Interesting propeller shape. Any idea?

[Castout]

688i propeller in RA
http://img.photobucket.com/albums/v319/roh_kudus/dump00734068.jpg

Hmm I think the unconventional shaped propeller is meant to optimize on speed but does it offer any other advantages?

I thought it was the Russian submarines which are fitted with propeller shaped to give them maximum speed(push power) while the US submarines are fitted with propeller shaped for optimum noise performance(least noise).

If this is the shape of a propeller for optimum speed how is the shape of the propeller designed for optimum(lowest) noise performance?

Is this propeller(as shown in the picture) realistic to be fitted in 688i class SSN?

[Dr.Sid]

As the propellers go, nobody who knows will tell you.

But on Microsoft maps there was picture some time of Ohio propeller. That propeller was for sure designed for stealth. And it is based on ww2 design, where the tip of the blade is extended back, so it looks like huge 7 bladed swastika.

I have never seen something like this though. Not on any model, any picture, not in any books on submarine design.

But it totally gives sense. Limiting part of the screw is the propeller tip. The tip moves at maximum possible speed (not to cavitate) and the rest of the blade moves slower then it could. The second screw could rotate faster with same tip speed .. and accelerate that not so well used middle part of the propeller disc. It would be something like propeller which tips moves slower then the blades (ultimate dream of any propeller designer).
Also the second propeller could be counter-rotating, which could help even more. It does not look so from the picture, but AFAIK it is DW's limit and DW can't do counter-rotating propellers.

So it would improve effectiveness - it could achieve better acceleration at same power, and it would need less power to achieve same acceleration. That means it could be even more silent.

Sure it would complicate a gearing, I mean a lot.

[-GrayOwl-]

We have made Oscar-I in –RA- Add-on, with two coutry - rotating propellers on one shaft.

Also TU-142 Bear have coutry - rotating propellers.

Other business what is it in any way is not connected to awful physics of the engine.

But visually, it is looked very well.

[Bubblehead Nuke]

I have made comments about the curvilinear shape of the screw before. It has to do with controlling cavitation formation. A screw on a boat is not like a screw in a chunk of wood. Nor is it like a wing, it can not 'stall'. There are many many reasons it is shaped like it is. What you see there is the rough shape. There are many things about the surface of the screw and exact shapes that are the real secrets.

The smaller propeller in the back spins ar the same speed and direction as the main propeller.

my other post: http://www.subsim.com/radioroom/showthread.php?p=967416&highlight=curvilinear#post967416

[Dr.Sid]

So that small prop actually used ? On 688 class ?

[Bubblehead Nuke]

So that small prop actually used ? On 688 class ?

This is not really a prop... and it does not do what you think is looks like it is doing.

Yes, it is there, and it is probably used on all 688's now. I can not tell you what it was called as it was (and for all I know still is) a classified item. I know our boat was testing working hardware of the original concept design. I can tell you for a FACT I know what it is, what it is there for, and how it works.

The reason for it goes beyond the scope of a sub sim.

[Dr.Sid]

Well now that we started .. who cares about the sim .. I just want to know what it is good for :rotfl:
Looks like another google night.

[Bubblehead Nuke]

Good luck on the search, this is a black topic.

[Dr.Sid]

Yeah .. it's perfectly allright .. I guess we all respect your oaths.

But I have found something. It's all matter of good search terms.

http://ci.nii.ac.jp/naid/110003873027/en

You can get whole PDF paper but it's mostly in japanese. Still the abstract says it all.

But it took me an hour.

[Castout]

As the propellers go, nobody who knows will tell you.

But on Microsoft maps there was picture some time of Ohio propeller. That propeller was for sure designed for stealth. And it is based on ww2 design, where the tip of the blade is extended back, so it looks like huge 7 bladed swastika.

I have never seen something like this though. Not on any model, any picture, not in any books on submarine design.

But it totally gives sense. Limiting part of the screw is the propeller tip. The tip moves at maximum possible speed (not to cavitate) and the rest of the blade moves slower then it could. The second screw could rotate faster with same tip speed .. and accelerate that not so well used middle part of the propeller disc. It would be something like propeller which tips moves slower then the blades (ultimate dream of any propeller designer).
Also the second propeller could be counter-rotating, which could help even more. It does not look so from the picture, but AFAIK it is DW's limit and DW can't do counter-rotating propellers.

So it would improve effectiveness - it could achieve better acceleration at same power, and it would need less power to achieve same acceleration. That means it could be even more silent.

Sure it would complicate a gearing, I mean a lot.

Any link for that swastika like prop?

This is not really a prop... and it does not do what you think is looks like it is doing.

