IRS and INS
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IRS and INS
I have not had the opportunity to use an IRS or INS nav system, and do not have any info on it.
I have the basics on INS - gyros accelerometers velocity and distance travelled. Must be intialized from a known coordinates. Don't know how it establishes true north other than by the refernce to coordintes it is given.
IRS I have no info on.
I think that it is the ability of IRS to use nav aids to determine position.
any takers?
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Thrust till you see god, then rotate
I have the basics on INS - gyros accelerometers velocity and distance travelled. Must be intialized from a known coordinates. Don't know how it establishes true north other than by the refernce to coordintes it is given.
IRS I have no info on.
I think that it is the ability of IRS to use nav aids to determine position.
any takers?
--------------------------------------------
Thrust till you see god, then rotate
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INS Inertial navigation System, Gyros and accelerometers determine position relative to the intitial way point that was programmed. Good system but after a few hours "drift" becomes a factor that must be considered. (Any thing physical such as bearings and motors eventually is effected by external forces, IE friction) A drift of 1.2 NM per hour is considered acceptable. remember that over six or seven hours, the distance could become critical.
IRS Inertial Reference System uses "Light" as the reference once the initial system is programmed. (This can be done directly through the GPS on some systems) The light signals, or lasers are unaffected by gravity and all other associated factors that is why it is more precise. (OK Einstien freaks, light does bend due to gravitational forces, but lets leave the quantum and other theories to the experts!)It is very complex and you should read any book you can find. Essentially, time and distance travelled by the light is measured and transformed in to position through triangulation. Hope this helps.
Regards
IRS Inertial Reference System uses "Light" as the reference once the initial system is programmed. (This can be done directly through the GPS on some systems) The light signals, or lasers are unaffected by gravity and all other associated factors that is why it is more precise. (OK Einstien freaks, light does bend due to gravitational forces, but lets leave the quantum and other theories to the experts!)It is very complex and you should read any book you can find. Essentially, time and distance travelled by the light is measured and transformed in to position through triangulation. Hope this helps.
Regards
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You tell the INS or IRS system where in the world it is. Magnetic north can be obtained from the aircraft compasses, and the clever little box of tricks will convert that info into a true north reference. Whether you have accelerometers and rate gyros(INS) or ring laser gyros(IRS), these are acceleration sensing systems which tell you how far you have travelled from your initial position. As alapt says, the laser gyros are far more accurate.
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The IRS during initialisation detects the rate and direction of Earth rotation. Thus the Latitude and TRUE North are determined. Longitude can not be sensed so it is necessary to insert present position to enter this component.Entry of an incorrect Latitude different from the IRS calculated one will be rejected.
A lot of other factors here but that is the main difference.
A lot of other factors here but that is the main difference.
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And airplanes with IRS do not have a magnetic compass, flux gate or any such thing. (Apart from a basic standby compass, similar and not as accurate to that in a Cessna 152). The flight instruments are fed from the inertial attitude, the direction of magnetic north is calculated from the True North sensed by the inertials and adjusted for local variation using a data base loaded in the IRS program.
During the setup period, which varies with the latitude of the airplane, the IRS senses the rotation of the Earth and uses that to determine True North, as well as Latitude. It needs Longitude to be given to it, and if the information is different to that which it had when last shut down, it will reject the coordinates you have given it. But if you override with the wrong Longitude again, it will accept it, and so will be skewed for the whole flight, and give incorrect positions, groundspeeds, headings and so on.
The program will search for DME/VOR signals in flight to update the displayed position, and will use this information if available. If not, (remote areas) it will use the IRS position for navigation. The program knows the location and altitude of all nav stations, all airfields and later versions also know the terrain, in the entire world! If available, it will of course use GPS to display the position, since GPS is the most accurate. On approach, it will use the LOC signal as a priority for position.
Most airplanes have three IRS fitted, and they "triple mix" to obtain an average of these for position. If one or two fail, it still works, but is not as accurate. The failed IRS is still usually available for running the flight instruments (But if that is the case it is necessary to update the Heading frequently, just as you do in the Cessna with a giro heading display).
Great system, but better may be on its way.
