Issue No. 3, Jul-Sep

A SERVICE PUBLICATION OFLOCKHEED-GEORGIA COMPANYA DIVISION OFLOCKHEED CORPORATION

EditorCharles I . Gale

Associate EditorsDoug BrashearJames A. LoftinVera A. Taylor

Art Direction & ProductionTeri L. Mohr

Vol. 12, No. 3, July-September 1985

CONTENTS

3

14

15

18

22

HTTB-The High Technology TestBedLockheed’s unique, flying laboratoryenters service.

Very High Pressure Hydraulics:It’s HereSystems using 8000 psi pressure.

nonflammable fluid are now beingtested.

New Lockheed-DesignedSyncrophaser Test Sets

Hercules Flap SystemA review of the major componentsand system operation.

Main landing Gear Friction WasherSplash Guard

Cover: Distinctive in both appearance and

purpose, this specially modified Herculesaircraft is Lockheed’s new High Technology

Test Bed, featured in this issue.

Published by Lockheed-Georgia Company, a D i v i s i o n ofLockheed Corporation. Information contained in this issueis considered by Lockheed-Georgia Company to be accurateand authoritative: it should not be assumed, however, thatthis material has received approval from any governmentalagency or military service unless it i s specifically noted. Thispublication is for planning and information purposes only,and it is not to be construed as authority for making changesan aircraft or equipment or as superseding any establishedoperational or maintenance procedures or policies. Thefollowing marks are registered and owned by LockheedCorporation: Hercules: and Written permission must be obtained from Lockheed-Georgia Company before republishing any material i n thisperiodical. Address all communications to Editor, ServiceNews, Department 64-31, Zone 278, Lockheed-GeorgiaCompany, Marietta. Georgia, 30063. Copyright 1985Lockheed Corporation.

M. M. HODNETT DIRECTOR

CUSTOMER INTEGRATED

SERVICE LOGISTICS SUPPORT

A. H. McCRUM J. L THURMOND

DlRECTOR DIRECTOR

CUSTOMER

SUPPLY

H T NlSSLEY

DlRECTOR

The High Technology Test BedAeronautical systemsmust be tested and proven to

much more stringent standards than typical ground-based systems. The most important test to establish thefunction and credibility of a system is the test flight.To satisfy the ever-increasing need to test or enhance thedevelopment of new systems and systems concepts, the

Lockheed-Georgia Com-pany has dedicated an air-craft to the specific supportof independent research anddevelopment projects, aswell as Lockheed researchand technology contracts.This aircraft is designatedthe High Technology TestBed (HTTB).

Inthepast, theabsenceofsuch a facility has sometimes

impeded the process of getting new systems from thedrawing board to installation on production aircraft.Substitution of expensive simulation facilities for theflight environment does not always yield satisfactory orreliable results. The use of models to analyze problemshas many limitations and often introduces test effectswhich can appear as significant as the phenomena be-ing observed. Other difficulties encountered in work-ing with models or simulations have to do with theprediction of scale effects-a complex business atbest-and test support interference effects.

In evaluating independent research and developmentprograms at Lockheed-Georgia, it was found that morethan 50 of them would benefit greatly from evaluationdone in a flight environment. Significantly, these pro-jects are from a variety of technology areas, and includesuch subjects as enhanced short takeoff and landing(STOL) capabilities, survivability improvements, ad-

vanced flight station design,and new avionics systems.

OBJECTIVES

Some performance and mission objectives for theHTTB were established on the basis of what are believedto be the technological and performance requirementsof the next-generation tactical airlifter. Among otherthings, the goal of the HTTB program in this contextis to help develop the capabilities that will allow the air-craft to fly to a target location anywhere in the worldusing passive navigation; that is, without assistance fromground or satellite navigation aids. Upon reaching thetarget area, the aircraft must be able to perform asfollows:

l Fly an approach at 75 to 80 knots, using onboard-generated centerline and glidepath (up to 7 degrees)guidance, in all weather conditions.

