R/C'ing the Revell 1/72 GATO Class Static Submarine Kit, Part-15
A Report to the Cabal:
When I was a young man, the first submarine I was stationed aboard was the USS TRUTTA. The 421 was a unit of Squadron 12, Key West Florida. I got there by transferring off the submarine tender, HOWARD W. GILMORE where I had been stationed, working a few years on MK-14 torpedoes in the below decks 'steam shop.' One morning, after the GILMORE had arrived in Key West, during muster, there was a call for volunteers to fill billets in some of the short handed boats there. Young, dumb and stupid, I met the requirements: I raised my hand, and by late afternoon me and my sea-bag were crossing the TRUTTA's gangplank, reporting for duty. It was the late 60's and the submarine service was desperate for warm bodies to fill billets. I never even went to Sub-School, just cross-decked and in a moment I went from Surf-Lant to Sub-Lant. First words I heard from Chief Thomson, my Division Officer: "Welcome aboard, kid, you'll like it here, here are you Qualification cards ... you're Dink, ass hole, get below!" Home.
The TRUTTA was a TENCH class boat and, because I was a Torpedoman I wound up in Deck Division, where I spent countless hours chipping paint, painting and otherwise performing maintenance on the boats decks and superstructure. The girls in Operations took care of the sail. In addition to my qualification program indoctrination, my in-port crawling on tank-tops, on and between exhaust and induction piping, vent risers, and the capstain/bow plane operating gear, and all the other crap crammed between superstructure and hull, I acquired an intimate knowledge of all the items that are fairleaded by the superstructure shell and Teakwood, metal, and fiberglass decks.
The bow plane retract mechanism was simply two-big side-by-side gear wheels, their shafts parallel with the boats longitudinal axis, that turned about one-hundred degrees in opposite directions during the bow plane deploy/retract cycle. Each gear wheel had a pin near its outer circumference, each pin making up to the upper end of a bow plane strut. During gear wheel rotation the strut would either raise or lower the bow plane. A dirt-simply system. The two big gears were surrounded in a very heavy gauge metal screen, it's intent to keep rags and other foreign material out of the gear teeth. The prim mover of the big gears was an electric motor in the overhead of the forward torpedo room -- the output of that motor went to a clutched gear splitter that permitted the motor output to either drive the bow plane retract mechanism or the forward capstan. Selection of that motors output was dictated by the 'rig for dive' bill; in port ('rig for surface') the motor drove the capstan, underway, it was hooked up to the bow plane retract mechanism.
Anyway ...
... When it came time to work out how to make a practical bow plane retract mechanism for this 1/72 Revell GATO, I fell back on what I knew worked and copied the mechanism as well as I could remember it: my TRUTTA Qualification notes are long gone, but I can still see in my mind (and smell) that area of the superstructure, just aft of the bow-buoyancy tank, it was a tight fit for a big Torpedoman, I can assure you.
Before I launch into a mechanism that is new to me I do a lot of technical sketching. And when I'm not laying pencil to paper, I think the arrangement over during the morning walk. The 1/72 GATO bow plane retract mechanism is a good example of such preliminary study:
Here you see just some of the doodles I did as I explored various schemes I considered to operate the plane struts in such a manner as to be scale and practical. Not too surprisingly, all these paper-studies did was to confirm that the prototype mechanism was the best way to do. In the upper left you can see the practical result of this study. The initial mockup used to validate the two-dimension study, and next to it, the unit that will go into the model.
I built this mockup of the GATO's bow plane retract mechanism in order to work out all the bugs, off-model. I took two nylon gear wheels, meshed them together as I remembered the wheels arranged on the TRUTTA, and from there everything just seemed to fall into place ... once again I was an eighteen-year-old, covered in grease, sweating like a pig, trying not to gag on the stench of dead sea-things rotting in the pools of water that collect in the troughs formed between tank-tops and pressure hull.
Since this mockup was only to verify the retract element I made simple fixed pins to hold the bow planes where they would normally connect to the bow plane operating shaft. The brass plane struts and pins replaced the plastic items provided in the kit. Note that I made holes in the leading edge of the planes through which I could insert/ remove the strut and operating shaft pins -- I like the ability to make changes and remove things for alteration, painting, or repair. Later, once everything is working to my satisfaction I'll fix the pins in place by filling the holes.
The mockup bow plane retract mechanism, with the planes in the 'rigged out' position, note that it's only the ganged rotation of the two gears, through an arc of about one-hundred degrees, that is all that is needed to drive the bow plane struts the distance needed to either raise or lower the lanes into position. Simple. I like it!
At this point I had not yet glued the two pieces that comprise each plane together, holding them here with pieces of blue low-tack masking tape.
Note the sectional drawing of the GATO bow where the retract mechanism gears site. It was important to graphically match the known position of the strut, where the strut penetrated the superstructure, and to determine what degree of arc and how long a moment arm was needed at each end point of that ark, to achieve the strut motion that would get the planes from fully retracted to fully extended. Simple. Once it worked on two-dimensional paper, I built this mockup and validated operation in the 'real world' of three-dimension. Often, without a 'proof' model like this, you will fail to identify paradoxes, and interference issues not readily observed in orthographic or isometric two-dimensional representation. Proof models used to be the preferred means of checking an arrangement before committing the design to end-use fabrication.