Yes, it is there, and it is probably used on all 688's now. I can not tell you what it was called as it was (and for all I know still is) a classified item. I know our boat was testing working hardware of the original concept design. I can tell you for a FACT I know what it is, what it is there for, and how it works.

The reason for it goes beyond the scope of a sub sim.

So it's not meant to add additional push force lol:)

[Dr.Sid]

Ohio propeller (and more):

http://images.google.com/images?hl=cs&q=submarine%20propeller&gbv=2

:ping:

[Bill Nichols]

Yeah .. it's perfectly allright .. I guess we all respect your oaths.

But I have found something. It's all matter of good search terms.

http://ci.nii.ac.jp/naid/110003873027/en

You can get whole PDF paper but it's mostly in japanese. Still the abstract says it all.

But it took me an hour.

Great find, well worth the hour it took you.

:up::up:

[Bubblehead Nuke]

Yeah .. it's perfectly allright .. I guess we all respect your oaths.

But I have found something. It's all matter of good search terms.

http://ci.nii.ac.jp/naid/110003873027/en

You can get whole PDF paper but it's mostly in japanese. Still the abstract says it all.

But it took me an hour.

Interesting abstract.....

I can not confirm nor deny....

[Task Force]

Non sence... The little prop powers the turbo drive that lets it travel at the speed of sound underwater...:rotfl:

of course... The article could be right... I guess the large prop helps it stay quiet, and produce speed effectivly because of its shape... and maby the smaller prop does like the artical says... or is some kind of thing to fool a distroyers listening equipments... to make it sound faster than it is... could also be there to fool homeing torpedos... (noise fools them...) may add to its speed when staying quiet... but im just guessing...:yep: I could keep speculating...

[goldorak]

Good luck on the search, this is a black topic.

Something to do with reducing cavitation and therefore enabling a sub to have higher speed at or near the surface ? :D
Just my guess.

[TLAM Strike]

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.

[Bubblehead Nuke]

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.

[Bill Nichols]

The Albacore still has one...

Yes, but I don't think she's going anywhere anytime soon!

http://www.ussalbacore.org/img/img_virtual_tour/05-lg.jpg


BTW, lots more Albacore pics here:

http://www.ussalbacore.org/html/virtual_tour.html

[Dr.Sid]

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:

[Bubblehead Nuke]

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.

:rotfl:

Nothing to see, they cut the steering rams in order to put the after access in the engineroom.

One other interesting thing they had was a rudder on the back of the sail.

[goldorak]

Nothing to see, they cut the steering rams in order to put the after access in the engineroom.

One other interesting thing they had was a rudder on the back of the sail.

Is there a reason why american subs didn't adopt the X-shape rudder/dive plane configuration of the Albacore ? Even the latest sub class, the Virginia class uses the standard + shape.
Other navies on the other hand use the X-shape such as on the Type 212.

[Dr.Sid]

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).

[Bubblehead Nuke]

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).

You pretty much hit on the head in my opinion. We liked the ability to go ALL manual if we had to. The X-Plane configuration would have really complicated it. Sure, you can make a combination control horn (think V-Tail RC airplanes and such), but that would be a complicated arrangement that is BEGGING to get jammed. Thus in a jam dive situation, you would have to control TWO different control surfaces in a combination to effectively control ships depth and heading. It is all about SIMPLICITY. In a causuality, I cared about the STERN planes, OR, the rudder, not both.

[Hitman]

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.

[Dr.Sid]

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.

[Bill Nichols]

You pretty much hit on the head in my opinion. We liked the ability to go ALL manual if we had to. The X-Plane configuration would have really complicated it. Sure, you can make a combination control horn (think V-Tail RC airplanes and such), but that would be a complicated arrangement that is BEGGING to get jammed. Thus in a jam dive situation, you would have to control TWO different control surfaces in a combination to effectively control ships depth and heading. It is all about SIMPLICITY. In a causuality, I cared about the STERN planes, OR, the rudder, not both.


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:

[Sledgehammer427]

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

[TLAM Strike]

http://img245.imageshack.us/img245/457/0212ect.jpg (http://www.imagehosting.com/)

The screw of a North Korean P-4 class Midget Submarine.

[Theta Sigma]

http://img245.imageshack.us/img245/457/0212ect.jpg (http://www.imagehosting.com/)

The screw of a North Korean P-4 class Midget Submarine.

Considering the origin, is that just for looks, or is there a practical advantage to that design?

[Dr.Sid]

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.

[Overkill]

I know this has been a dead topic for a long time but I came across it during a search. Thought I'd add this to it since it has some very good pictures of US Sub screws: http://imgur.com/a/IQBOi

[Furia]

Very interesting pics. :cool: