Applied to control the posit three-dimensional ea and the followers which provide a response Computer Action cams—the It can now be seen that the operation of three Fa” three-dimensional cam, the fuel cam, and the CDF Ct rovides an integrated effect which is applied to the 51° as grated effect whieh ne mit plot valve ing lever to feed a signal force to the limit pilot 07 ‘This valve then controls the hydraulic pressure supply and the drain from the governor pilot valve. The gover gavin is thus limited as a function of the positions of the Variable-Stator-Vane Control Note in Fig. 12-25 that the variable-stator-vane (VSV) pilot valve is affected by a follower on the three-dimen Sonal cam, Thus, the hydraulic pressure to the VSV servo is controlled by the position ofthe three-dimensional cam The servo is an actuator which moves the variable stator vanes as necessary to provide the correct angle of atack for the air flowing through the compressor. Two VSV aetua- tors are mounted on the compressor Idle System ‘The ground-flight idle system is designed to provide the correct idle speed for ground operation ofthe engine or for flight. The system is solenoid-activated by an electric sig nal from the pilot of flight engineer. When the solenoid is energized, the solenoid valve ports bypass fuel pressure to the idle-reset servo piston, which moves to reset the ile stop to the low-idle or ground-idle position. In the deener- {ized condition, the solenoid valve ports control pressure to the idle-reset servo piston, which then moves the idle stop to the high-dle position for fight conditions. Fuel Shutoff Lever ‘The fuel shutoff lever shaft is concentric with the power lever shaft and functions to rotate the fuel shutoff valve to the open or closed position. At the same time, it rotates the fuel-pump unloading rotor valve, thus permitting fuel pres- sure and spring force to move the differential pilot valve plunger down, This applies control fuel pressure to the bypass valve. The bypass valve spring plus the control pressure acts to permit bypass of excess fuel pressure and at the same time maintains operating pressure within the FCU during coastdown or windmilling ofthe engine. Game era TURBOSHAFT ENGINE {Atypical turboshaft engine incorporates a ga (Gas generator and a power tine sytem nities engine. The gas producer consists of a compressor, th combustion chamber, fuel nozzle or nozzles, and the ‘gas. producer turbine. This section produces the high-velovity, high-temperature gases which furnish the energy to nee Bis 332 Chapter 12. Gas Turbine Engine: Fuels and Fuel systems bine usually incor ne. The power tutb por 1 power turbine. THe Pre wheels) which extract the Tovar more stages tut yer power to the CUPOL sha from the Bases On for a turboshalt engine is of Al onto) ons, oe which Senses and reply comprised icer part of the engine and the other whi the gas-producet Pat -equirements of the power-tuing see ye co CE 4g ‘ron Pete trroducer speed. which, in turn, cerns the POWE! Parr ion of the power-turbine fuel go hed by the action i me OT "urbine speed. The power-tur hich senses power . ae Maid ore operator as the load requires, ang rod is selected DY a speed is ee go maintain this speed is automaticaly te, poe py power-aubine gevermor action on melee, weights which continually sense power turbine speed the speed sensing, the governor produces ations Through the garproduce fuel contol to schedule he wae (amount of fuel for the required operation rect gw for engine contol is established as a function of eompressor discharge pressure (P,), engine speed (N, for the gas producer and N, for the power turbine), and ga Bas Prprotle lever position. Note that these same par. rire are employed in the control of other turbine engines, met some controls utilize additional parameters for fuel anttrol, Turbojet engines utilize turbine inlet temperature gran important factor in fuel control; however, this isnot required for the engine control under discussion. Gas-Producer Fuel Control ‘The fuel control system described here is the Bendix sys- tem employed on the Allison series 250 turboshaft engine and is illustrated in Fig. 12-26. Note that the gas-producer fuel control and the power-turbine governor are intervon- nected so that each may affect the operation of the other as required, "The gas-producer fuel control is similar in many respects to other fuel controls described previously. Its pr ‘mary function is the same. Fuel entering the control encounters a bypass valve which maintains a constant dif ferential between fuel pump pressure P, and metered fuel pressure P,. Excess fuel is bypassed back to the entering side of the pump. The constant pressure differential i+ ees the ee valve; therefore, fuel flow will portion to the opening of the metering valve. The ee to which the metering valve is open is contol) pone the governor bellows and the acceleration