INS aligment
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Is the time for INS alignment hardcoded? If not, where can it be changed?
And if it’s hardcoded, would it be difficult for the devs to change that?
My question is because of the INS alignment time of the JA37: in real life it is ready at about 90 seconds in quick alignment mode (necessary for Swedish defence because of the short reaction time in case of a scramble: hostile flights above the Baltic sea had - and have - to be intercepted as fast as possible).
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just make sure GPS is on and you’re good to go in BMS with 90 seconds alignement
Simple as that -
I would do some experimenting to be sure that GPS overrides INS. One day I was practicing an instrument departure from Kunsan and I plugged in the exit point coordinates in STPT 2 and only did a <1 minute INS alignment. I was on the proper radial from Kunsan TACAN but when I hit STPT 2 my DME info was not matching what was on the chart. Either the GPS coordinates for the exit point on the chart were wrong, or the 1 minute INS alignment screwed things up.
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1.5 minutes, not 0.9 minutes.
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also, more up to date blocks of F-16 have a much faster alignment than that too.
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I thought they had a 4-minute alignment like the A-10C these days?
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4 min in full alignement for EGI, 8 min for INS. (30s for STRG ALN with EGI and 1 min with INS).
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I thought they had a 4-minute alignment like the A-10C these days?
AFAIK, The 4 Min alignment is for the laser Gyros, the old Gyros required the 8 minute alignment.
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INS is already laser. But it require 8 min.
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The 8min is for the “one time” static heading sampling (1?). Where the gyros detects the rotation of the earth to compute true North (geographic). I don’t think this is that important because once the a/c is moving it can no longer detect the earth’s rotation. And over time, the INS will degrade and will need support from the compass and GPS.
The compass gives magnetic North, however, some civilian GPS have an almanac to convert magnetic North to true North if GPS positioning is on-line. The $20k GPS(1990’s price) boards that I used had a global magnetic anomaly map and used these anomalies as a pseudo magnetic north pole. (ex. magnetic rock mountains)
The GPS can also compute a velocity heading. Enuff said, I don’t want to start another slip/slide/crab debate.
(1?)me thinks. maybe it’s used to check and adjust the pilot’s backup mechanical compass. <shrung>Would a loadout pork the compass?
EDIT: would a loadout effect the fluxgate compass? hmmmm</shrung>
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It really amazes me how can it couch the rotation of the earth when the engine is on… with all that turbulence…
Way sophisticated??? piece of equipment? -
newtons second and third laws in action.
so I guess its complexity, but in essence it is simplicity.
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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.
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I don’t think the INS alignment uses the gyro suite to compute positioning. You’re at an airport; you should already know where you are. What it does is compute True North to adjust the compass.
A magnetic compass can have proximity issues with iron devices (like bombs) and other devices that generate a magnetic field (like a TGP…maybe). I’m not sure if a fluxgate compass has proximity issues with magnetic fields and not so much iron devices. Not sure if the F-16 has one.
If you where to mount a magnetic compass in your car(or a/c) there are several step must be taken because the car is make of iron.
- with the compass out of the car point the car north.
- Mount the compass in the car and note that the compass is not reading north.
- There are two adjustment screws that are used to align the compass to read north.
- iirc you have to point the car west and repeat. One adjustment screw does north and the other does west. Me thinks
Now that you got your compass reading correctly, hang 4000lbs of bombs on the car and see what it does.
You can see the adjustment screws on the a/c compass
What I’m digging for is:
after you drop your bombs, would you have to do a IN FLT ALLIN to fix the compass.? -
I don’t think the INS alignment uses the gyro suite to compute positioning. You’re at an airport; you should already know where you are. What it does is compute True North to adjust the compass.
It cannot compute it’s current position. That must be entered within 2 minutes of starting a gyrocompass alignment. This is one area where BMS fudges how the system works as you never do this in the sim. During the alignment it is sensing true heading and earth turn rate. It adjusts the compass CARD on the HSI. It does nothing what so ever to the manual backup compass.
What I’m digging for is:
after you drop your bombs, would you have to do a IN FLT ALLIN to fix the compass.?Wow. Ok not sure why you are mixing up the manual backup compass and the INS system as other than for cross reference they have NOTHING to do with each other what so ever. No data is sent to or received from the backup compass. The only electrical connection it has at all is for lighting. Performing alignments on the INS adjusts the backup compass about as much as performing a BIT check on the FCR system. That is to say, none.
There are plenty of problems with navigating in a fighter aircraft via a magnetic compass and you have just pointed to one of many. Trust me if he is down to the compass only for navigation he has bigger problems on his hands than simply the magnetic deviation caused by some iron bombs that he is most likely going to be getting rid of.
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The 8min is for the “one time” static heading sampling (1?). Where the gyros detects the rotation of the earth to compute true North (geographic). I don’t think this is that important because once the a/c is moving it can no longer detect the earth’s rotation.
Without a solid gyrocompass alignment the INS system cannot set up the platform. Without the platform set up it cannot accurately know which velocities it senses are for what axis and thus the entire house of cards falls apart quickly. The farther and longer that system ran with that flawed setup the worse it would be (as with all inertial nav systems even with good alignments) but since it didn’t have a solid foundation in the first place it would be dependent on the GPS until the system was shut down and started again.
And over time, the INS will degrade and will need support from the compass and GPS.
Regardless of how good the INS system is it will degrade over time. Living on a roundish earth that rotates absolutely guarantees that.
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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)