The central control console is the primary operating station for the propulsion plant and is located in the CCS. The CCS is the main engineering watch station. This console provides the operator with the necessary controls and displays for starting and stopping the gas turbine engines. Controls on the central control console allow the operator to vary the ship's ahead or astern speed within established design limitations by changing the pitch of the propeller and the speed of the propeller shaft.

The central control console fig 6-25 provides two distinctly different methods of controlling the ship's progress through the water. The first method requires the operator to individually adjust three levers on the console. One lever changes the direction and amount of pitch applied at the ship's variable-pitch propeller. Each of the remaining two levers controls the speed of one of the gas turbine engines. This is a duplicate set of controls that are the same as the controls on the local control console.

The second and primary method of operating the ship's propulsion plant involves the use of a single control lever and a special-purpose digital computer contained in the control system. This technique for controlling the engines and the propeller pitch with one control and the digital computer is referred to as single-lever programmed control.

Single-lever programmed control of the ship's propulsion plant can also be maintained from the ship control console (SCC) located on the bridge. However, the lever on the bridge's SCC panel can be operated only after the operator in the CCS relinquishes control.

SHIP CONTROL CONSOLE

This station is located on the ship's bridge. This console has a throttle control, a propulsion plant alarm, and shaft speed and propeller pitch indicators.

CONSOLE OPERATING OVERVIEW

Using modern electronics, computers, and precisely placed sensing equipment, the operator at the central control console can "see" and manipulate the entire propulsion plant. The operator is assisted by sensor-scanning equipment that can check out the plant more thoroughly in a fraction of a second than an engine-room messenger could in 30 minutes. The scanning circuits are wired with information about the operating parameters of all the critical points monitored and will sound off immediately if these are exceeded. The operator's control is extended not only by remote operation of all engine controls but also by wired-in expertise from electronic components that "know" all the right steps and procedures for all normal plant operations as well as most emergency procedures.

There are two directions of information flow in a gas turbine propulsion system. The first is from the sensing and measuring devices on the plant equipment. The second is from the operator and the console to the engine control devices. The first or input flow begins as an electrical signal from a sensor. These signals are "conditioned" so that they can be handled by the digital computer. Some of the signals are displayed on indicators at the operating stations. Most of these indicators are for vital equipment functions.

The control of high-performance engines and other machinery is a complex operation. Automatic central-type operating systems permit a single operator to perform this operation by extending individual ability to sense and to control. As these systems prove their effectiveness and reliability, their use will increase.

ADVANTAGES AND DISADVANTAGES OF THE GAS TURBINE PROPULSION SYSTEM

The gas turbine, when compared to other types of engines, offers many advantages. Its greatest asset is its high power-to-weight ratio. This has made it, in the forms of turboprop or turbojet engines, the preferred engine for aircraft. Compared to the gasoline piston engine, which has the next best power-to-weight characteristics, the gas turbine operates on cheaper and safer fuel. The smoothness of the gas turbine, compared with reciprocating engines, has made it even more desirable in aircraft because less vibration reduces strains on the airframe. In a warship, the lack of low-frequency vibration in gas turbines makes them preferable to diesel engines because there is less noise for a submarine to pick up at long range. Modern production techniques have made gas turbines economical in terms of horsepowerper-dollar on initial installation, and their increasing reliability makes them a cost-effective alternative to steam turbine or diesel engine installation. In terms of fuel economy, modern marine gas turbines can compete with diesel engines and may be superior to boiler/steam turbine plants when these are operating on distillate fuel.

However, there are some disadvantages to gas turbines. Since they are high-performance engines, many parts are under high stress. Improper maintenance and lack of attention to details of procedure will impair engine performance and may ultimately lead to engine failure. A pencil mark on a compressor turbine blade or a fingerprint in the wrong place can cause failure of the part. The turbine takes in large quantities of air that may contain substances or objects that can harm the engine. Most gas turbine propulsion control systems are complex because several factors have to be controlled, and numerous operating conditions and parameters must be monitored. The control systems must react quickly to turbine operating conditions to avoid casualties to the equipment. Gas turbines produce loud, high-pitched noises that can damage the human ear. In shipboard installations, special soundproofing is necessary. This adds to the complexity of the installation and makes access for maintenance more difficult.

From a tactical standpoint, there are two major drawbacks to the gas turbine engine. The first is the large amount of exhaust heat produced by the engines. Most current antiship missiles are heat-seekers, and the infrared signature of a gas turbine engine makes it an easy target. Countermeasures, such as exhaust gas cooling and infrared decoys, have been developed to reduce this problem.

The second tactical disadvantage is the requirement for depot maintenance and repair of major casualties. The turbines cannot be repaired in place on the ship and must be removed and replaced by rebuilt engines if anything goes wrong. Here too, design has reduced the problem; an engine change can be accomplished wherever crane service or a Navy tender is available, and the replacement engine can be obtained.

SUMMARY

This chapter has given you some basic information on gas turbine engines and gas turbine control systems. For a more in-depth look at gas turbines, refer to Gas Turbine Systems Technician (Mechanical) 3 & 2, NAVEDTRA 10548-2.