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Lets talk Fire Control Systems (FCS)

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Lets talk about fire control systems.  How do they function and what makes them so expensive? 


As far as I understand basic fire control systems:
The operator/chip in the round/marker inputs the shell data.
A range finder finds the range of the target, and calculates the trajectory of the shell.
A sensor (dunno what they are called) finds the height difference between the AFV and the target, compensating for the elevation/depression. 
A temperature sensor gives the temperature to compensate for loss of power in the gunpowder and air density.
A wind sensor gives the wind speed, compensating for the wind. 
A sensor keeps track of barrel sway and its position and compensates for it.
Two encoders keep the positioning of the turret azimuth and gun elevation. 
A vision camera/vision software tracks the target, compensating and moving the turret according to the target. (Also tracks target heading?)
A laser surface velocimeter measures the targets speed, and compensates.


All this is feed into a microcontroller, which calculates the appropriate coordinates, which is feed to most likely two servos controlling the turret traverse and elevation. 
When the gunner squeezes the trigger, the systems safety is off and will pull the trigger when the gun aligns with the coordinates. 


The microcontroller also feeds the information into the AFV's main computer. Of course, some formulas and PID regulators would be used to gain the appropriate values. 


This is how I theorize the FCS of a modern AFV works. Top of line, as you can begin shaving off features to have it cheaper, though the vison camera probably comes for free if you have a thermal or digital sight.  Feel free to correct me if you want. 
If anyone has information about FCS or can add some more please do. 

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  • 1 year later...

I annex this old topic as the optics and FCS resource topic. Discussions welcome.


Relevant other topics:


Relevant old posts:


Basic thermal imager talk:


German night sights for the Leopard 2 PT:


M60A2 gunnery instructions, including description of several FCS functions.


Article about the FCS from COBELDA. The article uses this as the name for the FCS, but it actually stands for Compagnie Belge d'Électronique et d'Automation, a joint-venture between SABCA (Société Anonyme Belge de Constructions Aéronautiques) and Hughes:







This is the "SABCA FCS" used on Australian, late Belgian and early Canadian Leopard 1 tanks.


Regarding M60A3 and M1 Abrams:




This seems a bit odd for the following reason: The M21 ballistic computer used as part of the M60A3's fire control system only took a limited amount of into account, such as ammunition type, cant, parallax, pressure, wind and range data. The XM1's digital computer took into account the same factors:



Apparently both solutions required manual input for most factors, in case of the M60A3 wind and pressure needed to be entered manually just as well as range data in case of the laser rangefinder picking up multiple echoes (which due to the older laser rangefinder could happen somewhat often, requiring the commander to pick a reading). Then again the M1's FCS required an "extensive series of pre-operational computer programming steps":



Based on the Jahrbuch der Wehrtechnik, the the FLER-H ballistic computer used on the early Leopard 2 prototypes (and in a somewhat modified form on the Leopard 1A4 and TAM tanks) was able to automatically retrieve data for air pressure, cant, exterior temperature, parallax, propellant temperature, tilt, wind and other factors, resulting in the need to only enter range data manually (as the laser rangefinder's readings was to be checked by the gunner with his optical rangefinder).



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The AN/VSG-2 thermal imager of the M60A3 TTS.





Just 2.6x and 8x magnifcation. The Thermal Imagining Sight of the M1 Abrams' gunner offers 3x and 10x magnification. The WBG-X thermal imager used in the Leopard 2's EMES 15 gunner's sight provides options for 4x and 12x magnification. TOGS (II) also offers 4x and 11.5x magnification.


All these devices are based on the same 120 line variant of the Texas Instruments (US) Common Modules first generation thermal imaging array. In case of the M60A3 TTS, the recognition range (NATO vehicle target) was limited to 2,300 meters.




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The Fire Control Computer is the CDC model that the Abrams uses (or near the same), however the entire system was contracted to Marconi and afaik Vickers and Marconi wrote the software. This is my understanding from the Hanyes Manual and the Vickers Tanks Landships to Challenger 2 book, as well as reading the relevant parts of the Jane's AFV Retrofit book referenced by SH_MM.

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  • 1 month later...

I have some questions about the TShS and TShSM gunsights of modernized T-55/62 tanks.


1, TShS, what I do not understand, is how lead was calculated in this sight, since it does not have any ammo input. As far as I know, after lasing the target, the gunner needs to push a button, and should NOT track the target. A signal light turns on, and goes off after some time, based on the range. The gunner then notices what aiming mark the target was at when the light turned off, and applies lead based on this. How did the sight calculate the flight time of the shell if there is no ballistic computer? What about different kinds of ammo, BR-412, APDS, HEAT?  Or was this feature used only for a single type, lets say, APDS?


2, In the later TShSM sights, with the connected BV55/62 ballistic computer, what kind of HEAT shell was used for calculations? Old 3BK4/5, or the newer 3BK15/17? The two has very different ballistic properties, yet there is only a "BK" setting on the ammo selection switch on both TShSM-32PV and TShSM-41U. (strangely, there are two types of HE-FRAG shells supported by TShSM-41U)

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Some small correction regarding British thermal imagers. Some time ago it was revealed by BAE Systems that the Challenger 2 was still using a thermal imager based on the Common Modules. However these are not identical with the US-German Common Modules (i.e. with 60 x 1, 120 x 1 and 180 x 1 detector arrays dependening on application) but rather based on the UK Thermal Imaging Common Modules (aka UK TICM). There were two classes of the UK TICM - the TICM Class 1 for man-portable thermal imaging devices using a multi-element photoconductive array and the TICM Class II based on the SPRITE (Signal Processing In The Element) detectors.


From what I've found, the TICM Class II uses 8 SPRITE detectors, though experimental variants with 16 and 24 SPRITE detectors were also developed. Compared to conventional detector units, a SPRITE detector is significantly longer along the scan axis and is biased in so that the carrier drift velocity exactly matches the scan velocity - so when scanning each "pixel" is measured using the complete length of the detector, which is accumulated using an electrical current at the read out region near the end of the detector. This way the signal integration is done in the detector unit, eliminating the need for additional circuitry for time delay and integration (TDI).



a) is the "Horned OctoSPRITE" as fitted to the UK TICM Class II.


Functioning principle


Images from here.


I guess when speaking of pure detector technology, one could argue that the SPRITE detectors allow the UK TICM Class II to kind of act like a 1.5 generation thermal imager, but without needing the additional circuitry of a true second generation device. I.e. a sensor unit with 8 SPRITE detectors requires 24 connections to the circuitry while an equivalent thermal sensor with 64 elements (in an 8 x 8 array) would require 65 connections. The big downside of the TICM Class II is the fact, that apparently only systems with just 8 SPRITE detectors were fielded, hence there is a need for much faster scanning (movement of mirrors and/or prisms to shift the image section that is being "viewed" by the thermal imaging sensor), which more or less eliminates the advantages in image quality gained from the longer sensors (= longer exposure).


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