Torpedoes - experts needed

[Dr.Sid]

Hi .. it's me again being curious.

Does torpedoes have up and down side ? Are the supposed to swim in water with some orientation ? Or do they simply navigate in 3d, with symmetric sensors and ignore any bank (listing) ?

Do some torpedoes have bottom sounding ?

[SeaQueen]

The physics of underwater sound would imply that acoustic homers would have an asymetrical "cookie cutter" sensor, both vertically and in all likelyhood horizontally. Their sensors are just like any other sonar except higher frequency due to the size of the array you can fit in a torpedo's nose.

Hi .. it's me again being curious.

Does torpedoes have up and down side ? Are the supposed to swim in water with some orientation ? Or do they simply navigate in 3d, with symmetric sensors and ignore any bank (listing) ?

Do some torpedoes have bottom sounding ?

[Dr.Sid]

I mean .. do the torpedoes rotate along it's main axis without relying on some orientation or are they stabilized to have one side always up ?

Btw. sorry for my incompetence but what do you mean by 'cookie cutter' ? Only possible meaning I found is 'without original conception' .. which gives some sense but not really.

[Frame57]

Hi Sid, ran this one by a TM. It was explained to me that the guidance is X-Y. The (MK-48) will change depth in a vertical way and course in a horizontal way. Keep in mind I am only a knuckle dragging Machinist Mate, so I tried my best to explain to him what you are asking, but this is all I was able to get out of the fellow. from his experiences he did not think that there was any other dimensional or spatial ability in how a 48 gets from point A to B. I am surprized that there are not any TM's on this site. I know there are a few of us bubbleheads here. But then again, I am not sure if it is classified material. But if you ever have a question about submarine hydraulic systems, boy I can chat ya up on that one. (yeah right!):up:

[Dr.Sid]

Well I would bet on the strictly 2d, bank stabilized navigation too. Depth reader can be bank independent but then you have to steer up/down and you must know which direction it is.

I guess the stabilization must be active because torpedo can spin too easily with no extending planes and only little room for low-center-of-gravity based stabilization. And if it had low center of gravity it would bank into turn as sub does and then it would have little means to stabilize again.

As for propulsion, most types are gravity independent, and negative G would happen .. but some types can handle the negative G only for short amount of time. Also I guess some orientation would be important during storage, because of batteries, fuel tanks and so on.

So at the moment I think it is stabilized because it can help the navigation and some types of propulsion. The stabilization is done actively by steering planes based on some sensors (probably 3d gyros reset at launch). Center of gravity would be intentionally neutral (exactly in the axis) so torpedo does not bank in turns.

It would also mean there is some 'this side up' label on the torpedo.

[Bill Nichols]

It would also mean there is some 'this side up' label on the torpedo.

:yep: Yep.

[Dr.Sid]

Frame57: are you actually on the sea ? :o Or did you just call old friend (or recent friend) while being of duty ? They don't let you browse the forums on the internet while on the mission right ?

Bill: thanks, short and accurate, as always :up:

[Frame57]

No, I am retarded (OOPS, I mean retired). Spent three hitches on two different fast attacks, so I still stay in contact with some old shipmates. Oh, and I just recently joined the US Submarine league. Anyway, I searched high and low for some technical info, but did not come up with much. A lot of WW2 stuff out there. I have been trying to get info on the BQQ-10, just curious to find out how it performs against the BQQ-5's we had. I am excited today because i just received my fancy DW manual, now maybe I will give DW a shot. :D

[TopTorp '92]

Do understand correctly? Are you asking how the torpedo knows which way is up once it is fired into the ocean?
Both MK 48 and ADCAP have internal gyros that tell the weapon where to go as well as how to correct for changes in pitch and roll. The only caveat is that significant pitch/roll deviations will result in an internal shutdown before the weapon enables.

[Dr.Sid]

I mean if there is some bank held at all or if the torpedo is let to bank freely.

Anyway it's quite clear now that the bank is fixed. Thanks !

[TopTorp '92]

I mean if there is some bank held at all or if the torpedo is let to bank freely.

Anyway it's quite clear now that the bank is fixed. Thanks !

It banks freely
TopTorp

[Dr.Sid]

Lol .. it was clear .. until now. You said:

1) The only caveat is that significant pitch/roll deviations will result in an internal shutdown.

