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A SERVICE PUBLICATION OFLOCKHEED AERONAUTICALSYSTEMS COMPANY-GEORGIA
EditorCharles I. Gale
Associate EditorRonald M. Hulett
Art DirectorDarre1 C. Benfield
Vol. 15, No. 4, October-December 1981
CONTENTS2 Focal Point
Ted NissleyDirector, Customer SupplyLASC-Georgia
3 Understanding Aircraft CorrosionA practical guide to the principles ofcorrosion, and hints on establishingan effective corrosion control pro-gram.
12 Static Discharger MaintenanceTheir requirements are modest, butproperly maintained dischargers do abet ter job.
14 Fuel Quantity Indicator Harness TesterChecking the indicator wir ing for proble m s is quick and easy w i t h thistest outfit.
Cover: The onset of winter weather in manyp a r t s o f t h e w o r l d t h i s t i m e o f y e a rincreases airframe exposure to moistureand chemicals, and makes maintenanceactivities more difficult. That can be a win-dow of opportunity for costly corrosiondamage.
Semantics and Customer Supply
Ted Nissley
have a thorough understanding
What does the word “spare” mean to you? If you look itup in a dictionary, you will find several definitions, but tomost p eople the word suggests something extra, an itemover an d above what is needed, a replacement reserved forfuture use.
In the Customer Supply organization at LASC-Ceorgia.we know that such conventional definitions ran fall verywide of the mark. To today’s aircraft operator, spare partsare not really “spare”at all. They are crucial to thesafeandefficient operation of every airplane in his fleet.
Beyond this, spare parts are a vital fact of business life.Having a reliable and knowledgeable source of qualityreplacement parts can make the difference between profitand loss, between success and failure. At Lockheed, weof what spares and spares provisioning really means.
We have also made it our business to give renewed meaning to another common wordthat is often too loosely applied. That word is service. Customer Supply at LASC-Georgiacan fill your order for every part needed to keep your Hercules aircraft flying, but we are farmore than just a parts warehouse. We are a fully developed, full-time service organization,dedicated to providing the total supply needs of each of our customers, everywhere in theworld.
We are prepared to support your supply requirements at every maintenance level,whether it is line, organizational, or depot: and we arc prepared to do it at your conven-ience, not just ours. Our 24-hour telephone service, supported by the latest in comput-erized inventory control systems, ensures that you will get prompt answers to every supplyquestion, and immediate response to your spares requirements.
Our computerized systems ensure speed and accuracy, but the real key to the quality ofthe service we offer lies’in the comprehensive knowledge of the supply business offered byour professional people. Theyadviseeach of our customers concerning his supply needs ona one-to-one basis. When you contact us about your supply needs, you are assigned yourown, individual supply administrator. This courteous and experienced professionalbecomes your representative, ready and able to helpsatisfy all of your supply needs quickly,efficiently, and at a fair price.
Customer Supply at LASC-Georgia is proud to serve Hercules airlifter operators world-w i d e and we hope that you will give us the opportunity to assist you in solving your total supply and service requirements. We think you will agreethatwegivefreshdefinitiontoyetanother word that is often misused in today’s world. That word is value.
Ted NissleyDirector, Customer Supply LASC-GeorgiaLockheed Aeronautical SystemsCompany
H.L. BURNETTE DIRECTOR
CUSTOMER INTEGRATEDSERVICE LOGISTICS SUPPORT
CUSTOMERSUPPLY
TECHNICALPUBLICATIONS
RELIABILITYMAINTAINABILITYSUPPORTABILITY
A.H. McCRUM H T NISSLEY H T NISSLEY CE ADAMS H M SOHN
UnderstandingAircraft Corrosion
by Everett J. Smith, Specialist EngineerMaterials and Producibility Technology Department
The Hercules aircraft has been in production longer thanany other large aircraft. Yet outward appearances aside,there is little real resemblance between today’s Herculesand its predecessor of 30 years ago. The world’s mostfamous airlifter may still have a familiar face and form, butit has undergone countless changes over the years, changesthat continually improve its performance and extend itsservice life.
