~Lockheed

VOL. 10, NO. 3, JULY-SEPTEMBER 1983

A SERVICE PUBLICATION OFLOCKHEED-GEORGIA COMPANYA DIVISION OFLOCKHEED CORPORATION

EditorCharles I. Gale

Associate EditorsDaniel E. JolleyJames A. LoftinSteve Palmer

Art Direction & ProductionBill Campbell

Vol. 10, No. 3, July-September 1983

C O N T E N T S

2 Focal PointP. E. StoreyProgram ManagerC-130/L-100 Engineering

3 Controlling Rudder ThrustRearing Wear

Proper lubrication is thekey to long bearing life.

8 Chemical Control of Fuel TankInfestation

Biocidal shock treatments keepmicrobial growth in check.

IO Solid-State Oil TemperatureControl Thermostats

Oil cooling system operationreflects thermostat changes.

14 HF Antenna Wire BreakageSealing out corrosion keepsantenna wires on the job.

Cover: Cutaway view of the Hercules aircraftempennage.

Published by Lockheed-Georgia Company, a Division of

Lockheed Corporation. Information contained in thisissue is considered by LockheedGeorgia Company to be

accurate and authoritative. it should not be assumed, howeve,. that this material has received approval from anygovernmenta l agency or military service unless it isspecifically noted. This publication is for planning and

information purposes only. and it i s not to be construed

as authority for making changes on aircraft or equipment,

or as superseding any established operational or main-

tenance procedures or policies. The followng marks areregistered and owned by Lockheed Corpora t ion :

” “Hercules”, and “JetStar”.Writen permission must be obtained from Lockheed-

Georgia Company before republishing any material in thisperiodical Address all communications t o Editor. Service

News Department 64-22 Z o n e 278, Lockheed-GeorgiaCompany, Marietta, Georgia. 30063. Copyright 1983Lockheed Corporation.

Teamwork and Communicat ions

It is a real pleasure to be part of this issueof Service News magazine. We inLockheed engineering are proud of theHercules aircraft and would liketothankyou, the people who keep her flying, forhelpingthisremarkableairplaneachievesuch a long and outstanding record. Fly-ing and maintaining airplanes always re-quires a dedicated team, and we believethat the unique success of the Herculesrepresents modern aviation’s best and

P. E. Storeylongest-running demonstration of what real teamwork between manufacturer andoperator can accomplish.

Nothing is more vital to effective teamwork than welI-established and properly utiIizedlines of communication. This publication, for example, is an integral part of the Her-cules aircraft communications network. It makes itscontribution by ensuring that a broadrange of general information on technical subjects is readily available to all membersof the Hercules ”team (‘To see just one area where this can be important, we have onlyto recall that many changes have been made to the airframe, power plants, functionalsystems, and individual components of the Hercules aircraft since the first flight of theYC-130 in August of 1954. While safety items and other matters that should receive theimmediate attention of Hercules operators are covered in service bulletins, we havefound that Service News is an excellent medium for introducing and describing the variousimprovements and evolutionary refinements that have become part of the Herculesaircraft over the years.

One such improvementthat has been incorporated intotheaircraft relatively recent-ly is the solid-state oil temperature control thermostat. The article beginning on page10 offers a complete description of this new thermostat and its operational characteristics.I think this article is a good example of how our C-130/L-100 design engineers try to selectthe most appropriate mode of communication in responding to inquiries of generalinterest that have been received from operations and maintenance organizations inthe field.

Another area of vital interest to everyone involved in the Hercules aircraft programis maintenance. Our engineering staff, the service representatives of the Customer Ser-vice organization, and the operators who work directly with the aircraft regularly comeup with hints and maintenance ideas that can be beneficial to all. Here again, it is onlyby bringingthese ideas to the attention of others that they become truly useful. Severalitems of this type are presented in the other articles in this issue.

