Torpedo systems

[greenman407]

This post chronicles some of the history of Dave Merrimans efforts to produce a working torpedo and launch system.

Working up Masters, Tools and Parts for a 1/72 Revell GATO Open Shutter-Door Arrangement, Part-2

A Report to the Cabal:


While delivering all that wonderful information on world-war two era American submarine shutter doors to you I neglected to give any insight on the weapons system such a mechanism supports. I'm putting that right here.

Here's a close look at the configuration and function of the Caswell-Merriman 1/72 weapons system. For the sake of clarity I divide the discussion between the two sub-systems (the launcher and the weapon); dealing with each in detail. Near the end of this chapter I'll give you a quick look at some weapon systems I came up with along the way.

THE WEAPON The 1/72 scale weapon is a classic 'steam torpedo' shape and paint-job. The major departures from scale is the substitution of a propulsion nozzle tube for propellers and the canting of the stabilizers to induce a roll to the weapon as it travels through the water. The weapon is self-propelled and employs the rocket principle for locomotion: A charge of liquefied gas is introduced into the hollow weapon through plumbing while its in the launcher, the liquid introduced through the nozzle. The charge of liquefied gas stays within the weapon (and the launcher breech-block) as long as the weapon is secured within the launcher. In fact, through careful design, the weapon can not be charged off-launcher -- a safety measure: in the event of a catastrophic weapon failure (explosion), the debris is contained within the metal tube of the launcher. A charged weapon is only released through intentional launcher activation. I did not invent the gas propelled torpedo. Credit for that belongs to Mike Dorey.

The weapon is a cast resin structure, the only metal being the hollow nozzle tube that runs with its forward end terminating in the middle of the weapons hollow reservoir. Within the after end of the nozzle tube a convergent nozzle, with a throat diameter of .008", works to eject the gas at a reasonable velocity, producing the thrust needed to keep the weapon in motion once launched from the model submarine.

THE LAUNCHER The launcher comprises the torpedo tube and the attached mechanisms needed to charge and release the weapon when so commanded. Decades of part-time effort has gone into the design of the current launcher configuration. The major innovations has been the incorporation of a stop-bolt to insure the weapon can not leave the tube until the launcher is cycled from 'battery' to 'launch'; a means of easily introducing a charge of liquefied gas into the weapon; and using a fraction of that gas charge to squirt the weapon out of the launcher the moment it cycles to the launch condition.

Below we're looking at three standard hollow cast resin 1/72 torpedoes. A cheat is to paint them green if you want to represent modern 'homing' type torpedoes, or to paint them silver if you wish to represent an old steam powered type torpedo.

The lower weapon is cut-away to show how these things go together. Note that it's hollow and that the pick-up for the boiled off gas is the nozzle tube, to the extreme right this gas is ejected through the nozzle to thrust the weapon forward. The design of my torpedo has changed little in the past twenty years. They are easy to mass produce requiring only the inclusion of a resin plug forward and insertion of the nozzle tube aft during assembly.

[greenman407]

Re: Torpedo systems

A shot taken many years ago of an 1/72 torpedo shot out of a Thor 1/72 ALFA. Boy! ... I was lucky to get this shot, coordinating the snapping of the camera shutter with the command to my assistant topside to shoot the weapon was very hit-and-miss. Took an entire roll of film till I finally got this money-shot.

With a full charge of liquefied gas on board the weapon the weapons weight just about equals the buoyant force it produces, its displacement. So, with the weapon aboard the submarine, or the volume of water it takes to back-fill the empty torpedo tube, the net trim of the boat is the same -- with or without a weapons in the tubes.

This shot well illustrates the force of the ejection charge of gas behind the weapon at the moment of launch. Once the launcher breech-block slams to the 'launch' position, liquefied gas comes into contact with the relatively warm water. Immediately, behind the weapon the rapidly expanding gas shoves the weapon forward, sending it out of the tube at a very high velocity. As the gas ejected by the weapon is used up the weapon looses weight, but retains its displacement, as a consequence, the weapon begins to ascend, making its way to the surface where it ends its run some fifteen to sixty feet from the point of launch.

[greenman407]

Re: Torpedo systems

This is the entire 1/72 weapons system, packaged for sale. Available through the Caswell company. You get three weapons, a launcher, and spares to maintain the launcher. The charging hose and charge fitting are prominent in this shot, so I'll discuss their function: at the after end of the charging hose is a modified Schrader valve. When matted with the propellant charging adapter at the end of a can of air-brush propellant the two check-valves unseat, permitting the immediate transfer of liquefied gas between can and weapon. Releasing the connection between the two fittings results in the immediate closure of the check-valves and little liquid/gas is lost to the atmosphere. A charge of propellant is retained not only within the weapons cavity, but also in the bore of the breech-block and flexible hose. When the weapon is launched, this liquid quickly expands into a gas producing the impulse to send the jetting torpedo on its way, at a considerable velocity.