A significant number of these changes were made speci-fically for the purpose of increasing the airplane’s resis-tance to corrosion. Today’s Hercules not only incorporatesthe latest and best technology as far as materials of con-struction is concerned, but it also includes the latestadvances in sealing techniques, protective finishes, andcorrosion prevention.
More corrosion-resistant steel and aluminum alloys arenow used to prevent fatigue, stress corrosion cracking, andexfoliation corrosion. Today. many fasteners are also madeof these durable and resistant alloys. A corrosion- inhibitingfinish system consisting of an epoxy polyamide primer andaliphatic polyurethane top coat is applied to all exteriormetallic surfaces except those made of stainless steel ortitanium.
Every permanent exterior joint, from nose to tail andwingtip to wingtip. is faying surface sealed with a corrosioninhibiting sealant. Corrosion prevention techniques such asan integral fuel tank water removal system, shot peening tominimize stress corrosion cracking, and wing dry baydrainage and ventilation, to name but a few, all contribute tothe corrosion resistance of today’s Hercules aircraft.
Lockheed SERVICE NEWS Vl5N4 3
Faying surfaces are carefully sealed during manufacture to prevent moisture from entering
But thirty years of evolution in corrosion preventiontechnology does not mean that the Hercules aircraft is corro-sion proof. Today’s advanced anti-corrosion measuresmake life a little easier for maintenance personnel, but aworkable corrosion prevention and control program is still arequirement if maximum service life and economy of oper-ation arc to bc realized.
It is worth the effort. No aspect of aircraft maintenancepays greater returns in terms of long-range economic bene-fits, safety, and reliability than the prevention and control ofcorrosion.
The Corrosion Process
Building an effective corrosion control programrequires a working knowledge of some of the basic princi-ples of the corrosion process itself.
In a very real sense, the corrosion of metal componentsstarts the instant the manufacturing process is complete.The speed at which corrosion will proceed is dependentupon the type of material used, the fabrication and assemblymethods employed, the environment to which the structuresare exposed, and of course, the preventive measures takenby the individual operator.
Corrosion is a complex electrochemical action thatcauses metals to be transformed into oxides and salts. Thedriving force behind many of the most common corrosiveprocesses involves the intrinsic differences in electricalpotential between metallic elements. The reasons for thesedifferences can be traced to characteristics of the atomicstructure of the metals themselves.
Simply stated, differences in electrical potential amongmetals reflect how readily the individual metallic elementsgive up electrons in the presence of other metals.
Some metals, for example magnesium and zinc, give upelectrons quite readily. Such metals are chemically activeand thus corrosion-prone. Other metals, like copper andsilver, do not release their electrons as easily. They tend tobe more inert chemically, and resist corrosive action.
The Electromotive Series
The relationship between metals based upon differencesin their electrical potential and associated chemical activitymay be represented schematically in an ordered sequenceknown as the electromotive, or galvanic, series.
In the electromotive series, differences in electricalpotential are normally expressed in terms of electromotiveforce (EMF) and measured in volts. This provides a sys-tematic way of comparing the electrical effects involved,
4
and offers a quantitative basis for predicting the intensity ofpossible corrosive activity.
The chart below lists a number of metals commonlyused in aircraft structure in order of decreasing EME Mag-nesium, which is an active metal and gives up electronsrelatively easily, is shown at the top of the list with an EMFof -1.73 volts.
The Electromotive SeriesEMF of Common Metals and Alloys
EMF(Volts) Metal or Alloy
-1.73 Magnesium-1.63 Magnesium Alloys-1.10 Zinc-0.97 Beryllium-0.96 7072AluminumAlloy-0.82 7075AluminumAiloy-0.82 Cadmium-0.67 2024-T4Aluminum Alloy-0.64 Steel-0.49 Tin-0.38 Brass-0.20 copper-0.15 Titanium-0.10 Monel-0.08 Silver
Copper, a much less active metal, is listed near thebottom of the chart with an EMF of -0.20 volts. The dif-ference between these values, or corrosion potential,amounts to -1.53 volts. This means that when magnesiumand copper come into contact, there will hc a strong tend-ency for the magnesium to corrode rapidly unless extraor-dinary protective measures are taken.
