INS update/realignment

So I flew a couple of missions on a MP server with the Viggen (some with good success some with less) and found that the INS system drifts off pretty quickly. Setting up waypoints in MP is a bit of a problem as a result.

So basically after I return to my base after the first attack run, I shut everything down an re-arm. What I want is to re-align my INS so that new entered target waypoints etc. are as accurate as they can be. Is there any way to do that on the ground or does one have to use said radar waypoint method?

Also, how do I specify my LS waypoint (my base) on the ground as it usually doesnt seem to be present on MP server cartriges? Do I just pick , say the lat/lon of the middle of the field and specify the runway parameters on the CK-37?

The nav accuracy is really the only thing where I sometimes scratch my head and what hinders my success rate in MP.

I hope someonce has an answer. :smilewink:

Are you doing navigation fixes to keep your system aligned? If not, I HIGHLY suggest referring to that section in the manual so you can learn how that works and what the procedures are.

Another thing to keep in mind. If you fly low enough, your radar altimeter will work alongside your aircraft's computer to help keep your system properly aligned. If you fly higher than your radar altimeter can read, you will have to do visual fixes.

This is part of the deal when flying the Viggen. It is part of what makes it interesting and challenging.

Yes, I am aware of the nav fixes method, however this seems a bit inpractical in a dynamic environment. Also, thanks for the rad-alt tip, never knew it actually took rad-alt data to keep it aligned. Still learning the quirks as you can see.

A tip for how to do it on the ground:

While parked on the ground, open the F10 map and locate yourself.

Note the exact LAT-LONG position of your plane.

Create a waypoint using that position.

Switch your current waypoint to be that new waypoint.

Do the nav INS update (no radar).

Since you are right on top of the waypoint, you should get a pinpoint precise INS alignment.

Thanks for the tip! That's exactly what I was looking for.

Are you doing navigation fixes to keep your system aligned? If not, I HIGHLY suggest referring to that section in the manual so you can learn how that works and what the procedures are.

 

Another thing to keep in mind. If you fly low enough, your radar altimeter will work alongside your aircraft's computer to help keep your system properly aligned. If you fly higher than your radar altimeter can read, you will have to do visual fixes.

 

This is part of the deal when flying the Viggen. It is part of what makes it interesting and challenging.

Also be aware that using Your radar altimeter (TERNAV) only works properly over ground and does not work over sea.

With strong winds over sea, INS position drift can be huge.

Lots of confusion, here :)

My two cents on some thoughts on dead reckoning navigation in the Viggen:

After landing, refuel and rearm, before taxiing again, press CK-37 Data panel RENSA to clear mission data.

Load data cartridge or input waypoints as required, entering LS reference if in another initial airbase than the one loaded on mission data cartridge; the L1 reference will be automatically identical as entered LS reference (we can input a different L1/L2 as needed).

See kneeboard pages for airbases reference numbers.

We can use CombatFlite for mission design and data cartridge export. https://www.combatflite.com/

Manual page 132

When aligned at runway, with CK-37 on LS (initial waypoint) before take-off, do a manual Initial course update to align and correct the heading.

Manual page 160

It can be useful to make a first waypoint for navigation fix (visual or radar fix), just after take-off.

Manual page 169

Fly bellow 500m so TERNAV will automatically update. With data selector set on AKT POS, the 5th digit will display TERNAV status (it should be "5"); 6th digit will be calculated position error in kilometers.

Setting radar mode on LAND / SEA (LAND / SJÖ) should be changing the signal modulation on the radar altimeter, but accordingly with RC1 manual version it is not implemented.

If a long flight will precede target waypoint, have a IP point for navigation fix (visual or radar).

Manual, page 146

When on landing approach set the master mode selector to LANDN NAV, turn to LB 4100m circle at 500m alt to catch TILS and follow steering commands. Navigation fixes will be given automatically by TILS.

For a mission, we should have starting airbase LS, navigation waypoints B1, B2 etc, target waypoints M1, M2, etc, pop-up points U1, U2, etc, primary landing L1, secondary/divert landing L2.

Navigation fixes will update B1, B2, etc.

Updating target position M1, M2, etc with radar, will not update B1, B2 navigation waypoints.

