Controls and instrumentation - SYNCHRONIZING AND SYNCHROPHASING

want to read about :  Controls and instrumentation Electronic indicating systems

SYNCHRONIZING AND SYNCHROPHASING
58. Synchronizing and synchrophasing systems are  sometimes used on turbo-propeller engined aircraft to achieve a reduction of noise during flight.
59. On a multi-engined aircraft, a synchronizing system ensures the propeller speeds are all the same. This is achieved by an electrical system that compares  speed  signals  from  engine-mounted generators.  Out-of-balance  signals,  using  one engine  as  a  master  signal,  are  automatically corrected by electrically trimming the engine speeds until all signals are equal.

Controls and instrumentation Electronic indicating systems

want to read about :  Controls and instrumentation - Warning systems

Electronic indicating systems 
54. Electronic  indicating  systems  consolidate engine indications, systems monitoring, and crew alerting functions onto one or more cathode ray tubes (C.R.T.'s) mounted in the instrument panel. The information is displayed on the screen in the form of dials with digital readout and warnings, cautions and advisory messages shown as text.

Fig. 12-12 Typical electronic indicating display.

55. Only those parameters required by the crew to set  and  monitor  engine  thrust  are  permanently displayed on the screen.  The system monitors the remaining parameters and displays them only if one or more exceed safe limitations.  The pilot can, however, override the system and elect to have all main parameters in view at any time (fig. 12-12).

Controls and instrumentation - Warning systems

want to read about : Controls and instrumentation - Vibration
Warning systems
48. Warning  systems  are  provided  to  give  an indication of a possible failure or the existence of a dangerous condition, so that action can be taken to safeguard the engine or aircraft. Although the various systems of an aircraft engine are designed wherever possible to 'fail safe1, additional safety devices are sometimes  fitted.  Automatic  propeller  feathering should a power loss occur, and automatic closing of the high pressure fuel shut-off cock should a turbine shaft failure occur, are but two examples. On some engine types, the fuel system is fitted with a control  to enable the engine to be operated by manual throttling should a main fuel system failure occur.

49. In addition to a fire warning system (Part 14), a number of other audible or visual warning systems can be fitted to a gas turbine engine. These may be for low oil or fuel pressure, excessive vibration or overheating. Indication of these may be by warning light, bell or horn. A flashing light is used to attract the pilot's attention to a central warning panel (C.W.P.)

where the actual fault is indicated.

Controls and instrumentation - Vibration

want to read about :  Controls and instrumentation - Fuel flow

Vibration
44. A turbo-jet  engine  has  an  extremely  low vibration level and a change of vibration, due to an impending or partial failure, may pass without being noticed.  Many  engines  are  therefore  fitted  with vibration  indicators  that  continually  monitor  the vibration level of the engine. The indicator is usually a milli ammeter that receives signals through an amplifier from engine mounted transmitters (fig. 12- 11).

Fig. 12-11 Vibration transmitter and

indicator.

45. A vibration transmitter is mounted on the engine casing and electrically connected to the amplifier and indicator. The vibration sensing element is usually an electro-magnetic transducer that converts the rate of vibration into electrical signals and these cause the indicator pointer to move proportional to the vibration level.  A warning lamp on the instrument panel is incorporated in the system to warn the pilot if an unacceptable  level  of  vibration  is  approached, enabling the engine to be shut down and so reduce the risk of damage.

46. The vibration level recorded on the gauge is the sum total of vibration felt at the pick-up.  A more accurate  method  differentiates  between  the frequency ranges of each rotating assembly and so enables the source of vibration to be isolated. This is particularly important on multi-spool engines.
47. A crystal-type vibration transmitter, giving a more  reliable  indication  of  vibration,  has  been developed for use on multi-spool engines. A system of filters in the electrical circuit to the gauge makes it possible to compare the vibration obtained against a known frequency range and so locate the vibration source. A multiple-selector switch enables the pilot to select a specific area to obtain a reading of the level of vibration.

