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Wasn't there a 688 boat fitted with a contra rotating prop? Also a Permit had one too USS Jack I think. Albocore had one at one point as well.
And yes DW can do contra rotating props the DPRK's P-4 class SSM in LWAMI has one. |
The Albacore still has one. It is a sight to behold. The X planes were a little starnge to me.
The screws for the Jack are at the Albacore park. They are interesting in they are MIGHTY small in my opinion. No 688 had counter rotating screws. I do believe that one had a propulsor instead of a screw to test the then new Seawolf gear. |
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http://www.ussalbacore.org/img/img_v...tour/05-lg.jpg BTW, lots more Albacore pics here: http://www.ussalbacore.org/html/virtual_tour.html |
Cool .. :arrgh!:
Notice how the planes pairs are offset. The upper right (and lower left) ones are a bit more forward. It's so their axises wont collide. And they must not collide with the propeller shaft either. I'd really like to see this part from inside. Edit: Old man ? OLD man ? I've just turned 34, and that makes mi OLD ? :rotfl: |
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One other interesting thing they had was a rudder on the back of the sail. |
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Other navies on the other hand use the X-shape such as on the Type 212. |
My few cents .. X planes vs. cross
pros: - backup functionality - one pair can counter jam of the other pair (in pitch control, that's what matters) - lower draft and side extension with same effective surface area cons: - more complicated mechanism - not direct translation from controls to planes I guess the shallow water subs use X especially because lower draft. As for controls, they are computerized anyway (so one man can control it, as small sub cannot afford two man to do that). Complexity is not problem as you are always close to home. For attack subs, draft is usually not the main design element. The simplicity is useful especially if you want to fix it when far from home. Also bigger ship means bigger forces .. so some solutions which can be used on small sub (like having half-axis instead of full axis) might not work. The backup functionality can be done in different ways, like split control planes with backup HP system (though I'm not sure what system is used on let's say Virginia). |
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FYI double counterrotating propellers are usual in aeronautics, and the main effect is compensating the torque roll effect. IIRC that is also the same reason they are mounted in the torpedoes. It wouldn't amaze me if one of the functions in the 688s or the russian subs was to generate a counterbalance and allow the propeller to provide greater push without literally screwing the sub in a barrel roll effect. Also, a heavy roll must be compensated by rudders, and that slows down, adds friction and eventually, noise.
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Single screw is inefficient, and that is a problem for battery driven subs, and maybe for torpedoes too. Torpedoes have also very low bank stability, caused by their shape.
Subs have no problem with this stability. Screw only gives few degrees of bank during full power. However subs have problems with bank in turns. But even so, no bank control is used, only limiters on rudder while running at high speed. Actually I don't know about sub with tandem props. Except for Albacore. And Victor III RTM is told to have 'tandem prop' but by pictures, it looks more like those root fins, we have discussed earlier in this thread. So I guess it is not worth the trouble of coaxial shaft. |
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Here is an authoritative source that supports your opinion: "3D forces arising on X-type planes/rudders and generating both horizontal- and vertical-plane components make the submarine control more complicated. Therefore, a submarine with X-type control surfaces for all practical purposes can be controlled only by an automatic system and the failure of one plane/rudder pair may result in a serious accident, especially at high speed. Perhaps this is why X-type control surfaces are chosen only for diesel-electric submarines with their limited submerged speeds." Y.N Kormilitsin and O.A. Khalizev, "Theory of Submarine Design," p. 276 :know: |
WEll worth the mortarboard bill!
A single, large, slowly revolving screw is more effecient at noise reduction than a small, fast one is. I read that in Submarine by Tom Clancy |
http://img245.imageshack.us/img245/457/0212ect.jpg
The screw of a North Korean P-4 class Midget Submarine. |
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For what we know it looks similar to other designs, so I guess it is not just for look.
Highly swept back blades are supposed to reduce blade tip cavitation and the additional small blades to reduce hub vortex cavitation. Small sub for shallow water would be even more prone to cavitation. Sure, since it is North Korea, it may be by some newspaper photos to resemble smart design and it may not work well after all, but that you can't tell from the picture alone. |
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