Open linesofcommunication areindispensabletoeffectiveteamworknomatterwhatthe undertaking. The Hercules team - all of us from the design engineer in thefactoryto the maintenance specialist in the field - have shown for nearly thirty years whatgood communications can do when professional people work together on a qualityproduct. This is a tradition to build on. Remember that we in Lockheed engineeringare part of your team. We urge you to contact us through your local Lockheed servicerepresentativeordirectlyanytimewecan assistyou in getting all theperformanceandservice out of your Hercules airlifters that we build into them.

Sincerely,

C-130/L-100 Engineering

T.J. Cleland

CUSTOMER INTEGRATEDLOGISTICS SUPPORT

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\.ock.tlel!d SERVICE NEWS V10 N 3

FS 1127

Figure 1. Rudder thrust bearing location.

Lockheed has recently received reports of problemswith the operation of the rudder on some Hercules air-craft. There are indications that lack of regular servic-ing may have played a role in many of these cases.Since the rudder is generally a trouble-free item from amaintenance standpoint, its servicing may not alwaysreceive the attention it deserves.

Effects of Thrust Bearing Wear

The complaints included such things as jerky,erratic, or sluggish rudder movement, particularly atlow airspeeds, and a tendency for the aircraft to“hunt” about the vertical axis (yaw) when the auto-pilot was engaged. Investigation showed that in mostof the aircraft where these conditions were noted, thelarge roller bearing that supports the weight of the rud-der at its base turned out to be seriously worn.Replacement of the affected P/N C-12 or DA12-38AQrudder thrust bearing (Figure 1) cleared the discrepan-cies .

Subsequent study of the worn bearings by Lockheed

yielded strong evidence that the single most importantfactor in their premature demise was inadequatelubrication. The bearings had been allowed to run dry,and the resultant metal-to-metal contact destroyed thebearing surfaces in short order.

Once the nature of the problem had been estab-lished, Lockheed issued Service Bulletins 82-504 and382-27-26, discussing these findings and outlining arecommended course of action to prevent prematurerudder thrust bearing wear from occurring.

The service bulletins also provide helpful informa-tion concerning replacement of the bearing shoulddamage already be present. Since the informationcovered in these documents has broad applicabilityand can be of significant value in reducing main-tenance downtime wherever the Hercules aircraft isflown, we would like to review the salient points here.

Servicing Recommendations

In aircraft where the rudder appears to be function-

Lockheed SERVICE NEWS VlON3 4

ing properly and none of the symptoms of rudderthrust bearing wear described above are present, theonly immediate action recommended is to give thethrust bearing an extra lubrication as a precautionarymeasure. T.O. IC-130A-6WC-15 specifies that therudder thrust bearing is to be lubricated with MIL-G-Xl322 general-purpose grease, or the equivalent, ateach minor and major inspection. In the case of com-mercial Hercules aircraft, the service bulletinsreferenced above recommend an immediate extraapplication of lubricant and then lubrication at inter-vals of 1800 flight hours or 365 days, whichever occursfirst.

This should be sufficient as far as routine servicingis concerned, but it is very important that the lubrica-tion procedure be carried out conscientiously, and thatevery effort is made to ensure that an adequateamount of approved lubricant actually enters the bear-ing without damaging the bearing seals.

Lockheed also recommends that the rudder thrustbearing be routinely replaced whenever the rudder isremoved for some reason in the course of a main-tenance activity. The cost of the part is minimal com-pared to the time and effort required to get at it, andinstalling a new one whenever the rudder is already outof the way will help reduce the chances that the thrust

bearing will suddenly need to be replaced at a less con-venient time.

Thrust Rearing Replacement

If the condition of a rudder thrust bearing hasdeteriorated to the point that it is causing erratic rud-der operation, no amount of extra lubrication willrestore normal operation. Permanent damage to thebearing has probably already occurred, and the onlysolution is to replace it.

