INS aligment
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GPS is good(ish) for position but for attitudes and accelerations not so much. Flight information, FLCS and fire control would be crippled to put it mildly. Of course an aircraft designed without an INS wouldn’t be designed to be dependent on an INS
I’ve heard of self-correcting INSs having problems assuming long durations of constant attitude/accel was straight and level on some more ancient craft.
I’m positive that either the baro or radio altimeter can be used to update flight altitude “ACAL” in the F-16
As far as I know in-flight alignment doesn’t attempt position or gyrocompassing and it just sets the attitude with the heading set manually by the little knob on the center console near the HSI.
Terrain Referenced Navigation (TRN). Terrain referenced navigation (TRN) is provided by the digital terrain system
(DTS) capability hosted in the DTS/DTC. TRN correlates the aircraft position with respect to the digital terrain elevation data
(DTED) database stored in the DTS/DTC and maintains a confidence status on how well the position correlates. Data provided
by TRN is a backup source for the system navigation solution when GPS is not available for an extended period of time. The
TRN correlation of aircraft position to the DTED database supports the other DTS functions which include PGCAS, obstacle
warning and cuing (OW/C), and database terrain cuing (DBTC). TRN inertial altitude error estimate is used for the DTS auto
ACAL function (see ALTITUDE CALIBRATION)Altitude Calibration Options and Capabilities. There are two submodes provided to perform an altitude update.
These submodes are as follows:- Manual:
Radar Altimeter (RALT) ACAL
Fire Control Radar (FCR) ACAL
Head-Up Display (HUD) ACAL
Digital Terrain System (DTS) ACAL
Targeting Pod (TGP) ACAL. - Auto:
EGI
There are several pages on Altitude Calibration, I don’t think it would be useful for me to quote them. Like everything ells, this is equipment related and F-16 with different equipment have different capabilities. This is one of many examples.
- Manual:
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Some info on Laser gyros, not sure if you guys seen this
The bold sentence, is that what you guys where talking about when referring to magnetic compass besides the cockpit back up?
Not sure.
If the attitude mode is manually selected, the HDG knob on the IMSC can be used to convert the INU azimuth signal to a magnetic heading
reference.Me thinks,If the attitude mode is manually selected this is done by selecting ATT on the INS rotary knob. ATT mode disables INS-positioning and provide only INS-attitude(so it can servo drive the ADI). This means you or the INU have to use some other means of navigation other than INS. (ex. GPS, IFR, TACAN)
If the attitude mode is manually selected, the HDG knob on the IMSC can be used to convert the INU azimuth signal to a magnetic heading reference.
If this is the HDG knob used to calibrate the HSI compass card it can be manualy calibrated to anything. True north, Mag north using any device.
If the attitude mode is manually selected, the HDG knob on the IMSC can be used to convert the INU azimuth signal to a magnetic heading reference.
What device is used for INU azimuth signal ???
If this is the HDG knob used to calibrate the HSI compass card it can be manualy calibrated to anything. True north, Mag north using any device.
If the attitude mode is manually selected, the HDG knob on the IMSC can be used to convert the INU azimuth signal to a magnetic heading reference.
What device is used for INU azimuth signal ???
Awsome Info Gas.
I wish I had a searchable D1 pdf. My internet connect is too slow for the online D1. -
What device is used for INU azimuth signal ???
INU azimuth signal could be RLG heading. This lets the pilot manually calabrate the INU heading when INS is in ATT mode with Heading cal knob.
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Some info on Laser gyros, not sure if you guys seen this
The bold sentence, is that what you guys where talking about when referring to magnetic compass besides the cockpit back up?
You are confusing magnetic heading entered by the pilot with a magnetic compass. The HSI isn’t a compass but simply displays magnetic heading via the compass card from the INS data. Since during any IFA (which includes attitude mode) the pilot has to enter the magnetic heading that is why you are seeing the sentence you linked.
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The FLCS doesn’t care if your entire INS/GPS is down. It will work just fine. The only thing it requires from external sources are pitot and static pressure inputs to adjust flight control scheduling. It gets those from the air data system, not the INS or GPS.
The IFA mode you are referring to is just the attitude mode. Either an auto or manual IFA will give you more data than just attitude mode. However even the CDCs point to manual IFA or attitude mode is only good for getting your butt home. I’m not sure how much an auto IFA will drift or if GPS can keep that in line. Auto IFA is achieved with GPS data as well as some specific pilot inputs. All 3 modes require input from the pilot of the magnetic heading and the accuracy of any of those alignments is directly affected by how good the pilot is at entering that data accurately and following the cues to perform certain turns during the process.