The Corrosion Cell
Corrosion that takes place when metals of widely differ-ing EMF values come into contact depends upon the estab-lishment of what is known as an clcctrolytic, or corrosion,cell. The illustration on page 6 shows a laboratory setupdesigned to demonstrate the operation of a simple electro-lytic cell.
The EMF of the copper bar shown on the left is signiffi-cantly lower than that of the magnesium bar on the right. Ifthe two bars are immersed in an electrolyte (such as watercontaining dissolved salts) and connected by a conductingwire, the magnesium atoms in the bar on the right will beginto give up electrons and enter the electrolyte as positivelycharged magnesium ions.
Electrons freed by the process will flow from the mag-nesium bar to the copper bar through the connecting wire,where the electron flow can be measured with a milliamme-ter. An electrolytic cell is fundamentally a voltaic battery,and the forces involved can be surprisingly strong. Underthe proper conditions, a laboratory setup such as the oneillustrated on page 6 will produce enough current to illumi-nate a small light bulb.
Anodes and Cathodes
The transfer of electrons from the magnesium bar to thecopper bar results in a net negative charge on the copper bar.Viewed from the standpoint of the electrolyte, where thecorrosive processes are actually taking place, this has theeffect of making the copper bar the cathode of the cell, andthe magnesium bar the anode.
The presence of excess electrons at the cathode forgesan important link in the chain of electrochemical events thatserves to keep the corrosion process going.
These electrons are available to neutralize positivelycharged hydrogen ions from the electrolyte in the vicinity ofthe cathode, which are converted into atoms of hydrogen.The hydrogen atoms unite to form molecules of hydrogengas and then escape to the atmosphere. This process tends toremove electrons from the cathode, but they are imme-diately replaced by other electrons produced by furthercorrosion of the magnesium bar.
The corrosion process is also driven forward by chemi-cal action at the anode, where positively charged magne-sium ions at the anode react with hydroxyl (OH) and othernegatively charged ions in the electrolyte to form magne-sium hydroxide and other salts.
Magnesium ions are removed from the electrolyte by theformation of these insoluble, stable compounds; however,they are quickly replaced by additional magnesium ionswhich enter the solution as the anode continues to corrode.
The corrosion process thus tends to perpetuate itselfboth electrically and chemically. If left undisturbed, theprocess will continue until all of the magnesium has beenconsumed, and the source of the electron flow has beeneliminated.
Breaking the Corrosion Cycle
A careful examination of the electrochemical processesthat drive the corrosion cell shown in our example will pointup the fact that some rather special conditions must bepresent before such a cell can become active:
Lockheed SERVICE NEWS Vl5N4 5
CATHODE ANODE
ELECTRON FLOW
ELECTRON FLOW
ELECTROLYTIC CELL (SIMPLIFIED)
B A T T E R Y
NO WATER NO CURRENTNO CORROSION
BROKENCONDUCTOR
1. There must be a metal present which can serve as theanode of the cell.
2. There must be a metal present which can serve as thecathode of the cell.
3. There must be an electrically conductive path thatallows electrons to flow between the anode and thecathode.
4. There must be an electrolyte (usually water) coveringboth anode and cathode to complete the electrical circuit.
NO DISSIMILARELECTRODES
The elimination of any one of these conditions willprevent a corrosion cell from becoming established. andgreatly reduce the opportunity for corrosive action to takeplace.
This is a key point which underlies all corrosion preven-tion efforts. Virtually every approach to corrosion preven-tion depends upon successfully interrupting or interferingwith one or more of these preconditions for the establish-ment of corrosive processes.
6 Lockheed SERVICE NEWS Vl5N4
WATER FILM
GALVANIC CORROSION RUST (SURFACE CORROSION)
CADMIUM PLATED EXFOLIATIONSTEEL FASTENER
ALUMINUM SKINWATER ENTRY BYCAPILLARY ACTION
ANODE
Aircraft structure offers a rich field of opportunity formany differenttypes of corrosive action.
