Aero engine system john

GAS TURBINE ENGINE NOTE
JOHN KHAN| www.facebook.com/thejohn99
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LUBRICATION SYSTEM
PRINCIPLE OF ENGINE LUBRICATION
• PRIMERY PURPOSE-REDUCE FRICTION
• SECONDARY PURPOSE -TO ACT AS CUSHION,COOLING AND
CLEANING
• IN ADITION OIL FILM ACTS AS A CUSHION BETWEEN METAL
PARTS-IMPORTANT FOR PARTS SUBJECTED TO SHOCK LOAD
• IT ABSORVE HEAT FROM THE PARTS, SO HELP IN COOLING
• HELP IN FORMING SEAL BETWEEN PARTS TO PREVENT LEKAGE
• REDUCE ABRASIVE WEAR BY PICKING UP FORIGEN PARTICLE
• Prevents from corrosion

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PROPERTIES OF LUBRICATING OIL
VISCOSITY-
• MOST IMPORTANT PROPERTIES.THE RESISTANCE OF THE OIL TO
FLOW IS KNOWN AS VISCOSITY.
• IF FLOW FREELY-LOW VISCOSITY,IF FLOW SLOWELY-HIGH
VISCOSITY
• VISCOSITY OF OIL IS AFFECTED BY TEMP.VISCOSITY SHOULD BE
CHANGE MINIMUM WITH CHANGE IN TEMPERATURE.
• OIL SELECTED FOR ENGINE MUST BE LIGHT ENOUGH TO CIRCULATE
FREELY,YET HEAVY ENOUGH TO PROVIDE PROPER OIL FILM AT
ENGINE OPERATING TEMP.
• OIL USED IN PISTION ENGINE SHOULD BE OF HIGH VISCOSITY

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BECAUSE OF LARGE OPERATING CLEARANCE, HIGH OPERATING
TEMP,HIGH BEARING PRESSURE.
• AN SAE (SOCIETY OF AUTOMOTIVE ENGINEER) RATING FOR
PETROLIUM BASED OIL IS DETERMNED BY HEATING 60ML (CC)OF
OIL TO ONE SPECIFIC TEMP AND MEASURING THE FLOW TIME AS
THE OIL IS POURED THROUGH A CALIBRATED ORIFICE.ONE SUCH
DEVICE FOR CALCULATING THIS IS SAYBOLT -UNIVERSAL
SECOND(S.U.S) VISCOSIMETER.
• LETTER W OCCASIONALY INCLUDED IN THE SAE NUMBER.THIS
INDICATES OIL IS ALSO SUITABLE FOR USE IN WINTER...SUCH AS
SAE 20W
• SAE NO ONLY INDICATE GRADE OF OIL.IT DON'T SHOW OIL
QUALITIES.
• SYNTHETIC OIL DO NOT HAVE SAE RATING.IT HAS A KINAMATIC

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VISCOSITY RATING IN CENTISTROKE.
VISCOSITY INDEX-
• IT SHOULD BE HIGH.IT IS AN INDICATION OF HOW WELL THE OIL
WILL TENDS TO RETAIN ITS VISCOSITY WHEN HEATED TO ITS
OPERATING TEMPERATURE.
LOW VOLATILITY-
• EASE WITH WHICH LIQUID IS CONVERTED TO VAPOUR
STATE.VOLATILITY SHOULD BE LOW TO MINIMIZE EVAPORATION
AT HIGH ALTITUDE
ANTI FOAMING QUALITY-
• OIL FOAMING IS THE MEASURE OF THE RESISTANCE OF THE OIL TO
SEPARATE FROM ENTRAINED AIR.FOAMING SHOULD BE LOW FOR
MORE POSITIVE LUBRICATION.

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LOW LACQUER AND COKE DIPOSITE-
• KEEP SOLID PARTICLE FORMATION TO MINIMUM
FILM STRENGTH-
• EXCLLENT QUALITY OF COHESION AND ADHESION,A
CHARACTERISTICS OF OIL MOLECULES ALLOWING THEM TO STICK
TOGETHER UNDER COMPRESSION LOAD AND STICK TO SURFACE
UNDER CENTRIFUGAL LOAD
WIDE TEMPERATURE RANGE-
• APP.-60 DEGREE F TO +400 DEG F.
SPECIFIC GRAVITY-
• IS ACOMPARISON OF THE WT. OF THE SUBSTANCE TO THE WT. OF

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AN EQUAL VOLUME OF DISTILLED WATER AT SPECIFIED TEMP.
HIGH FLASH POINT-
• THE TEMP AT WHICH LIQUID WILL BEGIN TO GIVE OFF INGNITABLE
VAPOURS(FLASH).
HIGH FIRE POINT-
• THE TEMP AT WHICH THERE ARE SUFFICIENT VAPOURS TO
SUPPORT THE FLAME(FIRE)
CLOUD POINT-low
• THE TEMP AT WHICH IT WAX CONTAINED ,NORAMALLY HELD IN
SOLN, BEGINES TO SOLIDIFY AND SEPARATE INTO TINY
CRYSTALS,CAUSING OIL TO APPEAR CLOUDY OR HAZY.CLOUD
POINT TEMP IS SLIGHTLY ABOVE SOLIDIFICATION POINT.

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POUR POINT-
• THE LOWEST TEMP AT WHICH OIL FLOW OR CAN BE POURED.
OILINESS-
• DIFFERENCE IN REDUCING FRICTION WHEN OIL HAVING SAME
VISCOSITY BUT DIFFERENT OILINESSS ARE COMPARED UNDER THE
SAME CONDITION OF TEMP AND PRESSURE.IT IS THE WETTING
AFFECT THAT REDUCE FRICTION, DRAG AND WEAR.
ACIDITY
• IT IS THE CORROSIVE TENDENCY OF THE OIL
CORROSION RESISTANCE-
• OIL SHOULD BE OF CORROSION RESISTANCE NATURE,NON
CORROSIVE TO METAL.

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CHEMICAL AND PHYSICAL STABILITY-
• SHOULD HAVE CHAMICAL STABILITY AGAINST
OXIDATION,THERMAL CRACKING AND COKING AND IT MUST HAVE
PHYSICAL STABILITY WITH REGARDS TO PR AND TEMP.
TYPES OF OIL
ANIMAL BASE-THIS TYPE OF OIL IS HIGHELY STABLE AT NORMAL
TEMPERATURE.USED IN FIREARMS,SEWING MACHINE,CLOCK AND
OTHER LIGHT MACHINE.CANNOT BE USED FOR ENGINE BECAUSE IT
PRODUCE FATTY ACID AT HIGH TEMP.
EX-TALLOW OIL,LARD OIL,NEAT'S FOOT OIL,SPERM OIL
VEGITABLE BASE-(MIL-H-7644) COMPOSED OF CASTER OIL AND
ALCOHOL.IT HAS PUNGENT ALCOHOLIC ODOR AND IS GENERALLY
DYED BLUE.USED IN OLDER AIRCRAFT.NATURAL RUBBER SEAL IS USED

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WITH IT.FLAMMABLE IN NATURE.
MINIRAL BASE(MIL-H-5606)PROCESSED FROM PETROLEUM.ODOR
SIMILAR TO PENETRATING OIL AND DYED RED.SYNTHETIC RUBBER IS
SUITABLE WITH MINIRAL OIL.FLAMMABLE IN NATURE
• SOLID TYPE-MICA,SOAPSTONE AND GRAPHITE.DO NOT DISSIPATE
HEAR RAPIDELY ENOUGH FOR HIGH SPEED MACHINE.USED IN
POWDER FORM.
• SEMI-SOLID TYPE-GREASE IS EXAMPLE OF THIS TYPE OF
LUBRICANTS.IT IS A MIXTURE OF OIL AND SOAP.
• LIQUIED OR FLUID TYPE-USED IN INTERNAL COMBUSTION ENGINE
SYNTHATIC BASE OR PHOSPHATE ESTER BASE(SKYDROL)
FIRE RESISTANCE IN NATURE MEANS IT DOES NOT SUPPORT
COMBUSTION AND RETAIN THEIR CHARECTARISTICS AT HIGH TEMP.

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THAT CAUSE PETROLEUM OIL TO EVAPORATE AND BREAK DOWN INTO
HEAVY HYDROCARBON.
HYGROSCOPIC IN NATURE.
1.TYPE I,ALKYL DIESTER OIL(MIL-L-7808)
2.TYPE II,POLYSTER OIL(MIL-L-23699)
3.TYPE III
LUBRICATING SYSTEMS:
THE LUBRICATION SYSTEM SUPPLIES OIL TO THE VARIOUS MOVING PARTS
WITHIN THE ENGINE WHICH ARE SUBJECTED TO FRICTION LOADS AND
HEATING FROM THE GAS PATH.

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THE OIL IS SUPPLIED UNDER PRESSURE ALONG THE MAIN ROTOR SHAFT
AND TO THE GEARBOXES TO REDUCE FRICTION, TO COOL, AND TO CLEAN.
IT IS THEN RETURNED BY A SCAVENGING SYSTEM TO THE OIL STORAGE
TANK TO BE USED AGAIN AND AGAIN.
OIL CONSUMPTION IS LOW IN GAS TURBINE ENGINES AS COMPARED TO
PISTON ENGINES, THEY CAN BE AS SMALL AS 3 TO 5 QUART CAPACITY ON
BUSINESS JET SIZE ENGINES AND 20 TO 30 QUARTS ON LARGE
COMMERCIAL TYPE ENGINES.
TYPES OF LUBRICATION SYSTEM
WET-SUMP LUBRICATION SYSTEM
AN AIRCRAFT ENGINE THAT CARRIES ITS SUPPLY OF LUBRICATING OIL
IN A SUMP, OR COMPARTMENT, WHICH IS PART OF THE ENGINE

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ITSELF.
AFTER SERVING ITS LUBRICATING FUNCTIONS, THE OIL DRAINS BACK
INTO THE SUMP BY GRAVITY.
THE WET SUMP SYSTEM IS THE OLDEST DESIGN, AND IT IS STILL SEEN
IN AUXILIARY POWER UNITS AND GROUND POWER UNITS BUT RARELY
SEEN IN MODERN FLIGHT ENGINES.
COMPONENTS OF A WET SUMP SYSTEM ARE SIMILAR TO A DRY SUMP
SYSTEM, EXCEPT FOR THE LOCATION OF THE OIL SUPPLY.

