19 Engine Instruments Flashcards
What is N1?
N1 is the RPM of the fans of a jet engine given as a percentage
What is the formula for the Engine Pressure Ratio (EPR)?
EPR = Exhaust Pressure / Intake Pressure
What sort of pressure instrument is used to measure engine pressure?
Bellows
Describe a Mechanical RPM indicator:
- Aka
- Basic operating principle
- Require an external power supply
- Magnetic / Drag Cup indicator
- A cable is physically connected to the engine which spins a magnet. - The magnet sits within a ‘cup’ which is magnetised and try’s to spin with the magnet.
- The spinning cup applies a force to a spring which turns the needle
- The faster the engine, more force applied to the spring, further the needle moves
- No external power is required
What is a Tacho-Generator also known as?
- Electric RPM indicator
- Induction RPM indicator
Describe a Tacho-Generator RPM indicator which uses DC or 1 or 2 phase AC:
- Basic operating principle
- What is measured to give an indication on RPM
- Require an external power supply
- Engine is attached to a magnet which spins with it.
- The spinning magnet forms part of an electric generator
- The voltage from the generator is fed to an electric motor
- The motor applies a force to a spring which turns the dial
- The Induced Voltage supplied to the motor is measured to give RPM reading
- No external power supply is needed
What is the downside of using a Tacho-Generator RPM indicator which uses DC or 1 or 2 phase AC?
- The induced voltage measured is affected by the resistance within the cables
- This can lead to inaccuracies in the reading
Describe a Tacho-Generator RPM indicator which uses 3 phase AC:
- Basic operating principle
- What is measured to give an indication on RPM
- Require an external power supply
- Engine is attached to magnet which spins
- The magnet is surrounded by 3 sets of cables
- As the magnet spins it generates a current in each set in turn
- The frequency of these currents is measured to give an indication of the RPM
- No external power supply is required
Describe a Tacho-Probe RPM indicator:
- Aka
- Basic operating principle
- What is measured to give an indication on RPM
- Require an external power supply
- Electronic / Induction Probe
- A probe supplied with AC current is positioned next to the fan blades of a jet engine
- As the blade passes by the probe is creates a magnetic distortion in the current in the probe
- Frequency of the distortions is measured to give an indication of RPM
- ## Does require an external power supply
Name two engine performance indicators?
- Engine Pressure Ratio (EPR)
- N1
Describe a Mechanical or Float Gauge Fuel Level indicator:
- What it measures
- How it measures
- Any associated errors
- Measure the volume of fuel
- A float is placed in the fuel tank and moves up and down according to the level of fuel
- The float is attached to a variable resistor and a DC current
- The difference between the DC current and that which reaches the indicator gives a reading of fuel level
- Only measures volume which is effected by temperature
- Measurement is effected by the attitude of the AC
Describe a Electircal or Capacitance Fuel Level indicator:
- What it measures
- How it measures
- Any associated errors
- Measures the mass of the fuel
- Capacitors in the tanks read the capacitance at different locations
- The overall value derived from all capacitors indicates the mass of fuel
- This is compared to a reference capacitor which is always submerged
- No associated errors
If the reference capacitor in fuel tank breaks, can the fuel amount be read in that tank?
No
If the fuel quantity indicator for a tank is broken, can the AC still fly?
- Yes
- As long as the tank has a serviceable fuel flow indicator
Describe a Mechanical Fuel Flow meter:
- What it reads
- How it reads it
- Measures the fuel flow volume (Volume/hr)
- A plate or propeller is placed in the fuel pipe
- How much this is displaced or how fast it is turned indicates the volume of fuel flowing
Describe an Analogue Electrical Fuel Flow meter:
- What it reads
- How it reads it
- Measures the mass of fuel flow
- A motor or impeller causes the fuel to spin
- The fuel then flows into a torque meter
- The amount the torque meter turns gives an indication of the fuel flow mass
What pressure probe is used to the measure the pressure of a low pressure fuel pump?
Aneroid Capsule
What is the formula for Capacitance?
Capacitance = Dielectric Permittivity x (Area of Plates / Distance Between the Plates)
What does a Tachometer measure?
Angular speed
What is the purpose of a Micron Filter?
To remove small particles as a result of normal wear and tear of the engine
What is the purpose of Magnetic Chip Detectors?
- Attract and retain small particles the the lubricating flow
- Particles are coming from a component which is wearing rapidly or starting to break up
- Gives an indication of impending failure
How are vibration levels displayed?
- Displayed as a ‘Relative Amplitude’
- Relative to the amplitude measured by the manufacturer
What is the engine pressure ratio?
Ratio of the turbine outlet total pressure and the compressor inlet total pressure
As an AC climbs, what happens to N1?
- As pressure altitude increases, air density reduces meaning more thrust is required to maintain the same speed
- N1 is automatically adjusted accordingly
