INU Alignment - Is accelerated enough?

[rrasfly2]

I am wondering if anyone has been able to get the normal or precision alignment to work correctly. I’ve been following the steps in the manual but I’m still having issues. I got the accelerated alignment to work just fine but the other methods have a serious drift issue once I start moving. I can get the alignments to complete correctly and have a stable position in the start spot but as soon as I start taxing or flying, the INU starts drifting a few kilometers per minute. The faster I was going the worse the drift. Im assuming it has something to do with measured absolute Inertial velocity because i dont have this issue with the accelerated alignment. Any help would be appreciated.

-Rob

[Ephedrin]

Nope and I won't wait 20 minutes for an INS system to align when all I want is a nice Ka50 evening session with a couple of other people. I have a family xD  Turn on the BS and go for a walk with the dog or what xD

Edited December 17, 2022 by Ephedrin

[Rhinozherous]

Hello! 

I have read the INU part in the manual. But what do I really need for a mission with preplanned waypoints? 

I mean there is a big time gap between Accelerated and Normal (3 and 15mins) if I dont really NEED Normal alignment I always go with Accelerated. 

Thanks! 

Edited December 17, 2022 by Rhinozherous

[rrasfly2]

It just depends on what kind of mission you want to do and how you like to fly the bird. If you are like me and use lots of target points and data link points then having a good alignment is necessary. Going with the accelerated alignment leads to much quicker INU drift, especially if you are doing a lot of hard turns. You will even see a warning light pop on the overhead when you do anything more than a shallow bank. Normal alignment allows time for the alignment of more than just pitch roll and hdg. The only real difference I can see between normal and precise alignment is precise finds the aircraft heading for you. 

[Rhinozherous]

A fast special option for normal would be nice... If I get it right the manual says engines should be off during alignment. So sitting for 15mins doing nothing is boring

Dont get me wrong, I like realism, but there are things that need an (optional) shortcut. 

[Ephedrin]

jup... that's a very typical ground crew job after all.

[Rhinozherous]

Is it still the same that the ABRIS and INU is not coupled in any way? Because I always used only ABRIS for navigation... As long as I dont want to use the autopilot to fly me to a waypoint (route function...) or show the HUD direction to wpt I should be good with Accelerated alignment or not? 

The autopilot channels helping me fly the helo (Pitch, Bank, Yaw, Alt) are not affected by a minor alignment? 

Edited December 17, 2022 by Rhinozherous

[rrasfly2]

I’m beginning to think there’s a bug with the normal and precision alignment. Whenever I start up with a precision alignment facing south at Kobuleti, the system works fine with no noticeable drift during flight. But if I do the exact same startup procedure facing north, as soon as I start moving the INU starts drifting at a extreme rate. Over 5 Km per minute to the south typically. I get that most people don’t want to do the full alignment but I would like to know how to do the full startup myself including the alignment. I’m not asking for a quick alignment cheat, just for the normal and precision procedure to work. 
-Rob 

Edited December 17, 2022 by rrasfly2

[rrasfly2]

After doing some more trials with the new INU, I have found that if you follow the manual and do the precision alignment procedure with the engines off you will have a substantial drift that’s correlated to your initial heading used for the alignment and the speed and heading during the aircraft's first movements. I did the tests by doing several 10 minutes flight around some landmarks in Tbilisi and had observe drifts of 91 to 23 km after those flights depending on what the aircrafts heading was during the alignment. I measured the observed drift by just finding the distance between my position and the INU calculated position so it’s not actual drift rate but total INU error. That means the actual drift rate is probably much worse. I then tried the alignment procedures with the engines off but didn’t complete the procedure until after I had the motors on. I then repeated the flight and has a observed INU error of just about 1km. This confirms to me at lest that there is something bugged with the precision alignment. I have not tried this with normal alignment but if I get some time I’ll try to. I do have a few saved track files if anyone would like me to attached them. 
-Rob

[jubuttib]

91 to 23 km?! That's pretty immense.

