Improving the SubTech 1/60 ALBACORE phase-2 Kit, Part-7

A Report to the Cabal:

(Previous Cabal Reports can be found at the following sites: http://subpirates.com/ viewforum.php?f=1&sid=16b6e170bc52ee32508e6fb9d814efe4 and http://vabiz. com/d&e/articles.html )

I'm skipping ahead a little here so you can see what's involved in making a rational linkage system needed to operate the rudder and stern plane control surfaces. The objective is to translate the axial motion of the control surface pushrods, driven by the WTC's pushrods, to a radial (torsional) motion that rotates the control surfaces which in turn are acted upon the fluid flow to produce forces to maintain or change the vessels pitch and yaw angles.

Most 'modern' submarines employ a single shaft -- usually running through the hulls centerline with the stern control surface operating shafts in line and perpendicular to the propulsion shaft. (the Russian's, ever the contrarians, are loath to intrust a submarines get-up-and-go to a single screw and, until very recently, clung to designs featuring two screw propulsion systems). However, the single, centrally running propeller shaft arrangement presents a complication to both real and model submarine builders: how to best interconnect opposed control surfaces so they work as one, but to do so in such a way that the centrally running propulsion shaft is not interfered with.

The most common solution is to interconnect each set of opposed stern control surfaces (stern planes and rudders) through a horseshoe shaped 'yoke.' The propulsion shaft passes through the center of the 'U' and each end of the 'U' makes up to a control surface operating shaft. It is the design, fabrication, and use of these yokes that will be discussed here.

It's my preference to employ a very short propeller shaft in my r/c submarine models, that shaft suspended within two Oilite bearings, those bearings press fit within a bored solid foundation cast within the extreme after end of the vessels stern. The two bearings are so arranged as to pass on ahead and backing thrust loads directly to the vessels structure. An intermediate drive shaft from the propeller shaft, connecting to the WTC, transmits only torsional loads between the motor and propeller. I'll show you this scheme, in excruciating detail, near the end of this installment.

Obviously I've already made a resin casting ... "What! Did I miss something here?", you must be asking. Don't fret, I'll cover use of the phase-2 production tool to cast this item later. I'm presenting things a bit out of order here. In the meantime, learn something about control surface linkage function, design, and fabrication.

Read on: Test fitting the control surfaces to the internal yokes, within a freshly cast phase-2 tail-cone. As the specialized yoke masters are built they are installed and checked for operation. Working within the geometry of the conical tail-cone I check to verify noninterference between the yokes, propeller shaft (the projecting Dumas universal coupler), and pushrods, no matter the control surface position. To the extreme right you can see the two 1/16" brass wire pushrods, one going to the stern plane yoke, the other to the rudder yoke, projecting forward out of the cone.

The stern planes are in the full 'rise' position. Note how the leading edge of the stern planes just clear the trailing edge of the horizontal stabilizer. Each stern plane is operated through an 1/8" brass operating shaft that runs through each stern plane.

The soldered brass stern plane yoke is the small 'U' shaped item behind the larger, rudder yoke. Rotated ninety-degrees from one another, the two yokes produce the same effect: to translate the axial (longitudinal) motion of the pushrods to the torsional (radial) motion needed to rotate the control surface operating shafts. You're looking at raw, freshly built yoke masters, to later be further worked with filler and putties to beef up the areas where the brass 'U' shaped rod meets the 1/8" wheel collars. These yoke masters will be used to make cavities within a production spin-casting rubber tool, from which cast white metal model yoke parts will be produced.

Least I give you the impression I'm infallible, I note here that the work seen here constitutes the third attempt to get the geometry of these closely spaced, yet none-interfering yokes right. The care, time, and effort expended here results in the enduser of the ALBACORE kit to experience a trouble-free assembly of the control surfaces and linkages as they build the kit. It's the stern control surface linkages that normally presents the assembler nights of frustration and outright misery as he flounders around trying to make the tail-feathers work without having the internal linkages conflict. If I get it right here, the kit-assembler will profit. If I get it wrong, I blame SubTech!

Say you want to build the ALBACORE as she was configured with the X-tail? Just for fun I've rotated the phase-2 tail-cone here forty-five degrees so you can appreciate that the only mechanical difference (from a linkage standpoint) is just that: everything's simply rotated forty-five degrees.

The real magic needed to mix the two sets of control surfaces in the electronic (or mechanical mixing if you're 'old school') integration of the 'rudder' and 'elevator' signals from receiver to two servos. More on that later when I deal with the X-tail variants of the ALBACORE, which appeared from phase-3 on.

