Differential movement of bow planes?

[vasily]

In full scale subs, do the bow planes move differentially (like ailerons), or do they move up and down together? It would seem that they move differentially so that the sub banks into high speed underwater turns, rather than just up and down.
Anybody know?

[Ralph --- SSBN 598]

My experience is on nuke boomer.
The sail planes move together and are on a common shaft connected in the sail at the actuator horn.

The boat leans in to the turn due to the the center of gravity being low in the boat.
The hull acts sort of like a pendulum.
The faster you go the more lean induced.
The more turning input the more lean you get.

There is also lean due to propeller torque.
Once the boat speed catches up to the propeller speed, the boat levels out.

[wlambing]

Vasily,
Ralph is correct. Our planes move together. They are, however, adjustable in travel so that the faster you go the less they move. With the greater forces involved, you don't need a whole lot of travel to get a faster change in direction.

B^)

[vasily]

I like informed and unequivocal answers, like both of these. Thanks guys!
Jim

[bob the builder]

The boat leans in to the turn due to the the center of gravity being low in the boat.
The hull acts sort of like a pendulum.
The faster you go the more lean induced.
The more turning input the more lean you get.

There is also lean due to propeller torque.
Once the boat speed catches up to the propeller speed, the boat levels out.

I was always under the impression that the lean was at least partially induced by the hydrodynamic forces acting on the sail. In my experience, boats like the Akula or Alfa with shorter, faired sails don't bank as hard, whereas boats like the Type XXIII do so to a far greater degree due to the high, flat sails.

No?

[Ralph --- SSBN 598]

Bob,
You are correct.
Subs turn by pushing the stern out from the center line of the line of travel.
This induces pressure on the sail as the sail resists the sliding motion.
The smaller the small area the less effect the turning motion will have at a given speed.
The sail helps in the turning by giving the boat more area for the water to act on much like a keel on a sailboat.
The faster a boat goes, the less sail/keel area needed to make the same turn radius.
The sail on nuke boats is basically the turning pivot point on the hull.

The US tested this on the Permit class nukes.
Very small sail and much farther forward that the other classes.
Part of this was to test performance at high speeds.
This also tested the turning radius ability by moving the pressure (on the sail) forward.

The nuke hull being a cylinder slides through the water when turning because the round surface produces less resistance than a flat side hull.
The sail provides the needed resistance to reduce turning radius, gave a place for the crew for surface operations.
The sail also provided the means to counter act the torque from the propeller as demonstrated on the USS Skipjack class.
The sail is not on the hull center line but at a degree or two offset to counter act the propeller torque.

In a turn the sail induces yaw and then the stern planes can also be used to assist the rudders with the turn .
Much like an airplane really doesn't use the rudder to turn but is banked using the ailerons then the elevators to drive the plane up but in this case turn as the plane turns because it is in a banked position relative to the horizon.
The rudder is then used to control slip and maintain altitude/depth.

Sorry, I can get wordy at times.

[southern or]

I'm interested to know what the ride was like on the Barbells and their genesis, the Albacore. Both designs are completely different then the Current USN fleet. Then again, both were/are diesel electric.

[bob_eissler]

This is very enlightening. This means the sub has a much different turning radius surfaced or submerged right? How does the sub mass center affect turning? Mass centered on the sub or sail gives a shorter moment arm while mass farther forward has a longer moment.

[Ralph --- SSBN 598]

A modern USA nuke on the surface, only has the lower rudder to produce the turning force on the stern of the boat.
To turn, the stern is kicked out and the water pressure on the rest of the hull tries to resist the side slip.
The propeller is pushing the boat forward as the hull resits the slip.
So the bow moves out less quickly than the stern and this will result in the turning of direction of forward movement.
On the surface the entire hull slips away from the direction of the turn.

Submerged, both the lower and top rudder effect the turn with double the pressure to the turn.
There is more hull area resisting the slip in to the turn.
And now the sail comes in to play.
Not only does it resist the slip, it can as speed increases cause the hull to yaw slightly but enough to use the sail planes and or the stern planes to increase the turning effort.
Because of the sail adding slip resistance, the hull slips less at the bow and the hull seems to be pivoting at the sail.

The submerged turning radius is smaller than the surfaces turning radius.

I hope that was clear?

I do wonder if boats like the Parch having their sail so far back on the hull actually turn quicker.
I don't know and I haven't know anyone who might be able to answer that question.

I was on the George Washington USA 1st boomer.
I often wonder how the Typhoons handle with their sail so far back and the missile compartments forward of the sail.
Maybe someone here can expand on this topic.

[southern or]

.....
I was on the George Washington USA 1st boomer.
I often wonder how the Typhoons handle with their sail so far back and the missile compartments forward of the sail.
Maybe someone here can expand on this topic.

It's been forever, but when I was younger (much younger) I was told they used the twin screws to their advantage in turning.

[Ralph --- SSBN 598]

I think most boats, subs and surface boats, use the the propellers to help turn.
By slowing one side down or even reversing, the torque induced will help turn the boat.
I have seen big boats use this to swing the front of the boat away from the dock before going forward.

Slowing one side down while going forward, acts like a brake, while the other side continues to push, which would help turn the boat.
Rudders are relatively small and at slow speeds have little effect on turning.
Nuke boats have their rudder in front of the propeller and the prop wash does not push against the rudder going forward.
All is a trade off in design.

[Covert Shores]

At the opposite end of the spectrum, the SDV Mk.IX had independent forward hydroplanes and twin screws for incredible agility. Plus it was essentially hydroplane shaped.