Finn T55 Question

[Gman]

For those beloved Finn tankers on this Grate sight, did the upgrades to the T55M in Finnish service include improvements to the stabilisation ?  Or did it maintain original stab even when the FCS changed to the improved laser sytem ?

[bojan]

Sight was independently stabilized for sure.

[Stefan Kotsch]

The DNNS is meant?  What is the functional block diagram of the stabilization of the mirror? The DNNS is meant?  What is the functional block diagram of the stabilization of the mirror? 🙄

[Stefan Kotsch]

This is the block diagram for the DNNS-2 in the vertical. A control cycle is marked in red. An arrow goes out of the mirror to the right and is labeled "Angular velocity of the mirror in vertical". However, I cannot see an angular velocity sensor. Is there such a sensor on the mirror? That should be a gyro with 2 degrees of freedom. In this case, the DNNS would have its own (independent) control circuit for vertical mirror stabilization.

Is the field of view stabilized when the cannon is locked in the loading angle? That should actually be the case.

 

 

Edited November 11, 2021 by Stefan Kotsch

[sunday]

According to google translate "ELEVACIONI SENZOR" means elevation sensor, a vertical angle sensor

[Stefan Kotsch]

This sensor only measures the angle between LOS and gun barrel.

 

Edited November 11, 2021 by Stefan Kotsch

[sunday]

That sensor is a positive feedback, also. Perhaps the "implementer" contains some kind of model of the system.

[bojan]

4 hours ago, Stefan Kotsch said:

Is the field of view stabilized when the cannon is locked in the loading angle? That should actually be the case.

Yes.

[Gman]

For those who tanked both T55 and Leo1 (Stefan suspect you are one and only ?), did you note significant difference in ammo handling and reloading, culiminating in reduced ROF in T55 vs Leo1 ?   Cramped turret, less quality stabilisers and large ammunition for 100mm  seem to conspire to reduce performance on the move compared to Leo1 or improved  Swedish / IDF  Cent or other vehicles of same vintage ?

[Stefan Kotsch]

10 hours ago, bojan said:

15 hours ago, Stefan Kotsch said:

Is the field of view stabilized when the cannon is locked in the loading angle? That should actually be the case.

Yes.

And this is where it gets exciting. How exactly does it work? Which gyroscopes are involved for independent vertical and horizontal stabilization of mirror?

[Stefan Kotsch]

@Gman

The stabilizer in the T-55 wasn't that bad.  Shooting on the move was the main mode of operation.  Up to 1600 m actually no problem to shoot and hit while driving (15-20 km/h). Of course, no comparison with the Leopard1A5. That would be the comparison between the VW Beetle and Mercedes.

It is of course very cramped for the loader in the T-55.  APDS can only be loaded when the turret is at 12 o'clock. The APDS were all in the front right of the hull. But in that case, the strict rule was to point the hull in the direction of the enemy. Removing the cartridges from all the other holders was quite a feat in the confined space. The ready-to-use ammunition in the Leo's turret cage was a fine thing. Very quick and very convenient.  Curious about it, you couldn't lock the gun while loading.

[sunday]

1 hour ago, Stefan Kotsch said:

And this is where it gets exciting. How exactly does it work? Which gyroscopes are involved for independent vertical and horizontal stabilization of mirror?

Could you post a link to a full block diagram of the system? My google fu in some languages is not up to standards.

Edited November 12, 2021 by sunday

[Stefan Kotsch]

The full block diagram (vertical):

I don't know how to correctly translate RAZLAGAC (now corrected).  And where does the angle or angular velocity signal (normaly gyro required) for LOS stabilization come from when the gun is locked in the loading angle.

 

 

 

 

Edited November 12, 2021 by Stefan Kotsch
correction

[sunday]

Thanks!

Seems the gyro inputs are only considered in full stabilization mode, see the lowest signal path - that is the negative feedback of the elevation regulation. The "angular velocity gyro" could correct the reading of "angular velocity gun vertical" (angular velocity of elevation of gun). Then, the "lead angle and lead angle velocity box" outputs an angle setpoint that goes out of the POK (amplifier box) into the DNNS-2. There that setpoint is corrected by substracting from it the output of the "Implementer or transducer" (very likely a transducer of the angular position of the mirror).

Probably I explained myself poorly, but to me it looks like that lower gyroscope serves both the elevation of the gun and, with some correction from the ballistic computer, the elevation of the mirror, 

Edited November 12, 2021 by sunday

[bojan]

I can only translate what manuals and descriptions say, as I am neither a tanker nor electrical engineer.

I am not sure if it is official name in English, but "razlagac" is also called "rezolver" locally, which is corrupted "resolver".

If it helps...

Edited November 12, 2021 by bojan

[Stefan Kotsch]

7 minutes ago, sunday said:

looks like that lower gyroscope serves both the elevation of the gun and, with some correction from the ballistic computer, the elevation of the mirror, 

Yes, that is also my thought at the moment. But what if the cannon is locked in the loading angle? The gyro would have to have a much larger range of rotation than was previously the case for this purpose.  At least it would be an interesting solution. But so far nobody can confirm or deny this.

@Bojan

Yes, resolver would fit. "A resolver is a type of rotary electrical transformer used for measuring degrees of rotation."

Edited November 12, 2021 by Stefan Kotsch

[sunday]

Agree with Bojan.

On the loading angle thing, I do not see any switch in the diagram for that. Was there some kind of button that returned automatically the gun to firing position? With the diagram as it is, manual return to firing elevation seems possible.

I made a mistake in my previous post - the angle signal that POK sends to DNNS-2 is superelevation of the mirror with respect to the gun, as the DNNS-2 already has an input for gun elevation, input that is added to that angle signal from POK.

[bojan]

IIRC gun is returned to a a required elevation automatically after loading.

[sunday]

I think that automatic return is not in that diagram.

Edited November 12, 2021 by sunday

[Stefan Kotsch]

Just now, sunday said:

those three unlabeled inputs of the ballistic computer.

+ Meteo-Sensor (wind and temperature)

+ Commander's control panel (temperatur of gun powder)

+ ball. computer control panel (ammunition type)

 

[Stefan Kotsch]

27 minutes ago, sunday said:

I think that automatic return is not in that diagram.

That is the easiest task. When the brech block is closed after loading, a signal is issued to unlock the gun. The gun is moved until the elevation sensor reached the correct angle and computer&stabilization electronic says "OK, this fits that".

Edited November 12, 2021 by Stefan Kotsch

[Gman]

Very interesting information, thank you Stefan and Bojan.

I shudder to imagine how the loader/crew coped with the T55 with APFSDS ammo, assuming a longer rod penetrator means even less space to swing a sabot.

Really seems like a poor choice of ergonomics overall for the T54/55 with the size of gun overall, despite well armoured for it's time.

[bojan]

100mm APFSDS is not much longer than HE/HEAT/AP so it could fit in the racks. Here is local clone of Israeli M111 APFSDS:

[Gman]

@Bojan, I wasn't saying it wouldn't fit, just that it must be a nightmare to load and fire on the move inside such a cramped turret.   APDS is bad, can't see APFSDS any easier to work with.  No one accuses Soviets of good ergonomic design though !

 

[Wiedzmin]

Turret is not much more cramped than any other western tank of same generation, as for ergonomic ever tried to research any tank real ergonomic and not some cold war era bs ?

Edited November 15, 2021 by Wiedzmin