See also:

Chuck's AJS-37 Viggen Guide Part13 - Navigation & ILS Landing

https://drive.google.com/file/d/0B-uSpZROuEd3MThvSmxrN0pUMWM/view

Tutorials on Youtube

Bunyap

Start-up Part 2, Taxi, Takeoff

Visual/Radar Nav Fix, TERNAV System, Radar Terrain Avoidance

xxJohnxx

Navigation System Basics

Have fun! :)

Cheers.

Good stuff! So to keep it short, once I align myself on the runway I switch the CK-37 to BANA and enter the runway heading? Still haven't figured out how to perform the position update but I'm on it. :)

Thank you very much.

Good stuff! So to keep it short, once I align myself on the runway I switch the CK-37 to BANA and enter the runway heading?

No. BANA Data panel mode is only to input runway headings as if you want to input some road base/FARP with TILS channel and airstrip heading.

Use airbase reference numbers for inputing LS/L1/L2 and check output REF LOLA if displayed reference numbers are correct. These are the nuances on using a system designed in the 60s

On NAV master mode, align precisely the airplane with the runway and press reference button on stick (map key on flightstick if not yet) for a manual Initial course update to align and correct the heading.

Read on Manual page 132 about automatic and manual initial course.

For waypoint and LS/L1/L2 input, you have here the CK-37 input codes https://forums.eagle.ru/showthread.php?t=182229

https://forums.eagle.ru/attachment.php?attachmentid=157498&d=1487422933

I strongly advise for some CombatFlite testing on Data Cartdrige exporting. It is very easy to use, just write some coordinates from F10 map if you'll need accurate navigation IP and target positions. As F10 map will display DD MM SS, convert from DD MM SS to DD MM,mm (CombatFlite standard input), using CombatFlite tools. LS and L1 data will automatically added as inserted steerpoint will snap to existing airbases on database; data will be automatically be converted on export. There's the possibility to export maps and mission information as kneeboard pages.

Roger that! That is a pretty clear explanation. So if I understood correctly, I referably need to set my B waypoints to easily recognizable landmarks like bridges, small towns, coast outlines etc. then navigate to them visually, having B1 or say B2 selected, then once approaching said reference point I press T1 and when passing it TV fix to shift said waypoint to the actual desired location?

Another question: The starting base point (Ls) is set automatically right? Or can I use the REF LO/LA function to enter it while on the ground using the coordinates of let's say the middle of the runway?

Roger that! That is a pretty clear explanation. So if I understood correctly, I referably need to set my B waypoints to easily recognizable landmarks like bridges, small towns, coast outlines etc. then navigate to them visually, having B1 or say B2 selected, then once approaching said reference point I press T1 and when passing it TV fix to shift said waypoint to the actual desired location?

 

 

Another question: The starting base point (Ls) is set automatically right? Or can I use the REF LO/LA function to enter it while on the ground using the coordinates of let's say the middle of the runway?

Yep, use road junctions for visual fixes at daytime or individual bridges or recognizable lakeshores/coastlines that will appear on radar, at nighttime/low visibility conditions. Map keys or axis for radar gain for contrast enhancement and change radar amplifications modes (page 113), logarithmic for terrain/land cover types and linear for naval use.

Be careful with radar on navigation fixes. If radar off the fix will be visual; with radar on the fix will be a radar fix. So, if radar on and want to navigation visual fix, TURN RADAR OFF.

When loading data cartridge or entering LS reference (if in another initial airbase than the inputed on mission data cartridge), that information will be entered automatically.

[...] this seems a bit impractical in a dynamic environment. [...]

The AJ-37 was designed for an attack/interdiction mission, when GPS/GNSS systems were only on paper and radio navigation was inaccurate for this mission requisites. :)

There's the possibility to export maps and mission information as kneeboard pages.

I saw that in the latest stable DCS World release log…the heck if I can figure out how to do it though. Does it work in SP? Or just MP?

I saw that in the latest stable DCS World release log…the heck if I can figure out how to do it though. Does it work in SP? Or just MP?

I never used this capability, normally i display CombatFlite on another screen.