2) It banks freely.

As I understand it these two are contradicting. Or maybe you don't mean bank & roll to be the same as I do ?

[TopTorp '92]

Lol .. it was clear .. until now. You said:

1) The only caveat is that significant pitch/roll deviations will result in an internal shutdown.

2) It banks freely.

As I understand it these two are contradicting. Or maybe you don't mean bank & roll to be the same as I do ?

Shutdown is tricky, so I didn't really address all of the caveats. Also, I'm operating on decade old memory. So, just bear with me.

There are two systems protecting own-ship from a faulty torpedo that may turn and come after the home team.

From the moment the weapon is fired (TOF-Time of Fire) to the enabling point, that is the weapon slows to search speed, ACR (for anti circular run) protects ownship. This is the "internal shutdown" I referenced above. After the enabling point, ACR becomes disabled. ACR shutdown limits are technical and I no longer remember them. Pitch/roll is +- 5 degrees, I think. Gyro deviations are +- 168 til the first gyro null and then +- 5 degrees til enable.

After the enabling point, there is an additional safety feature for Mk 48 called ASH (anti self homing.) It is a discrete setting in the torpedo meaning it is either set in or out. It's too complicated to explain how it works because it uses counting system that counts twice as fast if the weapon changes course by a predetermined amount.

ADCAP is a digital weapon and no longer needs to know how to count the old MK-48 way. It uses FENCE after the enabling point and this feature not only protects ownship from a torpedo coming after ownship it also has lateral limits that prevents the weapon from homing on targets outside the lateral limits. Basically the weapon swims around in a digital box defined by the weapons operator. Any target outside the box is off limits. The idea is to protect hospital ships or if using the weapon in littoral waters, then the latteral FENCE settings may protect nearby civilian shipping.

The weapons operator may override both ASH and FENCE after TOF if the guidance wire remains in-tact. Unfortunately, if the wire breaks during an override command, then the safety feature remains permanently overriden til the weapon either runs out of gas or blows up.

To answer your original question, the weapon rolls freely after the enabling point has been reached. However, during the enabling run, there are safety limits that will shutdown the weapon if exceeded. It depends which phase you're talking about.

TopTorp

[Dr.Sid]

Nice new information.

Anyway .. do you mean that torpedo can bank 180 degrees and continue at that bank with no effect on navigation or propulsion ?

[TopTorp '92]

Nice new information.

Anyway .. do you mean that torpedo can bank 180 degrees and continue at that bank with no effect on navigation or propulsion ?

You're going to have to define your term. What is "bank"? I'm only familiar with pitch and roll.

Can it roll 180? Sure, so long as it rolls 180 after enable.

What if the weapon rolls 180 before enable? Then ACR shuts the weapon down.

What if the weapon rolls 180 during the wire clearance maneuver? I don't know. ACR will probably shut the unit down.

TopTorp

[Dr.Sid]

Ok .. let's define .. with an aircraft, that's easier.

Let's start with aircraft going straight and level.

If it points nose down or up (pushing or pulling stick) I call that pitching.
If the aircraft turns left and right only I call tad turning or yaw.

If wing on one side goes down and on the other side up without change in direction or or altitude, I call that rolling. Or banking. With ships the term listing is sometimes used too. Aircraft can perform maneuver called 'roll' where it rotates 360 degrees without changing direction or altitude like this.

All maned vehicles use fixed bank. Just because people are inside and they want to sit or something. So even if plane can turn upside down, except for acrobatic flying or dogfight they don't do that. Same for subs.

With torpedo (or AA missile for example) there is no much need to keep constant roll. While it could be useful to avoid fast rolling, which could complicate seeking, there may be no need to keep one side always up. On the other hand with those gyros inside, it would not be problem to do so.

The question is: can torpedoes go upside down ? Can they roll ? Do they prevent it somehow ?

I ask only for realism sake for my simulator. It's no big deal.

[TopTorp '92]

Ok .. let's define .. with an aircraft, that's easier.

Let's start with aircraft going straight and level.

If it points nose down or up (pushing or pulling stick) I call that pitching.
If the aircraft turns left and right only I call tad turning or yaw.

