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View Full Version : Ever been curious about the submarine TDC?



J Tiers
03-13-2010, 10:37 PM
AKA Torpedo data computer.... the mechanical computer that solved the aiming problem and commanded the settings on the torpedos.

Link to the manual is here...........

http://www.practicalmachinist.com/vb/general/fascinating-look-into-mechanical-computer-200451/

millwrong
03-14-2010, 12:22 AM
No, but I've always been really curious as to the depths subs are comfortable at. Seems that this info is strictly taboo!

oldtiffie
03-14-2010, 12:31 AM
http://en.wikipedia.org/wiki/Submarine_depth_ratings

http://www.google.com.au/#hl=en&source=hp&q=submarine+dive+depth&meta=&aq=7&aqi=g10&aql=&oq=submarine+div&fp=98f33b0d2303fec5

J Tiers
03-14-2010, 10:07 AM
Since the TDC is super-mechanical, with precision machining to the max, I am surprised so few appear to be interested in it here......

hoof
03-14-2010, 10:18 AM
Really enjoyed, thanks for posting

knudsen
03-14-2010, 11:05 AM
No, but I've always been really curious as to the depths subs are comfortable at. Seems that this info is strictly taboo!

Propeller shape is one of the best kept US military secrets. Ours are quiet, theirs are not.

JeffG
03-14-2010, 12:11 PM
Don't know about TDCs, but one of the early applications for electronic computing was to replace the mechanical fire control computers for large-gun warships, a similar but probably more complex problem. Torpedos are self-guided. The fire control computer had to account for target and own-ship motion, roll, weight of projectile, barometric pressure, temperature, etc. etc. I've always been amazed by the technology.

lynnl
03-14-2010, 12:51 PM
Propeller shape is one of the best kept US military secrets. Ours are quiet, theirs are not.

I'm not sure how true that is anymore. A Jap company (Sanyo I think) with whom we'd shared some of the machining secrets, turned around and sold (or gave away) that technology to the soviets. The US imposed sanctions, but the cat was already out of the bag.
This was all related to suppressing signatures visible from space by satellite.

BobWarfield
03-14-2010, 01:22 PM
I'm not sure how true that is anymore. A Jap company (Sanyo I think) with whom we'd shared some of the machining secrets, turned around and sold (or gave away) that technology to the soviets. The US imposed sanctions, but the cat was already out of the bag.
This was all related to suppressing signatures visible from space by satellite.

They didn't have a 5-axis needed to make the props before then.

Many interesting tidbits from the Cold War surrounding submarines. One that piqued my interest were the Russian torpedoes that could travel faster than sound underwater. This made the problem of detecting them all but impossible. They would arrive before sonar could spot them. There was even concern they might be used as a sort of underwater "cruise missile" that could deliver nukes to the shoreline before they could be detected.

I remember as a young lad back in junior high hearing about the Russians titanium hulled subs. It was an interesting learning experience to compute the depth at which a cylindrical hull would become heavier than the water it displaced due to the thickness of the hull. Once that happens, you get increasing negative bouyancy, which is a bad thing in a military sub.

Bathyscaphes dealt with it by literally using gasoline as a hot air balloon uses hot air to float the crew sphere. In any event, the Russians used titanium largely because it allowed their subs to go almost twice as deep given its strength relative to its weight.

Unfortunately, the Alfa class also circulated radioactive reactor coolant to heat the subs, so all that valuable titanium is highly radioactive and not salvageable. This can't be a happy result for their crews either.

Cheers,

BW

Al Messer
03-14-2010, 02:51 PM
"...faster than sound..." Over 650 miles per hour at sea level? I thought that around 30 knots was max for a torpedo.

knudsen
03-14-2010, 02:55 PM
I'm not sure how true that is anymore. A Jap company (Sanyo I think) with whom we'd shared some of the machining secrets, turned around and sold (or gave away) that technology to the soviets. The US imposed sanctions, but the cat was already out of the bag.
This was all related to suppressing signatures visible from space by satellite.

Huh, after we were their DOD for 50 years. Well, their economy broke; I guess they were hungry. Or the Ruskies sent a hot blond over.

