BK-90 and nav drift

Recently got back into the Viggen, but I have some issues with the use of the BK-90's.

Let's say I pre-plan a strike by entering a target waypoint. If I have a couple of minutes flight to the target area, there is usually some drift to the nav system. What is the best way to deal with this?

I have tried to mark targets on the radarscope instead, but the resolution is not there for ground units. At least not for me since the 2.5 graphics update. Islands, hills and coastlines are kind of ok.

Any tips on how to reliably target the BK-90's?

You can add some waypoints at landmarks and make a visual or radar fix. You have to choose these waypoints carefully, because it is not always easy to spot the landmark. It works but it is not very accurate.

Btw, the ternav system should automatically provide fixes to the nav system. If you make sure you fly over a few hills or mountains, the ternav should work ok.

In any case, nav system fixes, be it automatic or manual, are part of the mission plan.

In a typicall mission plan the waypoint before the target waypoint is usally the so called Ingress Point (IP), which is supposed to be placed on a recognizable landmark that can be used for a final nav fix before getting to the target.

Sounds really complicated to get it right... but I'll give it another try. Working with visual / radar fixes in Viggen is a bit confusing, with the E (or flashing E) waypoints.

You guys are saying that I somehow can make the ternav system automaticly keep nav system on point without drift?

Sounds really complicated to get it right... but I'll give it another try. Working with visual / radar fixes in Viggen is a bit confusing, with the E (or flashing E) waypoints.

 

You guys are saying that I somehow can make the ternav system automaticly keep nav system on point without drift?

Yep, just fly low so the nav system can monitor the terrain your flying over. It wont work if there is already a lot of drift in the system though so dont go high or over the Sea for long periods.

Thx for info!:)

Sounds more complicated than it is.

Once you do this a few times it becomes second nature.

Learn the procedures for radar fix (move the point on the map) and visual (hit the reference when over the point) and thats all you need to know. They are very simple to do.

Main thing is like QuiGon said in mission planning to set the IP WP over something you can recognize from the air and radar display. (Islands, river forks, small towns, mountain tops etc.

Just keep low and overfly hills and mountains whenever possible and you won't get much drift to begin with!

And I like to add that switching the Doppler to SJÖ-mode (= sea, switch by the throttle) will decrease navigational error when flying over sea.

And I like to add that switching the Doppler to SJÖ-mode (= sea, switch by the throttle) will decrease navigational error when flying over sea.

Thanks, I always forget to set that :)

Question: If I set the radar to passive mode, does it affect the TERNAV system in any way?

Question: If I set the radar to passive mode, does it affect the TERNAV system in any way?

The radar altimeter and the ground mapping radar are two separate systems. The ground mapping radar is a system with a big dish shaped antenna, located in the nose of the plane. The radar altimeter is probably located somewhere in the belly of the plane. The antenna will be much smaller. So, to answer your question, if you set the ground mapping radar to passive, the radar altimeter is not affected.

Thanks, I always forget to set that :)

 

Question: If I set the radar to passive mode, does it affect the TERNAV system in any way?

If the manual is correct and you put the radar in passive search(passive spanning) the TERNAV should be in "Mode 4" - "4: TERNAV OK and following, but not used. Commonly seen in mode SPA" page 169 AJS-37 RC1 manual.

But i never tried that/i never ensured that.

If the manual is correct and you put the radar in passive search(passive spanning) the TERNAV should be in "Mode 4" - "4: TERNAV OK and following, but not used. Commonly seen in mode SPA" page 169 AJS-37 RC1 manual.

But i never tried that/i never ensured that.

That page says that in SPA mode you can envounter ternav mode 4 (do not know why that is though). Where do you read a relation with the PS37A radar being in passive mode?

It does not make sense to me as the PS37A is not required for ternav (just turn it off, ternav works fine), for that the RHM is used. The PS37A is a forward looking radar operating in X-band, whike RHM systems are downward looking systems usually operating at lower frequencies.

Anyway, the best thing is to try it out. Switch the PS37A to passive mode and keep an eye on the ternav mode indicator.

I couldn't get the TERNAV status to 4 (ok and following, but not used). Not in SPA or in passive radar (or combinations).

I think I do understand why status 4 is seen in SPA. During recon the pilot is marking down targets and it is probably very annoying if the ternav system keeps sending fixes to the computer. Effectively that would make the target coordinates jump around. There does not seem to be a relation with passive PS37A radar though.

The manual does state explicitly that the radar altimeter is used by the TERNAV system, but switching it off does not disable the TERNAV. I've mentioned this in the bug section.

... the best thing is to try it out. Switch the PS37A to passive mode and keep an eye on the ternav mode indicator.

Thanks ... I did try it out and the Ternav seems to work fine, with status "5", as seen on this video:

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:)

Thanks for the vid. Nice livery btw!