A SERVICE PVBUCATON OF LOCKHEED AERONAUTICAL SYST!:MS COMPANY- GEORGIJ\

A SERVICE PUBLICATION OFLOCKHEED AERONAUTICALSYSTEMS COMPANY-GEORGIA

EditorCharles I. Gale

Art DirectorAnne G. Anderson

Vol. 16, No. 2, April-June 1989

CONTENTS

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3

13

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Focal PointI. R. FrewerProgram Manager,C-13011-100 Engineering

Troubleshooting HerculesAir Conditioning

Preventing Shutoff Valve ThermalExpansion Damage

Engine Rear Bearing Support and TailpipeFailures

RAAF Wins Top Honors in 1989 AirliftRodeo

Photographic Support: John Rossino

Front Cover: The “Spirit of Wisconsin,” first ofthe 440th TAW’s eight new C-130Hs, flies overdowntown Milwaukee.Back Cover: Australia’s champion airlift teamcelebrates its 1989 Airlift Rodeo victory (seepage 15).

Focal Engineering a Modern Classic

Engineering has been defined as the systematic applica-tion of scientific principles in the design and construction ofmachines, structures, and systems useful to mankind’s life-style. In the aerospace field, as elsewhere, few engineerstoday would agree that this definition adequately character-izes the work they do and the responsibilities they share. Thespecial challenges that the men and women of LockheedC-13O/L1OO Engineering’s branch at LASC-Georgia are calledupon to meet are unique.

J.R. Frewer

Traditionally, the engineering effort applied to the designof a new aircraft has been able to assume a rather limited lifecycleforthefinal product. Theadventofthe Herculesaircrafthas changed all of this. There is no precedent for the Her-cules aircraft. Nothing in the annals of modern aviationtechnology is remotely equivalent to the long-term successand continuing demand for this amazing airlifter.

The basic airframe of the Hercules has been solidly and conservatively engineered. It hasproved exceptionally adaptable to further development as increased operational requirementscontinue to be formulated on this solid foundation. Not only has the airframe become structurallystronger, but advanced construction materials and manufacturing processes also ensure greaterdurability and lower maintenance costs, which is especially pertinent in the environments inwhich this airplane is required to operate.

Against this background, it should come as no surprise that this well-designed basic structurehas also proved highly adaptable to the diverse needs of a wide variety of aircraft operators. Today,more than 50 distinct versions of the Hercules airlifter are doing the world’s work in every corner ofthe globe, each one carefully engineered to the customer’s needs, and optimized to perform itsintended mission.

As everyone knows, the aerospace industry has made some rapid advancements in bothperformance and reliability. The Hercules has proved similarly adaptable as these new tech-nologies have emerged to replace the old, allowing its users to enjoy the benefits of the latesttechnical advances in their aircraft. Hercules operators are able to choose from a wide selection ofstate-of-the-art avionic navigational systemsequipmentdesigned to meet thespecific needsoftheirparticular mission profiles.

Today’s technology continues to generate a “rolling wave” effect in the Hercules ProductionProgram. Development work has already been initiated to apply these latest advancements intechnology, which would include such features as the electronic flight instrument system (“glass”cockpit), digital autopilot, and self-contained navigation system, alongwith a host of other updatesand improvements. The major impact of these changes would reduce crew member componentrequirements and associated maintenance manpower, greatly reducing cost of ownership for thecustomer.

When the first Hercules aircraft rolled off the assembly line, it was built for the future, and thishas proved to be true. We, Lockheed C-13011-100 Engineering, take special pride that the same isstill true for every Hercules we build today. We intend to ensure, through support of our Manufac-turing organization and our customers, that this continues in the future.

Sincerely,

J. R. Frewer, Program ManagerC-130/1-100 EngineeringLockheed Aeronautical Systems Company

FIELDSUPPORT

H.L. BURNETTE DIRECTOR

SUPPLY TECHNICALSUPPORT PUBLICATIONS

RELIABILITYMAINTAINABILITYSUPPORTABILITY

&TRAINING

J.D. ADAMS D.R.STEELE C.E. ADAMS H.M. SOHN

A versatile, modern aircraft like the Hercules airliftermust be equipped to provide a safe and comfortable cabinenvironment under all operating conditions, at all times,everywhere.

It is instructive to consider just how demanding such arequirement can be. The outside air temperatures at thealtitudes where today’s aircraft routinely operate are com-monly 60 or 70 degrees below zero Fahrenheit. Yet the sameairplane that is expected to maintain a warm, pressurizedenvironment for its passengers and crew during high-altitude flight must also be able to provide air-conditionedcomfort at the destination airport, where the temperaturemay be 100 degrees above the zero mark.