During the setup period, which varies with the latitude of the airplane, the IRS senses the rotation of the Earth and uses that to determine True North, as well as Latitude. It needs Longitude to be given to it, and if the information is different to that which it had when last shut down, it will reject the coordinates you have given it. But if you override with the wrong Longitude again, it will accept it, and so will be skewed for the whole flight, and give incorrect positions, groundspeeds, headings and so on.
The program will search for DME/VOR signals in flight to update the displayed position, and will use this information if available. If not, (remote areas) it will use the IRS position for navigation. The program knows the location and altitude of all nav stations, all airfields and later versions also know the terrain, in the entire world! If available, it will of course use GPS to display the position, since GPS is the most accurate. On approach, it will use the LOC signal as a priority for position.
Most airplanes have three IRS fitted, and they "triple mix" to obtain an average of these for position. If one or two fail, it still works, but is not as accurate. The failed IRS is still usually available for running the flight instruments (But if that is the case it is necessary to update the Heading frequently, just as you do in the Cessna with a giro heading display).
Great system, but better may be on its way.
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"I think that it is the ability of IRS to use nav aids to determine position."
Actually, some of the later INS's used DME data to update position.
Please note, IRU's are very basic units and really don't use radio navaid data. All the mixing and prioritizing of navaid data on an IRS-equipped aircraft is usually done by Flight Management Computers. INS's are complete navigation units and do all the navigation number crunching internally.
"additionally the 'reference' bit refers to the ability of IRS to provide accurate pitch, bank and IVSI inputs to the avionics."
[Steve] Older generation airliners still made use of INS's for pitch, roll and (short term) compass indications part. The INS's also provided data to some airplane systems (e.g. Autopilot). Only the standby instruments used the old internal gyros (at least on the aircraft I worked on). Probably the main reason for calling laser gyro boxes "reference units" is for reasons stated above (It has no real Inertial "Navigation" capabilities in the sense of getting you from point A to point B).
Hope this helps.
Rgds.
Q.
Actually, some of the later INS's used DME data to update position.
Please note, IRU's are very basic units and really don't use radio navaid data. All the mixing and prioritizing of navaid data on an IRS-equipped aircraft is usually done by Flight Management Computers. INS's are complete navigation units and do all the navigation number crunching internally.
"additionally the 'reference' bit refers to the ability of IRS to provide accurate pitch, bank and IVSI inputs to the avionics."
[Steve] Older generation airliners still made use of INS's for pitch, roll and (short term) compass indications part. The INS's also provided data to some airplane systems (e.g. Autopilot). Only the standby instruments used the old internal gyros (at least on the aircraft I worked on). Probably the main reason for calling laser gyro boxes "reference units" is for reasons stated above (It has no real Inertial "Navigation" capabilities in the sense of getting you from point A to point B).
Hope this helps.
Rgds.
Q.
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Most of the above is correct but let's just clear up a few definitions.
In the acronyms IRS and INS the "S" is for "System" These are inertial systems that contribute to the aircraft navigation in assorted ways. An IRS uses an "IRU" where the "U" is for Unit. The same applies to an "INU" - the unit at the core of an inertial navigation system. An IRS may be an INS if it includes a navigational computer. More about this later...
"Reference" in the inertial reference system applies to the fact that the system uses inertial means to produce the aircraft roll, pitch and yaw alignment references used for the attitude and directional instruments. There is then no need for vertical gyros, directional gyros or magnetic compass systems.
"Navigation" in the inertial navigation system refers to the fact that the system uses the inertial data to compute the aircraft position and provide other outputs such as groundspeed or track.
Older INS systems had a mechanical inertial navigation unit, using mechanical gyros to keep an inertial platform horizontal and referenced to true north. Accelerometers on the platform sensed acceleration along the aircraft axes and a digital computer used the accelerometer outputs to calculate the navigation parameters and provide outputs to display them.
