Navigation Error - no GNSS?

[dooom]

Hmmm. I am building a 8 x Multiplayer mission but when I playtest as server (flying a client) i get a navigation error in the system bar of ABRIS. If i click GNSS FsK, to satellite feed is being recognized, yet Route mode and moving map on Abris are functioning?

 

Help? Does anyone know how to remedy the missing GNSS feed?

[Frederf]

Are you in a canyon? What does the satellite-azimuth-elevation picture look like?

[Waldo_II]

I think that once the GNSS system fails, then the ABRIS will use the INU to calculate where you are on the moving map system.

 

The route mode works because that functions entirely on the INU, I think. The navigation computer that the route mode uses is completely separate from the ABRIS- remember that only some models of the Ka-50 have the ABRIS, others have only sheets of paper. All Ka-50s have the navigation computer.

[dooom]

my mission I am working on is attached in link below - it is a plain near Kutaisi... pretty open IMO - i just played Dragons Convoy Hunting and that mission GNSS works - mucho canyon there.

http://forums.eagle.ru/showthread.php?t=53702

 

:huh:

[Frederf]

the ABRIS will use the INU

 

It does not!

[dooom]

i can't figure this out - looking at the right panel - i see nav and IFF power are still disabled after the autostart sequence... could that be it? turning them on doesnt seem to help

[Waldo_II]

It does not!

No? Well, then, I'm out of explanations.

[dooom]

so... should i chalk this up as a bug? I'm really trying to fix this.

 

should the nav and iff toggles go on with the Left win +home sequence? would these impact the GNSS?

[Frederf]

No, the IFF switch is purely a plaything prop... doesn't actually do anything in the sim.

 

The "Nav" switch is actually the ground chief's version of the K-041 switch on the left side of the cockpit. The pilot shouldn't even be turning the "Nav" switch on, but using the K-041 switch instead.

 

None of this impacts the ABRIS/GNSS system which is almost entirely isolated from every other sytem. You normally get a Navigation Error in the top of the display when you first turn ABRIS on since it takes a few moments for it to gather a position picture.

 

The really telling things are going to be the diagnostic/status pages within the ABRIS as it relates to satellite signal strength, nav state, etc. The MENU page should have statuses of the input instruments (FM 7-21):

 

NAV. SENSORS

GNSS.................READY

ALTIMETER.........READY

 

That would be step 1. Step 2 would be checking signal qualities as shown in FM7-89.

[BeachAV8R]

When you look at the GNSS page, how many satellites are showing as available?

[dooom]

None. No satelittes shown in gnss fsk. Check out the mission file linked above

[Frederf]

You mean the Op Chimney Sweep mission? I get NAV SENSORS: GNSS NO on the main page. I'm guessing that's because the mission itself has disabled all satellites. If less than a few satellites are usable then you get NO and NOT READY for the marginal case of 2-3 satellites.

 

All it takes to get the whole ABRIS system as far as GNSS positioning working is Battery 1 and the ABRIS master power switch on. It's a pretty compartmentalized deal.

Edited May 9, 2010 by Frederf

[Frogfoot1606687865]

The GUI manual states "When creating missions, it is up to you to decide who will be allied with whom. You are free to create realistic alliances or make very fanciful ones. We leave it to you to decide. Note the countries you place in a mission will determine the type of navigation satellite coverage available. For example: for GPS coverage, USA must be included in the mission."

I assume this then mean that only Russia has access to the GNSS satalites and not Georgia.

Tom

[dooom]

that must be the ticket Frog - i'll add USA as ally and see what happens. thanks buddy... lets see what happens with it.

 

gracias

:thumbup:

edit:

 

darn... seems I can't add a coalition after the mission has been made. that sucks. anyone know if there is a way?

Edited May 10, 2010 by dooom

[Frogfoot1606687865]

Not that it really matters, as without INU drift being incorporated the ABRIS seems to be just as accurate with or without satellite coverage.