An air conditioning system that can provide a comfort-able interior climate over such a wide range of conditionsmust be an effective one indeed. The Hercules not only hasan air conditioning system designed to meet these environ-mental challenges, it has two.

Hercules Environmental Control

Each Hercules aircraft is equipped with two separate airconditioning systems, one for the cargo compartment andone for the flight station. The capability of the two systemsand the equipment they contain are identical for all practicalpurposes.

Lockheed SERVICE NEWS V16N2

The major components of the cargo compartment sys-tem are located in the forward part of the right wheel well.In the case of the flight station system, most of the compo-nents are under the flight station on the right side of theaircraft.

Both systems may be used at the same time, or eithercan function individually. At sea level, each system canprovide about 70 pounds per minute of conditioned airthrough its associated distribution ducts.

This air can be used to maintain interior temperatures atthe desired levels, provide cabin pressurization, and furnishventilation. When operated simultaneously, the two sys-tems can maintain 7.5 degrees F inside the aircraft when theoutside temperatures are in the range from -65 to +I00degrees F.

System Basics

Efficient troubleshooting of air conditioning problemsbegins with a good, fundamental knowledge of systemdesign, With this in mind, let us review in simplified formthe basic components contained in the Hercules air condi-tioning systems, their relationship to each other, and theoperation of each system as a whole.

In this discussion we will address mainly the cargocompartment system; however, the same information can

3

Cargo compartment air conditioning unit, forward right wheelwell fairing.

also be applied ‘to the flight station system since the opera-tion of both systems is identical and most of the componentsare interchangeable.

The following information deals primarily with the newair conditioning systems installed as a production changeon LAC 4653 and up, except for the U.S. Marine Corps, forwhom the new systems were installed on BUN0 160625 andup. These changes were also incorporated on LAC 4579through 4652 on aircraft sold to the USAF Greece, Spain,and Nigeria.

A new solid-state temperature control system wasinstalled as a production change on aircraft beginning withLAC 4579. This new temperature control system can be

Figure I

installed on aircraft with the old air conditioning systemprovided all the system components listed below arechanged:

n Temperature control boxn Compartment temperature sensor Duct anticipator sensor Duct high-limit (overheat) sensorn Temperature selector rheostat

Cargo Compartment System

The air which exits from the conditioned air outletsstarts out as bleed air from the engines at a temperature ofabout 600 degrees F, or from the APU at about 400 degreesF. This air is ducted through the flow control and shutoffvalve to an air-to-air heat exchanger and from there to amixing valve which is used for temperature control (seeFigure 1).

In the heat exchanger, the bleed air is cooled to a temper-ature of about 140 to 200 degrees F by a cross flow ofambient air. This partially cooled air is ducted to an expan-sion (cooling) turbine and to a bypass valve (low-limitvalve). The cooling turbine is capable of reducing the tem-perature to well below freezing; however, an automaticcontrol system provides a low-temperature limit of about 37degrees F by bypassing some partially cooled air around theturbine.

This cold air is ducted through a water separator to theconditioned air supply duct and then to the distributionducts overhead in the cargo compartment. Compartmenttemperature is controlled by mixing hot air with the cold air

Lockheed SERVICE NEWS V16N2

coming from the water separator. The temperature controlvalve regulates this mixture. Automatic and manual controlsystems are provided to operate the valve.

Heat Exchanger Anti-Icing System

On aircraft prior to LAC 4947, the refrigeration unit isequipped with a hot air anti-icing system for the heatexchanger. Controls and indicators for the anti-icing systemare contained on a small panel located just to the right of theoverhead anti-icing control panel in the flight station.

If the heat exchanger ices up, resulting in a significantreduction in cooling air flow, there will be an appreciablerise in the heat exchanger cooling fan discharge duct tem-perature. A temperature sensor installed in the dischargeduct will detect this condition and illuminate an amberwarning light on the control panel.

Placing the control switch to the ON position opens theanti-icing valve to supply hot air from the bleed air inlet ofthe heat exchanger to a spray tube in the cooling air inletplenum. A green light on the panel illuminates to indicatethat the valve has opened.

When the ice melts and cooling air flow is again estab-lished, the amber light will go out and the system can beturned off. If the amber light does not go out within 30seconds, it means that the obstruction is caused by somesubstance other than ice and the affected air conditioningsystem must be shut off.

Aircraft LAC 4947 and up do not have this heatexchanger anti-icing system. These airplanes are equippedwith a heat exchanger of different design which is notsusceptible to icing, thus eliminating the requirement foranti-icing.

