Gyro Compass Flashcards
What are the main properties of a rotating body?
- Gyroscopic inertia
- Precession
What is gyroscopic inertia?
Angular momentum - A rotating body will remain at rest or in constant rotational motion unless an external force acts upon it.
A rotating body’s spin axis will remain pointing at a fixed position in space unless an external force is applied
What is Newtons 1st law of motion or the law of inertia?
An object remains at rest or in uniform motion in a straight line unless acted upon by an external force
What is precession?
A force acted upon a rotating body will act at right angles in the direction of rotation
What are the effects of precession on a rotating body?
When a force acts to tilt the plane of rotation, the rotating body will turn
When a force acts to turn the rotating body, the plane of rotation will tilt
What are the two effects acting on a free gyro on Earth?
- Gyro drift
- Gyro tilt
What is Gyro drift?
With the gyro on the Earths surface pointing at a fixed point in space, the Earth will rotate under it and show an apparent change in azimuth of the gyro
Where is gyro drift more pronounced?
Maximum drift at the poles and zero drift at the equator
What is gyro tilt?
The gyro points at a fixed point in space. As the earth rotates under the gyro, this fixed point will show apparent movement and the gyro will follow the fixed point resulting in the gyro tilting.
A change in latitude over the curvature of the Earth will also result in gyro tilt as it remains on this fixed position.
Where is gyro tilt most pronounced?
Gyro tilt is maximum at the equator and zero at the poles
How does a North seeking gyro work?
A gyrocompass is only equally balanced and horizontal to the plane of the Earths centre when on the meridian, as it was when first installed. In any other position, it has an external force acting on it.
As soon as it moves in azimuth to East or West of the meridian due to Earths rotation under it, precession causes tilt. As soon as it moves in latitude causing tilt, precession turns it in azimuth.
When tilted, the mercury reservoir on the low side now fills up creating a weight force on the gyro in a downward direction which causes precession to turn the gyro back towards the meridian.
Dampening ensures this does not happen too fast so that the gyro is never allowed to sway too far from the meridian.
How long does a gyro take to dampen?
approx 90 minutes
What are the static errors of the gyro?
- Alignment error
- Transmission error
- Variable errors - Dynamic error
- Speed/latitude error
- manoeuvring error
What is gyro alignment error?
the gyro and lubber line are not aligned or the lubber line and the ships fore/aft centreline are not aligned
What is gyro transmission error?
There is a difference between the master compass heading and the heading on gyro repeaters
