gato shutter doors

While working up the operating instructions for our just released 1/72 weapon system, I got myself into a
somewhat detailed discussion about how to integrate the launcher into various type model submarines. As the
prim example of that presentation I showed how I achieved the integration on the very popular Revell 1/72
GATO model kit. As most of you know, that particular kit is a wonderful subject for conversion to r/c, so, it was
a natural to further convert this excellent kit into a practical torpedo shooter.
As built out of the box, this kit represents a GATO class submarine with all six bow tubes in the closed configuration. Below is a quick look at how I went about creating the masters for the bow, which are needed to represent the model with all six torpedo tube muzzle doors in the open position. Read on:
The Revell 1/72 GATO class model reflects the single shutter-door mechanism seen on this rather poorly maintained museum ship. Note that the single piece shutter doors are scalloped (concave portions of hull and
shutter-door plating) at their forward ends. The lower door, because of its much tighter location near the stem,
has the scallop running the entire length of the door. Note in the center of the upper and middle shutterdoors there is a narrow rub-strip or 'land' intended to absorb the shock of an errant weapon banging against
the boat as it scoots out the tube. The other design of shutter doors, seen on world-war two era American
submarinesm, features telescoping two-element shutter-doors, and that arrangement will be discussed in a
moment.
Another shot of that museum boat.
The scalloping on the hull plating
ahead of the shutter-door is there to
afford clearance of the torpedo. The
scalloping on the shutter door forward
edge is to provide fairing with the hull
scalloping, needed to minimize drag
inducing turbulence.
Since I'm representing the muzzle
doors of the entire bow nest 'open', I
was compelled to come up with a
non-functioning assembly of parts that
both represented a reasonably scale
appearance and practically provided
for the clearance at the bow to permit
the free passage of a launched
weapon. Here I'm test fitting the masters of the assembly. Note how I've
represented the shutter-doors in the
'muzzle-door open' condition. Eventually the
assembly would comprise seven pieces that,
when assembled, would constitute a drop-in
unit that, when married with the Revell kit -suitably modified by having it's molded-inplace shutter doors cut way -- would present
a scale like look of a GATO class submarine
ready to loose weapons forward.
A dry-dock shot of a damaged boat employing the single-piece shutter doors.
And here, for comparison sake, we see the two-element shutter door. Notice that the forward ends of each
shutter-door assembly extend out nearer the stem than the single-door shutters, insuring adequate clearance
of the weapon. It's the forward section of the two-element door that forms a 'wedge' shape, without the need of
scalloping, to attain a reasonably streamlined arrangement.
But, for this more faired in type shutter-door
arrangement there is the downside of
added complexity, what with the sliding
bearings and toggles needed to swing the
forward door section inboard as the after
element of the door slides forward over it. In
either arrangement, single-door or twoelement door, the after edge of the shutterdoor is linked to the muzzle door -- its the
motion of the muzzle door, swinging inboard
as it opens, that carries the shutter door
forward and inboard.
Gluing the muzzle-door hinge pins to the muzzle bulkhead. The various materials these masters were built up
from include, .040" polystyrene sheet, thin strip styrene sheet, RenShape block, polystyrene rod, Evercoat
Metal Glaze filler, and Nitro-Stan putty. The muzzle doors are turned discs that started life as resin
sprues. Most gluing was done with thick and thin formula Cyanoacrylate.
I'm showing how the shutter-door piece fits onto the forward face of the muzzle bulkhead. The muzzle bulkhead fits into the bow of the model and not only stands in as a scale element of the display, but also provides
the vital function of being the forward foundation element of the six tube launcher nest. I pressed the six muzzle door hinge pins (turned pieces of polystyrene rod) into service as indexing tabs by mounting them to the
muzzle bulkhead -- they work to
keep the shutter-door piece centered during installation.
Installing the stiffeners to the bowbuoyancy tank bottom plate. This
was the only bonding job where I
used a cohesive. Note the use of
an assembly jig for the job.
