Nav Aids 20
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What is the basic function of an inertial system?
To determine an A/Cs position using internal sensors rather than external references.
Is an inertial system most stable in the short term or the long term?
The short term, as it suffers from drift in the long term.
How does the AHRS differ from an inertial Nav system?
The AHRS uses a magnetometer or GNSS info to update gyroscopic data.
What is the basic principle of an inertial system?
Accelerometers sense movement along the A/Cs 3 axis and gyroscopes provide orientation and rotational rate outputs.
What type of inertial system maintains the Global Frame of reference?
The stable platform inertial systems.
What is the main difference between an INS and an IRS
- With INS the inertial output is fed into an inertial nav computer whish calcs the nav solutions, ther is no FMS.
- In an IRS the inertial output is fed as raw data into the FMs, which then uses this for nav and other functions.
What inputs does a north referenced stable platform INS access to provide corrections to the platform gimbal motors during the ALIGN mode?
The latitude and longitude setting, the accelerometers and the east gyro.
what are the primary components of an inertial system?
3 Accelerometers, 3 gyroscopes, and a microprocessor.
What are the 2 primary requirments during alignment?
That the A/C remains stationary, and that the crew inputs the current position into the FMS's CDU within the alignment time.
In a north referenced stable platform INS, what is gyro compassing?
The process during alignment, by which the platform is levelled and aligned with true north using gravity.
In a north referenced stable platform INS, when does gyro compassing occur?
When the system is in the ALIGN mode.
What is the basic function of the gyros in an inertial system?
To provide orientation and rotational rate outputs.
What is the function of the Gyro stabilised platform?
To maintain the accelerometers level regardless of the aircrafts attitude.
What is the basic function of the accelerometers in an inertial system?
To sense movement in one or other of the planes of reference.
how are the accelerometers in a stable platform inertial system compensated for pitch attitude changes?
By maintain the platform level with the earth.
How are the accelerometers in a strapdown inertial system compensated for pitch attitude changes?
The gyros sense the pitch attitude changes and the software withing the microprocessor makes the necessary compensations, by subtracting the estimated local gravity.
How are the accelerometers in a stable platform inertial system compensated for the earths rotation?
The stabalised platforms are forced to tilt in proportion to the earth's rate of rotation.
What is the horizontal component of the earths rate of rotation proportional to?
the cosine of the latitude.
How are the accelerometers in a strapdown inertial system compensated for the movement of the aircraft over the ground?
The software in the microprocessor compensates by carry out the calc V/(R+h) and then subtracting the resultant transport error.
What is the product of the first integration of the N-S accelerometer in an inertial navigation system?
Velocity along the local meridian
what is the product of the 2nd integration of an accelerometer output?
What are the advantages of a Strapdown over a Stable platform INS?
The strapdown is more reliable since it contains few moving parts.
How does a strapdown system differ from a stable platform INS?
Strapdown IRS has it's inertial sensors strapped to the A/C, stable uses gimbal motors to maintain the inertial sensors level with the earths horizon (Global frame of reference)
What are the disadvantages of a Strapdown system of a stable platform system?
Increased computational complexity
What type of gyros are typically used on a strapdown inertial system?
Ring Laser Gyros
How does an inertial system calulate magnetic north?
the positional output of an inertial system is referenced to true north. Variation is then applied from a database.
Is north referenced INS suitable for navigation in polar regions?
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