CHAPTER 10 POWER PLANT INSPECTION, REPAIR, AND TESTING The purpose of this chapter is to familiarize you with the types and authorized repair limits for Intermediate Maintenance Activities (IMAs). Intermediate maintenance applies to those maintenance functions normally performed in centrally located facilities for support of the operating units. The facilities are designated as Aircraft Intermediate Maintenance Departments (AIMDs) at sea or Fleet Readiness Center (FRCs) on shore. The primary purpose of the IMA or FRC is to support and supplement the work of organizational maintenance activities. Squadron personnel assigned to the IMA, ashore or afloat, are assigned to perform the total work (within their skills) of the intermediate activity and not just the work related to support of the squadron from which they were assigned. The Gas Turbine Maintenance Program defines the repair functions of AIMD power plants. Repair capabilities are different for each particular engine and AIMDs. It is important that you become familiar with the repair capabilities and functions of your IMA. This chapter covers some of the procedures and equipment used in an intermediate maintenance department. Because of the number of different engines used in naval aviation, the maintenance procedures in this chapter are general in nature. Components and repair limits discussed are representative. Do not refer to them when working on a specific engine or its components; always refer to the applicable MIMs of the specific aircraft type. LEARNING OBJECTIVES When you have completed this chapter, you will be able to do the following: 1. Recognize the types of repairs accomplished at the intermediate maintenance level. 2. Identify the repair limits for the intermediate level of maintenance. 3. Identify the different methods of cleaning and marking engine parts. 4. Identify the different types o f test cells and their components. 5. Recognize the purpose and entries o n the engine test log sheets. THREE-DEGREE GAS TURBINE ENGINE MAINTENANCE PROGRAM The Gas Turbine Engine Maintenance Program was formed under the three-degree concept as specified in Commander Naval Air Forces Instruction (COMNAVAIRFORINST) 4790.2(series). Under this concept, each engine’s intermediate maintenance manual defines specific engine maintenance actions as either first-, second-, or third-degree functions. These functions are largely determined by the degree of difficulty and frequency of repair ( Figure 10-1 frames 1, 2, 3). First-Degree Repair First-degree repair is the repair of a damaged or non-operating gas turbine engine and its accessories or components. When the compressor rotor is replaceable, the repair includes compressor rotor replacement and/or disassembly. 10-1 s manua con a ns ac ve con en , you mus rus s ocumen or se ec p ay o v ew e ac ve con en . If you can read this warning, you may not have yet activated this document.
Transcript
8/16/2019 Power Plant Inspection, Repair and Testing Gas turbine
The purpose of this chapter is to familiarize you with the types and authorized repair limits forIntermediate Maintenance Activities (IMAs). Intermediate maintenance applies to those maintenancefunctions normally performed in centrally located facilities for support of the operating units. The
facilities are designated as Aircraft Intermediate Maintenance Departments (AIMDs) at sea or FleetReadiness Center (FRCs) on shore.
The primary purpose of the IMA or FRC is to support and supplement the work of organizationalmaintenance activities. Squadron personnel assigned to the IMA, ashore or afloat, are assigned toperform the total work (within their skills) of the intermediate activity and not just the work related tosupport of the squadron from which they were assigned.
The Gas Turbine Maintenance Program defines the repair functions of AIMD power plants. Repaircapabilities are different for each particular engine and AIMDs. It is important that you becomefamiliar with the repair capabilities and functions of your IMA.
This chapter covers some of the procedures and equipment used in an intermediate maintenancedepartment. Because of the number of different engines used in naval aviation, the maintenanceprocedures in this chapter are general in nature. Components and repair limits discussed arerepresentative. Do not refer to them when working on a specific engine or its components; alwaysrefer to the applicable MIMs of the specific aircraft type.
LEARNING OBJECTIVES
When you have completed this chapter, you will be able to do the following:
1. Recognize the types of repairs accomplished at the intermediate maintenance level.
2. Identify the repair limits for the intermediate level of maintenance.
3. Identify the different methods of cleaning and marking engine parts.
4. Identify the different types of test cells and their components.
5. Recognize the purpose and entries on the engine test log sheets.
THREE-DEGREE GAS TURBINE ENGINE MAINTENANCE PROGRAM
The Gas Turbine Engine Maintenance Program was formed under the three-degree concept asspecified in Commander Naval Air Forces Instruction (COMNAVAIRFORINST) 4790.2(series). Underthis concept, each engine’s intermediate maintenance manual defines specific engine maintenanceactions as either first-, second-, or third-degree functions. These functions are largely determined by
the degree of difficulty and frequency of repair (Figure 10-1 frames 1, 2, 3).
First-Degree Repair
First-degree repair is the repair of a damaged or non-operating gas turbine engine and itsaccessories or components. When the compressor rotor is replaceable, the repair includescompressor rotor replacement and/or disassembly.
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Second-degree repair is also the repair of a damaged or non-operating gas turbine engine and itsaccessories or components. The difference is that second-degree repair will normally include therepair/replacement of turbine rotors and combustion sections. Repairs include afterburners and thereplacement of externally damaged, deteriorated, or time-limited components, gearboxes, oraccessories. Minor repair to the compressor section is made in second-degree repair. The repair orreplacement of reduction gearboxes and torque shafts of turboshaft engines comes under second-
degree repair. The repair or replacement of compressor fans of turbofan engines also comes undersecond-degree repair activities.
Third-Degree Repair
Third-degree repair encompasses major engine inspections and the same gas turbine engine repaircapability as second-degree maintenance. Certain functions that require high maintenance man-hours and are of a low incidence rate are excluded. The functions described represent broadgeneralities. Refer to the appropriate engine maintenance plan or intermediate maintenance manualto determine the degree of assignment for specific repair functions.
Figure 10-1 — Three levels of maintenance, (Frames 1 first degree, 2 seconddegree, 3 third degree).
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Once an engine arrives at an AIMD/FRC activity, it is cleaned and evaluated for repair. If inducted forrepair, a major inspection and all repairs required to place the engine back in ready for issue (RFI)status are accomplished. The first steps for inspecting aircraft engines include the cleaning and themarking of parts. After cleaning, engines are inspected in accordance with applicable MaintenanceInstruction Manual’s (MIMs) or disassembled for further repair.
CleaningGood mechanics clean all engine parts thoroughly before inspecting them. Cleaning and closeinspection make it possible to detect faults that endanger safe engine operation and maximumperformance. The primary purpose of engine parts cleaning is to accomplish the following:
Permit thorough inspection of components for flaws, damage, and dimension wear.
Prepare surfaces for repair (plating, welding, or painting).
Remove organic or inorganic coatings for inspection of underlying surfaces or remove coatingsadversely affecting engine performance.
