Controlled Surfaces: Planes and Rudder Once the submarine is submerged it would be very difficult to to continuously obtain and maintain the desired depth by taking air in and out of the ballast tanks. For this reason modern nuclear submarines are equiped with hydroplanes. These are big planar surfaces that can rotate in order to change their angle from the horizontal. Nuclear subs have fairwater planes, stern planes, and a rudder. The locations of these "controlled surfaces" are shown in the anatomy section of this webpage. An excellent view of the fairwater planes can be seen on the introductory picture of the home page of this site (On the newer fast attack submarines the fairwater planes have been moved down onto the bow of the sub extending from the forward main ballast tanks). Changing the angle of attack (illustrated below) of the planes creates lift forces that act on the submarine and change its depth. (Picture from "Engineering Fluid Mechanics", Crowe,Elger,and Roberson, 2001.) Once an angle of attack is placed on the plane in the direction indicated above (the plane is rotated upward), the water flowing over the top of the plane must travel a greater distance in the same amount of time which amounts to an increase in velocity. Since Bernoulli's equation states that pressure is inversely proportional to velocity, the pressure on the top of plane becomes negative if the sea pressure at an infinite distance (sea pressure unaffected by the plane) from the plane is taken as absolute zero. Conversely, the pressure accross the bottom of the plane increases and becomes greater than the surrounding sea pressure. An illustration of these pressure distributions is shown below. Since Force = Pressure * Area, the positive force acting upward on the bottom of the plane and the negative force acting downward on the top of the plane can be summed to produce a net force upward (negative force downward = positive force upward). So the pressure distribution on the top of the plane and the bottom on the plane both contribute to the upward force applied to the plane which is transferred to the hull of the submarine. This force pushes the sub upward to a more shallow depth. The opposite occurs if the planes are rotated downward. The stern planes are configured as flaps on the after-end of a rigid, non-rotating plane. So when they are rotated they actually change the angle of the entire submarine and the change in depth is directly aided by the propulsion of the ship acting in the direction of depth change. The rudder is configured the same as the stern planes and works on the same principles to change the direction of the ship. The ship must have a forward velocity in order for the planes to have any effect. An appropriate force diagram for a plane would be as follows: (Picture from "Engineering Fluid Mechanics", Crowe,Elger,and Roberson, 2001.) If the shear stress of the water flowing over the plane is taken into account and the above force diagram is observed then the total force over the entire surface can be calculated using the following integration: Home / Basic Anatomy of a Nuclear Submarine / Surfacing and Submerging / Propulsion / Bibliography