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FIGURE SHOWS AN ENGINE WITH A WET SUMP LUBRICATION SYSTEM
AND THE OIL CONTAINED IN ITS ACCESSORY GEARBOX. THE BEARINGS
AND DRIVE GEARS WITHIN THE SUMP ARE LUBRICATED BY A SPLASH
SYSTEM. THE REMAINING POINTS OF LUBRICATION RECEIVE OIL FROM
A GEAR TYPE PRESSURE PUMP, WHICH DIRECTS OIL TO OIL JETS AT
VARIOUS LOCATIONS IN THE ENGINE.

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MOST WET SUMP ENGINES DO NOT INCORPORATE A PRESSURE
RELIEF VALVE AND ARE KNOWN AS VARIABLE PRESSURE SYSTEMS.
WITH THIS SYSTEM THE PUMP OUTPUT PRESSURE DEPENDS DIRECTLY
ON ENGINE REVOLUTIONS PER MINUTE.
SCAVENGED OIL IS RETURNED TO THE SUMP BY A COMBINATION
OF GRAVITY FLOW FROM THE BEARINGS AND ALSO SUCTION CREATED
BY A GEAR TYPE SCAVENGE PUMP LOCATED WITHIN THE PUMP
HOUSING.
THE VENT LINE IS PRESENT TO PREVENT OVER PRESSURIZATION OF
THE GEARBOX. GAS PATH AIR SEEPING PAST MAIN BEARING SEALS
FINDS ITS WAY TO THE GEARBOX VIA THE SCAVENGE SYSTEM AND
THE VENT LINE RETURNS THIS AIR TO THE ATMOSPHERE.
DRY-SUMP SYSTEM (ENGINE LUBRICATION SYSTEM)

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THE OIL IS HELD IN AN EXTERNAL TANK, DRAWN FROM THE TANK AND
CIRCULATED THROUGH THE ENGINE BY AN ENGINE-DRIVEN PRESSURE
PUMP. AFTER LUBRICATING THE ENGINE, THE OIL DRAINS INTO A
INTEGRAL SUMP FROM WHICH IT IS PICKED UP AND RETURNED TO
THE OIL TANK BY A SCAVENGER PUMP.MOST GAS TURBINE ENGINES
UTILIZE A DRY SUMP LUBRICATION SYSTEM CONSISTING OF
PRESSURE, SCAVENGE, AND BREATHER VENT SUBSYSTEMS.

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THE MAIN OIL SUPPLY IS CARRIED IN A TANK MOUNTED EITHER
INTEGRALLY WITHIN THE ENGINE OR EXTERNALLY ON THE ENGINE OR
IN THE AIRCRAFT. A SMALLER SUPPLY IS CONTAINED IN A GEARBOX
SUMP WHICH ALSO HOUSES THE OIL PRESSURE PUMP. OIL
SCAVENGES PUMP, OIL FILTER, AND OTHER LUBE SYSTEMS
COMPONENTS. ANOTHER SMALL AMOUNT OF ILL IS RESIDUAL WITHIN
THE OIL SYSTEM LINES, SUMPS AND COMPONENTS.
HOT-TANK LUBRICATION SYSTEM
A LUBRICATION SYSTEM OF A GAS TURBINE ENGINE IN WHICH THE OIL
COOLER IS IN THE PRESSURE PORTION OF THE SYSTEM. HOT OIL
RETURNS DIRECTLY FROM THE ENGINE INTO THE TANK WITHOUT
BEING COOLED. AN ADVANTAGE OF THIS IS THAT A MAXIMUM HEAT
EXCHANGE OCCURS BECAUSE OIL HAS LESS ENTRAINED AIR IN THE
PRESSURE SIDE OF THE LUBRICATION SYSTEM. THIS FACTOR ALLOWS

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FOR SMALLER OIL COOLER TO BE USED, AND A WEIGHT SAVINGS
OCCURS.
COLD-TANK LUBRICATION SYSTEM
IN THE COLD TANK SYSTEM THE OIL COOLER IS LOCATED IN THE
SCAVENGE SUBSYSTEM, WHICH ALLOWS THE OIL TO RETURN TO THE
SUPPLY TANK IN A COOLED CONDITION. THE OIL IS STILL AERATED
FROM THE ACTION OF ROTATING PARTS WITHIN THE ENGINE AND A
REDUCED HEAT EXCHANGE IS SAID TO OCCUR. THIS IS TURN CREATES
NEED FOR THE USE OF A HIGH VOLUME OIL COOLER.
ALSO, SOME ENGINES HAVE NORMALLY HIGHER OIL
TEMPERATURES THAN OTHER. THIS HIGH OIL TEMPERATURE IN THE
OIL TANK CAN AFFECT OIL SERVICE LIFE, SINCE THE BULK OIL STORAGE

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IS AT A HIGHER TEMPERATURE FOR A LONGER TIME. IF THIS IS THE
CASE, A COLD TANK SYSTEM WILL MOST LIKELY TO BE USED.
OIL – SYSTEM COMPONENTS:
THE OIL-SYSTEM COMPONENTS USED ON GAS TURBINE ENGINES
ARE AS FOLLOWS:
• TANK(S)
• PRESSURE PUMP(S)
• SCAVENGER PUMPS
• FILTERS
• OIL COOLERS
• RELIEF VALVES

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• BREATHERS AND PRESSURIZING COMPONENTS
• PRESSURE AND TEMPERATURE GAGES
• TEMPERATURE REGULATING VALVES
• OIL JET NOZZLES
• FITTINGS, VALVES AND PLUMBING
• SEALS.
OIL TANK:
THE OIL SUPPLY RESERVOIR IS USUALLY CONSTRUCTED OF SHEET
ALUMINUM OR STAINLESS STEEL AND IS DESIGNED TO FURNISH A
CONSTANT SUPPLY OF OIL TO THE ENGINE DURING ALL AUTHORIZED
FLIGHT ATTITUDES. IN MOST TANKS, A PRESSURE BUILD- UP IS DESIRED
TO ASSURE A POSITIVE FLOW OF OIL TO THE OIL PUMP INLET AND TO
SUPPRESS FOAMING IN THE TANK WHICH IN TURN PREVENTS PUMP

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CAVITATIONS. THE BUILDUP IS ACCOMPLISHED BY RUNNING THE TANK
OVERBOARD VENT LINE THROUGH A RELIEF VALVE TO MAINTAIN A
POSITIVE PRESSURE OF APPROXIMATELY THREE TO SIX POUNDS PER
SQUARE INCH GAUGE (PSIG). THAT IS, THE TANK VENT RELIEF VALVE
WILL RELEASE EXCESS AIR AT A PRESSURE DIFFERENTIAL OF THREE TO
SIX POUNDS PER SQUARE INCH- DIFFERENTIAL (PSID) BETWEEN THE
TANK AND AMBIENT OR TANK AND VENT SUB-SYSTEM. AFTER SHUT
DOWN A SMALL BLEED ORIFICE IN THE RELIEF VALVE ALLOWS FOR
DEPRESSURIZATION OF THE TANK.

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SOME DRY SUMP OIL TANKS ARE THE INTEGRAL TYPE. WHILE THE
EXTERNAL SHEET METAL TYPE IS A SEPARATE ASSEMBLY LOCATED
OUTSIDE THE ENGINE, THE INTEGRAL OIL TANK IS FORMED BY SPACE

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PROVIDED WITHIN THE ENGINE. IT CAN BE A PROPELLER REDUCTION
GEARBOX THAT HOUSES THE OIL OR SOMETIMES A CAVITY BETWEEN
MAJOR ENGINE CASES.
THE DISTINCTION BETWEEN THE WET SUMP AND DRY SUMP IS
THAT THE WET SUMP IS LOCATED IN THE MAIN GEAR BOX AT THE
LOWEST POINT WITHIN THE ENGINE, FACILITATING SPLASH
LUBRICATION. THE DRY SUMP IS SELDOM LOCATED AT THE LOW POINT
ON THE ENGINE. IT MAY OR MAY NOT GRAVITY FLOW OIL TO THE MAIN
OIL PUMP INLET.
TODAY, SOME OIL TANKS ARE CONFIGURED WITH A REMOTE
PRESSURE FILL CAPACITY. AN OIL PUMPING CART CAN BE ATTACHED TO
THE TANK AND THE OIL HAND PUMPED INTO THE TANK UNTIL IT IS AT
THE PROPER LEVEL, AT WHICH TIME OIL STARTS TO FLOW FROM THE

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OVERFLOW. THE OIL FILLER CAP IS USUALLY REMOVED DURING THIS
OPERATION TO PREVENT OVER-SERVICING IN CASE THE OIL OVERFLOW
IS NOT PROPERLY CONNECTED. THE HAND GRAVITY OIL TANK FILLING
METHOD IS, HOWEVER, STILL THE MOST COMMON. THE SCUPPER
SHOWN ON THE ILLUSTRATION IS PRESENT TO CATCH OIL THAT IS
SPILLED DURING SERVICING OR DURING CAP BLOW OFF AND TO ROUTE
THIS SPILLAGE THROUGH A DRAIN POINT LOCATION AT THE BOTTOM
OF THE ENGINE. DUE TO THE POSITION OF THE FILLER CAP, IT IS NOT
POSSIBLE TO OVER SERVICE BY THE HAND GRAVITY METHOD. MANY OF
THE NEW FILLER OPENINGS ARE FITTED WITH A FLAPPER SEAL, IN THE
EVENT THE OIL FILLER CAN IS INADVERTENTLY LEFT OFF.
IN PLACE OF A DIPSTICK, SOME OIL TANKS INCORPORATE A
SIGHT GAUGE TO SATISFY THE REQUIREMENT FOR A VISUAL MEANS OF
CHECKING OIL LEVEL. HOWEVER, THESE GLASS INDICATORS TEND TO
CLOUD OVER AFTER PROLONGED USE AND MANY OPERATORS HAVE

