Answers - Engine Instument Systems | Aircraft Systems

Answers - Engine Instument Systems

1. a
Electronic fuel flowmeters (vane-type or mass-flow type) are what many modern aircraft use to measure the amount of fuel consumed by an engine. Fuel flowmeters monitor the amount of fuel that flows past a given point and display this flow rate in the cockpit as pounds of fuel consumed per hour.

2. b
Most light aircraft equipped with continuous-fuel injection systems utilize a fuel flow indication system that measures the pressure drop across the injection nozzles to determine fuel flow (answer B). With this type of system, a higher fuel flow results in a greater pressure drop and a corresponding increase in fuel flow is indicated in the cockpit.

3. c

4. a
In an autosyn system installed in the fuel system of turbine engine aircraft, fuel-flow data are transmitted using the aircraft's electrical system.

5. a
The only fuel flow indicating system that utilizes an impeller and turbine is the synchronous mass flow system. In this type of system both the indicator rotor and needle are driven by an electrical signal.

6. b
Most light twin-engine aircraft utilize a fuel flow indication system that measures the pressure drop across the injection nozzles to determine fuel flow. With this type of system, a higher fuel flow results in a greater pressure drop and a corresponding increase in fuel flow is indicated in the cockpit. However, if an injector nozzle becomes restricted, the pressure drop across the nozzle becomes greater and produces a false or high fuel flow reading.

7. b

8. b
A computerized fuel system (CFS) utilizes a transducer mounted in the fuel line leading to the engine to provide fuel flow in gallons or pounds per hour, gallons or pounds remaining, time remaining for flight at the current power setting, and gallons used since startup or reset. Of the four items listed, three are provided by a CFS.

9. a
In both a motor driven impeller and turbine, and a motorless fuel flow indication system a flow meter transmitter converts the fuel's mass-flow rate into electronic signals that produce a fuel flow indication in the cockpit.

10. b

11. c

12. b
The purpose of an exhaust gas analyzer is to indicate the fuel/air ratio being burned in the cylinders. It identifies cylinders that are running too rich or too lean, and can be used to fine tune the fuel metering system

13. b
A typical electric tachometer consists of a three-phase generator mounted to the engine that is connected electrically to a three-phase synchronous motor in the tachometer instrument. The engine-mounted generator produces a three-phase current that is sent to the synchronous motor where a rotating field is produced in the stator. The rotating field causes the rotor to turn which, in turn, moves the tachometer's indicating needle.

14. c
A thermocouple is a circuit of two dissimilar metals connected together at two junctions to form a loop. When there is a temperature difference between the two junctions an electromotive force is produced which can be measured with a galvanometer. Therefore, when a thermocouple temperature indicating system is used on a reciprocating engine, the thermocouple's hot junction is placed at the cylinder whereas the system's cold junction is at the instrument.

15. b
The typical electric tachometer system utilizes a threephase AC generator coupled to the aircraft engine and connected electrically to a synchronous motor indicator mounted to the instrument panel. The generator transmits three-phase power to the synchronous motor at a frequency that is proportional to the engine speed. The exact frequency determines the motor speed which, in turn, produces the instrument indication.

16. b
Because a thermocouple produces its own milliamp current flow, a temperature indicating system using thermocouples does not require any external power. However, most systems do use external power and an amplifier to improve the response.

17. b
A thermocouple is a circuit of two dissimilar metals connected together at two junctions to form a loop. When there is a temperature difference between the two junctions an electromotive force is produced which can be measured with a galvanometer. The greater the temperature difference the greater the voltage produced.

18. b

19. a

20. a
A manifold pressure gauge measures the absolute pressure within an engine's intake manifold. However, if a break exists in the line between the manifold pressure gauge and the manifold, the gauge will only be able to display the prevailing atmospheric pressure.

21. b
In both wet and dry-sump lubricating systems, the oil temperature bulb is located somewhere in the oil inlet line between the supply tank and the engine. This means the oil temperature gauge in the cockpit indicates the temperature of the oil entering the engine.

22. c

23. b
A thermocouple type of temperature indicating system produces a current flow in one direction when there is a difference in temperature between the hot junction and the cold junction. Therefore, if the leads to the temperature gauge are reversed, the temperature gauge pointer movement will reverse and the needle will peg out at the meter's zero side.

24. a

25. c

26. a
Powerplant range markings show minimum, continuous, limited, and maximum ranges. These ranges may not exceed the engine's Type Certificate Data Sheet specifications and, in some cases, may be less than those specified.

27. b
Thermocouple leads are designed for a specific installation. For example, in order to function properly there must be a specific amount of resistance in the thermocouple circuit. Thus, their length or cross sectional size cannot be altered unless some compensation is made for the change in total resistance. A thermocouple system for a typical turbine engine, for example, has eight ohms of resistance.

28. a

29. a
The typical electric tachometer system uses a threephase AC generator coupled to the engine to send information to an AC synchronous motor that is attached to the indicator.