Selection of cleaning materials and processes for any engine part is determined by the nature of thesoil, the type of metal or coatings, and the degree of cleanliness necessary for a thorough inspectionand repair.
Generally, engine parts operating in relatively low temperature ranges (cold section parts) arecleaned by solvent washing, degreasing tanks, and vapor degreasing. Cleaning engine parts thatoperate in hot sections of the engine (combustion and turbine sections) require more comprehensivecleaning.
Soft carbon deposits are removed by degreasing and steam cleaning. Degreasing removes dirt andsludge by immersing or spraying the part with cleaning solvent. Hard carbon deposits are removed bydecarbonizing, brushing, scraping, or grit-blasting. The following text provides general cleaningprocedures to familiarize you with the methods and materials used for cleaning parts. Always refer tothe appropriate maintenance manual for the latest cleaning procedures. Constant changes are madein cleaning and finishing (coatings) materials.
Degreasing (Solvent Cleaning)
Small accumulations of grease, oil, and dirt may be removed by hydrocarbon solvent cleaning. Thismethod is not effective in removing baked-on oil deposits or most surface coatings.
WARNING
Many of the chemical solutions and their components usedin cleaning, inspecting, and repairing are toxic, flammable,and extremely corrosive. Improper mixing or use of these
chemicals can produce violent reactions, rapid heatgeneration, and explosive/toxic gases. Personnel
performing maintenance procedures should consult theapplicable MIMs and be familiar with the safety precautionsassociated with the hazardous materials or equipment. The
warnings in these technical manuals identify the types of
hazards and precautions to take. The Material Safety DataSheets (MSDS) and your safety office have specific
information for hazardous material in your work center.
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Dry-cleaning solvent (MIL-PRF-680B) is the recommended cleaner. Solvent cleaning uses a tank withcleaning solvent to soak the part clean. Some tanks have pumps to provide mechanical agitation tohelp clean parts. You can also use a soft bristle brush to remove stubborn stains. The cleaning tankshould have a hinged, counterweighted cover so it can be covered when not in use. Since someplastic- and rubber-based materials are attacked by hydrocarbon solvents, steam clean these parts toremove contaminants.
Steam Cleaning
Steam cleaning is a cleaning process used when you do not want to remove paint and surfacecoatings. To properly clean with steam, it is necessary to add cleaning compounds. Do not steam
clean oil-impregnated parts.
Set steam valve to the proper strength and force required for the job. Hold the steam gun about 12inches from the part at a 45-degree angle. When cleaning plastic parts, you should be careful to avoidheat buildup. After cleaning thoroughly, dry the part and apply corrosion prevention compounds.
Vapor Degreasing
Vapor degreasing removes oil, grease, and preservative compound by solvent vapor. A flat bottomtank with heating coils on the bottom and cooling coils midway around the tank is required. The part issuspended in the vapor area below the cooling coils. Heated cleaning solvent vapor condenses onthe cool part. It dissolves oils, grease, and preservatives. Cleaning action stops when the part
reaches the vapor temperature. If further degreasing is necessary, the part must be cooled beforeusing vapor degreaser again. Vapor degreasing cannot be used on titanium parts becauserecommended solvents cause stress corrosion at high temperatures.
Decarbonizing
Decarbonizing is the chemical removal of carbon deposits. Decarbonizing agents are detergents,sodium silicates, chlorinated hydrocarbons, and various acid solutions. This cleaning method iseffective for paint stripping, rust removal, and general cleaning of ferrous and high temperature parts.Parts are soaked in hot or cold tanks and rinsed with high-pressure water.
Some carbon removers attack aluminum and magnesium parts if they are left in the solution too long.There is also the possibility of a chemical reaction when aluminum, magnesium, and steel parts areimmersed in the same tank. This practice often results in damage to magnesium parts, such asdissimilar metal corrosion.
Upon removal from cleaning solutions, rinse the parts in a soap-and-water solution or with apetroleum solvent. Change the rinse water frequently to prevent a buildup of acid or alkaline in the
WARNING Degreasing solvents are flammable, and their vapors aretoxic. Keep all solvents away from open flames, and useonly in well-ventilated areas. Avoid solvent contact with
skin, eyes, and clothing by wearing rubber gloves, a faceshield or goggles, and an apron or coveralls.
WARNING Carbon removers require careful handling. Wear goggles,
rubber gloves, and aprons when using these solutions.
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water. Air-dry the engine parts, and then coat them with a corrosion preventive if they are not to beprocessed further.
Decarbonizing loosens most hard carbon deposits remaining after degreasing. The complete removalof all hard carbon deposits generally requires brushing, scraping, or grit-blasting. Use caution duringthese procedures to avoid damaging parts. In particular, do not use wire brushes or metal scraperson machine surfaces or bearings.
Abrasive Blasting
Use abrasive blasting to remove hard carbon or lead deposits, rust, and heat scale. The type (wet ordry) and size of abrasives vary for different engine parts. Mask all openings, identification markings,and other areas as required before blasting. Grit materials such as ground corn, apricot or peach pits,walnut shells, clover seed, and cracked wheat or rice are in general use.
Dry grit blasting is sometimes done in a sandblast cabinet. The part must first be degreased or putthrough a decarbonizing solution, and then rinsed and dried thoroughly. After grit blasting, remove thedust by air blasting, and clean with petroleum solvent or hot water. Some types of soft grit leave alight grease film on the part. Remove this film by degreasing if the part is to be subjected tofluorescent penetrant inspection.
Wet abrasive blasting is an effective method to remove heat scale, carbon deposits, and temporarymarkings, and to produce a uniform satin finish on metals. This type of blasting removes metal, but soslowly that dimensions change very little.
MARKINGS
Marking engine parts and assemblies aids in identification, reassembly, and tracking the service lifeof parts. All marks are applied to produce maximum legibility and durability without affecting thefunction or serviceability of the part. Markings are either permanent or temporary. Permanentmarkings are those markings that remain during the entire service life of the part. They are appliedduring manufacturing or after modification of parts. Temporary markings maintain identification ofparts or reference positions during ordinary handling, storage, and final assembly. Temporary
markings ensure parts may be returned to original assembly position. If a part is going to be cleaned,inspected, and repaired, temporary markings will probably be removed by solvents during cleaning. Ifpart identification needs to be maintained, attach tags or place parts in separate containers.
Temporary Markings
Certain materials must be used for temporary marking during assembly and disassembly. Use onlyapproved pure dye markers to mark engine hardware. Using nonapproved markers can leave harmfulelements on engine parts. You may use layout dye (lightly applied) to mark parts that are directlyexposed to the engine gas path. Some exposed items are the turbine blades and disc, turbine vanes,and combustion chamber liners.