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GONE BACK TO THE DIPSTICK.
PRESSURE PUMPS:
THE FUNCTION OF THE OIL PRESSURE PUMP IS TO SUPPLY OIL
UNDER PRESSURE TO THE PARTS OF THE ENGINE THAT REQUIRE
LUBRICATION. MANY OIL PUMPS CONSIST OF NOT ONLY OF A PRESSURE
LUBE ELEMENT BUT ONE OR MORE SCAVENGE ELEMENTS AS WELL ALL
IN ONE HOUSING.BOTH THE GEAR AND GEROTOR TYPE PUMPS ARE
USES IN THE LUBRICATING SYSTEM OF THE TURBINE ENGINE.
SCAVENGER PUMPS:
SCAVENGER PUMPS ARE SIMILAR TO THE PRESSURE PUMPS BUT
ARE OF MUCH LARGER TOTAL CAPACITY. AN ENGINE IS GENERALLY
PROVIDED WITH SEVERAL SCAVENGER PUMPS TO DRAIN OIL FROM
VARIOUS PARTS OF THE ENGINE. OFTEN ONE OR MORE OF THE
SCAVENGER ELEMENTS ARE INCORPORATED IN THE SAME HOUSING AS

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THE PRESSURE PUMP. DIFFERENT CAPACITIES CAN BE PROVIDED FOR
EACH SYSTEM, DESPITE THE COMMON DRIVING SHAFT SPEED, BY
VARYING THE DIAMETER OR THICKNESS OF THE GEARS TO VARY THE
VOLUME OF THE TOOTH CHAMBER. A VANE-TYPE PUMP MAY
SOMETIMES BE USED.
THE THREE MOST COMMON OIL PUMPS ARE:
• GEAR TYPES.
• GEROTOR TYPE
• THE VANE TYPE,
ALL ARE CLASSED AS POSITIVE DISPLACEMENT PUMPS BECAUSE THEY
DEPOSIT A FIXED QUANTITY OF OIL IN THE PUMP OUTLET PER
REVOLUTION. THESE CATEGORY PUMPS ARE ALSO REFERRED TO AS
CONSTANT DISPLACEMENT TYPES BECAUSE THEY DISPLACE A

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CONSTANT VOLUME PER REVOLUTION.
• GEAR PUMP
THE GEAR TYPE PUMP CONSISTS OF A DRIVING AND DRIVEN GEAR. THE
ROTATION OF THE PUMP WHICH IS DRIVEN FROM THE ENGINE
ACCESSORY SECTION, CAUSES THE OIL TO PASS AROUND THE OUTSIDE
OF THE GEARS IN POCKET FORMED BY THE GEAR TEETH AND THE PUMP

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CASING. THE PRESSURE DEVELOPED IN PROPORTIONAL TO ENGINE RPM
UP TO THE TIME THE RELIEF VALVE OPENS, AFTER WHICH ANY FURTHER
INCREASE IN ENGINE SPEED WILL NOT RESULT IN AN OIL PRESSURE
INCREASE.
• GEROTOR PUMP:
THE GEROTOR PUMP HAS TWO MOVING PARTS, AN INNER
TOOTHED ELEMENT MESHING WITH AN OUTER TOOTHED ELEMENT.
THE INNER ELEMENT HAS ONE LESS BOTH THAT THE OUTER AND THE

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“MISSING TOOTH” PROVIDES A CHAMBER TO MOVE THE FLUID FROM
THE INTAKE TO THE DISCHARGE PORT. BOTH ELEMENTS ARE MOUNTED
ECCENTRICALLY TO EACH OTHER ON THE SAME SHAFT.
THE GEROTOR PUMP, SOMETIMES, REFERRED TO AS GEAR-ROTOR,
UTILIZES A PRINCIPLE SIMILAR TO THE VANE PUMP. THE GEROTOR USES
A LOBE-SHAPED DRIVE GEAR WITHIN AN ELLIPTICALLY SHAPED IDLER
GEAR TO DISPLACE OIL FROM AN INLET TO AN OUTLET PORT.
NOTICE THAT THE INNER DRIVING GEAR HAS FOUR LOBES (TEETH)
AND THAT THE OUTER IDLING GEAR HAS FIVE OPENINGS. THIS
ARRANGEMENT ALLOWS OIL TO FILL THE ONE OPEN POCKET AND
MOVE INLET OIL THROUGH THE PUMP AS IT ROTATES UNTIL A ZERO
CLEARANCE FORCES THE OIL FROM THE DISCHARGE PORT. THE

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PRINCIPLE OF OPERATION IS THAT THE VOLUME OF THE MISSING
TOOTH MULTIPLIED BY THE NUMBER OF LOBES IN THE OUTER GEAR
DETERMINES THE VOLUME OF OIL PUMPED PER REVOLUTION OF THE
OUTER GEAR.
• VANE TYPE PUMP

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THE PUMP COULD BE A SINGLE ELEMENT TYPE OR ONE ELEMENT
OF A MULTIPLE PUMP. MULTIPLE PUMPS OF THIS TYPE GENERALLY
CONTAIN ONE PRESSURE ELEMENT AND ONE OR MORE SCAVENGE
ELEMENTS, ALL OF WHICH ARE MOUNTED ON A COMMON SHAFT. THE
DRIVE SHAFT MOUNTS TO AN ACCESSORY GEAR BOX DRIVE PAD AND
ALL PUMPING ELEMENT ROTATE TOGETHER.
PUMPING ACTION TAKES PLACE AS ROTOR DRIVE SHAFT AND
ECCENTRIC ROTOR, WHICH ACT AS ONE ROTATING PIECE DRIVE THE
SLIDING VANES AROUND. THE SPACE BETWEEN EACH VANE AND PAIR
FLOODS WITH OIL AS IT PASSES, THE OLD INLET OPENING AND CARRIES
THIS OIL TO THE OIL OUTLET. AS THE SPACES DIMINISH TO A ZERO
CLEARANCE, THE OIL IS FORCED TO LEAVE THE PUMP. THE
DOWNSTREAM RESISTANCE TO FLOW WILL DETERMINE THE PUMP

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OUTPUT PRESSURE UNLESS A RELIEF VALVE IS PRESENT TO REGULATE
PRESSURE.
VANE PUMPS ARE CONSIDERED TO BE MORE TOLERANT OF DEBRIS
IN THE SCAVENGE OIL. THEY ARE ALSO LIGHTER IN WEIGHT THAN THE
GEROTOR OR GEAR PUMPS AND OFFER A SLIMMER PROFILE. THEY MAY
NOT HOWEVER, HAVE THE MECHANICAL STRENGTH OR OTHER TYPE
PUMPS.
FILTERS:
THE THREE BASIC TYPES OF OIL FILTER FOR THE JET ENGINE ARE THE
CARTRIDGE OR PAPER TYPE

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SCREEN TYPE
SCREEN-DISK TYPES (CUNO FITER)

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THE SCREEN, AND SPACER TYPE FILTER, ALSO KNOWN AS AN EDGE
TYPE FILTER
THE CARTRIDGE FILTER MUST BE REPLACED PERIODICALLY WHILE THE
OTHER TWO CAN BE CLEANED AND REUSED.
IN THE SCREEN DISK FILTER THERE ARE A SERIES OF CIRCULAR SCREEN
TYPE FILTER, WITH EACH FILTER BEING COMPOSED OF TWO LAYERS OF
MESH TO FORM A CHAMBER BETWEEN THE MESH LAYERS. THE FILTERS
ARE MOUNTED ON A COMMON TUBE AND ARRANGED IN A MANNER

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TO PROVIDE A SPACE BETWEEN EACH CIRCULAR ELEMENT. LUBE OIL
PASSES THROUGH THE CIRCULAR MESH ELEMENTS AND INTO THE
CHAMBER BETWEEN THE TWO LAYERS OF MESH. THIS CHAMBER IS
PORTED TO THE CENTER OF A COMMON TUBE THAT DIRECTS OIL OUT
OF THE FILTER.

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ALL OF THE VARIOUS TYPES OF FILTERS WILL INCORPORATE A BYPASS
OR RELIEF VALVE, EITHER AS IN INTEGRAL PART OF THE FILTER OR IN
THE OIL PASSAGES OF THE SYSTEM, TO ALLOW A FLOW OF OIL IN THE
EVENT OF FILTER BLOCKAGE, WHEN THE PRESSURE DIFFERENTIAL or
delta-p rating REACHES A SPECIFIED VALVE (ABOUT 15 TO 20 PSI, THE
VALVE WILL OPEN AND ALLOW OIL TO BYPASS THE FILTER. SOME
FILTERS INCORPORATE A CHECK VALVE THAT WILL PREVENT EITHER
REVERSE FLOW OR FLOW THROUGH THE SYSTEM WHEN THE ENGINE IS
STOPPED. FILTERING CHARACTERISTICS VARY BUT MOST FILTERS WILL
STOP PARTICLES OF APPROXIMATELY 50 µ.
HOW THE FILTER ASSEMBLY FUNCTIONS:
AN OBSERVATION OF THE PAPER DISPOSABLE AND SCREEN MESH
FILTERS WOULD REVEAL THAT MOST ARE HEAVILY PLEATED OR, IN THE

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CASE OF STACKED FILTER, THEY CONSIST OF MANY TWIN SCREENS. THIS
IS TO PROVIDE A MAXIMUM SURFACE AREA FOR FILTRATION. THE
SCREEN TYPES HAVE AN ACTUAL MICRONIC SIZE, MEASURABLE IN
MICRONS. THE FIBER TYPE FILTERS HAVE AN EQUIVALENT MICRONIC
RATING.
IN-LINE BOWL TYPE FILTER WHICH COULD BE EITHER DISPOSABLE
OR CLEANABLE. A TYPICAL RATING FOR THIS FILTER IS 40 MICRONS.
THIS MEANS IT WILL FILTER OUT PARTICLE LARGER THAN 40 MICRONS
IN DIAMETER.
OBSERVE THAT OIL FILLS THE BOWL (SUMP) THEN FORCES ITS WAY
THROUGH THE FILTERING ELEMENT TO THE CORE, EXISTING AT THE
PORT NEAR THE SPRING SIDE OF THE BYPASS RELIEF VALVE. ON A COLD
MORNING WHEN OIL IS HIGHLY VISCOUS, OR, IF FILTER CLOGGING
RESTRICTS OIL FLOW THROUGH THE ELEMENT, THE DIFFERENTIAL

