PT3 - Inertial nav & FMS & EFIS & FANS Flashcards
INS
Inertial Navigation System
INS _ Platform (= mounted on a gimbal assembly)
2 accelerometers (N/S and E/W)
Possible third for vertical acceleration
3 integrating gyros (Long, Lateral, Normal)
3 gimbal motors (Pitch, Roll, Vertical)
Integrator
Time multiplication device
Integrating gyroscope
One degree of freedom gyro using viscous spring
INS _ Compensate for apparent wander
Earth rate : 15 sin(lat)
Transport rate : V/R (R = earth radius)
INS _ Alignment
Accelerometers leveled (velocity set to 0) Platform orientated to True North
INS _ Alignment steps
Warm up period
Coarse alignment : roughly leveled and aligned in azimuth
Coarse leveling : pitch and roll at 90°
Fine leveling : zero output from accelerometers
Gyro compassing : verification of position
Schuler period
Oscillation of 84.4 minutes
Bounded error
Return to 0 within the Schuler cycle
Unbounded error
Cumulative error
INS mode
OFF - STBY - ALLIGN - NAV - ATT REF
INS _ STBY mode
Power supplied
Insert the start position
INS _ ALLIGN mode
Platform leveled and aligned
- -> READY NAV illuminate
- -> switch to NAV mode
INS _ ATT REF mode
Disconnect computing and loses alignment
Gyros used for attitude and heading informations
INS _ BATT light
INS running on battery
INS _ NAV mode
Used for navigation
INS _ FROM/TO display
Waypoints between which INS assume it is flying
INS _ DIM control
Change the brightness
INS _ ALERT light
Aircraft approaching next waypoint
2 min before in auto mode
2 min before : on - 30 sec : flashing in manual mode
INS _ WARN light
System malfunction occurs
INS _ AUTO-MAN_RMT switch
Pilot implication
INS _ INSERT control
Enter info into the system
INS _ HOLD control
Update INS position
INS _ TK/GS display
Aircraft track - Ground speed
INS _ HDG/DA display
True heading - Drift angle
INS _ XTK/TKE display
Cross track distance - Track angle error
INS _ POS display
Present latitude - Present longitude
INS _ WPT display
Waypoint latitude - Waypoint longitude
INS _ DIS/TIME display
Distance to next waypoint - Time to next waypoint
INS _ WIND display
Wind direction - Wind speed
INS _ DSR TRK/STS display
Desired track - Blank
INS _ TEST display
All digits illuminates
INS _ Waypoint 0
Last INS position change
INS _ Initial set up
Slight latitude error : not recognized by INS
Gross latitude error : recognized by INS
Wrong longitude input : not verified
IRS
Inertial Reference System
IRS _ System
Strap down system
Laser gyros
INS _ System
Stand alone system
Mechanical gyros
Inertial navigation
Determination of vehicule’s location without external reference
IRS _ Outputs
Primary attitude Heading Acceleration Angular rate Inertial velocity Position Wind data Calculated data
INS _ Outputs
Primary attitude Heading Acceleration Position Track Angle Error Distance to waypoint Time to waypoint
IRS _ Inputs
3 laser gyros 3 inertial accelerometers Initial position Barometric altitude True Air Speed
IRS _ Laser gyros
Based on Sagnac effect
Sagnac effect
2 beams of light rotating in opposite direction
Condition : whole number of wave length
Measure of a frequency difference
–> Compute a rotation
IRS _ Laser gyros - Construction
3 mirrors 2 beams of light Helium neon 2 photo electric cells 1 piezo electric dither motor
IRS _ Laser gyros - Drift
Major source of error
IRS _ Laser gyros - Accuracy
The longer the path the greater the accuracy
IRS _ Laser gyros - Lock in
Synchronization of the beams
–> no more fringe pattern
IRS _ Alignment
True North : with earth rotation measured
Latitude : compute and compare with the inserted one
Alignment : mathematical leveling process
= Establishing the trihedron
IRS/INS _ Advantages
Activation : no spin up time
Maneuvering : insensitive to “g” attitude
Construction : mechanically simple and highly reliable
Range : wide dynamic range
Drift : small drift rates
Radio altimeter _ Principle
Measuring aircraft’s height above ground level from 2500ft.
Radio altimeter _ Use
Automatic landing system
Ground Proximity Warning System (GPWS)
Radio altimeter _ Emission
Frequency Modulated Continuous Wave
Change of frequency between emission and reception : compute frequency difference
SHF band
4200 to 4400 MHz
UHF band
1600 to 1660 MHZ
Radio altimeter _ Working angles
Pitch : 30°
Bank : 60°
Radio altimeter _ Pointer
Disappear behind mask
Altitude over 2500 ft.
Fault in transmitted signal
Altimeter switched off
Radio altimeter _ Press to test button
Press : turn the indicator = test
Turned : select a Low Altitude Index
Radio altimeter _ Boeing
2500 to 1000 ft. : nothing
1000 ft. to decision height - 100 ft. : white circle
decision height - 100 ft. to decision height : amber circle
Radio altimeter _ Accuracy
Higher between 3% and 1 ft.
Radio altimeter _ Delay
Residual height = difference between antenna on the fuselage and bottom of the trailing wheels
Cable length
FSM _ LNAV
Lateral NAVigation