Water Separator Low-Limit Temperature ControlSystem

Since the refrigeration unit is capable of producing airtemperatures below freezing, a low-limit temperature con-trol system is required to maintain the air temperature abovefreezing in order to prevent icing of the water separator.

Partially cooled bleed air from the heat exchangerbypasses the cooling turbine through the low-limit valveand mixes with the cold air output from the turbine. Atemperature control box operates the valve in response tosignals from a temperature sensor installed in the waterseparator outlet duct.

The valve is driven open or closed to provide more heator less heat as required to maintain a temperature of approx-imately 37 degrees F at the output of the water separator.The valve is driven in pulses in order to minimize over-shooting.

Whenever the air conditioning master switch is posi-tioned to OFF, a relay is energized which disconnects thecontrol box outputs from the valve and applies power todrive the valve fully open. This is done to reduce thestarting shock load on the turbine bearings the next time thesystem is turned on. When the system is turned on, thevalve will pulse toward closed as air flows through thesystem.

Failure of the low-limit system may result in icing of thewater separator, restricting airflow. As airflow decreases,duct pressure on the inlet side of the water separatorincreases. This pressure is sensed by a pressure switch. Ifthe pressure reaches approximately 14 psi differential, thepressure switch actuates to energize a relay, which thenenergizes the flow control and shutoff valve closed.

This shuts off the air conditioning system, and a holdingcircuit on the relay keeps the system shut off until power isremoved from the circuit. The normal way to reset thesystem is to turn the master switch off and then back on.However, since this action will momentarily shut off theother air conditioning system also, a pressure bump can beexpected if the aircraft is pressurized.

If the system is reset and then shuts off again, it is best toleave it shut off until the problem can be isolated andcorrected.

Compartment Temperature Control

Compartment temperature control is accomplished byallowing bleed air to bypass the refrigeration unit and mixwith the cool air from the water separator. The hot air isadded into the conditioned air supply duct downstreamfrom the water separator. The amount of hot air bypassed is

Temperature control boxes, aft side of FS 245 bulkhead

Lockheed SERVICE NEWS V16N2 5

Figure 2

regulated by the temperature control valve. Both manual left side of the cargo compartment at fuselage stationand automatic controls arc provided for operation of the 357. The flight station unit is located at the right aftvalve. corner of the overhead control panel.

Automatic Temperature Control

Figure 2 shows a schematic of the temperature controlsystem. In automatic operation, the valve is positioned byoutputs from a temperature control box in response tosignals from three temperature sensors and a temperatureselector rheostat. These function as follows:

n The temperature selector rheostat serves as the sys-tem’s basic control. It establishes the temperature levelwhich the system must maintain. The selectors for bothflight station and cargo compartment systems are locatedon the overhead air conditioning control panel in theflight station.

n The compartment temperature sensor functions as theprimary sensing unit for temperature control. It providesactual compartment temperature information to the con-trol box. The cargo compartment unit is located on the

The duct anticipator sensor is sensitive to temperaturechange. It helps to control the driving time of the temper-ature control valve to prevent overshooting. The antic-ipator sensor is installed in the conditioned air supplyduct downstream from where the cool air from the waterseparator and hot bypass air are mixed.

The duct high-limit sensor is a safety control. It limitsthe temperature so that the ducts will not be subjected toexcessive heat. The high-limit sensor is installed in theconditioned air supply duct downstream of the anticipa-tor sensor.

Signal inputs from the temperature selector rheostat andcompartment temperature sensor are compared in the con-trol box. If selected temperature and actual temperature arenot the same, an error signal is generated to produce theappropriate “more heat” or “less heat” output signal to thetemperature control valve.

6 Lockheed SERVICE NEWS V16N2

This is a pulsed output, in which the length of the pulsesis proportional to the temperature difference. A large dif-ference in temperature produces longer pulses, and a smalltemperature difference results in shorter pulses.

The duct anticipator function differs from that of thecompartment temperature sensor and high-limit sensor inthat while the other two sensors are concerned with thetemperature itself, the duct anticipator provides input forcomparing temperature change. Its purpose is to control therate at which changes in temperature take place.

As the temperature control valve drives in response to ademand for an increase or decrease in heating or cooling,the duct temperature begins to change. This change isdetected by the duct anticipator, which causes a signal to bedeveloped in the control box opposing the temperaturedifference error signal.

The result is to inhibit the valve driving signal. As ducttemperature stabilizes, the anticipator circuit is satisfiedand the temperature change signal is removed. If the com-partment temperature has not reached the desired level bythen, an error condition still exists and the temperaturecontrol valve will begin to drive again.

