Is the M1A1 Laser Rangefinder modeled accurately?

[IndustrialDonut]

So I was doing some experimenting on the firing range with the M1A1, M1A2, M60, and well a variety of vehicles that I have gotten a decent grasp of handling the gunner's role in and came upon noticing something.. In the M60, for example, when you track and lase a moving target, the turret will jump ahead of the target with the reticle within the sight then being offset to remain on the target, firing shortly after without the target changing speed or direction will likely hit, as it should, but then if you were to re-lase the target with the reticle offset, it's actually lasing the ground where the gun is pointed, and while the reticle won't really move, you generally won't hit the target if you're firing HEAT in particular. This all makes sense to me. I hope it makes sense to you, because I'm not the best at explaining things.. Anyway, onto the M1A1, as we all know it only has a mirror in the GPS that pivots vertically, not horizontally, similar to the M60 (I don't actually know if the M60 has a pivoting vertical mirror at all but regardless), and so I was expecting similar results when I started messing around with it too. What I found, is that, after tracking and lasing a moving target, upon RE-lasing this target, the laser would always be directed right onto the RETICLE of the sight, and not along the direction of the barrel/turret. So, if that makes sense, then I'm wondering is the M1A1's LRF really able to pivot and track the reticle from within the GPS while the GPS itself cannot? Where is the LRF exactly on the M1A1? It was just very unexpected to see that. It makes sense for it to happen in the M1A2, I had thought, since the LRF would obviously be aligned with the GPS at all times, but, yeah.. Just confused on this..

[MAJ_Fubar]

Nope, it's modeled accurately.  Compared to the TTS on the M60A3, lead in the M1 series is calculated "dynamically", meaning the lead angle offset is applied to the gun and not the sight while the tracking rate is sampled several times a second.  On the M60, lead angle offset is fixed based on the last 1.5 seconds of angular turret movement.  The reticle offset and subsequent movement when changing tracking rate on the M1 is an artifact of the lack of horizontal stabilization in the sight head.  Lastly, as you noted, on the M60 once a target is lased the laser will be in coincidence with the gun-target line at that particular range and not the TTS, and will remain so until the TC presses the RESET and BTL RNG buttons on the laser R/T.

Edited January 8, 2017 by MAJ_Fubar

[IndustrialDonut]

37 minutes ago, MAJ_Fubar said:

Nope, it's modeled accurately.  Compared to the TTS on the M60A3, lead in the M1 series is calculated "dynamically", meaning the lead angle offset is applied to the gun and not the sight while the tracking rate is sampled several times a second.  On the M60, lead angle offset is fixed based on the last 1.5 seconds of angular turret movement.  The reticle offset and subsequent movement when changing tracking rate on the M1 is an artifact of the lack of horizontal stabilization in the sight head.  Lastly, as you noted, on the M60 once a target is lased the laser will be in coincidence with the gun-target line at that particular range and not the TTS, and will remain so until the TC presses the RESET and BTL RNG buttons on the laser R/T.

So, does the M1A1 have a pivoting barrel within the turret then like the Leopard 1A5 and Leopard 2's? How is the lead applied to the gun and not the sight, while the sight is fixed on the same horizontal azimuth as the turret? This is what I'm wondering, and subsequently how the laser rangefinder on the M1A1 is not subject to the same effect as the M60.. Thank you for your response too

[MAJ_Fubar]

Attached is more than you ever wanted to know about the M1A1's FCS; just check page 27 to answer your question. Note that the FCS for almost all current western MBTs work the same way, with only minor differences.

Fire Control Supplement.doc

Edited January 8, 2017 by MAJ_Fubar

[TSe419E]

Also, if I understand it correctly, the laser for the M1s is part of the GPS while the laser for the 'A3 is not.

[IndustrialDonut]

Wow thank you so much both of you actually on page 15 of the document you linked me there's a diagram where the laser for the rangefinder actually passes through the same mirror that the reticle itself is projected onto, basically as TSe419E said, and therefore they're always in-line - I was not expecting this to say the least. It really amazes me what the tank engineers come up with..

[Maj.Hans]

On 1/8/2017 at 8:32 AM, IndustrialDonut said:

So, does the M1A1 have a pivoting barrel within the turret then like the Leopard 1A5 and Leopard 2's? How is the lead applied to the gun and not the sight, while the sight is fixed on the same horizontal azimuth as the turret? This is what I'm wondering, and subsequently how the laser rangefinder on the M1A1 is not subject to the same effect as the M60.. Thank you for your response too

 

No, none of those vehicles have a pivoting barrel in the turret AFAIK...

 

When he says "applied to the gun" he means "applied to the turret".  All rotation of the gun/turret is accomplished together.

 

What he means is that in the Leopard 2's (and the 1A5's) the GPS has a mirror inside of it that allows the sight to look slightly left or right so that the reticle stays perfectly centered in the sight as lead is applied.

In the M1A1 this mirror is absent, so the view through the sight follows the gun as the FCS applies the lead, and therefore the reticle itself moves to the side so that it stays on target.

[Ssnake]

Technically, the mirror is there in the M1A1 ... it just can't apply lateral movement (yaw). This was added with the M1A2 upgrade.