CAUTION
Do not use any temporary marking method that leaves aheavy carbon deposit. Do NOT use any marking that leavesa deposit of copper, zinc, lead, or similar residue, such as
pencil or black grease pen. These deposits may causecarbonization or intergranular attack when the part gets
very hot. Parts marked with unauthorized materials shouldhave all traces of markings removed before using them.
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Permanent markings should be positioned in the area of lowest stress. Do not apply markings within0.030 inch of corners, radii, fillet, or edges. Choose an area where markings will not be worn off orobliterated by contact with another part. If possible, place new markings next to original markings.
Always refer to applicable engine manuals and power plant changes for recommended markingmethods and details. Some of the methods of permanent markings include using a metal stamp,vibropeen, blasting, and acid-etching.
GENERAL ENGINE REPAIR AND INSPECTIONS
Before starting disassembly of an engine, check the applicable technical instructions to confirm thescope of repair necessary. Use the step-by-step procedure and repair limits contained in the currenttechnical publications for the particular engine. In the process of engine disassembly, manyassociated parts become accessible for inspection. Inspect these parts as closely as possible toprevent later failure. During assembly and disassembly, make sure you use the proper equipment tosupport the engine. This will prevent overstressing during maintenance. In addition to preventingstress, it allows proper alignment of parts being removed or installed.
Immediately upon removing each subassembly or individual part from the engine, transfer it to a parts
rack. Arrange the part to protect it or the assembly from damage. Provide proper covering andsupports to protect shafts, gears, studs, or any projecting piece from being bent, scratched, orotherwise damaged. Be careful to prevent the entrance of dirt and other foreign materials into theengine. Whenever practicable, use temporary covers to seal all openings in dismantled engines.Cover the ends of all removed tubing. Take extreme care not to lay carbon seals and plates on thesealing surfaces. Provide appropriate containers to hold each part separately until the time forreinstallation. During disassembly, examine all parts and assemblies for cracks, scoring, and burning.Check the engine for indications of work incorrectly performed during any previous repair or overhaul.
You must pay particular attention to the material requirements for the nuts and bolts used in theturbojet engine. Hot sections require common hardware (nuts, bolts, safety wire, and cotter pins) thatare resistant to high operating temperatures. Other engine parts may require special hardware, and it
is imperative that all properly coded parts (if serviceable) be placed in their original positions.
Welding is permissible on some parts of the turbojet engine. Refer to the applicable technicalinstructions before attempting to repair an engine or component by welding.
Compressor Section Repairs
Most intermediate-level maintenance activities are responsible for the replacement of compressorsections and the repair of those compressor blades in the later compressor stages that cannot beserviced without the removal of the compressor halves. Compressor repair usually results fromforeign object damage (FOD), although other failures occur. A number of compressor failures may bebroadly classified under air leaks and compressor contamination. The AIMD or FRC may also be
required to modify the compressor rotor or stator blades as a result of a technical change or bulletin.Modifications may include reworking the components, changing blades by stages, or replacing theentire rotor assembly.
NOTE
Compressor cases are machined in matched sets. Damagebeyond repair to one case is cause for rejection of theopposite case. A new compressor rotor is not required
when replacing the entire case assembly.
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Accumulation of dirt on the compressor blades reduces the aerodynamic efficiency of the blades. Dirthurts engine performance. The efficiency of the blades is impaired by dirt deposits similar to that of anaircraft wing under icing conditions. High exhaust gas temperature (EGT) may result when foreigndeposits are on compressor components. On some turbojet engines, high EGT requires early engineoverhaul. Slow acceleration could also result from foreign material obstructing the compressor outletvanes. This obstruction could result in a needless engine overhaul.
Compressor Leaks
Air leaking from the compressor results in low engine performance. Air leakage may occur betweenthe high and low compressors, or at some intermediate stage. It may also occur because of bleed-airvalves stuck open or cracks in the compressor case itself. Air leaks in the compressor are foundthrough engine monitoring or low engine performance; for example, when the engine fails to meetminimum powerrequirements for takeoff.
Compressor Failures
Loose objects often enter
an engine’s compressoreither accidentally orthrough carelessness.Thousands of dollars’worth of damage to acompressor rotor canresult from a tool left in theair intake (Figure 10-2 ). Anut and bolt holding plierstogether came loose andwent through the
compressor, causing thedamage shown in theillustration. A simple solution to the problem is a tool checklist.
Internal mechanical failures, such as a compressor blade breaking off, result in compressor efficiencyloss. These failures are difficult to detect. Broken blades and vanes result in high exhaust gastemperatures or an increase in compressor round per minute (rpm) due to loss of efficiency. Ofcourse, mechanical failures of compressor blades could result in severe damage to the compressor,combustion chamber, and the turbine as FOD.
Compressor Blade Damage and Repair
Table 10-1 lists the blade damage inspection limits chart. Defining and showing examples of damagemay help you to recognize damage and make repair of damage easier. Figure 10-3 shows examplesof possible blade damage to an axial-flow engine. The damages are enlarged to show detail; if youknow by close examination what causes the damage, you may be able to reduce the cause.
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Figure 10-3 — Blades showing various types of damage.
You may make minor repairs to compressor blades, provided the repairs are made without exceedingallowable limits in the prescribed MIMs. Well-rounded damage to leading and trailing edges isacceptable without rework. No rework is necessary provided the damage is in the outer half of theblade. The indentation may not exceed values specified in the MIMs. A figure 10-4 frame 1, 2, and 3illustrates representative repairable limits. Figure 10-5 shows examples of blade repairs.
When working on the inner half of the airfoil, you should treat damage with extreme caution. Make noattempt to remove damage by straightening. Inspect repaired compressor blades by dye check,magnetic particle inspection, or by fluorescent penetrant inspection methods. Remove all traces ofthe damage. All surfaces must be smooth. All repairs must be well blended. No cracks of any extentare tolerated in any area. Bowed or bent blades are not reused. If gauges are not available, therepaired blades are aligned and compared with a new blade of the same stage.
Use a smooth file when removal of considerable amounts of material is necessary. File or blend atright angles to the width of the blade. If you cannot reach the damaged area with a file, use coarseemery cloth. A medium stone can be used on areas that have been reworked with a file or emerycloth. Use a medium stone for areas containing small nicks and dents.
Use fine emery cloth and/or a fine abrasive stone to polish the reworked area. Polish until the finish
looks and feels like the original. If two blended areas overlap to form a sharp point or ridge, blend outthe point or ridge. Blend the contour surfaces with a medium stone and finish with emery cloth and/ora fine abrasive stone. The finished repair should be as much like the original finish as possible.
Front compressor blades that require replacement are replaced by blades having the same momentbalance code. The moment balance codes are marked on the front face of the root of the blade. Atthe original buildup of the compressor rotor discs and blades, a set of blades coded according toindividual moment were installed. The installation on the disc minimizes the static imbalance due tovariations in the blade moment. The blades are numbered in clockwise sequence, as viewed from thefront. Install blades in their correct numbered position. Make sure new blades are correctly numberedfor the blades they replace.