Lockheed SERVICE NEWS V16N2

This operation continues until actual and selected tem-perature are equal. The selected temperature is thusapproached gradually, which helps prevent overshooting.Because of this action, it takes a few minutes for cabintemperature to stabilize when the system is first turned on orwhen the temperature selection is changed.

Whenever the selected temperature is considerablyhigher than actual temperature (I5 degrees or more), thetemperature control valve could drive fully open longbefore the large volume of interior air is heated to thedesired temperature, resulting in excessively high duct tem-peratures. The high-limit sensor protects the distributionducting in this situation by producing a signal in the controlbox that will remove the more heat signal to the valve andapply the less heat signal.

When the duct temperature drops about 20 to 30degrees, the high-limit circuit resets and normal control isin effect again. The system can cycle on this high limit untilthe interior temperature has risen to about the desired leveland normal control can cause the temperature control valveto cut back.

The high-limit circuit is also designed to protect thesystem from a faulty sensor. If the sensor becomes eitheropen or shorted, the temperature control valve will bedriven closed.

Manual Temperature Control

Manual operation for more heat is accomplished bytoggling the temperature control switch to WARM. Themanual more heat drive signal goes through the control

Left: Air conditioning controls, flight station overhead controlpanel. Left, below: Cargo compartment temperature sensor.Below: Underwing area, right side.

Aft side of FS 245 bulkhead, on right.

box for two reasons; first, the output signal is pulsed toprevent a too-rapid rise in duct temperature, and second, totake advantage of the duct high-limit protection circuit.Even though the valve is driven open in pulses, the drivingtime is somewhat faster than in AUTO because the ductanticipator circuit has no effect during manual control.

When the temperature control switch is positioned toCOOL, power is applied directly to the valve to drive ittoward closed. The valve will drive continuously (no puls-ing) until it reaches the fully closed position or until theswitch is released.

Air Conditioning Systems Interconnect

The conditioned air supply ducts from the cargo com-partment system and flight station system are connected byan interconnect duct. If either system is not operating,conditioned air can be supplied from the operating systemto the other compartment.

A four-position valve in this duct controls the distribu-tion of air between the two systems. The valve is controlledby the flight station airflow switch (labeled FLT STA AIR-FLOW) on the air conditioning control panel. The switchpositions indicate how much of the conditioned air from theflight station unit will be ducted to the flight station, with theremainder going to the cargo compartment.

In the MIN position, only about 30% of the air from theflight station unit will go to the flight station. In the NOR-MAL position, about 60% will go to the flight station, inINTMED about 80%, and in MAX, all the air from theflight station unit will go to the flight station.

With both systems operating, normal airflow is from theflight station system to the cargo compartment. Therefore,if the cargo compartment system is shut down, air willcontinue to flow to the cargo compartment from the flight

station system unless the FLT STA AIRFLOW switch ispositioned to MAX.

Note that if the flight station system has to be shut downfor some reason, it may be necessary to turn on the cargocompartment air recirculation fan (or floor heat) in order toget any appreciable airflow to the flight station. This createsa back pressure in the duct, which is necessary to force airto flow up to the flight station.

Also, the flight station airflow switch should be posi-tioned to MIN to fully open the interconnect valve. Inciden-tally, this valve is powered by II.5 volts AC from theessential AC bus. It is the only environmental systemscontrol valve that does not operate on 28 volts DC.

Floor Heat System

The floor heat system provides additional heat in thecargo compartment floor area when needed. It is an inde-pendent system which can be used in conjunction with orindependently of the air conditioning systems. The systemis controlled by the UNDERFLOOR HEATING switch onthe air conditioning control panel.

Figure 3

8 Lockheed SERVICE NEWS V16N2

Two valves control floor heating, a solenoid-controlled,air-operated shutoff valve and a motor-driven temperaturecontrol valve. The valves are located in the upper rightwheel well area next to the cargo compartment flow controland shutoff valve.

Underfloor heating is accomplished by mixing bleed airwith ambient underfloor air and piping the mixture throughforward and aft distribution ducts. The amount of bleed airsupplied is regulated by the floor heat temperature controlvalve.

Temperature control is completely automatic. The valveis operated by a temperature sensing and control unit whichis mounted next to the ejector assembly under the centerfloor panel between the wheel wells at fuselage station 497.This unit senses the temperature of the underfloor air beingdrawn into the ejector, and operates the temperature controlvalve to continuously supply the amount of bleed airrequired to maintain a temperature of approximately 75degrees F.

