Torpedo settings...Real life?

BigWalleye · 04-25-17, 11:23 AM

And there was nothing called a "TDC " on a German submarine. There was a Torpedo Vorhaltrechner, a TVR, which performed similar fire control calculations. But the TVR was not just a TDC in German.The TVR lacked the US TDC's Position Keeper capability, but did have a lead angle calculator - a useful capability which the TDC lacked. There were other design differences as well. Both TDC and TVR had the capability to set torpedo run parameters while the torpedo was in the tube, although the mechanics were somewhat different. For more information search for TVR, not TDC.

Sniper297 · 04-25-17, 12:03 PM

I don't know how you figure the TDC didn't have lead angle capability, target speed, relative bearing, and AOB equals lead angle - which was automatically updated in the torpedo gyrocompass. Put the crosshairs on the target, hit the button to send the latest bearing to the TDC, which sets the gyro angle for the correct lead angle, and shoot. Don't even need to know the lead angle, TDC sets that automatically.

CaptBones · 04-25-17, 05:11 PM

The link from Rhodes and the link and comments from Sniper297 are very good and quite thorough answers to most of the original question.

If you want to see some additional technical details about the adjustment mechanisms on and inside the torpedo itself, have a look at the G7a drawings at uboatarchive.net. Take note of the "lugs" on the top of the "engine compartment" body and the upper tail fin; they are there to ensure the torpedo is lined up in the tube to mate with the adjustment spindles.

As for maintenance; like all other complex modern weapons, torpedoes were (and still are) designed and built to be "easily" maintained. The crew did not have to take them apart and put 'em back together again in order to do the routine maintenance. Yes, you did have to pull them from the tubes, but the handling gear in the torpedo room was designed specifically to be able to pull the fish from the tube, do the maintenance and put it back in the tube without serious disassembly.

The most frequent maintenance action was just removing, regreasing and reinstalling; every time you open the outer doors and flood the tube, you're introducing the steel "hull" of the torpedo (and all of those fittings on it) to one of its biggest enemies...saltwater. The next biggest maintenance problem was based on the type of propulsion. For the G7a you had to check the levels in the fuel tank and lube oil tank and the pressure in the air flasks. For the G7e, the primary check was the battery charge and water level in the cells. There were fittings to add fluids/air if necessary and there were also numerous grease fittings, including the steering rudder and depth rudder linkages.

All-in-all, plenty to do to keep the torpedomen occupied.

Tupolev · 04-25-17, 10:12 PM

http://www.tvre.org/en/torpedo-fire-...german-u-boats

Some good info on how fire control data (gyro angle) was input.

There's an amazing amount of info on that whole site. Well worth reading.

T

BigWalleye · 04-26-17, 10:41 AM

Quote:

Originally Posted by Sniper297

I don't know how you figure the TDC didn't have lead angle capability, target speed, relative bearing, and AOB equals lead angle - which was automatically updated in the torpedo gyrocompass. Put the crosshairs on the target, hit the button to send the latest bearing to the TDC, which sets the gyro angle for the correct lead angle, and shoot. Don't even need to know the lead angle, TDC sets that automatically.

We are talking about 2 different uses of the term "lead angle". I used it in the sense of shooting at a moving target,where the shooter "leads the target" to compensate for target motion. The TVR provides this lead angle, deflection angle, aim point offset, call it what you will, for the Approach Officer (or German equivalent). The TDC does not.

As you correctly described it, the TDC continuously updates the torpedo gyro angle setting, based on the target estimated position from the Position Keeper. It is fully automatic. Once the target position, course, and speed have been entered, the Approach Officer can point the periscope at a seagull. If the correct target position, course, and speed have been entered in the TDC, and IF the target course and speed do not change, then the torpedo will intercept the target. At firing time, the Approach Officer is out of the fire control loop.

For a variety of reasons, some more valid than others, there were US skippers who prefered a less automatic fire control procedure. The "Dick O'Kane" Constant Bearing Technique is an example. Once the fire control party has determined gyro angle for the desired torpedo impact geometry, the Approach Officer observes through the periscope until the target crosses an offset aim point (based on estimated speed) and gives the command to fire. ("Fire on the wire.") The TDC Angle Solver is used to calculate the gyro setting - and set the gyro - but it does not provide any assistance in determining the aim point offset. There were tables and rules of thumb for this.

The TVR, on the other hand does not have a fully automatic mode, because it does not have a Position Keeper. Once target position, course, and speed are entered and the TVR is activated, the TVR calculates an impact point based on the current periscope bearing and sets the gyro angle accordingly. The TVR does automatically introduce an aim point offset, based on target position, course, and speed. The Approach Officer needs to put the periscope wire on the intended impact point on the target. If target position, course, and speed were entered correctly, the torpedo will impact the target at the aim point. This allows for a spread to be fired simply by moving the periscope. It also allows for rapid shifting of targets in a convoy, where all ships have the same course and speed, and approximately the same range - TVR data do not have to be changed.