The first step in removal and replacement of therudder thrust bearing is to remove the rudder and rud-der counterbalance assembly from the aircraft. Theapplicable authorized maintenance manual for yourairplane contains the information necessary to com-plete these tasks. It is essential that you strictly observeall safety precautions set forth in the maintenancemanual to prevent possible injury to yourself or otherswhile performing maintenance on the rudder andassociated components. Be sure to remove allhydraulic and electrical power from the airplanebefore you begin.

Once you have removed the rudder and ruddercounterbalance assembly from the aircraft, move therudder torque arm to one side. Next, remove the cotter

Figure 2. Counterbalance, torque arm, and rudder support cone fitting with associated hardware.

COUNTERBALANCE

339729 RUDDERTORQUE ARM

374462-l RUDDER

CHAMFEREDWASHER

AN310-12 NUTAN380-4-7 PIN

356755-l RUDDER THRUSTBEARING SUPPORT FITTING

5 Lockheed SERVICE NEWS VlON3

GREASE FITTINGFWD

C-l 2 OR DA1 2-38AQTHRUST BEARING

370174-l RETAINER

NAS517-3-8 SCREWAN96001O WASHER NAS517-3-6 SCREW

MS21 042-3 NUT AN960D1O WASHERNASl291-3 NUT

(3 LOCATIONS)

RUDDER THRUSTBEARINGSUPPORT FITTING

Figure 3. Rudder thrust bearing installation.

pin, the nut, and the P/N 342974 thrust bearingwasher from the rudder support cone fitting (Fig. 2).Examine the nut and washer for signs of damage,corrosion, or wear. If they are sound, they may be savedfor reinstallation.

Now remove the rudder support cone fitting and thethrust bearing chamfered washer, P/N 356651-1, fromthe rudder thrust bearing support fitting. Keep thecone fitting and washer so that they can be reinstalledlater. Locate the roller bearing and the retainermounted in the rudder thrust bearing support fitting(Figure 3).

Next remove and put aside the four nuts, washers,and screws from the thrust bearing retainer. Be sure tokeep the nut, screw, and washer removed from thefront of the retainer in a separate place from the otherretainer hardware; the front screw is longer than theother three, and uses a different washer and nut.

Remove the retainer from the support fitting, and saveit for reinstallation.

Press firmly with your fingers on the top of thethrust bearing to disengage the bearing from the fit-ting. You may find it helpful to use a drift pin and ahammer to lightly tap the top outer edge of the bearingto loosen it.

Before you install a new thrust bearing, flush thegrease fitting with new lubricant to remove any cakedgrease from the fitting and the grease path; then use asoft cotton cloth to wipe out the inside of the supportfitting. Next, insert a new bearing up into the rudderthrust bearing support fitting. Use your fingers to pushfirmly on the bottom side of the bearing until the bear-ing is seated in the support fitting.

Reassembly

Install the bearing retainer in the bottom of the sup-

Lockheed SERVICE NEWS Vl ON3 6

Airdrop: a time when the smooth and precise operation of all flight controls plays a crucial role.

port fitting and secure the retainer, using the fourscrews, nuts, and washers that were put aside earlier.Be sure that the longer of the four screws and itsaccompanying nut and washer are installed throughthe forward side of the retainer (Figure 3).

After you have the retainer in place, install theoriginal cone fitting by inserting it down through thebearing. Be sure that the P/N 356651-1 chamferedwasher is inserted onto the shaft of the cone fitting sothat the washer rests between the fitting and the bear-ing. After this step, insert the P/N 342974 thrust bear-ing washer onto the shaft of the cone fitting and securethe whole assembly with the nut that was originallyinstalled. You should obtain a new cotter pin fromsupply and install it through the hole in the threadedend of the rudder support cone fitting.

It is a good idea at this stage of the job to check thatthe four rudder hinge pins and hinge bearings are in agood state of repair.