be! ding tanned by the action of the derichment valve Sua staring. The maximum range of movement of The an valve is controled by the minimum flow stop and mum pean few stop. The unit also incorporates 8 mes valve, and lief valve, a manually operated shule! Than bellows-operated start-derichment valve on tes bration of the gas-producer fuel control is bs Htiacs: x meuomeshanical. ; ie = drawing in Fig. 12-27 illustrates how Pressure controlled to operate @ metering valve: # thee the drawing, xix pressure P_. which may be compared 10 reid to the controller and flows through oe eet of ow through the ac bled wil determine bleed Terence between P. and modified pressure P. The the ire determined by the position of the governey Fate of Figs gowernor vate is completely ctose tere wil, rae ea trough the ar bleed and will equal Py Since Tene ee a a comparatively high fevel, te pressure {9 ihe bellows chamber would cause the bellows fo collapse a epctering valve to open through the finkage to the metering valve re vnc governor valve is closed, pressure P is much ower than P, This allows the bellows fo expand and close the metering valve The metering valve in the gas-producer fuel control is operated by lever action in accordance with the movement opie governor bellows and the acceleration bellows. Note Ghat the governor bellows and acceleration bellows are Siiectod by variations in P, and P,, Pressures P, and Pe Senved by passing pressure P. through two air bleeds. The Sarr airflow through these bleeds is controlled by action Bf ine governor as modified by throttle positon and the {nfluence ofthe power-turbine governor Before lightofT and acceleration, the metering valve is set at a predetermined open position by the acceleration Tehiows Under the influence of ambient pressure. At this point, ambient pressure and P_ are the same because the Compressor is not operating. “The start-derichment valve is open during lightoff and ‘acceleration until a preestablished P. is reached. The open Gerichment valve vents pressure P, f0 the atmosphere, thus Slowing the governor bellows to move the metering valve {oward the minimum flow stop. This keeps fuel flow at the ean fuel schedule required for starting and acceleration. As CSmpressor rpm increases, the derichment valve is closed ty B. acting on the derichment bellows. When the derich- rent valve is closed, control of the metering valve is returned to the normal operating schedule in which the effects of P, and P, as regulated by the governor are operat ing through the governor bellows and acceleration bellows. ‘During acceleration, P, and P, are equal to the modified CDP P, up to the point where the speed-enrichment orifice is opened by the governor flyweight action. This action bleeds pressure P, while pressure P, remains at a value ‘equal to P... Under the influence of the P, ~ P, pressure drop across the governor bellows, the metering valve moves to a more open position, thus increasing fuel flow as ‘required for acceleration. ‘Gas-producer rpm (N,) is controlled by the gas-producer ‘control governor. The governor flyweights operate the gov- ‘emot lever which controls the governor bellows (P,) bleed at the governing orifice. The flyweight operation of the governor lever is opposed by a variable spring load which is changed in accordance with the position of the throttle acting through the spring-scheduling cam. Opening the ‘govemor orifice bleeds pressure P, and allows pressure P, to control the governor action on the bellows. The P Z action on the bellows moves the metering valve to a more ‘closed position until metered flow is at steady-state require- “The governor-reset section of the gas-producer fuel con- ‘tol is utilized by the power-turbine governor to override ‘speed-governing elements of the fuel control, to change toad conditions applied (0 Power assembly apply force (0 the govel io nor springs. moat the effect of the Bover” power-Turbine Governor he power-turine ection of tn ei aay force directed to the mids by increasing OF the needed gas ener- ne calls upon the #88 rf Fring on the load reo provide the acti ful ge uel contol, whic SP a oe as reued to proce 8). shown in Fig. 12-26, the power-trbine ey seta iea'by the power turbine governor JV Tt poe tubing (Ps goveror-spring load which OpPone® the ir spaca flyweighls. As the desired Sper rermeahed, the speed weighs, operaing a6) the gover- are move link wo open the power-turine 22/7 orig ved iyweights also open the overspeey Dies ori ice bt ata hgher speed than that at which We 128° roma once (P,) 8 peed goverturine goveror, like the gss-producer Fett con Ptizes controlled air pressure to accomplish its or Compressor discharge pressure P_ enters the aif Pape eshich ix a pressure regulator, The output of the 3r vate i regulated pressure P, which is applied to one side tile diaphragm in the governor-reset section of the 8S, Craducer fuel