Heatblur F-14 Tomcat

Engines and Throttle Controls

The F-14A is powered by two Pratt & Whitney TF30-P-414A while the F-14B is powered by two General Electrics F110-GE-400, both of which are afterburning turbofan engines.

To provide the engines with an even subsonic airflow the F-14 has the AICS or Air Inlet Control System. This system controls the variable geometry intakes by moving the variable ramps mounted in them to slow the airflow. This is accomplished using various sensor inputs run through a calculation using set schedules which decides the positions of the ramps.

In addition, the TF30 uses two systems to improve reliable operation, the Mid Compression Bypass System (MCB) and the Mach Lever.

The MCB helps mitigate high angle of attack airflow onto the compressor fans to reduce the risk of an engine stall. This system vents air from the compressor section to bypass duct to stabilize the airflow for later compressor stages. Normally this system uses angle of attack and Mach number sensor data to activate, but with the landing gear handle in the down position this it is only activated with zone 5 afterburner. Additionally the WCS commands the MCB to activate with extension of the refuelling probe as well as when launching AIM-7 or AIM-9 missiles, air to ground rockets or firing the M61 Vulcan gun.

The Mach Lever also mitigates the risk of an engine stall by controlling min and max rpm allowed as a function of Mach number. In addition it also increases the minimum rpm in high angle of attack regimes while subsonic.

The two F110s in F-14B, on the other hand, are controlled by the AFTC (Augmenter Fan Temperature Control unit). The AFTC is an early engine control computer akin to an early version of a FADEC (Full Authority Digital Engine Control) used on newer turbine engines. This system controls both the engine itself as well as the variable exhaust nozzles controlling the engine exhaust gases and removes the need for the MCB and Mach Lever for the F110. The lack of such a system in the F-14A controlling its TF30s is one of the reasons for them being deemed less reliable than the F110s.

In case of a failure in the AFTC the MEC (Main engine control) is capable of assuming control of the engines to provide a fall-back, mechanical control. The normal mode, AFTC, is the primary mode (PRI) and called as such while the fall-back MEC is the secondary (SEC) mode. The selection of primary or secondary is automatic in case of a failure in the AFTC but can also be manually selected. Of note is that in secondary mode the engine nozzles are fully closed and disabled in addition to the afterburners being disabled with a corresponding loss of engine performance.

In addition both engines also drive separate fuel, hydraulic and electric generators to create redundancy.

Note: The main difference between the TF30 and F110 engines (apart from lesser thrust in the TF30s) is that the TF30s are more sensitive to the quality of the airflow entering the compressor face. In general it is wise to avoid anything less than military power or afterburner while in high angle of attack maneuvers as well as avoiding large rudder inputs or asymmetric engine throttle settings. That said, the TF30s in the HB F-14A module have been extensively tuned using available data and SME expertise, resulting in an accurate modelling of an engine undeserving of its bad reputation. One “advantage” of the TF30’s mechanical fuel control is its high speed thrust, resulting in higher top speeds than the F110 can achieve. If flown within normal parameters, the TF30 engines behave well if a tad underpowered compared to the F110s.

Throttle Controls

The throttles in the F-14 have detents preventing unintentional engine start and shutdown and unintentional selection of afterburner. In addition the throttles also controls several different systems depending on throttle position as shown in the diagram above. The most critical of these being the fuel cutoff and ignition systems in the respective engines.

For throttle operations there are three modes:

• Manual Mode: A mechanical mode in which the engines are controlled by mechanical linkages directly from the throttles to the engines. The manual mode is designed as a backup mode and may be inexact because of the mechanical nature of the controls.
• Boost Mode: The normal mode of operation in which electrical paths control actuators moving the same engine controls as the mechanical linkages but more exactly and with lesser force required.
• Approach Power Compensator Mode (Auto Throttle Mode): A system which allows for automatic throttle control for optimal angle-of-attack during approaches.

The controls for the throttle mode are located on the inlet ramps/throttle control panel to the side of the main throttles and allows for selection of all three modes. The auto throttle mode is solenoid held and will revert to boost mode if the criteria for automatic controls are not met.

To allow selection of auto mode the throttles need to be between 75 to 90% rpm, the gear handle needs to be down and with no weight on the wheels. If these criteria are no longer met, the throttles are manually overridden with force or the Cage/SEAM button on the left throttle is depressed the solenoid releases the switch and it reverts to boost.

For additional autothrottle tune the gain of the system can be set on the inlet ramps/throttle control panel. The settings are hot, normal or cold with hot increasing the throttle gain (and effective thrust) and cold decreasing it. These settings correspond to cold or hot external temperatures but should be set according to observed throttle control.

The RATS or reduced arrestment thrust system is a system limiting engine thrust after touchdown to limit it to levels appropriate for carrier environments. The system is enabled by weight on either main landing gear and is disabled by selection of afterburner on the throttles.

