INS/IRS Flashcards
How does an INS find true North?
Senses the angular rate of the A/C change, since A/C is stationary the angular rate is due to the earths rotation and therefore can find true north. Since magnitude is
dependant on latitude the IRU computer can also estimate the latitude of the aircraft.
When did INS start to come?
1970s
What’s the benefits of INS/IRS?
Very accurate
Is independant of outside Communication and ground stations.
What’s the principle of operation of INS?
It’s a sophisticated form of dead reckogning starting from known positions and measures the aircrafts accelerations
What info can you get from an INS?
- Present position
- Track
- Drift
- GS
- Dist to go
- Time to go
- Cross track displacement
- Track angle error
- Can generate pitch and roll data
What are the 3 effects of motion?
Which one can be measued without any external referances?
- Postion change
- Velocity
- Acceleration
Accleleration can be measured without any external references.
Describe the “integration” process for an INS/IRS?
- Accelerations, meters/sec/sec is integrated once to:
- Velocities, meters/sec which is integrated agian to:
- Present pos, meters which is converted to Dist Gone
Accelerometers measures accelerations which then are integrated twice. By knowing where we started and adding up how far we have gone we can get present position.
When did IRS start to come?
1990
When is a system usually given the name IRS?
When the referencedatum is a Laser Ring Gyro
What are the benefits to an IRS compared to an INS?
- Greater system integration
- Laser Ring Gyros
- Greater Computing power
What channels does an IRS use?
What is the difference compared to an INS?
IRS uses 3 channels:
- Forward
- Sideways
- Down (needs barometric input to stabilize it)
INS only uses the first two
What more can IRS do that INS can’t?
IRS have a database of LAT/LONG and VARIATION so t can compute magnetic heading between N73 and S60
Over that magnetic variation changes too rapidly
How does a Laser Ring Gyro functions?
Measures angular rotation.
Measures the path of two light beams. If triangle rotates it takes longer time for the one beam to reach the end point. Time difference is too small to measure so the frequency shift is used instead.
Photons (light) is sent out from the Cathode. Anodes attracts them. They split up and moves towards the mirrors. Cavity if filled with a gas (helium/neon) mix that acts as a conducting medium
LRG:s can suffer from Laser Lock which is when the beams sychromize and doesn’t show any output even when a/c changes direction. Diether motor to set up vibrations(that later are ignored) can be used to avoid it.