Once I cut out the bow-buoyancy tank bottom plate I outfitted it with pieces of square stock to represent stiffeners. This work was done as the plate piece was held onto a stiffener assembly jig -- simply a piece of MDF
that had been marked off to indicate stiffener spacing. A piece of double-sided clear adhesive tape was used to
secure the plate to the MDF jig as I glued the stiffener pieces in place with solvent cement.
Note that when you look through the flood-drain holes (limber holes) at the base of the bow-buoyancy tank,
you can clearly make of the internal stiffeners at the bottom of the tank. Also seen to good advantage here is
the test fit shutter-door piece butting up against the muzzle bulkhead (that piece temporarily secured in place
with two opposing 2-56 machine screws). The only masters not yet prepared are the horizontal plates that
separated each well
Priming the masters. Once everything is in good shape I'll create tools (rubber molds) off them, and from those
tools I produce kit parts.
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 cannot 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.
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
sho:, 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.
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.
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 stopbolt 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 setscrew, 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.
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!
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?!.....
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.
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.
A close-up of the four firing valves arrayed around the linkage cam. All this nonsense replaced today by microsolenoid 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 actuator.
I finished up the tools that will be used to produce the needed resin shutter-door and nest foundation parts.
And I took some better shots of the launcher cut-away unit for you.
Yes, these this will be a commercially available fittings kit. The Caswell company will be your source. This fittings kit will permit you to quickly modify the Revell 1/72 GATO kit to mount our 1/72 weapons system. What
I'm showing is a full-up six tube forward launcher nest, but you may go with any number of launchers that your
pocket-book will permit. I've endeavored to make things removable and expandable, so If you go with, say, two
tubes -- and at a later date you want to install four more launchers to make it a full package -- then, no problem. The way I've designed it, the entire launcher is removed from the bow of the model in only seconds.
This shot shows what all the work was about: creation of kit parts that would assemble into a set of open shutter doors -- parts not provided with the stock 1/72 Revell GATO kit. Now, after I cut open the 'closed' shutter
doors on the kit, install an assembled 'open' shutter-door assembly, couple that with our weapon system, the
GATO kit becomes a practical torpedo shooter. Note that a black painted shutter-door assembly is seen here -that unit to be installed into my already painted and running r/c GATO, soon to be converted over to a torpedo
shooter.
In time I'll produce a like fittings kit for that horrible 1/72 scale, I-53 kit that invaded our shores a year or so ago.
The ultimate objective is to achieve cast polyurethane resin parts that will form the shutter-door assembly. And
the foundation for the torpedo tube nest foundation. At the top of the below shot you see the two mold halves
(the upper halves of these tools not in the shot) with recently cast resin parts still in place. Below are the plastic, RenShape, and machined resin masters.
Some detail illustrating how the tool making process was accomplished:
In the shot below we see the end-game: the assembled resin shutter-door piece, and the six torpedo tubes of
the forward launcher nest all secured together in correct alignment by use of the nest foundation piece and
muzzle bulkhead (part of the shutter-door assembly). The nest foundation piece assures centering of the nest
within the hull and places the pitch angle of the tubes along the pitch angle of the shutter-door assembly shutter wells.
Below we see a set of flash infested cast resin parts that, when cleaned up and assembled, make up the
shutter-door assembly and nest foundation.
After much mock arranging of the various masters I settled on dividing the masters into two tools. The thick,
heavy masters would form one tool, and the thin, light-weight masters were all grouped as a second tool. The
idea is to minimize the use of the expensive mold making rubber. Here you see the masters set approximately
half-way in backing clay -- as the objective is to make two-piece rubber tools you have to mask off about onehalf of the master in a masking medium, like the oil clay you see here. This to avoid encapsulating the
masters.The surface of the clay forms the flange face, the plane that separated the eventual two halves of the
rubber tools.
