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INS alignment Initial POS doesn't matter.


NeMoGas

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As the title says, no matter what LL you enter it seems to make no difference. I spawned at Maykop and entered Vaziani's LL as if it were my initial POS. It aligned perfectly right over my parking spot at Maykop. Shouldn't it be offset or something? Is this a bug or an incomplete feature?

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Dont really know but as it is linked to the GPS maybe it takes the current position and the initial position was a parameter for the Harriers without GPS.

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Yes as far as I know, and It was aligned even when I set the INS selector knob to NAV which is supposed to only use the INS and not the GPS. The whole point of entering the initial POS into the INS is so it knows where it started and therefore can figure out where it has gone.

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Just tried it myself. It alligns perfectly with completely wrong coordinates, without switching to IFA or something else. This seems to make the whole alignment process useless. :huh:

 

EDIT: O.K. tried it again. It's only the moving map. Wrong coordinates stay wrong.


Edited by Cornelius
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So after further testing waypoints added with an incorrect initial POS when INS knob is set to NAV are indeed navigating me to the wrong place. However when you add the waypoint it does appear over the correct POS on the map. Also when on the data page of the EHSD with AC selected the initial POS LL changes from what was entered when you flip the INS knob to NAV. As I am not an expert on the system I don't know how it should work. To me it does seem at the very least that the moving map should correspond to the initial POS after alignment.

 

Maybe a dev can chime in and explain how it should work.


Edited by NeMoGas
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So after further testing waypoints added with an incorrect initial POS when INS knob is set to NAV are indeed navigating me to the wrong place. However when you add the waypoint it does appear over the correct POS on the map. Also when on the data page of the EHSD with AC selected the initial POS LL changes from what was entered when you flip the INS knob to NAV. As I am not an expert on the system I don't know how it should work. To me it does seem at the very least that the moving map should correspond to the initial POS after alignment.

Maybe a dev can chime in and explain how it should work.

 

+1

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However when you add the waypoint it does appear over the correct POS on the map.

 

 

Wrong alignment should fool the system about where YOU are, not about where waypoints are.

If the coordinates are good, they will show on the right place on the moving map.

However, things should go wrong if you add points in azimuth/ range relatively to you, do mark points or stuff like that.

 

 

And I'm talking without GPS update.

 

 

 

At least to my understanding

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Yeah that makes sense that the waypoint would appear over the correct spot on the moving map. So maybe the only real issue is having the moving map align over your true position, even with incorrect initial POS data. The moving map displays your correct position at all times as far as I can tell. This is why when you add a waypoint and it appears over the correct spot on the map it should navigate you to that spot. However when you add the waypoint it shows it over the correct spot on the map but all steering cues on the HUD and EHSD are still wrong.

 

Basically it seems as if the moving map is totally unaffected by a correct or incorrect initial POS.


Edited by NeMoGas
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Yeah that makes sense that the waypoint would appear over the correct spot on the moving map. So maybe the only real issue is having the moving map align over your true position, even with incorrect initial POS data. The moving map displays your correct position at all times as far as I can tell. This is why when you add a waypoint and it appears over the correct spot on the map it should navigate you to that spot. However when you add the waypoint it shows it over the correct spot on the map but all steering cues on the HUD and EHSD are still wrong.

 

Basically it seems as if the moving map is totally unaffected by a correct or incorrect initial POS.

 

I’m sorry, I read your message several times, but it’s difficult to follow your ideas.

 

But I will try to explain.

 

See the moving map like a paper map: even if you don’t know where you are, you can still mark waypoints on the map if you have the coordinates.

 

All the difficulty of air navigation is figuring out where you are.

 

If your position is true, you can figure the right course and range to a waypoint.

But, if your position is wrong, your course and range to the waypoint will be wrong.

 

Now let’s go back to the moving map + INS.

 

The INS system is monitoring your position and put you on the map.

But INS system drift with time. So after some time your position on the map won’t match the real world. And when you go to a waypoint, you will be on it on the map but not on the real world.

It’s the same thing if you fool the initial position.

 

So you need to update regularly the system.

 

That update now is very much simplified or non-existant because of INS systems with embedded GPS.

I don’t know specifically the Harrier system and how it is coupled to INS.

I don’t know the impact of wrong INS input, do GPS correct it ? Maybe...maybe not.

 

Also what is doing the INS during alignment procedure ?

It isn’t figuring out your current position, you are supposed to know it and tell him.

But the system is using it’s accelerometer sensors to figure out where the real North is.

So maybe if you fool the initial position, it won’t compute the right North direction.