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BY-PASS VALVE WILL OPEN, ALLOWING UNFILTERED OIL TO FLOW OUT
TO THE ENGINE.
DURING A BYPASS CONDITION, THE AMOUNT OF OIL IS REDUCED
FROM THAT WHICH WOULD FLOW NORMALLY THROUGH THE FILTER
SCREEN, BUT IT WILL PROVIDE INITIAL LUBRICATION DURING
STARTING OR SUFFICIENT LUBRICATION FOR AT LEAST REDUCED
POWER OPERATION IN FLIGHT. If SYSTEM PRESSURE IN WHICH THIS
FILTER IS LOCATED IS REGULATED TO 45 POUNDS PER SQUARE INCH
GAUGE (OIL-IN PRESSURE), AND THE NORMAL PRESSURE DROP ACROSS
A CLEAN FILTER IS FIVE POUNDS PER SQUARE INCH GAUGE, THEN 40
POUNDS PER SQUARE INCH GAUGE OIL OUT PRESSURE IS ASSISTING
THE 25 POUNDS PER SQUARE INCH SPRING IN HOLDING THE BYPASS
VALVE CLOSED. AS FILTERS BECOME BLOCKED BY DEBRIS OR IF OIL IS
CONGEALED DURING A COLD WEATHER START, THE PRESSURE DROP
ACROSS THE FILTERING ELEMENT WILL INCREASE. WHEN THE PRESSURE

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DROP EXCEEDS THE RATING OF THE BYPASS VALVE SPRING, THE VALVE
WILL OPEN BYPASSING UNFILTERED OIL DIRECTLY FROM THE INLET TO
THE OUTLET. WHEN THE BYPASS VALVE OPENS, THE PRESSURE
DOWNSTREAM OF THE FILTER DOES NOT RETURN TO NORMAL. THE
DOWNSTREAM PRESSURE REMAINS AT THE SAME VALUE, LOWER THAN
THE UPSTREAM PRESSURE BY THE PSID RATING OF THE BYPASS VALVE.
IF THE PRESSURE WERE TO RETURN TO NORMAL, THE PRESSURE DROP
WOULD NO LONGER EXIST WHICH IS NEEDED TO HOLD THE BYPASS
VALVE OPEN.
PRESSURE REGULATING VALVES (RELIEF VALVES)
PRESSURE REGUATING VALVES, OR RELIEF VALVES ARE DESIGNED
TO EITHER MAINTAIN THE PRESSURE AT A PRESCRIBED VALUE OR TO
KEEP THE PRESSURE FROM GOING BEYOND SOME LIMIT. AS SUCH,
THESE VALVES CAN BE DESCRIED AS EITHER AN OPERATING TYPE OR A

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SAFETY TYPE. THE OPERATING TYPE IS TYPICALLY OFF ITS SEAT BY THE
TIME THE ENGINE REACHES IDLE, MAINTAINING A SET PRESSURE EVEN
AS THE ENGINE IS ACCELERATED TO TAKE OFF THRUST. THE SAFETY
TYPE IS TYPICALLY ON ITS SEAT, AND WOULD ONLY OPEN AND LIMIT
THE PRESSURE IN A CIRCUMSTANCES WHEN IT WOULD NOT BE SAFE TO
LET IS GO ANY HIGHER.
ON ENGINES WITH OPERATING TYPE RELIEF VALVES, THE LOCATION
OF THE VALVE CAN BE EITHER UPSTREAM OR DOWNSTREAM OF THE
MAIN OIL FILTER.
THE LOCATION OF THE VALVE WILL PLAY A SIGNIFICANT ROLE IN WHAT
HAPPENS DURING AN OIL FILTER BYPASS CONDITION. FOR EXAMPLE, IF
THE VALVE IS DOWNSTREAM OF THE FILTER AND THE FILTER CLOGS,
THE PRESSURE AT THIS POINT WILL NOT CHANGE. THE PRESSURE THAT
WILL CHANGE IS THE VALUE UPSTREAM OF THE FILTER AND THAT IS

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WHAT WILL CREATE THE "PSID" THAT CAUSES THE FILTER TO BYPASS. IF
THE RELIEF VLAVE IN UPSTREAM OF THE FILTER, THE UPSTEAM
PRESSURE WILL REMAIN CONSTANT DURING A BYPASS CONDITION AND
THE DOWNSTREAM PRESSURE WILL DROP.
OIL COOLERS:

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THE OIL COOLERS IS USED TO REDUCE THE TEMPERATURE OF THE
OIL BY TRANSMITTING HEAT FROM THE OIL TO ANOTHER FLUID.
SINCE THE FUEL FLOW THROUGH THE COOLER IS MUCH GREATER THAT
THE OIL FLOW, THE FUEL IS ABLE TO ABSORB A CONSIDERABLE
AMOUNT OF HEAT FROM THE OIL, THUS REDUCING THE SIZE OF THE
COOLER GREATLY, AS SHOWN IN FIG 15-8(B), AS WELL AS THE WEIGHT.
THERMOSTATIC OR PRESSURE SENSITIVE VALVE CONTROL THE
TEMPERATURE OF THE OIL BY DETERMINING WHETHER THE OIL SHALL

43
PASS THROUGH OR BY PASS THE COOLER.
Low Pressure Warning Light:
The cockpit pressure gauge will more likely tap into the oil system, downstream (output
side) of the main oil filter, to indicate the actual oil pressure being delivered to the
engine.

44
Many aircraft are also configured with a low pressure warning light. When power is
turned on in the aircraft, this light will illuminate. Then as oil pressure builds in the
system during starting, the light will go out at a preset value equal to the low or “red
line” limit for the cockpit oil pressure gauge.
If the warning light does not go out after start-up or if it comes back on during
operation, the operator will look at the pressure gauge to confirm the extent of the low
oil pressure condition and then take the appropriate action by reducing power or by
shutting the engine down. If the filter clogs during engine operation, the “low pressure”

45
warning light acts as a bypass warning light. Its micro-switch is set so that the cockpit
light will come on at the pressure at which the filter will start to bypass oil.
Filter Pop-Out Warning
Some filters which do not have pressure drop indicators or warning lights are
configured with a warning pop-out button on the filter bowl. Figure shows a filter bowl
with an impending bypass button. The button will pop out when filter inlet pressure
reaches a preset value to provide a visual warning that the filter is about to bypass or
that it has already bypassed. Once the problem is resolved, the button is reset by hand.

46
During cold weather starting, high oil pressure may cause the oil filter differential
pressure bypass valve to open. This however will not cause the impending bypass
button to pop out. The pop-out assembly contains a thermal low temperature lockout
to prevent it from tripping. As the oil warms up to approximately 100o
F the thermal
lockout is disengaged and the indicator is ready to warn of filter contamination.
Last Chance Filters:
Quite often, last change filters are installed in oil lines to prevent plugging of the oil
jets. Because of their remote location within the engine, last change filters are
accessible for cleaning only during engine overhaul.
Magnetic Chip Detectors:
Many scavenge systems contain permanent magnet chip detectors which attract
and hold ferrous metal particles which would otherwise circulate back to the oil tank
and the engine pressure subsystem, possible causing Wear or damage. Chip detectors
are a point of frequent inspection to detect early signs of main bearing failure.

47
As a general rule, the presence of small fuzzy particles or gray metallic paste is
considered satisfactory and the results of normal wear. Metallic chips or flakes are an
indication of serious internal wear or malfunction.
indicating type magnetic chip detector-It has a warning circuit feature. When
debris bridges the gap between the magnetic positive electrode in the center and the
ground electrode (shell), a warning light is activated in the cockpit. When the light

48
illuminates, the flight crew will take whatever action is warranted, such as in-flight shut
down, continued operation at flight idle, or continued operation at normal cruise,
depending on the other engine instruments readings.
Rotary air Oil Separator(DE-AERATOR)
De-Aerator provides a means of separating entrained air from the scavenge oil.
The rotary separator is an impeller, or centrifuge- like device, located in the
main gearbox near the vent outlet. as the oil-laden vent air enters the rotating
slinger chamber, centrifugal action throws the oil outward to drain back into

49
the sump, while clean vent air is routed out of the engine or to a pressurizing
and vent valve and then overboard.
SEALS:
DYNAMIC (RUNNING) SEALS USED IN GAS-TURBINE ENGINES CAN
BASICALLY BY DIVIDED INTO TWO GROUPS:
• RUBBING OR CONTACT SEALS :
RUBBING OR CONTACT SEALS ARE USED IN APPLICATIONS WHERE A
MINIMUM AMOUNT OF LEAKAGE IS ALLOWED AND A HIGH DEGREE
OF SEALING IS REQUIRED. FOR EXAMPLE, THEY ARE USED TO SEAL
ACCESSORY DRIVE SHAFT WHERE THE SHAFT EXISTS FROM THE
ACCESSORY GEAR CASE, AND FOR VARIABLE-STATOR-VANE BEARING
IN THE COMPRESSOR CASE. CARBON RUBBING SEALS ARE OFTEN
USED FOR, BUT NOT LIMITED TO SEALING THE MAIN INTERNAL