7

Before you install the rudder and the counterbalanceassembly, thoroughly lubricate the new bearing withMIL-G-81322 lubricant via the grease fitting locatedon the aft side of the support fitting (Figure 3). Becareful not to dislodge the bearing seals by exertingexcessive pressure on the trigger of the grease gun.Slight pressure is all that is necessary to provide suf-ficient lubrication. After you lubricate the bearing,you can complete the job by reinstalling the rudderand the counterbalance assembly as outlined in theappropriate flight controls technical manual.

Lockheed SERVICE NEWS VlON3

It isn’t every day that a new product appears whichcombines several important, virtues in one convenientpackage, but it happened in the case of a chemicalknown as ethylene glycol monomethyl ether. This com-pound, which is more commonly referred to by one ofits several trade names (see table, page 9 ) or as MIL-I-27686 anti-icing inhibitor, was originally developedby Phillips Petroleum Company as an anti-icing agentfor aircraft fuel tanks. Added to turbine fuel, MIL-I-27686 does indeed reduce the hazards of icing in air-craft fuel systems. But it can do other useful things aswell. MIL-I-27686 acts to depress the flash points ofsuch volatile fuels as JP-4, and it also kills themicroorganisms that can cause corrosion of aircraftstructure and blockage of fuel systems.

Control Strategies

It is this last feature of its activity that will be of in-terest to us here. Military turbine fuels such as JP-4,JP-5, and JP-8 have all contained MIL-I-27686 for anumber of years. Its biocidal properties, together withgood housekeeping practices at fuel storage facilities,have enabled U.S. military operators to keep theproblem of microbial growth in the fuel tanks of theiraircraft well under control.

But turbine fuels furnished with MIL-I-27686 anti-

icing additive usually cost more, and their availabilityis limited in certain areas. As a result, many otherHercules aircraft operators do not regularly use fuelsthat contain this ingredient. Some rely on goodhousekeeping at their fuel supply facilities and on theautomatic water extraction systems built into the fueltanks of their aircraft. This approach has been suc-cessful for some operators, but over the long run it canbe risky.

Another group of operators also use fuels that con-tain no biocidal anti-icing additives, but manage tocontrol microbial infestation of their fuel tanks quiteeffectively nonetheless. They do it by periodically add-ing a biocide to the fuel they use, a process commonlycalled shock treatment. When prudently applied andused in conjunction with good fuel storage housekeep-ing, this method can be effective in controllingmicrobial growth. The biocidal shock treatment ispopular among air transport operators, not onlybecause of the relatively low cost, but also because itcan be administered with little extra effort when theairplane is out of service for periodic maintenance,such as at the letter checks.

Unfortunately, improper employment of the shocktreatment method can be both ineffective in killingmicroorganisms and possibly damaging to fuel cells,

Lockheed SERVICE NEWS Vl ON3 8

sealants, or power plants. With these concerns inmind, we would like to suggest some guidelines for theuse of biocides in the fuel tanks of Hercules aircraft, inparticular when they are used in conjunction with theshock treatment method of infestation control.

Treatment Techniques

There are two different products which are com-

monly used to shock-treat microbial growth in the fueltanks of turbine-powered aircraft. One we have

already mentioned. MIL-I-27686 is approved for con-tinuous use in the fuel tanks of Hercules aircraft, but italso works well as a shock treatment. When it is to beused in this way, MIL-I-27686 should be mixed withfuel at a concentration of 1 to 1.5 gallons of additive to1000 gallons of fuel.

The other product that has proven effective wasdeveloped specifically as a biocide and has no signifi-cant anti-icing or flash point modifying effects. It iscalled Biobor JF, and it is manufactured by StandardOil Company (Ohio), Midland Bldg., Cleveland, OH44115. Biobor JF contains boron, and boron is an ele-ment which may affect the longevity of turbine bladesif present in fuel in sufficient quantity. The use ofBiobor JF is therefore subject to certain restrictionsimposed by the engine manufacturer. It may be usedon an intermittent basis, such as would be the case fora shock treatment, provided that the concentrationused is such that the fuel contains no more than 20parts per million elemental boron. A safe concentra-tion is about 12.5 ounces of Biobor JF for each 1000gallons of fuel.

