INS aligment
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My point is that if the (non-back-up) compass worked perfect, you wouldn’t need to wait around to find the direction witch the earth turns. The (non-back-up) compass with an almanac would provide true heading. I guess you agree that the INS needs a external heading correction and a corrected alligned compass would be best?
Most of us know the issues with the pilots’ backup compass type….what’s wrong with the “other” compass?
Why can’t it be used for allignment? The INS is going to have to use it sooner or later. My guess was loadout distortion. what’s yours?? -
I understood how it could discover latitude from Coriolis forces but longitude has to be supplied to the INS somehow, right? The symmetry of a sphere suggests it can’t be discovered by a set of gyros.
as mentioned, the INS does not calculate where it is by alignment.
it calculates its present displacement from its original location by measuring all accelerations applied to it.
alignment is needed to be able to accurately read those accelerations.
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The rate gyros and the accelerometers work together to determine attitude. The software is able to isolate the earths’ 1g gravity vector(one of the damnest thing I’ve ever seen). The accelerometer works like bubble level. (no drift in attitude)
A compass aligns the INS package with the earth. The rate gyros can hold heading but it is subject to drift.
The accelerometers measures the acceleration vectors(x,y,z) and with a clock computes a velocity vector.
The velocity vector with the clock computes position.
(if you level and travel a 400mph for 1 hour you traveled 400miles) -
All very useful information, thanks for that, but my original question still stands. For the JA37 the minimal alignment time is 90 seconds, full alignment is 3 minutes. It would be great if it could be implemented.
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My point is that if the (non-back-up) compass worked perfect, you wouldn’t need to wait around to find the direction witch the earth turns. The (non-back-up) compass with an almanac would provide true heading. I guess you agree that the INS needs a external heading correction and a corrected alligned compass would be best?
You are thinking about it backwards. The INS system senses true heading and adjusts the compass card on the HSI based on that. Not the compass directing the INS. Initial heading is not the problem with INS systems as to why they need external help to maintain accuracy. Earth rotation and movement of the platform across a non flat surface (the surface of the earth) is what induces these errors.
Most of us know the issues with the pilots’ backup compass type….what’s wrong with the “other” compass?
Why can’t it be used for allignment? The INS is going to have to use it sooner or later. My guess was loadout distortion. what’s yours??Ok to be as plain as possible the backup/whiskey compass is not used in ANY fashion by the INS system. It is never referenced at any stage of the INS system. It is purely a backup instrument for the pilot in case both INS and GPS go down. It suffers from magnetic variation via bombs, electrical systems in the aircraft, sudden changes in aircraft velocity and heading, blah blah. There are a million things that affect it’s accuracy. It is understood to have these limitations and is only there for rough back up reference or in emergency circumstances.
The only external information that the INS needs for alignment is it’s current location in latitude/longitude coordinates entered at the start. It figures out it’s own true heading all by itself during the gyrocompass alignment.
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A compass aligns the INS package with the earth.
Wrong. The system is aligned via the lat/long coordinates entered by the operator, the sensed gravity vector direction, and the sensed earth rate. It determines heading this way, not by a compass.
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Wrong. The system is aligned via the lat/long coordinates entered by the operator, the sensed gravity vector direction, and the sensed earth rate. It determines heading this way, not by a compass.
You believe there is way to senses the earth’s rotation while in flight.
You believe the only compass in the a/c is the backup compass. BTW, I know backup compass is not intergraded into any system in the a/c. use a little intuition.
You don’t believe there is algorithm in the INS software that correct for the “known” spinning of the earth spinning under the a/c.
You believe that the clock in the INS is perfect.
You believe that accelerometers are perfect.
You believe that light ring rate gyros are perfect.
You believe that Analog to Digital converters are perfect.
ok, enuff said…… -
All very useful information, thanks for that, but my original question still stands. For the JA37 the minimal alignment time is 90 seconds, full alignment is 3 minutes. It would be great if it could be implemented.
Post #2 was good. I’ve done ramp starts and rolled out as soons as every thing was turned on. It worked in single player. If you need more bells and wissels you need a Dev.
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Wrong. The system is aligned via the lat/long coordinates entered by the operator, the sensed gravity vector direction, and the sensed earth rate. It determines heading this way, not by a compass.
Stubbies is right. There is no compass entry for INS/IRS alignment.
INS/IRS is giving a true heading.
Mag heading is given by software computation based on location, true heading and known Mag variation table.
Software mag heading is compared with mag heading coming from “heading central” (do not remember English name).
Bkp compass is only a backup working without electric power. It can have from 1 to 5° deviation due to electromagnetic perturbation (electronic devices and a/c body). It must be calibrated periodically on ground by technical staff. -
The system is aligned via the lat/long coordinates entered by the operator.