Corrosion in Nature
Studying a laboratory corrosion cell such as the oneillustrated on the previous page is helpful in gaining anunderstanding of the physical principles behind some of themost common corrosive processes affecting metals. Theactual course of events in nature is much more complex,however, and involves countless variations and permuta-tions of the process.
For one thing, the components of aircraft structuremake use of a variety of metallic elements, used in numer-ous alloys of diverse composition. The same materials maythen be subjected to many different kinds of treatments,tempers, finishes, and coatings during manufacture, all ofwhich have an effect on susceptibility to corrosion.
For another, aircraft structure is physically intricate.Parts of every conceivable size and shape are manufacturedfor use in aircraft, and then riveted, welded, bolted, andbonded together to make up the final assembly. Such com-plexity and diversity yield a rich field for corrosive action,and it can show up in many different ways.
It is also important to remember that corrosion cells donot always involve such relatively straightforward proc-esses as our example of dissimilar metals coupled throughan electrolyte. Differences in electrical potential sufficientto give rise to corrosive action can sometimes be traced tosmall variations in chemical composition on or at the sur-face of the same piece of metal.
Impurities, inclusions, and foreign substances adheringto metal structure as a result of surface damage may have asimilar effect. Differences in oxygen potential that candevelop between two areas of the same metal structure arealso an important cause of corrosive action. Another majorsource of damage involves direct exposure to corrosiveagents such as acids, alkalis, and atmospheric contami-nants.
Types of Corrosion
When corrosion takes place, the visual evidence varieswith the metal involved. In the case of aluminum andmagnesium, corrosion usually appears as surface flaking,
Lockheed SERVICE NEWS Vl5N4 7
etching. or pitting,often combined with a gray or whitepowdery deposit. On copper and copper alloys, the corro-sion forms agreenish film called patina. With steel. it is thefamiliar reddish rust. When the deposits are removed, thesurfaces may appear etched and pitted, depending upon thelength of exposure and severity of’ attack.
This is the most common type of corrosion. When anarea of unprotected metal is exposed to the atmosphere withits contaminants, there will be a uniform attack over theentire area. On polished materials, this is first seen as ageneral dulling of the surface. If the attack is allowed tocontinue. the surface will become rough or frosted inappearance.
If surface corrosion is allowed to go untreated. it canprogress to another type of corrosion, called pitting. Pitsform in localized areas, often hidden under powderydeposits. If permitted to continue, pitting corrosion maywork its way completely through the metal.
Fretting Corrosion
This type of corrosion is caused by close-fitting partswhich are allowed to rub together. The results of fretting areremoval or pitting of metal in the area of contact: andgalling, seizing, cracking. or fatigue of the metal. There isalso a loss of tolerance in accurately fitted parts, and loosen-ing of bolted or flanged surfaces.
Filiform Corrosion
Filiform corrosion usually forms on aluminum skinsurfaces under an organic coating, especially in a warm andhumid environment. It appears on the painted surface asthreadlike filaments, and when the filaments are broken,corrosion will be visible on the aluminum skin. New andimproved finish systems are making occurrences of thistype of corrosion less frequent
Microbial Corrosion
In this case, corrosion is caused by living microorga-nisms. Microorganisms have demonstrated that they canlive quite well at the interface between water and a variety ofdifferent hydrocarbons. They feed on fuel hydrocarbonsand hydrocarbon-type coatings and materials. As thecolony grows, a sludge made up of concentrations of cells
Filiform corrosion often appears as threadlike raisedareas under organic coatings.
and acidic by-products is created which adheres to structureand corrodes it.
Besides causing corrosion, microorganisms can alsocause problems within the fuel system. Once established, itis no easy undertaking to eliminate a microbial infestation.The fuel tank must he drained, purged, cleaned with soapand water, and then sterilized with an alcohol and watersolution.
It is much easier to prevent microorganisms frombecoming established in the first place. Use a biocidaladditive such as MIL-I-27686 regularly, keep fuel storagetanks as free of water as possible, and drain any accumu-lated water from the aircraft fuel tanks every day.