Examine this shot and you will see that all four surfaces produce a 'rise' force on the submarine -- and that's the beauty of the X-tail type stern control surface arrangement: all four surfaces can act in unison to produce both yaw and pitching forces, at the same time!

The installation of the control surfaces on the 'enhanced' phase-2 tail-cone is no different from on the standard ALBACORE kit vacuformed styrene plastic tail-cone. Assembly goes like this: Each stern plane is positioned between the horizontal stabilizer bearings (one inboard against the hull, and one outboard at the tip) which are integral to the horizontal stabilizer. Then an operating shaft (a length of 1/8" brass rod) is inserted into the outboard bearing hole, through the control surface, into the inboard bearing, and on into the hull where the inboard tip of the operating shaft is inserted into one end of the stern plane yoke. A set-screw within the stern plane leading edge and on the joke makes fast the operating shaft to the stern plane and yoke, effectively slaving the stern plane to the yoke.

The full-flying rudders operating shafts simply plug straight into the stern plane yoke. However, without the protection of a fixed stabilizer and accompanying bearing posts, the rudders are subject to handling and grounding damage. This is why I endeavor to make the rudder yokes as robust as room permits.

You see to advantage here the stern planes, stern plane operating shafts, stern plane yoke, and pushrod. Set-screws in the stern planes and yoke make the plane-shaft-yoke assembly work as one in rotation. Other than situations where the submarine is struck from the stern, or backs into something you can appreciate by looking at this shot, how well protected the stern planes are from collision damage or fouling, being so well protected by the stoutly mounted fixed horizontal stabilizers.

Stern planes, rudders and their respective linkages. It may appear that I've made the 'U' shaped portions of the yokes too thick of section. But, keep in mind that the brass, in this gauge, is overly stout for the job, the eventual model parts will be cast from soft white metal where the thick section of the yoke will compensate for the ductility of the principally Tin alloy from which they are manufactured.

The stern planes will not be subject to any excessive loads, just those presented by the fluid flow over them as they are deflected. However, the rudder linkage will be subjected to shock loads imparted through grounding (the bottom rudder being entirely exposed to bottom contact) and handling. The rudders are not protected by stabilizers and it is the rudder yoke which is most subject to deformation or breakage as a consequence of use -- something I keep in mind when designing rudder yoke and operating shaft -- I've made this rudder yoke master as stout as possible while keeping it small enough to fit the very tight confines at the extreme end of the tapering stern tail-cone where it resides.

The masters for the stern plane and rudder yokes went together from 3/32" brass rod and 1/8" i.d. brass wheel-collars, all soldered together with 60/40 lead/tin alloy, using acid flux to clean the joints and insure good flow of the adhesive once up to temperature. Soldering is not welding or fusing. A solder union is an adhesive bond. Silver soldering and brazing are also bonding operations. General rule of thumb that determines if a union is welded or bonded: if the base metal melts, it's a fusion weld, a cohesive fusion of the two metals (in some cases with a third metal introduced, a 'filler'). If only the filler metal (a solder) is melted, its an adhesive bond.

Getting the size and shape of the two yokes to work within the tight confines of the tail-cone was a bit of a trick. It took me three attempts each one to get it right. You see some of the discarded attempts in the center of the shot.

The propeller and associated running gear on the 'enhanced' ALBACORE tail-cones are of a design I favor: a short propeller shaft suspended upon two Oilite bearings press-fit within a bored out resin plug 'foundation' at the stern of the hull. The Oilite flanged bearings absorb ahead and astern thrust loads as well as any transverse loads presented by the propeller shaft. All but torsional forces are transmitted to the hull at the stern -- no thrust loads are placed on the gear-train or motor with this scheme. Here you can just make out the thin stainless steel washer between propeller hub and flanged face of the ahead thrust bearing set into the end of the tail-cone.

The propeller shaft, at its forward end is attached a Dumas type universal coupler -- which makes up to an intermediate drive shaft that fits between WTC and propeller shaft. At the other end of the propeller shaft would fit the propeller (and into a projecting portion of the shaft would fit the dunce-cape). Next to the shaft are the two Oilite bearings and their respective thrust washers.

The assembled propeller shaft. Now you get a clear pictures of how the two bearings are mounted within the foundation at the stern of the tail-cone, omitted here for clarity. These oil impregnated, open-celled, foamed bronze bearings both lubricate and center the propeller shaft as it turns, with little mechanical wear at all. The propeller and Dumas coupler, secured with 6-32 set-screws, sandwich the two bearings and their washers in place on the shaft