 

So in the end, the waypoints will show at the right spot on the map, but the system won’t actually get you there.

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Sorry I guess I could have explained what I ment better.

 

The problem with the INS is that I can tell it my default position is Sokhumi even when im really at Beslan, and once the alignment is done it knows im really at Beslan.

 

Added waypoints or mark points will be incorrect as they should be. However the moving map will display your location over your true position. In the example above it would show me at Beslan even though I told it I was at Sokhumi.

 

As far as I know the reason you input your starting location before you begin the INS alignment is so the system knows where in space it is.

 

As you said the INS uses gyros, accelerometers, and magnetometers to know how far in any direction it has moved. It does not however know where in the world it is unless you tell it before the INS alignment or couple it to the GPS.

 

So my question is then, how does our Harrier know where it is even when we intentionally try to fool it?

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Ok we are clear now.

I don’t know, if it’s a code problem or a GPS effect ?

If a GPS effect is possible, it can only occur in IFA mode. Not in Nav. So we have to try in Nav mode.

 

What I don't understand is why you have to set the IPP if IFA is to be used. In the A-10C, the EGI picks up the IPP from the GPS before aligning the INS.

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we tried it already..

 

And regarding your second point:

 

SINS and IFA are the only alignment modes in which neither aircraft present

position nor local magnetic variation are required to be entered by the pilot

before starting the alignment process.

 

Pocket Guide, p57


Edited by Cornelius
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In the A-10C, the EGI picks up the IPP from the GPS before aligning the INS.

Not sure if that is accurate when compared to RL. In the F-16 with EGI, the pilot still had to enter initial position. It could have been the Harden Aircraft Shelters (HAS) interfering with the GPS, but IIRC, that is the normal way to start alignment in RL, you enter you initial position manually.

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Not sure about the AV-8B but AFAIK the coordinates and magnetic variation are 'initial starting values' that the INS/GPS then refines (unless told otherwise) i.e. I don't enter an initial value into my andriod phone for it give an accurate Lat/Long location.

 

An example from a upgraded RF-5E Tigereye INS/GPS alignment


Edited by Ramsay

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The INS without being coupled to the GPS needs accurate coordinates.

 

When the INS selector knob is set to NAV it relies solely on the Inertial Navigation System as far as I know. Without accurate coordinates your true location will start off with an error and only drift even more the longer you fly.

 

This is the entire context of this thread lol.

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The INS without being coupled to the GPS needs accurate coordinates.

 

When the INS selector knob is set to NAV it relies solely on the Inertial Navigation System as far as I know. Without accurate coordinates your true location will start off with an error and only drift even more the longer you fly.

 

This is the entire context of this thread lol.

 

it goes round in circles... :wacko:


Edited by Cornelius
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Can anyone explain or clarify, after INS alignment which is the best mode to switch to? NAV or IFA? NAV in the manual states (degraded mode navigation) what does that mean?

 

Should we just be using IFA so that we don't get this "drift" between map position and true location in space?

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Can anyone explain or clarify, after INS alignment which is the best mode to switch to? NAV or IFA?

IFA is the best mode as it couples the GPS to the INS and feeds correction updates from the GPS.

 

If the GPS signal is lost, the navigation system will fallback to INS

 

NAV in the manual states (degraded mode navigation) what does that mean?

NAV mode uses INS without updates from the GPS, so is like flying an older aircraft without GPS.

 

In NAV mode, position 'fixes' (like in the Viggen) are made using

 

• TACAN (+/- 1nm)

• overfly (+/- half altitude, max 1nm)

• Designated waypoint ( +/- 0.1 nm)

 

INS drift, position updates and a stored navigation database aren't modelled in DCS

 

IRL it is recommend to use NAV mode every 5th flight to ensure the INS system is working correctly and errors are not being masked by the GPS

 

Should we just be using IFA so that we don't get this "drift" between map position and true location in space?

IMHO yes, as IFA is the preferred/more accurate mode and INS drift/updates isn't modelled.

 

For detailed information :

 

The AV-8B INS and GPS is described from page 285 (1.11 and 1.12) in the AV-8 Tactical Manual Vol 1 (A1-AV8BB-TAC-000.pdf)


Edited by Ramsay

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I don't enter an initial value into my andriod phone for it give an accurate Lat/Long location.

 

Your cellphone already knows approximate position from cellphone network or is constantly receiving update from GPS.

When I used portable car GPS, and I turned it on hundreds of kilometres from where it was turned off, it could take several minutes to fix the position.

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