Tony Ennis
03-14-2010, 03:13 PM
I don't believe a FTS torpedo exists. There are (were?) submarine-launched rockets that dropped their payload - a torpedo - near the target however. Those could be pretty fast.

JoeCB
03-14-2010, 03:24 PM
Yes, all those early fire control devices were very special and very secret. I believe most if not all the WWII devices were straight up mechanical computers. Maybe someone can verify that. The Norden (sp?) bomb sight gave our side a real advantage in precision bombing.

Joe B

ikdor
03-14-2010, 03:25 PM
There are some seriously fast torpedoes though:
http://en.wikipedia.org/wiki/VA-111_Shkval

Igor

John Stevenson
03-14-2010, 03:26 PM
http://www.answerbag.com/q_view/7151

.

loose nut
03-14-2010, 03:29 PM
Yes, all those early fire control devices were very special and very secret. I believe most if not all the WWII devices were straight up mechanical computers. Maybe someone can verify that. The Norden (sp?) bomb sight gave our side a real advantage in precision bombing.

Joe B

In theory it was great, in practice it didn't work that well, the real world has to many variables for a system like that. They only work right under perfect conditions.

loose nut
03-14-2010, 03:36 PM
Don't know about TDCs, but one of the early applications for electronic computing was to replace the mechanical fire control computers for large-gun warships, a similar but probably more complex problem. Torpedos are self-guided. The fire control computer had to account for target and own-ship motion, roll, weight of projectile, barometric pressure, temperature, etc. etc. I've always been amazed by the technology.


Torpedoes are self guiding now, under certain conditions but back then they where not and sophisticated fire-control systems where developed to aim them. The fire control problem for hitting an aircraft or a ship is primarily the same as targeting a ship with a torpedo, in someways it is easier because the x-y axis oscillation and cross-roll of the launching platform doesn't enter into the equation.

BobWarfield
03-14-2010, 03:57 PM
These faster than torpedos are called "supercavitating". They travel inside a bubble of air and are essentially rockets. The article was in Scientific American. There are some references to it, but I didn't find the original article:

http://people.exeter.ac.uk/tkirsano/Sciam.htm

Cheers,

BW

lynnl
03-14-2010, 04:48 PM
Huh, after we were their DOD for 50 years. Well, their economy broke; I guess they were hungry. Or the Ruskies sent a hot blond over.

The Japanese gov't wasn't the culprit. It was somewhat similar to corporate espionage as I recall. This took place some 25-30 years ago, but the way I remember it, is that we'd made the technology available to various "friendly" entities, with their assurances it would remain within "friendly" shores.

Tony Ennis
03-14-2010, 04:48 PM
I'm shocked they could ever hit a target. The multiplier hardware is very clever.

The Artful Bodger
03-14-2010, 06:45 PM
Yes, all those early fire control devices were very special and very secret. I believe most if not all the WWII devices were straight up mechanical computers. Maybe someone can verify that. The Norden (sp?) bomb sight gave our side a real advantage in precision bombing.

Joe B

A number of WWII era (also a little before and for some time after) computers were based on electro-magnetic devices related to and including 'magslips' and 'selsyns'. I have a box of such bits including 'followers' and 'resolvers' etc also a couple of tiny little mechanical differentials. These devices came from wind finding radars which calculated upper atmosphere winds by tracking reflectors on baloons. One of the manuals associated with these bits says the basic principal was a British state secret from WWI.

darryl
03-14-2010, 06:47 PM
My head started to hurt just a few pages into the manual. My hat is off to anyone who can come up with stuff like that. Must have been some pretty sharp tacks around then-

mlucek
03-15-2010, 07:28 PM
Yes, all those early fire control devices were very special and very secret. I believe most if not all the WWII devices were straight up mechanical computers. Maybe someone can verify that. The Norden (sp?) bomb sight gave our side a real advantage in precision bombing. I was at an airshow a few years back where there was a display on the Norden bombsights. The guy manning the display collected and restored the sights for a hobby. He told me that the sights were more accurate then anything else in their day, but still not all the relatively accurate.

The bombardiers all had to sign some top secret oath to protect the device at all costs. It was removed from the planes after all missions and kept under lock & key, etc. The guy said a lot of the secrecy was propaganda and mind games played against the enemy to make them fearful of it.