Controls and instrumentation - Fuel flow

want to read about : Controls and instrumentation - Fuel temperature and pressure

Fuel flow

Fig. 12-10 Fuel flow transmitter and

indicator.

43. Although the amount of fuel consumed during a given flight may vary slightly between engines of the same type, fuel flow does provide a useful indication of the satisfactory operation of the engine and of the amount of fuel being consumed during the flight. A typical system consists of a fuel flow transmitter, which is fitted into the low pressure fuel system, and an indicator, which shows the rate of fuel flow and the total fuel used in gallons, pounds or kilogrammes per hour (fig. 12-10). The transmitter measures the fuel flow electrically and an associated electronic unit gives a signal to the indicator proportional to the fuel flow.

Controls and instrumentation - Fuel temperature and pressure

want to read about : Controls and instrumentation - Oil temperature and pressure

Fuel temperature and pressure
41. The  temperature  and  pressure  of  the  low pressure fuel supply are electrically transmitted to their respective indicators and these show if the low pressure system is providing an adequate supply of fuel without cavitation and at a temperature to suit the operating conditions.  The fuel temperature and pressure  indicators  are  similar  to  those  for temperature and pressure indication.
42. On some engines, a fuel differential pressure switch, fitted to the low pressure fuel filter, senses the pressure difference across the filter element.  The switch is connected to a warning lamp that provides indication of partial filter blockage, with the possibility of fuel starvation.

Controls and instrumentation - Oil temperature and pressure

want to read about : Controls and instrumentation - Turbine gas temperature


Oil temperature and pressure 


35. It is essential for correct and safe operation of the engine that accurate indication is obtained of both  the  temperature  and  pressure  of  the  oil.  Temperature  and  pressure  transmitters  and indicators are illustrated in fig 12-9.

Fig. 12-9 Oil temperature and pressure transmitters and indicators.

36. Oil temperature is sensed by a temperature- sensitive element fitted in the oil system. A change in temperature causes a change in the resistance value and, consequently, a corresponding change in the current flow at the indicator. The indicator pointer is deflected  by  an  amount  equivalent  to  the temperature change and this is recorded on the gauge in degrees centigrade.
37. Oil pressure is electrically transmitted to an indicator on the instrument panel. Some installations use  a  flag-type  indicator,  which  indicates  if  the pressure is high, normal or low; others use a dial- type gauge calibrated in pounds per square inch (p.s.i.).

Controls and instrumentation - Engine speed

want to read about :  Controls and instrumentation - Engine torque

Engine speed
21. All engines have their rotational speed (r.p.m.) indicated. On a twin or triple-spool engine, the high pressure assembly speed is always indicated; in most instances, additional indicators show the speed of  the  low  pressure  and  intermediate  pressure assemblies.
22. Engine  speed  indication  is  electrically ransmitted from a small generator, driven by the engine,  to  an  indicator  that  shows  the  actual evolutions per minute (r.p.m.), or a percentage of he maximum engine speed (fig. 12-5).

Fig. 12-5 Engine speed indicators and

generator.

The engine speed is often used to assess engine thrust, but it does not give an absolute indication of the thrust being  produced  because  inlet  temperature  and  pressure conditions affect the thrust at a given engine speed.
23. The engine speed generator supplies a three- phase alternating current, the frequency of which is dependent upon engine speed. The generator output frequency  controls  the  speed  of  a  synchronous motor in the indicator, and rotation of a magnet assembly housed in a drum or drag cup induces movement of the drum and consequent movement of the indicator pointer,
24. Where  there  is  no  provision  for  driving  a generator, a variable-reluctance speed probe, in conjunction with a phonic wheel, may be used to induce an electric current that is amplified and then transmitted to an indicator (fig. 12-6).  This method can be used to provide an indication of r.p.m. without the need for a separately driven generator, with its associated  drives,  thus  reducing  the  number  of components and moving parts in the engine.

