15.14 - Engine Indication systems Flashcards
List the 6 primary engine indications displayed in the cockpit?
- Engine Pressure Ratio
- Engine Rotational Speeds (N, N2, N3 if applicable)
- EGT (Exhaust Gas Temperature)
- Fuel Flow
- Engine Vibration
- Engine Torque
What is used to measure EGT for the purpose of temp indication?
Thermocouples made of chromel and alumel conductor wires.
What is “EPR” and what does it measure?
Engine Pressure Ratio (EPR) measures engine power. It works on the basis that thrust is proportional to the energy rise when comparing intake pressure and turbine discharge pressure.
EPR = Tubrine Discharge pressure / Intake pressure
What sensors are used to measure Engine Speed and briefly describe their principal of operation? (2 sensors)
Tachometer Generator – Used for older engines and consists of a three phase AC tachometer generator driven from an accessory gearbox fitted to the relevant spool. A synchronous motor driven indicator displays an analogue reading in the cockpit or frequency as a % of RPM in a ‘digital’ cockpit.
Magnetic Pickup (Phonic Wheel) – A single or double pole magnetic sensor where it’s magnetic field can be intercepted by a part of the rotating assembly such as fan blade tips can be utilised to measure RPM.
Monitoring Engine temperature to determine engine performance is known as what kind of monitoring?
Condition or secondary monitoring.
List the primary Engine instruments (6)
- Engine Pressure Ratio
- Engine Rotational speeds: - N, N2 (and N3 if used)
- Exhaust Gas Temperature
- Fuel Flow
- Engine Vibration
- Engine Torque
List the secondary Engine instruments? (5)
- Oil Pressure
- Oil Temperature
- Oil Quantity
- Fuel Temperature
- Fuel Pressure
What metals are EGT probes made from and what colour are their connections?
EGT probes are commonly referred to as ‘‘thermocouples’’
EGT probe consists of a thermocouple of chromel and alumel
Chromel is white
Alumel is green
Where is EPR normally measured?
Pt2 probe or intake probe exists in fron of the intake ‘‘bullet’’
Pt7 probe or Turbine Discharge probe is located in a manifold just aft of the turbine final stage
Engine Pressure Ratio = Turbine Discharge Pressure / Intake pressure
What type of sensor is normally used to measure oil temperature (what metal is used)?
The most common type of oil sensor is the Resistance Bulb.
Pure nickel is the metal used
(change in temp. = change in resistance)
is possible to use thermocouple - Iron and constantan
On most oil pressure gauges what does the indicated pressure represent?
The difference between system vent pressure and main system pressure
How are engine oil contents measured? (2 methods)
The Reed Switch Transmitter - A reference voltage, supplied by the EICAS computer, is applied across the switches and resistors. At least two or three switches will close at any one time as the height of the float varies with oil level.
The Variable Capacitance Transmitter - same principle as those located in aircraft fuel tanks - dielectric value of oil and air - capacitance
How and why is fuel temperature measured?
Fuel temperature is measured by a temperature bulb (varying voltage which is read out)
Fuel temperature is measured to warn the operating crew of impending fuel filter blockage resulting from the formation of ice crystals in the fuel
How is fuel pump tank pressure normally monitored?
a Simpe Pressure Switch is used
How is fuel flow normally monitored? (2)
- The Synchronous Mass Flow Meter
- The Motorless Mass Flow Meter
Torque sensing systems are located where?
Teeth machined on the front end of both shafts are aligned at zero torque. When a torque load is applied to the inner shaft by driving a propeller, the inner shaft will twist through an angle proportional to the load. The outer shaft, being only connected at the rear, will not
twist as it is not subject to the load. The teeth on the inner shaft move out of alignment with the teeth on the outer shaft.
The electronic sensor can detect the angle of misalignment and convert it to a reading on the Flight Deck indicator.