 

It would be great if it was modeled as then you could put in a few INU fix positions over bridges / Radio Towers on the way to the TP, as inyour scenario you wouldnt necessarily have GPS/GLONASS. You would need to include detailed notes on the fix points in your Brief. It has always anoyed me with the Georgian Oil war campaign that INU fix points were included on many missions but with no indication of what to use as the fix point. (The ECRAN would warn the you were within range of the fix point, but without a note in the brief it was pointless.)

Tom

[Frederf]

Not that it really matters, as without INU drift being incorporated the ABRIS seems to be just as accurate with or without satellite coverage.

 

That's a silly sentence. I agree with your emotion but ABRIS = GNSS, PrPNK = INU. The ABRIS no more uses INU than the PNK-800 uses GNSS.

 

If you restrict the ABRIS to less than a large number of satellites you will see altitude errors and (I think) 2D position errors.

[Frogfoot1606687865]

Frederf[/left];900258]That's a silly sentence. I agree with your emotion but ABRIS = GNSS,

PrPNK

= INU. The ABRIS no more uses INU than the PNK-800 uses GNSS.

 

If you restrict the ABRIS to less than a large number of satellites you will see altitude errors and (I think) 2D position errors.

 

 

In the real KA50 that may well be the case but in the simulation

satellite availability does not seem to effect the functioning of the ABRIS. You can test this for yourself by setting up a new mission with just georgia on red and add a KA50 and fly about you will see NAV ERROR on the ABRIS and no satellites on GNSS page, however the moving map will display your position and altitude correctly.

The ABRIS does have a feed from the RADALT, and this can be seen by turning off the k-041 and checking the MENU page on the ABRIS, you get and Altitude sensor error, However with no satellites and no RAD alt input the ABRIS still shows the correct altitude data.

 

So my 'Silly' assumption was that there must be some redundancy built into the system, namely that the INU is connected to the ABRIS. This is quite common on Nav systems, where the 'drift errors' of the INU can be corrected when the GPS/GNSS has an acceptable PDOP/HDOP and conversely the AMMS can revert back to a lower precision sensor when the primary system (GPS/GNSS) fails or degrades. Hell even the satnav in my car has an 'inu' input, if I drive through a tunnel and lose GPS signal the speed of the vehicle is used to update the moving map until I emerge at the other end.

 

Tom

Edited May 11, 2010 by Frogfoot

[Frogfoot1606687865]

Frederf, the manual actually states that some type of redundency exists in the system, however I am sure it is not modled correctly.

 

'Calculations of aircraft motion parameters in case of the GNSS failure, using the last received data on the ground speed and actual track angle. This mode is used for one minute after the GNSS failure, whereupon the NAV ERROR message is displayed'

 

Tom

[Frogfoot1606687865]

As a further test I just started up the 'Shooting Gallery' mission and manually disabled all the visible satellites, (50,51,52,45,46,44,35 and 34) and gradually degraded the system from 3D to 2D then to NAV error, and was able to fly for a whole tank of fuel (at 32x real time) and the whole time the ABRIS showed NAV ERROR but the AMMS and ALT functions worked fine.

Something definitely not right here.

 

Tom

[Frederf]

NAV ERROR on the ABRIS and no satellites on GNSS page, however the moving map will display your position and altitude correctly.

Yup, ABRIS map moves despite no GNSS data. In fact it moves with the INU (and just for fun the K-041) turned off as well. It's hard coded to work perfectly no matter what which is a hole in the simulation.

 

The ABRIS does have a feed from the RADALT, and this can be seen by turning off the k-041 and checking the MENU page on the ABRIS, you get and Altitude sensor error, However with no satellites and no RAD alt input the ABRIS still shows the correct altitude data.

The ABRIS has three altitude sources: GNSS, BARO, and RADIO. This appears to be the only way that the ABRIS "breaks" correctly. In the case of no GNSS data the altimeter data feed automatically switches to the BARO source as a backup. You can test this with a no-satellite situation (my favorite is to turn the GNSS>SYST>BUILT option from GLONAS/GNSS to GLONAS and since there aren't any GLONAS satellites around in the stock missions I use, instant GNSS failure. Also you can set a 89° elevation mask).