50
BEARING AREAS, ESPECIALLY IN THE ENGINE’S HOT SECTION.
• NONRUBBING LABYRINTH OR CLEARANCE SEALS :
NON-RUBBING CLEARANCE OR LABYRINTH TYPE SEALS ARE, AS THE
NAMES IMPLY, DEVICES THROUGH WHICH A SPECIFIC AMOUNT OR
LEAKAGES CAN TAKE PLACE BECAUSE THERE IS NO ACTUAL CONTACT
BETWEEN THE ROTATING AND STATIONARY PART OF THE SEAL. THE
UNIT CONSISTS ESSENTIALLY OF ONE OR MORE THIN STRIPS OF METAL
ATTACHED TO A HOUSING THROUGH WHICH THE SHAFT ROTATES. THIS
ARRANGEMENT MAY OCCASIONALLY BE REVERSED, WITH THE THIN
METAL STRIPS ATTACHED TO THE ROTATING SHAFT. BY ESTABLISHING
THE CORRECT PRESSURE DIFFERENTIAL ACROSS THE SEAL THE
DESIGNED AMOUNT OF LEAKAGE CAN OCCUR IN THE DESIRED
DIRECTION.
BREATHERS AND PRESSURIZING SYSTEMS:

51
IN MANY MODERN ENGINES INTERNAL OIL LEAKAGE IS KEPT TO A
MINIMUM BY PRESSURIZING THE BEARING SUMP AREAS WITH AIR
THAT IS BLED OFF THE COMPRESSOR. THE AIRFLOW INTO THE SUMPS
MINIMIZES OIL LEAKAGES ACROSS THE SEALS IN THE REVERSE
DIRECTION.
TO PREVENT LARGE QUANTITIES OF AIR TO DELIVERED IN THE OIL
TANK FROM SCAVENGE PMP, SUMP AND TANK PRESSURES ARE
MAINTAINED CLOSE TO EACH OTHER BY A LINE CONNECTING THE TWO.
IF THE SUMP PRESSURE EXCEEDS THE TANK PRESSURE, THE SUMP VENT
CHECK VALVE OPENS, ALLOWING THE EXCESS SUMP AIR TO ENTER THE
OIL TANK. THE VALVE ALLOWS FLOW ONLY INTO THE TANK, SO OIL OR
TANK VAPORS CANNOT BACK UP INTO THE SUMP AREAS. TANK
PRESSURE IS MAINTAINED A SMALL AMOUNT ABOVE AMBIENT.

52
Fuel system
Gas Turbine Fuels
Jet fuels are liquid hydrocarbons similar to kerosene, some
blended with gasoline. Hydrocarbon fuel is a compound of
hydrogen and carbon found in coal, natural gas, and crude oil..
Jet fuels are not color coded as are reciprocating engine fuels,
but they do have a natural straw color.
The following jet fuels are most commonly utilized in
commercial general aviation.

53
Turbo fuel A: Commonly called Jet A or “civil aviation
Kerosene”, it essentially contains no gasoline blend and is the
primary fuel for commercial and general aviation use in the
United States. Newer military fuel JP-8 is similar to Jet A.
Turbo Fuel A-1: commonly called Jet A-1, it is designed as a
low temperature fuel with a lower freezing point that Jet-A, it is
used by most international airlines.
Turbo Fuel B: Commonly called Jet B, it is blend of
approximately 30 percent kerosene and 70 percent gasoline and
described as a wide – cut fuel. It has a very low freezing point and
low flash point. It is primarily used by the military and similar to
military fuel JP-4.

54
• Jet A, Jet A1 and Jet B commercial fuels are
interchangeable for use in most gas turbine engines
• Military JP-8, JP-5 and JP-4 are generally suitable alternate
fuels,
• aviation grades 80-145 octane reciprocating engine fuels
are often emergency alternate fuels for turbine engines,
When comparing the BTU value of fuels such as Jet-A and
Aviation gasoline, it is interesting to note that Jet-A has more
BTU’s per gallons, but aviation gasoline has more BTU’s per
pound. The numbers are as follows:
Jet A 6.74 lb/gal (18,660 BTU/lb) = 125.364 BTU’s per
gallon

55
AV Gas5.87 lb/gal (18,900 BTU/lb) = 110.943 BTU’s per
gallon
FUEL REQUIREMENTS:
1. Be pumpable and flow easily under all operating
conditions.
2. Permit engine starting under all ground conditions and
give satisfactory flight relighting characteristics.
3. Give efficient combustion under all conditions.
4. Have as high a calorifice (heat) value as possible.
5. Produce minimal harmful effects on the combustion
system or turbine blades.
6. Produce minimal corrosive effects on fuel system
components

56
7. Provide adequate lubrication for the moving parts of the
fuel system
8. Reduce fire hazards to a minimum.
Fuel Handling And Safety:
• The normal handling cautions exist for jet fuels as for any
other flammable or explosive liquid. Especially important
is the requirement during refueling that the grounding
probe must be in place before the refueling nozzle
contacts the filler opening. This must be done to avoid
having any static sparks.
• Jet fuel in tanks is often more dangerous than gasoline.
Gasoline usually maintains a vapor–to-air mixture so rich

57
that ignition is less likely to occur. This is not the case with
jet fuel, as it is often at its best mixture to ignite.
• Personnel handling aviation fuels should observe a
number of practical and precautionary measures that
reduce the undesirable contact with fuel products. These
measures include the following:
1. Avoid all unnecessary contact and use protective
equipment to prevent contact.
2. Remove promptly any fuel product that gets on the
skin
3. Do not use fuels or similar solvents to remove oil or
grease from the skin

58
4. Never wear fuel soaked clothing. Remove immediately
and clean before re-use.
5. Avoid breathing fuel vapors. Maintain well ventilated
work areas.
6. Clean up spilled products immediately. Keep spills out
of sewers, streams and waterways.
7. Be familiar with proper first aid techniques for
handling unexpected/gross contracts and contact proper
medical authorities immediately for assistance.
Fuel Additives:

59
The most common fuel additives are the anti-icing and anti-
microbiocidal agents. Anti-icing additives keep entrained water
from freeze up without the use of fuel heat, except at very low
temperature. Microbiocidal agent kills microbes, fungi, and
bacteria which form a slime, and in some cases a matted waste in
fuels system.
A popular brand of hand-servicing type anti-icing and anti
biocidal mixture is called PRIST ®. It is designed to be added
during servicing and is capable of reducing the freezing
temperature of the fuel by 25° F.
Water detection In Turbine Fuel:
All aviation fuels contain some dissolved water and free water.
Dissolved water is like humidity in the air in that it cannot be seen.

60
It is not a problem as long as it remains dissolved. Free water, also
called entrained water, is present in tiny droplets and is visible. It
is water in excess of the water that dissolves. Large quantities of
free water (over 30 parts per million) can cause engine
performance loss or even flame out.
One of the principal concerns during fuel servicing is to deliver
fuel into the aircraft that is free of un-dissolved (free) water. It is
desirable; therefore, to test the fuel as it enters the aircraft to
ensure that free water has been effectively removed by the
clean-up system.
A HYDROKIT (Exxon trade name) is a quick, go/no-go test for
detecting the presence of minute quantities of un-dissolved water
in turbine fuel. The HYDROKIT indicator powder, packaged in a ten
milliliter evacuated test tube, gives a distinct pink/red color

61
change in the presence of 30 parts per million or more of
un-dissolved water in fuel. An important consideration for fuel
handlers is to realize that the Specific Gravity of jet fuel is closer
to water than is the Specific Gravity of Avgas. Therefore, jet fuel
can hold more water in suspension that avgas without showing it.
Thrust Specific Fuel Consumption ( TSFC):
TSFC is a ratio of fuel consumption to engine thrust. This ratio
is usually included in any set of engine. it is the amount of fuel in
pounds consumed by an engine while producing one pound to
thrust during one hour of operation.
TSFC =

62
Turbofans And TSFC
One of the reasons for turbofan efficiency over the turbojet
was discussed previously in terms of Kinetic Energy loss in the hot
exhaust.
Another reason for the TSFC advantage of the turbofan lies in
the fact that, if more power is required more fuel flow is required.
In the turbofan engine, the turbine wheel can be designed to
absorb more energy to drive a larger fan and give the engine
more total thrust. In this way, the hot exhaust velocity need not
be increased to affect an increase in thrust. In the turbofan,
Propulsive Efficiency will remain relatively unchanged, but in the
turbojet an increase in exhaust velocity will cause a loss of
Propulsive Efficiency.

63
TSFC In Flight :
The reason TSFC is higher at operating altitude than at ground
operating condition is that, in order to keep engine power up
when inlet density is dropping, more RPM (by way of increased
fuel flow) is needed to maintain correct mass airflow. The
increase in fuel flow per pound of thrust results in a higher TSFC.
thrust is remaining fairly constant as airspeed increases,
therefore, in terms of the TSFC formula (TSfC = Wf ÷ fn) as fuel
flow increases for a given thrust the TSFC value increases.

64

65
When considering a flight speed increase and an altitude
increase, TSFC also increases for a comparable sea level power
setting. Consider the following points:
1) Wf decreases to about 40percent of its sea level value
when going to altitude (A)
2) Flight thrust (Fn ) drops to about 20 percent of its sea level
value (B)
3) TSFC increases as a result of the relationship of fuel flow
remaining higher than thrust when applied to the TSFC
formula ©
TYPES OF CONTROLS:
Modern fuel and engine control can be divided into three basic
groups:

66
1.Hydro-mechanical
2.hybrid
3.electronic engine control
The first two may sense some or all of the following engine variables:
• Pilot’s demands
• Compressor-inlet temperature
• Compressor- discharge pressure
• Burner pressure
• Rpm
• Turbine temperature
The electronic controls, especially the full authority digital electronic
control (FADEC), which may be part of a sophisticated engine electronic
control (EEC) system, will sense many more operating parameters.
Electronic system may also use fiber optics instead of wire to provide
immunity from electromagnetic (EM) effects. Fiber optic systems are

67
safer (no fire hazard), have fewer components, and require less
maintenance.

