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ATPL Instruments > INS / IRS > Flashcards

INS / IRS Flashcards

1
Q

What is an inertial navigation system

A

A fully self contained navigation system which needs to external reference

Developed in the 70’s / 80’s

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2
Q

How does a INS work

A

Track distance change calculated by measuring a/c accelerations

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3
Q

How many time do you integrate acceleration to get velocity

A

Once

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4
Q

How many times do you integrate acceleration to get distance

A

Twice

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5
Q

What direction is the INS platform orientated

A

Relative to true north

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6
Q

How many rate gyros does a INS have

A

3 rate gyros

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7
Q

How many accelerometers does a INS have

A

3

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8
Q

How many gimbals does the INS platform have

A

3

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9
Q

What for a east gyro in the INS detect

A

Movement around east west axis

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10
Q

What does the north gyro detect in the INS

A

Movement around the N/S axis

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11
Q

What does the azimuth gyro detect in the INS

A

Movement up and down

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12
Q

3 key phases of INS

A

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

2) levelling
3) align with true north

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13
Q

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

A

Moves southward

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14
Q

Steps of the mode selector unit for the INS

A

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

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15
Q

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

A

Power supply for INS has failed

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16
Q

How long can a INS take to align

A

Up to 15 mins

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17
Q

How does the gyro know it’s aligned

A

No n/s accelerations due to earth rate

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18
Q

Where does INS align quickest

A

Equator

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19
Q

Where can the INS not be aligned

A

Above 70°N

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20
Q

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

A

Keeps platform level and aligned

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21
Q

Control display unit functions: TK

A

True track

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22
Q

Control display unit functions: GS

A

Ground speed

23
Q

Control display unit functions: HDG

A

True heading

24
Q

Control display unit functions: DA

A

Drift angle

25
Q

Control display unit functions: XTK / TKE

A

Distance off track / angle between track / desired track

26
Q

Control display unit functions: POS

A

Position as latitude / longitude

27
Q

Control display unit functions: dist / time

A

Distance and time to next waypoint

28
Q

Control display unit functions: WAYPT

A

Lat / long of selected waypoint

29
Q

Control display unit functions: WIND

A

Wind direction / speed

30
Q

Control display unit functions: DARTK / STS

A

Desired track and system Status

31
Q

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

A

Horizontal acceleration

= unbound error

32
Q

How to calculate TAS from INS

A

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

33
Q

How does INS create magnetic heading output

A

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

34
Q

What are unbound errors in the INS

A

Ones that get worse

Topple / drift
Apparent wander
A/c manoeuvre errors

35
Q

What is Schuler oscillations

A

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

36
Q

What is the period of schuler oscillations

A

84.4 minutes

37
Q

What type of error is a Schulers error

A

Bound error

38
Q

What is Kalman filtering

A

Blending of inertial positions with gps + radio nav

In modern a/c

39
Q

What power supply is used by a INS

A

Ac for normal operations

Dc for backup

40
Q

If INS fails what can is be used as

A

Attitude reference

41
Q

How many IRS does a short / medium haul aircraft have

A

2

42
Q

How many IRS does a long range aircraft have

A

3

43
Q

How is a IRS similar to a INS

A

Has accelerometers and gyros

Except they are laser gyros

3 solid state accelerometer

3 ring laser gyros

44
Q

How is IRS different to INS

A

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

45
Q

What at the components of a accelerometer in the IRS

A

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

46
Q

What are the components of a ring laser gyro IRS

A

3 mirrors
1 one way murror
1 laser

47
Q

How does a ring laser gyro work

A

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

48
Q

What is laser lock

A

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

49
Q

How to fix laser lock

A

A dither motor is used to vibrate the laser ring gyro

Doesn’t cause rotation just vibration + active hum

50
Q

What is ADIRS

A

Air data computer + inertial reference unit

51
Q

Do strap down systems suffer from schuler oscillations

A

Yeh

52
Q

How long does the IRS take to align

A

8-10 mins

53
Q

What happens if the IRS loses alignment in flight

A

Navigation ability is lost

IRS May be re aligned in flight for attitude data only

ATPL Instruments (18 decks)

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