INS / IRS

Question 1

What is an inertial navigation system

Answer 1

A fully self contained navigation system which needs to external reference

Developed in the 70’s / 80’s

Question 2

How does a INS work

Answer 2

Track distance change calculated by measuring a/c accelerations

Question 3

How many time do you integrate acceleration to get velocity

Answer 3

Once

Question 4

How many times do you integrate acceleration to get distance

Answer 4

Twice

Question 5

What direction is the INS platform orientated

Answer 5

Relative to true north

Question 6

How many rate gyros does a INS have

Answer 6

3 rate gyros

Question 7

How many accelerometers does a INS have

Answer 7

3

Question 8

How many gimbals does the INS platform have

Answer 8

3

Question 9

What for a east gyro in the INS detect

Answer 9

Movement around east west axis

Question 10

What does the north gyro detect in the INS

Answer 10

Movement around the N/S axis

Question 11

What does the azimuth gyro detect in the INS

Answer 11

Movement up and down

Question 12

3 key phases of INS

Answer 12

1) initial power up (caging)
Locks gyros
Warms oil
Gets up to speed

2) levelling
3) align with true north

Question 13

If a/c flies north what happens to the accelerometer weight bob

Answer 13

Moves southward

Question 14

Steps of the mode selector unit for the INS

Answer 14

1) off
2) SBY - allow to set up / warm oil
Green light = ready nav

3) align or nav
If align = more accurate but can go straight to nav

Question 15

What is the red batter annunciator light for the more selector unit INS

Answer 15

Power supply for INS has failed

Question 16

How long can a INS take to align

Answer 16

Up to 15 mins

Question 17

How does the gyro know it’s aligned

Answer 17

No n/s accelerations due to earth rate

Question 18

Where does INS align quickest

Answer 18

Equator

Question 19

Where can the INS not be aligned

Answer 19

Above 70°N

Question 20

What happens in the INS when switched from align to nav mode

Answer 20

Keeps platform level and aligned

Question 21

Control display unit functions: TK

Answer 21

True track

Question 22

Control display unit functions: GS

Answer 22

Ground speed

Question 23

Control display unit functions: HDG

Answer 23

True heading

Question 24

Control display unit functions: DA

Answer 24

Drift angle

Question 25

Control display unit functions: XTK / TKE

Answer 25

Distance off track / angle between track / desired track

Question 26

Control display unit functions: POS

Answer 26

Position as latitude / longitude

Question 27

Control display unit functions: dist / time

Answer 27

Distance and time to next waypoint

Question 28

Control display unit functions: WAYPT

Answer 28

Lat / long of selected waypoint

Question 29

Control display unit functions: WIND

Answer 29

Wind direction / speed

Question 30

Control display unit functions: DARTK / STS

Answer 30

Desired track and system Status

Question 31

How is the component of gravity sensed if there is a error during alignment of the INS

Answer 31

Horizontal acceleration | = unbound error

Question 32

How to calculate TAS from INS

Answer 32

INS need the addition of information from ADC to create TAS as INS on its own is just groundspeed

Question 33

How does INS create magnetic heading output

Answer 33

Converts true heading using a database of variation magnetic and track values

Question 34

What are unbound errors in the INS

Answer 34

Ones that get worse Topple / drift Apparent wander A/c manoeuvre errors

Question 35

What is Schuler oscillations

Answer 35

The inertial platform behaves like a pendulum with length equal to earth radius

Question 36

What is the period of schuler oscillations

Answer 36

84.4 minutes

Question 37

What type of error is a Schulers error

Answer 37

Bound error

Question 38

What is Kalman filtering

Answer 38

Blending of inertial positions with gps + radio nav In modern a/c

Question 39

What power supply is used by a INS

Answer 39

Ac for normal operations Dc for backup

Question 40

If INS fails what can is be used as

Answer 40

Attitude reference

Question 41

How many IRS does a short / medium haul aircraft have

Answer 41

2

Question 42

How many IRS does a long range aircraft have

Answer 42

3

Question 43

How is a IRS similar to a INS

Answer 43

Has accelerometers and gyros Except they are laser gyros 3 solid state accelerometer 3 ring laser gyros

Question 44

How is IRS different to INS

Answer 44

Platform it fixed directly to airframe = strap down system Actual platform = generated mathematically to the a/c axis by computer = knows where true north is by calculation

Question 45

What at the components of a accelerometer in the IRS

Answer 45

Small proof weight attached to free end Piezo- electric layer is located at the point of max strain on the beam Acceleration perpendicular to the beam will cause it to bend

Question 46

What are the components of a ring laser gyro IRS

Answer 46

3 mirrors 1 one way murror 1 laser

Question 47

How does a ring laser gyro work

Answer 47

If not rotating then the laser beams both reach the detector at the same time / frequency If rotation = one length longer than the other / frequency change

Question 48

What is laser lock

Answer 48

If rotating rate measured is very small /slow (in the IRS) sometimes not registered

Question 49

How to fix laser lock

Answer 49

A dither motor is used to vibrate the laser ring gyro Doesn’t cause rotation just vibration + active hum

Question 50

What is ADIRS

Answer 50

Air data computer + inertial reference unit

Question 51

Do strap down systems suffer from schuler oscillations

Answer 51

Yeh

Question 52

How long does the IRS take to align

Answer 52

8-10 mins

Question 53

What happens if the IRS loses alignment in flight

Answer 53

Navigation ability is lost IRS May be re aligned in flight for attitude data only