Bug in Shkval range calculations

Here's the bug(s):

1) After a laser ranging event, the Shkval will randomly start displaying an erroneous range value after a bit of slewing around. In the attached track, it keeps subtracting 2.4km from the actual value. There are no obstructions, and this is done from an altitude of like 200 meters above the ground. Nothing should be obscuring the Shkval. The erroneous range value can be fixed by re-lasing, but after the re-lase and subsequent slewing, the range value will again turn erroneous.

2) After launching a Vikhr, sometimes the displayed range at the bottom of the Shkval will change from the correct range value to an erroneous range value at the moment of Shkval launch. The erroneous range value is perhaps 2/3 of the actual range. Furthermore, in the attached track, this bug will only occur when the Vikhr is launched at a target between 7 and 8 km.

3) I have spent some time trying to narrow this bug (or bugs) down, but have so far not been met with success. Note that this is a very busy mission, and I get like 7 or 8 frames a second in it. The bug will appear regardless of whether the helo is manually ramp started or air started.

Anyone know how to reproduce this bug? Anyway, it's very annoying, as it will require you to lase, re-lase, lase, re-lase, and burn out your laser after just one load of weapons. Basically, if I have to come back to re-arm and refuel even just once, I better damn well bust my landing gear and get them to repair my chopper if I don't want a fried laser halfway into the second Vikhr load.

Anyway, the track is attached. Watch when I try to slew the Shkval around to different targets around the FARP. Also, watch later, when I fire Vikhrs at at targets between 7km and 8km distant.

Sorry for the zooming in and out problems. Saitek rotaries, even on the pricey X65F, are pieces of @#$*ing @$##.

buggy shkval range.trk

Maybe the BS INS/DTS has erronous terrain data in BS2. Something that differs from the terrain we see. Maybe there is an 'invisible' hill that is obstructing the INS to calculate the distance correctly from what we actually see...

Maybe the BS INS/DTS has erronous terrain data in BS2. Something that differs from the terrain we see. Maybe there is an 'invisible' hill that is obstructing the INS to calculate the distance correctly from what we actually see...

I don't believe that it behaves like an invisible hill, as if I had closed to guns engagement range, I believe the -2.4km subtraction wouldn't have changed. I believe it acts more just like a constant, erroneous value that gets subtracted. Furthermore, other missions in this same area do not have the problem.

It seems to me that the best way to narrow this problem down would be to keep removing things from the mission until the problem disappears.

Mine does the same thing, but I also had this problem with Black Shark 1. After laser-ranging, all I had to do to lose correct distance measuring was to move the Shkval gate around a bit.

I guess the maximum range it shows is 15km, and once I moved as far as 15km and slewed it closer to the helicopter its measuring went completely bananas.

I don't know how the real thing works, but it seems it's not entirely coupled with the Black Shark INS, since it loses distance estimation way to easily.

There is elevation data in the ABRIS, but then again, the PVI and ABRIS are two fully independent systems, so it seems the range estimation as we move it around is more like a "guesstimation" from the system than actual INS-derived information.

Maybe some of the developers that have actual documentation in its functionality could shed some light into our doubts. :smartass:

When the Shkval is moved after a laser-ranging, or you never ranged in the first place, range is determined using your aircraft height above the ground and the angle of the camera. There is no terrain database for it to use, however, so it does not take into account changes in elevation or the curvature of the earth (not that the curvature is a big deal at such short ranges). Also, I don't know how lack of a radar altitude affects the calculation. You could test this (and I plan to do so myself when I get a chance) by picking a target a ways out (7km or so) and seeing what happens (by staying in the same position and only altering altitude) from an altitude below 300m (where you will have a valid radar altitude) and above 300m (when the height above the surface essentially becomes unknown).

Does the laser ranger fire during or at all when you fire a Vikhr? I think #2 was that the Vikhr wouldn't hit and would end up falling short.

Does the laser ranger fire during or at all when you fire a Vikhr?

No.

So what "could" cause the vikhr to fall short and the laser rangefinder to show an erroneous range?

So what "could" cause the vikhr to fall short and the laser rangefinder to show an erroneous range?

A bug? :D

The laser rangefinder isn't ranging during an entire engagement with Vikhr. The laser for ranging is separate from the beam used to guide the missile. The missile doesn't know or care what the range to the target is, it just tries to stay inside the guidance beam.

I understand that but what I'm asking is What could cause the Vikhr to fall short when firing from a hover with no lateral movement and for the range to drop at the time of firing?

This exact same thing has happened to me a few times while flying Black Shark 1.

Last time it happened was in that mission from Dragon's MP pack in which one must first destroy the 4 HAWK sites to the east.

Turned the laser on, selected the weapon, locked the target up, waited until the count down reached zero and fired. Baam! Vihkr flew straight into the ground.

Locked it up again and Baam. Right into the ground again.

Then I recaged the Shkval, turned laser off, and did the whole process from the start. Worked flawlessly for the remainder of the mission.

I has already happened a whole bunch of times. Never have I been able to replicate it, but it does happen from time to time. :smartass:

When the Shkval is moved after a laser-ranging, or you never ranged in the first place, range is determined using your aircraft height above the ground and the angle of the camera. There is no terrain database for it to use, however, so it does not take into account changes in elevation or the curvature of the earth (not that the curvature is a big deal at such short ranges). Also, I don't know how lack of a radar altitude affects the calculation. You could test this (and I plan to do so myself when I get a chance) by picking a target a ways out (7km or so) and seeing what happens (by staying in the same position and only altering altitude) from an altitude below 300m (where you will have a valid radar altitude) and above 300m (when the height above the surface essentially becomes unknown).

