70-84 – (CFM56) Flashcards
Purpose of the aft eng mount?
The aft mount restrains engine movement in all directions except forward and aft.
Purpose of the fwd eng mount?
The forward mount carries the engine thrust, vertical and side loads.
Eng bearing locations?
The forward sump is in the fan frame and is the location of bearings No.1, No.2 (fan/booster shaft) and No. 3 (High Pressure (HP) shaft).
The aft sump is in the turbine rear frame where are bearings No.4 for the HP shaft aft and No.5 for the LP shaft.
Explain the main interfaces of engine control:-
FADEC is the entire system managing engine performance.
EEC/ECU is the central computer (the brain) of the FADEC, processing data and controlling the engine.
EIU is the interface that facilitates communication between the aircraft systems and the FADEC.
The ECU is dual channel, which is in control if both channels are healthy?
Active and Stand-by Channel selection alternates after
every engine start.
What happens if EIU power is lost?
If the EIU electrical power is lost, the EIU fails and engine start
or restart is not possible.
How is the ECU powered?
A/C electrical power when N2<58%.
The Permanent Magnet ALTERNATOR (PMA), which is also called Control Alternator, supplies the ECU when the engine is running and N2>58%.
What’s the max starter crank time?
The maximum starter time cycle is 2 minutes.
The starter limitations are the following:
- 4 consecutive cycles, each of 2 minutes maximum,
- Wait 20 seconds between cycles,
- after 4 cycles, wait 15 minutes before attempting a new start,
- and no running engagement of the starter when N2 is above 20%.
WHAT HAPPENS IF EGT (EXHAUST GAS TEMPERATURE) OVERLIMIT OR STALL OCCURS IN AUTOMATIC MODE
4 AUTO start attempts are made.
What 2x systems help reduce compressor surge?
Variable Bleed Valve (VBV) system and a Variable Stator Vane
(VSV) system.
Both systems are fuel operated by the HydroMechanical Unit (HMU)
and controlled by the Electronic Control Unit (ECU).
how is the clearance between the blade tips and the casings actively controlled?
The High Pressure Turbine Active Clearance Control (HPTACC)
system uses stage 4 and 9 HPC air to heat or cool the High
Pressure Turbine (HPT) shroud support structure.
How are VBV (Variable Bleed Valve) and VSV (Variable Stator Vane) controlled?
Operated by the HMU (Hydro Mechanical Unit) by the ECU (Engine Control unit.)
4 Stages of VSV and 12 VBV installed
How is VBV position calculated?
A lever, integral with a hinged door, is connected to a feedback rod,
which transmits the angular position of the door to an RVDT. This
sensor gives the position feedback to the ECU.
How many compressor stages are there?
LPC - Fan /Stage 1
Booster 2-5 (4 stages total)
HPC - 1-9
How many turbine stages are there?
LPT - 4
HPT - 1
What is bypass air known as?
secondary flow and produces up to 80% of the thrust.