Precautions and Recommendations

No matter which of the two recommended biocidaladditives is selected for use in a shock treatment pro-gram to control fuel tank microbial infestation, certainprecautions apply:

q Make sure that the fuel tank being treated is at least10% full of fuel before introducing the biocide. A highconcentration of addit ive can be damaging toelastomeric substances such as sealants and rubber.

n Additives should not be poured directly into thetanks in concentrated form, but should be metered intothe fuel slowly as the tank is being fueled so as to blendthe fuel and additive homogeneously.

q Use the recommended mixture of additive and fuel.As noted above, too high a concentration of MIL-I-27686 can harm elastomeric fuel system components.On the other hand, too low a concentration of thisinhibitor in the fuel may act as a nutrient for themicroorganisms instead of a biocide. Biobor JF must

9

also be carefully measured. Too much would exposethe engines to excessive boron. Too little will result inunsatisfactory biocidal activity.

n Allow the treated fuel to stay in the tank longenough to kill the microbial invader. Dwell time shouldbe a minimum of 24 hours; preferably 48 to 72 hoursfor optimal results. A 24-hour contact with the treatedfuel will kill up to 98% of the microorganisms.

Perform the shock treatment on a regular schedule.Operational conditions will vary among operators,which means that some aircraft will be more subject toinfestation than others. Accordingly, the frequency oftreatment required will vary from one geographicalregion to another. As a rule of thumb, the shock treat-ment should be administered about every three to fourmonths.

n When the fuel tanks are given regular treatments ofbiocide, the aircraft can be returned to service withtreated fuel. However, the fuel should be removed ifthe concentration and quantity of dead microbialresidue are considered sufficient to lead to blockage ofthe fuel system. Anytime that the contamination is suf-ficient to require fuel removal, the affected tankshould be flushed with fresh fuel or treated fuel beforebeing refueled. If the contamination in the tank isdeemed too much to remove by flushing, the tankshould be opened, cleaned, and sterilized in accor-dance with the procedures in the appropriate fuelsystem maintenance instructions.

Additional information on this subject can be foundin two articles which appeared previously in thispublication: “Controlling Microbial Growth in Air-craft Fuel Tanks,” Volume 2, Number 2 (April - June1975) and “Maintenance of Integral Fuel Tanks,”Volume 9, Number 4 (October - December 1982).

Lockheed SERVICE NEWS Vl ON3

Each engine nacelle of the Hercules aircraft is pro-vided with a movable oil cooler flap. Its purpose is toregulate the flow of air through an oil coolerassembly. The oil cooler flap is controlled by an oiltemperature control thermostat, which is located be-tween the outlet of the oil cooler and the engine oiltank (Figure 1). A few years ago, Lockheed intro-duced a reliable new solid-state oil temperature con-trol thermostat, built by Dataproducts New England,to be used as a replacement for the glass-mercury typethermostat that was then in use. This led to confusionon the part of a few of our operators because the solid-state thermostat changed some of the operatingparameters of the oil cooling system. In this article wewill discuss dome of the changes in system perfor-mance, and pass along a helpful recommendationmade by Lockheed engineering concerning its opera-tion.

Thermostat Temperature Settings

The glass-mercury type oil temperature control ther-mostat was designed to maintain oil temperature be-tween 79.5'C and 82°C. In reality, this type of ther-mostat actually controlled oil temperature at approx-imately 85'C, which is the upper limit of the normaloil temperature range of 60°C to 85°C. Since theglass-mercury thermostat maintained oil temperatureat the upper limit, there was no margin of error forany problem, such as component aging, that causedeven a slight temperature increase. For this reason,

Lockheed SERVICE NEWS VlON3 10

many glass-mercury thermostats were removedbecause they had begun to control the oil temperatureat 86'C, which is out of the normal range. Since theglass-mercury thermostat control point was set soclose to the upper temperature limit and thissometimes led to problems, Lockheed decided that thenew solid-state thermostat should be set to control oiltemperature closer to the middle of the normal oiltemperature range of 60°C to 85°C. The new ther-mostat was therefore designed to maintain oiltemperature between 69.5'C and 75°C. By setting thethermostat to control oil temperature at the middle ofthe normal range, thermostat replacement due toslight increases in oil operating temperatures becameunnecessary. A second reason for lowering the controltemperature is that the cooler the engine oil is control-led, the lower the engine overhaul cost will be becauseof a reduction in oil coking.