control. Governor pressure P,, developed Prnen pressure P, passes through the P, bleed. is applied 19 Tre opposite side of the diaphragm. Wiien the governor or fice is closed, P, and P, are equal and produce no effect on the governor-reset diaphragm. When the governor orifice is ‘opened by action of the flyweights, P, is reduced. The effect of P,— P, on the diaphragm is to produce force through the’ govemnor-reset rod to the gas-producer gover nor lever (power output link) to supplement the force of the flyweights in the gas-producer governor, This opens the P, orifice and bleeds P,, thus causing the gas-producer gover. hor bellows to move the fuel metering valve to a more Closed position. This, in tun, reduces gas-producer speed. Gas-producer speed cannot exceed the gas-producer fuel ‘governor setting. ‘The governor-reset diaphragm is preloaded to establish the active P, ~ P, range. This is accomplished by means of peas as shown in Fig. 12-26. 1¢ overspeed orifice in the power-turbine governor beds fom the governing sytem ofthe aes . This gives ‘overspeed: alee system a rapid response to Ny ELECTRONIC ENGINE CONTRO! Because of the need to contol precisely the many factors involved in the operation of modem pretense ngines, airlines and manufacturers have worked together 1 develop elesonc engine contol (EEC) systems that mrolong engine life, sve fel, improve relia, re : ight crew workload, and reduce maintenance costs, The Electronic Engine Controls. 333.AMBIENT AIR PRESSURE (Pa) x AIR BLEED: = BELLOWS: FUEL (Pa) PRESSURE (P.) FUEL (Ps) wf MeTERING VALVE MODIFIED PRESSURE IP.) GOVERNOR VALVE. FIG, 12-27 Simplified drawing showing the use of pneumatic control for a fuel metering valve. cooperative efforts have resulted in two types of ECS, one being the supervisory engine control system and the other the full-authority engine control system. The supervisory control system was developed and put into service first, and is used with the JT9D-7R4 engines installed in the Boeing, 761. Essentially, the supervisory EEC includes @ computer that receives information regarding various engine operat ing parameters and adjusts a standard hydromechanical i FCU to obtain the most effective engine operation. The hydromechanical unit responds to the EEC commands and. actually performs the functions necessary for engine opera- tion and protection, ‘The full-authority EEC is a system that receives all the necessary data for engine operation and develops the com- ‘mands to various actuators fo control the engine parameters within the limits required for the most efficient and safe Ace AIRCRAFT ELECTRICAL POWER =e cockpit ENGINE ELECTRONIC contROL deacrivare Q SwiTcH — ( AIRCRAFT INTEGRATED DIAGNOSTIC. SYSTEM ‘cocker THRUST LEVER RESOLVER ELECTRONIC SUPERVISORY CONTROL SvsTeM AIG. pes Integration of supervisory EEC with arcrat systems. (ASME) 36° Chapter 12. GasTurbine Engine: Fuels and Fuel Systems supervisory EEC System 1 system employed wit te 0 ee acludes a hydromechanie FTOD-TRA tabola ard IEC described ea CU sac oa EEC 103 unit, a hydromechanica, es, a Hamilton St contro, permanent-agnet altar air-leed and vane Over for the EEC separate from the ar to provide elect Psd an engine inlet pressure and tem. craft eleewie Ste 2p, and Tg. The hydromechanical perature probe to Se"ontrof such basic engine functions ris of the syle, OnE A celeraion, high-pressure tutomatc 27Nay governing, VSV compte posto, rotor speed (etaringai-bleed cone, and bumer pres: moda ag The EEC provides precision thst map. Se Ed Sat dy seen Nat BOT NE ep int EPR cm oF staal EPR. Ic also provides control of modula an ae se cooling and turbine-cooling ai valves and turbine onmation regarding parametric and control sys- transmits on for possible recording. Such recorded data tem etaed by maintenance tecbaicians in eliminating faults in the system. ea nmcrisory EEC, by measuring EPR and integra ing trust fever (nrotle) angle, altitude data, Mach num- +e ie air pressure Pink ac temperature 7. and toa irtemperature in the computation, is able to maintain con- Sant thrust from the engine regardless of changes in ai pressure ar temperature, and flight environment. Thrust Ehanges occur only when the thrust lever angle is changed, and the thrust remains consistent for any particular position Of the thrust Iever. Takeoff thrust is produced in the full forward position of the thrust lever. Thrust settings for climb and cruise are made by the pilot a the thrust levers ‘The digital supervisory DIGITAL AIRDATA cowPuTeR AIRCRAFT THRUST. MANAGEMENT SYSTEM <> = anc RCRA alll le ArT at MAINTENANCE ras ray Monon eu Cocke FAULT UGHTImoved 16 position that provides the comet EPR forthe thr desire. The EEC i dengned so hte engine wil Gckly and preity adjust o new thst setng wit thangs fever ino ner jhe sdromechanical FCU trough a tongue mtr eletoby draulic servo system. : i nh Tn a supervisory EEC