God Damned CAD!
Modifications to the bow plane pieces involved the continuation of the two bearing pin (strut and operating shaft) grooves to the leading edge of the surfaces -- this done to permit removal of the pins once the two-piece bow plane parts had been permanently welded together.
At the base of the bow plane strut there is a doughnut shaped pin bearing, the hole in the center of this doughnut is chamfered on both faces, this permits the doughnut to not only rotate about the strut shaft, but to also 'wobble' along the axis of the strut pin. It's this wobble that is the problem with the kit provided strut piece: there is not enough to permit the thirty-degree rise and thirty-degree dive to the planes without binding. Also, the metal struts I've fabricated are much stronger, therefore better suited to resist handling and collision damage. Also, the metal is more receptive to the modifications needed as I finalize the shape and dimensions that will make the struts practical parts of the bow plane retract mechanism.
A better look at the bow plane strut and doughnut at its base. Note the chamfer at the hole through which the strut pin passes, there's an identical forty-five degree chamfer on the other face around the hole. This permits the 'wobble' needed so that the planes cannot only rotate around the pin for retract/deploy, but to also rotate in pitch, a displacement that is along the longitudinal axis of the pin. Neat!
If I remember right, the actual boats made use of a ball interface between pin and doughnut, which tightened the tolerance between strut and pin, no matter the angular displacement between them. But, I don't have the patience or time for such refinement. I'm happy with a .015" slop between the parts, I can live with that!
Oh ... F you, Kevin!
Close-up on how the bow plane strut pin fits within the bow plane strut doughnut. As you can see, the planes are free to move radially about the bow plane operating shaft pin and to move about the pitch axis as well.
At the upper end of the bow plane strut you can make out the brass tube cleaves that makes up to the operating arm of the retract mechanism geared wheel. Just like on the real boats! "Don't get your pinkies in there, kid, it'll wreak your whole day!"
At the lower end of each bow plane strut is a 'doughnut' that fits over a pin within the bow plane. It is about this pin that the strut doughnut must rotate (rig out/rig in), but also 'wobble' (dive/rise). Here I'm turning some machine brass round stock to the correct outer diameter of the doughnut, I then bored out the rod, then chamfered one face. After parting a doughnut off the stock the part is flipped on the chuck and the other face chamfered. The chamfering done with a ball router bit secured in the tail-stock chuck attachment.
A simple 'bow plane strut assembly jig' was made from some shelving material. To the left I've arrayed the four pieces that make up a strut: a lathe turned 'doughnut', the doughnut-to-strut pin, and a transverse running retract mechanism bearing tube. The doughnut, pin, and strut are soldered together (the pin is a strength member), then this assembly is placed on the jig and the bearing tube soldered in place. The jig insures that the bearing tube goes on at the correct distance from doughnut center and to the correct orientation to the doughnut. Later, the bearing tube is reduced in length with a carbide cutoff wheel. The metal strap and thumbnut are used to hold a strut in place as I solder on the bearing tube.
The planes in the 'rigged out' position. The mockup unit here permitted me to make modifications off-model; to do the tough stuff while having complete access to it -- the ability to avoid this kind of work outside of the tight confines of the bow made this a quick and almost pleasurable task.
The bow plane retract mechanism mockup with the planes in the 'rigged in' position. I'll make up a Dumas universal coupler to one of the gears and will run a torque shaft aft to a mechanism at the rear of the WTC that will produce the one-hundred degree rotation needed to cycle the planes between 'rigged in' and 'rigged out.' To achieve slow scalelike mechanism actuation speed I'll install one of those digital rate control modules between the retract servo and receiver -- I'll dial that thing in for a three-second cycle time. Faster than the real thing, but close to true 'scale speed.'
The only modification to the kit hull was to reduce the length of the bow plane operating shaft bearing tubes -- this to make room for the bell crank, part of the linkage needed to make the bow planes a practical set of control surfaces. Here I'm using a hacksaw blade to do the job.
The kit provided parts that make up the bow plane operating shaft were used stock --plenty fat enough to take the expected loads. The only modification from kit methodology was to not glue the two halves of the operating shaft together. Instead, I sandwich them together under the clamping pressure of the wheel-collar that comprised the foundation of this removable bell crank. To install/remove the two-piece operating shaft I tightn/loosen the set-screw in the bell crank and slide it in/out to free up the interface points of the two halves of the operating shaft. A bit of flexing and the two halves can be slid in or out of the hull operating shaft foundations.
Keep it simple, stupid!
I modified the interface point between operating shafts and planes by eliminating the plastic pins at the terminus of the operating shaft. I drilling longitudinal holes in place of those pins. A brass pin now secures the operating shaft to the planes -- much stronger than the original small cross-sectioned, short of length, molded in place plastic pins.
Just for fun here I'm showing off the kit provided bow plan strut. Nice looking, but not too practical for an r/c version of this kit.