What if?

[redboat219]

One motor drove the inner shaft, a second motor drove the outer shaft through a gear drive. That simple -- two un-coupled motors, each driving one of the two concentric shafts. Dirt simple.

David,

How would this set-up compare to using a single but more powerful motor coupled to a differential type gearing to drive the 2 shafts?

[He Who Shall Not Be Named]

How would this set-up compare to using a single but more powerful motor coupled to a differential type gearing to drive the 2 shafts?

Too complicated to make the shafts watertight. Also, the many gears of the differential, if used in the wet, will water-hammer to death.

David,

[Subculture]

Noooo, say it ain't so. Dave the gearbox on my 1:1 Mini has it's gears, including the differential immersed completely in oil. My contra-rotating Nautilus props have a differential set-up and that has to run in the wet owing to the wacky design. I've factored in plenty of clearance, and they'll only run slow (props are 6.6" diameter on a 48" long hull).

Were the handling problems owing to the x-tail? I believe they had similar problems with the 1:1 scale Albacore. Perhaps one of the reasons why the US navy hasn't revisited the x-tail concept?

[toppack]

the many gears of the differential, if used in the wet, will water-hammer to death.

Water-hammer???
Now I'm curious, water is a good lubricate, as long as components are made of materials not damaged by water, such as Delrin, Nylon or brass.
It seems there would be about same hammering in Water as there would be in low viscosity Oil?
What do you mean?

[He Who Shall Not Be Named]

Noooo, say it ain't so. Dave the gearbox on my 1:1 Mini has it's gears, including the differential immersed completely in oil. My contra-rotating Nautilus props have a differential set-up and that has to run in the wet owing to the wacky design. I've factored in plenty of clearance, and they'll only run slow (props are 6.6" diameter on a 48" long hull).

Were the handling problems owing to the x-tail? I believe they had similar problems with the 1:1 scale Albacore. Perhaps one of the reasons why the US navy hasn't revisited the x-tail concept?

Your observation about your gears running in liquid is well taken, Andy, and here's what's going on: It's all a function of tolerance; how much back-lash will you permit in the gear train.

Your installations that use gears in the wet (and mine, what a proper Machinist would describe as a 'bloody sloppy fit'; or a gross non-interference fit, to use nice words) works because the water/oil can squirt by the meshing teeth. During the initial ALBACORE phase-4 work up I destroyed two 'precision fit' differential units operating them in the wet -- the water-hammer was so bad it warped the pinion shafts off their bearings. Awful! Yes, I use gears in the wet, but the tolerance of fit is wide.

As to the ALBACORE and my Navy, I'll address that in a bit.

With the ALBACORE model the problem is not of the X-tail producing unexpected forces, it was simply that the magnitude of the forces it produced were of such a large amount that neither I or the on-board angle keeper could anticipate or damp out the pitch rate when the boat got cooking. This is where an APC with proper 'intelligence' (quickening/retarding logarithms punched into the microprocessors and conditioned as a function of ESC command) would have been a nice thing to have. But, I'm a dumb-ass retired Torpedoman, what do I know of such black-magic, Voodoo, BS?

The Navy (because of Rickover's influence primarily) is very conservative as to submarine control sub-systems. Basically the Navy policy is this: if the control surfaces of a combatant submarine can't be directed with a man in the loop with no computer/integrator assist, we don't want it.

By their very nature, short of mechanical mixing, you can't operate the X-tail without electrically producing a vector sum of pitch and yaw and applying the resultant to a set of actuators. No sailor can think that quick on his feet to physically override the two rams pilot-valves in a coordinated way to get a set of X-tail control surfaces to produce the desired forces ... not while he's being blasted helm orders (he's in some deep, dank pocket near shaft alley, not in Control) through his sound-powered head-set. Nope -- not in my Navy! As we do it local control of the stern control surfaces is done with only two slobs with phones, one working the stern and the other working the rudder ram pilot-valves. We can loose all electrical power and still maneuver the boat. Betcha them nasty old European's and their fancy, girly-man, X-tailed sub's can do that!

David,

[Subculture]

This is where an APC with proper 'intelligence' (quickening/retarding logarithms punched into the microprocessors and conditioned as a function of ESC command) would have been a nice thing to have.

David,

Hmmm, yes it would, wouldn't it. ;)

[redboat219]

Dual Drive Sub

I remember seeing a photo of a Permit/Sturgeon model undergoing hydrodynamic testing in an old publication of National Geographic. The unique thing about the model was that along with the usual stern planes and screw she sported a front row of blades along the circumference of the hull ( something like SubCulture's Nautilus avatar) midway between the sail and bow. Allegedly this contra-rotating prop set-up offered superb maneuvering capabilities. I guess the design fell out due to it's mechanical complexity. Would be nice to see it duplicated in RC.