I tested the Precision alignment also with engines turned off while aligning, as per the manual, and got some tens, maybe 100 meters of drift over two laps of a 3 waypoint route, a total flight distance of about 100 km and about half an hour of time. The aircraft does some weird stuff when in "desired track" mode, not really following the track the way I'd expect/remember from BS2, but the routes align decently. Another thing that throws it off is that when heading to WP1 in DT, the helicopter will fly all the way to the waypoint and THEN start turning, whereas for waypoints 2+ the DT mode will start turning before reaching the waypoint, as it should. I'll need to devise a new test around this...

 

I also tested by using the fastest alignment, i.e. just the basic one that happens once you turn on the INU. I did this with the APU running and powering the heli, out of interest. WIth this I got WAY more drift, but even so by the end it was "just" a couple of km off. EDIT: Just to note, I did do the manual heading correction for the fast align.

Edited December 19, 2022 by jubuttib

[rrasfly2]

My results were pretty close to yours when I didn’t confirm the alignment till after both motors were running. Did you use external power during the alignment?

edit- disregard I just tried it again without using external power during the alignment and my results are the same with the extreme drift rate. 

Edited December 19, 2022 by rrasfly2

[Mr_Blastman]

On 12/17/2022 at 10:08 AM, Rhinozherous said:

A fast special option for normal would be nice... If I get it right the manual says engines should be off during alignment. So sitting for 15mins doing nothing is boring

Dont get me wrong, I like realism, but there are things that need an (optional) shortcut. 

Yep, ground crew pre-alignment is necessary for proper online play.  Homie got no time for 15 minute alignment.

 

[SnuggleFairy]

8 hours ago, rrasfly2 said:

After doing some more trials with the new INU, I have found that if you follow the manual and do the precision alignment procedure with the engines off you will have a substantial drift that’s correlated to your initial heading used for the alignment and the speed and heading during the aircraft's first movements. I did the tests by doing several 10 minutes flight around some landmarks in Tbilisi and had observe drifts of 91 to 23 km after those flights depending on what the aircrafts heading was during the alignment. I measured the observed drift by just finding the distance between my position and the INU calculated position so it’s not actual drift rate but total INU error. That means the actual drift rate is probably much worse. I then tried the alignment procedures with the engines off but didn’t complete the procedure until after I had the motors on. I then repeated the flight and has a observed INU error of just about 1km. This confirms to me at lest that there is something bugged with the precision alignment. I have not tried this with normal alignment but if I get some time I’ll try to. I do have a few saved track files if anyone would like me to attached them. 
-Rob

I'm achieving similar results. Something is messed up

[jubuttib]

8 hours ago, rrasfly2 said:

My results were pretty close to yours when I didn’t confirm the alignment till after both motors were running. Did you use external power during the alignment?

edit- disregard I just tried it again without using external power during the alignment and my results are the same with the extreme drift rate. 

 

Interesting, maybe I should record a video showing my exact process and then results. Xmas break going on, so not really much else to do either...

[rrasfly2]

Please do! I hope it’s just something I’m doing wrong. 

[Tarres]

6 hours ago, jubuttib said:

Interesting, maybe I should record a video showing my exact process and then results. Xmas break going on, so not really much else to do either...

Waiting for your test. Maybe some user error from my end.

 

[jubuttib]

1 hour ago, Tarres said:

Waiting for your test. Maybe some user error from my end.

 

Gonna have to be tomorrow, still need to edit the recordings etc.

But I what I can say is that I started to see very significant drift with Precision alignment, whether done via ground power only or APU, and doing the most basic alignment of just turning the INU on and waiting for the 3 minute alignment (and then doing the manual heading correction on the ground) was working GREAT this time. I have no idea why the results are so different from last time...

