02 Inertial Reference System (IRS)

Question 1

What are the main components of an IRS and what is their function?

Answer 1

• 3 x Laser ring gyros which sense angular acceleration

- 3 x Accelerometers which sense linear acceleration

Question 2

What is the principle of operation of an IRS?

Answer 2

Mathematically aligns to the AC trihedron and the position + attitude in space

Question 3

What are the steps for alignment of an IRS?

Answer 3

• Automatic test of the battery
• Calculates the horizontal plane
• Senses the drift
• Calculates the lat and the direction of true North

Question 4

What are the outputs from the IRS?

Answer 4

• Latitude and Longitude
• Ground speed
• Heading (true and magnetic)
• Attitude
• Vertical speed
• W/V

Question 5

With regards to the IRS, what do the following command options mean:

• Align
• Nav
• ATT

Answer 5

• Align: Unit refines alignment, AC cannot move
• Nav: Unit aligns and operates normally once aligned
• ATT: Unit re-aligns to retrieve attitude during flight

Question 6

What is the principle of operation of a Laser Ring Gyro?

Answer 6

Uses the principle of wave interference due to the Doppler effect during rotation

Question 7

What issue can a Laser Ring Gyro suffer from and what can be added to prevent it?

Answer 7

• Can suffer from Laser Lock: Inability to sense very low rates of rotation
• A ‘Dither Motor’ (vibrator) can be attached to remove this issue

Question 8

What are the key differences between an INS and an IRS?

Answer 8

• INS is used for stand alone navigation where as an IRS is used in conjunction with the FMS
• IRS is much more accurate