Periodic inspection of both the ground storage andaircraft fuel tanks for indications of microorganisms andcorrosion is also prudent, particularly when the biocidaladditive has not been used regularly.
Intergranular and Exfoliation Corrosion
Intergranular and exfoliation corrosion describe dif-ferent stages of the same process, which is essentially anattack on the grain boundaries of metal. In the intergranu-
lar-exfoliation process, intergranular corrosion is the firststep. and always starts from a surface pit or pinhole thatexposes interior layers of the metal to moisture.
The opening may he very small, and there may he littlevisible evidence of damage. As intergranular corrosionprogresses. however, pressure is exerted at the grain bound-aries by the corrosion products, causing a lifting and flakingat the surface. At this point, the attack has changed fromintergranular corrosion to exfoliation corrosion.
Entrapped moisture caused corrosion in this rainbowfitting.
Tensile stress and exposure can result in destructivestress corrosion cracking.
Effects of Corrosion
The question asked most often by maintenance man-agers about corrosion is how long it will take for a corrodedpart to fail. No one can answer such a question with anydegree of accuracy. How fast corrosion progresses dependsupon the composition of the materials, the finish, the seal-ing method, the environment, and how well the part inquestion is maintained in service.
Left unchecked, however, it is certain that corrosionwill eventually cause structural failure. All corrosion mustbe removed as soon as practicable. The surface then must bechemically treated and refinished. When prompt attention isgiven to corrosion problems as soon as they are discovered,further damage can be prevented.
Stress corrosion cracking is caused by the simultaneouseffect of constant tensile stress and corrosion. Residualstress may have been induced during processing of the part,or cracking could occur because of sustained operating orstatic loads introduced during installation of the part oraircraft operations. To avoid stress corrosion cracking dur-ing maintenance operations, do not force fit parts, andalways make sure that the finish system remains intact.
The Program Advantage
Piecemeal efforts. no matter how well intended, cannotbe expected to keep corrosion in check vet-y long. There isno real substitute for a well organized and highly structuredprogram of corrosion prevention .
Locktreed SERVICE NEWS V15N4 9
Remember that it is corrosion, more often than anythingelse, that causes an aircraft to be retired before its full lifeexpectancy has been reached. Many improvcmcnts havebeen made to enhance the corrosion resistance of the Hcr-cules airliftcr through the years, but an enlightened preven-tive maintenance program is still required if its maximumpossible service life is to be realized.
Moisture and dissimilar metals led to corrosion in thiswing plank.
How much maintenance is required depends mostly onthe types of missions flown, and the environment in whichthe aircraft operates and resides. Each operator shouldtherefore develop his own corrosion prevention and controlprogram, one which will provide a systematic and com-prehensive approach that is tailored to his particular opera-lion.
The program must be designed to support the aircraftthroughout its service life, but it should not be so rigid thatchanges cannot easily be made as aircraft missions, mate-rials, and operational requirements change. Once a goodprogram has been established, the payoff in the formof reduced maintenance costs, less aircraft downtime,and improved aircraft safety will be both immediate andenduring.
Building a Program
The term “program,” as used here, refers to more thanjust a written plan, although appropriate documentation is
an important part of a successful program. Rather, theprogram concept in this application is intended also toencompass overall management, training of personnel,maintenance of adequate manpower; as well as proper facil-ities, equipment, and tools. Although the program shouldinclude both prevention and control measures, it shouldbe centered on where the most benefit may be realized-prevention.
It is also important that every person associated with thecorrosion prevention and control program be highly moti-vated, and committed to getting the job done properly.Without such personal commitment the program is doomedto failure from the start.
The first step in corrosion-control planning should be toconduct an objective review of what is already being doneand how well it is heing accomplished. This review shouldinclude, as a minimum, the following items.
Detcrminc the type of environment in which the aircraftoperates. Although the home station may be in an accept-able environment, where the aircraft actually operatesmay not bc as acceptablc.
