On Condition Maintenance

航空

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航空

On Condition Maintenance
• Modern commercial turbofan engines are designed for, and
usually maintained using on condition maintenance plans
– The engine is serviceable when is installed
– Periodic inspections are done, using several methods
• Borescope inspections
• External inspections
• Magnetic Chip Detector inspection
• Trend Monitoring and Analysis
– Results are compared to limits in Maintenance Manuals
– The engine is serviceable, or unserviceable, based upon the results
of these inspections
On-Condition Maintenance Program
• On wing maintenance (Flight line maintenance)
– Scheduled on wing inspection programs
• Engine hardware inspections
• Borescope inspections
• MCD inspections
– Troubleshooting and fault correction (Unscheduled)
• On-condition workscoping and performance restoration
– Performance removal decision
• Trend Monitoring Data (SAGE)
• Results of on-wing inspections
– On condition workscope planning
• Life Limit Parts (LLP) control
Engine Thrust is Found via the Conservation of
Axial Momentum, i.e. Momentum Balance
Po
Wo, Vo
PS8
FN W8, V8
CONTROL VOLUME
FN = W8 * V8 + A8 (PS8-P0) - W0 * V0
NOZZLE RAM
GROSS THRUST DRAG
Thrust is produced by accelerating a mass of air
Core Versus Booster Airflow
N2K25
Airflow Versus Corrected Core Speed
Airflow - lb/sec
Booster Flow
Core Flow
60 70 80 90 100
CFM56-7B Thrust increase
10 20 30 40 50 60
Ambient
temperature
7B18
7B26
7B24
7B22
7B20
7B27
7B26/B1
7B24/B1
7B22/B1
7B27 Bump according to
N1, EGT, N2 Versus TAT
Thrust increase versus 7B27
10 20 30 40 50 60
Ambient temperature
4
3
2
1
5
N1 limited EGT limited N2 limited
%
Typical T/O condition: Sea level / 0.25 Mn
CFM56-7B27 Thrust increase
Engine Performance Principles (1)
• CF6 and CFM56 engines are controlled
with N1 as the power setting parameter.
For any flight condition: as N1 is
increased, engine thrust is increased.
• The increased N1 and thrust are
achieved by adding energy to the system
in the form of fuel.
• As thrust and fuel flow are increased,
engine exhaust gas temperature (EGT)
increases.
Fuel Flow
Thrust
or N1
EGT
Thrust or N1
Thrust
Fan Speed (N1)
Engine Performance Principles (2)
• As an engine deteriorate or damage
occurs: the efficiency of the engine
cycle is decreased.
• Lower efficiency results in more fuel
and higher temperature being required
to achieve the same N1 or thrust.
• Engine Performance Monitoring”
involves monitoring the change in these
parameters (EGT, Fuel Flow, N2, etc.)
at constant fan speed NI.
Thrust or N1
EGT
Fuel
Flow
Thrust or N1
Takeoff EGT Margin and OATL
EGT
FRT TAT
EGT Redline
EGT
Margin
OATL
Engine
Performance
Deterioration
OATL
Takeoff EGT Characteristics
Constant
Thrust
Decreasing
Thrust
N1
TAT FRT
Constant
Thrust Decreasing
Thrust
Thrust
TAT FRT
EGT
TAT FRT
Increasing
EGT
Constant
EGT
To meet aircraft performance requirements,
the engine is designed to provide a given
thrust level to some “flat rate” temperature
(FRT). At temperature above FRT, thrust
decreases and aircraft performance is
adjusted accordingly
N1 for power management schedule
increases with TAT (up to FRT) to maintain
constant thrust. After FRT, power
management N1 (and thrust) decreases
EGT increases with TAT to FRT, then
remains constant.
09.04.11 CFMI Proprietary Data -
Unauthorized disclosure prohibited
11
Flat Rated Concept - Thrust Rating Versus Ambient
Temperature
-10 0 10 20 30
40
Rated Thrust at
Sea Level Standard
Full Throttle not to be
used below Flat Rated
Temperature Range
Part Throttle Range
Full Throttle
Range
“Part Throttle” Flat Rated Engine
Flat Rated
Temperatur
e
Full Throttle Below Std. Day
Temp. - Thrust Exceed Rated
Level
Full Throttle Above Std. Day
Temp. - Thrust Drops Below
Rated Level
Rigged to Rated
Thrust at Full
Throttle Under Sea
Level Standard
Conditions
“Full Throttle” Engine
-10 0 10
20

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On Condition Maintenance