CONTROL SURFACES

The propeller is capable of only moving the submarine forward.  To effectively move in any direction within the ocean, the Ohio class has three sets of control surfaces.



A captain, standing between the periscopes, keeps his body aligned with gravity as the ship makes a sharp up angle.  IMAGE SOURCE: We Are the Mighty




HOW THEY WORK

Control surfaces behave similar to aircraft wings.  The difference is that instead of the wing's shape, it is the rotation of the surface that creates a pressure differential.  It starts by taking advantage of the relative momentum of passing seawater.  The rotation causes water to deflect in different ways on either side of the surface.  For a given direction of rotation, a high pressure zone is formed on the side in which the surface was turned.  A low pressure zone is formed on the opposite side.  This pressure difference produces a non-zero net force in the direction of the low pressure zone, a force that translates to the entire ship.

Figure 2: Rudder moment when rudder is moved to starboard

TYPES OF CONTROL SURFACES

The three types of surfaces the Ohio class has are the rudder, stern planes, and fairwater planes.  The location of these surfaces play an important role.  Both the rudder and the stern planes are located right at the end of the 560 ft long ship.  This is done to maximize the length of the moment arm in order to maximize the desired changes.  For the rudder, this means that the submarine can conduct the tightest turn possible.  For the stern planes, this puts an up or down angle on the ship, allowing the propeller to quickly push it to a new depth.

The fairwater planes are located on the sail, which is the tower that defines the iconic shape of a submarine.  This location is placed closer to the center of the ship as an alternative, slower depth adjustment.  Using the fairwater planes has a tendency to allow the ship to change depth while staying relatively level.  Realistically, driving the ship requires the skill to vary the combined use of all three control surfaces.


IMAGE SOURCES: Submarine Group Nine, Facebook

The control surfaces are mechanically connected to huge hydraulic pistons such that they convert the linear motion of the piston into rotational motion on the planes.  These pistons are controlled from valves in the hydraulic system.  The position of these valves are also controlled hydraulically in response to operating what are colloquially known as "the sticks" in the control room.


IMAGE SOURCE: Free Republic


Author: David Atwood    |    Physics 212    |    02 January 2019    |    Design: HTML5 UP