Chp 3 ( Electrical And Indicating System) Flashcards
Why is it important for pilots to monitor engine conditions?
It enables them to monitor engine performance and recognize any impending failure, allowing necessary action to prevent an air incident.
What systems are monitored on a basic GTE?
- Engine Temperature (JPT, TIT, TET, EGT, TGT, T6)
- Oil Pressure and Oil Temperature
- Engine RPM (N, RPM%)
- Torque %
- EPR (Engine Pressure Ratio)
- Fuel Flow
- Vibration
How is Jet Pipe Temperature (JPT) monitored?
It is monitored by a totally independent system that takes a signal from either a set of thermocouples or pyrometers.
What are thermocouples?
Thermocouple probes transmit the temperature signal to the indicator and consist of two wires of dissimilar metals joined together inside a metal guard tube.
How do thermocouples generate a signal?
As heat is applied to the junction of the two wires, a small electrical current is generated, which is transmitted to a junction box, amplified, and displayed in the cockpit as degrees Celsius.
What materials are typically used for thermocouple wires?
They are usually made from nickel-chromium and nickel-aluminium alloys.
What is a pyrometer?
A pyrometer is an optical device that views the turbine blades and is connected to an infra-red detector via a fibre optic cable.
What does a pyrometer measure?
It enables a rapid, accurate measurement of temperature.
What is required for the proper functioning of a pyrometer?
It requires a supply of bleed air to keep the lens clean and sophisticated signal processing.
Why is oil pressure and temperature measurement essential?
It is essential for correct and safe operation of the engine.
How is oil temperature sensed?
Oil temperature is sensed by a temperature sensitive element fitted in the oil system.
What happens when there is a change in oil temperature?
A change in temperature causes a change in the resistance value, leading to a corresponding change in current flow at the indicator.
How is oil temperature displayed?
The indicator pointer is deflected by an amount equivalent to the temperature change and recorded on the gauge in degrees Celsius.
How is oil pressure transmitted?
Oil pressure is electrically transmitted to an indicator on the instrument panel.
What types of indicators are used for oil pressure?
Some installations use a flag-type indicator, while others use a dial-type gauge calibrated in pounds per square inch (p.s.i.).
How is engine RPM measured?
A small electrical generator driven from the external gearbox produces alternating current that drives a motor within the cockpit instrument.
What does the cockpit instrument do with the engine RPM?
The rotary motion is converted into linear motion of an indicating gauge.
What do cockpit gauges typically read?
Cockpit gauges may read engine and/or main rotor RPM as a percentage figure of the normal operating RPM, or actual RPM.
What additional RPM information may be shown on multi-spool engines?
Individual spool speeds on multi-spool engines (N1, N2 etc.) may also be shown.
What is Engine Torque?
Power produced by a Turbo-Prop or Turbo-Shaft engine, indicated as Engine Torque and displayed in the cockpit as Torque Pressure (psi) or Torque Percentage. Pilots can use this indication to monitor engine health and performance.
What is EPR?
Engine Pressure Ratio (EPR) is used as a performance or thrust setting instrument on larger aircraft with Turbo-Jet or Turbo-Fan engines, measuring the ratio between turbine discharge pressure and compressor inlet pressure.
How does a Gas Turbine Engine produce thrust?
It increases the pressure energy of a gas and converts it into kinetic energy in the form of high velocity exhaust, creating a reacting force referred to as thrust.
What does fuel flow indication indicate?
The rate of fuel consumption can indicate satisfactory engine operation; too low or too high for a given EGT/RPM could point to a system fault.
How is fuel flow sensed in a gas turbine engine?
By a transmitter situated in the fuel supply to the engine, which consists of two cylinders placed end to end, guiding fluid through an impeller and a turbine.
What drives the impeller in the fuel flow transmitter?
A synchronous motor, which is hermetically sealed to prevent fuel contact with electrical wiring.
What does the impeller do to the fuel?
It gives the fuel a velocity at right angles to the direction of fuel flow, changing the momentum of the fuel.
How is angular velocity maintained in the fuel flow transmitter?
It is held constant due to the fixed rate of rotation of the impeller, making the change in angular momentum directly proportional to the change in mass of fuel flowing.
What happens to the torque exerted by the fuel?
The fuel exerts a torque proportional to the mass rate of flow, which tends to turn the turbine against restraining springs.
What converts the movement of the turbine to a cockpit signal?
A magnesyn transmitter attached to the turbine converts the amount of movement to a signal for cockpit indication.
How is fuel flow displayed in the cockpit?
Fuel flow is displayed on an instrument indicating the rate of flow in pounds or kilograms per minute or hour. Each engine has its own indication.
What does a change in vibration indicate in turbo-jet or turbo-shaft engines?
A change in vibration can indicate the impending failure of an engine component.
How is vibration typically sensed in engines?
Vibration is typically sensed by piezoelectric accelerometers that produce an electric current when squeezed by vibration forces.
What can vibration detection systems do?
They can activate a cockpit warning if a predetermined level of vibration is reached or record/display the frequency of vibration for source identification.
How has modern technology changed cockpit instrumentation?
Modern technology allows all instrumentation to be displayed on one LCD screen, including navigation and weapons.
What feature do the latest cockpit designs include?
The latest designs can include voice activation for the display.