68

69

70

71

72

73
Electronic Engine Control (EEC) / Full Authority Digital Electronic
Control (FADEC)
• It is actually a basic of hydro mechanical control with addition of an
electronic sensor circuit, which is powered by a/c bus or by
alternator.
• The FADEC is the primary interface between the engine and the
aircraft. It is located on the fan case.
• It takes complete control of engine system in response to
command input from a/c. provide information to the a/c for flight
deck indication, engine condition monitoring, maintenance
reporting and troubleshooting.
• Much more is accomplished by this control that simply sending a
signal to the fuel metering unit to establish a fuel flow to the
nozzles.
• The FADEC accomplish the following

74
1. Perform fuel scheduling and provides limit protection for N1
AND N2
2. Control engine parameter during starting and prevent EGT
limit to exceed
3. Manage thrust according to 2 mode ,manual and auto
thrust
4. Provides optimal engine operation by controlling comp.
airflow and turbine clearance
5. Control 2 thrust leaver interlock solenoids
FADEC COMPONENT
• EEC Containing two identical computer designated channels “A”
and “B”. Each time the engine starts, alternate channels will
automatically be selected. The channels are linked together by an
internal mating connector for crosstalk data transmission.

75
• HMU, convert electrical signal from EEC to hydraulic pr to drive
engine v/v, actuator.
• Peripheral components such as v/v, actuators and sensor used to
control and monitoring
The FADEC affects the engine in the following manner:
1.Efficiency of the engine is improved by controlling the following:
a.Anti-surge bleed valves.
b.Variable –stator vanes
c.Cooling airflows
d.Engine oil cooling
e.Integrated drive generator (IDG) oil cooling (over ride only)
f. Nacelle cooling
g.Fuel heating.

76
2.Basic engine-control functions are enhanced, such as the following
a.Starting
b.Idle
c.Acceleration
d.Deceleration
e.Stability
f. Thrust control
3.The engine is protected by limiting
a.Critical speeds and pressures
b.Thrust
c.Over boost.
4.Operational reliability of the engine is improved by using
a.A two-channel control
b.An automatic fault detection circuitry and fault logic system
c.An automatic fault-compensation system

77
d.Redundant inputs and outputs.
5.Engine maintenance is made easier by the incorporation of systems
for
a.Engine monitoring
b.Self-testing
c.Fault isolation
6.Interface between the flight deck and the engine is improved
through
a.Automatic engine pressure ratio (EPR) control
b.Limit protection
c.Automatic agreement between the throttle-lever position and
engine thrust.
FADEC INTERFACE

78
FADEC system is a BITE system means it is able to detect its own
internal and external fault. To perform its task FADEC communicates
with a/c computer via EEC.
EEC receive operational command from common display
sys.(CDS),display electronic unit(DEU)which is an interface between
EEC and a/c sys.
Both CDS – DEU 1 and 2 provide the following data from the two
Air Data ad Inertial Reference Units ( ADIRU ) and the flight
Management Computer (FMC).
• Air data parameters (altitude, total air temperature, total pressure
and Mach number) for thrust calculation.
• The position of the Throttle Resolver Angle (TRA).

79
FADEC Design
The FADEC system is fully redundant and built around the
two-channel EEC. The valves and actuators are fitted with dual sensors
to provide the EEC with feedback signals. All control inputs are dual,
but some parameters, used for monitoring and indicating, are single.
To enhance system reliability, all inputs to one channel are made
available to the other, through a Cross channel data Link (CCDL). This
allows both channels to remain operational even if important inputs
to one of them fail.
The two channels, A and B are identical and permanently
operational, but they operate independently from each other. Both
channels always receive inputs and process them, but only the channel

80
in control, called the Active channel, delivers output commands. The
other is called the Stand-by channel.
Active and Stand-by channel selection is performed at EEC
power-up and during operation.
The BITE system detects and isolates failures, or combinations of
failures, in order to determine the health status of the channels and to
transmit maintenance data to the aircraft.
Active and stand-by selection is based upon the health of the
channels, and each channel determines its own health status. The
healthiest is selected as the Active channel.
When both channels have an equal health status, Active/Stand-by
channel selection alternates with every engine start as soon as N2 is
greater than 10,900 RPM. If a channel is faulty and the Active channel
is unable to ensure an engine control function, this function is moved

81
to a position which protects the engine and is known as the fail safe
position.
Closed Loop Control Operation
In order to properly control the various engine systems, the EEC
uses an operation known as closed loop control. The EEC calculates a
position for a system component, known as the command. The EEC
then compares the Command with the actual position of the
component, known as the Feedback and calculates a position
difference, which is known as the demand.
The EEC, through the Electro-Hydraulic Servo valve (EHSV) of the
Hydro-Mechanical Unit (HMU), sends a signal to a component (valve,
actuator) which causes it to move. With the Movement of the system
valve or actuator, the EEC is provided with a feedback of the

82
component’s position. The process is repeated until there is no longer
a position difference.
Input Parameters
All sensors are dual, except few that are not installed on every
engine.
To perform its calculations, each channel of the EEC receives a
local value and a cross channel value, through the cross Channel data
Link (CCDL). Both values pass through a validation test program in
each EEC channel. The right value to be used is selected depending on
the assessed validity of each reading, or an average of both values
might be used.
In case of a dual sensor failure, a model value, computed from the
other available parameters, is selected. This is the case for the
following parameters.

83
• The fan speed (N1)
• The high pressure compressor speed (N2)
• Compressor discharge static air pressure (Ps3)
• The high pressure compressor inlet air temperature (T25)
• The position of the fuel metering valve (FMV)
• The position of the variable bleed valves (VBV)
• The position of the variable stator vanes (VSV)
For all other parameters, if the EEC is not able to select a valid
value, failsafe values are selected.
EEC Location:
The EEC is a dual channel computer housed in an aluminum
chassis, which is secured on the right hand side of the fan case at the
2’o clock position. Four mounting bolts, with shock absorbers, provide
isolation from shocks and vibrations.

84
To operate correctly, the EEC requires cooling to maintain internal
temperatures, within acceptable limits. Ambient air is picked up by an
air scope, located on the right hand side of the fan inlet cowl. This
cooling air is routed up to the EEC internal chamber, around channel A
and B compartment, and then exist through a cooling air outlet.
EEC Reprogramming
Each EEC can be reprogrammed with a Portable data Loader (PDL).
This PDL connects to the EEC at three of the cannon plug locations, and
then both are powered up to allow the latest software to be
downloaded. After the downloaded, a display on the PDL will show
either “Load complete” or “Transfer Fail”
Engine Rating Identification Plug:
The engine rating/identification plug provides the EEC with engine
configuration information for proper engine operation. It is plugged

85
into one of the connectors on the EEC and attached to the fan case by
a metal strap. It remains with the engine even after EEC replacement.
The plug includes a coding circuit, soldered to the plug, which the EEC
interprets and uses to determine how much thrust the engine will be
able to produce.
The EEC stores schedules, in its non-volatile memory, for all
available engine configurations. During initialization, it reads the plug
by looking for voltages on certain pins. Depending on the location and
voltage present at specific pins, the EEC will select a particular
schedule. In case of missing or invalid ID plug, the EEC uses the value
stored in the non-volatile memory for the previous plug configuration.
The ID plug is equipped with fuse and push-pull links. The fuse
links provide the EEC with thrust information at power up. They are
made by metallization of an area between two contacts on the plug.

86
These links can only be opened by burning them out, thus their
reconfiguration is not possible.
Bump is an option provided to achieve power levels greater than
the normal take off levels within specific limitations. Specific bump
rating capabilities may be set by the engine ID plug. The bump rating
does not influence power levels which are at, or below Max.
Continuous thrust. For any available bump, the redline value for N1 N2
and EGT remain identical to the baseline rating.
When new engine are built, a small variation may exist in the
amount of thrust they will create at a certain N1 speed. To account for
this, the ID plug may include a modifier to slightly after the N1 speed
and made an engine identical to what is considered the “norm”. Even
though the modifier may cause an engine to have a lower N1 speed the

87
signal sent to the flight desk gage will not show this reduction. In a
twin engine airplane, both N1 tachometers will show the same RPM.
Interface with Aircraft:
The inputs to the FADEC come from the following:
1.The power levers position in term of electric resolver angle. Two
analog signals come from each power-lever resolver,which is
mechanically linked to power or thrust lever on flight deck. (the
resolver is an electromechanical device to measure angular
movement)
2.The air data computers ( ADC) provide information in the form of :
a.Total pressure
b.Pressure altitude
c.Total air temperature

88
3.The flight-control computer for adjusting the engine pressure ratio
(EPR) for all the engines as a part of the engine thrust trim system
(ETTS). The ETTS logic starts when the engine pressure ratio (EPR)
on any two engines is above 1.2 there are two modes of ETTS
operation.
a.In the master mode, the high EPR and the low EPR engines are
adjusted to the middle EPR engine
b.In the target mode, a target EPR from the flight management
system ( FMS) is used to set all three engines.
4.Seven discrete (electrical signals) inputs :
a.Pt2/Tt2 probe heat.
b.Fire
c.Alternate mode select
d.External reset ( fuel-control switch)
e.Bump rate selector

89
f. Maintenance (data retrieval)
g.Engine location identification
5.Two sources of 28 VDC power (dc bus and ground test power)
Outputs from the FADEC are as follows:
• Engine pressure ratio
• Low-speed (N1). There is a back up N1speed output from
channel “B”
• Exhaust gas temperature (EGT)
• High-speed spool (N2)
Flap/slat position and weight on wheels status is also sent to the
FADEC. The flight control computer (FCC) acts as a backup for the air
data computer (ADC)
FADEC Interface with engine:

90
All data input to the FADEC is validated through a series of
comparisons and checks. For example, compressor rotor speeds are
compared to each other and checked to ensure the proper range
(0-120 percent)
Inputs to the FADEC from the engine are as follows:
• N2 rpm, Power comes from the FADEC alternator and is used for
limiting scheduling systems and setting engine speeds.
• N1 rpm, which comes from the FADEC speed transducer (a
transducer is a device used to transform a pneumatic signal to
an electrical one) and is used for limiting and scheduling
system. It is also used as an alternate mode.
• Compressor exit temperature (Tt3 ) which comes from the
diffuser case, is used to calculate starting fuel flow.