Or taken directly from GPS device (if GPS is good and pilot is validating this position)
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Or taken directly from GPS device (if GPS is good and pilot is validating this position)
All is correct but one note to remember, INS alignment uses manual or GPS latitude entry only for alignment. Longitude is a comparison of the manual or GPS longitude coordinates entry with last know Longitude stored in the memory.
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All is correct but one note to remember, INS alignment uses manual or GPS latitude entry only for alignment. Longitude is a comparison of the manual or GPS longitude coordinates entry with last know Longitude stored in the memory.
100%
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It is possible for an INS to discover its latitude on its own. I know this to be true. The motion around the Earth’s axis is unique for every latitude (N S pair). Heading and local vertical are self-discovered during attitude alignment. The combination of accelerations suggest a loop path the vehicle takes around the Earth. With knowledge of the craft’s azimuth and local vertical it can be combined with the path the craft is taking around the Earth’s axis to find latitude uniquely.
I would guess that the F-16 does not derive latitude for navigation purposes but does check the calculated against the entered as large discrepancies will prove to be unusable in flight.
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Stubbies is right. There is no compass entry for INS/IRS alignment.
INS/IRS is giving a true heading.
Mag heading is given by software computation based on location, true heading and known Mag variation table.I was thinking it’s like “witch came first the chicken or the egg?”
If you takeoff without allignment there is no heading tape?
Does INS heading drift? Note that when heading NW, in a roll the INS heading will be handed off to all three gyros.
Mag heading must be in an ICP page because I didn’t see a switch for it. -
Mag heading is given by software computation based on location, true heading and known Mag variation table.
.My 1984 D1 says the HSI compass card is the “INS magnetic heading”. I didn’t find that it was computed from True North. And the HSI compass card is INS servo driven just like the ADI.
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You can only base very little when comparing BMS with 1984 F-16. The only similarities is that it is still an F-16 and…. yeah all the system are different. Engine, avionics, hell even the structure is different.
This one is better but still only a reference, nothing more and not 100% -
page 1-163
The face of the HSI is a compass card driven by the INS so that aircraft magnetic heading is always read at the upper
lubber line.I do not understands much (certainly not this), but I do not think this says anything about INS using magnetic heading, I will keep looking.
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Anyone got a 1F-16()-2-34GS-00-1?
PS
Not the same as a -34 {1F-16()-34-1-1} -
For the OP, sorry do not mean to continue derailing your thread, I do believe that is you want to fly the JA-37, just performing an 90 alignment should be sufficient in BMS
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Some EGI info
EMBEDDED GPS/INS NAVIGATION SYSTEM (EGI).
-Description. The EGI system utilizes GPS, and INS to keep an estimate of aircraft position, velocity, heading, attitude,
and altitude. This estimate is referred to as the system navigation solution. To integrate the information from these two sources
and determine the system navigation solution, the system uses a Kalman filter. The Kalman filter mathematically combines the
information from these sensors to produce a more accurate aircraft position estimate than could be expected from the sensors
alone. To insure accuracy of the navigation solution, the system utilizes INS performance model information along with GPS
data to determine the drifting behavior of the INS. In this manner, the system can continue to be accurate even with the loss of
GPS information. EGI includes the following features:
EGI Blended NAV Solution
24-Channel SAASM (Selective Availability Anti-Spoofing Module) GPS Receiver
Direct-Y GPS Acquisition
Fiber Optic Gyro (FOG) INU
DTE Load of EGI GPS Keys and Almanac Data
Automatic Entry of Align Coordinates
EGI Auto IFA
Alignment Refinement Capability
Navigation Database (5,000 steerpoints)
Emergency Airfields.- The EGI system supplies three distinctive navigation solution; INS-Only free inertial solution, GPS-Only solution and
a GPS/INS blended solution. EGI navigation solutions are available upon completion of a ground gyrocompass (GC) alignment
(NORM or STOR HDNG), an automatic or manual in flight alignment (IFA) or when the EGI is in the NAV mode by either
placing the function knob is in the NAV position or auto naving by moving the aircraft with the EGI function knob in NORM. - After each flight is completed, the LN-260 observes and computes a percentage of errors at shut down and stores it in
non-volatile memory. The next time the EGI is turned on, corrections are made to the free inertial solution before NAV is
selected or 80 knots. Errors from Gyro Bias, Gyro Scale Factor, Accel Bias, and Accel Scale Factor are not allowed to build on
subsequent flights.
- The EGI system supplies three distinctive navigation solution; INS-Only free inertial solution, GPS-Only solution and