. Clear a standard 50-foot obstacle and touch downon a soft field (not a paved runway) within 4 feet laterallyand 20 feet longitudinally of a predetermined spot, witha descent rate of around 10 feet per second.

l Have a landing distance not exceeding 1500 feet fromthe base of the 50-foot obstacle.

All of this, by the way, is to be done on a hot dayat a gross weight of 140,000 pounds.

THE AIRCRAFT

As a result of these and other requirements, aLockheed Model L-100-20 was acquired from a commer-cial operator. Delivered in February of 1984, the aircrafthad approximately 5900 hours total time and was in ex-cellent condition. The stretched civilian Hercules aircraftwas chosen for the job because of its proven reliability.Another consideration was that large quantities of dataexist to establish the norms needed for evaluating ef-fects of new systems concepts and modifications. Also,the extra 100 inches of fuselage length on the L-lOO-20means added space for test equipment and monitoringsystems instrumentation.

INITIAL MODIFICATIONS

The first step in the modification program was to con-vert the aircraft from a cargo hauler to an engineeringtest bed. To facilitate this, the Lockheed Airborne DataSystem (LADS) was installed. This is one of the moresignificant modifications built into the HTTB for ex-perimenters. LADS has been developed over the lastdecade and is constantly being refined and improved.The purpose of this system is to process data in a rapid,reliable, and cost-effective way. The system has perform-ed exceptionally well, and has already more than paidfor its own hardware and development costs.

4

With the LADS, test data is available for studyalmost immediately after a data point is flown.

Lockheed SERVICE NEWS Vl2N3

The instrumentation contains engineering unitdisplays, time code generators, telemetry transmitters,tape recorders, a power distribution network, and twominicomputers. The system is modular and has morethan 1000 data channels available. In-flight data isgathered using thousands of feet of wiring installed toconnect the instrumentation to virtually every signifi-cant location on the aircraft. Exceptional care has beentaken to ensure that electrical noise is isolated andrejected at the source, allowing sensors, wires, andnecessary input modules to provide a high-quality digitaldata signal. This yields a system that is quiet and ac-curate. As a result of this installation, the flight testengineer has hard-copy, finished and plotted data avail-able moments after a data point has been flown.

Other modifications accomplished to enhance the air-craft’s capabilities as a flying test bed are as follows:

l An avionics equipment rack and an instrumentationconsole were added in the cargo compartment in sucha manner as to allow the total cargo area of the aircraftto remain available for test purposes.

l Two additional stations were added on the flight deck:one for the flight test avionics engineer, the other forthe flight test director.

l A bus interface was developed to permit LADS to

REMOTEACQUISITION

TYPICALINPUT MODULE

SYSTEM

DISPLAYS

The HTTB LADS Network

Lockheed SERVICE NEWS V12N3 5

extract data from MILSTD-1553B and ARINC 429 databusses. The purpose of these busses is to sort out thepriority data to be transmitted from the various sensorsso that the hard-wired connections to the Central Pro-cessing Unit (CPU) can be optimized.

. A special on-board structural computer (OBSC)system was installed to perform individual aircraft track-ing (IAT) in real time, using inputs from dedicated straingages and accelerometers.

l A state-of-the-art airspeed measuring system, angleof attack, and angle of sideslip measuring vanes wereinstalled.

l A cockpit management system (CMS) was added toprovide additional panel area for the new avionicssystems and to alleviate crew workload. The CollinsCMS 80 system that was selected is digital data buscompatible.

l The HF and VHF communications equipment wasinterfaced with the CMS, and the VHF radio was up-graded for improved tuning.

l A Delco Carousel IV inertial navigation system (INS)was installed and interfaced with the CMS.

l A Honeywell LASERNAV INS was installed forevaluation.

l The weather radar system equipment was upgraded.

Following the initial modifications to the HTTB air-craft, 120 flight hours were logged over 41 flights forthe purpose of establishing and recording the flyingqualities of this particular airplane. A total of 81 simu-lated assault-type landings were made by four differentpilots at 1.28 times stall speed and a descent rate of 650feet per minute on VFR approaches. This reference datawill be utilized in the future to determine the improve-

6 Lockheed SERVICE NEWS V12N3

EXTENDEDCHORD LONG CHORD

SAND/DUST-,SEPARATOR

FAST ACTING

MULTIMODE

STALL WARNINGLLLTV LEADING EDGE

FLlRiLASER SYSTEMS DEVICE

Many of the HTTB’s structural modifications are designed to enhance STOL performance.

ments in performance offered by each of the manymodifications to be made to the aircraft.