Include the quality of water used for washing aircraftin your survey. Aircraft should never be washed withbrackish water or water containing significant levels ofchemicals or mineral salts. A check on the contents of thelocal water supply is a must.
Inspection during PDM revealed corrosive action hiddenunder a skid pad.
IO Lockheed SERVICE NEWS Vl5N4
l Compare job requirements to the training and back-ground of all personnel within the maintenance organiza-tion. Those people directly involved with corrosioninspection and removal, and quality assurance personnel,normally require more in-depth training than other main-tenance personnel.
l Review facilities, equipment, and tools required to per-form corrosion prevention and control operations. Thebest way to do this is to compare what is being done towhat is required in maintenance manuals. This statementmay seem a bit strange, but there are some organizationsthat perform corrosion prevention maintenance in a man-ner that barely resembles the true requirements, oftenbecause of shortfalls in one or more of these areas.
Once all of the reviews have been completed and a clearpattern of needs and requirements has been established,formalize the corrosion prevention and control program. Itis always best to develop a written plan of action so thateveryone concerned will understand what is expected.
As the old saying goes, “Don’t sweat the small stuff.”Concentrate the effort on primary structure of the aircraft,and take care of the other structure afterward. This is not tosay that secondary structure is not important. It is impor-tant, but sound primary structure is of critical importancefor safety, and extending aircraft service life and safeoperations.
Lockheed Aeronautical Systems Company stronglyencourages every Hercules operator to establish a com-prehensive corrosion prevention and control program toprotect the investment he has in his aircraft. Lockheed alsostands ready to help. Factory corrosion engineers are avail-able to provide the expertise required to develop an effectiveprogram for each operator’s particular needs.
For further information, please contact:
C-130/Hercules Service DepartmentAttention: C.R. KelleyD/64-21, Z/668Lockheed Aeronautical Systems CompanyMarietta. GA 30063
Lockheed SERVICE NEWSVl5N4 11
There is an old saying that good things come in smallpackages. Certainly this applies to airframe components:some of the smallest and simplest parts do their jobsfaithfully day after day, attracting little attention and requir-ing minimal care. A case in point are the static dischargers.
Static dischargers perform the vital function of com-batting the buildup of P-static. If the weather conditions areright, an aircraft moving through the air may pick upelectrical charges which can accumulate enough power tocause audible noises in radio equipment. This phenomenonis called precipitation static, usually shortened to justP-static.
Causes of P-Static
P-static usually occurs when the aircraft is passingthough bad weather such as freezing rain, ice crystals, dust.sand. or snow. However, P-static may also occur in appar-ently clear weather. An electrical charge is transferred tothe aircraft each time it impacts with a particle suspended inthe air.
When charging conditions are present, the electricalpotential on an aircraft can rapidly reach values of 100,000to 200,000 volts or more. If the electrical field around anaircraft becomes strong enough, the result can be ionizationof the air at the edges of the structure, and short bursts ofelectricity called corona pulses will leave the aircraft.
The energy released by the corona pulses, whichbecome coupled to the radio antennas, causes hroad-bandradio frequency noise. This noise can assume a variety offorms, from popping, to buzzing, to roaring sounds,depending upon the intensity of the charging rate. Theeffect of the noise generated by P-static can range frommerely being a nuisance to making radio communicationcompletely impossible.
Controlling Static Discharge
P-static cannot be prevented, but the effects can beminimized by adequate electricalbonding of the aircraftexterior and by the use of static dischargers. Each compo-nent that is installed on the exterior of the Hercules aircraftduring manufacture is electrically bonded to the fuselage,
wings. or empennage. including all access panels, doors,and antennas. This bonding provides a continuous path forelectrical charges to get to the dischargers. and it alsoprevents gaps which charges would tend to jump, thusgenerating more P-static.
Each Hercules aircraft is delivered with 17 wick-typestatic dischargers installed. Four dischargers are installedon each aileron, three on each elevator. and three on therudder. These dischargers allow P-static which has built upon the aircraft to discharge noiselessly through the multiplestrands of a wick. This effectively decouples the noisebursts from the aircraft.