Figure 3 shows the electrical control circuit for the floorheat system. When the air conditioning master switch is

Lockheed SERVICE NEWS V16N2

placed in an “on” position (NO PRESS, AUTO PRESS, orMAN PRESS) and the floor heat switch is positioned to ON,power is supplied to the control unit and to the shutoff valve.

The shutoff valve is energized and air-actuated open.The control unit senses underfloor temperature andprovides as appropriate more heat and less heat outputs todrive the temperature control valve.

When the system is turned on, power is supplied toenergize a relay which then supplies 3-phase power tooperate the cargo compartment air recirculation fan. Fanpower is supplied from the LH AC bus. This requires the useof ground power or at least two engine generators. When thesystem is turned off, the fan can be operated by a separateFAN switch located next to the floor heat switch on the airconditioning control panel.

An overheat thermoswitch is installed next to the aftdistribution duct at fuselage station 577. It is located so as tosense the temperature of the air coming out of the distribu-tion duct at that point.

If a malfunction of the control system occurs such thatthis air temperature reaches 180 degrees F, the thermoswitchactuates to remove power from the shutoff valve, causing itto close. Since the thermoswitch will automatically resetwhen the temperature drops about 20-30 degrees, the sys-tem will cycle on and off unless turned off by the floor heatswitch.

Since floor heating is a separate system, it is necessaryto provide a means of shutting off the system in the event ofan emergency. This is accomplished by a relay which is

Floor heat thermostat and control box.

Bimetallicthermoswitch

controlled by the EMERGENCY DEPRESSURIZATIONswitch on the air conditioning control panel. When thedepressurization switch is actuated, the relay is energized toremove power from the floor heat shutoff valve, causing it toclose.

n It is assumed in the following procedure that the circuitwiring is good. If you have replaced the suspected faultycomponent indicated in the procedure and the troublestill exists, check the circuit wiring.

System Airflow Check

TROUBLESHOOTING THE SYSTEM

As with most aircraft systems, it is not always easy topinpoint the source of a problem in the Hercules air condi-tioning system immediately. It generally requires systema-tic troubleshooting, and often the best question is where tobegin.

Connect ground power and operate the APU for the airsupply. Make sure the compartment air conditioningswitch, emergency depressurization switch, and tempera-ture selector rheostat are in NORMAL. Turn the masterswitch on and place the temperature control switch inAUTO. The airflow from the ducts should be almost strongenough to force your hand away.

There are several troubleshooting approaches that atechnician may utilize to correct problems in a discrepantair conditioning system. These range anywhere fromchecking system circuits and operation with an advancedsystem tester such as the Lockheed PN 3402247-l Tempera-ture Control Analyzer, to replacing one component at a timein a process of elimination.

If flow is weak, or if there is no flow, check the positionof the flow control valve. The position indicator on the sideof the valve should indicate about one-third to one-halfopen. The valve operation is affected by ambient conditionsand bleed air system pressure; therefore the exact positionmay vary somewhat, depending on operating conditions.

It is unfortunately not possible to offer a new procedurethat will solve all air conditioning ills in a few minutes, norshould you abandon your present troubleshooting method ifit is getting the job done in a reasonably efficient manner.What we would like to offer here, however, are some ideasand suggestions which you may find helpful in improvingyour own troubleshooting technique.

Trouble reports written against the air conditioningsystem in the Hercules aircraft usually fall into one of twocategories. Either the system won’t cool (or heat) properly,or the temperature is reported to be fluctuating excessively.Also, occasionally a problem with the airflow from thecargo compartment (or flight station) system may bereported.

If the Temperature Control Analyzer is not available, agood troubleshooting approach to use also happens to be avery basic one. Start by isolating one component in thesystem and then, if that component proves satisfactory, addanother component and then another in a logical sequenceuntil the entire system has been covered or the faulty com-ponent found and replaced.

Cargo compartment air conditioning system components, upperright wheel well area: (1) Air conditioning shutoff relay. (2) Flowcontrol valve. (3) Floor heat shutoff valve. (4) Floor heat temperaturecontrol valve.

In cases where you have a good idea of the cause of thetrouble, it won’t be necessary to run the complete check; thefinal proof, however, must be that the system works prop-erly after the suspected component has been replaced.

Be sure to check for system leakage at duct joints,especially at the water separator. Visual inspection willusually pinpoint this type of trouble.

Note particularly the following:

n You will need a volt-ohm-milliammeter (VOM) to trou-bleshoot this system.

A failed cooling turbine will also result in reducedairflow; however, this condition will also be accompaniedby an inability of the system to provide adequate cooling.

n In the steps below, the phrase “turn the master switch on” When you finish the airflow check you can shut downmeans place the air conditioning master switch in the NO the APU. It isn’t needed to accomplish the temperaturePRESS position. control system check.

