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Is INS in M2000C broken?


rale26

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It seems weird that after full INS alignment, cold start and 40nm trip to IP, INS is already 0.5nm off. I usually fly older stuff so not sure if this issue is widespread across the modules or its just M2000C?

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I am trying to say that gyro drift feels totally unrealistic. Cessna 172 with ADF/NBD (1940's tech) flown by decent pilot outbound in pitch black should have less than 0.5nm error over 40nm distance. I have hard time believing that military relies on such low precision device. What would be a real life purpose of device like that? You can't target anything nor you can fly around in bad weather as well.


Edited by rale26
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It seems weird that after full INS alignment, cold start and 40nm trip to IP, INS is already 0.5nm off.

 

Note: The waypoint HUD marker "+" is misplaced, the "real" waypoint position is near the bottom of the top "tick".

 

https://forums.eagle.ru/showthread.php?p=4197651#post4197651

 

When checking if the alignment of the HUD waypoint marker had been fixed in the latest Open Beta, I did notice gyro drift seemed faster i.e. I carried out an update and watched the "+" move in active pause (drift used be something to watch on the PCN's changing numbers, not on the HUD).

 

Note: I'd want to recheck the speed of the INS drift before reporting it as a bug, as I was looking at the "+" position, rather than rate of change i.e. it could have been user error.

 

IIRC INS drift used to equal ~ 1 Nm per hour


Edited by Ramsay

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Indeed it should be around 1nm per hour for a class1 alignment.

I'm not sure drift is broken, but drift value shown on pcn when performing an update clearly is.

In some missions, i stayed 20mn at parking after alignment class 1 was performed, then started up and fly 20mn for a CCRP IP bomb run. When i performed a INS update on PI, drift value shown on PCN went from 40nm up to 70nm...

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It seems weird that after full INS alignment, cold start and 40nm trip to IP, INS is already 0.5nm off. I usually fly older stuff so not sure if this issue is widespread across the modules or its just M2000C?

 

Did you input your starting coordinates before starting the INS alignment ?

Helljumper - M2000C Guru

 

Helljumper's Youtube

https://www.youtube.com/channel/UCK3rTjezLUxPbWHvJJ3W2fA

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I'm not sure drift is broken, but drift value shown on pcn when performing an update clearly is.

The drift value shows the INS's distance to the current waypoint and whose co-ordinates will be use to update the aircraft's position (Prep 00).

In some missions, i stayed 20mn at parking after alignment class 1 was performed, then started up and fly 20mn for a CCRP IP bomb run. When i performed a INS update on PI, drift value shown on PCN went from 40nm up to 70nm...

I'm not sure what you are doing, as AFAIK you can't update if the waypoint/dirft is more than 15 nm away.

 

ATM INS update is always perfect so Prep 00 = aircraft position on F10 map (not the waypoint/landmark co-ordinates).

 

At a guess, it sounds like a bad initial alignment.

 

Which map were you flying / can you share a track ?

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I'm not sure what you are doing, as AFAIK you can't update if the waypoint/dirft is more than 15 nm away.

 

ATM INS update is always perfect so Prep 00 = aircraft position on F10 map (not the waypoint/landmark co-ordinates).

 

At a guess, it sounds like a bad initial alignment.

 

Which map were you flying / can you share a track ?

 

Indeed you can't validate the update if drift is more than 15nm, so in my case, i have to press INS update several times to lower drift in order go below 15 Nm and validate it. Indeed once i validate it, INS Udpate resest dirft to 0 whereas it displays another drift value on PCN.

 

My whole squadron noticed the same stuff, and we all do class 1 alignment each time. We had it on Persian gulf, but i have the same issue on any map. We noticed it while doing an INS update with PI mode activated. I have to check if i get the same issue with regular radar update or with overfly update.

Track is available in the bug section regarding this issue (in the thread where several issues are reported with tracks, created by MyHelljumper).

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My whole squadron noticed the same stuff, and we all do class 1 alignment each time. We had it on Persian gulf, but i have the same issue on any map. We noticed it while doing an INS update with PI mode activated. I have to check if i get the same issue with regular radar update or with overfly update.

 

Track is available in the bug section regarding this issue (in the thread where several issues are reported with tracks, created by MyHelljumper).

The PI tracks in myHelljumper's thread are set in the Caucasus map and the waypoint is on the river mouth, so shows no/little drift i.e. the HUD's waypoint "+" is correct ?

 

IMHO it's important to differentiate between INS offset bombing and INS drift/update when discussing system modelling/errors.

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The PI tracks in myHelljumper's thread are set in the Caucasus map and the waypoint is on the river mouth, so shows no/little drift i.e. the HUD's waypoint "+" is correct ?

 

IMHO it's important to differentiate between INS offset bombing and INS drift/update when discussing system modelling/errors.

 

Yes it's correct.

It shouldn't be differentiated, as radar INS update (Recalage Oblique) can be done in two ways: with OBL mode or with PI mode, and they should behave the same.

It should even be the same than with overfly, as the INS treats the Radar INS Update as an overfly update.

 

I'll try with overfly and OBL updates using the same mission used for the PI track, to compare drift displayed on PCN.

It should display the same, whatever method is used for INS Update.

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So i made several tests on latest Open Beta, on INS drift value given on PCA

 

As far as i'm concerned, 2 good news, 1 (very) bad news:

- Good: Overfly update seems to give correct INS drift value.

- Good: radar INS update in OBL and PI modes seem to give the same INS drift value

 

- Bad: Radar INS update is totaly broken as far as i can tell.