After impressing indexing dimples (with the aid of a drill bit shank) into the clay backing material -which will form indexing tits into the rubber -- I wrapped masking tape around the mold-board over which the
backing clay and masters had been laid down. The brass rods form sprues through which catalyzed resin will
later be introduced into the tool cavities. Also pressed into the clay flange faces was a network of channels
forming the vent network; escape paths through which air would leave the eventual rubber tool cavities as the
air within the cavities was displaced by resin.
After pouring the first half of the tools, and waiting for
the rubber to cure, I pulled the first tool halves off the
masters, laid on a heavy coat of mold-release oil into
the open cavities, inserted the masters back into the
cavities, applied mold-release over the flange face of
the rubber tool halves, built up another masking tape
containment dam, and poured the second tool halves.
The completed tools were assembled, filled with resin,
pressurized to 30 PSIG for an hour, the tools opened
up, and the raw cast resin parts removed from the
tools.
Silicon mold-release oil coats the parts and has to be
scrubbed off. I use fresh lacquer thinner and an abrasive
pad, a stiff little brush is used to scrub into areas not
reached by the pad. Some pieces are scrubbed while still
attached to their sprue and vent networks. Failure to properly clean the resin parts will give you nightmares later as
you attempt to bond and paint the parts.
After block sanding away the flash from around edges of
all resin pieces, the shutter-door assembly was assembled
with the aid of thick and thin Cyanoacrylate adhesives. If
the master pieces fit coherently into a proper assembly,
then so too will the resin parts!
The six torpedo tubes of the forward nest are all
bonded to the nest foundation piece using RTV silicone adhesive. To insure proper orientation of the
tubes the muzzle bulkhead is temporarily fit to the
muzzle end of the tubes during the hour or so it
takes for the RTV adhesive to cure hard enough for
the unit to be handled.
Another look at the launcher and how the weapon
integrates with it.
I should have mentioned this before: A good deal of
engineering inspiration came from my study of the
work of Ron Perrott. This Britisher has been in the
game much longer than me and has contributed
many innovations to this hobby -- just one of which
was a design he published decades ago about a
means of securing the weapon in its tube in order to
avoid cook-offs. Though my launcher does not use
his specific idea, it was the principle of the thing that
stayed with me over the years.
The flexible hoses permit swinging up and out of the
launcher charge fitting so the weapon and launcher
can be charged up with liquefied Propel type gas.
This will conclude this chapter of the Cabal Report -- I'm getting a bit afield of the title subject by getting into
the mechanics of a launcher selection and activation gizmo. So ... before things get really stupid ... I'll conclude
this with a look-see on how I came up with a mechanism that employs only one servo -- one channel of the r/c
system -- to launch six weapons, one at a time, each at your specific command from the transmitter.
It's one thing to stick a bunch of launchers into the bow of the model submarine, but it's another thing to come
up with a means of getting each launcher, at your command, to launch a weapon. You could take the easy approach and put three servos in the SubDriver to control two launchers each, but that takes up a lot of valuable
real-estate within the SubDriver and also takes up three channels of r/c system in the process ... three channels your system likely does not have!
I'm a bit of a mechanic, so I put my rather vast skill-set to work and devised a clock-work escapement that was
set in motion by a single servo; a linkage -- through the use of a ratchet wheel, some cam-shaft gearing, and
cam tripped launcher triggers -- that does the
job of getting the individual launchers from
the battery to the launched condition, when ...
and only when ... I want them to.
Right we see an unpainted, yet to be installed
cast resin shutter-door assembly made up to
the completed launcher nest, designed to fit
the bow of my 1/72 Revell GATO r/c model
submarine. The Model itself is in background
and has already received its painted shutterdoor assembly. The design objective of this
particular launcher nest was to provide clearance of the torque tube that actuates the bow
plane retraction mechanism as well as
the bow plane pushrod. Without interference.
Note the rather involved mechanics of the
nest launcher selector -- bolted to the after
end of the nest foundation piece.