Accordingly with the tutorial, the CombatFlite generated *.png files will be at 'Documents\CombatFlite\Kneeboard'. Cut and paste on 'Saved Games\DCS\Kneeboard'.

https://www.combatflite.com/blog/viggenkneeboard

Just noticed this thread and I'm a bit confused about all the fuss about aligning on the ground in the Viggen. :huh:

The Viggen has no INS system, meaning that it's NAV system is not gyro based and doesn't need alignments the way INS equipped aircaft do. The Viggen "aligns" its NAV system automatically upon takeoff, as it takes the coordinates of the LS waypoint (your home base) to reset the NAV system to them when passing 200 km/h during takeoff. You just need to make sure you have selected the LS waypoint and have switched your Master Mode from BER to NAV less than 2 minutes prior to takeoff. That's it.

Just noticed this thread and I'm a bit confused about all the fuss about aligning on the ground in the Viggen. :huh:

 

The Viggen has no INS system, meaning that it's NAV system is not gyro based and doesn't need alignments the way INS equipped aircaft do. The Viggen "aligns" its NAV system automatically upon takeoff, as it takes the coordinates of the LS waypoint (your home base) to reset the NAV system to them when passing 200 km/h during takeoff. You just need to make sure you have selected the LS waypoint and have switched your Master Mode from BER to NAV less than 2 minutes prior to takeoff. That's it.

My original question was weather it is possible to re-align the nav system on the ground after having done a couple bombing runs between the base and the target. Now I know how to use the visual or radar fix method. LS is pretty much set automatically and can not be entered manually, right?

My original question was weather it is possible to re-align the nav system on the ground after having done a couple bombing runs between the base and the target.

That's exactly what the Viggen does automatically on takeoff by using the LS waypoint.

LS is pretty much set automatically and can not be entered manually, right?

You can manually enter it just like any other waypoint. You can either enter a reference number for any of the known airbases (you can look them up on the airbase list on the kneeboard), which automatically sets the runway heading(s) as well, or you enter the runway coordinate manually (e.g. for road bases), but then you also have to manually enter the runway heading in BANA mode. Entering LS manually will be necessary if you landed on a different base than you started from and want to take off again.

Just noticed this thread and I'm a bit confused about all the fuss about aligning on the ground in the Viggen. :huh:

 

The Viggen has no INS system, meaning that it's NAV system is not gyro based and doesn't need alignments the way INS equipped aircaft do.

Now I am confused ... Does it work by integrating velocity, heading etc.? Nothing more?

Now I am confused ... Does it work by integrating velocity, heading etc.? Nothing more?

It pretty much uses ADR and acceleration data + a doppler radar at low altitudes + a TERNAV system using the radar altimeter to compare the terrain below to stored map data in order to update its position.

Now I am confused ... Does it work by integrating velocity, heading etc.? Nothing more?

The Viggens NAV system is pretty much a INS, but without the gyro. Instead of getting movement inputs from the gyro like an INS does, the Viggens NAV system gets supplied with those inputs from the normal flight sensosr (pitot tube, barometric altitude, etc). There are some other systems that assist here, like the doppler system that adjusts for wind and (since the AJS upgrade) the TERNAV system as Airhunter said. But because the Viggens NAV system uses normal flight sensors instead of highly precise gyros and accelorometers, it is more susceptible to drift than a regular INS.

It pretty much uses ADR and acceleration data + a doppler radar at low altitudes + a TERNAV system using the radar altimeter to compare the terrain below to stored map data in order to update its position.

The Viggens NAV system is pretty much a INS, but without the gyro. Instead of getting movement inputs from the gyro like an INS does, the Viggens NAV system gets supplied with those inputs from the normal flight sensosr (pitot tube, barometric altitude, etc). There are some other systems that assist here, like the doppler system that adjusts for wind and (since the AJS upgrade) the TERNAV system as Airhunter said. But because the Viggens NAV system uses normal flight sensors instead of highly precise gyros, it is more susceptible to drift than a regular INS.

Thanks for the explanations!

For clarity: it does have gyros, but only for attitude sensing. The nav system is just dead reckoning based on initial position, attitude, course, airspeed and wind speed. The position is calculated cumulatively every 110 milliseconds or something like that. What you're doing when pressing the reference button on the stick has more to do with getting an accurate initial position than anything else, AFAIU.

It's kind of an oddball solution, but it did have some advantages in the 1960's. Just like true INS (but unlike radio beacon-based systems like TACAN that were common at the time) it can't be jammed and isn't reliant on infrastructure that can be destroyed, while offering far faster cold starts than INS, and avoids an additional complicated and expensive gyro installation. The downsides were considered to be possible to live with in the tactical context the Viggen was designed to operate in.