Engine Controls and Control Systems

In document NATOPS Flight Manual Navy Model C-130T Aircraft (Page 87-98)

Systems and Equipment

2.1.7 Engine Controls and Control Systems

Engine control in the flight range of operation is based on regulation of engine speed by propeller constant-speed governing and control of torque through regulation of fuel flow. Note that the throttle acts only as a power control.

It exercises no direct control over the propeller, which is controlled entirely by the propeller regulator to regulate engine speed and to limit the low blade angle. The fuel control regulates the rate of increase and decrease of fuel metering for acceleration and deceleration. The TD control system functions at all throttle positions (MAXIMUM REVERSE through TAKE-OFF) either as a temperature-limiting or a temperature-controlling system. When performing temperature limiting, the system operates to prevent overtemperatures by “taking” a portion of fuel flow when maximum allowable TIT is exceeded. When performing temperature controlling (past 65_ of throttle travel, fuel correction lights out), it adjusts fuel flow to obtain the desired temperature. This is accomplished by using a voltage signal from a potentiometer, positioned by the throttle, as a reference for desired TIT. The system compares this reference with actual TIT and adjusts fuel flow to obtain the desired temperature. The TD control system may be operated to provide a fixed correction of fuel flow. By positioning the TEMP DATUM CONTROL VALVE switches in LOCKED while the throttles are in the temperature-controlling range, all of the TD control valves are locked in the position in which they have been set by the temperature-controlling systems. When the TEMP DATUM CONTROL VALVE switches are positioned in LOCKED, the electronic fuel correction warning lights should remain out through all throttle movements. Should an overtemperature condition occur, the light, or lights, will come on indicating that a “take” signal has been initiated, that the TD valve brake has been released, and that fuel correction has been lost. The light will stay on until the TD system is reset. In throttle positions below FLIGHT IDLE, the throttle selects propeller blade angle as well as fuel flow. The TD control system still functions to limit TIT.

An engine is stopped by closing a fuel shutoff valve on the fuel control. The valve is closed electrically when the condition lever is at GROUND STOP if the control circuit is completed through a landing gear touchdown switch, when the condition lever is pulled to FEATHER, or when the fire emergency handle is pulled. The valve is also closed mechanically when the condition lever is pulled to FEATHER. Propeller feathering can be accomplished by pulling the condition lever to FEATHER, or by pulling the fire emergency handle.

For starting an engine, a speed-sensitive valve and a speed-sensitive control, which contains three speed-sensitive microswitches, provide automatic control of all functions involved in the starting cycle. The speed-sensitive switches turn on the fuel, control ignition, parallel fuel pump elements, initiate starting fuel enrichment, close a manifold drip valve, and switch the electronic datum control system from starting limiting to normal limiting. The speed-sensitive valve controls the compressor bleed valves. These operations are timed according to engine speed to ensure that the proper sequence of starting operations is followed. For airstarts, the engine condition lever operates switches that start the propeller feather pump motor to provide pressure to decrease the propeller blade angle and to apply power to the speed-sensitive control, energizing fuel and ignition control circuits.

2.1.7.1 Throttles

The throttles (seeFigures 2-3and2-4)are quadrant mounted on the flight control pedestal. Throttle movements are transmitted through mechanical linkage to an engine-mounted coordinator. The coordinator transmits the movements through mechanical linkage to the propeller and to the engine fuel control, and it also actuates switches and a potentiometer that affect electronic TD control system operation. Each throttle has two distinct ranges of movement, taxi and flight, that are separated by a stop (seeFigure 2-3). Both ranges are used for ground operation, but the taxi range must not be used in flight. In the taxi range, the throttle position selects a propeller blade angle and a corresponding rate of fuel flow. In the flight (governing) range, throttle position selects a rate of fuel flow and the propeller governor controls propeller blade angle. The throttles have four placarded positions as follows:

1. MAXIMUM REVERSE (0_ travel) gives maximum reverse thrust with engine power approximately 40 percent of takeoff power.

2. GROUND IDLE (approximately 18_ travel) is a detent position. This is the ground-starting position at which blade angle is set for minimum thrust.

Note

Throttles must not be moved out of GROUND IDLE detent during ground starting because the resultant increase in propeller blade angle might overload the starter, reducing the rate of engine acceleration.

Figure 2-3. Engine Control Quadrant

Figure 2-4. Flight Control Pedestal

3. FLIGHT IDLE (34_ travel) is the transition point between the taxi and flight (governing) ranges. A step in the quadrant limits aft travel of the throttle at this position until the throttle is lifted.