Cool, FLCS operates without any accelerometers? Doesn’t it normally trim to hold local acceleration though?
I don’t see a single antenna GPS computing heading either. Heading is where the nose is pointing. Velocity vector is the FPM. If the a/c is crabbing these two vectors are not the same. Single antenna GPS has no idea where the nose is pointing. Maybe the Air Data Package to solve for crab angle.
I think the F-16’s FLCS does not use the INS. GasMVS said he found mechanical rate gyros in the main landing gear bay. IIRC, FLCS only uses two accelerometers on pitch to do the 1g zero stick thing.
…and the question is answered. FLCS does use accelerometers just not the INU’s.
Single antenna GPS does not do attitude. I know a multi antenna GPS system will
I hadn’t considered multi-point GPS. Does the F-16 have this?
There are several pages on Altitude Calibration, I don’t think it would be useful for me to quote them. Like everything ells, this is equipment related and F-16 with different equipment have different capabilities. This is one of many examples.
Yeah I forgot about all the other ways you could ACAL.
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The bold sentence, is that what you guys where talking about when referring to magnetic compass besides the cockpit back up?
The pit backup compass is used to align the INS-heading (gyro). Use Heading Cal knob to enter the pit backup compass heading on the HSI compass card. Then INS converts the mag heading to ture heading. Then INS-heading will display true heading on the HUD and HSI compass card will be servo drive by the INS to display Mag heading.
NOW WE KNOW……I feel like somebody has stolden paint out of my “paint by number set”…thanks for putting the paint back.
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.I hadn’t considered multi-point GPS. Does the F-16 have this?
I don’t think so. I would check the antenna location diagram in the D1.
iirc one of the multi point market goals was to messure wing flex on the C-5A. That was 20years go. And I heard the C5 allready uses a fibre optic system at that time. I don’t know where Trimble is now days. They didn’t help us. I bought Novatel.
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Cool, FLCS operates without any accelerometers? Doesn’t it normally trim to hold local acceleration though?
…and the question is answered. FLCS does use accelerometers just not the INU’s.
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How does me saying that the flight control system doesn’t use any INS/GPS data somehow translate into the FLCS system doesn’t use accelerometers? It in fact does have an accelerometer called the normal/lateral accelerometer. It also uses 3 rate gyros but those are all part of the flight control system hence not using external data other than air data. Those four components are only used for flight controls.
I hadn’t considered multi-point GPS. Does the F-16 have this?
None of the ones I ever worked on did.
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The pit backup compass is used to align the INS-heading (gyro). Use Heading Cal knob to enter the pit backup compass heading on the HSI compass card. Then INS converts the mag heading to ture heading. Then INS-heading will display true heading on the HUD and HSI compass card will be servo drive by the INS to display Mag heading.
NOW WE KNOW……I feel like somebody has stolden paint out of my “paint by number set”…thanks for putting the paint back.
NOT for normal on the ground alignments. The ONLY time that is used is in the air for IFA alignments because it cannot sense true north to get magnetic north hence it needs to be told. That is NOT the normal mode of operation.
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Cool, FLCS operates without any accelerometers? Doesn’t it normally trim to hold local acceleration though?
…and the question is answered. FLCS does use accelerometers just not the INU’s.Some info on this, these are part of the flight control system, as Stubbies2003 posted previously.
Roll Rate Gyro Assembly. The roll rate
gyro assembly is a metal encased assembly consisting of four
rate gyros (Figure 1-13). Each gyro is a spring-balanced,
floated rate gyro, containing a permanent magnet torquer for
self-testing, a monitor for detecting gyro speed, and a pickoff
transformer for transmitting a signal output. This gyro assembly provides redundant outputs and is mounted near the
aircraft center of gravity behind access panel 3308.Yaw Rate Gyro Assembly. The yaw rate
gyro assembly (Figure 1-15) is a metal encased assembly
consisting of four rate gyros. Each gyro is a spring-balanced,
floated-rate gyro containing a permanent magnet torquer for
self-testing, a monitor (of spin motor lead-phased voltage
characteristics) for gyro speed, and a pickoff transformer to
provide a signal output. The roll rate gyro assembly provides
quadrex redundancy. The gyro is mounted near the aircraft
center of gravity behind access panel 3308.Pitch Rate Gyro Assembly (2741A3). The pitch
rate gyro assembly is a metal encased assembly consisting of
four rate gyros (Figure 1-16). Each gyro is a spring-balanced,
floated rate gyro containing a permanent magnet torquer for
self-testing, a monitor for detecting gyro speed, and a pickoff
transformer for transmitting a signal output. This gyro assembly provides four discrete and redundant outputs and is
mounted near the aircraft center of gravity behind access
panel 3308.Normal/Lateral Accelerometer (2721A3). The normal/lateral accelerometer (Figure 1-15) is a metal-encased
assembly containing eight identical force-balanced transducers. Four transducers sense normal acceleration and four
transducers sense lateral acceleration. An accelerometer
mount assembly is provided between the accelerometer and
the airframe. -
Some info on laser gyros
You mean THIS? :wfish:
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Impostor! A real gyro doesn’t use tortillas
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How does me saying that the flight control system doesn’t use any INS/GPS data somehow translate into the FLCS system doesn’t use accelerometers?
