Gyro Theory - Mariner Scout Ship Tradewind

Report
Navigation
Compasses
Gyro Theory
• A Gryro compass is a North Seeking
Gyroscope
• A spinning wheel held by two GIMBALS
• Has 3 axies of angular freedom
– Spin Axis
– Horizontal Axis
– Vertical Axis
Gyrocompass
• Gyroscope
• 3 axes
– Spin
– Torque
– Precession
Precession axis
Spin axis
Torque axis
• Gyrorepeaters
Compasses - Abbreviations
• Gyrocompass
• Magnetic Compass
PGC
– Steering Compass
– Standard Compass
PSTC
PSC
Gyro Theory
• Physics – A Gyro Scope will always point in
one direction (in this case TRUE NORTH)
• Precision – Apply force to the spin axis and the
gyro scope will rotate, not in the direction in
which the force was applied but 90 degrees
from that force vector.
Gyro Compasses
• Ships normally have 2 gyro compasses
– Main – Orientated N/S used for Navigation
– Auxiliary – Oriented E/W for combat systems or as
a backup for Navigation.
• Located deep within the ship
• On the center line
Gyro Uses
• Gyro Repeaters
– Located on the bridge wings, Navigation Table,
Dead reckoning plot
– Are used for Fire Control for gunnery systems –
Pitch, yaw, and Roll
– Centerline Pelorus – Center of Bridge used as the
most accurate reference
Gyro Error
• Mechanical Device – has some inherent error –
THE KEY IS TO KNOW WHAT IT IS AND
HOW TO CORRECT FOR IT
• Sources of error
–
–
–
–
Mechanical Friction
Ship’s motion
Electronic malfunctions
Power Fluctuations
Determining Error
• Visual Range
• Triangulation
– Adjusting three or more lines of position to find
location and bearing .
• Compare course with a known true course
– Entering and exiting port or in a channel
• Celestial Azmiuths and Amplitudes
• Comparison with a gyro of known error
Gyro Error
• Error – the difference between the true bearing and the
Gyro reading
• Expressed in degrees East or degrees West
Gyro Least, error East
Gyro Best, error West
Gyro Bearing + East Error = True Bearing
Error Example
You are dead center on a Range Bearing 173
Degrees True and your Gyro reads 175 Degrees
PGC what is your Error?
GYRO = 175
True = 173
GYRO is BEST ERROR is WEST
175 – 173 = 2 degrees West
Shipboard Compasses
• Three principle references of direction
– Ships longitudinal axis
RELATIVE BEARING (R)
– Local magnetic meridian MAGNETIC BEARING (M)
– True meridian
TRUE BEARING (T)
Relative Vs. True
• Relative bearings Can NOT be plotted so
must converted
Relative Bearing + Ship’s Head =
True Bearing
090 + 090 = 180
Magnetic
• The Earth is a core of Iron which acts as a large
magnet with its poles aligned with the earth’s axis
• NOT located at 090 North Latitude
– Difference is VARIATION
• Magnetic Meridians - Skewed due to
irregularities in the Earth’s
core
Applying Variation
• Variation is found by referencing the compass
rose closest to the ship’s position
Deviation
• Each ship is made of Steel and Iron
• It has its own magnetic field that can effect changes in
the ship’s magnetic compass
• Determined by angle in which the Keel is laid during
initial construction
• Equipment – electronics can also cause deviation
• Expressed in Degrees East
and West (rounded to nearest
.5 Degree)
• Changes with the ship’s heading
Degaussing
• Degaussing system - electrical installation designed to
protect ships against magnetic mines and torpedoes
• Purpose – counteract the ship’s magnetic field and
establish a condition such that the magnetic field near the
ship is, as nearly as possible, just the same as if the ship
were not there
• Degaussing installation consists of permanently installed
degaussing coils wrapped around ship on underside of
hull, control unit to control the coil current, and compass
compensating equipment to prevent disturbances to mag
compasses
– Coil is a large diameter electrical wire
– A, F, L, M, Q Coils
Compass Error
• Deviation + Variation =
Compass Error
Observed Bearing Least =
Error East
Observed Bearing Best =
Error West
Ex. Deviation = 3 West
Variation = 13 West
3 + 13 = 16 West
Example
• USS Princeton is on course 125 degrees true
when you lose your gyro scope. The
Navigation gives you the following:
• Variation = 8 degrees West
• Deviation = 2.5 degrees East
Example
•
•
•
•
•
•
Truly – True Course = 125
Valiant – Variation = 8 W
Marines - Magnetic Course = 133
Don’t - Deviation = 2.5 E
Cry – Compass – 133 –2.5 = 130.5
Because of ADD WEST
Application of Compass Error
Can
Dead
Men
Vote
Twice
At
Elections
Compass Head
Deviation
Magnetic Head
Variation
True Head
Add
East
What the mag compass reads
What the magnetic heading is
What the true heading is
Sample Problem #1
•
•
•
•
Degaussing is ON
Ship’s Magnetic Compass reads 030° PSTC
Var is 11° W
Find ship’s true head
Interpolation
•
•
•
•
•
Bill and Jorge decide to split a pizza.
The pizza costs $9.00 and has 6 slices.
Bill eats 5 slices
Jorge eats 1 slice
How much should Bill pay?
Interpolation
•
•
•
•
Eating all the pizza slices costs $9.00
Eating none of the pizza costs $0.00
So Bill has eaten 5/6 of $9.00
5/6 times $9.00 = $7.50
This is interpolation - calculation of an
internal value by assuming a linear
relationship with surrounding data.
Sample Problem #2
C
D
M
V
T
AE
Sample Problem #2
C
D
030
M
V
T
AE
Sample Problem #2
C
D
M
030 (-3)
V
T
AE
Sample Problem #2
C
D
M V
030 (-3)
027
T
AE
Sample Problem #2
C
D
M V
T
AE
030 (-3)
027
Reinterpolate - We assumed that the magnetic
head was 030, we now see it was 027
Sample Problem #2
Reinterpolate - We assumed that the magnetic
head was 030, we now see it was 027.
Value for 030 = 3.0W
Value for 015 = 3.5W
3.0W-3.5W = -0.5W
Sample Problem #2
030 - 015 = 15 degrees
027 - 015 = 12 degrees
So we are 12/15 of the way from 015-030
12/15 times -0.5 = -0.4
BUT we round to the nearest .5 so it is -0.5
3.5W - 0.5W = 3.0W
Or no change (in this case)
Sample Problem #2
C
D
M V
T
030 (-3)
027
Reinterpolate
027
AE
Sample Problem #2
C
D
030 (3)
M
V
T
027
Reinterpolate
027
(11)
AE
Sample Problem #2
C
D
030 (3)
M
V
T
027
Reinterpolate
027
(11)
016
AE
Questions?
• Homework – Read Chapter 8 pg. 129-147
• 1st Homework due Tuesday
• 2nd due Next Thurs

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