91
• Exhaust-gas temperature (Tt4.95 ) which comes from the exhaust
case, is used for indication.
• Fuel temperature (Tfuel), which comes from the fuel pump, is
used to schedule the fuel heat-management system.
• Oil temperature ( Toil) which comes from the main gear-box, is
used to schedule the fuel heat-management system and to
schedule the integrated drive generator (IDG) oil-cooing
system.
• Inlet total temperature ( Tt2), which comes from the inlet cowl
on the wing engines and the bell mouth on the tail engine. It is
used to calculate fuel flow and rotor speed.
• Inlet total pressure (Pt2), which comes from the same sources
as Tt2, is used to calculate EPR.
• Exhaust gas pressure (Pt4.95), which comes from the exhaust
case, is also used to calculate EPR.

92
• The engines electronic control (EEC) programming plug is used
to determine the engine thrust rating and EPR correction.
• Burner pressure (Pb), which comes from the diffuser case, is
used for limiting and surge detection.
• Ambient pressure (Pamb), which comes from the inlet cowl, is
used to validate altitude and Pt2
FADEC Fault Definition Logic.
The purpose of the FADEC fault-reporting system is to identify the
types of failures in the control system and to display these fault
messages on the engine and alert display (EAD). Several tests that can
be made under varying conditions include circuit checks in one or both
channels, position checks, and sensor checks. Cross checks will indicate
if a channel parametric or position input differs from the other
channel’s input by more than the permitted amount.

93
Both channels are tested to determine their health, and if both
channels are good, one channel is in command. On the next engine
start, the other channel is in command. A channel switch-over may
occur based on the ability of a channel to control.
Channel control, capability is determined by assigning a weight to a
fault. Both channels compare their weights, and the channel with the
least weight will be chosen to control the engine. Weight is determined
by assigning a priority to the inability to command a function and giving
that priority a number.
Each FADEC channel can use only its own drivers. The healthiest
channel is always in command and is known as the local channel. The
other channel is known as the remote channel. Fig. shows which units
are critical and which are noncritical. It also shows which torque motors
(TM) receive voltage from the FADEC.

94
Engine Control in Idle and Normal Power Range
Idle speed:
Minimum (ground) idle speed is selected by potting the power lever
in the idle position. When this is accomplished, the FADEC will select the
idle speed that will satisfy all of the following parameters.
• N2 to prevent IDG output.
• N2c2 for constant approach or taxi thrust (N2c2 is the corrected high
pressure rotor speed, derived from Tt2 .The N2c2 schedule biased by
altitude and Tt2 ensures go-around/take off power within Federal
Aviation regulations)
• N1 for engine-icing protection.
• Pb to support service or anti-ice air bleeds.
• Wf/Pb ratios to prevent burner blowout.
• Minimum W1 for safe operation.

95
Normal or Engine Control Modes:
The FADEC has two modes for setting the power of the engine. The
EPR mode is the rated or normal mode, while the N1 mode is the
alternate or fault mode.
Normal mode:
When a thrust-level request is made through the thrust lever, the
thrust-lever resolver angle, or throttle-resolver angle (TRA), input
causes an EPR command calculation using rating curves biased by Mach
number, Tt2, Pt2, and aircraft bleed status. The FADEC will then adjust
fuel flow so that EPR actual equals EPR command.
The normal or rated power levels are:
• Maximumn power available ( take off or maximum continuous)
• Maximum climb.

96
At approximately 78 degrees TRA maximum power available is
calculated by the FADEC. If the altitude is less than approximately
14,100 ft, the FADEC calculates a takeoff power rating. But if the
altitude is greater than 14,100 ft, the FADEC calculates a rating for
maximum continuous power. At approximately 68 degrees TRA, the
FADEC calculates the maximum climb-power rating. To get all other
power levels, except idle, it is necessary to set the thrust lever.
Alternate or N1 Mode:
If the FADEC cannot control in the EPR or normal mode, it will go to
the N1 mode and a fault is enunciated on the engine and alert display
(EAD). In the N1 mode, the FADEC schedules fuel flow as a function of
the thrust-lever position and the /TRA input will cause the FADEC to
calculate an N1 command biased by Mach number, altitude, and Tt2. In
reverse thrust, the FADEC goes to the N1 mode, and N1 is biased by Tt2

97
Control in the N1mode is similar to that of a hydro mechanical fuel
control system. Moving the thrust lever fully forward will cause an over
boost of the engine. Thrust is set using lap charts and the TRA versus
thrust will vary over the flight envelope.
Using the FADEC control panel shown in figure, the N1 mode may
manually selected, but the lock up logic that keeps the thrust at the
same level as it would be in the EPR mode is removed. The mode select
switch on the FADEC control panel may be used to return to the EPR
mode if the fault is cleared.
EEC Programming Plug:

98
The EEC programming plus located on the FADEC “A” channel
housing, selects the applicable schedules with the FADEC for the
following:
• Engine thrust rating
• EPR modification data
• Engine performance package
• Variable- stator-vane schedule.
• 2.9 bleed-valve thermocouple selection.
The EEC programming plug data is input to the FADEC “A” channel,
while the “B” channel EEC programming-plug input is cross-wired and
cross-talked from the “A” channel. During test-cell operation, the
EPR/thrust relationship is compared, and the engine gets a correct EEC
programming plug. If the FADEC must be replaced, the EEC
programming plug must remain with the engine.

99
If the engine is stated without the EEC programming plug installed,
the FADEC goes to the N1 mode. But nothing will happen with the
FADEC operation if the EEC programming plug disconnects in flight.
Interface Components:
Fuel Temperature Probe:
A dual element, alumelchromel thermocouple, located on the top
right side of the fuel pump, provides the FADEC with information
relating to fuel heating and engine oil cooling.
Oil Temperature Probes:
Two other similar devices inform the FADEC about scavenge oil
temperature and no. 3 bearing-oil temperature, and provide input for
engine oil cooling-system control, oil-temperature warning indication
and IDG oil-cooling override.

100
Tt2Temperature Probe
This dual-element probe is located on the diffuser case and provides
the FADEC with information for heat-soaked engine start logic.
Tt4.95 Temperature Probes
Four thermocouples measure EGT and send their signal to the
thermocouple junction box and then to the FADEC. The temperature
sense is used only for input to the indication system. There is no EGT
limiting function in the FADEC.
Exhaust Gas Pressure Probes
The two probes measure Pt4.95 pressure, are manifolded together,
and send their averaged pressure to the FADEC.
Alternator

101
The alternator provides the FADEC with power and N2 speed signal.
It also sends N2 information to the flight deck.
Speed Transducer
The speed transducer supplies the FADEC “A” and “B” channels with
the N1 signal by sensing the frequency at which the 60 teeth on the low
pressure compressor/low-pressure turbine (LPC/LPT) coupling pass by
them.
Pt2 /Tt2 Probe
The inlet pressure/temperature probe supplies the FADEC with
engine-inlet pressure and temperature information. The pressure
sensor is a total pressure probe that sends its signal to both FADEC
channels. The temperature sensor is a dual-element resistance type.
One element sends its signal to the “A” channel, while the other sends

102
its signal to the “B” channel. The probe is continuously electrically
heated.
Fuel Nozzles:
Fuel Nozzles, also called fuel distributors, are the terminating
point of the fuel system. They are located in the inlet of the
combustion liner to deliver fuel in a defined quantity. Fuel cannot
be burned in a liquid state. It must first be mixed with air in

103
correct proportions by atomization or vaporization. There are five
types of spray nozzles: the Simplex nozzle, the variable port
(Lubbock) nozzle, the Duplex nozzle, the spill-type nozzle, and the
air spray nozzle.
a. Fuel Nozzles (Pressure-Atomizing Type)
The pressure-atomizing type of nozzle receives fuel under high
pressure from a manifold and delivers it to the combustor in a
highly atomized precisely patterned spray. The cone shaped,
atomized spray pattern provides a large fuel surface area of very
fine fuel droplets. This optimizes fuel-air mixing and ensures the
highest heat release from the fuel. The most desirable flame
pattern occurs at higher compressor pressure ratios.

104
Consequently, during starting and other off-design speeds, the
lack of compression allows the flame length to increase.

105

106
It the spray pattern is also slightly distorted, the flame rather
than being held centered in the liner, can touch the liner surface
and cause a hot spot, or even burn through. Another problem that
distorts the spray pattern is contaminant particles within the
nozzle, or carbon buildup outside the nozzle, orifice. This can
cause hot streaking, which is an un-atomized stream of fuel which
forms and tends to cut through the cooling air blanket and
impinge on the liner or on downstream components such as the
turbine nozzle.
Fuel pressures sufficient for good atomization are very high.
Small to medium sized engines will have a fuel pressure at the fuel
nozzle of 800 to 900 pounds per square inch- gauge and large
engines up to 1,500 pounds per square inch gauge.

107
Some fuel nozzles are mounted on pads external to the engine
to facilitate removal for inspection. Others are mounted internally
and are only accessible when the combustion outer case is
removed. The duplex nozzle shown in figure is an externally
mounted design. The duplex nozzle shown in figure is an integrally
mounted type.
Simplex fuel Nozzle:

108

109
The simplex design is basically a small round orifice which
provides a single spray pattern and incorporates an internally
fluted spin chamber to impart a swirling motion and reduce axial
velocity of the fuel to provide atomization as it exists the orifice.
The internal check valve, present in the simplex nozzle shown, is

110
there to prevent dribbling of fuel from the fuel manifold into the
combustor after shutdown.
Some fuel systems with simplex nozzles as their main fuel
distributors incorporate a second smaller simple nozzle, called a
primer or starting nozzle, which spray a very fine atomized mist
for improved light off. After light- off start/primer systems are
generally turned off.
Another configuration with simplex nozzles is called “sector
burning”. The engine is started on one-half or more of the fuel
nozzles and operated in that manner up to ground idle speed.
Then, at approximately flight idle speed, fuel pressure is
sufficiently high to overcome a check, valve, which allows the
remaining fuel nozzles to flow.

111
Duplex fuel Nozzles

112

113
There are two common types of duplex fuel nozzles the single
line and the dual line type.
1) Single Line duplex Fuel Nozzles.