If wing on one side goes down and on the other side up without change in direction or or altitude, I call that rolling. Or banking. With ships the term listing is sometimes used too. Aircraft can perform maneuver called 'roll' where it rotates 360 degrees without changing direction or altitude like this.

All maned vehicles use fixed bank. Just because people are inside and they want to sit or something. So even if plane can turn upside down, except for acrobatic flying or dogfight they don't do that. Same for subs.

With torpedo (or AA missile for example) there is no much need to keep constant roll. While it could be useful to avoid fast rolling, which could complicate seeking, there may be no need to keep one side always up. On the other hand with those gyros inside, it would not be problem to do so.

The question is: can torpedoes go upside down ? Can they roll ? Do they prevent it somehow ?

I ask only for realism sake for my simulator. It's no big deal.

I can't answer for the physics. I can only speak for the safety shutdowns once the weapon is in the water.

ACR protects the ship before the enabling point and I would consider a torpedo travelling upside down before enable a sure violation of any ACR limitation. So, it can't go upside down before enable without shutting down on ACR.

Once the weapon has enabled, it may go upside down, fly out of the water and attack helocopters, do anything within physical limits so long as it doesn't violate ASH or FENCE if those settings were programmed into the weapon.

You gotta remember that the WWII experience spooked everyone (including the Germans) with torpedoes returning to the firing submarine. So, safety measures were installed and stay that way to this day.

By the way, what would your torpedo be doing upside down that it couldn't do right side up?

TopTorp

[Dr.Sid]

If it has fuel based propulsion it can malfunction (most engines do, except for short time negative G). Even some kind of batteries needs proper orientation.
If the navigation system does not counter it, it can fail to keep to depth. Seekers can have non-conical detection areas where orientation could matter. If there is bottom sounder on the torpedo it could use proper orientation too.

All that can be handled by design .. but is it ?

[TopTorp '92]

If it has fuel based propulsion it can malfunction (most engines do, except for short time negative G). Even some kind of batteries needs proper orientation.
If the navigation system does not counter it, it can fail to keep to depth. Seekers can have non-conical detection areas where orientation could matter. If there is bottom sounder on the torpedo it could use proper orientation too.

All that can be handled by design .. but is it ?

Not to my knowledge do torpedos have any such design issues. I don't think any torpedo has any upside down/orientation concerns. Even when the MK-48 would home on the helo's compression waves (an actual exercise, jumped out of the water in an attempt to attack and reattack) the weapon had no issues about orientation. I mean, these weapons will go in circles, jump out of the water for a long time before they run out of fuel or hit something.

Also, the closest the MK-48/ADCAP comes to other such erratic manuevers is during the wire clearance phase which lasts about 10 seconds.
TT

[jmr]

Even when the MK-48 would home on the helo's compression waves (an actual exercise, jumped out of the water in an attempt to attack and reattack)

Now that would be a sight to see.

[goldorak]

Even when the MK-48 would home on the helo's compression waves (an actual exercise, jumped out of the water in an attempt to attack and reattack) the weapon had no issues about orientation
TT


:huh: I want this behaviour in lwami mod 3.09, or 4.x :|\\
Just for knowledge's sake how high can a torpedo jump out of the water ?
Now this would be a great feature to have in dw, to blow out of the water those pesky helo's using dipping sonar.

[Dr.Sid]

Funny .. going from speed 40kts the theory says

h=(v*v)/(2*g)

40kts=20.57 m/s

h=21.56 m.

This is for torpedo going straight up from the water and without air resistance, which will have some effect, especially for faster torpedoes.

Just few more speeds:

40kts - 21.56m
50kts - 33.72m
60kts - 48.56m

Anyway in reality torpedo will not leave water at 90 degrees pitch, and when leaving at different angles it will start to pitch down while leaving water which both will affect the height. Anyway it seems torpedo can easily jump out of the water.

[goldorak]

Well if the torpedo is not going vertical but lets say going at a 45 degree angle at 60 knots, it can achieve a height of 27m (without considering friction).
Even if you account that friction could reduce the height of 50% we are still talking about 13.5m maximum height out of the waters. :p I doubt it could hit a stationary helo using its dipping sonar but you never know. :rotfl:

[Bubblehead Nuke]

If memory serves me right, there was an actual helicopter strike by an exercise torpedo during an ASW exercise.