Of course take all that with a grain of salt. Here's more info from WikiPedia :

http://en.wikipedia.org/wiki/Norden_bombsight


...The Norden was marketed as the tool to win the war; and it was often claimed that the bombsight could drop bombs into pickle barrels....

In practice the Norden never managed to produce accuracies remotely like those of which it was theoretically capable.

In Europe the Norden likewise demonstrated a poor real-world accuracy. Bombing was computed by assessing the proportion of hits falling within 1,000 ft and 2,000 ft circles about an MPI (mean point of impact). To achieve a perfect strike, a bomber group would have to unload all its bombs within the 1,000 ft circle. By the spring of 1943 some impressive results were being recorded. Over Vegesack (http://en.wikipedia.org/wiki/Vegesack) on 19 March, for instance, the 303d Bombardment Group (http://en.wikipedia.org/wiki/303d_Bombardment_Group) dropped 76 per cent of its load within the 1,000 ft ring. Under perfect conditions only 50 percent of American bombs fell within a quarter of a mile of the target, and American flyers estimated that as many as 90 percent of bombs could miss their targets.[4] (http://en.wikipedia.org/wiki/Norden_bombsight#cite_note-3)[5] (http://en.wikipedia.org/wiki/Norden_bombsight#cite_note-4)[6] (http://en.wikipedia.org/wiki/Norden_bombsight#cite_note-5) Nevertheless many veteran B-17 and B-24 (http://en.wikipedia.org/wiki/B-24) bombardiers swore by the Norden.

Many factors have been put forth to explain the Norden's poor performance. Over Europe the cloud cover was a common explanation, although performance did not improve even in favorable conditions. Accuracy did improve with the introduction of the "master bomber" concept, under which only a single aircraft would actually use the Norden while the rest simply dropped on their command. This suggests that much of the problem is attributable to the bombardier. Over Japan, bomber crews soon discovered strong winds at high altitudes, the so-called jetstreams (http://en.wikipedia.org/wiki/Jetstream), but the Norden bombsight worked only for wind speeds with minimal wind shear. Additionally, the bombing altitude over Japan reached up to 30,000 feet (9,100 m), but most of the testing had been done well below 20,000 ft (6,100 m) An additional factor was that the shape and even the paint of the bomb mantle greatly changed the aerodynamic properties of the weapon; and, at that time, nobody knew how to calculate the trajectory (http://en.wikipedia.org/wiki/Trajectory) of bombs that reached supersonic speeds during their fall.

In both theaters of war, one vulnerability was that when the bombardier auto-piloted the aircraft using the bombsight, the aircraft was more susceptible to anti-aircraft fire and collisions with other allied aircraft.

As a mechanical device, the Norden bombsight used complex machinery consisting of many gearwheels (http://en.wikipedia.org/wiki/Gearwheel) and ball bearings (http://en.wikipedia.org/wiki/Ball_bearing), which were prone to produce inaccuracies if not properly maintained. In fact, many bombsights were rushed to war use without thorough testing. Often the bombardier had to oil and repair failures himself. For some time into the war equipped and qualified groundcrew (http://en.wikipedia.org/wiki/Groundcrew) technical staff were simply not available in sufficient numbers.

Tony Ennis
03-15-2010, 07:31 PM
The Nordon bombsight was a 2D autopilot. It was flying the plane for the bombing run. Straight and flat... Easy meat.

Tony Ennis
03-15-2010, 07:34 PM
My hat is off to anyone who can come up with stuff like that. Must have been some pretty sharp tacks around then

The math isn't that difficult. I find the mechanical aspects of the device (and the torpedo) to be mystifying. I don't understand gyros, for example. So this gyro is going to change the direction of the torpedo? How does this work? etc etc. Read the section on the adders and 'integrators' (multipliers). The 3d cam surface is brilliant. I wonder how they machined that.

alanganes
03-15-2010, 08:35 PM
Unfortunately, the Alfa class also circulated radioactive reactor coolant to heat the subs, so all that valuable titanium is highly radioactive and not salvageable. This can't be a happy result for their crews either.

BW

I used to work with a guy who had come from what was the USSR. His dad was a career navy guy there and he grew up living on various naval bases. He said that around those places, you could always tell the submariners, as they all had little or no hair.