STOL MODIFICATIONS

As a result of wind tunnel testing and other research,a number of modifications to the basic aircraft that willenhance its short takeoff and landing characteristicshave been or are scheduled to be made. Some of thesemodifications are:

l New double-slotted trailing edge flaps to provide in-creased lift as well as increased drag at approach powersettings for improved STOL operations.

l A high-camber leading edge extension has been testedand proven to be quite effective in increasing maximumlift coefficient, both in landing and cruise configura-tions.

l A larger dorsal fin and horsal fins (extensions of thehorizontal stabilizer leading edge root fillet - see illustra-tion above) were installed to improve low speed handl-ing qualities and control. These devices are approximate-


ly 5 feet in maximum span and have a root chord thatextends almost to the wing trailing edge.

l The primary flight control systems are being changedfrom the present configuration, which consists of directmechanical linkages assisted by hydraulic boost, to “ful-ly powered” controls, in which the mechanical linkagesfrom the flight station controls operate only thehydraulic control valves of the appropriate boost units.

l Three spoiler panels are to be added to the upper sur-face of each wing to improve roll control at low air-speeds, roll stability augmentation, and precise descentcontrol. Assymmetric deployment of the spoilers willapproximately double the roll control capability of theailerons at low engine power and achieve even better per-formance as power is increased to levels used for STOLlanding approaches. For descent control, the spoilers aredeployed symmetrically. For safety, the spoiler deflec-tion is automatically decreased as stall speed isapproached. The spoiler actuation system is truly a high-technology system, featuring an 8000 psi hydraulic sys-tem, direct-drive valves, nonflammable chlorotrifluoro-ethylene (CTFE) fluid, and control intelligence provided

by the fight control computer.

l For improved roll sensitivity, the throw of the con-trol wheel is to be reduced from 120 degrees to 70degrees. Roll response with full control wheel input willapproach 30 degrees of bank in 2.5 seconds in landingconfiguration. This is made possible by the improvedroll control offered by extended chord ailerons combinedwith spoiler deflection.

l The rudder and elevator trim tabs will no longeroperate in the manner we have become used to. The tabswill be actuated by a brushless DC motor, which getsits orders from the flight control computer. The tab sur-faces on the HTTB perform a different function thantheir predecessors. These tabs serve to aid the hydraulicboost unit in moving the control surfaces when inputsare received from the flight station, and are consideredas a part of their respective primary flight controlsystems.

l Stability augmentation for the yaw and pitch axes isaccomplished by “smart” actuators directed by the flightcontrol computer. The dual rotary actuators mechanical-ly position the hydraulic control valves of the flight con-trol boost units as commanded by the computer. As aresult, stability augmentation is accomplished by move-ment of the entire control surface rather than just mov-ing the tabs. This should allow the stability augmenta-tion system more authority in low-speed flight. Stabili-ty augmentation in the roll axis, as mentioned earlier,will be accomplished by the multi-mode spoiler systemand orchestrated by the flight control computer.

l A long-stroke main and nose landing gear system isbeing developed that will allow a sink rate of up to 15feet per second. This will allow the HTTB to make preci-sion landings on short and unprepared fields.

OTHER KEY MODIFICATIONS

l A special syncrophaser system that featuresadjustable phase angles.

l A strap-on autothrottle system designed by Lockheedfor easy retrofit to existing C-130 aircraft. As it is cur-rently configured, it is usable only during cruise flight,but evaluations will be made for its potential use dur-ing conventional and STOL approaches.

l Additional engine instrumentation for determiningengine health in flight is being installed.

l Linoflex couplings of a new design are being installedas replacements for several of the Wiggins couplings inthe fuel system for evaluation purposes.