He was dipping and thus low to the water and got dinged up but was able to return to base.

[SandyCaesar]

If memory serves me right, there was an actual helicopter strike by an exercise torpedo during an ASW exercise.

He was dipping and thus low to the water and got dinged up but was able to return to base.

:huh::huh::huh:

Whoa!

No more Stingers, no more Iglas, no more ballast blows-F9's-"where the hell is that Seahawk"s. Just AAW torps.:rock: :arrgh!:

Joking, of course. I've seen torps broach the surface in DW (stock and LWAMI), but I doubt you could get them to hit aircraft.

BTW, just slightly off-topic: you know how real-life passive/wakehoming torpedoes are supposed to be "undecoyable"? How might this work as a counter! Imagine: after the sonarman yells "torpedo in the water" and after it's been verified as a wakie, a helo covers the ship's wake at 50 feet...:hmm: It'd probably scramble the wakehoming system nicely, though if the torp had a Doppler proximity detonator it might suck for the helo.

[Dr.Sid]

I doubt helo can build wake strong enough (especially deep enough).

[SandyCaesar]

I dunno, it was just an idea. But, after seeing photos (a Seahawk pictured here (http://upload.wikimedia.org/wikipedia/commons/f/f5/SH-60F_Seahawk_dipping_sonar.jpg)) and reading reports of the gale-force winds generated by some of the bigger helos (CH-53, for instance), I got the impression that the downdraft area was pretty damn big.
(http://upload.wikimedia.org/wikipedia/commons/f/f5/SH-60F_Seahawk_dipping_sonar.jpg)

[TopTorp '92]

I doubt helo can build wake strong enough (especially deep enough).

In fact, MK-48 (I don't know about ADCAP) has been known to home on the bottom of the ocean floor, because the search mechanism gets good returns off the bottom. The torpedo behaves similarly in higher sea states because of good returns off wave motion.

[SeaQueen]

I'm pretty sure that absolutely none of this should have been posted.

Lol .. it was clear .. until now. You said:

1) The only caveat is that significant pitch/roll deviations will result in an internal shutdown.

2) It banks freely.

As I understand it these two are contradicting. Or maybe you don't mean bank & roll to be the same as I do ?

Shutdown is tricky, so I didn't really address all of the caveats. Also, I'm operating on decade old memory. So, just bear with me.

There are two systems protecting own-ship from a faulty torpedo that may turn and come after the home team.

From the moment the weapon is fired (TOF-Time of Fire) to the enabling point, that is the weapon slows to search speed, ACR (for anti circular run) protects ownship. This is the "internal shutdown" I referenced above. After the enabling point, ACR becomes disabled. ACR shutdown limits are technical and I no longer remember them. Pitch/roll is +- 5 degrees, I think. Gyro deviations are +- 168 til the first gyro null and then +- 5 degrees til enable.

After the enabling point, there is an additional safety feature for Mk 48 called ASH (anti self homing.) It is a discrete setting in the torpedo meaning it is either set in or out. It's too complicated to explain how it works because it uses counting system that counts twice as fast if the weapon changes course by a predetermined amount.

ADCAP is a digital weapon and no longer needs to know how to count the old MK-48 way. It uses FENCE after the enabling point and this feature not only protects ownship from a torpedo coming after ownship it also has lateral limits that prevents the weapon from homing on targets outside the lateral limits. Basically the weapon swims around in a digital box defined by the weapons operator. Any target outside the box is off limits. The idea is to protect hospital ships or if using the weapon in littoral waters, then the latteral FENCE settings may protect nearby civilian shipping.

The weapons operator may override both ASH and FENCE after TOF if the guidance wire remains in-tact. Unfortunately, if the wire breaks during an override command, then the safety feature remains permanently overriden til the weapon either runs out of gas or blows up.

To answer your original question, the weapon rolls freely after the enabling point has been reached. However, during the enabling run, there are safety limits that will shutdown the weapon if exceeded. It depends which phase you're talking about.

TopTorp

[Frame57]

Before you know it. The author's of "Blind man's bluff' will steal the info and put it a book.:yep:

[OptimusX]

What exactly is the wire clearance phase?

[TopTorp '92]

What exactly is the wire clearance phase?

The weapon clears the wire to avoid entanglements in the propulser assembly.