 

With altitude source set on GNSS, wiggle the QFE knob on the barometric altimeter. Notice the ABRIS altitude doesn't change. Change source to BARO, notice that wiggling QFE causes it to change value. Now set altitude source to GNSS again but break the GNSS data. The altitude will fall back to BARO information despite still showing "GNSS" as the altitude source on the setup page. The QFE knob affects the altitude on the ABRIS.

 

When set to RADIO, lacking GNSS data, and then turning off the K-041, the ABRIS shows incorrect altitude extrapolated from the last climb/descent rate from the RADIO source.

 

So my 'Silly' assumption was that there must be some redundancy built into the system

It's not a bad idea that the GNSS-based navigation instrument would integrate into another system... it just appears to be reality. I've been told time and again from ED programmers and people more in-the-know than me that in DCS:BS the PNK-800 is not updated in any way by GNSS data.

 

There is a chance of confusion about the following part from the Flight Manual (page 7-36)

 

7-20: MENU/CONTROL/K-041 sub-mode page

The K-041 page is used to check the status of the K-041 navigation and targeting system. When in “WORK” MODE, a countdown timer in seconds is displayed next to the TIME OUT field. This indicates the time until the next INS navigation fix from GNSS.

Current aircraft coordinates; heading, track angle, and speed are also displayed here.

 

It's fictional and non-functional. http://forums.eagle.ru/showthread.php?t=36283 Check out posts #10-12.

'Calculations of aircraft motion parameters in case of the GNSS failure, using the last received data on the ground speed and actual track angle. This mode is used for one minute after the GNSS failure, whereupon the NAV ERROR message is displayed'

All that means is that the ABRIS is designed to assume straight line motion if it loses data for 60 seconds before giving up entirely. This is what your car's GPS system is doing as well. It's not getting any real position data from the INU or otherwise, just a blind mathematical prediction.

 

It's not possible to observe this behavior in terms of latitude and longitude since the ABRIS (in-game) continues to be accurate in the absence of GNSS data (which is obviously a shortcoming of the game). However we can see the extrapolation (even to negative radio altitudes) when all sources of altimeter data are cut off.

Edited May 11, 2010 by Frederf

[Frogfoot1606687865]

I just stumbled upon an interesting fact. I was sure I had seen nav errors in the ABRIS on one of the many videos on BS, do I had a quick scan through them. The one from SimHQ shows clearly the ABRIS losing satallite fix and drifting at about 5:10. So it looks like the patch may have broken it.

 

Tom

Edited May 11, 2010 by Frogfoot

[Zenra]

I just stumbled upon an interesting fact. I was sure I had seen nav errors in the ABRIS on one of the many videos on BS, do I had a quick scan through them. The one from SimHQ shows clearly the ABRIS losing satallite fix and drifting at about 5:10. So it looks like the patch may have broken it.

 

Tom

That is very interesting, and I hope suggests that maybe it would be easy to fix.

 

As I expect is the case for many DCS: BS fans I am drawn by its depth and fidelity of the systems simulation and getting things like this to work right really adds to the suspension of disbelief.

 

And, if INU drift could be introduced, that would be just glorious!

[Frogfoot1606687865]

I too hope it has been addressed in the upcoming patch.

I have also done some further investigation with regards to doing an INU update in the game. This also seems to be broken. I set an update point at a good landmark, and at about 10 k out I did a update (so if it was working correctly the inu and ABRIS would be 10 k adrift. However the INU self co-ords did not change. and the auto pilot continued to fly to my destination without the deliberate error. (i was expecting to be 10k out at my final destination.

 

Any Ideas?

 

Tom

[Frederf]

Yeah I noticed both of those things, the GNSS accuracy degradation while reading old threads and the fact that the INU update procedure is "all show" in that it doesn't change your self coords. I didn't know it used to work back in 1.00