AHRS Flashcards
That is the purpose of AHRS?
Monitors the change of aircraft attitude in free space and provides secondary source of data for nav system.
What does the AHRS provide?
Attitude - Pitch, roll + yaw
Yaw rate - angular rate about the vertical axis
Pitch and roll rates
Accelerations - in three earth axis (Lat, long + vert)
Velocity - vertical velocity
Magnetic heading - angle of the aircraft longitudinal axis relative to magnetic north.
True Heading - angle obtained from magnetic heading compensated by mag variation.
How is the difference between the mounting plates and aircraft datum adjusted?
Electronically in the SEU during the alignment phase.
How many SEU’s are there and where are they located?
2
AV Bay upper forward shelf, left and right. inside of the GCU’s.
How are the SEU’s mounted?
-/+ 2 deg to the three principal aircraft axes (lat, long, normal) Residual misalignments (boresight angles) measured to -/+ 0.05 and is stored in the SEU Nonvolatile memory (NVM)
What does each SEU contain?
3 single axis fibre-optic gyros
3 silicon accelerometers
How is the MDU aligned?
Within 1 deg of the longitudinal axis.
Where is the Magnetic detector unit? (MDU)
Rear fuselage (Tail cone) right side.
What is the purpose of the MDU?
It detects the direction of the earths magnetic field to establish a heading reference through a pendulous flux valve.
How is the MDU powered?
26Vac from a step-down transformer.
How are the SEU’s powered?
28Vdc supply SEU 1 DC ESS BB 1 + SEU 2 DC ESS BB 2
26 V 400Hz AC Supply for synchro and MDU referencing (No 1 +2 Vac BB)
Where are the AHRS Switches?
Left side of the overhead console.
What happens after the AHRS are selected on?
After 5 secs, the SEU initialisation and alignment phase starts and automatically aligns, on ground and air.
What information does AHRS display on the PFD?
Attitude Indicator (AI)
Vertical Speed Indicator (VSI)
Horizontal Situation Indicator (HSI)
How is extreme slip indicated on the AI?
Half of the simulated ball disappearing at the outer scale marks.
On the HSI how is the aircraft heading shown?
As a digital readout at the top of the compass card.
What indications will you get on the IDU’s if the AHRS system is in any condition other than fully aligned?
Functional status indicators display:
STANDBY
COMP CAL
ALIGNING
DG
flashing for 5 secs at 1 Hz and then remain steady.
Repeated on IDU map format and hover format displays.
After power is applied to the AHRS how long does it take to start the alignment phase?
5 secs.
If the AHRS does not receive inputs of latitude and mag variations from the AMS what happens?
Stored parameters are used but accuracy is not guaranteed.
During alignment what is the automatic mode of operation?
Slave (to the MDU)
How long approximately does it take the system for ground alignment?
30 secs.
What is the purpose of a compass swing?
To calibrate the AHRS
Compensate for magnetic disturbances in the aircraft Determine any residual errors in the system
How often does the compass swing need to be carried out?
Every 52 weeks.
How long will it take to align the AHRS on a ship?
120 seconds.