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Pitting or corrosion, if within the allowed tolerance, is not serious on the compressor stator vanes ofaxial-flow engines. Do not attempt to repair any vane by straightening, brazing, welding, or soldering.Use crocus cloth, fine files, and stones to blend out damage. Remove a minimal amount of material,and leave a surface finish comparable to that of a new part. The purpose of this blending is tominimize stresses, which concentrate at dents, scratches, and cracks. Maximum blend out of limitsdamage greater than 50 percent of the stator assembly vanes requires assembly replacement. Whenvanes are damaged to the maximum blend out of limits in any 60-degree sector of one stage, replacethe assembly. Send parts damaged beyond maximum repair limits to overhaul for repair andreplacement of vanes. The use of pre-bored compressor vane and shroud assemblies permits thereplacement of one-half of any low compressorstator. The inspection and repair of air inlet guidevanes and swirl vanes on engines require the use ofa strong light. Attach this light to a rigid support toenable positioning in hard-to-reach areas. Inspectall sections of both screen assemblies for breaks,rips, or holes. Screens may be tin-dipped to tightenup the wire mesh, provided the wires are not worntoo thin. If the frame strip or lugs have separatedfrom the screen frames, rebrazing may benecessary.
Inspect guide and swirl vanes for looseness.Inspect the outer edges of the guide vanes. Payparticular attention to the point of contact betweenthe guide and swirl vanes. Check for cracks anddents due to the impingement striking of foreignparticles. Also, inspect the edges of the swirl vanes.Inspect the downstream edge of the guide vanesvery closely, as cracks are more prevalent in this
area. All cracks which branch out in such a mannerthat a piece of metal could fall into the compressoris cause for rejection.
Blending of hollow vanes on the concave andconvex surfaces, including the leading edge, islimited; some small, shallow dents are acceptable.The damage may be rounded or gradual contourtype, but not a sharp or V-type. Do not allow anycracked or torn vane material to exist in thedamaged area.
Blend the trailing edge if one-third of the weld seamremains after repairs, as shown in Figure 10-6 .Concave surfaces of rubber-filled vanes may haveallowable cracks extending inward from the outerairfoil. These cracks are allowable provided there isno suggestion of pieces breaking away. Using alight and mirror, inspect each guide vane trailingedge and vane body for cracks and damagecaused by foreign objects. Cracks in the vane bodyare cause for rejecting the entire weld.
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The combustion section can be removed, repaired, or replaced in part or entirely depending on theextent of damage encountered. The combustion section consists of liners, support duct, outer andinner case, and the first stage turbine nozzle assembly. Most repairs to this section are accomplishedby welding or replacement of components.
Combustion Chamber Liners
Inspect combustion chamber liners for cracks by using dye penetrant or the fluorescent penetrantmethod of inspection. Cracks converging so that metal could break loose or any loose, cracked, ordamaged swirl vanes are cause for rejecting a liner. Remove liners having buckled areas in a weldseam. Areas that have more than a three-sixteenths-inch wave, which does not include the weldseam, require removal from service (Figure 10-7 ).
Combustion chamber liners may be retained in service with some flaws. For example, liners withcracks less than 0.125 inch long starting from combustion air holes (no more than three per section)7may remain in service. Liners with radial or circumferential cracks less than 0.750 inch longextending from or around the crossover tubes or igniter plug bosses may also remain in service. Youmay reuse combustion liners that are burned. Rework cracked deflectors to remove the cracked areaby blending or cutting before reuse. Burning of the cooling louver must not exceed two tabs totally
burned or a total area of two tabs per liner.
Combustion Chamber Support
Cracks in the combustion chamber support can be repaired by inert-gas fusion welding. Repairs mustnot result in distortion or misfit of parts at assembly. If a hole is distorted as a result of welding, use afile to restore it to its original configuration. The weld bead must be blended by hand after the weldingSee Figure 10-8 .
Combustion Chamber Inner and Outer Ducts
Operational cracks in the inner and outer outlet ducts are permissible. The cracks may not exceed 3
inches in length. Repair cracks more than 3 inches long and exceeding 75 percent of the entirecircumference of the duct by gas fusion welding. When repairing a duct, use a silicon carbide grindingwheel. Grind a 90-degree “V” groove, 0.035-inch deep, for the entire length of the crack. It ispermissible to remove some of the parent material when grinding. Adequate depth is necessary to besure that the grinder removes all material from the crack. Repairs must not result in distortion or misfitof the parts at assembly. File out any distorted hole, as a result of welding, to restore it to the originalconfiguration. Figure 10-9 gives an example of inner and outer ducts repair limits.
Turbine Section Repairs
Inspect turbine sections and components thoroughly because of the extreme heat encountered in thissection. Turbine sections can be replaced in whole or in part. The turbine rotor is usually repaired by
changing individual blades or an individual rotor. It is not feasible to describe all of the damageconditions that may be found in the turbine. If the damage is within prescribed limits, but there isdoubt about the rework, you should replace the turbine rotor or part.
Some first-stage turbine blades are coated with a protective coating to prevent sulfidation. Alpak isdiffused coating of aluminum and chromium used for protection of the turbine blades. Without thiscoating, these blades are very susceptible to sulfidation.
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Figure 10-10 — Examples of unacceptable sulfidation
of turbine blades and vanes, frames 1 and 2.
Turbine Blade Sulfidation
Sulfidation is high-temperaturecorrosion. Sulfidation starts with theexcessive levels of sodium and sulfurin the air and fuel mixture entering theengine. This type of environmentattacks turbine blades and stator
vanes. Sulfidation first appears as arough or crusty surface on the leadingedge and concave surface of theairfoil. It progresses to scaling, splitting(delamination), and eventual metalloss. The sulfidation processaccelerates with an increase in sulfurintake and an increase in engineoperating temperature.
All blades should be inspected forsulfidation. This form of corrosion is
permissible if evidenced only by arough or crusty appearance at theleading edge, on the concave side ofthe airfoil section, or on the platform atthe root of the airfoil. The rotor shouldbe replaced if there is evidence ofsplitting, delamination, separating, flaking, or loss ofmaterial in any area of the blade. Figure 10-10 frames 1and 2 shows an example of unacceptable sulfidation ofturbine blades.
Turbine BladesYou may inspect turbine blades on axial-flow engines,and clean them in the same manner as compressorblades. However, because of the extreme heat underwhich the turbine blades operate, they are more easilydamaged. Inspect the turbine blades for stress rupturecracks and deformation of the leading edge (Figure 10-11).
