R/C'ing the Revell 1/72 GATO Class Static Submarine Kit, Part-3

A Report to the Cabal:

Over at the SC site George Protchenko (Crazy Ivan) has been chronicling his buildup and modification of the 1/72nd Revell GATO kit; he's another guy working to modify this static display kit into a practical, well running r/c submarine. He's doing pioneering work, and because of that he's taking some arrows. WTC/hull fit issues, for example. However, he's done an excellent job of illustrating how best to arrange the control surface linkages in the tight confines at the stern, and in such a way as to make room for a pair of torpedo tubes back there. No small feat!

But David Welch gets credit as the first guy (I know of) to get the Revell GATO into the water. Though he's doing battle with his boats trim at the moment he'll work it out.

Being first at something often turns you into a spear catcher -- but it's the overcoming of the problems encountered and passing on the solutions to problems that form the reward for this kind of vanguard work.

Anyway ... David reported a severe roll problem. Obviously he's suffering the consequences of a too short metacentric height, i.e., the coupling between the boats center of gravity and center of buoyancy is too tight -- all that topside weight, no doubt. Congratulations, Dave, you get bragging rights as the first pioneer to catch a spear in the chest with this new kit. In spite of that Dave was able to sail around enough to evaluate the turn and he reports that the model has a tight turning radius. Very good news. I was worried about that.

George and David Welch have been very forthcoming with their respective articles over at the Subcommittee site with comprehensive texts and some fine photography. Both David and George (and I mention this because many authors don't have the guts to do this) have been very plain spoken as to the problems each has encountered with his specific buildup and operation of their submarines; both have taken pains to identify difficulties encountered and the thought processes behind the solutions formulated as each worked to convert these static kits to an r/c vehicles.

These two guys have come up with very useful observations and solutions ... some of which I will shamelessly steal and apply to my effort.

You can watch Crazy Ivan's work at, http://s181686668.onlinehome.us/phpBB2/ messageboards.php5

And Big Dave's work at, http://s181686668.onlinehome.us/phpBB2/messageboards. php5

A vehicle at rest and immersed in a fluid (be it submarine or balloon, or The Great Pyramid) is acted on by that fluid, and will stabilize (if other forces, of greater magnitude, do not interfere) in an orientation, with respect to gravity, that places the vehicles center of mass directly below the vehicles center of lift (center of buoyancy). And it's the metacentric height that dictates the magnitude of the righting forces about the roll and pitch axis that stabilize the vehicle, the farther the vertical distance between the center of gravity from the center of buoyancy, the more stable the vehicle.

If our model submarine stabilizes on its side or upside-down, we have to alter the distribution of weight within to properly align and distance the center of gravity and the center of buoyancy. When talking about static stability, the prim reference axis is parallel with the principle force of gravity (a force line perpendicular with the ground beneath our feet).

This GATO kit is too heavy in the topside areas of the hull. The cure is to either reduce the existing structures topside weight or add more weight to the keel -- In the former fix you add fixed ballast weight low in the hull and in the in the later you add buoyant foam high in the hull, to restore the net trim of the boat. Both fixes work to increase the boats metacentric height.

This is not news to Dave or George, they both well understand and appreciate these facts. The problem they and I face is that the 1/72 scale Revell GATO kit has a lot of unnecessary topside weight -- most of that in the form of upper hull structure (located under the superstructure). The obvious means of increasing this boats static stability is to remove as much upper hull structure as possible, but not so much as to compromise the structures integrity or scale fidelity of the display.

I had already planned on taking those measures with my buildup of that kit and Dave's observation gave me further reason to be absolutely ruthless in my efforts to eliminate topside weight.

I'll remind the reader that I'm modifying this kit employing a 'minimalist' approach; I'm using simple tools and practices, the kind available to the 'average' r/c submarine enthusiasts -- the objective here is to present a methodology and assembly/ modification approach that can be handled by the great unwashed out there in r/c submarine land

This effort of mine, to convert the Revell GATO into an r/c submarine, is a commercial enterprise: I'm going to market a package containing a WTC-2.5/GATO's, instructional DVD, customizing parts, and written instructions needed to convert the Revell GATO kit into a practical, well running r/c submarine; those instructions directed at basic skill level customers utilizing simple hand and power tools.

So, yes, you will see some processes here that could be handled better with nontypical machine tools, fabrication techniques and exotic casting and tooling tricks. But, if I did that I would loose my target audience here: Common kit-assemblers ... the great unwashed ... Joe-six-pack ... Mutt and Jeff ... Subcommittee Groupie's ...

Remember, this kit is intended for static scale, so the designers of this display piece built the thing for strength, not proper mass/weight distribution. The hull and superstructure items are separate pieces -- a wise move, you're supposed to see the tank-tops of the hull when you look through the open limber holes on the sides of the superstructure. Nice if you're building a museum quality display piece, just a luxury if you're building an r/c submarine out of the thing. There is indeed a significant amount of hull weight that can be removed (over six ounces!!) by cutting out hull sections under the superstructure. Above you see the hull section of the kit marked out in felt pen, denoting where to cut away portions of the upper hull. That's a lot of plastic!

