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Flashcards in Jet Engine Deck (11):

What is a Hot start

When the EGT exceeds the safe limit of an aircraft, it experiences a “hot start.” This is caused by too much fuel entering the combustion chamber or insufficient turbine rpm.


What is a hung start

If the engine fails to accelerate to the proper speed after ignition or does not accelerate to idle rpm, a hung or false start has occurred. A hung start may be caused by an insufficient starting power source or fuel control malfunction.


What is EPR

An engine pressure ratio (EPR) gauge is used to indicate the power output of a turbojet/turbofan engine. EPR is the ratio of turbine discharge to compressor inlet pressure.


What is N1

N1 represents the rotational speed of the low pressure compressor and is presented on the indicator as a percentage of design rpm.


What is the parameter to set thrust between GE90 and Trent892?


N readings are more reliable due to their independence from other measured parameters. The EPR, albeit its indication of thrust, on the other hand needs carefully positioned probes, which must provide both pressure and temperature data to a computer. This EPR control depends upon two probes providing minimum 4 data, in contrast to the N sensor which needs only rotational speed data from a single sensor. In case of an inability to control thrust using EPR, the thrust control system always falls back upon a more reliable N1.


Advantages of 3-spool

-each spool works at optimal speed ->fuel efficient

-easier to start because only one shaft to be turned


How does jet engine work?

1. Intake
2. Compression
3. Combustion
4. Exhaust

The cycles occur continuously in the gas turbine


Major aircraft systems powered by hydraulics

Control surfaces
Speed brakes and ground spoilers
Auto pilots
Normal/alternate brakes
Landing gear
Nose wheel steering


What is hydraulic system

The hydraulic fluid is pumped through the system to an actuator or servo. A servo is a cylinder with a piston inside that turns fluid power into work and creates the power needed to move an aircraft system or flight control. The selector valve allows the fluid direction to be controlled. This is necessary for operations such as the extension and retraction of landing gear during which the fluid must work in two different directions.


How is pressure supplied to hydraulics system? Where's the power come from?

Pressure is supplied through a pump. The pump provides a continuous flow of fluid which covert hydraulic pressure into mechanical energy.

The Boeing 777 is equipped with three hydraulic systems. Primary hydraulic power for the left and right systems is provided by two EDPs (engine driven pump)and supplemented by two on-demand ACMPs(AC motor pump). Primary hydraulic power for the center system is provided by two ACMP and supplemented by two on-demand air turbine-driven pumps (ADP). The center system provides hydraulic power for the engine thrust reversers, primary flight controls, landing gear, and f laps/slats. Under emergency conditions, hydraulic power is generated by the ram air turbine (RAT), which is deployed automatically and drives a variable displacement inline pump. The RAT pump provides flow to the center system flight controls.


What is the pressure of hydraulic?

In a 777, The left, center, and right systems deliver hydraulic fluid at a rated pressure of 3,000 psi (207 bar) to operate flight controls, f lap systems, actuators, landing gear, and brakes.