30. c
If a turbojet engine is undamaged and the turbine blades are clean a high exhaust gas temperature (EGT) for a given engine pressure ratio (EPR) identifies an out-of-trim condition. Furthermore, on turbine engines that utilize centrifugal flow compressors, compressor rpm is a direct indication of the thrust being produced. Therefore, on some turbine-powered aircraft, rpm is the primary indicator of the thrust produced.

31. b
Engine pressure ratio (EPR) is the ratio of the total pressure leaving the turbine to the total pressure entering the engine and indicates the amount of thrust produced by an engine. EPR is calculated by dividing the total turbine outlet pressure by the total compressor inlet pressure.

32. a
The thermocouples used in turbine engines are usually constructed of chromel, a nickel/chromium alloy; and alumel, a nickel/aluminum alloy. These are dissimilar metals which produce a milliamp current flow when heated.

33. b
Items 2, 4, 5 and 8 cannot be repaired by a maintenance technician and, therefore, the instrument must be removed from the aircraft and sent to a certified instrument repair station. The remaining items (items 1, 3, 6, and 7) can be repaired by an aviation technician and do not require the removal and replacement of the instrument.

34. a
A Bourdon tube is a metal tube that is formed in a circular shape with an oval or flattened cross section and is used to measure both pressure and temperature. When air or liquid pressure enters the open end of a Bourdon tube, the tube has a tendency to straighten out. By the same token, if a Bourdon tube is filled with a gas and sealed at both ends, changes in temperature will cause the sealed gas to expand and contract thereby causing the tube to move. Through a series of gears, this movement is then used to move an indicating needle.

35. c
Bootstrapping occurs when a turbocharger system senses small changes in temperature or rpm and continually changes the turbocharger output in an attempt to establish an equilibrium. Bootstrapping typically occurs during part-throttle operation and is characterized by a continual drift of manifold pressure.

36. c

37. c
The mean effective cylinder pressure in an engine is the average pressure produced in the combustion chamber during an operating cycle. Therefore, the higher the manifold pressure, the higher the mean effective cylinder pressure.

38. b
A "hot" start is a start in which the turbine temperature exceeds specific limits. To minimize the chance of a hot start the temperature at the turbine should always be monitored when starting a gas turbine engine. Depending on the aircraft, turbine temperature is monitored by watching the turbine inlet temperature, exhaust gas temperature, or interstage gas temperature.

39. a
Spectrometric Oil Analysis programs must include samples taken at regular intervals and should begin when an engine is new. The ability of an analysis program to predict problems is based on comparing data taken from a number of samples over a known time period. Therefore, an accurate trend forecast cannot be made after an engine's first oil analysis.

40. a
Inlet anti-ice systems use compressor bleed air to prevent ice formation on inlet ducts. When air is bled off the compressor, less pressure is available at all stations downstream, and EPR drops. Therefore, the application of engine anti-ice will cause a noticeable shift in the EPR indication in the cockpit.

41. b

42. c
A possible cause of high EGT, high fuel flow, and low RPM in a gas turbine engine is turbine section damage or loss of turbine efficiency. The purpose of the turbine blades is to convert the energy from the gases coming off the combustor into rotary motion to drive the compressor. If the turbine is damaged, it won't convert as much energy and the rpm will remain low, the exhaust gas temperature will increase, and the engine will burn more fuel at given rpm settings.

43. c

44. a
The engine pressure ratio (EPR) indicator is, for the majority of turbine powered airplanes, the primary indicator of engine thrust. EPR represents the ratio of the total pressure aft of the turbines to the total pressure at the engine inlet.

45. c
The exhaust gas temperature (EGT) indicator provides a relative indication of the turbine inlet temperature (TIT). Engineers who design an engine know how much heat energy the turbine section will absorb from the gases flowing through it. Therefore, TIT can be calculated as a function of EGT.

46. c

47. c
In a gas turbine engine, the turbine discharge pressure sensor is located immediately aft of the last turbine stage. The readings taken from this sensor and the compressor inlet pressure sensor are used to determine the engine pressure ratio.

48. a
Gas turbine engine tachometers are usually calibrated in percent rpm. This allows various types of engines to be operated on the same basis of comparison.

49. c
Typically, instruments that provide low or negative pressure readings utilize a sensitive diaphragm or bellows that expands and contracts to drive an indicator needle.

50. b.

51. c
Modern AC tachometers utilize a three-phase AC generator coupled to an engine and connected electrically to an indicator mounted in the instrument panel. As an engine runs, the three-phase generator transmits a frequency that is proportional to the engine speed of a synchronous motor mounted to the indicator. The transmitted frequency causes the synchronous motor to turn at a specific rpm and provide a specific indication.

52. a
The exhaust gas temperature (EGT) gauge provides a pilot with a means of properly adjusting the fuel/air mixture for efficient operation.

53. b.