AH-1000 Product Knowledge What is an AHRU? Flashcards
AHRU
Attitude, Heading Reference Unit
AHRS
Attitude, Heading, Reference System
AH-1000 AHRS Ship Set
2 AHRUs, 2 AHRU mounting rays, 2 External Configuration Modules, 2 Magnetometer units (also called MSU’s, magnetic sensing units)
HG2205AB03 AHRU Product Description
The HG2205AB03 AHRU contains a set of three gyros, three accelerometers, and a microprocessor that computes the AHRU solution. From these it generates pitch and roll attitude, magnetic heading, body rates, and accelerations. Magnetic heading is slaved to an external three-axis magnetometer the KGM 7010.
Why do airplanes have an AHRS?
An AHRS provides the information a Pilot needs to Aviate.
Aviate: What information is needed?
Pitch/Roll/Yaw angles, Pitch rate, Roll rate, Yaw rate, lateral acceleration, longitudinal acceleration, and normal acceleration
Pitch rate
how quickly the aircraft is rotating around the pitch/lateral axis.
Roll rate
how quickly the aircraft is rotating around the roll/longitudinal axis.
Yaw rate
how quickly the aircraft is rotating around the vertical axis.
Pitch, Roll and Yaw angles
these are referred to as the aircraft’s attitudes.
Lateral Acceleration
forces pushing the aircraft sideways.
Longitudinal Acceleration
forces pushing the aircraft forward/backward.
Normal Acceleration
forces pushing the aircraft in the vertical axis.
Inertial Reference Units
Inertial reference units are devices that measure motion in reference to a point in space. AHRU is a type of IRU. It contains sensors like the following:
Gyroscopes – measure rotation (angular acceleration) around an axis.
Accelerometers – measure linear acceleration along an axis.
IRU Nomenclature (Commercial Nav)
IRU/IRS- a navigation grade inertial reference unit/system.
AHRU/AHRS- attitude heading reference unit/system. (not nav grade).
SAHRS- super AHRS, near nav grade AHRS (doesn’t require MSU)
General Industry
IRU/IRS – an inertial reference unit/system (any grade).
INU/INS – inertial navigation unit/system (nav grade IRS)
AHRU/AHRS – attitude heading reference unit/system.
AHRU Math
∫(body rates) ∂t = attitude angles
ex: roll rate 5°/sec for 9 seconds = 45°
∫(body accelerations) ∂t = velocities
ex: 10 mph/sec for 5 seconds = 50mph
Nav Math
∫(velocities|attitudes) ∂t = change in position
ex: 50 mph x 3 hours = 150 miles
So why can’t an AHRU navigate?
RPE:
Radial position error – where you are vs where you think you are.
Widest requirement:
2 NM/Hr up to 18 NMs
How does the AH1000 download software get loaded?
It gets loaded on the ARINC 429.
ARINC 429
the standard for local area networks on commercial and transport aircraft. This protocol ensures that a uniform language exists between the countless components that go into creating safe and successful flights. This common language helps to eliminate both system error and human error.
How many stages of sensor compensation are there for the AH1000?
3 stages
How does the AHRU estimate gyro biases for the pitch and roll axises?
The AHRU uses its own accelerometers to estimate gyro biases for the pitch and roll axis. The magnetometer inputs are used to estimate the Z axis gyro bias.
How much can the real time bias compensate up to?
up to +/- 220 deg/hour bias
What happens when the box or plane is tipped up?
Pitch angle should change. The lateral acceleration should not change.
Normal acceleration should change due to gravity.