Layout is everything in machining,
sheet-metal, wood working, and toolmaking. It starts with a plan, then lofting
the plan dimensions to the raw materials that will be cut, bent, bored, and
pounded into the desired shape. here
I'm marking off the outlines of the two
cam-shaft bearing plates onto some
.030" brass sheet. Once everything is
indicated I'll use the band saw, drillpress and vertical mill to cut out the
bearing plates.
The most exacting chore here was
creation of the ratchet wheel and
ratchet pawl. The ratchet wheel started
out as a disc of machine-brass
rod turned and bored on the lathe, the
six ratchet arms were cut out with a
diamond disc once I had plotted out six
radiating lines onto the face of the disc.
The ratchet pawl was formed from K&S brass square section tube. The pin at the wrist of the pawl is 1/16"
brass rod which would have its ends peened over once the pawl was made up to its arm.
While working up the nest launcher selector I
found it useful to use a machine vice to grab the
resin base of the launcher foundation piece. The
vice freed up both hands for more important tasks.
Here I'm fitting the ratchet-wheel atop the starboard cam-shaft. The pawl is yet to be outfitted
with its spring.
Another thing: You see that my work stations have
a white towel laid down. The surface won't let
tools roll off the table, and the white reflects light
up and onto the work -- things dropped are easier
to see on the white towel as well.
Note that even with the bow full of launcher nest
there is still room for the bow plane retract torque
tube and bow plane pushrod
Loading a weapon with the assistance of a 3/16" acrylic
rod. The weapon is pushed back till its base makes
contact with the launchers stop disc, at that point you
push forward on the launchers breech-block till the trigger rod engages it, securing the launcher in the 'battery'
condition. Later, at the moment the weapon is
launched, a cam makes contact with the after end of
the trigger rod, pushing it off the breech-block, permitting its travel aft, placing the launcher in the 'launch'
condition.
Ready to load the weapons. The weapon loading
ram is a length of 3/16" acrylic rod.
When charging a launcher-weapon, it's a good idea
to hold the charge fitting with pliers as you press the
Propellant can charging adapter in place -- will keep
you from freezing your pinkies off!
I have the choice of either loading weapons and charging
them with the launcher in place, like you see in this shot,
or your can remove the launcher and doing your loading
and charging of the launcher off-model. I like to have options!
Note that on top of the launcher there is a 'sequence indicator', a dial -- attached to the top of
the port cam-shaft -- that indicates which is the
next launcher to be fired with the next push of the
ratchet pawl.
Each cam-shaft has three attached cams, each
cam sixty-degrees apart. It's the job of the port
cam-shaft to fire the three port tubes, the starboard cam-shaft works the starboard tubes. The
two came shaft rotate in unison in a clock-wise
direction. All six cams are so staggered from one
another so that only one tube at a time is fired with
each push-pull cycle ratchet pawl.
Pointing to one of the six cams. These make contact
with a launcher trigger, unseating the after end of the
trigger rod from the breech-block. Unseated, the compressed breech-block spring slams the breech-block
aft, carrying along the interlink rod which unlocks the
stop-bolt ball, launching the weapon.
The disassembled Nest Launcher selector. I work to
make my mechanisms service friendly, i.e. the parts
break down easily by the use of common fasteners.
One fastening trick is to use O-rings as poor-man Drings -- fasteners that fit a radial grove in shafting that
prevents the shaft traveingl through its support bearing.
Each bearing plate secured to the cast resin launcher
foundation piece with 4-40 machine screws. The Orings held the cam-shafts secure under the lower bearing plate, and the ratchet wheel and sequence indicator dial secured the cam-shafts at the upper bearing
plate.
Spring pressure keeps the ratchet pawl up tight
against the ratchet wheel but gives enough to permitted the pawl to ride over the ratchet wheel spokes on
the return pull of the servo. One of the Caswell Inc. KliCon magnetic couplers, seen here, makes up to the
SubDriver's weapon system servo pushrod. Note the
indexing marks on the ratchet wheel and nylon gears
-- big aids when re-assembling the mechanism.