I made a new test pattern that's not above water (that might interfere with the doppler system), a near square that's almost perfectly North, East, South and West, for 10 nautical miles each, and flew around it 3-4 times per run (comes out to something like an hour or more flying the route). I used barometric altitude hold and desired track autopilot, BUT I only started on the second waypoint, instead of WP1, because WP1 for whatever reason always seems to lead to the helicopter shooting past it and oscillating heavily on the way back, which can cause increased misalignment.

So I manually flew to WP1, then around 1-1.5 km before it I selected WP2, put the helicopter on desired heading for the initial turn, and turned route mode on. After the helicopter had more or less turned towards WP2 and settled down, I switched to desired track for the rest of the test. No other inputs were really used, other than by accident, except turning the altitude hold on and off every now and then and adjusting the collective, to keep within the control authority of the alt hold channel. Burning fuel affects how much collective you need after all, and I didn't want to balloon to the sky. Oh, and to repeat the loop, what with the 6 waypoint limit on the Ka-50, I made waypoint 5 the same as WP1, and WP6 the same as WP2. So after the aircraft had settled on its track towards WP6, I switched the target to WP2, which made the loop restart.

I'll try to make a more comprehensive post tomorrow, but I'll just post these two images now. The one that gets heavily out of whack is the Precision alignment, done with just ground power, and the other is a quick and dirty 3 minute alignment done with the APU powering things.

One difference I did notice between the two was that the error/warning light for "aircraft position is being roughly calculated" didn't come up ever during flight when using Precision alignment, and came up during every single turn when using the 3 minute alignment.

nullnull

Edited December 19, 2022 by jubuttib

[jubuttib]

Oh, and here are the tracks. Two runs with the 3 minute alignment with APU, one Precision with APU and one Precision with just ground power.

And just for kicks, here are also the TACView files for the runs, put them up on Anonfiles due to size:

https://anonfiles.com/D8Nf11N6y9/Ka-50_drift_tests_TACView_zip

The 4 soldiers are there to mark the waypoints.

Ka-50 INU drift test tracks.zip

[Tarres]

Thanks a lot.

Only thing it´s better to have the Self-coord. in the PVI in order to compare with the self-coordinates in the Abris.

[jubuttib]

1 hour ago, Tarres said:

Thanks a lot.

Only thing it´s better to have the Self-coord. in the PVI in order to compare with the self-coordinates in the Abris.

Yup, but since it wasn't mentioned in the guide then I'm not doing it for the purposes of the test.

EDIT: oooh you mean in terms of drift, since the track doesn't actually show where the waypoints are... Gotcha.

Edited December 19, 2022 by jubuttib

[jubuttib]

Startup videos for how I did my tests, "fast" and "Precise" with APU power. Precise without APU power is basically the same, except that instead of turning on the batteries etc. I just connect the ground power and turn on external DC and AC.

 

 

[Hobel]

vor 20 Stunden schrieb Mr_Blastman:

Yep, ground crew pre-alignment is necessary for proper online play.  Homie got no time for 15 minute alignment.

but as far as I understand the manual

Accelerated is only a Stored INU NORM?

[rrasfly2]

Accelerated alignment and normal alignment use the same procedure for the gyrocompass (figuring out the aircraft heading). It simply uses the last recorded heading which is why you’re required to realign the HSI to the mag compass. They also both spin up the other rings used for determining pitch and roll. Normal alignment also adds the alignment of some accelerometers to sense aircraft motion in the X,Y, and Z axis. I not sure what the Aircraft is using to determine acceleration data when you do a accelerated alignment since the accelerometers are not aligned. My guess is air data and Doppler. That’s why when you start turning hard after doing a accelerated alignment you’ll get a AC nav Calc warning light. 

[Hobel]

vor 10 Minuten schrieb rrasfly2:

That’s why when you start turning hard after doing a accelerated alignment you’ll get a AC nav Calc warning light. 

hmm, so with me it already lights up with very very light movements.

[rrasfly2]

I’m not sure what the exact parameters are that cause the light to pop but if you do a normal or a precision alignment the light won’t pop even if you start pulling some hard turns because the The NAV system is using the accelerometer data.