INS Flashcards
INTEGRATION VELOCITY
~gives change of position
~present positon relative to a known starting positon
~integration of vertical velocity gives vetical distance travelled
Measuring velocuity
~starting velcoity and size of the accelrretion need to be known
Types of inertial system
~inertial navigation system (INS) :gyro stabilise platform
~inertial reference system (IRS):
Platform integrated into the flight management system
Know as strap down system as they are fixed units
Stablised platform usually found in old INS
The strap down system usually found in modern IRS
Long range a/c need at least 2 IRS
It can also provide attitude and heading since is a gyroscope INS
Electromechanical sensors ,accelerometers
~an electromechanical accelerometer uses a pendulum arrangemnt to detect accelration in one dimesion
~at the bottom of the pendulm has a pick off
1st integration to find»_space;velocity (time x accel)
2nd intergration to find distance(distance) (which gives the lattitude. In the N/s acceloretemet)
And then the intergration is done for the E/W accelrotmeter and is fed the lattitude to find the chlong (depart x secnat lat0
The gyro platfrom is orientated to the true north and the a/c has the database of tthe avriation to get the magnetic north
Gyro stabilisation using 3 RATE integration gyros
One gyro detecs rotation about the east /west axis
One north/south axis
One vertical axis ,in the horizontal azimuth plane
Rate intergratiting gyros
Output angle is proportioanl to the amount of change of the iput angle
~output rotation is greater than input rotation
Much more sentive than displacemnt gyro
A torque motor opposes themotion of the output axis
Intial alignment
~the a/c must be stationary:
-instial power up (caging)
-levelling
-gyro compassing
Gyro compassing
~aligning the platform to true north
~topple is sensed by platform
~if properly aligned to ttrue north the platform would be slowly rotating around its north/south axis
~apparent topple caused by rotation of the earth
~should be no rotaion around the east/west axis
~any roation must be due to misalignmnet
Effect of latitude during alignment
~less tople at high laititudes
~aligmnetn is less accuarte
~takes longer
~alignmnet not possible at very high latitudes
Once aligned ,an ins can be operatated at thigh latitudes
Aligmmnet take like 10/20 min at mid lat
In motion alignmnet cannot be carried out with an INS
XTk/TKE
Xtk: how far off are you form the desired track
Tke : how much turn you need to get the desired track
Dsrtk/sts
Left/right
At 2 minute for the next waypoint the the amber light will start to flash ,if in auto
In manual mode,the alert light will remian lit and the a/c will contune on current track and will not turn towards the next waypoint
Bounded error
When the longitude is inserted wrongly result in a constant error
Unbounded error
Incorrect latitude input error ,making an increase in distance error
Input comparison
If calculated and inputted lattitudes dont match ,either
~the alignmnet is bad
~the crew enetered an incorrect latitude
Stablised platform variants
~2 accelerometer platform ,common if vertical velocity not required
~displacemnt gyro,obsolute
~wander angle platform ,not aligned with refence to true north
~system detecs topple on both axes to determine orientation
~changes in orientation are tracked
Latitude
1 degree of latitude is equal to 60nm
Longitude
Chlong (min) = departure /coslat
Ground speed
Adding the velocity components togheter
The inertial system calculates groundspeed not tas
Inertial system corrections
~topple and drift due to earth rotation
~topple and drift due to transport
~a/c manouvres (changes of attitude or heading)
~additional factors:
~coriolis effect
~centripetal acc
~Schuler oscillation (84,1 min)
Erros
~source of error:
-the accuracy pf sensing rotaion raets and acc
-incorect inital longitude /misalignment of the platform
-computational error by ins
~a value for the position error oif am INS is 1/2 nm per hour or more ,or average of 1,5 nm per hour
Interial system and reversion
~uses oner AC and one DC supply for aligment
~uses AC for normal operation with DC as a backup
~if AC fails ,the system fails
Unless it has a batetery to keep it alive unitl power is restores