Changes in System Performance

One consequence of lowering the oil temperaturecontrol point is that the operation of the oil cooler flapis different from what it is when the cooler flap is con-trolled by a glass-mercury thermostat. This means thatif an aircraft has both types of thermostats, there maybe differences noted in the automatic operation of theoil cooler flaps. There have even been instances whenoil cooler flaps controlled by a solid-state thermostatwould stay open after takeoff, while the flaps con-trolled by glass-mercury thermostats started moving

OIL TANKPRESSURIZING VALVE

OIL TANK

OIL QUANTITY TANK UNIT

POWER UNIT OILPRESSURE TRANSMITTER

REDUCTION GEAR

‘OIL TEMPERATUREONTROL THERMOS

OIL COOLERFLAP ACTUATOR

OIL COOLER/ \OIL COOLER FLAP

OIL COOLERREGULATOR VALVE

TAT

Figure I. Engine oil supply system.

toward the closed position.

One such occurrence involved a Hercules aircraftequipped with three glass-mercury thermostats andone solid-state thermostat. On the ground, with all oilcooler flap switches in automatic, the cooler flaps werefull open (Figure 2). As power was applied for takeoff,the oil cooler flaps that were controlled by the glass-mercury thermostats moved toward the closed positionand the oil temperatures stabilized at 85°C. The coolerflap controlled by the solid-state thermostat remainedopen until the oil cooler flap switch was placed toCLOSE. When the flap reached 40%, the switch wasplaced back to AUTOMATIC, at which time the flapcontinued to close to about 5% open. With this oilcooler flap at 5%, the oil temperature stabilized at76°C.

The reason that the solid-state thermostat-

controlled oil cooler flap did not automatically close inthis case can be traced to the interaction of the oiltemperature control thermostat and the thermostaticbypass and relief valve assembly in the oil coolerregulator valve.

The oil cooler regulator valve directs oil into orbypasses oil around the oil cooler, depending on thetemperature of the oil (Figure 3). When thetemperature of the oil is less than 54°C (+/-3”), thethermostatic bypass and relief valve is fully open. Thisallows most of the oil flowing into the oil coolerregulator valve to bypass the oil cooler. At approx-imately 54'C, the bypass valve starts to close andshould be fully closed when the oil temperaturereaches approximately 68°C. With the bypass valvefully closed, all the oil entering the regulator valve goesthrough the oil cooler.

11 Lockheed SERVICE NEWS VlON3

Figure 2. Oil cooler flaps-shown full open prior to takeoff.

Notice, however, that the 68°C closing temperatureof the thermostatic bypass and relief valve is only1.5'C below the low end of the oil temperature controlthermostat closing temperature (69.5'C). With the“fully closed” temperature of the bypass valve soclose to the low end of the closing temperature of theoil temperature control thermostat (69.5'(C), thebypass valve may not fully close to force all oilthrough the oil cooler. The bypass valve does not closefully because the oil cooler acts as a heat sink. Thisheat sink effect allows the thermostatic bypass andrelief valve to respond as though the oil temperaturewere cooler than it actually is. Since the bypass valve isnot fully closed, oil that is hotter than the closingtemperature of the bypass valve reaches the oiltemperature control thermostat. As long as thetemperature of the oil reaching the oil temperaturecontrol thermostat is greater than 69.5'C, the coolerflap will remain open. This keeps full air flow movingthrough the oil cooler, which further aggravates theheat sink effect.