10 Lockheed SERVICE NEWSV16N2

Low-Limit System Check

A malfunction of the low-limit system can cause tem-perature control problems. If the system fails in the “hot”condition, the temperature control system will not be able toprovide sufficient cooling. If the low-limit system fails inthe “cold” condition, the water separator may ice up. Thiscondition can result in reduced airflow or a system shut-down. The reduced airflow may be accompanied by icecrystals coming out of the conditioned air outlets.

A faulty low-limit temperature sensor can produceeither of the conditions mentioned above. A shorted sensorwill cause the valve to drive fully open; an open sensor willcause the valve to drive fully closed. You can check thesensor with a VOM. The resistance should be 220 +/- 4 ohms at75 degrees F. Add 3 ohms for each 5 degrees above 75degrees and subtract 3 ohms for each 5 degrees below 75.

1 To begin the system checkout, turn the master switch toOFF and check the position of the low-limit valve. Itshould be fully open. If the valve is fully open, proceedwith the next step.

If it is not, turn the master switch on and disconnect theelectrical connector from the valve. Turn the masterswitch to OFF and check for 28 volts DC on pin A (moreheat) of the circuit connector. If the voltage is present,replace the valve. If the voltage is not present, replace thelow-limit relay.

2. This step checks the less heat drive. Turn the masterswitch on and pull the CABIN PRESS & AUX VENTcircuit breaker. Pulling this circuit breaker prevents thevalve from driving full open every time the masterswitch is turned to the OFF position.

If the ambient temperature is above 40 degrees F, thelow-limit valve should begin pulsing toward closed (lessheat). If it does this, go to Step 4. If it does not, turn themaster switch to OFF and disconnect the electrical con-nector from the valve. Turn the master switch back onand check for pulsing 28 volts at pin B of the circuitconnector. If the voltage is present, replace the valve; ifnot, proceed with the next step.

3. Turn the master switch to OFE reconnect the valve, anddisconnect the electrical connector from the low-limitsensor. Turn the master switch back on. The valveshould pulse toward closed. If it does this, replace thesensor; if it does not, replace the low-limit control box.

4. This step checks the more heat drive. Turn the masterswitch to OFF Disconnect the electrical connector fromthe low-limit sensor and remove the sensor from theduct. Reconnect the electrical connector to the sensorand turn the master switch back on.

Allow the valve to drive toward closed so that it is notfully open, then dunk the sensor in a cup of ice water.The valve should begin to pulse toward open. If it doesnot, turn the master switch to OFF, disconnect the elec-trical connector from the sensor, jumper pins A and B inthe circuit connector, and turn the master switch backon. If the valve still does not drive, replace the controlbox; if it does, replace the sensor.

Remember to reset the CABIN PRESS & AUX VENTcircuit breaker when you are done.

One final point. If air conditioning system shutdownwas experienced and the low-limit system tests out OK,check the water separator pressure switch. A continuitycheck across pins A and B of the switch should show anopen circuit. If not, the switch is bad.

Temperature Control Problems-General Hints

A “too hot” or “too cold” problem usually falls intoone of two categories:

The system works in manual but not in auto.n The system will not work in either auto or manual.

If the system works in manual but not in auto, suspectthose components which provide automatic control, inother words, the sensors and the control box.

If the system does not work in either automatic ormanual control, the most likely suspect is the temperaturecontrol valve. However, do not rule out the possibility of abad control box, since the control box supplies the power tothe temperature control switch.

Checking Temperature Sensors

Bad temperature sensors can cause “too hot” (systemwon’t cool), “too cold” (system won’t heat), and “excessivefluctuation” complaints. The compartment sensor, ductanticipator sensor, and high-limit sensor can all be checkedfor proper resistance the same as the low-limit sensor. Thepins to check on the sensors are:

n Cargo compartment temperature sensor B-Cn Cargo compartment duct anticipator sensor C-D

Cargo compartment duct high-limit sensor A-Cn Flight station compartment temperature sensor B-Cn Flight station duct anticipator sensor A-Bn Flight station overheat sensor A-B

The resistance of all these sensors should be 220 4 ohmsat 75 degrees F, plus 3 ohms for each 5 degrees over 75,minus 3 ohms for each 5 degrees below 75.

Lockheed SERVICE NEWS V16N2 11

Temperature Fluctuation Problems

The system should be able to maintain the selectedtemperature within plus or minus two degrees at the com-partment sensor. Excessive fluctuation (hunting) can becaused by the following:

n A dirty compartment temperature sensor. An inoperative blower motor.n A bad duct anticipator sensor.n A bad temperature control box.

