Inertial Navigation System INS/IRS/MEMS Flashcards
What does INS stand for?
Intertial Navigation Systems
The major advantage of INS is what?
that it requires no external signals
INS depends on what?
The laws of inertia to determine position
Once a starting position is known, by latitude and longitude, the INS computer will:
determine any new position by measuring the inertial forces acting on the aircraft.
Because a change in motion is proportional to the applied force, acceleration can be determined by:
measuring the external forces on the aircraft.
We can measure the reaction force to determine the aircraft’s acceleration and therefore its acceleration and velocity.
This can be accomplished using:
Accelerometers
Autonomous navigation use:
sensitive accelerometers
What does LVDT stand for?
Linear Voltage Differential Transducer
The LVDT is a transformer device with a core that can move:
in a linear direction
If the core is in the middle - the output from S1 cancels the signal from S2. The output will be:
null or 0.0 VDC
By comparing the phase of the LVDT output signal with the input:
the direction of the cores movement can he sensed
What are Piezoelectric accelerometers?
solid state devices that use the piezoelectric effect as in quartz crystals
The Piezoelectric accelerometer uses microscopic crystal structures that:
create sm voltages when stressed
Capacitive accelerometers are designed with:
a tiny, nearly microscopic, capacitor with movable plates
G-forces move the plates a small amount, changing the capacitance and capacitive reactance. The change can be:
sensed and used to measure acceleration
What does MEMS stand for?
Micro Electro Mechanical System
A common type of accelerometer used in autonomous navigation systems is:
a solid state type with a silicon inertial sensor known as a Micro- ElectroMechanical System (MEMS)
A second type of MEMS is a:
Surface Acoustic Wave or SAW
With a SAW, resonating elements are:
placed on a beam suspended between a frame and a mass
Disadvantage of Solid State Accelerometers:
It may go into “lock-in”
During very slow turn rates, the phase difference between the laser beams is:
Very small
It is possible, in this condition (very slow turn rates), for the two laser beams to couple and:
“Lock in” indicating no acceleration
FOG, works using the same principles as the LRG but is:
different in construction.
What does FOG stand for?
Fiber-Optic Gyro
An Inertial Navigation System: IRS, uses a combination of accelerometers and gyroscopes to determine:
the aircrafts attitude. It can have navigational capabilities.
The heart of an IRS is 3 LRGs and 3 accelerometers mounted on a platform. The platform is contained in an LRU called:
Inertial Reference Unit (IRU)
and is mounted in the avionics/equipment bay
The Stable Platform is sometimes called:
the Tilt Table
which is gimbaled and uses motors and gyro’s to maintain platform stability and alignment magnetic north as well as a local vertical
The second type of platform is known as the:
Strapdown Platform
This type is directly attached to the airframe
IRS provides information to the:
(there’s 7)
EFIS, FMS, INS, IFCS, weather radar, antiskid, and FDR
The IRS can be integrated with other systems or:
be a standalone (independent system)
Initialization of the system can take 10 minutes and must be:
accomplished before the first flight or if the aircraft is moved while the system is off.
During initialization, the aircraft should not be:
moved
To start the initialization, the crew enters what?
the latitude and longitude of the aircraft
Each IRS has its own:
align and condition light and Mode Selection
What is used to enter the position data?
the keyboard
If the align light is flashing:
an error in data entry has occurred or the aircraft has been moved
If the align light is extinguished:
the unit is in align mode
Placing the mode selector in the align position does what?
initiates the alignment
In attitude mode the IRS does not:
navigate the aircraft and only provides output information of pitch and roll attitude.
From the Attitude Mode, the system needs to be:
aligned again before being used for navigation.
From the other measurements the IRS can determine:
True North
Once initialized, the IRS can be used to:
measure acceleration around any of the three axis precisely.
The IRS can be combined with an:
Air Data Inertial Reference Unit (ADIRU)
also known as an
Air Data Inertial Reference System (ADIRS)
ADIRUs are mounted in triplicate on:
transport category aircraft
Like the air data system, the ADIRU requires:
ADMs (Air Data Modules) to convert air pressure to a digital signal.
The FMS coordinates what?
IRS position, dependant navigation systems position and flight plans.
You should think of the IRS as an attitude and direction indication system that has:
navigational capability
What is INS?
a navigation system with attitude and direction capability
Often used as a synonym for IRS
INS is ATA code:
34-20
34 is navigation
Like IRS, the INS system is susceptible to:
Precession
(drift)
What is integration drift?
the accumulation of small errors over time
Aviation INS will drift up to:
1.5 kilometers per hour
The heart of the INS is the:
navigation unit
The Control Display Unit is similar to that of the:
FMS with data entered into a keypad
What is Kalman Filtering?
a software program that takes measurements over time and estimates true values and then predicts a future value
What is GPS aided alignment:
the most common form of alignment today
What is Optical Alignment:
the use of a small mounted telescope known as a theodolite.
This works only on gimbaled systems, such as INS
Gyroscope alignment only works if:
the aircraft is stationary. Gyrocompass alignment does not determine longitude. It is therefore not as accurate as GPS or optical alignment.
What is Transfer Alignment:
If there are more than one INS in operation, the INS needing alignment can be synchronized with the aligned INS. To confirm alignment the crew may have to perform special maneuvers to verify the accuracy.