8

ADVANCED FLIGHT STATION

Major modifications to update the flight station arealso taking place. A “soft” mockup has been con-structed which depicts the structural modifications tothe instrument panel, control column, and control wheelthat are necessary to install a CRT display system. Ahead-up display (HUD) system is under development forthe pilot side of the cockpit. The STOL laws developedfor the HTTB and proven on the flight simulator at theManned Vehicle Systems Laboratory will be pro-grammed into it.

SURVIVABILITY IMPROVEMENTS

Improvements that will increase the aircraft’s abilityto negotiate hostile environments will be studied andtested on the HTTB aircraft. Improvements will beinvestigated in two areas:

1. Prototype installations of survivability enhancementsystems such as electronic countermeasures (ECM) andinfrared/radar signature reduction equipment will beflight-tested on an instrumented electronics range.Results will be compared with simulation data to verifysystem operation.

Lockheed SERVICE NEWS V12N3

2. To enhance C-130 systems survivability, several areasare being studied for incorporation on the HTTB.


l The addition of a third, full-time hydraulic systemto supply the flight controls system and redistributionof hydraulic power for flight controls offers a signifi-cant improvement in C-130 survivability.

The analysis, simulation, flight testing, and evalua-tion that will be performed in the HTTB program willenhance the development of survivability improvements,not only in the systems of currently manufactured air-craft, but those of future aircraft designs.

SAMSON POD

One of the independent research and developmentprojects to be evaluated on the HTTB aircraft is theSAMSON pod. The SAMSON (Special Avionics Mis-sion Strap On Now) pod is a 25.foot long 1360.gallon

external fuel tank, modified to accommodate an easilyattachable self-contained avionics package. A standardC-130 external fuel tank was chosen for this applicationbecause of its availability, known aerodynamiccharacteristics, and structural integrity. Electrical powerfor the electronics housed in the pod is supplied by agenerator driven by a ram air turbine (RAT). The RATgenerator can provide 4 KVA of power even at landingspeeds. At cruise airspeeds it can produce 20 KVA. Thiswill be sufficient electrical power to operate a wide vari-ety of avionics systems such as a forward-looking in-frared (FLIR) scanner and low light level television toprovide passive landing guidance for STOL landingoperations.

One of the interesting features of the SAMSON podis that all the control and data links with the aircraft

-------FORWARD-LOOKINGINFRARED RADAR

DATA LINK WINDOW (FLIR)

SAMSON Pod Installation

10 Lockheed SERVICE NEWS Vl2N3

W indow-moun ted infrared data link e q u i p m e n t

j A ram air turbine (RAT) driving a built-in generatorsupplies the SAMSON pod’s electrical power.


are optical, requiring no hard-wired connections whenthe pod is installed on the aircraft. The infrared datalinks look through the existing fuselage windows, requir-ing no airframe modifications for installation. Theoperator consoles for the SAMSON pod are set on air-craft pallets which can be expeditiously removed or in-stalled in the cargo compartment.

There has been interest expressed by several C-130operators in the various proposed configurations of theSAMSON pod, and uses such as maritime patrol, borderpatrol, radio relay, and low-level terrain-followingguidance systems.

MOBILE DATA CENTER

Included in the HTTB data system is a mobile datacenter - a van that has a telemetry and television linkwith the aircraft and can provide on-site real-time pro-cessing of data as well as plotting and printing of datain the field. Data processing equipment installed in thevan includes a VAX-11/751 computer, complete withprinter, plotters, tape recorders and video terminals. The33-foot long van accommodates four technicians andcan be transported in the cargo compartment of theHTTB, giving the HTTB system worldwide test capabi-lity. When the HTTB lands at a test site, the van can

11

be quickly driven off and set up to analyze data relayedby telemetry from the test aircraft.

WORLDWIDE INTEREST

tal agencies, technical societies, and educational institu-tions. More than 40 newspaper and magazine articleshave been published about the HTTB and itsaccomplishments.