Clean the compartment temperature sensor and ensurethat the blower is operating (master switch on). If tempera-ture still fluctuates excessively, check the resistance of theduct anticipator sensor. If this unit checks good, replace thecontrol box.

Troubleshooting “Too Hot” Problems

The items that can cause a “too hot” condition are:

n A temperature control valve failed in the open position.n A shorted compartment temperature sensor.n A bad temperature control box.

Note: If the system works in manual but not in auto, usemanual control to make sure the valve is not fully closed andskip to step 2.

1.

2.

To check the valve, turn the master switch on and holdthe temperature control switch in the COOL position.The valve should drive continuously toward closed (nopulsing). If it does, go to the next step.

If not, turn the master switch to OFF and disconnect theelectrical connector from the valve. Turn the masterswitch on, hold the temperature control switch inCOOL, and check for 28 volts at pin B of the circuitconnector. If the voltage is present, replace the valve; ifnot, check terminal 4 (center terminal) of the tempera-ture control switch. If the voltage is not present here,replace the temperature control box.

Turn the master switch to OFF and disconnect the elec-trical connector from the compartment sensor. Turn themaster switch back on and place the temperature controlswitch in AUTO. The valve should start pulsing towardclosed. If it does, replace the sensor; if not, replace thecontrol box.

Troubleshooting “Too Cold” Problems

The items that can cause “too cold” problems are:

A temperature control valve failed in the closed position.

n An open compartment temperature sensor. A bad temperature control box.n An open or shorted high-limit temperature sensor.

Note: If the system works in manual but not in auto, usemanual control to make sure the temperature control valveis not fully closed and skip to step 3.

1. To check the valve, turn the master switch to OFF anddisconnect the electrical connector from the valve.Jumper pin B of the circuit connector to pin A of thevalve and pin C of the circuit connector to pin C of thevalve (you are connecting the less heat command line tothe more heat side of the valve). Turn the master switchon and hold the temperature control switch in COOL.The valve should drive continuously toward open. If itdoes not, replace the valve.

2.

3.

Use a VOM to check for an open or shorted high-limitsensor. Check pins A-B on the flight station sensor orpins A-C on the cargo compartment sensor. The resis-tance should be as given earlier in this article.

Turn the master switch to OFF and disconnect the elec-trical connector from the compartment sensor. Jumperpins B and C in the circuit connector. Turn the masterswitch back on and place the temperature control switchin AUTO. The valve should pulse toward more heat. If itdoes, replace the sensor; if not, replace the control box.

When you have finished, be sure to reconnect and appro-priately safety-wire all electrical connections.

A properly functioning air conditioning system is notjust a matter of comfort in a modern aircraft. It is also vitalto the safe and effective operation of the cabin pressuriza-tion system, a system which makes efficient high-altitudeflight a practical reality.

Fortunately, the air conditioning system of the Herculesaircraft, with its proven reliability, high capacity, and built-in redundancy, can be relied upon to turn in a top perform-ance day after day with relatively little attention. Whenservice is required, however, the information providedabove should help you get your Hercules airlifter back onthe job in the shortest possible time.

Service News wishes to thank C. E. Madison for hisinvaluable assistance in the preparation of this article.

Lockheed SERVICE NEWS V16N2

Firewall Shutoff Valves

PREVENTING SHUTOFF VALVETHERMAL EXPANSIONDAMAGEby Bill Simpson, Staff Engineer

Project Engineering Hydraulics Group

Valve motor burnout or valve housing damage inengine-driven hydraulic pump suction line shutoff valves issometimes blamed on internal limit switch misadjustmentor failure.

Although at first glance the valve housing and housingend plate may appear to have been damaged by over-drivingof the valve gate mechanism, further investigation usuallyreveals that excessive hydraulic pressure distorted the hous-ing and jammed the gate, which in turn caused the motor toburn out.

The excessive pressure is caused by thermal expansionof hydraulic fluid trapped in the suction line, a factor whichcan have serious consequences during wide swings in theambient temperature. The reason why the fluid becomestrapped can usually be traced to failure to follow throughwith the procedures described in paragraphs 3-23 through3-25 of T.O. C-130H-2-3.

When an engine or an engine-driven hydraulic pump isremoved from the airplane, and the hydraulic lines aredisconnected at the firewall quick disconnects or at thepump, the maintenance manual directs that a 3/8-inch jumperhose be installed to connect the case drain and suction linesto prevent loss of fluid or contamination of the system.

Once the jumper hose has been installed, it is importantthat proper attention be paid to the position of the motor-operated firewall shutoff valve and pump shutoff valve ofthe removed engine.