The measures taken at the factory to combat P-statictend to become less effective during normal use of theHercules aircraft because of everyday wear and tear.Periodic inspection and maintenance arc required to main-tain the effectivcncss of the anti-static protection, and it isimportant that the condition of the static dischargers not beneglected.
Static Discharger Types
Hercules aircraft built before Lockheed serial numberLAC 4432 were equipped with type AN/ASA-3 dis-chargers. These dischargers consist of a 13-inch conductingcotton wick enclosed in a plastic tube. The tube is flattenedon one end and enclosed in a metal sheath which is attachedto the airplane skin.
All Hercules aircraft built subsequent to LAC 4432 areequipped with CM3-J2 dischargers. These units are of all-metal construction consisting of a 7% inch braided metalcable inserted in a metal sheath for attachment to the air-craft. The CM3-J2 dischargers are interchangeable with theearlier type.
Discharger Maintenance
The AN/ASA-3 type of discharger is subject to wear andshould be inspected on a prcilight basis to determine thatabout I.5 inches of wick extend from the plastic sheath. Ifthe wick is dirty or badly frayed, trim off the worn portionand trim back the plastic sheath to 1.5 inches from the end ofthe wick, fraying out the remaining portion of the wick.
When wicks have been trimmed back to a length of less than6 inches, the discharger must be replaced.
The CM3-J2 discharger should be periodically checkedto determine if the ends of the wire protruding from themetal sheath are balled or bent. Damaged wires may betrimmed back until the distance between the end of themounting base and the end of the protruding wires is 6.25inches, Dischargers less than 6.25 inches long or badlybent. broken, or corroded should be replaced.
CM3-J2
TYPICAL EMPENNAGE TYPICAL WINGINSTALLATION INSTALLATION
CM3-J2 AND AN/ASN-3 STATIC DISCHARGERS
by E.D. Allen, Staff EngineerSupport Equipment Group
A tester has been developed for checking ortroubleshooting fuel quantity indicator harnesses foropen circuits and intermittent or improperly fabricatedsolder connections (shield terminations or “zaps”).
TANK BOUNDARY CONNECTORTEST BOX
FAULTINDICATORTEST BOX
(DELTA MILLI OHMETER)
FLIGHTSTATION CONNECTORTEST BOX
FUEL QUANTITY HARNESS TESTER
The tester consists of three boxes which are stored ina convenient carrying case. A complete set of operatinginstructions is included in the lid of the case. One of thetest boxes is attached to the fuel quantity harness at thetank boundary connector. The second box is attached tothe indicator harness at the flight station. The third box,a fault indicator (delta milliohmeter), is attached to theflight station test box.
Thecircuit being checked is selected on both test box-es. The fault indicator box, a balanced resistance bridge,is adjusted so that its indicator lamps go out. The solderconnections on the harness being tested are flexed andthe lamp on the fault indicator box comes on if an inter-mittent or poor connection exists.
An open circuit is indicated when rotating the zeroadjust knob cannot extinguish the lamps on the fault in-dicator test box.
The tester can also be used to check any other harnessinstalled on the airplane for open circuits and intermit-tent or poor solder connections.
The following circuits can be checked, using the equip-ment described above:
l Shield to hi-Z wirel Shield to tank unit lo-Z wirel Shield to compensator lo-Z wire
The advantage of this method is that it can detect thevery small changes in resistance which are indicative ofintermittent or poor connections (instantaneous responsein the 20 to 70 milliohm range).
Part number 3403184-l has been assigned to the tester.The unit is still in the prototype state, but it will be putinto production upon positive response.
If you would like further information regarding theharness tester, please contact the following:
For price quotations please contact the following:
Supply Sales and ContractsDepartment 65-11, Zone 451LASC-GeorgiaMarietta, GA 30063Telephone (404) 494-4214Telex 804263 (LOC CUST SUPPL)
Support Equipment GroupDepartment 63-51, Zone 451LASC-GeorgiaMarietta, GA 30063Telephone (404) 494-4271Telex 4946693 (Lockheed MARA)
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