Initiating Automatic Operation

This situation can be alleviated by manually closingthe oil cooler flap to raise the temperature of the oil

enough to fully close the bypass valve, which thenforces all the oil through the cooler and removes theheat sink effect. With the oil cooler warmed up, thesystem will work normally in the automatic mode; i.e.,during subsequent takeoffs, the cooler flap will moveclosed along with the glass-mercury thermostat con-trolled oil cooler flaps, albeit to a few percent moreopen position.

Lockheed engineering’s recommendation istherefore the following: if a solid-state thermostat-controlled oil cooler flap does not automatically closeafter takeoff, place the oil cooler flap switch toCLOSE until the flap reaches 40% and then put theswitch back to AUTOMATIC. The oil cooler flap willcontinue to close until it reaches approximately 5%;the oil temperature should stabilize at approximately76°C.

Under certain circumstances it may require a littlemonitoring to obtain optimum performance from theoil cooler flaps with the solid-state thermostats in-stalled, but the advantage of greater system reliability,plus the added benefit of maintaining oil temperaturesat a lower level, will far outweigh any transient in-convenience that may be experienced as an indirectresult of the modernization of the system.

Lockheed SERVICE NEWS Vl ON3 12

FROM COOLER

SMALL FLOWTO COOLER

THERMOSTATICBYPASS &

TO TANKRELIEF VALVE

HOT OILCOOL OIL OR

SURGE RELIEF

OIL COOLER REGULATOR VALVE

REGULATOR VALVE

Figure 3. Oil cooler and oil cooler regulator valve detail.

13 Lockheed SERVICE NEWS VlON3

A broken HF antenna is at best an inconvenience;if it breaks during flight, there may be unwelcome sideeffects that go beyond the obvious things such as crip-pled communications. A loose antenna wire whippingaround in the slipstream is likely to leave a trail ofunsightly superficial damage on the empennage, and ifit is lost from the aircraft completely, the falling wirecan pose a hazard to personnel and facilities on theground.

Two AML-61 antenna masts provide anchor pointsfor the HF antenna wires on most Hercules aircraft.One is attached to each side of the fuselage just aft ofthe flight station (Figure 1). The two wires run aft fromthese masts and attach to a common bracket on thevertical stabilizer. When a wire breaks, it usually occursat the point where the antenna wire enters the mastchuck assembly.

Figure 1. The forward end of each HF antennawire is anchored to an AML-61 antenna mast.

The most common cause of wire failure has beenshown to be corrosion. Laboratory examination of thechuck assemblies in a number of cases where theantenna wire had failed indicated that the principal cor-rosion product was iron oxide (rust) from the copper-coated steel antenna wire and copper-coated steel chuckspring. The stainless steel chuck assembly body andspring locating screw and the brass chuck jaws areapparently not corroding. An exploded view of the wirechuck assembly and its installation is shown in Figure 2.

Evidently, the problem begins when the coppercoating of the antenna wire is broken during prepara-tion for installation. If the wire is nicked at all, itexposes the steel core of the wire, which subsequentlyrusts. The copper coating on the spring is probablyrubbed off during normal service use, which causes theexposed steel to rust when moisture enters the antennamast.

Lockheed engineering recommends three steps to betaken to prevent corrosion within the antenna mast:proper assembly of the antenna mast and wire, properpreparation of the antenna wire, and the addition ofa corrosion preventive compound to the chuckassembly.

Cutting the Antenna Wire

The first step after attaching the antenna wire to thestrain insulator near the vertical stabilizer is to cut theantenna to length. There are several things to considerbefore actually cutting the wire. Most important of theseis not to cut it too short. Make full allowances and thencut. It is relatively easy to trim more off if necessary.Also, be sure that the wire is not kinked or bent. Wipeit clean and inspect for damaged insulation, embeddedforeign particles, and other defects which might reducethe effectiveness of the insulation.

