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INSTRUMENT > GYROSCOPIC SYSTEMS > Flashcards

GYROSCOPIC SYSTEMS Flashcards

1
Q

What are the properties of a Gyroscope?

A

Rigidity in space and

Precession

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2
Q

What type of Gyros are there?

A
  1. Tied gyros
  2. Earth gyros
  3. Rate Gyros
  4. Solid state laser gyros
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3
Q

What is a Tied Gyro used for and what axis gyro is it?

A

Used for DI:s

Horizontal axis gyro

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4
Q

What is an Earth Gyro and what axis gyro is it?

A

Used for Artificial Horizons

Vertical axis gyro

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5
Q

What’s a Rate gyro used for and what axis gyro is it?

A

Measuring rate of turn

It’s a horizontal axis gyro

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6
Q

What’s Laser gyro used for?

A

Used in IRS systems

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7
Q

What 3 types of Gyro wander is there?

A
  1. Real wander
  2. Apparent wander
  3. Transport wander
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8
Q

What is apparent wander of a gyro?

A 
Drift and Topple
Is due to the rotation of the earth
Drift is the horizontal component
Topple is the vertical component
HADPET
VET
Wander rate is 15,04 deg/hr
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9
Q

What is transport wander?

A

When the gyro is moved east or west

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10
Q

Difference between INS and IRS?

A

INS is the early system that started in the early 70:s and then developed into IRS
IRS have vertical data and magnetic heading info
IRS is also more integrated with the aircrafts systems

An INS is a collection of components that together provide a system that is able to provide navigation computations and solutions. An IRS is different in that it is a single box that contains an Inertial Reference Unit [IRU] and a computer to produce reference information.

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11
Q

What is the principle of operation of INS?

A

Accelerometers measures accelerations, meter/sec/sec
Integrates it once to Velocity, meters/sec
Integrates it a second time to Dist gone, m

By knowing where we started and adding up how far we have gone we can get present position

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12
Q

What are the 3 effects of motion for INS purposes?

A
  1. Position change
  2. Velocity
  3. Acceleration

Only acceleration can be measured without external references

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13
Q

What info can get out of an INS/IRS system?

A 
Present position
Heading
Track
Drift
Ground speed
Dist to go
Time to go
Cross track displacement
Track error angle
Avionics data, pitch and roll
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14
Q

What makes INS/IRS suitable for polar/high lat navigation?

A

It’s not dependent on magnetism

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15
Q

When did IRS:s start to come?

A

From about 1990

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16
Q

How does an IRS work?

A

Uses a Laser Ring Gyro instead of a spinning disc rotor type gyro like the INS system
3 IRS:s send their output to a central computer

17
Q

What channels does an IRS have?

What channels does an INS have?

A
  1. Forward
  2. Sideways
  3. Down

INS doesn’t have the down channel
Vertical channel of the IRS is unstable so it needs barometric altitude input to stabilize it

18
Q

How does IRS compute magnetic heading and between which altitudes is it working?
Why not at other latitudes?

A

IRS have a data base with LAT/LONG and VARIATION to compute magnetic heading
Magnetic output is only between N73 deg and S60 deg
Beyond that magnetic variation changes too rapidly

19
Q

How many Laser Ring Gyros are used for IRS?

A

3

One for: Pitch, yaw and roll

20
Q

What does a Laser Ring Gyro measure?

A

Angular rotation

21
Q

How does a Laser Ring Gyro work?

A

Measures the path of two light beams
Light beams, photons, are sent out from the bottom of the triangle called the cathode
They split up and move towards the mirrors set up in each corner of the triangle. Cavity is filled with a helium/neon gas mixture which acts as a conducting medium
Photocell detectors at the top of the triangle collects the beams and depending on time difference to get there it can tell the direction and rate of rotation
Time difference is too small to measure so the frequency shift is measured instead
If triangle rotates right when beams are sent out it takes longer for the left beam to reach the end point.

22
Q

What is Laser Lock in a Laser Gyro?

A

If the beams synchronize they can give zero output even when a/c changes direction.
Can be avoided by a Dither motor which sets up vibrations. These vibrations are taken out of the equation by the receiving photocell detectors

23
Q

What’s the decay rate of INS accuracy?

A

1-2 nm per hour

24
Q

With Laser ring gyros. Which of the 2 beams will have the lower frequency?

A

The one travelling the longer distance

25
Q

How does an INS find true north?

A

An INS finds true north by using a process called gyro compassing. Inside the IRU, the 3 gyros sense angular rate of the aircraft. Since the aircraft is stationary during alignment, the angular rate is due to the earth’s rotation. The IRU computer uses this angular rate to determine the direction of true north. The magnitude of the earth’s rotation is also measured which allows the IRC to estimate the aircraft’s latitude. This latitude is then compared to the latitude entered into the computer by the pilot during initialisation

INSTRUMENT (11 decks)

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