Revell really did the superstructure right! It comprises five major parts, less the fairwater: two side pieces just aft of the bow plane recesses, to capture the limber holes and slit (break) between superstructure side and hull tank-tops, the upper edges of these pieces flanged to capture the top forward and middle superstructure pieces; the top forward superstructure piece covers bow-buoyancy, planes, and extends aft a bit past the molded in foreword escape trunk hatch, this piece slotted at the sides to capture the lip of the molded in flanges shared by the bow piece and two superstructure side pieces; The top middle superstructure piece also engages the two side pieces and then continues on aft of those with its own vertical portions, it will later secure to some of the transverse pieces I left on the upper hull; the top after piece of superstructure takes it all the way back to the 'turtle back', and this item will to be glued to some of the remaining upper hull transverse pieces.

As you can clearly see, when the superstructure pieces are laid in place, they cover the openings I'll dig into the upper hull. The trick was to leave just enough transverse pieces in the upper hull to keep that structure sound, even after I make the horizontal cuts either side that will separate upper hull from lower hull. I'm going to split this hull at it's near maximum beam width to insure good access to its interior for WTC installation, good access to the control surfaces linkages and, later, torpedo launching systems. I'm too old and short of temper to be farting around with tight fitting access points on my models, Damit!

I deferred gluing the five superstructure pieces to the upper hull until the splitting of the upper from the lower hull half job had been completed.

Test fitting of the superstructure pieces --necessary to determine how much upper hull I could cut away and not have it be too apparent to the careful observer --was easily done by taking advantage of the interlocking nature of these items. Only a few pieces of masking tape and a few rubber bands were needed to hold everything together as I fit things together. Nice and tight ... I love this kit!

The bow and stern of this kit are separate items and must be welded to the main hull section. I took advantage of that feature to remove the lower wild registration pin holders in the stern -- these would only get in the way of the eventual control surface pushrods and rudder and stern plane operating shafts. I snipped them off with dikes and then ground the remnants flush with the surface of the plastic part. I'm not sure yet, but I believe I can use the existing, molded in place operating shafts on the stern planes and rudder pieces -- again, me thinks the designer's of this kit had r/c submariner's in mind when they laid things out.

The nominal wall thickness of the Revell kit parts is 3/32". But, God bless 'em, the fairwater is much thinner and they shaved the wall thickness in the areas of the superstructure/tank-top breaks and limber holes inboard to a gauge that very closely represents the thickness of the plate used on the prototypes. Revell did a wonderful job on this big scale model kit! They built this thing strong and stout -- but produced the parts thin and delicate where they had to be.

There is such a substantial matting face between the parts here that the elimination of some (even all) of the wild registration pins would not present any alignment problems during assembly. Fortunately, the bow and stern sections did not evidence the major warp encountered in the main hull pieces, so the pins were only a luxury during their assembly.

Before gluing the bow and stern sections to the hull proper I removed the transverse bulkheads that capped each end of the main hull. It was a simply matter to hold the stern piece onto the main hull flange as I brushed in large amounts of Ambroid ProWeld cohesive cement. In less than thirty-seconds the weld was tacky enough for me to let go and do the same with the bow piece. The fit was near perfect, very little Evercoat Metal Glaze filler will be needed later to make the radial seam between main hull and bow and stern pieces go away. This kit is t-i-g-h-t!

Before cutting out the pieces of upper hull I weighed it. Later, after cutting the pieces away from the upper hull, I found that I had removed over six ounces of ugly fat ... not bad!

On a WTC-2.5 type cylinder that six ounces I won't have to push into the air represents about three inches of linear length in the ballast tank, that is to say, my eventual WTC ballast tank length will be three inches shorter than it would have been had I not cut out all that topside material off the hull. And I've also increased the models metacentric height. A win-win.

Note that I leave the areas of the upper hull containing the transverse alignment pins alone (all well saturated with cohesive cement during main hull assembly and now permanently welded between the vertically split main hull sections). All open spaces on the hull will be covered up by the superstructure pieces.

Here I'm using a hacksaw blade holder to guide the flimsy blade along as I finish the cuts started with a Dremel Moto-Tool cutoff wheel.

Where straight lines are needed I use the edge of an old hacksaw blade (one face of the blade has a piece of #100 sandpaper glued to it to produced a non-slip surface) to guide the cutoff wheel as I pull the tool along making, in this case, a transverse cut atop the hull. If you're careful to adjust tool speed and to weight the interior of the model with sandbags to avoid resonance caused 'chatter,' you can achieve quick, low kerf cuts. An acquired skill, I can assure you. If you can't ... break out the Bondo!

After marking out what had to be removed, the initial cuts were done with the Moto-Tool. The cuts were completed with the hacksaw blade, then the edges of the holes finished with file and sanding block. And here's the finished work. Took about two hours to mark out, cut, and smooth the openings.

It was important to maintain the outboard pointing superstructure mounting pins --used to align and secure the two superstructure side pieces near the bow. Upon the transverse pieces I left atop the hull would sit the other superstructure pieces.

The skeletal remains of what was once the top of the hull. Next move is to plot two horizontal lines, near the maximum beam of the hull, port and starboard, parallel with the boats keel, then use the rotary Moto-Tool saw to separate upper from lower hull half. Then things should get ... interesting!