4. TAKE-OFF (90_ travel) is the maximum power position.

The throttle quadrant is also divided into two unmarked ranges with respect to control of the electronic TD control system. The crossover point is at 65_ throttle travel, at which point the switches in the coordinator are actuated. Below this point, the electronic TD control system is limiting TIT. Above this point, it is controlling TIT if the TD valve switches are in the AUTO position.

2.1.7.2 LOW SPEED GROUND IDLE Control Buttons

Four LOW SPEED GROUND IDLE control buttons (seeFigure 2-5) on the control pedestal may be pushed in to reduce engine rpm to approximately 72 percent at any time the throttles are in the range between 9_ and 30_. The low speed ground idle buttons send a signal to the fuel topping governor on the fuel control, to reduce fuel flow to the engine. This allows the fuel nozzles to cool down and extends engine life. In addition, this allows the aircraft to taxi at a slower speed without having to use excess braking. Moving the throttles out of this range will automatically disengage the LOW SPEED GROUND IDLE buttons. Power is supplied from the essentialdcbus through the LOW SPEED GND IDLE circuit breakers on the copilot side circuit breaker panel.

Figure 2-5. Low-Speed Ground Idle Buttons

CAUTION

D With engines in low-speed ground idle, movement of throttles beyond the limits of 9_ to 30_ (coordinator angle) at ambient temperatures above 80 _F may cause engine stall and overtemperature. Therefore, the recom-mended procedure for coming out of low-speed ground idle is to disengage the buttons manually with the throttles in GROUND IDLE detent.

D If all four engines are operated at low-speed ground idle, the APU generator must be on since the engine-driven ac generators will not supply ac power.

If theAPUgenerator fails and the BUS TIE switch is in the TIED position, the LOW SPEED GROUND IDLE buttons must be disengaged manually in order to restore ac power and to prevent a drain on the battery. If the BUS TIE switch is not in the TIED position, the LOW SPEED GROUND IDLE buttons will disengage automatically.

2.1.7.3 Throttle Friction Knob

A friction knob (seeFigure 2-4) on the throttle quadrant adjusts the amount of friction applied to the throttles to prevent creeping or accidental movement.

2.1.7.4 ENGINE CONDITION Levers

Four pedestal-mounted condition levers (seeFigure 2-4) are primarily controls for engine starting and stopping and propeller feathering and unfeathering. They actuate both mechanical linkages and switches that provide electrical control. Each lever has four placarded positions as follows:

1. RUN is a detent position. At this position, the lever closes a switch that places engine fuel and ignition systems under control of the speed-sensitive control. For engines No. 2 and No. 3, the ice-detection system is energized.

2. AIRSTART is a position attained by holding the lever forward against spring tension. In this position, the lever closes the same switch closed by placing the lever at RUN and, in addition, closes a switch that causes the propeller feathering pump to operate.

3. GROUND STOP is a detent position. In this position, the lever actuates a switch that causes the electrical fuel shutoff valve on the engine fuel control to close only if the landing gear touchdown switches are closed. The switch also closes the nacelle preheat control circuit making this system operable, if installed.

4. FEATHER is a detent position. When the lever is pulled toward this position, mechanical linkages transmit the motion to the engine-mounted coordinator and from the coordinator to the propeller and to the shutoff valve on the engine fuel control. Switches are also actuated by the lever as it is pulled aft. The results of moving the lever to FEATHER are the following:

a. The propeller receives a feather signal and mechanically and electrically energizes the feather solenoid valve.

b. The fuel shutoff valve on the engine fuel control is closed both mechanically and electrically.

c. The propeller feathering pump is turned on.

d. The nacelle preheat system remains operable only when the aircraft is on the ground (if installed).

CAUTION

When pulling a condition lever to FEATHER, pull it all the way to the detent to ensure that the propeller is fully feathered when the engine fuel is shut off. If the lever is left at midposition and the NTS is inoperative, an engine decoupling is possible.

2.1.7.5 TEMP DATUM CONTROL VALVE Switches

Four temperature datum control valve switches (seeFigure 2-6) are mounted on a control panel on the flight control pedestal. Each switch has AUTO, LOCKED, and NULL positions. The switch positions are used as follows.

The AUTO position permits normal operation of the electronic TD control system by applying single-phase, ac power to the amplifier through a FUEL & TEMPERATURE CONTROL circuit breaker on the pilot lower circuit breaker panel.