Stress rupture cracks usually appear as fine hairlinecracks. These cracks are found on or across the leading
or trailing edge at a right angle to the edge length. Visiblecracks may range in length from one-sixteenth inchupward.
Deformation, due to over temperature, appears aswaviness along the leading edge. The leading edge mustbe straight and of uniform thickness along its entirelength, except areas repaired by blending. Stress rupturecracks or deformation of the leading edge are oftenmistaken for foreign material impingement damage. Whenany stress rupture cracks or deformation of the leading
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Figure 10-13 — Measuring the turbine bladeto shroud ti clearance.
edge of the first-stage turbine blades is found,suspect an over temperature condition. Checkthe individual blades for stretch, and the turbinedisc for hardness and stretch.
Inspect the turbine blade outer shroud for air sealwear. If you find evidence of shroud wear,measure the thickness of the shroud at the wornarea. Use a micrometer (or another suitablemeasuring device) to be sure of a good reading inthe bottom of the narrow wear groove.
Turbine Stator Vanes
The inspection of turbine vanes is accomplishedin the same manner as described in the previoussection for the compressor vanes. Damage maybe greater as turbine vanes experience extremelyhigh heat. Blend minor nicks and dents with finestones or emery cloth. Visually inspect the vanes
for signs of bowing. Replace bowed vanes thatare in excess of the allowable clearance withvanes of the same classification. Use astraightedge and feeler gauge stock to measurebowing (Figure 10 -12 ). Damage that does notcrack the metal or reduce the vane thickness bymore than allowed is acceptable without rework.This is true if the damage is of a gradual contourshape and not sharp or V-shaped. Round bottomdents on the leading edge may be acceptable
without rework. Dents must not exceed allowablelimits in depth and must not crack or tear the vane.Blend sharp indentations to remove stressconcentration.
Determine how many vanes you need to replaceon the particular engine before you measure thenozzle guide vane area. If the replaced bladesexceed the allowed number and you must measurethe area, it is better to replace the assembly.
One of the final procedures in the maintenance of
the turbine section of a turbojet engine is to check
for clearances. The service instructions manual
gives the procedures and tolerances for checking
the turbine. Figures 10-13 and 10-14 show
clearances being measured at various locations.
Use special manufacturer’s tools to obtain accurate
readings. Also, use the tools described in the
service instructions manual for specific engines.
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Figure 10-14 — Measuring the turbine wheel toexhaust cone clearance.
Figure 10-15 — Afterburner duct and nozzle
assembly.
Exhaust Section Inspection
The exhaust section of the turbojet engine isvery susceptible to heat cracking. Inspect thissection thoroughly, along with the combustionsection and turbine section of the engine. Theexhaust section of an afterburning engine issubject to extreme heat and pressures. Inspect
the external area of the exhaust cone and tailpipe for cracks, warping, buckling, and hotspots. Hot spots on the tail cone are a goodindication that a fuel nozzle or combustionchamber is not functioning properly. If there isan afterburner, inspect the afterburner flapsegments for burning, warping, ormisalignment. Figure 10-15 shows anafterburner duct and nozzle assembly with flapsegments closed. Inspect the afterburnersynchronizing gear segments for worn and
missing teeth and security of installation.Inspect the nozzle actuation pistons for cracksand/or bent, chafed, or scored piston rods.Inspect the roller guides for warpage and theturnbuckle for security of installation.
Inspect the internal area of the exhaustpipe and afterburner for evidence of hotstreaks, buckling, and warping,including the flame holder. Also, inspectall external fuel and hydraulic lines forevidence of distortion, buckling, or
leakage. Accomplish the repair andreplacement of parts of the exhaustsection using the latest technicalinstructions for that particular engine.
Main Engine BearingsInspection
Because of the high rpm, main enginebearings are critical sections of anengine. The number of main enginebearings may differ from one engine model to another. With the engine disassembled and in thevertical position, all bearings and housings can be inspected and replaced as necessary.
Accessories Drive Section and Mating Gear Inspections
The accessories drive section contains the various gearboxes for driving the accessories. Thesegearboxes should be inspected for cracks and worn areas, and the splines should be checked forproper fit and clearances. When you remove or replace gearboxes, the splined drive shafts must becarefully removed or installed to prevent spline damage.
Most mating gears require backlash as well as end clearance checks. You should carefully inspectthe gear and spline teeth for irregular or excessive wear, galling, and flaking. Usually, runout
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measurements are not required if there is no evidence of gear teeth spalling. These checks mayrequire partial assembly of the parts, and will be accomplished during assembly of the components.
JET ENGINE TEST CELLS
For a jet aircraft engine to operate properly, it must be adjusted properly. The checks for properadjustment can best be made during controlled operation of the engine. The various types of testfacilities, or test cells, are designed for service testing of the jet engine according to procedures and
manuals published by the Naval Air Systems Command (NAVAIRSYSCOM). Most engine test cellsare used at the intermediate-or depot-level maintenance facilities.
Operators of these test facilities are required by COMNAVAIRFORINST 4790.2 (series) to be certifiedby completion of the following basic methods of operator training:
1. Formal local (in-service) training and On the Job Training (OJT) can be provided under thesupervision of a Naval Air Technical Data and Engineering Service Command (NATEC) jet testsupervisor (JTS) representative or designated Gas Turbine Engine Test Systems (GTETS)Qualifier for the test cell and type engine regardless of command assigned. Training shall beobtained at the IMA/FRC or activities using the standardized training in conjunction with locallyprepared site-specific OJT. OJT syllabuses shall be developed and maintained by the programmanager/coordinator, GTETS Qualifiers, and Quality Assurance (QA) personnel and beapproved for use by the Maintenance Officer/Production Officer. Marine Corps personnel willuse the Maintenance Training Management and Evaluation Program (MATMEP) individualqualification record for Aircraft Power Plant Test Cell Operator.
2. NATEC on-site training can be provided by a NATEC JTS representative and is normallyrequested by the activity to be performed coincident with the initial installation and calibrationof the test facility. NATEC on-site training can also be requested to improve technicalknowledge and skill to improve operational readiness and allow for the maximum use ofpropulsion testing facilities, equipment, and human resources across all IMA activities.
3. Upon completion of training, the nominee must satisfactorily complete a written examadministered by the QA/Training Management Office and a practical exam (pass/fail)
administered by a GTETS Qualifier or NATEC JTS representative. Both written and practicalexaminations shall be prepared by QA/Training Management Office, GTETS Qualifiers, orNATEC JTS representatives and maintained by QA/Training Management Office. TheMaintenance Officer/Production Officer will issue a letter of certification indicating the enginetest system and type engine(s) and completion of OJT under the direct supervision of a seniorpetty officer or civilian technician who is a certified test stand operator and who has beendesignated by the activity’s commanding officer to provide this training.