The TDC and TVR reflect two distinctly different design philosophies - computer automated fire control versus computer assisted fire control. Which is better? Coke or Pepsi?

Sniper297 · 04-26-17, 11:42 AM

Um,

"We are talking about 2 different uses of the term "lead angle". I used it in the sense of shooting at a moving target,where the shooter "leads the target" to compensate for target motion."

Lead angle is firing at where the target will be when the projectile (in this case a torpedo) crosses the target track. Unless you're shooting at a moving target you don't need a lead angle.

The TDC had the same capability of shooting multiple targets and/or spreading by shifting crosshairs, there was a button on both periscopes and the TBT to send a new bearing to the TDC - if the speed and course of the target(s) didn't change all you needed was a new bearing. And the TDC had enough sense to fire at where the target would be rather than where it is at the moment the button was clicked, that's lead angle. I agree that the actual lead angle is nice to know if for no other reason than a double check on the accuracy of the TDC solution, but I'm sure there was someone on the plotting team responsible for checking that. Many skippers had someone on the attack team standing by with a "banjo" and Is/Was just in case, especially early in the war when the TDC reliability was still unknown.

BigWalleye · 04-26-17, 01:59 PM

Sniper, I understood perfectly well what you meant by "lead angle" which was precisely why I clarified my use of the term and subsequently refered to "aim point offset" to avoid further confusion. If you can post the source for information that the USN's Torpedo Data Computer Mark 3 provided an aim point offset, I would certainly like the chance to read it. I don't see anything in OP 1056.

Sniper297 · 04-26-17, 02:49 PM

Well, a quick google search turns up this;

http://www.fleetsubmarine.com/tdc.html

Relevant part is "In addition to the standard angle solver" - the function of calculating the lead angle was such a basic part of the system it was only mentioned in passing. If it wasn't programmed to calculate the lead angle it wouldn't have been very useful, unless the ordinance that you're shooting has a velocity of 186,000 miles per second it's rather pointless to shoot at a moving target where it is now rather than where it will be.

Fire control computer on a modern tank is a good example - there's a wind speed and direction system on the turret, if the gunsight automatically compensates for crosswinds why would you need a readout to tell you what the crosswind factor is? My thinking is if the German TVR had a separate readout for lead angle more power to them, if the TDC didn't have a dial for that it was probably because it would have been redundant.

I've used both systems, I currently have a German ATO career and a US Pacific career active in SH4, and even though I don't use the PK much I still find the TDC easier to use simply because the "own ship" and "target" dials one above the other makes it easier to visualize the situational awareness "picture" for the approach. I have used the "angle off" method where you estimate the intercept angle, set the fish for a zero gyro angle, then offset the scope 10 to 15 degrees and fire when the target hits the crosshairs, but that's usually reserved for the S-class which wasn't supposed to have a TDC in real life.

BigWalleye · 04-26-17, 03:58 PM

Sniper, please read my last post. I am not, and have never been, talking about the variable which you call "lead angle." I concede that the variable which you call you call "lead angle" is calculated by the TDC. Please either do me the courtesy of addressing my question regarding the aim point offset, or at least stop arguing against claims which I did not make. At the very least, please read my posts comprehensively before replying. Thank you.

04-26-17, 11:42 AM	#6
Sniper297 The Old Man Join Date: Dec 2005 Location: Philadelphia Shipyard Brig Posts: 1,386 Downloads: 160 Uploads: 19	"You say tomato, I say tomahto" Um, "We are talking about 2 different uses of the term "lead angle". I used it in the sense of shooting at a moving target,where the shooter "leads the target" to compensate for target motion." Lead angle is firing at where the target will be when the projectile (in this case a torpedo) crosses the target track. Unless you're shooting at a moving target you don't need a lead angle. The TDC had the same capability of shooting multiple targets and/or spreading by shifting crosshairs, there was a button on both periscopes and the TBT to send a new bearing to the TDC - if the speed and course of the target(s) didn't change all you needed was a new bearing. And the TDC had enough sense to fire at where the target would be rather than where it is at the moment the button was clicked, that's lead angle. I agree that the actual lead angle is nice to know if for no other reason than a double check on the accuracy of the TDC solution, but I'm sure there was someone on the plotting team responsible for checking that. Many skippers had someone on the attack team standing by with a "banjo" and Is/Was just in case, especially early in the war when the TDC reliability was still unknown.

04-25-17, 11:23 AM	#1
BigWalleye Sea Lord Join Date: Jul 2012 Location: On the Eye-lond, mon! Posts: 1,987 Downloads: 465 Uploads: 0	And there was nothing called a "TDC " on a German submarine. There was a Torpedo Vorhaltrechner, a TVR, which performed similar fire control calculations. But the TVR was not just a TDC in German.The TVR lacked the US TDC's Position Keeper capability, but did have a lead angle calculator - a useful capability which the TDC lacked. There were other design differences as well. Both TDC and TVR had the capability to set torpedo run parameters while the torpedo was in the tube, although the mechanics were somewhat different. For more information search for TVR, not TDC.