system, any fant nthe EEC tha adverely affects engine operation causes inodat reversion to control By the hydromechanical PCU. A the Same time, te system sends an annuncator light signal (0 the covkpt to inform te ere ofthe change in operating mode. A switch in the cockpit enables the crew t change from EEC contol to hydromechanical contol if it deemed advisable ‘The supervisory EEC i integrated wit the srralt sy tems as indicated In Fg, 12-28, The input and outpot5 hale are shown by the directional arrows. Although the BEC ullizes aircraft electric power for some of i fune- tons, the electric power forthe asic operation ofthe EEC is supplied by the separate engine-drven permanent-mag- netalternator mentioned ear “The output signals of the supervisory EEC that affect engine operation ae the adjustment ofthe bydromechanical FFCU and commands to solenoid-actuated valves fo contol of modulated turbine case cooling and turbine-coling ai Full-Authority EEC ‘A full-authority EEC performs all functions necessary to operate a turbofan engine efficiently and safely in all modes, such as starting, accelerating, decelerating, takeoff, ‘limb, cruise, and idl. It receives data from the aireraft and ‘engine systems, provides data for the aircraft systems, and issues commands to engine control actuators. ‘The information provided in this section is based on the Hamilton Standard EEC-104, an EEC designed for use with the Pratt & Whitney 2037 engine. The unit is shown in Fig, 12-29. This is a dual-channel unit having a “crosstalk” capability, so that either channel can utilize data from the ‘ther channel. This provision greatly increases reliability to the extent that the system will continue to operate effective- ly even though a number of faults may exist. Channel A is the primary channel, and channel B is the secondary, or backup, channel. “The following abbreviations and symbols are used in this section to identify functions, systems, and components: ACC Active clearance control BCE Breather compartment ejector EEC Electronic engine control EGT Exit (exhaust) gas temperature EPR Engine pressure ratio FCU_ Fuel control unit LVDT Linear variable differential transformer N,_Low-pressure spool rpm High-pressure spool rpm ‘Ambient air pressure Bumer pressure Permanent-magnet alternator Static compressor air pressure Engine inlet total pressure FIG. 12-29 Hamilton Standard EEC-104 electronic engine control (Hamilton Standard) TRA Throttle resolver angle T,, Engine inlet total air temperature 7h, Exhaust-gas temperature w,) Fuel flow 7 Figure 12-30 is a block diagram showing the relation- ships among the various components of the EEC system. Input signals from the aircraft to the EEC-104 include throttle resolver angle (which tells the EEC the position of the throttle), service air-bleed status, aircraft altitude, total air pressure, and total air temperature. Information regard- ing altitude, pressure, and temperature is obtained from the air data computer as well as the Pa/T,, probe in the engine inlet. ‘Outputs from the engine to the EEC include overspeed ‘warning, fuel flow rate, electric power for the EEC, high- re rotor speed N,, stator vane angle feedback, posi- tion of the 2.5 air-bleed proximity switch, air/oil cooler feedback, fuel temperature, oil temperature, automatic clearance control (ACC) feedback, TCA position, engine luilpipe pressure P,., bumer pressure P,, engine inlet total pressure P, low-pressure rotor speed N,, engine inlet total temperature T', and exhaust-gas temperature (EGT or T,.). Sensors instalfed on the engine provide the EEC with mea- ‘urements of temperatures, pressures, and speeds. These data are used to provide automatic thrust rating control, ‘engine limit protection (overspeed, overheat, and overpres- sure), transient control, and engine starting. Outputs from the EEC to the engine include fuel flow torque motor command, stator vane angle torque motor command, air/oil cooler valve command, 2.5 air-bleed torque motor command, ACC torque motor command, oil bypass solenoid command, breather compartment ejector solenoid command, and TCA solenoid command. The actu- ators that must provide feedback to the EEC are equipped with linear variable differential transformer (LVDTs) to produce the required signals, During operation of the engine control system, fuel flows from the aircraft fuel tank to the centrifugal stage of the duat-stage fuel pump. The fuel is then directed from the pump through a dual-core oil/fuel heat exchanger which provides deicing forthe fuel filter as the fuel is warmed and the oil is cooled. The filter protects the pump main-gear stage and the fuel system from fuel-borne contaminants, Electronic Engine Controls. = 33710 not soLkwoiD AND VALVE ‘Ano VALVE 10 TeAsOLENOID ee NAINGhArT oe cyan a ourwurs To ems! nos SteoNDan 1 freon evrass |Next aq SS) BS Fue FuevswuTare no, _-} conte lea EOMMAND, alnvoit conten’ FILTER PRESSURE Sure wan ute Powe oun. mt Tae ENGINE GEAR 80x FIG. 12-30 Simplified block via (Harmiten Standard) High-pressure fuel from the main-gear stage of the fuel pump is supplied to the FCU, which, through electrohy- Araulic servo valves, responds to commands from the EEC to position the fuel metering valve, stitor vane actuator, and airfoil cooler actuator. Compressor air-bleed and ACC Actuators are positioned by electrohydraulic servo valves that are controlled directly by the EEC, using redundant forque motor drivers and feedback elements. ‘The word “redundant” means tht units or mechanisms are designed wit backup features so that a failure Fu pump discharge peste is td power the nator vine 23 nedsce eee and ACC scator, The BEC naive : ‘weather ejector and the ac ee 338 Chapter 12 Gas-Turbine Engine: Fueh and Fuel Sy Suey FueL— RETURN FUEL — O— ctecrnicaL caste $= ver uines gram of the EEC system with the Hamilton Standard EEC-104, ‘The EEC and its in in Fig. 12-31, Note th side of the en with vibr terconnected components are shown iat the EEC is mounted on the top left wine fan case. The mounting is accomplished ion isolators (shock mountings) to protect the ‘The benefits of substantial benefits are tse the thot lever angle ton positon ti results in alignment ri e ‘of the EPR command from the EEC With the reference in ee stems FIG. 1FIG. 12-31 Drawing showing EEC units on an engine ACTUAL ENGINE _- PRESSURE RATIO. NEEDLE [REFERENCE INDICATOR COMMAND ENGINE. PRESEURE RATIO. NEEOLE ACTUAL ENGINE PRESSURE RATIO FAG. 12-32 Drawing of an engine pressure ratio gage. Reduced fuel consumption is attained because the EEC controls the engine operating parameters 50 that maximum thrust is obtained for the amount of fuel consumed. In addi- tion, the ACC system ensures that compressor and turbine blade clearances are kept to a minimum, thus reducing pressure losses due to leakage at the blade tips. This is accomplished by the ACC system as it directs cooling air through passages in the engine case to control engine case temperature. The EEC controls the cooling airflow by send- ing commands to the ACC system actuator. Engine trimming is eliminated by the use of the full- authority EEC, When an engine is operated with a hydro- ‘mechanical FCU, it is necessary periodically to make adjustments on the FCU to maintain optimum engine per- formance. To trim the engine, itis necessary to operate the ‘engine on the ground for extensive periods at controlled speeds and temperatures. This results in the consumption of substantial amounts of fuel plus work time for maintenance personnel and downtime for the aircraft, With the full- authority EEC, none of these costs is experienced. ‘The fault-sensing, self-testing, and correcting features designed into the EEC greatly increase the reliability and maintainability of the system. These features enable the system to continue functioning in flight and provide fault (Hamiton Standard) information that is used by maintenance technicians when the aircraft is on the ground. The modular design of the electronic circuitry saves maintenance time because circuit boards having defective components are quickly and easily removed and replaced. Garrett Digital Fuel Controller The BEC designed for operation withthe Garrett TFE-731- S turbofan engine is called a digital fel controler (DFC) and is a full-authority system. The DEC is shown in Fig 12-33, ‘The DFC for the TFE-731-5 engine performs the follow- ing functions: ith varying altitude, ai 1. Maintains required thrust speed, and inet air temperature T, 2, Maintains adequate surge margin throughout the operating range and during acceleration and deceleration of the engine 3, Provides automatic fuel enrichment during starts. nal Movies schedules for minim and maxim fet flow. 5. Provides temperature limiting at all times. FIG, 12-33 Garrett digital fuel controller (AlliedSignal, inc.) 339 Electronic Engine Controls6, Automatically detects overypeed and culo valve 7, Provides for synch MB Provides for arate anf toa backup mae élecrc powers rece below inna ree il 9, Provide for use of her faut speeds in ining engine speed a 1 lever (th powe The DIC ili 8 HOB The power levers input so the, cg J Fi, 12~34 shows the inp ined ode select switch, DFC and theo engine soo! speed engine fe conftt pu corte from the cockpit and Inputs an i, auch as the 1 te n the engine itself. he es Seat ct l.control.(AliedSignay, nc.) Chapter 12 Gas-Turbine Engin Fuels and Fue! Systems FIG. 12-34 Simplified block diagram of a digital fu 340 | | |DFC outputs include u proportional drive For regain DAC oa ne el cma tel are sn dco 10 ovenpeed rt includes an extensive, builtin test feature Cae eee aha ee ropcenet uit saree ag components and for self-dingnesing the COP weer capable o caning fut sory a annunsi ing faults onthe cockpit panel display 4. wat quaties should turbine fuels posses? + What Swe fypes of turbine fuels are in common hat ae the Wat are the etferences between jet A and as riven jet and jet B 4S wnat is the danger in mixing jet A and it eh 3 Ja jet A and et 8 5? Ls tne principal components in a turbine-engine fuel gsm. 2 ce the fuet-ooted ol cooler usualy loa cea inte sytem Why 1 located at this pont? Trust ate eco ro eine ne pinepie of operation of 2 duplex fuel nozzle. 