4. Navy and contracted GTETS Operators and Qualifiers are required to maintain proficiency foreach type engine for which they are certified. As a minimum, GTETS Operators and Qualifierswill run any type/model aircraft engine each 90 days, and will run at least one engine for each
type certified every 12 months. Engine runs for proficiency may be run on any type test cellwith a certified operator for that test cell, and will be documented in the individual’squalification/certification record. Every attempt should be made to maintain proficiency on alltype engines for safety and effectiveness. Failure to maintain proficiency on one type enginewithin a one-year period will result in loss of certification for that specific type engine.
5. Navy and contracted GTETS Operators will be recertified every 24 months. Recertification willconsist of a written examination administered by QA/Training Management Office and apractical exam (pass/fail) administered by a GTETS Qualifier or NATEC JTS representative onany one type engine for which they are certified. Afloat activities that are unable to operatetheir test cell for extended periods of time (greater than 3 months) may perform their
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recertification practical exams at another activity with a NATEC JTS representative or GTETSQualifier designated in writing for that type test cell. Additionally, for planning purposes andoperational commitments, recertification exams can be completed up to 3 months prior to theGTETS Operator’s certification expiration date. Recertification exams should place emphasison safety and emergency procedures. GTETS Operators exceeding 24 months will not beconsidered certified until they have completed refresher training by a GTETS Qualifier orNATEC JTS representative and successfully completed a written and practical examination.GTETS Operators failing either the written or practical examinations will be required to
complete refresher training or complete the entire OJT syllabus, as determined by the programmanager/coordinator.
All certified test cell operators must hold a valid support equipment (SE) license and ensure that eachparticular engine and engine test system is indicated on the license. Refer to COMNAVAIRFORINST4790.2 (series) for training and licensing procedures.
Engine testing is accomplished primarily in a test cell or test house that is fully equipped to measurethe entire desired engine operating parameters. The building is usually of concrete construction andcontains both the control and engine rooms, although in some installations only the control or theinstrumentation room is enclosed. Most of these cells have noise silencers installed in the inlet stackfor noise suppression and a water spray in the exhaust section for cooling. Many of the test cells use
computers to automatically record all instrument readings and correct them to standard dayconditions. A typical enclosed test facility is described in the following paragraphs. Portable universalengine run-up test systems and the engine test log sheets are also described.
Jet Engine Test Instrumentation (JETI) System
The JETI provides full performance engine test capability at the AIMD/FRC, ashore and afloat, formanual and automatic testing of gas turbine engines. The system capabilities include instrumentationdata acquisition, engine and facility control, and status display. These enhanced capabilities allowinterface and control of Full Authority Digital Electronic Control (FADEC) aircraft engines and arerequired to properly test and evaluate the performance of the F414-GE-400 engines. The JETIsystem also enhances full performance testing capabilities for legacy engines such as the F404-GE-
400/402, and the GTC36-200/GTCP36-201 Auxiliary Power Units (APU). The JETI is a CommercialOff-The-Shelf (COTS) Personal Computer (PC)-based test system that interconnects two majorfunctional elements, the Engine under Test (EUT) and the test facility. The JETI provides anenhanced computer-based measurement and automated data control system for the purpose ofintermediate level testing of aircraft gas turbine engines in either an indoor or outdoor environmentboth afloat and ashore. It is designed to monitor and display all parameters of an engine being tested,and allows out-of-airframe testing and troubleshooting. The system integrates six different functions:
Instrumentation
Data Acquisition
System Processor-Controller Programmable Throttle System
Distributed Electrical Power
Operator-Maintenance Control and Display
The system also provides a printout of the calculated engine performance data during normal testing.
The test equipment is capable of handling 30,000 pounds of jet thrust during performance tests. Thetest facility building configuration has an engine mass airflow capacity of 180 pounds per second, orapproximately 17,000 pounds of thrust, including afterburner operation.
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Figure 10-16 — JETI work stations, frames 1 and 2.
All three versions of the JETI (shipboard, land-based (fixed), and land-based (transportable) areplanned to have the same number of cabinets with identical instrumentation. The difference in facilityconfiguration is the control room floor plan. There are no restrictions anticipated for site activation ofland-based (T-10B/T-36A) installations. Shipboard configuration will differ based on the existing floorplan. A Ship Alteration (SHIPALT) may be required to accommodate the difference in size ofinstrumentation cabinets required to facilitate installation of the JETI system. Funding for necessarySHIPALTs will be provided on an as required basis. The installed dimensions of the system are eightfeet high by eight feet wide by two feet deep, with an installed weight of 1,800 pounds.
In the original installations, the JETI interfaces with the existing test systems utilizing commonhardware items such as Electrical Junction Boxes (EJBs), Mechanical Junction Boxes (MJBs),Programming Harness Boxes (PHBs), power supplies, ancillary equipment, power interface busesetc., but will have separate cabling, software, and stand-alone computer control systems. The JETIpower distribution systems, electrical and electronic test instrumentation, system indicators, facilityand test system interface components, and controls are contained in specifically configured cabinetassemblies and control console assemblies contained in the environmentally controlled test facilitycontrol cab. Ninety-five percent of the test system components are contained within the test facilitycontrol room area.
The following paragraphs provide a general description of the System Control Cabinet/Test Console
Assemblies and major system subassemblies of the JETI system.
Test Control Console Assembly I
Figure 10-16, frames 1 and 2, shows thisconsole, which permits monitoring andcontrol of the EUT. Major assemblies andsubassemblies contained in this consoleinclude the following:
Two Rack-Mounted ControlComputers (TPS Computer and Data
This console permits monitoring and controlof the EUT and houses the mount for theengine control dual throttle lever assemblies.Major assemblies and subassemblieshoused in this console include:
Flat Panel Touchscreen Display Assembly
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This cabinet assembly provides the electrical interface buses consisting of terminal blocks andinterface wiring required for intersystem connections.
Data Acquisition Instrument Cabinet AssemblyThe DAQ Cabinet Assembly houses two rack-mounted 1261B Versa Module Europa Extension forInstrumentation (VXI) bus chassis (upper and lower) that contain the system data collectionelectronics. The upper chassis contains the bulk of the acquisition instruments as well as theInterface Test Adapter (ITA). The Lower Chassis (1261 VXI) (Figure 10-16, frames 1 and 2 ) containsthe following:
Vibration Analyzer
2-Channel 1553 Controller
Counter-Timer
Second Harmonic Signal Conditioner Instruments
Subassemblies contained in the Lower Chassis include the following:
Mainframe Extender Module
Vibration Monitor Module
1553 Bus Interface Module
Second Harmonic Signal Conditioner Module
Receiver Assembly
ITA
Control Cabinet Assembly
Figure 10-16, frames 1 and 2 shows the Control Cabinet Assembly which contains the systeminstrumentation required to monitor engine parameters specified by the manufacturer as being criticaland necessary for final test. Sub-assemblies contained in this cabinet assembly include:
Power Distribution Module Assembly
Uninterruptible Power Supply (UPS)
400 hertz (Hz) Alternating Current (AC) Power Supply
Panel Assembly – Power Strip Facility Equipment Control Cabinet (T-10B [land-based] Test Facility)
Variable Height Stand Assembly
The variable height stand assembly, or thrust bed, is used to support, restrain, and position theengine in the desired testing altitude. This assembly is also used to transfer the engine from the trailerto the thrust bed. The thrust bed positioning system and the thrust measuring system are part of thevariable height stand.
