Hello everyone, time for some get-to-know for the F/A-18C engines and the related monitoring systems. I’ll run over the most important functionalities in this article, although for more details it is suggested to read the official A1-F18AC-NFM-000 manual which is available on internet and watch the ED’s cockpit walkthrough video for the cockpit panels and switches locations.

ENGINES

The aircraft is powered by two General Electric engines: the F404-GE-402. The military thrust of each F404-GE-402 engine is approximately 10,900 pounds with maximum afterburner thrust in the 18,000-pound class. The aircraft thrust-to-weight ratio is in the 1 to 1 class. The engine is a low bypass axial-flow turbofan with afterburner. The three-stage fan (low-pressure compressor) is driven by a single stage turbine. Approximately one-third of the fan discharge air is bypassed to the afterburner for combustion and cooling. The seven-stage high-pressure compressor is also driven by a single stage turbine. The first and second stage compressor stators are variable. Fourth stage compressor air is used by the engine anti-ice system. A set of variable inlet guide vanes are mounted in front of both the fan and compressor to direct the inlet air at the best angle for the existing engine operation. Atomized fuel and compressor discharge air is mixed and ignited in the combustion chamber. These ignited gases then pass through the compressor and fan turbines and out the engine exhaust. Afterburner operation uses added atomized fuel mixed with the combustion discharge gases and the bypass fan discharge air to produce additional thrust. The electrical control assembly, variable exhaust nozzles, main fuel control, and afterburner fuel control provide coordinated operation of the engine through every part of its envelope. The engine accessory gearbox, driven by the compressor rotor, powers the lubrication and scavenge oil pumps, variable exhaust nozzle power unit, alternator, main fuel pump and control, and afterburner fuel pump and control. An aircraft-mounted auxiliary power unit is used to start the engines.

The electrically operated inlet duct doors (one for each inlet) automatically open at Mach 1.33 (accelerating) and close at Mach 1.23 (decelerating). The doors are controlled by the flight control computer.

ENGINE CONTROL SYSTEM

The engine control system consists of the throttle, main fuel control, electrical control assembly (ECA) and afterburner fuel control. Throttle movement is mechanically transmitted to a power lever control. The power lever control acts as a power booster and positions the main fuel control. If the automatic throttle control is engaged, it schedules the power lever control for existing engine power requirements and the throttle follows this movement. Below MIL power, throttle movement and compressor inlet temperature (through the main fuel control) control the compressor speed (rpm). At MIL and above, fan speed is controlled by the ECA as a function of inlet temperature. At and above military power, the ECA senses engine and aircraft parameters computes engine schedules and maintains engine limits.

IGNITION SYSTEM

The ignition system contains an independent engine mounted alternator, electrical control unit, ignition exciter, the main igniter and an afterburner igniter. During engine start, moving the throttle from OFF to IDLE turns on the ignition. Ignition remains on until the engine reaches 45% rpm. Engine ignition also comes on if a flame-out occurs or when the afterburner is selected. Afterburner ignition comes on when the throttle is moved into afterburner and remains on until an afterburner light-off is sensed. If more than 50% afterburner is selected, ignition is automatically turned on if an afterburner blowout occurs.

ENGINE CRANK SWITCH

An engine crank switch is on the left console. The switch has positions of L (left), OFF and R (right). During engine start, placing the switch to L or R starts engine crank for the corresponding left or right engine. The switch is electrically held in the L or R position. As the engine accelerates to a self-sustaining rpm, the switch automatically returns to OFF.

Ensure engine speed is below 30% N2 before actuating the engine crank switch. Failure to do so may shear the air turbine starter shaft.

