R/C'ing the Revell 1/72 GATO Class Static Submarine Kit, Part-14 A Report to the Cabal: I've invested over two weeks of continuous work to this project, and it's time to stick the WTC into the hull, install some fixed ballast weight low in the hull, some countering buoyant foam high in the hull (but no higher than the designed waterline -- which is just about the level of the upper/lower hull break) and to toss this puppy into the kiddi-pool and see what we got! (I need no active control of the ballast system for this, just insure that the vent valve is closed. I can flood the tank by inverting the model underwater, and drain the tank by yanking the model out of the water and letting the water drain out of the tank). Specifically, I need to know if the ballast tank is sized too big or too small; will the ballast tank produce the reserve buoyancy needed to get the boat up to designed waterline from the submerged condition or not? I'll answer the question by doing the following: First, I adjust the fixed ballast weight and foam till I get the boat to adopt a stable submerged trim (to flood the ballast tank I simply hold the model underwater, upside-down, till the bubbles stop coming up), the boat underwater stabilizing on a level keel, and nearly neutrally buoyant. Once happy with submerged trim I put it back in (the ballast tank is dry) and see where the waterline falls in surface trim. And that will tell the tale: do I have too much or too little ballast tank volume. Film at eleven, gang. Once I make the required changes to the ballast tank volume to achieve near design water line freeboard I will freeze the WTC-2.5/GATO design, finalize produce production jigs, produce final tools, and start pooping these things out to the Great Unwashed! But, before all that, let's get the control surfaces and their linkages in there and working right -- these items present meaningful weight and displacement forces, so I can't get a firm handle on the boats trim till their in place. A look at the just about completed running gear and stern control surface linkage setup for the Revell GATO r/c submarine. As you can see there are gobs of room back here to work in. Unlike single shaft designs, where you have to work with yokes and jumpers to clear the control surfaces around a central shaft, multi-shaft designs like this usually have the running gear so arranged as to be well clear of the aft control surface operating shafts and bell cranks and pushrods. Note that the WTC has four pushrods coming out of it. The two outboard pushrods engage the rudder and stern plane linkages. The two inboard, currently unused, pushrods will make up to the bow plane retract and operating linkages... more on those gadgets once I figure out how I'm going to build 'em.
Look at all that unused room! Just two intermediate drive shafts and two pushrods with no crowding of these items what so ever. I love this subject. Note that I employ my 'servo pushrod adjusters' in this installation. These are simply a length of brass tube that sleeves over the control surface pushrod. At the after end of the pushrod adjuster is soldered a wheel collar who's set screw engages and holds fast the pushrod within. The forward end of the pushrod adjuster is hammered flat and drilled and outfitted with a Du-Bro socket ball (the peenin-place kind). The pushrod runs about half the length of the adjuster. Adjustment is done by loosening the adjuster set-screw, centering the servo, then moving the push rod in or out of the push rod adjuster till the control surface is centered, then the set-screw is tightened. That's all there is too it. The ball and socket connection between adjuster and WTC servo output push rod makes for a quick make/break connection between WTC and model with no slop (backlash) at all. The intermediate drive shafts, that interface between WTC motor outputs and propeller shafts, are simply slipped onto the respective Dumas couplers during WTC installation and fall out when the WTC is pulled from the model. Though appearing a bit crowded in there, arrangement of the servos and the other gear within the after dry space of the interim WTC-2.5/GATO works out very well, even when stuffing in four miniservos (stern plane, rudder, bow plane, and bow plane retract mechanism). In the last ten years the size of the angle keepers and fail-safe boards has been reduced by a factor of three. These smaller devices (and the r/c receivers and ESC's are much smaller these days too) make it possible to outfit such a small cylinder with all the gear one could possibly want to cram into their boat.
And here you see the assembled units that comprise the GATO's tail feathers: the rudder, skeg piece and stern planes. It's obvious in this mockup how the pushrods make up to the control surface operating shafts through their respective bell cranks. Less the bell cranks, which have to be removed beforehand, the entire rudder-stern plane assembly can be pulled from the model, after removing the two 2-56 machine screws that secure the skeg piece to the hull skeg -- that's all there is to removal and installation of these items to the hull. Great idea, George! I've pulled the stern planes off the bearings within the skeg piece to demonstrate to you how the skeg piece is the key to permitting access to these control surfaces. By making the skeg piece removable, you can remove these stern control surfaces, anytime, without damaging the model. The cast white metal bell crank on the rudder operating shaft is from my 1/96 SEAWOLF fittings package and was pressed into service on this 1/72 GATO kit. The stern plane bell crank-pushrod interface item is home-brewed and designed to be easily slipped onto the operating shaft -- more on this gadget later.
I face a bit of a problem with the long moment arm of the stern plane bell crank -- that 'Z' shaped piece of 1/16" brass rod running through the stern plane operating shaft. If I'm to realize high angle control surface deflections then I'll have to use either a very long servo arm or build a 'motion multiplier' lever external of the WTC motor bulkhead. We'll see. I'm a pretty smart guy... I'll work something out. The completed rudder and stern plane linkages, installed within the hull. The stern plane bell crankpushrod interface device is simply dropped down on the top of the stern plane bell crank (the 'Z' bent piece of 1/16" brass rod), its securing set-screw driven home and it's on! The rudder operating shaft has its cast white metal bell crank made up during rudder installation -- when the rudder is about halfway up into the skeg, the bell crank is slipped over the rudder operating shaft, the rudder pushed home, the two screws of the skeg piece made up, and the set-screw of the rudder bell crank driven home. Simple.
I came up with this rather bizarre looking bell crank-pushrod interface unit. I had to have something like this, that was removable, so I could get the stern planes in and out of the hull as needed. After punching a 1/16" hole vertically through the stern plane operating shaft I inserted a 'Z' bent piece of brass rod -- this becoming the stern plane bell crank. Unfortunately this has to be unreasonably long in order to clear the tight confines within the pinched skeg area of the hull, it has to be tall/long to access its top so you can make up the linearly running pushrod that makes up to the motor-bulkhead. This makes the stern plane operating shaft a bit flimsy and may not be a practical arrangement. We'll see. If I break the stern planes I'll substitute a solid brass operating shaft for the current styrene one -- a quick fix. (Editor s note this is now replaced with a brass shaft!) A close-up look at how the bell crank-pushrod interface piece goes together. Look on it as simply two wheel colors put together through an axial which orients one wheel color perpendicular to the other. The taller wheel collar goes on the 1/16" shaft that forms the stern plane bell crank, the shorter wheel collar secures the pushrod onto the shaft of the taller wheel collar. I soldered a brass clevis to the after end of the push rod. The clevis was made by heating and beating the after end of a short length of brass tube to a flat, drilling a 1/16" hole, soldering the clevis to the push rod, and installing the clevis to the 1/16" brass stud projecting from the starboard side of the bell crank-push rod device. The reason the stern plane makes use of such a narrow bell crank is that the small size of the 1/16" rod permits me to slide the entire stern plane assembly on or off its foundation -- permitting me access to the entire unit for adjustment or repair.