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