The HTTB program has received a great deal of The HTTB program has been received withworldwide attention. Its most recent appearance was at enthusiasm by the aerospace and academic com-the Paris Air Show, where the Federation Acronautique munities. Manufacturers of aerospace vendor parts andInternationale presented Lockheed with certificates systems have responded to the HTTB program by shar-recognizing the HTTB’s world record-setting perfor-mance in short takeoff, time-to-climb, and landingdistance. In setting the records, the HTTB took off in427 meters (1401 feet). It climbed to 3000 meters (9843feet) in 3 minutes, 57.4 seconds; to 6000 meters (19,685feet) in 9 minutes, 0.35 seconds; and to 9000 meters(29,528 feet) in 17 minutes, 41.71 seconds. Gross weightat takeoff was 44,725 kilograms (98,600 pounds). Thelanding roll was 335 meters (1099 feet) at a gross weightof 43,091 kilograms (94,998 pounds).

ing their expertise and contributing nearly 8 milliondollars worth of advanced-technology equipment. Thisvery active response reflects the industry consensus thatthe HTTB concept and the unique opportunity to in-tegrate advanced concepts into flight test hardware thatit offers represent a significant step forward in aerospaceresearch capability.

THE SYSTEM

The HTTB system - the modified aircraft, LADS,and the mobile data center - allow testing optionsranging from evaluating a single, small element to a full-scale, highly complex systems test. Interactive flighttesting is another exciting possibility with the HTTB.While in flight, telemetry can be received by a groundstation at Lockheed-Georgia. From there it can bedistributed to sophisticated computers for advanced pro-

The HTTB was earlier involved in six tours that in-eluded visits to various universities around the countryand the Society of Flight Test Engineers symposium atSt. Louis, Missouri.

In addition to the tours mentioned above, there havebeen over 80 program briefings to various governmen-


cessing, and at the same time shared with other users.For example, while a test is in progress, onboard TVcameras focused on the flight station crew can bemonitored by human factors engineers developing stan-

dards for advanced flight station design. Simultaneously,other test engineers can receive the same data to feedto a flight simulator for a different part of the test.

In addition to Lockheed-Georgia’s own technologyresearch programs, the HTTB system is being madeavailable to government agencies, universities, and othercompanies for technology evaluation in an airborneenvironment. For further information on the HTTBsystem, call or write to:

R. H. Sandt, ManagerAdvanced Technology Program SalesDept. 67-12, Zone 22Lockheed-Georgia CompanyMarietta, Georgia 30063Telephone (404) 424-4914


An advance in technology and the vehicle that allowsdevelopment of that advance have arrived at the sameplace at the same time. Such is the case with the 8000-psihydraulic system which will provide power to the newspoilers on the HTTB aircraft.

The use of 8000-psi hydraulics has been under seriousdevelopment by all major airframe companies since J.N. Demarchi and R. K. Haning of North AmericanRockwell Corporation authored Technical Report NR72H-20, “Application of Very High Pressure HydraulicSystems” in March, 1972. The HTTB offers a unique op-portunity to study the operating characteristics of8000-psi hydraulics in a specially instrumented, function-ing aircraft.

The HTTB will have three independent X000-psihydraulic systems. These systems will be installed in ad-dition to the three 3000-psi hydraulic systems which arepresently on the aircraft, One of the new systems will bepowered by an 8000-psi engine-driven pump. The twoother systems will be powered from two of the existing3000-psi systems, utilizing power transfer units which willboost the pressures from 3000 psi to 8000 psi. The powertransfer units consist of a 3000-psi motor driving an8000-psi pump. There is no fluid transfer across thesystem boundaries.

Survivability requirements established for new militaryaircraft have provided a major stimulus for the develop-ment of 8000-psi hydraulic systems. These standards banuse of any flammable hydraulic fluids, which effectivelyeliminates most of the conventional fluids currently inservice.

As part of the effort to solve this problem, a nonflam-mable fluid is now under development at the Air Force

Wright Aeronautical Laboratories (AFWAL) at Wright-Patterson Air Force Base. The principle component ofthis fluid is chlorotrifluoroethylene, or CTFE. Severallaboratory test programs sponsored by the U. S. militaryare presently evaluating the use of CTFE in 8000-psisystems and the effect of this medium on pumps, seals,and valves.