And here we see a weapon within its launcher. This particular launcher in cut-away to demonstrate function. (Boy! Just like shop-class back at Tappan Jr. High-School. But back then I was slicing up carburetors for display, not production torpedo launchers!).

here we see the launcher in the 'battery' condition: The weapon is seated with the breech-block O-ring firmly engaging the outside of the weapons nozzle tube, making a gas-tight fit. It is through the hollow bore of the breech-block through which the propellant liquefied gas is introduced into the weapon through its nozzle tube. Note that an interlink rod, attached to the top of the breech-block, travels forward and works to push down on the stop-bolt ball situated over the front end of the torpedo. This element was the key improvement to the system now in production: providing an assured means of holding the weapon securely within the launcher until the launcher is positioned to the 'launch' condition.

Two important functional and safety issues resolved with this design: positive retention of the weapon until the launcher transitions from battery to launch condition; and assurance that the user can not fully charge the weapon unless it is safely contained within the brass tube of the launcher -- should the resin walls of the weapon fail, the exploding debris will be completely contained by the launcher structure itself.

[greenman407]

Re: Torpedo systems

The launcher in the 'launched' condition: The breech-block pushed aft (by the breech-block spring, not included in this shot), clearing the weapon nozzle for discharge of propellant gas into the breech end of the tube. And, as the breech-block travels aft, the interlink rod pulls clear from the top of the stop-bolt ball, permitting the stop-bolt ball to be pushed up and clear of the bore of the torpedo tube permitting the weapon to advances forward without hindrance.



And here we see a launcher field-stripped. This shows the level of tear-down the user can get into should the sub-system require repair or adjustment. Note how the interlink rod rides in a tube bearing atop the launcher tube and engages at its forward end the stop-bolt ball as the interlink rods after end is secured, with a set-screw, to the breech-block. What holds the breech-block forward against the spring pressure is the trigger rod, seen just above the breech-block. Sliding the after end of the trigger rod transversely about .125" releases the breech-block so it can spring back, transitioning the launcher from battery to the launch condition. Correct travel amount of the breech-block and stop-bolt ball interlink rod is set by positioning the retaining wheel-collar.

[greenman407]

Re: Torpedo systems

Very 'old school' launcher system seen here. Though the weapon design and mode of fabrication has remained pretty much the same over the years; the launcher design, in form and function, has been greatly simplified and made more reliable. This particular launcher did not have any positive means of holding the weapon securely in the tube and 'cook-offs' (inadvertent launch) constantly plagued the system. Lots of mechanism seen here producing marginal performance. Not good. Note the U-shaped copper reservoir for impulse gas. and under it the rotary impulse-valve rack ... awful design!

What the hell was I thinking!? Rube Goldberg, call your office!

[greenman407]

Re: Torpedo systems

Another look-back in time to another attempt to perfect a weapons system. This one built to 1/96 scale ... done during my Crazy Period. The launcher sub-system, for the first time, incorporated a stop-bolt ball and though there were a host of little problems that plagued the system to eventual abandonment, the stop-bolt ball mechanism was retained for inclusion in future launcher designs. Other than that, this system too was a Plumber's nightmer of clock-work escapement, firing valve distribution manifold and tubing, and pneumatic launcher actuators. What the hell was I thinking?!.....

[greenman407]

Re: Torpedo systems

The model that sported the weapon system is a Thor Design and Development THRESHER/PERMIT class 1/96 model kit. Note the many holes I punched into the launcher tubes -- an effort to throttle down the launching velocity of the weapons. When things worked (rarely!) it was a magnificent adventure to go out there, hunting and hitting other model ships and submarines. But, most of the time, it was the little things that tripped me up from having a consistently good time with the system : leaking hoses, low actuator gas supply, sticking linkages, or the occasional r/c 'glitch' resulting in an un-intentional launch. Problems aside, this attempt took many, many steps forward to a more reliable, easier to manufacture and use system. This was my first attempt at a practical pneumatically actuated launcher. This one employing a mechanical firing valve.

[greenman407]

Re: Torpedo systems

This gadget was the firing-valve distributor. Four launchers, so there were four firing valves. Each valve, when tripped by a linkage cam would shoot a bit of gas to a piston actuator atop the launcher. The piston would shove the breech-block to the launch condition, firing the weapon.

[greenman407]

Re: Torpedo systems

A close-up of the four firing valves arrayed around the linkage cam. All this nonsense replaced today by micro-solenoid valves mounted on a small manifold block.



The cam was driven by an escapement which consisted of a ratchet and ratchet pawl -- the ratchet pawl pulled by the servo. The problem with this system is the complexity and size of the firing valve distributor and the need for a dedicated gas supply to drive the launcher actuators.