Down elevator
The depth rudder is used for fine control and for turning (or rolling ) a submarine about its longitudinal or transverse axis when submerged . In the case of a submarine, the angle of attack of the control surface and thus the upward or downward force changes by operating the depth rudder.
The down elevator is a movable surface that is attached either to the bow of the submarine, to the command tower or - most often - to the stern. Today, especially in larger submarines, the depth rudder and the main rudder usually form a control pad with the drive propeller in the middle .
In order to initiate a diving process in a large submarine, the depth rudder alone is not sufficient to counteract the buoyancy of the submarine body. In order to dive with a submarine, diving and control cells are therefore necessary. These are tanks that are filled with water to increase weight when diving and with air to surface.
The down rudders only take over the fine-tuning when the submarine is submerged. The arrangement of the forward depth rudder varies greatly in modern submarines. Depth rudders attached to the tower are not able to support the diving process and make it difficult to ascend in icy water. Only small submarines sometimes have dynamic depth control, ie they only steer with depth rudders and have no diving or control cells. This technology is mainly used in unmanned submarines ( diving robots ) and in model making.