Newer Inertial Reference Systems use sensors, usually "Laser Ring Gyros" to measure the rotational rates around the aircraft axes. A digital computer uses these rotational rates to calculate the aircraft attitude. The crew insert the current location at start-up and the computer resolves the earth rates sensed by the gyros to deduce the aircraft alignment in inertial space. Once alignment is complete the system provides constant monitoring of aircraft attitude in roll, pitch and yaw as well as true heading. A database of the earth's magnetic variations then allows the system to calculate and display magnetic heading. The platform with the laser gyros and navigation accelerometers is bolted to the airframe and doesn't move (which is why such systems were once referred to as "strap-down" systems.) The inertial position is calculated by comparing the attitude data and the linear accelerations along the aircraft axes. Inertial Reference Systems are generally linked to a Flight Management System (FMS) to perform navigation, with the FMS constantly monitoring nearby DME stations to provide automatic position updates to the inertial position calculated by the IRS.
Honeywell built a "LaserNav" system that provided navigation data through a Control and Display Unit (CDU) that could accept enough waypoints to fly a long sector without reprogramming. It was thus an Inertial Navigation System with a built-in Laser Inertial Reference Unit providing the inertial data. No FMC was required. I assume that the LaserNav System is still in production.
So, an IRS provides attitude and direction display data by inertial means and provides inertial position for navigational use, either through an FMC or by its own built in computer/CDU interface.
An INS uses inertial means to calculate and display navigational data and can navigate an aircraft through a set of waypoints entered by the crew. It may or may not provide attitude and directional information too; an IRS may thus be an INS if it has its own navigational computer and CDU.
Hope that helps with the differences between INS and IRS...
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Through difficulties to the cinema
[This message has been edited by Blacksheep (edited 23 April 2001).]
In the acronyms IRS and INS the "S" is for "System" These are inertial systems that contribute to the aircraft navigation in assorted ways. An IRS uses an "IRU" where the "U" is for Unit. The same applies to an "INU" - the unit at the core of an inertial navigation system. An IRS may be an INS if it includes a navigational computer. More about this later...
"Reference" in the inertial reference system applies to the fact that the system uses inertial means to produce the aircraft roll, pitch and yaw alignment references used for the attitude and directional instruments. There is then no need for vertical gyros, directional gyros or magnetic compass systems.
"Navigation" in the inertial navigation system refers to the fact that the system uses the inertial data to compute the aircraft position and provide other outputs such as groundspeed or track.
Older INS systems had a mechanical inertial navigation unit, using mechanical gyros to keep an inertial platform horizontal and referenced to true north. Accelerometers on the platform sensed acceleration along the aircraft axes and a digital computer used the accelerometer outputs to calculate the navigation parameters and provide outputs to display them.
Newer Inertial Reference Systems use sensors, usually "Laser Ring Gyros" to measure the rotational rates around the aircraft axes. A digital computer uses these rotational rates to calculate the aircraft attitude. The crew insert the current location at start-up and the computer resolves the earth rates sensed by the gyros to deduce the aircraft alignment in inertial space. Once alignment is complete the system provides constant monitoring of aircraft attitude in roll, pitch and yaw as well as true heading. A database of the earth's magnetic variations then allows the system to calculate and display magnetic heading. The platform with the laser gyros and navigation accelerometers is bolted to the airframe and doesn't move (which is why such systems were once referred to as "strap-down" systems.) The inertial position is calculated by comparing the attitude data and the linear accelerations along the aircraft axes. Inertial Reference Systems are generally linked to a Flight Management System (FMS) to perform navigation, with the FMS constantly monitoring nearby DME stations to provide automatic position updates to the inertial position calculated by the IRS.
Honeywell built a "LaserNav" system that provided navigation data through a Control and Display Unit (CDU) that could accept enough waypoints to fly a long sector without reprogramming. It was thus an Inertial Navigation System with a built-in Laser Inertial Reference Unit providing the inertial data. No FMC was required. I assume that the LaserNav System is still in production.
So, an IRS provides attitude and direction display data by inertial means and provides inertial position for navigational use, either through an FMC or by its own built in computer/CDU interface.
An INS uses inertial means to calculate and display navigational data and can navigate an aircraft through a set of waypoints entered by the crew. It may or may not provide attitude and directional information too; an IRS may thus be an INS if it has its own navigational computer and CDU.
Hope that helps with the differences between INS and IRS...
**********************************
Through difficulties to the cinema
[This message has been edited by Blacksheep (edited 23 April 2001).]