114

115
The duplex nozzle referred to as a single line duplex type,
receives its fuel at one inlet port and becomes a flow divider to
distribute fuel through two spray orifices. Often, as shown the
round center orifice, called the pilot, or primary fuel, sprays at a
wide angle during engine start and acceleration to idle. The
annular outer orifice, referred to as main or secondary fuel, opens
at a preset fuel pressure to flow along with the pilot fuel. Fuel of
much higher volume and pressure flowing from this outer orifice
causes the spray pattern to narrow so that the fuel will not
impinge on the combustion liner at higher power settings.
There are engines with single line (or dual line) duplex nozzles
that have flow angles which are different from what is identified

116
in the preceding paragraph. The CFM56 turbofan has single-line
duplex nozzles which have the widest flow angle coming from the
secondary, and a narrower angle from the primary. With
advancements that have taken place in combustor design, to
include better control of airflow and the flame zone within the
combustor, engines today are able to have secondary fuel flow at
a wider angle and still keep the flame away from the metal.
The duplex nozzles also utilize spin chamber for each orifice.
This arrangement provides an efficient fuel atomization and fuel
air mixture residence time, as it is called over a wide range of fuel
pressure. The high pressure supplied to create the spray pattern
generally 800-1500 pounds per square inch-gauge, also gives good
resistance to fouling of the orifices from entrained contaminants.

117
The head of the fuel nozzle is generally also configures with air
holes which provides some primary air for combustion but are
mainly used for cooling and cleaning the nozzle head and spray
orifices. At times of starting fuel flow only, the cooling airflow is
also designed to prevent primary fuel from back flowing into the
secondary orifice and carbonizing.
Airflow in the direction of the fuel nozzle orifice results from
the pressure differential that exists between high pressure
secondary air outside the liner and the lower pressure primary air
within the liner, these cooling air holes must be kept clean, or
carbon build up and heat erosion will be accelerated.
A distortion of the orifice flow area by carbon buildup around
the head of the nozzle can distort the spray pattern. This buildup

118
can be seen on a bore-scope check on some engines and if, severe
enough, could required removal of the nozzles for cleaning. This
could in some installations, even require an engine tear-down to
remove the carbon buildup. However, a recent development in
decarbonizing allows he engine to be flushed with a special
solution through the fuel manifold. This purging under pressure
loosens and removes the carbon and is a routine line maintenance
procedure on some newer aircraft.
2) Dual-line Duplex Fuel Nozzles :

119
A second type or duplex nozzle, called a dual line duplex type
is quite similar to the single line except that it contains no flow
divider check valve to separate primary and secondary fuel. The
check valve in this system is located in the Pressurizing and Dump

120
Valve and is labeled “Pressurizing Valve”. The pressurizing valve
acts as a single, main flow divider for all of the fuel nozzles,
whereas in the single line duplex nozzle, each has its own flow
divider in the form of its check valve.
variable-port or Lubbock nozzle

121
The variable-port or Lubbock nozzle, made use of a spring
loaded piston to control the area of the inlet ports to the swirl

122
chamber. At low fuel flows, the ports sere partly uncovered by the
movement of the piston; at high flows, they were fully open. By
this method, the square-law pressure relationship was mainly
overcome, and good atomization was maintained over a wide
range of fuel flows. The matching of sets of spray nozzles and the
sticking of the sliding piston due to the dirt particles were,
however, difficulties inherent in the design and this type was
eventually replaced by the duplex fuel spray nozzles.
Spill-type nozzle
The spill-type nozzle can be described as being a Simplex spray
nozzle with a passage from the swirl chamber for spilling fuel
away. With this arrangement it is possible to supply fuel to the
swirl chamber at a high pressure at all times. As the fuel demand

123
decreases with altitude or reduction in engine speed, more fuel is
spilled away from the swirl chamber, leaving less to pass through
the atomizing orifice. Constant use of a relatively high pressure by
the spill spray nozzle means that even at the extremely low fuel
flows that occur at high altitudes there is adequate swirl to
provide constant and efficient atomization of the fuel.
The spill spray nozzle system, however, involves somewhat
modified types of fuel supply and control system. A means has to
be provided for removing the spill and for controlling the amount
of spill flow at various engines operating condition. A
disadvantage of this system is that excess heat may generated
when a large volume of fuel is being recirculated to the inlet. Such
heat may eventually lead to a deterioration of the fuel.

124
Air Blast or spray Fuel Nozzles :

125

126
The air blast fuel nozzle is a newer design and is being more
widely used in various sized engines because it enhances the
atomization process and produces finer fuel droplets. This nozzle
is said to be more effective during starting when low fuel pressure
causes atomization problems. By using a high velocity airflow, air
blast nozzles more completely atomize the fuel than can be
accomplished with fuel under pressure along. This nozzle also has
an advantage in that it utilizes a lower system working pressure
than the basic atomizing types of nozzles.
Fuel Nozzles (Vaporizing type)

127
The vaporizing fuel nozzles connect to a fuel manifold in an
arrangement similar to the atomizing type. Instead of delivering
the fuel directly into the primary air of the combustor, as the
atomizing type does, the vaporizing tube premixes the primary air

128
and fuel. Combustor heat surrounding the nozzle causes the
mixture to vaporize before exiting into the combustor flame zone.
Whereas the atomizer nozzle discharges in the downstream
direction, the vaporizer discharges in the upstream direction and
the mixture then makes a 180 turn to move downstream. This
arrangement provides a slow moving fine spray over a wide range
of fuel flows and is said to produce more stable combustion in
some engines than can be achieved by atomizing nozzles,
especially at low revolutions per minutes. Some vaporizers have
only one outlet and are referred to as cane shaped vaporizers.

129
The tee-shaped vaporizer, is one of a set of eleven utilized in
some models of the Lycoming T-53 turbo-shaft engines. Because
vaporizing nozzles do not provide an effective spray pattern for
starting the T-53 incorporates an additional set of small atomizing
type spray nozzles which spray into the combustor during starting.
After light-off, start fuel is terminated on spool-up to idle. This

130
system is generally referred to as a primer or starting fuel system.
The Rolls Royce Olympus engines in the Concorde SST, and several
other engines, utilize the vaporizing fuel nozzles and primer fuel
nozzles systems, but these systems are not in wide use
throughout the industry.
Fuel Pressurizing and Dump Valve:

131

132
A pressurizing and dump valve (P & D valve) is used along with
a duplex fuel nozzle of the dual inlet line type. Rather than
providing a flow divider in each nozzle, as with the single line
duplex fuel nozzles, this arrangement allows for one central flow
divider, called pressurizing and dump valve. The term
“Pressurizing” refers to the fact that at a pre-set pressure, a
pressurizing valve within the P & D valve opens and fuel flows into
the main manifold as well as through the pilot manifold.

133
The term dump refers to a second internal valve which has the
capability of dumping the entire fuel manifold after shut down.
Manifold dumping is a procedure which sharply cuts off
combustion and also prevents fuel boiling as a result of residual

134
engine heat. This boiling would tend to leave solid deposits in the
manifold which could clog the finely calibrated passage ways.
A pressure signal from the fuel control arrives at the P & D
valve when the power lever is opened for engine start. This
pressure signal shifts the dump valve to the left, closing the dump
port and opening the passage way to the manifolds. Metered fuel
pressure builds at the inlet check valve until the spring tension is
overcome and fuel is allowed to flow through the filter to the pilot
manifold. At a speed slightly above ground idle, fuel pressure will
be sufficient to overcome the pressurizing valve spring force and
fuel will also flow to the main manifold.
The tension on the pressurizing valve spring is normally
adjustable as a line maintenance task. A valve opening too early
can give an improper fuel spray pattern and create hot starts or

135
off idle stall. A late opening valve can cause slow-acceleration
problems. To delay the opening of the secondary manifold and
eliminate hot start or off idle stalls, the adjusting screw would be
turned in to increase tension on the pressurizing valve spring.
Conversely, to cause early fuel flow to the secondary manifold
and enhance acceleration, the adjuster would be termed
outward.
To shut off the engine, the fuel lever in the cockpit is moved to
off. The fuel control pressure signal is then lost and spring
pressure will shift the dump valve back to the right opening the
dump valve port. At the same time, the inlet check valve will
close, keeping the metered line flooded and ready for use on the
next engine start.
Drain Tanks:

136

137
Dump fuel, in years past, had been allowed to spill onto the
ground or siphon from a drain tank in flight. Current FAA
regulations, however, prohibit this form of environment pollution
and now the drain tank fuel must be captured, perhaps by hand
draining. To prevent hand-draining, several types of recycling
systems have recently evolved. One such system returns fuel to
the aircraft fuel supply. Another type of system pushes fuel, which
formerly would have been dumped out of the fuel nozzles by
introducing bleed air into the dump port. This prolongs
combustion slightly until fuel starvation occurs. In the system
shown in figure, a full tank causes a float valve to actuate and
drain the tank via an educator type flow system.
Dump Valve:

138
The dump valve, sometimes, called a drip valve, is
incorporated in the low point of fuel manifold which utilize the
simplex and the single line duplex types of fuel nozzles. Its sole
purpose is to drain the fuel manifold after engine shutdown. It is

139
subject to the same environmental restrictions discussed for the P
& D valve. The function of its dump valve is identical to the dump
valve in the P & D valve.
Combustor Drain Valve:

140
The combustor drain valve is a mechanical device located in
the low point of a combustion case. It is closed by gas pressure

141
within the combustor during engine operation and is opened by
spring pressure when the engine is not in operation. This valve
prevents fuel accumulation in the combustor after a false start or
any other time fuel might tend to puddle at the low point.
A false start in this case is a no-start condition or hung start
condition which results in a fuel soaked combustor and tail pipe.
Draining of fuel in this manner prevents such safety hazards as
after-fires and hot starts. This drain also removes un-atomized
fuel which could ignite near the lower turbine stator vanes
causing serious local overheating during starting, when cooling
airflow is at the lowest flow rate.
As mentioned in the P & D valve discussi0on, if the dump line
is capped off as an ecology control, the fuel manifolds will drain

142
through the lower nozzles and fuel will evaporate in the
combustor or exit the combustor via the mechanical drain valve
into an aircraft drain receptacle. Maintenance personnel will
periodically drain this tank as a pollution control measures before
it spills over onto the ramp.

143

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