4 " pozz manual fuel contol not sutale for @ gasturbine engine? nvout? A ean die-out? 40, What Isai t condo 10. Mime the engine operating » controlled (parame ting Shute efficient and sal fe engine ‘12. Which ed in the prev cous question are generally em the operation of anFCu? Fe mati a hydromechanical FC? 43 pete te function of 2 fuel metering section ina hydromechanical FCU. aria the function of the COMPUTES section? 45. What pe the metering system 10" We Feces FCU, 46. Prmat engine operating parameters ae sensed by the zemputing section of the CES FCA ne Gescripe the function of the EVES ant 18 eth principal pats of the EVC3 Pet 12. Marat engine operating parameters ara ¢ by the Woodward {uel contr for the ‘General Electric CF gaseturbine engine? 6 oes pe the operation of the speed governor? the Woodward FCU. ewWoodwiare Fine VSV seve controlled In the woodward FCU? Seat Foe the basic design of a fuel control for 2 ‘urboshaft engine ost aat the difference between 2 supervisor EEC anda full-authority EEC? Sars ipenetits are derived from use of 2 full authority EEC?Ceeennnnneeeeeeeeeeeeeeeee eee A SN Turbine-Engine Lubricants 13 and Lubricating Systems peru Teac Ter) ie vied Early gas turbines used oils that were thinner than those tused in piston engines, but these oils were produced from the same mineral crude oil. When gas turbines that operated at higher speeds and temperatures were developed, these mineral oils oxidized and blocked the filters and oil pas sages. The development of low-viscosity synthetic oils overcame the major problems encountered with the early mineral oils. Lubricating Oils Lubricating oils for gas-turbine engines are usually of the synthetic type. This means that the oils are not manufac tured in the conventional manner from petroleum crude oils. Petroleum lubricants are not suitable for modern gas- turbine engines because of the high temperatures encoun- tered during operation. These temperatures often exceed '500°F [260°C]. and at such temperatures, petroleum oil tend to break down. The lighter fractions of the oil evapo- rate, thus leaving carbon and gum deposits; the lubricating characteristics of the oil rapidly deteriorate, too. ‘Synthetic oils are designed to withstand high tempera- tures and still provide good lubrication, The first generally acceptable synthetic lubricating oil conformed to MIL-L- 7808 and is known as type I, an aklyl diester oil. During recent years, type Il oil, a polyester lubricant, has been found most satisfactory. This oil meets or exceeds the requirements of MIL-L-23699. ‘Lubricants for gas-turbine engines must pass a variety of exacting tests to ensure that they have the characteristics required for satisfactory performance. Among the charac- teristics tested are specific gravity, acid-forming tenden- ‘cies, metal corrosion, oxidation stability, vapor-phase cok- ing, gear scuffing, effect on elastomers, and bearing perfor- mance. These tests are designed to provide indications that the oil will supply the needed lubrication under all condi- tions of operation. Viscosity of Synthetic Oils. The viscosity of the syn- thetic oils used in gas-turbine engines is generally expressed in units of the centimeter-gram-second (cgs) system, Under, this system, the basic unit for the coefficient of absolute ‘viscosity is the poise (P), named for the French physiolo- gist Jean L. M. Poiseuille (1799-1869). If we imag} plate being drawn across the surface of 1 layer of oil the Force necessary to move the plate at a given measure of the viscosity of the oil. If the lay thick and the plate is moved at the rate of 1 cm/s, the total tpumber of dynes of force required to move the plate, divid fd by the area of the plate in square centimeters, wall equal the coefficient of viscosity in poises. To express this in dif- ferent terms, when 1 dyne (dyn) will move a -cm plate at @ rate of 1 emis across the surface of a liquid with a thick tess of 1 om, the coefficient of absolute viscosity is I P. "The viscosity of turbine-engine oil is considerably less than 1 P; therefore, the centipoise (1 cP = 0.01 P) is used t0 express the viscosity. ‘Because the density of oil is an important factor, it is ‘common practice to employ the unit for kinematic viscosi- ty in establishing the characteristics of gas-turbine lubri- ants, The unit for kinematic viscosity is the same as the poise when the density of a liquid is 1 gram per cubic cen- fimeter (p/cm?). Kinematic viscosity is expressed in stokes (St) [m2/s x 