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The thrust bed positioning system is essentially a pneumatic-powered, hydraulic oil-driven devicecapable of raising and lowering the test engine to any altitude within operating range. Operatingcontrols are mounted on the left front A-frame of the thrust bed.
In addition to supplying lifting force for height positioning of the thrust bed, oil pressure is used todrive the calibration cell cylinder whenever controlled thrust pressure is required.
Thrust Measuring SystemThe thrust measuring system becomes operative when the thrust button is acted against by the loadcell as a result of slight forward motion of the engine under power. If desired, the load cell may bepreloaded by the preload unit. As thrust is developed by the engine, and the pressure between thebutton and the cell produces an electric potential within the cell. The electric current thus establishedis connected to the thrust-measuring circuit box, where it is amplified sufficiently to power the thrustindicator. The thrust indicator is calibrated to read directly in pounds of engine thrust.
Exhaust Augmenter Assembly and Exhaust Gas Cooling System Assembly
The exhaust augmenter assembly (augmenter) and the exhaust gas cooling system assembly(exhaust cooling system) are provided to ensure proper disposition of engine exhaust by controllingexhaust gas, flow characteristics, and temperature. These factors can be monitored, both manuallyand automatically, with the controls and instrumentation installed. For example, if exhaust stacktemperatures in excess of a preset temperature are experienced during afterburner operation, theafterburner is automatically cut off by a latching relay. When this occurs, the afterburner cannot berelit until safe temperature conditions prevail and the relay is reset. Provisions have been made formanually overriding the exhaust stack temperature control system should it fail or otherwise proveinadequate. Another helper of the exhaust augmenter is a noise attenuation device, comprising of acarbon steel pipe which is aligned axially with direction of exhaust from the jet engine. The carbonsteel pipe is positioned within an augmenter within the test cell. Cold air enters the front end of thecarbon-steel pipe. Adding three times the mass of cold air to that of the hot jet exhaust allows the hot
jet exhaust to mix with the cold air forming an engine exhaust-cool air mixture. When the engineexhaust-cool air mixture reaches the outlet end of the carbon steel pipe, its temperature is reducedfrom 3800 degrees F. to less than 1200 degrees F., which substantially reduces noise generated bythe jet exhaust. Located in proximity to the rear end of the carbon steel pipe is an annular regionwhich is formed between perforated side plates within the carbon steel pipe and the inner wall of theaugmenter. The flow is diffused as the flow area expands in the annular region. The combination ofthe carbon steel pipe and the annular region slow the velocity of the jet engine exhaust-cool airmixture, further reducing noise production from the jet engine.
Fuel System Monitoring Assembly
The fuel system monitoring assembly (fuel system) consists of the devices required for fuel filtration,
flow and specific gravity measurement, and flow control.The fuel system consists of two 10,000-gallon underground fuel tanks, two fuel pumps, two motor-driven fuel line valves, the fuel system monitoring assembly, and various controls and pilot lights atthe control board. The fuel system is interlocked to the basic interlock system, to the CO2 fire-extinguishing system, and to the exhaust gas cooling system.
Engine Oil Assembly
The engine oil reservoir and engine auxiliary lubricating oil-cooling system component assembly(lubricating system) provide a 20-gallon engine oil reservoir and an auxiliary means of cooling engineoil to a controlled temperature.
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The engine oil reservoir system is made up of a 20-gallon tank equipped with suitable fittings, a sightgauge, and breather vent. The engine lubricating oil is supplied from the storage tank, by way of theoil outlet to the engine lubricating system and back to the tank, through the oil inlet. The amount of oilin the tank can be readily determined by observing the oil level in the sight gauge. The storage tank islocated at an extension of the connector panel in the test cell.
The auxiliary lubricating oil-cooling system is provided for use as required by specific engines. Referto applicable engine test instructions. It consists of an oil temperature regulator valve, a heatexchanger, and suitable plumbing. Water, by way of the oil temperature regulator valve, passesthrough the cooling elements of the lubricating oil heat exchanger, which is used to cool the engine oilcirculating through the exchanger. The temperature of the oil returned to the engine is sensed by theoil temperature regulator valve by a sensing bulb installed in the heat exchanger oil line. The oiltemperature regulator reacts to the bulb signal by positioning a poppet valve. This increases ordecreases water flow through the heat exchanger, thus maintaining the oil outlet temperaturebetween proper limits. The oil temperature regulator is provided with a hand wheel so that thetemperature range may be adjusted to maintain outlet oil temperature within the allowable range. Thewater used for cooling the engine lubricating oil flows from the main water supply system to the loadbank water tank (containing heating elements), and then to the oil temperature regulator valve.
Compressed Air Component Assembly
The compressed air component assembly (compressed air system) provides pneumatic power, airsystem hardware, and pneumatically operated controls and actuating cylinders necessary for remotecontrol of numerous devices throughout the test facility.
The air compressor (a two-stage, air-cooled, electric motor-driven system) is located in the pumproom, and is controlled by a switch located on the master control center in the control room. Twoplug-in outlets supply unregulated compressed air for test cell utility purposes as required. Air filtrationand partial dehydration are accomplished by two float-type air filters for two main branch supply lines.The pressure to each branch line is controlled by two manually set air pressure regulators. Beyondthe pressure regulators, the air system branches off to the various control components for other majorsystems, such as the fuel system and the exhaust gas cooling system.
Intercommunication System
The intercommunication system consists of an eight-station intercom master in the control room, asuitable amplifying system, and two remote stations equipped with trumpets and microphones. Thesix spare station switches at the master control are not used as installed. The master unit is equippedwith a volume control, a push-to-talk button, and push-to-talk lock button. Remote stations areequipped with push-to-talk buttons only. Station No. 1 is located in the test cell; station No. 2 islocated at the test cell observation port.