The part where I assumed that the only gyros on the aircraft were in the INU.
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For a normal ramp start we have twenty minutes. There is really no reason not to do a full alignment. If you have to scramble, the INS seems pretty reliable with the aforementioned ninety seconds. Air alignments are effective too if you can find time in your flight to fly straight and level for a couple of minutes. The INS is an invaluable tool which is internal so that it is protected for your benefit as an aircrew member so you can always find your way no matter what.
Raven
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I think the OP was about another way to enter the 3D world.
Ramp
90 second Ramp
Taxiway
TakeoffI do a 90 second ramp on solo flight.
If you do a 90sec ramp on a mission, the package stpt times will be off and you’ll be early for push. I’m not sure the AI will do a 90sec ramp. I’ve never tried it with AI. -
For a normal ramp start we have twenty minutes. There is really no reason not to do a full alignment. If you have to scramble, the INS seems pretty reliable with the aforementioned ninety seconds.
100% … Not doing INS alignment is “passive cheat” once again.
IRL … you HAVE to perform a full alignment each time you fly. In case of GPS failure, INS remains you only way to get a position (except using pilotage chart or radionav) and INS is no optional.
Stored heading alignment are only made in specific cases (Live/Hot Scramble) and internal drift is bigger than with a nominal alignment.
Air alignments are effective too if you can find time in your flight to fly straight and level for a couple of minutes.
In flight align is for emergency only and do not give you a position. It is only to re-align (approximately) gyros in attitude (ADI/HUD) in case of temporary total loss of power … you loose INS positioning.
the package stpt times will be off and you’ll be early for push.
Plan holding pattens as it should be.
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If anyone is interested in R/L workings of aligning an aircraft’s positioning system, it has to do with something called compass rose. If you ever fly into an airport with a maintenance hanger that does alignment look for a circle that has an indicator facing magnetic north. There is scheduled maintenance where you have to take the aircraft to compass rose and align it with the heading and AVI calibrates all the nav equipment. When someone does an INS load before takeoff they are initializing the system to place the aircraft at the correct location in relation to the calibration at compass rose.
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If anyone is interested in R/L workings of aligning an aircraft’s positioning system, it has to do with something called compass rose. If you ever fly into an airport with a maintenance hanger that does alignment look for a circle that has an indicator facing magnetic north. There is scheduled maintenance where you have to take the aircraft to compass rose and align it with the heading and AVI calibrates all the nav equipment. When someone does an INS load before takeoff they are initializing the system to place the aircraft at the correct location in relation to the calibration at compass rose.
Sorry guy but the only thing that would ever require a compass rose on the F-16 would be the whiskey compass and I never saw that check done once in the 19 years I was working F-16s. The INS system through the normal alignment / entering of current coordinates and sensing the earth’s rotation gives your true heading. No compass roses required here.
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Stubbies is right. INS has absolutely nothing to do with a compass nor with magnetic field of the earth.
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A compass rose is for calibrating the standby compass, and for doing TACAN maintenance. If you have a station you can receive from that location.
Not all INS systems are ring laser equipped - in the older mechanical ones they may in fact get some input from a magnetic anomaly detector, which aids the alignment and nav solution by estimating local mag var. Those are becoming increasingly rare, though.
One of the more annoying problems with GPS aided INUs is that due to the GPS aiding during alignment the inertial unit can actually break or degrade and that can go undetected until someone operates them in an un-aided mode…by which time it’s generally a bit too late. So they need to be spot checked without using GPS at least occasionally.