The LOCKED position may be set when the throttles are in temperature-controlling range, to provide a fixed-percentage correction on the metered fuel flow throughout the engine operating range and will permit the fuel control to compensate for changes in ambient temperatures in order to maintain a symmetrical shaft horse-power at flight idle. If the TD control valve switch is then positioned at LOCKED, the TD valve is locked at whatever position it is in at the time. The TD valves remain locked and the fuel correction lights remain out through all throttle movements, unless an overtemperature condition is sensed by the amplifier. When the switch is in the AUTO or LOCKED position, the TD valve for an engine is unlocked and set to a “take” position if TIT for the engine exceeds approximately 1,083 _C. If a valve is unlocked by its control system to correct an overtemperature condition, the fuel correction light for that engine comes on to indicate that the valve is unlocked.

Figure 2-6. Temperature Datum Control Valve Panel

Note

The switches lock the TD valves only when they are positioned at LOCKED while the throttle is in temperature-controlling range and the fuel correction light is out.

The NULL position removes ac power from the control system amplifier; the TD valve, receiving no control signals, returns to its null position so that it does not correct the fuel flow according to TIT. The TD valve brake is released by dc power supplied through a FUEL & TEMPERATURE CONTROL circuit breaker on the pilot lower circuit breaker panel.

The NULL position of these switches is used to deactivate the control systems when erratic fuel scheduling is suspected or when the engines are not operating.

2.1.7.6 Electronic Fuel Correction Lights

The four amber press-to-test ELECTRONIC FUEL CORRECTION lights (seeFigure 2-7) are located on the pilot instrument panel. The lights are illuminated in the temperature-limiting range (throttles below 65_) and extinguished in the temperature-controlling range (throttles above 65_), if the TEMP DATUM CONTROL VALVE switches (see Figure 2-6) are in the AUTO position. The lights will be illuminated below 65_ throttle and extinguished above 65_

throttle, but will illuminate again if temperature limit is reached when the TEMP DATUM CONTROL VALVE switches are in the LOCKED position.

Figure 2-7. Electronic Fuel Correction Lights

2.1.7.7 Starting Control System

The starting control system (Figure 2-8) automatically controls fuel flow and ignition during ground and air starts.

Electrical power for the control circuits is supplied from the essential dc bus through engine START CONTROL circuit breakers and the IGNITION CONTROL circuit breakers on the copilot side circuit breaker panel. The

automatic control of the starting control system has a speed-sensitive control and a speed-sensitive valve, which is engine-driven and performs the following functions:

1. On acceleration to 16-percent rpm — The fuel shutoff valve in the engine fuel control is opened, the ignition relay is energized completing circuits to the ignition exciter, the engine fuel pump paralleling valve closes, the fuel enrichment valve opens, and the manifold drip valve closes.

2. On acceleration to 65-percent rpm — Ignition system is deenergized, fuel pump paralleling valve is opened to return pumps to series operation, manifold drip valve is deenergized (it is then held closed by pressure).

3. On acceleration to 94-percent rpm — Electronic TD control system is switched from start limiting to normal limiting, and the speed-sensitive valve opens to allow 14th-stage bleed air to force the 5th- and 10th-stage compressor bleed valves closed.

Figure 2-8. Engine Start Control System (Simplified Diagram)

2.1.7.8 Normal Engine Starting Sequence

During a normal start, the following actions take place automatically (providedChapter 8checklist procedures have been followed) as listed inFigure 2-9. An examination of the sequence will be helpful in understanding the overall operation of any start.

PERCENT ENGINE RPM

(APPROXIMATE) ACTION CONTROLLED BY

0 to 94 TIT limited to 830_ by TD control Speed-sensitive switch 0 to 94 5th- and 10th-stage compressor bleeds

open Speed-sensitive valve

Electronic fuel correction light on Throttle and electronic fuel correction switch

16 Fuel shutoff opened Speed-sensitive switch

50 psig fuel manifold pressure Fuel enrichment off Manifold pressure switch

60 Starter switch released Pilot

Bleed valves are located in the 5th and 10th stages of the compressor to allow more rapid acceleration of the turbine during starting and to minimize compressor surge or stall problems. The opening and closing of the 5th- and 10th-stage bleed valves is controlled by an engine-driven centrifugally actuated valve. On acceleration, the bleed valves are open from 0 to 94 percent at which point the engine-driven speed-sensitive valve opens to allow control air pressure flow from the 14th stage to close the bleed valves. The bleed valves remain closed until engine speed decelerates below 94 percent.

2.1.7.10 ENGINE GROUND START Switches

Four spring-loaded ENGINE GROUND START switches are located on the overhead control panel (seeFigure 2-10). Holding the ENGINE GROUND START switch to the START position opens the starter regulator valve to permit bleed air from the bleed air manifold to drive the engine starter turbine. The ENGINE GROUND START switch should be released to OFF at 60-percent engine rpm.