If the remaining engines are to be operated on an air-craft with the jumper hose installed, the suction boost pumpof the system being operated should be turned on, but boththe suction line shutoff valve and the pump shutoff valve ofthe removed engine must be shut off.

This prevents the hydraulic fluid from being heatedexcessively by the high rate of flow which would result fromboost pump pressure being continuously dumped to return

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through the open valves in the empty nacelle. These valvesmust not, however, be left in the closed position after theengine run has been completed and suction boost pump hasbeen shut down.

When the case drain and suction lines are connected bya jumper hose, the motor-operated firewall shutoff valveand pump shutoff valve should be left in the open positionunder all circumstances other than during an engine run.This will protect the motor-operated shutoff valve frompossible damage by preventing a buildup of pressure inthe jumper hose during rapid changes in the ambienttemperature.

LOW PRESSUREWARNING SWITCH

FIREWALLSHUTOFF VALVE

Engine Rear Bearing Supportand Tailpipe Failures

by Dare1 Traylor, Service Analyst CoordinatorC-13O/Hercules Field Service Department

Lockheed has recently received a number of reports Excessive turbine vibration will usually cause crack-describing cracking of the engine turbine rear bearing sup- ing of other components besides the turbine rear bearingport or tailpipe. In many cases there has been no clear in- support or tailpipe. Inspect such items as sheet metaldication as to the cause of the trouble or evidence of mounting brackets in the QEC, the TD valve mountingassociated problems. Experience has shown that failures brackets, external oil tube mounting brackets, and soof this type can usually be traced to one or more of the forth. Damage to these parts as well is an indication thatfollowing conditions: excessive turbine vibration is present.

Improper installation of the tailpipe clampassembly.Excessive turbine vibration.Turbine vane-to-spacer rubbing.

Cracking caused by improper installation of the tail-pipe clamp assembly will not normally be accompaniedby any other failures or symptoms of trouble. The bestway to avoid problems of this type is to carefully followthe explicit instructions for installation and torquing ofthe tailpipe assembly that are found in the final chapterof the appropriate Engine Power Package Build-up In-structions (-10) for your aircraft.

Turbine vane-to-spacer rub will also cause vibrationthat can result in turbine rear bearing support or tailpipefailure. One of the tell-tale signs of turbine rub is thepresence of ferrous metal dust or granular material in thebottom of the turbine bearing support. If turbine rub issuspected, the problem should be investigated in accor-dance with Allison document T56-A-15/LFE CSL 1531to determine the serviceability of the engine.

Lockheed SERVICE NEWS V16N2

The Royal Australian Air Force’s No. 36 Squad-ron was the big winner at the 1989 Airlift Rodeocompetition, held during the week of June 5th atPope Air Force Base in North Carolina. More than1,600 airlift professionals competed in a week ofintense flying, even though the weather was oftenunfavorable. Thunderstorms and low ceilingsmade operations difficult and disrupted flyingschedules on some days. Forty teams from aroundthe world competed in the event, including Aus-tralia, Canada, France, West Germany, Israel,Japan, and the United States.

No. 36 Squadron not only won the trophies forbest C-130 crew and best foreign crew, but the unitwas also the prime contributor to Australia’s big-gest ever win as “Best Overall Wing.” It is only thefourth time in the Rodeo’s ten-year history that ateam from outside the U.S. has captured the toptitle.

The RAAF’s No. 36 Squadron, currently based inRichmond, New South Wales, was originallyformed in March 1942 with DC-2 aircraft at Laver-ton, near Melbourne in Victoria. During World WarII, it operated in the southwest Pacific theater astransport support squadron, principally in andaround New Guinea. After the war, the squadron

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was based in several different areas around Aus-tralia, and even spent two years operating out ofJapan. In 1958, the 36th was relocated to its presenthome at Richmond, near Sydney in New SouthWales.

The 36th squadron was equipped with its firstHercules aircraft, the C-130A, in 1958. Australia wasthe first nation after the U.S. to make use of theC-130 Hercules. The RAAF accumulated 148,061accident-free flying hours with the C-130As beforethese aircraft were replaced with C-130Hs in 1978.Since then, the C-130H aircraft have flown in excessof 90,000 accident-free hours.

The RAAF also operates the C-130E, which isflown by No. 37 Squadron, also based at Rich-mond. Between No. 36 and No. 37 Squadrons, theRAAF has accumulated over 448,000 accident-freehours using three different models of the Herculesaircraft. No. 36 Squadron is presently looking for-ward to its 50th anniversary in 1992, which shouldalso be the same year it will achieve 100,000 flyinghours in the C-130H.

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