THROTTLE

Movement of the throttles is transmitted by mechanical linkage to the engine mounted power lever controls. The engine mounted power lever controls convert the linear mechanical movement from the throttles to rotary motion that moves the fuel control input arms. During manual operation, pneumatic throttle boost actuators powered by environmental control system (ECS) air reduce the force required to move the throttles. During automatic throttle control(ATC) operation, the pneumatic boost actuators are disengaged. A friction adjusting lever is mounted next to the right
throttle. Advancing the throttles from OFF to IDLE (during engine start) opens the engine fuel control shutoff valves and activates engine ignition. Finger lifts, on the front of each throttle, must be raised to place the throttles OFF. With weight on the wheels, launch bar retracted and the arresting hook UP or with the weight off the wheels, afterburner operation is initiated by advancing the throttles through the MIL detent gates into MAX. On the ground, an afterburner lockout system helps guard against inadvertent afterburner selection. With weight on the wheels and launch bar extended or the arresting hook DOWN, the afterburner lockout extends and the finger lifts must be raised or a force of approximately 32 pounds must be applied before the throttles can be moved to MAX. A retractable in-flight IDLE stop extends with the weight off the wheels and provides a higher IDLE rpm and reduced acceleration time to MIL. During high g manoeuvres when moving the throttle to idle, the flight idle stop may retract and allow selection of ground idle. With weight on the wheels, the in-flight stop is retracted and the ground IDLE stop is used. Moving the throttles to OFF closes the engine fuel control shutoff valves, stopping fuel flow to the engines.The throttle grips contain switches that provide various systems control without moving the hand from the throttles.

 

Dispense Switch

The dispense switch is located on the top inboard side of the right throttle. The switch is used to dispense flares and chaff.

                                         ALE-47 Countermeasure System

Forward     Provides semi-automatic consent. Dispenses chaff singles (C/F mode).

Center       OFF

Aft             Initiates the selected manual program. Dispenses flare singles (C/F mode).

Integrated Fuel/Engine Indicator (IFEI) Engine Display

If one or more of the engine parameters are blank or frozen, that parameter may be invalid. If the parameter is invalid, the associated engine caution will be inhibited.

The integrated fuel/engine indicator (IFEI) engine display, located on the lower left side of the main instrument panel, contains a left and right liquid crystal display for RPM(N2)%, TEMP(EGT)°C , FF (fuel flow) PPH, NOZ (nozzle position)%, and OIL (oil pressure) psi. During engine starts without external electrical power, only RPM and TEMP are displayed by battery power until the APU comes online. With the APU online or external power, all engine data is displayed. If the IFEI stops receiving data from the signal data computer, the IFEI flashes the last data received until communication with the signal data computer is restored.

RPM                Displays engine N2 rpm from 0 to 199%.

TEMP               Displays turbine exhaust gas temperature (EGT) from 0 to 1,999°C.

FF                   Displays main engine fuel flow only (afterburner fuel flow is not displayed).

NOZ                Displays exhaust nozzle position from 0 to 100% open in 10% increments.

OIL                 Displays engine oil pressure from 0 to 195 psi in 5 psi increments.

 

Engine Monitor Display (EMD)

If one or more of the engine parameters are blank or frozen, that parameter may be invalid. If the parameter is invalid, the associated engine caution will be inhibited.

The engine monitor display may be selected on either DDI by pressing MENU, then pressing ENG. LEFT EPE and RIGHT EPE appear at the top line of the EMD. If a malfunction exists, pressing RECORD will assist the ground crew during troubleshooting.

INLET TEMP                 Engine inlet temperature in °C.

N1 RPM                       Fan speed in % rpm.

N2 RPM                       Compressor speed in % rpm.

EGT                           Exhaust gas temperature in °C.

FF                              Fuel flow in pounds per hour.

NOZ POS                    Nozzle position in %.

OIL PRESS                  Oil pressure in psi.

THRUST                     Thrust in %.

VIB                           Engine vibration in inches per second.

FUEL TEMP                Engine inlet fuel temperature in °C.

EPR                          Engine pressure ratio (ratio of exhaust pressure to ambient inlet                                       pressure).

CDP                         Compressor discharge pressure in psia.

TDP                         Turbine discharge pressure in psia.

Caution and Advisory Displays

L or R OVRSPD                           Designated fan or compressor rpm high.

L or R EGT HIGH                         Either engine EGT over limit.

L or R IN TEMP                           Designated engine inlet temperature is out of limits.

L or R STALL                              Stall detected.

L or R FLAMEOUT                       To prevent false cautions the system is deactivated until                                                    after normal engine start and anytime the throttle is                                                        placed below IDLE.

INLET ICE                                 Icing condition in either engine inlet.

L or R DUCT DR                        Designated inlet duct door closed above Mach 1.33 or                                                       open below Mach 1.23.

L or R OIL                                PR Designated engine oil pressure out of limits.

L or R BOOST                           LO Designated fuel boost pressure low.