Engine Starting and Ignition System
The starting of a jet engine or any other type of gas turbine engine requires that the engine be rotatedat a speed that will provide sufficient air for the required fuel-air ratio. Provisions are made forenergizing the ignition system to fire the spark (igniter) plugs at the proper time, and for the engine tobe accelerated until the power developed by the turbine is adequate for self-sustained rotation. Initialrotation of the engine during starting may be accomplished by use of either an electrically operatedstarter motor or a compressed, air-operated, air turbine starter motor. The electric starter motorrequires a source of direct current (DC) voltage. The air turbine motor requires a source ofcompressed air.
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Figure 10-17 — Aircraft test and evaluation facility.
Fire-Scope 2000 Fire Suppression System
This system is water mist technology providing the advantage of rapid fire extinguishment. Thesystem uses minimal amounts of water, distributed evenly around the engine casing, avoiding anydamage to the turbine by cooling it too rapidly. Thirteen spray nozzles are placed around criticalareas of the engine and six spray nozzles for the fuel supply area. The water system is pressurizedby eight compressed air cylinders, and driven by an electronic control box.
Aircraft Test and Evaluation Facility (ATEF)
A Hush House is a facility primarily designed for military fighter aircraft use. The Hush Houseprovides an enclosed work area for preparing the aircraft or un-installed engine, also equipmentrooms and an environmentally controlled, acoustical control room for test operators to work in duringengine operation. The Acoustic treatment provided by the facility reduces the environmental impacton the surrounding area by reducing the sound created by running aircraft engines.
Hush houses are also capable of testing un-installed jet engines mounted on a movable test standwith support equipment to supply fuel and air for engine running. Engine operation and testing in linewith the engine requirements is controlled and monitored using a computerized system. The test bayis sized to allow the users’ aircraft to be safely installed and restrained while running the engine(s)through their full performance tests as determined by the aircraft/engine to enable performance
issues to be identified and corrected. Various aircraft systems can also be checked while the aircraftengine(s) are running as per the Aircraft requirements (Figure 10-17).
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Figure 10-18 — Portable universal engine run-up test system, frames 1 and 2
PORTABLE UNIVERSAL ENGINE RUN-UP TEST SYSTEMS
Figure 10-18, frames 1 and 2, shows some of the more commonly used portable engine run-up teststands. These stands provide the aircraft maintenance activities with a portable and universal systemfor the operational and functional testing of jet aircraft engines. Figure 10-19, frames 1 and 2, showsa T-56 Turbo Prop Engine Test System in use today. The T-56 Turbo Prop Engine Test Systemconsists of an instrumentation and control cab, a fuel system installation, an engine test bed, fourflood lights, interconnecting cables and hoses with various adapters used with specific engine
models.
These systems perform the basic functions of checking all the engine performance characteristicsagainst the engine manufacturer’s operational parameters, as approved by NAVAIRSYSCOM. The
test cells display engine temperatures, vibrations, fuel metering, fuel flow pressures, thrust, lube oiltemperatures and pressure, compressor pressure, hydraulic oil pressure, anti-ice pressure, turbinerpm, and position indications such as nozzle and stator vane and throttle.
Some engines require special testing consoles. The console provides the electrical circuits tosatisfactorily conduct functional and performance tests.
The console provides junction facilities to connect the cell power to the engine, a system for remotecontrol measurement of throttle position, a transmitter and receiver to indicate inlet guide vaneposition, and a DC electronic indicating system for measuring nozzle position. A thermocouple type of
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Figure 10-19 — Turboprop engine test system, frames 1 and 2.
anti-icing temperature indicator, a starter circuit, and switches and cables necessary for operation ofthe engine and console under test conditions are included in some consoles.
Just as starting procedures vary with the various types of engines, the controls and instrumentationvary with different test cells. Checking the engine for proper operation consists primarily of readingengine instruments and then comparing the deserved values with those given by the manufacturer forspecific engine conditions, atmospheric pressures, and temperatures.
NOTEThese test systems may be used at any site location that
has been provided with adequate tie-downs (eitherconcrete embedded or buried expansion anchors).
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The engine test log records the data obtained during the engine test run. The log provides a record ofthe engine tests for future reference and acts as documentary proof that the engine was subjected tothe prescribed test procedures. The data must be complete, accurate, neat, and legible. Upon receiptof the engine for testing, the operator will enter the name of the testing activity, the engine model,serial number of the engine, and the date of the engine test.
During the test, record all unusual occurrences in the remarks section of the test log, while recording
all starts, shutdowns, times for accelerations, times for adjustments and settings during all operationacycles. During starts, record the time of day the engine was started, maximum turbine inlettemperature encountered, and the duration of that temperature, as well as recording the time foracceleration and stabilization.
At the end of the test, record the engine coast-down time. Coast-down time is defined as the timeelapsed from the moment fuel is cut off to the time the engine comes to a complete stop. Coast-downtime has no absolute value. A record maintained for engines will show what the expected averagecoast-down time should be. Any engine with an abnormally short coast-down time should be viewedwith suspicion and investigated for compressor rub or other malfunctions. The operator is required tosign all the test run logs, and is held responsible for the accuracy and completeness of all the test
data.Test schedules will vary with each different model of engine and manufacturer. Always refer to theappropriate engine manual when performing engine test runs.
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10-7. How often do you need to be recertified to operate an engine test cell?
A. Every 12 monthsB. Every 16 monthsC. Every 24 monthsD. Every 30 months
10-8. How many different functions does the JETI system integrate within the engine test cell?
A. 2B. 4C. 6D. 8
10-9. What is the purpose of the variable height stand assembly?
A. Support, restrain, and position the JETI equipmentB. Support and position the fire suppression systemC. Support and position the fuel tank system
D. Support, restrain, and position the engine
10-10. What is the other name given to the Aircraft Test and Evaluation Facility?
A. Big HouseB. Care HouseC. Hush HouseD. Quiet House
10-11. What requirement is needed for portable test cell use?
A. Adequate tie downsB. Level groundC. Noise safety areaD. Open field
10-12. What are engine test logs used for?
A. Record test cell operator’s on the job trainingB. Record engine performance data during a test runC. Record engine life cyclesD. Record the periodic maintenance equipment inspections
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CNATT makes every effort to keep their manuals up to date and free of technical errors. Weappreciate your help in this process. If you have an idea for improving this manual, or if you find anerror, a typographical mistake, or an inaccuracy in CNATT manuals, please write or email us, usingthis form or a photocopy. Be sure to include the exact chapter number, topic, detailed description, andcorrection, if applicable. Your input will be brought to the attention of the Technical Reviewcommittee. Thank you for your assistance.
Write: CNATT Rate Training Manager230 Chevalier Field AvenuePensacola, FL 32508COMM: (850) 452-9700 Ext. 3102 for the N7 Director.DSN: 922-9700 Ext. 3102 for the N7 Director.
E-mail: Refer to any of the Aviation Rating pages under CNATT on the NKO web page for currentcontact information.