The new fluid is nonflammable, but it weighs approx-imately two and one-half times as much as MIL-H-5606or MIL-H-83282, the hydraulic fluids now used on theC-130 and many other aircraft. When CTFE fluid is us-ed in conjunction with an 8000-psi system, however, theincrease in fluid weight can be compensated for by theincrease in pressure load, which allows significant reduc-tions in the amount of fluid required and the size ofhydraulic system components. In fact, the use of 8000-psihydraulics in place of the conventional 3000-psi systemon an airplane the size of the Hercules aircraft coulddecrease the weight and volume of hydraulic system com-ponents sufficiently to virtually eliminate any weightpenalty imposed by the use of CTFE fluid. The use ofthe new fluid and 8OOO-psi pressures can thus provide theadvantage of a nonflammable fluid medium without ad-ding to the total weight of future hydraulic systems.

The CTFE fluid currently being formulated by the AF-WAL carries the designation A-02. It is based uponSafetol 3.1 oil, manufactured by Halocarbon ProductsCorporation, 82 Burlews Court, Hackensack, N.J. 07601.Limited quantities of A-02 CTFE fluid are availablethrough the Materials Laboratory at Wright-PattersonAFB, OH 45433.


New Lockheed-Designed

by Earl Cunningham, Electronics Group EngineerRaymond Yearty, Supply Sales Planner Senior

Servicing the synchrophaser system of the Herculesaircraft is often tedious and time-consuming, especiallyfor an operator having both vacuum tube and solid-statesynchrophasers. Recent technological advances, however,have led to the development of new test equipment whichsimplifies testing procedures, saving both time andmoney. This article introduces the Lockheed-designedtest equipment now available for synchrophasermaintenance.

Flightline Maintenance

Lockheed has used the latest in digital circuitrytechnology to produce a new highly compact Syn-chrophaser System Test Set, P/N 3402801-5 (Figure 1).This test set was designed to combine in one lightweightbox all of the equipment necessary for functional testingof both solid-state and tube-type synchrophasers. The3402801-5 test set takes the guesswork out of servicing the synchrophaser by using digital readouts instead ofanalog meters. In addition, the reliability of this newunit is enhanced by the use of easily maintainable solid-state circuitry.

The Lockheed test set eliminates the need for addi-tional equipment previously used in performing enginetrim and assessment of synchrophaser performance. Itprovides functional test capability of all synchrophasersystem components, go-no-go testing of the propellerpickup, and measures propeller angle. The set includesa switchable solid-state megohmmeter, voltmeter andoscilloscope output, as well as the required interfacecables.

Figure 1. P/N 3402801-5 Synchrophaser SystemTest Set.


A Master Percent RPM Indicator (Figure 2), part ofthe Synchrophaser Test Set described below, can be pro-cured separately under P/N 3402875-l. This unit is usedto perform engine power trim with a high degree ofaccuracy in both ground and flight conditions. It weighs2 pounds and requires calibration only once a year.

Shop Maintenance

For Hercules aircraft operators wanting greatercapability, Lockheed has designed a Synchrophaser TestSet, P/N 3402801-7 (Figure 3), that can be used for shoprepair of both types of synchrophasers. This test set hasseveral unique features designed to virtually eliminateoperator error. First, the circuity used to generate phaseangles is entirely digital. This enhances accuracy andeliminates routine calibration checks. Also, when phaseangles are changed during the testing procedure, this testset provides a unique method of preventing latch-up of

the overspeed and underspeed circuits in the syn-chrophaser. This shortens and simplifies the test pro-cedure because the knobs and switches traditionally usedto set up test conditions are largely eliminated. All suchvariables are stored in an EPROM (Erasable Program-mable Read Only Memory) installed in the test set.When the operator has completed meter readings forone test step, he simply depresses two push buttons onthe test set panel and is then ready to take meter readingsfor the next procedure. All test conditions areautomatically established by the EPROM.

Extender cards are provided with each test set toenable troubleshooting and adjusting of detailed systemcomponents. A complete test of either type of syn-chrophaser can be performed by a relatively in-experienced technician in approximately 60 minutes.This test set also includes the capability of testing thesolid-state synchrophaser 2 l/2% RPM limit circuit.