Finally, and implemented only for the F110-GE-400, is the asymmetric limiter, preventing asymmetric afterburner engagement if only one afterburner lights by keeping that afterburner at minimum afterburner thrust until the other afterburner also lights.

Engine and Throttle Control Switches and Indicators

The inlet ramps/throttle control panel contains most other engine related controls.

1. THROTTLE MODE switch: Sets throttle mode to AUTO, BOOST or MAN modes respectively, with auto being spring-loaded back to boost but held in place electrically as mentioned above.
2. THROTTLE TEMP switch: Controls the gain of the automatic throttle system also described above.
3. INLET RAMPS switches: Enable (AUTO) or disable, stow (STOW) the variable intake ramps.
4. Engine crank switch: Used to crank the engines to 20% rpm allowing for engine start by moving the respective throttle to idle from cut-off. The air to start the engine is sourced from an external air supply if connected or the other engine if no external source exists. At 50% rpm the crank switch automatically returns to off/center position. If this does not occur it should be manually set to off to prevent damage to the air turbine starter.
5. BACK UP IGNITION switch: Enables the backup ignition system in case of a failure in the main ignition circuits that are normally enabled by moving the throttles out of the cut-off position.

Note: F-14B only.

1. ASYM LIMITER switch: On the ASYM limiter/engine mode select panel enables or disables the asymmetric afterburner thrust limiter. Default position is ON and the switch has a guard cover keeping it in that position.
2. ENG (engine) MODE SELECT switches: Setting the left (L ENG) and right (R ENG) to PRI, primary or SEC, secondary modes respectively.

Note: F-14A only.

The MCB Test Panel, located in the RIO pit on the right horizontal panel, is used to test if the MCB system functions. The TEST switch set to the TEST position activates the test circuit which lights the two test lights for the left and right engine respectively if their MCB circuits function.

The ENG/PROBE ANTI-ICE switch on the external environmental control panel enables the engine anti-ice and intake ramp anti-ice mode in addition to the various probe heaters. The ORIDE position enables the system, the AUTO position enables the system if icing is detected and the OFF position disable it.

Engine Instrument Group (EIG), Related Indicators and Caution Lights

The ENGINE INSTRUMENT GROUP displays engine RPM, TIT (Turbine Inlet Temperature, F-14A) or EGT (Exhaust Gas Temperature, F14B) and FF (fuel flow) to the pilot to allow for engine monitoring.

Note: Pictured above are the TF30 engine indicators, F110 EIG coming soon.

The exhaust nozzle position indicators display respective engine’s current engine exhaust nozzle position, with zero being fully closed and full clockwise rotation being fully open. The F-14A indicates 0 to 6 units while the F-14B indicates 0 to 100 percent open (tens indicated on gauge).

The oil pressure indicators display respective engine oil pressure allowing the pilot to check that engine oil pressure is at acceptable levels.

The caution lights relevant to engine operation are located on the pilot’s caution - advisory panel, and at the sides of the HUD.

The caution lights on the sides of the HUD are the engine stall warning lights which flashes at a 3 Hz rate when an engine stall is detected. The warning light on the left side of the HUD indicates an engine stall in the left engine and the one on the opposite side the right engine. This is also combined with an audio warning, a modulated tone at 320 Hz.

Below the left engine stall warning light is, amongst others, the AUTO THROT (auto throttle) caution light which illuminates for 10 seconds when the auto throttle system is disengaged by other means than the throttle mode switch.

On the main caution - advisory panel the relevant engine caution and warnings lights are:

• INLET ICE: Caution light indicating ice detection on the detector in the left engine inlet.
• L & R INLET: Caution lights indicating failure in AICS for respective variable intake system.
• OIL PRESS: Caution light indicating low oil pressure in either engine.
• BLEED DUCT: Caution light indicating hot air leakage in either engine.
• L & R RAMPS: Caution lights indicating respective engine intake ramp not being locked into position when supposed to.
• L & R GEN: Caution lights indicating that respective engine generator is inoperative.
• L & R OIL HOT: Caution lights indicating that respective engine oil is too hot.
• L & R FUEL PRES: Caution lights indicating engine fuel pressure below 9 psi in respective engine fuel boost pump.

F-14A TF30-P-414A only lights:

• L & R OVSP/VALVE: Caution lights indicating engine starter system malfunction or N1 rotor overspeed in respective engine.

F-14B F110-GE-400 only lights:

• START VALVE: Caution light indicating that the starter valve is open. Control engine crank position if lit after engine start completion.
• L & R ENG SEC: Caution lights indicating that respective engine is operating in secondary mode.
• RATS: Caution light indicating that RATS (reduced arrestment thrust system) is enabled.

Note: F-14A specific lights not yet implemented.