To determine the length of wire to be cut, unwindenough wire to reach the antenna mast, allowing forabout three inches to extend into the mast. Again,remember that overestimating the length is preferablesince some adjustment can be made by the tension take-up unit at the aft end of the antenna. As much as aninch can also be taken up in the forward mast.However, once the wire has been inserted in the grip-ping jaws of the tension take-up unit, it is not practicalto remove it to gain more slack. With these things inmind and the wire pulled along beside the antenna mast,cut the wire at a point which will allow you to obtainthe desired tension after installation of the antenna.

Installation

The antenna is secured in the mast by a l/2-inch

Lockheed SERVICE NEWS Vl ON3 14

AMC-5 IANTENNA MAST

SLEEVE

Figure 2 AIVIL-6 I antenna mast a s s e m b l y and chuck assembly detail

length of bare antenna conductor clamped in a spring-loaded brass chuck. Therefore, enough insulation mustbe removed from the end to expose a l/2-inch lengthof conductor with the wire end square and free fromburrs. Accurate removal of the insulation is bestaccomplished using a wire retriever tool made tothe military standard MS251 19-1. Insert the wire endinto the tool until it bottoms in the counterbore. Placea thin knife in the slot and, while applying pressure onthe blade, rotate the wire one complete revolution.Remove the wire from the tool, grip the partially severedsection of the insulation with pliers, and carefully twistit off. The exposed l/2inch length of conductor mustbe free from nicks, burrs, and scratches to permit freeentry into the chuck assembly, and its copper coatingmust be intact.

Reinstall the chuck assembly locating screw. The sug-gested corrosion preventive compounds are listed belowin order of preference: MIL-S-8660, silicone compound(Dow Corning DC-4); MIL-G-6032, plug valve grease;MIL-C-11796, Class 1, corrosion preventive compound;or MIL-C-16173, Grade 1 or 4, corrosion preventivecompound.

Slide all of the antenna mast attaching parts (exceptthe chuck) onto the antenna wire, as illustrated in Figure2. They go on in this order: antenna support sleeve, rub-ber washer, end seal screw, and the adjusting screw.These parts should be pushed back on the wire approx-imately 12 inches before attaching the antenna. Slip theantenna wire bearing over the conductor and insert thefull length of the bare wire conductor into the chuckassembly. Three or four sharp in-and-out motionsshould be made to ensure proper gripping of the con-ductor by the chuck jaws.

After assembly, carefully remove the locating screwon the end of the chuck assembly and fill it with corro-sion preventive compound. Also, sparingly apply cor-rosion preventive compound to the outside junctionpoint between the chuck jaws and antenna wire.Remove any compound that may get on the exterior ofthe chuck assembly so that the wire will bond electricallyin the fitting when installation in the mast is complete.

After installation of the wire in the chuck assembly,slide the adjusting screw and bearing forward againstthe chuck assembly and, using special tool AMC-51,screw the adjusting screw into the antenna mast. Slidethe end seal screw into the mast and tighten with specialtool AMC-51. Then slide the rubber washer forwardagainst the end seal screw and secure in place by screw-ing the antenna support sleeve into the antenna mastuntil it is finger-tight. Do not use pliers to tighten thesupport sleeve. Coat the tip of the support sleeve lightlywith corrosion preventive compound to repel entranceof moisture where the wire enters the sleeve.

When the antenna is completely installed, that is,complete with strain insulator and tension take-upinstalled and antenna connected to the vertical stabilizer,additional tension may be applied to the antenna wireby screwing the adjusting screw further into the masthead. The adjusting screw will travel approximately oneinch past the flush position.

As with any procedure such as this one, refer to thetechnical manuals before taking any action. Check theappropriate technical manual for instructions on theproper tension at the tension take-up unit. Finally,recheck both antennas for any discrepancies after theinstallation is complete. With careful attention to theinstallation procedure, there should be no problem withcorrosion in the antenna wire.

15 Lockheed SERVICE NEWS VlON3