Figure 2. P/N 3402875-I Master Percent RPM Indicator.


Figure 3. P/N 3402801-7 Synchrophaser Test Set.

Figure 4. Iron lung panel, tachometer test andsynchrophaser test plug.

The new synchrophaser system test sets were designedto make testing and repair of the synchrophaser moreefficient. Through ease of operation and improvedaccuracy, these Lockheed-designed test sets should provea great advantage to Hercules aircraft operators.

If you would like additional technical or procurementinformation about the -5 and -7 synchrophaser test sets,please direct your inquiries to the Manager, Supply Salesand Contract Department, at the following address:

Lockheed-Georgia CompanySupply Sales and Contracts DepartmentDept. 65-11, Zone 451Marietta, Georgia 30063Telephone (404) 424-4214TELEX 804263 LOC CUST SUPPL


H E R C U L E S F L A P SYSTEM

Our capacity for taking things for granted issometimes amazing. We assume our car will start thenext time we turn the key, that our ball-point pen willwrite every time. And that’s as it should be. We shouldalso have the right to assume all the systems in ourairplane will function properly. For instance; as long asutility hydraulic pressure and DC electrical power areavailable, the flaps on the Hercules aircraft shouldoperate - and usually do. But suppose we are lackingone or the other - or both - ingredients. What then?Sure, we all know how the flap system works, but let’srefresh our memory.

through the emergency flap brake valve to the flap selec-tor valve.

Figure 1.

The major components of the system are the selectorlever in the flight deck (Figure l), the flap drive controland motor (Figure 2), the flap brake, the flap control(selector) valve, the emergency flap brake valve, and theasymmetry sensing switches and brakes (Figure 4).

The four (two per wing) Fowler-type wing flaps aremanually controlled and hydraulically actuated. Move-ment of the-control lever in the flight deck quadrant istransferred through the interconnecting cable system tothe flap drive control unit. Switches in the flap drivefollow-up unit are actuated, completing the circuit toeither the up or down solenoid of the flap selector valveas selected (Figures 5 and 6). Utility system hydraulicpressure is directed by the flap selector valve to drivethe flaps in the desired direction. This fluid passes

PANEL LIGHT

FRICTION LOCK KNOB

FLAP QUADRANT PANEL


The normal (deenergized) position of the emergencyflap brake valve diverts utility system hydraulic pressureto the flap selector valve and connects the hydraulic linefor the asymmetry brakes to the utility system returnline. More about these brakes later.

The first action of the hydraulic pressure is to releasethe spring-actuated flap brake mounted on the flap drivegear box. With the brake released, the hydraulic motoris driven in the direction called for by the selector han-dle. When the flaps reach the selected position, follow-up switches in the flap drive unit are actuated, deenergi-ing the flap selector valve and removing pressure fromthe drive motor and brake. Flap movement stops andthe spring-loaded brake engages to hold the flaps inposition.

Flap operation is basically the same in either direc-tion - the reversible hydraulic motor drives either up ordown as selected. Flow regulators and restrictors main-tain a uniform pressure drop through the motor, preven-ting overspeeding or cavitation due to air loads beingimposed while the flaps are retracting.

During normal operation of the flaps, the asymmetrybrakes, located at the extreme outboard ends of the tor-que shafts, are spring-loaded off to the release position. Figure 3. Flap asymmetry sensing assembly.


Figure 4.WING FLAPS SYSTEM SCHEMATIC

FLAP

The asymmetry brakes are applied by hydraulicpressure. In the normal (deenergized) position, theemergency flap brake valve keeps the brakes’ hydraulicline open to return. Mounted along with the brakes anddriven by the torque shafts are the asymmetry sensingassemblies (Figure 3), consisting of three switches each.As long as the torque shafts are moving together(synchronized), the sensing switches can’t complete thecircuit to the emergency flap brake valve. If a torqueshaft should break or otherwise get out of synchroniza-tion, further rotation will cause a pair of switches toclose at the same instant, completing the circuit to theemergency flap brake valve (Figure 7). When this valveis energized, pressure is diverted from the flap selectorvalve to the asymmetry brakes, stopping flap movementand locking the flaps in position. The emergency flapbrake valve has a manual release for resetting the valveonce the solenoid is deenergized. Note that this shouldbe accomplished only on the ground to prevent a worse“split-flap” condition.

