R R Control Limits for Control System Figure 009
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Each channel receives its dedicated N1 and N2 speed signal, but can operate with cross channel data. The governors operate valid signal only. Although aerodynamically limited, N1 is also protected by a VSV failure closure when N1 reaches an overspeed. This limits the energy to the LP rotor and limits its maximum speed to a lower aerodynamic value.
(3) EGT Limit Protection During starting sequences the ECU monitors EGT. (Ref. 80-00-00)
D. Power Management
(1) Rating Control
(a) ECU integrates all the engine thrust setting curves to provide automatic engine thrust ratings control. ECU computes power management LIMIT and COMMAND parameters. These parameters are available for the following engine thrust modes :
- MAXIMUM TAKE-OFF and GO-AROUND (TO/GA)
- FLEXIBLE TAKE-OFF (FLX TO)
- MAXIMUM CONTINUOUS (MCT)
- MAXIMUM CLIMB (MCL)
- IDLE
- REVERSE.
The rating distribution in the flight envelope is given in the
referenced illustration.
(Ref. Fig. 010)
All transition are blended and automatic.
The rating structure is based on EGT limits hold above corner
point and thrust flat rated below corner point.
The implementation is done by controlling the corrected Fan speed
which correlates closely with thrust at given Mach number and
altitude.
For all ratings (take off, max continuous and max climb ratings)
, the ECU controls the FAN speed corrected to total temperature.
That corrected fan speed is a function of:
- ambient static pressure PO for altitude effect.
- delta ambient temperature delta TO for temperature effect
- mach number ECS bleed and anti-ice bleed are also taken into account by the ECU to compute the corrected fan speed at a given rating. ECS bleed is taken into account by a Delta N1K applied to the N1K computed from the rating curves. (Ref. Fig. 011) The intent is to keep the same EGT with and without ECS bleed.
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Rating Distribution Figure 010
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R R ECS Bleed Effect Figure 011
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E E Anti-icing bleeds are taken into account by a delta ambient temperature applied to the real one. This has for effect to translate the corner point. (Ref. Fig. 012) Engine rating is defined by the configuration of a rating plug on the ECU. The ECU will identify the rating available. ECU will have memory provisions for several different engine ratings.
(b) Flex Take-off FLEXIBLE TAKE-OFF rating is set by the assumed temperature method with the possibility to insert any assumed temperature value higher than the maximum one certified for engine operation to provide for the maximum derate allowed by the certifying Authorities. The purpose is to obtain reduced thrust operation. FADEC permits: Flexible take-off procedure with constant retarded throttle lever position, allowing the application of full take-off power when full forward throttle lever position is selected. At this given retarded throttle lever position, and in the flex TO mode, the FADEC assures that the thrust obtained all along the FLEXIBLE TAKE-OFF at ambient temperature (T1) and with assumed temperature (TA), is the same as thrust obtained during MAXIMUM TAKE-OFF at TA actual ambient temperature.
(c) Idles The FADEC controls idle speed : MINIMUM IDLE sets the minimum fuel flow requested for ensuring correct aircraft ECS system pressurization as defined in the referenced illustration and compatible with specific system requirements, such as : (Ref. Fig. 011)
- Aircraft Configuration
- Minimum Aircraft Accessories Speed
- Bleed for engine de-icing
- Minimum permissible core speed
- Maintain engine oil temperature within max limits.
APPROACH IDLE is set at an engine power which allows the engine
to achieve the specified GO-AROUND acceleration time. APPROACH
IDLE is set in response to an aircraft request signal.
(d) Reverse (Ref. Fig. 013) The FADEC controls the engine thrust rating during reverser operation. Engine power is set automatically by the ECU to the level required for correct deploy and stow operations in all ambient conditions.
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