10-4] or centistokes (cSt), | cSt being equal to {0.01 St. Kinematic viscosity in stokes is equal to absolute viscosity in poises divided by the density of the liquid in ‘grams per cubic centimeter. The Saybolt Universal viscosi- ty of an oil having a kinematic viscosity of 5 cSt is approxi- mately 42.6. This is roughly equivalent to what is known as 20-weight lubricating cil. Type Il synthetic lubricant is also described as a S-centistoke (cSt) oil. This means that the oil must have a minimum Kinematic viscosity of 5 cSt at a temperature of 210°F 99°C]. This specification is necessary because the oil must maintain sufficient body to carry all applied loads at operating temperatures. Care in Handling Synthetic Lubricants We must emphasize that the handling of synthetic lubri- ants requires precautions not needed for petroleum lubri- ccants, Synthetic lubricants have a high solvent characteris- tic which causes them to penetrate and dissolve paints, ‘enamels, and other materials. In addition, when synthetic oils are permitted to touch or remain on the skin, physical injury can result. It is therefore essential that the technician handling synthetic lubricants take every precaution to censure that the lubricants are not spilled or allowed to be in. contact with the skin. If a synthetic lubricant is spilled, it 343shoul cae up nmi y wing ap. wai trading uae caning eS Gone entcblshed bythe cat operator #9 ober afl oe ier cana rang ot esting sti sym be nan fe cena hat 2 Mt Secarat pe and ance d OTS Tortie scr ae governed sppoved sic an mcrae poets elie lnc sitnc opting ca mae LUBRICATING SYSTEM COMPONENTS Oil Tank Each engine is provided with an oil tank which is mounted con the engine and secured by a strap. The tank holds ‘enough oil to lubricate the engine with some reserve for ‘cooling and safety. A baffle serves to minimize sloshing of the oil in the tank and a deaerator in the tank separates most Of the air from the returning oil, thus minimizing foaming, ‘An example of a typical oil tank is shown in Fig, 13-1. DE-AERATOR TRAY lL PRESSURE TRANSMITTER FROM ENGINE. BEARINGS Wren BZ reruen on. BD Ain ano on mist FIG. 13-4 Oitank, Roi Rayey 344 chapter pressure oil PUMP ration ayers consist OF # tae sine an othe cee Dearing pplies Mer engine components. The prey. es, and fear pump. develope Ie Bet ar ath atk tated ing Oat pup is ilusrated in Fig, 13.3 se ive psa (genera es 5.8 and 89.9 PA) 10 Spray rings ¢ oil the engine im which drives, and necessory sure oi pump by trapping. eegine, Ae Not turbine ene Neen 40 a 1 Pate engine's be scavenge Oil System ystems are usually of the dry-sump rom the engine and stored Gas-turbine lubrication § types in that the oil is seavenged f : ‘spe tank, Scavenge pumps return oil from the engine's iran cavities ta sump in an accessory drive gearbox or directly to the oil tank “the scavenge system may consist of several stages— that is, individual pumps that draw oil from the different tagine bearing cavities. Scavenge oll pumps are normally Of higher capacity than engine-driven pumps because of the tir that mixes with the oil (foaming) in the bearing cavities ‘A scavenge pump operates in much the same manner as a pressure pump. More information on oil pump design and operation can be found in Chap. 4 siohT GLASS SYSTEM RELIEF VAive 13 Turbine-Engine Lubricants and Lubricating sy sternsHIGH priessune Gone ‘TRappeo voLUME (icin FEED PUM Sraiwon IN'SCAVENGE PUMP) cass Dow pressure on. Hn Pressure ov Low PRESSURE Inter FG, 13-2 Principle of a pressure oil pump. (Rolls-Royce) PLEATED WIRE MESH FILTER, Oil Filter The pressure section of the main oil pump forces oil through the main ol filter located immediately downstream. ‘of the pump discharge, A typical pressure and scavenge oil ier for a gas-turbine engine is illustrated in Fig. 13-3. Phe oll enters the inlet port of the pressure filter, surrounds the filter cartridge, and flows through the cartridge to the inner oil chamber and out to the engine, If the filter becomes clogged, the oil is bypassed through the pressure relief valve to the discharge port, A differential pressure of 14 t0 16 psi (96.53 to 110.32 kPa] is required to unseat the relief valve. The size of the filter mesh is measured in microns, which is a very small mesh. A red blood cell is about 8 microns in size. Many of the contaminants in the oil that need to be removed are very small, requiring this type of filter, Additional information on filters is presented in Chap. 4 Magnetic Chip Detector Magnetic chip detectors can be installed in the scavenge lines, oil tank, and accessory gearbox if the optional chip detector provisions are on the engine. A magnetic chip detector, illustrated in Fig. 13-4, is installed in the side of WIRE MESH ‘SUPPORT RESIN IMPREGNATED. WITH FIBER Lubricating System Components 345a RG 34 Mamenc chip deer Gais-oyce! fe Sie case This detecnce indicates the presence of