04-25-17, 12:03 PM	#2
Sniper297 The Old Man Join Date: Dec 2005 Location: Philadelphia Shipyard Brig Posts: 1,386 Downloads: 160 Uploads: 19	I don't know how you figure the TDC didn't have lead angle capability, target speed, relative bearing, and AOB equals lead angle - which was automatically updated in the torpedo gyrocompass. Put the crosshairs on the target, hit the button to send the latest bearing to the TDC, which sets the gyro angle for the correct lead angle, and shoot. Don't even need to know the lead angle, TDC sets that automatically.

04-25-17, 05:11 PM	#3
CaptBones The Old Man Join Date: Nov 2010 Location: Rockton, IL Posts: 281 Downloads: 208 Uploads: 0	The link from Rhodes and the link and comments from Sniper297 are very good and quite thorough answers to most of the original question. If you want to see some additional technical details about the adjustment mechanisms on and inside the torpedo itself, have a look at the G7a drawings at uboatarchive.net. Take note of the "lugs" on the top of the "engine compartment" body and the upper tail fin; they are there to ensure the torpedo is lined up in the tube to mate with the adjustment spindles. As for maintenance; like all other complex modern weapons, torpedoes were (and still are) designed and built to be "easily" maintained. The crew did not have to take them apart and put 'em back together again in order to do the routine maintenance. Yes, you did have to pull them from the tubes, but the handling gear in the torpedo room was designed specifically to be able to pull the fish from the tube, do the maintenance and put it back in the tube without serious disassembly. The most frequent maintenance action was just removing, regreasing and reinstalling; every time you open the outer doors and flood the tube, you're introducing the steel "hull" of the torpedo (and all of those fittings on it) to one of its biggest enemies...saltwater. The next biggest maintenance problem was based on the type of propulsion. For the G7a you had to check the levels in the fuel tank and lube oil tank and the pressure in the air flasks. For the G7e, the primary check was the battery charge and water level in the cells. There were fittings to add fluids/air if necessary and there were also numerous grease fittings, including the steering rudder and depth rudder linkages. All-in-all, plenty to do to keep the torpedomen occupied.

04-25-17, 10:12 PM	#4
Tupolev Hauptman Join Date: Mar 2013 Location: FL410 Posts: 174 Downloads: 75 Uploads: 0	http://www.tvre.org/en/torpedo-fire-...german-u-boats Some good info on how fire control data (gyro angle) was input. There's an amazing amount of info on that whole site. Well worth reading. T

04-26-17, 01:59 PM	#7
BigWalleye Sea Lord Join Date: Jul 2012 Location: On the Eye-lond, mon! Posts: 1,987 Downloads: 465 Uploads: 0	Sniper, I understood perfectly well what you meant by "lead angle" which was precisely why I clarified my use of the term and subsequently refered to "aim point offset" to avoid further confusion. If you can post the source for information that the USN's Torpedo Data Computer Mark 3 provided an aim point offset, I would certainly like the chance to read it. I don't see anything in OP 1056.

04-26-17, 02:49 PM	#8
Sniper297 The Old Man Join Date: Dec 2005 Location: Philadelphia Shipyard Brig Posts: 1,386 Downloads: 160 Uploads: 19	Well, a quick google search turns up this; http://www.fleetsubmarine.com/tdc.html Relevant part is "In addition to the standard angle solver" - the function of calculating the lead angle was such a basic part of the system it was only mentioned in passing. If it wasn't programmed to calculate the lead angle it wouldn't have been very useful, unless the ordinance that you're shooting has a velocity of 186,000 miles per second it's rather pointless to shoot at a moving target where it is now rather than where it will be. Fire control computer on a modern tank is a good example - there's a wind speed and direction system on the turret, if the gunsight automatically compensates for crosswinds why would you need a readout to tell you what the crosswind factor is? My thinking is if the German TVR had a separate readout for lead angle more power to them, if the TDC didn't have a dial for that it was probably because it would have been redundant. I've used both systems, I currently have a German ATO career and a US Pacific career active in SH4, and even though I don't use the PK much I still find the TDC easier to use simply because the "own ship" and "target" dials one above the other makes it easier to visualize the situational awareness "picture" for the approach. I have used the "angle off" method where you estimate the intercept angle, set the fish for a zero gyro angle, then offset the scope 10 to 15 degrees and fire when the target hits the crosshairs, but that's usually reserved for the S-class which wasn't supposed to have a TDC in real life.

04-26-17, 03:58 PM	#9
BigWalleye Sea Lord Join Date: Jul 2012 Location: On the Eye-lond, mon! Posts: 1,987 Downloads: 465 Uploads: 0	Sniper, please read my last post. I am not, and have never been, talking about the variable which you call "lead angle." I concede that the variable which you call you call "lead angle" is calculated by the TDC. Please either do me the courtesy of addressing my question regarding the aim point offset, or at least stop arguing against claims which I did not make. At the very least, please read my posts comprehensively before replying. Thank you.