Well I reckon these calculations are off. Not because I assume the shkval should work flawlessly. I always thought it was intended this way. Nevertheless it gave me the idea to recheck a problem I had a while ago with BS1 (http://forums.eagle.ru/showthread.php?t=79476). It would be nice if we could enter coordinates, that are talked to us (via TS/Vertigo/Mumble) by a A10 searching the area, but it never worked as intended because the height was always of when you tried to slew the shkval to a entered NAV/TGT point. So I did two tracks, one on a heigh airfield, one on an airfield near the sea. In the heigh track you can see that the range assumption of the shkval fits the entered NAV/TGT exactly, while the automaticly created target has the wrong range in the abris, although the coordinates are exactly the same. On the other hand, the shkval turns to the correct point when using the automaticly created NAV/TGT point and is either to heigh or to low (tracks are named accordingly) when using the entered one.

so long

Mathias

ins low.trk

ins heigh.trk

Ok, I tested the whole thing a bit further and did a track. It uses the shooting range mission, so it should be easy to reproduce. In the track you see that the shkval range gets set to a wrong value as soon as you slew it. I also set up some NAV/TGTs to show that they get wrong values and also that these values kind of correlate with the wrong shkval range.

Could someone please try to reproduce the range issue using the shooting range? Just fire the mission up, lase some place where you don't get a lock and slew the shkval afterwards.

so long

Mathias

shooting-range shkval calculation.trk

I'll have a look as soon as I can get a chance.

I'll have a look as soon as I can get a chance.

sweet, thanks :-)

Well, you're not going to like my results. I watched your shooting range track and more or less did the same thing you did. I picked a target about 4.5km away (I think it was 4.7km, but anyway) and lased it for range (I did this once with an invalid target, a tank hulk, and again with a valid target where I had to break the lock to slew). In both cases, if I slew left or right, the range does not change at all. Slewing all the way left and/or right carves a nice little arc out in front of the aircraft and the range indication never changed. Slewing up and down did change the range, but only by very small increments that seemed correct.

I did this all at an altitude of 50m, so maybe that has something to do with it? I think you were at around 300m, so I think I will try again at that altitude.

Well, you're not going to like my results. I watched your shooting range track and more or less did the same thing you did. I picked a target about 4.5km away (I think it was 4.7km, but anyway) and lased it for range (I did this once with an invalid target, a tank hulk, and again with a valid target where I had to break the lock to slew). In both cases, if I slew left or right, the range does not change at all. Slewing all the way left and/or right carves a nice little arc out in front of the aircraft and the range indication never changed. Slewing up and down did change the range, but only by very small increments that seemed correct.

 

I did this all at an altitude of 50m, so maybe that has something to do with it? I think you were at around 300m, so I think I will try again at that altitude.

Quite on the contrary, I like your results and already expected that there is more to it. I will check later if I am able to get your results when I am hovering at 50m.

so long

Mathias

Ok, I did another test and well... I cannot confirm your results. Could you please send me a track where you measure the range and don't get the it mixed up after the laser stops?

I tried several different heights and also checked if it might be related to the barometric altimeter but no joy.

so long

Mathias

shooting-range shkval calculation different heights.trk

I've had this too, had inf at 3.5ish according to the range finder. No targets locked (night), after two bursts, i had to lase again, because it dropped back to the same value every time.

I was at around 450 AGL, no obstacles in the LOS. (or anywhere near it).

The inf was standing on a parking space on an airport.

Well, you're not going to like my results. I watched your shooting range track and more or less did the same thing you did. I picked a target about 4.5km away (I think it was 4.7km, but anyway) and lased it for range (I did this once with an invalid target, a tank hulk, and again with a valid target where I had to break the lock to slew). In both cases, if I slew left or right, the range does not change at all. Slewing all the way left and/or right carves a nice little arc out in front of the aircraft and the range indication never changed. Slewing up and down did change the range, but only by very small increments that seemed correct.

 

I did this all at an altitude of 50m, so maybe that has something to do with it? I think you were at around 300m, so I think I will try again at that altitude.

Hey ho. Any news? Have you tried it at 300m already or are you willing to share a track where the range calculation works?

so long

Mathias

Another tester has duplicated your results and has brought it up to the developers, although I'm not sure an official bug report has been created yet. For myself, I was able to get a very small "jump" in range, but only on the order of 100-200 meters. While I cannot say what exactly is currently being done about this issue, I can say with confidence that it is known, has been brought to the attention of the developers, and is not going to be forgotten. In the meantime, I will keep trying to duplicate it myself, but another tester already has great track files showing exactly what you are talking about, so even if I can't get it to happen, it's definitely not just you.

Ok, thanks for the heads up :-)

so long

Mathias

Another tester has duplicated your results and has brought it up to the developers, although I'm not sure an official bug report has been created yet. For myself, I was able to get a very small "jump" in range, but only on the order of 100-200 meters. While I cannot say what exactly is currently being done about this issue, I can say with confidence that it is known, has been brought to the attention of the developers, and is not going to be forgotten. In the meantime, I will keep trying to duplicate it myself, but another tester already has great track files showing exactly what you are talking about, so even if I can't get it to happen, it's definitely not just you.

Excellent, I'm glad to hear that... though the range jump can be MUCH worse than just 100-200 meters, as you can see in the track I posted at the beginning of the thread. Now, if I could only just figure out the "crazy Shkval" problem... I'm not giving up on that damn one yet.

During Tests

i had this Proplem at high Temperatures it has been nearly EXTREME.

When i Tweaked the Temperatures and Barometric pressure down.

it was going to become more and more normal.

Can Someone else test with Temperatures and Barometric pressure?

Hope it will help.