ADVISORY
L or R HEAT Designated engine anti-ice switch ON

Automatic Throttle Control (ATC)

The automatic throttle control is a two-mode system that automatically maintains the angle of attack (approach mode) or airspeed (cruise mode) by modulating engine thrust in the range of flight idle through military. The automatic transition between the two modes or single-engine engagement is not possible. When either mode is engaged, the ECS air to the torque boosters is shut off, the throttles are initially backdriven, a stop is extended in the power lever control (PLC) to limit throttle travel from flight idle to MIL, and an ATC advisory is displayed on the HUD. If either mode does not engage when selected, or automatically disengages after engagement, the ATC display flashes for 10 seconds and is then removed from the HUD. If a force of approximately 12 pounds (with friction off) is applied to either throttle the system automatically disengages. This force is sufficient to permit the hand to follow throttle movement without causing disengagement. It is recommended that the friction lever be in the full aft position and both throttles set between flight idle and MIL before engaging ATC. If a mechanical failure occurs, a force of approximately 68 pounds (with friction off) is required to override the system. When either mode is engaged, changing the FLAP switch between AUTO and HALF or FULL automatically disengages the system. If the system is disengaged for any reason, it remains disengaged until reengagement is initiated by the pilot.

NOTE

Momentary force applied to the throttle(s) (throttle rap) may not disengage the ATC system. The force must be applied and held for a minimum of 0.10 second.

If the ATC commands the throttles to MIL, it may not be possible to manually advance the throttles into the afterburner range without first disengaging the ATC through momentary throttle reduction using more than 12 pounds of force.

If the throttle(s) are being held against the flight idle or MIL stop as ATC is disengaged, the stops may not disengage until pressure is removed from the throttle(s).

 

ATC Approach Mode

The ATC approach mode is engaged by pressing and releasing the ATC button on the left throttle with the FLAP switch in HALF or FULL and the trailing edge flaps extended at least 27°. When ATC is engaged in the approach mode, the flight control computer modulates engine thrust to maintain on-speed AOA. The computer uses inputs of AOA, normal load factor, stabilator position, pitch rate, and angle of bank to generate command signals. These signals drive the engine mounted throttle control units which in turn command the engine fuel controls. The computer uses AOA as the primary input to generate command signals. However, normal load factor provides increased stability, stabilator position provides increased or decreased thrust for pilot induced pitch changes, pitch rate provides lead during pitch manoeuvres, and bank angle provides additional thrust during banking maneuvers. Normal disengagement is accomplished by pressing the ATC button or applying and holding the force to either throttle.

Automatic disengagement occurs for the following reasons:

  • Flap AUTO up
  • AOA sensor failure
  • Two or more failures of either trailing edge flap
  • Trailing edge flap deflection less than 27°
  • ATC button fails
  • FCES channel 2 or 4 fails
  • WOW FCS reversion to MECH or to DEL in any axis
  • Left and right throttle angles differ by more than 10° for more than 1 second
  • Bank angle exceeds 70°
  • Any internal system failure
  • Selection of GAIN ORIDE

 

ATC Cruise Mode

The ATC cruise mode is engaged by pressing and releasing the ATC button on the left throttle with the FLAP switch in AUTO. When ATC is engaged in the cruise mode, the existing airspeed is used by the flight control computer to modulate engine thrust to maintain this existing airspeed. The existing airspeed is the airspeed being sent from the ADC to the flight control computers via the mission computers. An ADC failure inhibits the ATC cruise mode of operation. The FCC uses true airspeed from ADC via the mission computers at the time of engagement to generate a command signal. This signal is then used as a reference to generate an error signal that drives the engine mounted throttle control units. Normal disengagement is accomplished by pressing the ATC button or applying and holding force to either throttle.

Automatic disengagement occurs for the following reasons:

  • Flaps HALF or FULL ATC button fails
  • FCES channel 2 or 4 fails
  • FCS reversion to MECH or to DEL in any axis
  • Left and right throttle angles differ by more than 10° for more than 1 second
  • ADC true airspeed failure
  • ADC degrade
  • Any internal system failure

Now, that’s it for today, I know this is a heavy technical know-how stuff, but it the bare minimum stuff that a prospective virtual Hornet pilot can be expected to know. Next article will be on fuel and introduction to FCS.

Happy Hunting!!

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As a kid, I grew up on MiG airbases and was literally hooked to the smell of jet fuel in the morning. And ever since, I am in love with aviation and everything related to it.

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