Figure 2-10. Engine Starting and Fuel Enrichment Panel 2.1.7.11 Engine Fuel Enrichment Switches

The ENGINE FUEL ENRICHMENT switches are located on the engine starting panel (seeFigure 2-10). They are toggle switches with NORM and OFF positions. In NORM, each switch allows the engine fuel enrichment valve to be controlled by the speed-sensitive control and manifold pressure switch during starting. The OFF position is provided to permit deactivating the fuel enrichment system for any engine. During the engine starting cycle the fuel enrichment system furnishes unmetered fuel to the TD valve to supplement normal flow through the fuel control.

This enriching starts at 16 percent rpm and lasts only until fuel manifold pressure reaches approximately 50 psi.

Note

If fuel enrichment is used and the engine does not start, the drip valve should drain all excess fuel in the engine overboard when the start is discontinued. If the drip valve fails to drain the excess fuel, it is advisable to place the ENGINE FUEL ENRICHMENT switch to OFF for the next starting attempt and motor the engine, with the condition lever in GROUND STOP, to eliminate the accumulated fuel from the engine to preclude a hot start or torching.

Characteristics of the starts will vary during extreme cold weather. With fuel enrichment off, light-off occurs between 22.0- and 26.5-percent rpm and several seconds may elapse between maximum turbine-starter-driven rpm and light-off. Torching may occur also. Starting with fuel enrichment normal produces light-off between 19.0- and 27.0-percent rpm with rapid engine acceleration. If a stalled start takes place, it can be noted by rpm lag at about

40-percent rpm and a sharp TIT increase. When the engine is still hot from previous operation, stalled starts are more likely to occur with fuel enrichment on. After an unsuccessful attempt to start the engine with fuel enrichment OFF, the next attempt should be made with fuel enrichment normal.

2.1.7.12 ENGINE BLEED AIR Switches

The ENGINE BLEED AIR switches, located on the anti-icing and deicing control panel, are three-position (OFF, ON, OVRD) toggle switches. Each switch controls a pressure-actuated, dual solenoid-controlled pressure regulator.

When the bleed-air switch is in OFF, the regulator shuts off all airflow to or from the engine. When the switch is in the ON position, the regulator regulates airflow from the engine to the bleed-air manifold to approximately 50 psi and prevents airflow into the engine nacelle if the bleed-air manifold pressure is above approximately 50 psi. Low bleed-air manifold pressure will allow airflow into an engine nacelle. When the switch is in OVRD (override), the regulator is fully open and permits air flow in either direction. It is necessary to use the OVRD position during engine starting, nacelle preheating (if installed), and for engine inlet air scoop anti-icing with the engine not running. A check valve is provided to prevent backflow into the engine diffuser. The bleed-air regulators receive 28-Vdc power from the essential dc bus through the BLEED AIR FIRE SHUTOFF VALVES circuit breakers on the copilot side circuit breaker panel. The regulators go to the closed position when deenergized.

2.1.7.13 Feather Valve and NTS Test Switch and Lights

The feather valve and NTS check system (seeFigure 2-18) consist of a FEATHER VALVE AND NTS CHECK switch, four indicator lights (one for each engine), four NTS check relays (one for each engine), and a feather valve switch and an NTS switch in each propeller control assembly. When the FEATHER VALVE AND NTS CHECK switch is in the VALVE position, it completes the light circuits from the essential dc bus through the lights and contacts of each NTS check relay to the feather valve switch in each propeller control assembly. If the feather valve is positioned by the condition lever for feathering the propeller, it completes a circuit to ground for the corresponding indicator light. The light will come on to indicate that the feather valve is in position to feather the propeller. When a propeller is feathered by a fire emergency control handle, the corresponding light will not come on, although the

The feather valve and NTS check system (seeFigure 2-18) consist of a FEATHER VALVE AND NTS CHECK switch, four indicator lights (one for each engine), four NTS check relays (one for each engine), and a feather valve switch and an NTS switch in each propeller control assembly. When the FEATHER VALVE AND NTS CHECK switch is in the VALVE position, it completes the light circuits from the essential dc bus through the lights and contacts of each NTS check relay to the feather valve switch in each propeller control assembly. If the feather valve is positioned by the condition lever for feathering the propeller, it completes a circuit to ground for the corresponding indicator light. The light will come on to indicate that the feather valve is in position to feather the propeller. When a propeller is feathered by a fire emergency control handle, the corresponding light will not come on, although the

In document NATOPS Flight Manual Navy Model C-130T Aircraft (Page 87-98)