Controls and instrumentation - Engine torque

want to read about : Controls and instrumentation - Engine thrust

Engine torque

Fig. 12-4 A simple torquemeter system.

18. Engine torque is used to indicate the power that is developed by a turbo-propeller engine, and the indicator is known as a torquemeter.  The engine torque or turning moment is proportional to the horse-power and is transmitted through the propeller reduction gear.



19. A torquemeter system is shown in fig. 12-4. In this system, the axial thrust produced by the helical gears is opposed by oil pressure acting on a number of pistons; the pressure required to resist the axial thrust is transmitted to the indicator.

Controls and instrumentation - Engine thrust

want to read about : Controls and instrumentation - INSTRUMENTATION


  Engine thrust
10. The thrust of an engine is shown on a thrust- meter, which will be one of two basic types; the first measures turbine discharge or jet pipe pressure, and the second, known as an engine pressure ratio (E.P.R.) gauge, measures the ratio of two or three parameters. When E.P.R. is measured, the ratio is usually that of jet pipe pressure to compressor inlet pressure. However, on a fan engine the ratio may be  that of integrated turbine discharge and fan outlet pressures to compressor inlet pressure.

Fig. 12-3 Electro-mechanical E.P.R. transmitter.

11. In each instance, an indication of thrust output is given, although when only the turbine discharge pressure is measured, correction is necessary for variation of inlet pressure; however, both types may require  correction  for  variation  of  ambient  air temperature.  To  compensate  for  ambient atmospheric  conditions,  it  is  possible  to  set  a correction figure to a sub-scale on the gauge; thus, the minimum thrust output can be checked under all operating conditions.
12. Suitably  positioned  pilot  tubes  sense  the pressure or pressures appropriate to the type of indication being taken from the engine.  The pilot tubes are either directly connected to the indicator or to  a  pressure  transmitter  that  is  electrically connected to the indicator.
13. An  indicator  that  shows  only  the  turbine discharge pressure is basically a gauge, the dial of which may be marked in pounds per square inch (p.s.i.), inches of mercury (in. Hg.), or a percentage of the maximum thrust.

Controls and instrumentation - INSTRUMENTATION

want to read about :Controls and instrumentation - CONTROLS


INSTRUMENTATION

Fig. 12-2 Diagrammatic arrangement of engine control and instrumentation.

9. The performance of the engine and the operation of the engine systems are shown on gauges or by the operation of flag or dolls-eye type indicators. A diagrammatic arrangement of the control and instru- mentation for a turbo-jet engine is shown in fig. 12-2.

Controls and instrumentation - CONTROLS

want to read about :Controls and instrumentation - INTRODUCTION

 
CONTROLS
4. The control of a gas turbine engine generally requires the use of only one control lever and the monitoring of certain indicators located on the pilot's instrument panel (fig. 12-1). Operation of the control (throttle/power) lever selects a thrust level which is then maintained automatically by the fuel system (Part 10).

Fig. 12-1 Pilot's instrument panel - turbo-jet engines.

5. On engines fitted with afterburning, single lever control is maintained, although a further fuel system  is required to supply and control the fuel to the after burner (Part 16).

Controls and instrumentation - INTRODUCTION

INTRODUCTION
1. The  controls  of  the  gas  turbine  engine  are designed to remove, as far as possible, work load from the pilot while still allowing him ultimate control of the engine. To achieve this, the fuel flow is auto-matically controlled after the pilot has made the initial power selection (Part 10).
2. All engine parameters require monitoring and instrumentation is provided to inform the pilot of the correct functioning of the various engine systems and to warn of any impending failure. Should any of the automatic governors fail, the engine can be manually controlled by the pilot selecting the desired thrust setting and monitoring the instruments to maintain the engine within the relevant operating limitations.
3. The multitude of dials and gauges on the pilot's instrument panel may be replaced by one or a number of cathode ray tubes to display engine parameters.  These are small screens capable of displaying all of the information necessary to operate the engine safely.