ALIGN-TO-NAV – The IRU enters navigate mode from alignment mode upon completion of alignment. NAV-TO-ALIGN - The IRU enters the align down mode from the navigate mode. NAV-TO-ALIGN-TO-NAV – The IRU enters the align downmode and after 30 seconds, automatically re- enters the navigate mode
ALIGN-TO-ATT or NAV-TO-ATT – The IRU enters the erect attitude submode for 20 seconds, during which the MSU ALIGN annunciator illuminates. The IRU then enters the attitude mode. MSU Annunciators ALIGN – Indicates that the IRU is in the alignment mode. A flashing ALIGN annunciator indicates incorrect LAT/LONG entry, excessive aircraft movement during align.
NAV RDY – Indicates that the alignment is complete. FAULT – Indicates an IRS fault. ON BATT – Indicates that the back-up battery power is being used. BATT FAIL – Indicates that the back-up battery power is inadequate to sustain IRS operation during back-up battery operation (less than 21 volts). NO AIR – Indicates that cooling airflow is inadequate to cool the IRU.
INERTIAL SYSTEM DISPLAY UNIT (ISDU)
INERTIAL REFERENCE UNIT (IRU) The IRU is the main electronic assembly of the IRS. The IRU contains an inertial sensor assembly, microprocessors, and power supplies and aircraft electronic interface. Accelerometers and LRG in the inertial sensor assembly measure acceleration and angular rates of the aircraft. The IRU microprocessors performs computations required for: Primary Attitude. Present Position. Inertial Velocity Vectors. Magnetic and True North Reference. Sensor Error Compensation
GYROCOMPASS PROCESS The three gyros sense angular rate of the aircraft. Since the aircraft is stationary during alignment, the angular rate is due to earth rotation. The IRU computer uses this angular rate to determine the direction of true north. INITIAL LATITUDE During the alignment period, the IRU computer has determined true north by sensing the direction of the earth’s rotation. The magnitude of the earth’s rotation vector allows the IRU computer to estimate latitude of the initial present position. This calculated latitude is compared with the latitude entered by the operator during initialization.
ALIGNMENT MODE The systems software performs a vertical levelling and determines aircraft true heading and latitude The levelling operation brings pitch and roll attitudes to within 1 accuracy (course levelling), followed by fine levelling and heading determination. Initial latitude and longitude data must be entered manually, either via the IRS CDU or the Flight Management System CDU. The alignment time is approximately 10 minutes
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- Fall '19
- Inertial navigation system, Gyroscope, IRU, Equipment