 

I'll elaborate on the latest:

i've attached 2 track file from the same mission:

- one where i did an overfly update, i get a ~0 Nm drift, and when i press on REC to cancel the update, drift values are removed, REC and VAL lights are off and i get back to my initial PCN window: everything is fine.

- one where i did several OBL INS update, on the first one i get a 21Nm drift, REC is blinking, click on REC then a second drift value appears (instead of going back on initial PCN window) 5 Nm, click on REC again and then finally i get back on initial PCN window. I do it several times, and i still get the same behaviour.

 

I also noticed that slant range given by radar is way off (which could explain weird drift values).

Farther you are from the waypoint, bigger is the error ratio between slant range displayed in the HUD and theoretical slant range.

 

Attached also an example where we can see a radar slant range of 16,6km when plane is at 4840 Feet AGL(1,47km) and 4 Nm (7,4km) from the waypoint. If i'm not too bad at maths it should be displaying a 7,54 km slant range instead of 16,6km

 

I also tested it on a instant action mission and i get the same stuff (so not related to my mission).

Wonder if you guys can reproduce the same stuff. Will report it in bug section if that's the case :thumbup:

Overfly INS update.trk

OBL INS update.trk

test1.thumb.jpg.97ec79bace9e256401e162210d6ecb78.jpg


Edited by Steph21
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The video is from 2018, are we sure something didn't change since? Also, are you using DCS time compression?

last time I tried in january 2020 - still could align mid-air

yes, time compression there in the video

[sIGPIC][/sIGPIC]

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I posted this video in a separate thread two years ago in the bug section and the only reply from the devs was "Thank you, I will have a look with the testers"

 

the issue's abandonded since then

[sIGPIC][/sIGPIC]

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Wonder if you guys can reproduce the same stuff. Will report it in bug section if that's the case :thumbup:

 

Yeah, I can agree with most of your observations, I assume OBL's ranging info is just eye candy as INS updating is incomplete/WIP (CCRP likely uses the slant range to the ground under the cursor/diamond).

 

Taking control of your tracks did show you'd disabled INS drift, so your attached tracks aren't a valid representation of INS updating.

 

i.e. both track "options" files show they were recorded with Options -> Special -> M-2000C ---> Disable Gyro Drift = Checked

 

 

["M-2000C"] = 
       {
           ["UNI_ALIGNED"] = true, [color="Red"]<--- Alignment not needed at start[/color]
           ["AOA_SHOWINHUD"] = false,
           ["TDC_GatePPI"] = 5,
           ["TDC_PPI_is_Polar"] = false,
           ["CPLocalList"] = "default",
          [color="Red"] ["UNI_NODRIFT"] = true, <---  Gyro Drift disabled[/color]
           ["TDC_KBPrecission"] = 100,
       }, -- end of ["M-2000C"]

The same is also true for the CCPL and CCPI tracks uploaded to myHellJumper's thread.

 

A quick way to check if INS drift is enabled is to select Prep 00, switch PCN to Lat/Long, use active pause (LShift+LWin+Pause) and fast forward time (LCtrl+Z) ---> the aircraft's position (Prep 00) should drift approx 0.01 minute of latitude per minute (0.11' in 10 minutes).

 

(LCtrl+Y shows the co-ordinate bar in the cockpit, LAlt+Y cycles to Degrees Decimal Minutes)

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Yes i've disabled INS drift on purpose.

I have the same behavior with drift enabled, except of course that waypoint '+' is drifting and getting back on perfect position once update is validated (whatever the update precision).

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Some of you posted that normal drift is 1nm/hour. There is a graph in this wikipedia article which shows precision of about 650m. Are there diffent classes of INS systems? Is 1nm based on reference system or it is just DCS interpretation of the whole thing?

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Just found this one.

 

 

"INS accuracy will drift with time; this can occur for many different reasons. Older stabilised platform INS (1970’s and early 1980’s) may have position errors of 2 nautical miles (nm) per hour. Modern strap-down LRG INS tend to have error rates of 0.6 nm/hr."

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Some of you posted that normal drift is 1nm/hour. There is a graph in this wikipedia article which shows precision of about 650m. Are there diffent classes of INS systems? Is 1nm based on reference system or it is just DCS interpretation of the whole thing?

 

1nm/hour is just a ball park figure.

 

INS accuracy will drift with time; this can occur for many different reasons. Older stabilised platform INS (1970’s and early 1980’s) may have position errors of 2 nautical miles (nm) per hour. Modern strap-down LRG INS tend to have error rates of 0.6 nm/hr.

 

https://www.skybrary.aero/index.php/Inertial_Navigation_System_(INS)#Alignment

 

For the AV-8B drift is said to be less than 1 nm per hour, I don't know the RL figure for the Mirage.

 

Updating can introduce larger errors i.e.

 

• Overfly CEP = 1/2 Altitude (max 1.0 nm)

• Designate CEP = 0.1 nm

 

... and the greater the position error, the greater the drift rate, so IRL pilots don't lie to their INS.

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Yes i've disabled INS drift on purpose.

I have the same behavior with drift enabled, except of course that waypoint '+' is drifting and getting back on perfect position once update is validated (whatever the update precision).

 

Then the behaviour you're reporting is unrelated to "INS drift" and purely about CCPL and CCPI i.e. offset bombing ?

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Today I tried again to see if there are any improvements after recent update. On the same track I got about 0.3nm off after INS alignment, cold start and 40nm fly to the waypoint. Which is a bit better than before but ... now my INS radar update is broken. I tried assigning keyboard, hotas no go. Even if I press button in the plane it doesn't light up INS UPDATE and VAL buttons.

 

 

 

Weapons off, radar on, radar altimeter on, OBS on, INS in NAV mode, diamond visible. What I am missing here?

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