metal contamination without the necessity of opening the filter. ‘Wines she deercuor picts up ferrous-metal particles, the cen sez pling becomes srcended to the case_ If a warning light is counected herweca the center terminal of the detector and pound, Se git will born and indicate metal particles on Sie detecere. The decector can also be removed from the HIP ORTECTOR engine and be inspected for metal particles by the mainte. rnance technician, Oil Coolers Some systems employ a fuel-cooled oil cooler such as that illustrated in Fig. 13-5, others utilize ram air for cooling FUEL OUTLET—— pec nd tl ters do ot empl sole. The ae tel ae tered 0 af “ota systems brsaie the Syptruring to the oil tank is quite or etn fuel oll cooler consists of an out case seta bouses the cooler core, Fue! and ol eles and exits nr paseages in the cooler (se FE, 142) Metered, Fe fuel control unt passes through the core Wet foe Sports the eat fom he il. The hot of Dases around se pes and i bale 0 that i panes back: and forth roe tubes to give maximum exchange of be sss gh the fuel cools the oil by means of « heat ser te oi and fue are separate and never come 2 exctaneth each other. Ifthe cooler were to become conte, x bypas valve sich asthe one shown in Fig: 15-S bloeig unseat and allow ol © flow around the cooler Oil Breather System ‘anol breather system connects the engine bearing c4¥ An othe accessory drive gearbox, and the oil tak. OW tes jets and vapor are removed from the breather Soper by a cenzfugal separator located jn the actesso- stay gearbox. After passing through the separator unit {s exhausted overboard tae ech a vent pipe. A centrifugal breather i illustrated im y the clean oil-free breather ai Fig. 13-6. Oil Indicating and Warning Systems ‘The temperature and pressure of the oil are enitical to the Fe Jer and safe running of the engine. Provision is there {ea mode for these parameters to be indicated in the cock- ina typical ol indicating and waming system such 35 tha own in Fig. 13-7, the oil quantity indicating system oxygen SOBA ano oeaearen ses consists of & capacitance tank unit probe electrically ms setted to an indicator on the instrument panel to Form & aectcitance bridge circuit. A change in oil level aliens Tau unit capacitance. The resulting flow of curre tank uate a motor which postions a potentiometer WiPes Hh vocndicator to rebalance the circuit. The indicator dia} pointer is connected to the potentiometer wiper and moves Path the wiper to provide the oil quantity indication. The components of the oil pressure indicating system age te il pressure transmitter and an indicator. The oj pressure transmitter senses oil pressure in the exten Pe Pree juanifold and also senses ambient pressure. The Gt tare oe between these (wo pressures is measured and So" (erepeT nto an electrical signal which actuates the oil pres- sure indicator indi eaperatre indicating system consists of an} temperature indicator and a temperatue-sensing Pale The wer Peperature bulb conlans a resistance clement whic ail Seen? tesitance wit temperature, This resistance of the Talp controfs the current flowing through the indicste® fleflection coil, and therefore controls the angular position of the pointer. Be aaning light on the instrument pane! is used to make the fight crew aware of a low oil pressure or oft ANSE byptss condition. The operation ofthis system can Be SE=2 in Fig. 13-7. LUBRICATING SYSTEMS Gas-turbine engines have been designed and manufactured cary different configurations; thus, there afe corre” vpndingly different designs for the lubrication systems of such engines. cP are three basic oil circulating systems, known a5 2 pressure relief valve system, a fll flow system, and a tla Pessiyciem. The major difference lies in the control of oil flow to the bearings. pressure Relief Valve System In the pressure relief valve system, the oil flow to the tearing chambers is controlled by limiting the pressure in the feed line to a given value. This is accomplished by the tee of a spring-loaded valve which allows oil to be directly Teumed from the pressure pump outlet to the oil tank, oF pressure pump inlet, when the design value is exceeded: M he valve opens at a pressure which corresponds to the {dling speed of the engine, thus giving a constant feed pres- Sure over normal engine operating speeds. However, increasing engine speed causes the bearing chamber pres- ware to rise sharply. This reduces the pressure differential tetween the bearing chamber and feed jet, thus decreasing the oil flow rate to the bearings as the engine speed increas- ee To alleviate this problem, some pressure relief valve systems use the inereasing bearing chamber pressure 10 hpment the relief valve spring load. This maintains ¢ con- stant flow rate atthe higher engine speeds by increasing the pressure in the feed line a the bearing chamber pressure increases. Lubricating Systems 347