As with any other system, our troubles can start withminor malfunctions that may be compounded by in-advertent or hasty action. Let’s say we select flaps downand nothing happens. The hydraulic system looks nor-mal, so we assume that the problem must be electrical.Then we go to the flap selector valve located on the left

WING FLAPS SYSTEM SCHEMATICUP OPERATION


side of the cargo compartment forward of the left wheelwell and actuate the manual override button to theDOWN position. It is spring-loaded off and must beheld in until the desired flap position is reached. Theflaps start moving down, and suddenly the pilot calls“split flaps!” as the airplane rolls. Imagine performingthis operation during a maneuver such as a turn ontofinal approach on a turbulent day. Things could get outof hand in a hurry.

But, you say, the asymmetry sensing switches wouldimmediately sense the out-of-sync operation of the flapsand lock them in place. Look at the electrical schematicagain. The asymmetry sensing switches are poweredthrough the same circuit breaker as the control system.Trouble in the control circuit could very well render theasymmetry circuit inoperative. So, if you aren’t surewhere the trouble lies, actuate the manual override ofthe flap selector valve in small increments and verify syn-chronized flap movement before going past the pointof no return.

Note that if the emergency flap brake valve hasalready been energized by the asymmetry sensing cir-cuit, it must not be reset until the aircraft is on theground. The “split-flaps” condition could drive beyondthe point of aircraft control.

WING FLAPS SYSTEM SCHEMATICDOWN OPERATION

When hydraulic pressure is not available, the flaps canbe cranked down by hand (or up, for that matter). Justfollow the placarded directions. Again, check for syn-chronized flap movement - remember, hydraulicpressure and electrical power are required to set theasymmetry brakes.

The flap position indicator is powered through aseparate circuit breaker; it will function even duringmanual operation. It indicates the position of the flapdrive control assembly, but it will not indicate a “split-flaps” condition.

CODE- UTILITY PRESSURE

UTILITY RETURN

WING FLAPS SYSTEM SCHEMATICASYMMETRY BRAKES ON


New production Hercules aircraft now incorporateimprovement that reduces the possibility of partial mainlanding gear retraction during operation in cold climates.The problem results from ice build-up on the frictionwashers, rendering them temporarily ineffective in theperformance of their function.

The improvement is a splash guard which will shieldthe friction washer area from ice, slush, and other con-taminants. The splash guard will also benefit operatorsin dry, dusty conditions.

The splash guard was developed several years ago forthe Canadian Air Force because of problems they had

encountered with partial retractions, as well as con-tamination of the friction washer area with dry debris.Since then, other operators have modified their aircraftto include the splash guards and have found them tobe cost-effective and reliable.

The modification is not very difficult to accomplish,but does require jacking the aircraft, using wing andfuselage jack points. This is necessary in order to replacethe P/N 352301 or P/N 352301-3 spacer with a thickerP/N 352301-5 spacer. Once this is accomplished, it is

Figure I.

-TRUNNION (REF)

MS38542-14 CLAMP(ADDED)

FRICTION WASHER

BALLSCREW

352301-5 SPACER (ADDED)-DELETE 352301 OR 352301-3

NUT (REF)

LOCKING SCREW (REF)

3630008 SPLASHGUARD(ADDED)

MAIN LANDING GEAR SPLASH GUARD INSTALLATION (CROSS SECTION).


Figure 2. Main landing gear splash guard installed.

a simple matter to clamp the splash guard in place overthe main landing gear ball screw (see Figure 1). Specificinstructions for performing this improvement as well asordering details, weight and balance information, andmanpower requirements may be found in Hercules Ser-vice Bulletin #82-470 or Commercial Hercules ServiceBulletin #382-32-34.


Documents

Issue No. 3, Jul-Sep