 37

what makes the slip indicator work

Answer 37

a ball suspended in liquid

Question 38

what does the slip indicator show

Answer 38

if the aircraft is out of balance

Question 39

what kind of measurement is atmospheric pressure

Answer 39

a static measurement

Question 40

what instruments require a static measurement

Answer 40

altimeter, ASI, vertical speed indicator

Question 41

what does the static port do

Answer 41

measure atmospheric pressure

Question 42

what is the alternate static source

Answer 42

needed incase static port is blocked

Question 43

what do you do if there is no alternate static source available and the static port is blocked?

Answer 43

break glass of VSI instrument

Question 44

cockpit pressure is ... than outside atmospheric pressure

Answer 44

lower

Question 45

what kind of pressure does the altimeter use

Answer 45

static

Question 46

how does the altimeter work

Answer 46

- as altitude increases --> static pressure decreases - altimeter senses this and displays pressure decrease interpreted as altitude

Question 47

high to low pressure or temperature = altimeter overreads or underreads?

Answer 47

overreads

Question 48

what does vertical speed indicator measure?

Answer 48

measures rate of change of static pressure

Question 49

how does the vertical speed indicator work

Answer 49

static pressure fed into capsule within VSI - calibrated leak also feeds pressure into main casing of VSI -- difference between casing pressure and the pressure inside the capsule causes VSI needle to indicate a vertical speed

Question 50

what does the accelerometer do?

Answer 50

compensates for instrument lag in displaying vertical speed

Question 51

how is dynamic pressure measured

Answer 51

pitot head -- pitot within pitot head collects air being forced into it as a result of forward motion

Question 52

what is the pitot head susceptible to

Answer 52

susceptible to icing --> has heating element (the switch) has a drain to drain water

Question 53

what is the airspeed indicator fed by

Answer 53

dynamic pressure

Question 54

when should pitot heat be on

Answer 54

whenever flight in moist air/cloud

Question 55

how is the airspeed indicator fed

Answer 55

takes a feed from pitot head - sum of dynamic and static pressures

Question 56

what would happen to the airspeed indicator if static pressure wasn't taken into account

Answer 56

aircraft gains altitude = ASI indicates a decline in airspeed as pressure reduces

Question 57

what errors can the airspeed indicator show

Answer 57

position errors, density errors, IAS and CAS corrections needed

Question 58

what happens to the altimeter if the static system fails

Answer 58

remain indicating the same altitude

Question 59

what happens to the VSI if the static system fails

Answer 59

slowly return to zero

Question 60

what happens to the ASI if the static system fails

Answer 60

will continue to read accurately if constant altitude is maintained, will overread if descent is commenced and will underread if climb is initiated

Question 61

what happens to the ASI if the dynamic system fails

Answer 61

will show a decrease in airspeed if descent is commenced, will show an increase in airspeed if climb is initiated

Question 62

what happens if both pitot and static ports become blocked

Answer 62

no change shown even if aircraft altitude or airspeed changes