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Flashcards in Inertial Navigation and IRS Deck (28):
1

1st integration

= acceleration x time = speed

Must know a starting speed

2

2nd integration

Speed x time = distance

Distance is a modified position

Must know starting speed and distance so can’t happen without 1st integration

3

Alignment process - INS

Gyro spins up and liquid warms

Platform will be physically levelled

Works out its position in space - using gravity and direction to true north using the earth rotation and associated drift

4

Typical alignment time - INS

10 mins

5

Errors of using INS

Can’t change the start position during flight

Bounded/unbounded errors

6

Bounded errors - INS

Fixed, constant over time

May be compensated for if you know the error

Schuler period - 84.4 mins
As everything is tied to the centre of the earth, the INS will be pendulous over 84.4 mins flights

7

Unbounded errors - INS

Varying over time so cannot be compensated for

E.g sensing errors

Can be seen as residual GS when parked after a flight

Position uncertainty is worst

8

INS is “ “ system

Stabilised platform system

9

Gyros in a INS

Vertically aligned

3x rate gyros with 1 degree of freedom - sense all 3 axis

10

Accelerometers in a INS

2x accelerometers - N/S aligned and E/W aligned

Can have 3 if doing altitude

11

Outputs from the INS

POS lat/long
GS
Track
Attitude/HDG - not all sense these
W/v

12

Inputs to the INS

Only requires TAS for w/v

13

Loss of alignment in flight - INS

Navigation loss

Maybe realigned for attitude

14

Inertial reference system is a “ “ system

Strapdown system

Physically fixed to the a/c structure

15

Laser gyro on a IRS

Uses the Doppler principle to measure acceleration

Rotation of the fringe pattern = acceleration

Change in the phase difference/freq of the 2 lasers = acceleration

16

How does the IRS calculate the local horizon

Senses gravity by using accelerometers to mathematically align the direction of the local horizon with the a/c trihedron

17

Accelerometers on an IRS

3x accelerometers - linear accelerometers

18

Alignment time

10-12min @ mid lats

19

Outputs of the IRS

Track
GS
Attitude
Heading
Vertical speed

20

Inputs IRS

Still has TAS inputs for wind

21

Loss of alignment - IRS

Nav lost

Can be realigned for attitude - flying s+l for a while and enter heading

22

Mid latitudes how long does a laser gyro take to align

10min

23

TR/GS

Instantaneous track mode and GS

24

XTR/TKE

Distance left/right and tracking error

25

DSRTK/STS

Required track between waypoints and system serviceability mode

26

ATT

Heading and attitude information

27

Gyros in the INS are corrected for

A/c manoeuvres, ER, TW and coriolis

28

The IRS measures

Both angular and linear accelerations