Engine-Driven Hydraulic Pu1nps !

A SERVICE PUBLICATION OFLOCKHEED-GEORGIA COMPANYA DIVISION OFLOCKHEED CORPORATION

Edi tor

Charles I . Gale

Associate EditorsDaniel E. JolleyJames A. LoftinSteve Palmer

Art Director & Production

Bill Campbell

Vol. 10, No. 2, April-June 1983

CONTENTS

2

3

9

10

12

15

Focal PointM. J. Walters

Staff Engineer

Engine-Driven HydraulicPumps: A Brief History

Aft Cargo Door ActuatorModification

Life Raft Vent Valve Positioning

Upper Bumper Stop RepairProcedure

Jammed ring spring assemblies can

be restored to service.

StarTipProtecting UHF and VHF

Blade Antennas

Cover: The Republic of Indonesia is made upof over 13,000 islands and its need for efficientmaritime patrol capability is clear. Our coversshow the nation’s first marit ime patrolHercules aircraft, a C-130H-MP.

FINE-TUNING FOR SUCCESS

The hydraulic system of the Hercules air-craft first achieved operational status in itspresent form in the C-1306, and we havebeen “fine-tuning” it ever since. That finetuning has resulted in a hydraulic system thatcompares favorably with the most recentdesigns in the industry, no matter which per-formance parameter is examined. There issolid evidence to support this claim. It is con-firmed repeatedly in the reports we receivef rom those among our customers whooperate other state-of-the-art airplanes inaddition to the Hercules airlifter. M. J. WALTERS

The performance record of the Hercules aircraft hydraulic system comes as no surpriseto those of use who work with it every day. The basic formula for this success could hardlybe more straightforward: start with a well-designed system, monitor every aspect of itsoperation over months and years, and improve or update it as required to ensure that itsperformance will remain second to none.

Most successful formulas seem to contain a secret ingredient that adds somethingspecial. Ours is the way those updates and improvements are carried out. Before anychanges are made in this hydraulic system, we make sure that the result will be a bettersystem and a substantive advantage for the operator. That is what fine-tuning is all about.

Let’s look at a few examples. The kind of engine-driven hydraulic pumps installed asstandard equipment in new-production Hercules aircraft has been changed several timesover the years as better designs have become available. Those we use now incorporatemany engineering advances, and include even a thermal off-stroke feature to protectagainst overheating. The lead article in this issue of Service News gives additional detailsabout the improvements that have taken place in this area.

Another interesting example has to do with the electrically powered suction boostpumps that are used to ensure positive inlet pressure at the main engine-driven pumps. Theboost pumps we install today were developed specifically for the Hercules aircraft.Hydraulic fluid circulates freely past the motor windings to the bearings in these pumps,yielding a four-fold increase in pump life compared to conventional pumps used in thesame application.

Clean fluid is of paramount importance in every hydraulic system. In the Hercules air-craft, the main return and case drain lines are now equipped with filter elements that willremove particles three and five microns in size respectively. The result is hydraulic fluid asfree of particulate contaminants as that in any airplane flying today - and longer trouble-free service for every component in the system.

There is of course much more. Improvements that have been incorporated in theHercules aircraft hydraulic system include everything from a special shuttle valve to ensurereliable emergency n o s e landing gear extension to brake fuses that limit the amount of fluidlost in the event of hose failure.

We are proud of our hydraulic system. It has operated flare launchers, air compressors,aerial refueling systems, retractable skis, winches that pull survivors of sea disasters tosafety, and all sorts of other things that were never envisioned when the system was design-ed. It is a practical, proven system that has demonstrated its reliability and adaptabilitymany times over in the past, and will continue to do so in the future. After all, we are stilltuning.

M. Walters, Staff Engineer

T.J. Cleland Director

CUSTOMER INTEGRATED CUSTOMERSERVICE LOGISTICS SUPPORT SUPPLY

A. H McCrum J L THURMOND M M. HODNETT

DIRECTOR DIRECTOR DIRECTOR

Engine-Driven Hydraulic Pumps:ABRIEFHISTORY

by M.J. Walters, Staff Engineer

There is a strong family resemblance between theHercules aircraft that were built a quarter of a centuryago and those that are coming off the assembly linetoday. The explanation is simple: many of theadvanced features incorporated in the basic design ofthe world’s most versatile airlifter have not been allthat easy to improve upon.

But appearances seldom tell the whole story, andthis is especially true in the case of the Hercules air-craft. Despite superficial similarities between the oldand the new, almost everything about this remarkableairplane has undergone carefully considered evolu-tionary change over the years. The extraordinary

adaptability of its major operating systems has longbeen one of the Hercules aircraft’s unique strengths.

In this article we would like to look at one particulararea of one system in some detail, the engine-drivenhydraulic pumps. We will want to examine thechanges that have evolved, and make note of the effectthese improvements can have on such maintenance-related considerations as configuration control andinterchangeability.

System Evolution

The C-130B came off the production line equipped

Figure 1. Baseline hydraulic configuration on Hercules aircraft LAC 3501 to LAC 4181.

PIN 6 9 5 9 0TO BOOSTER3 - l R E L I E F V A L V E

R E S E R V O I R S.

P / N 695903- 1R E L I E F V A L V E

6 9 5 9 1 5 - 1

N O . 3 ENGINED R I V E N P U M P ,N Y A B

N O . 4 ENGI

P R E S S U R EL I N E

SUCTIONL I N E

PRESSUREL I N E P R E S S U R E M A N I F O L D

3 Lockheed SERVICE NEWS VlON2

with P/N 66WBD300 New York Air Brake Companyengine-driven hydraulic pumps. The New York AirBrake (NYAB) pump requires a bypass loop connect-ing the case drain line and the suction line (Figure 1).The bypass loop is required because the design of thepump is such that is receives its lubrication from thehydraulic fluid in the suction line. This causes no dif-ficulty unless one of the engine-driven pump switcheson the copilot’s instrument panel is placed to OFF orthe fire emergency handle for an engine is pulled.When this happens, the normal source of lubricatingfluid for the affected pump is no longer available eventhough the need for lubrication is still present.

Here is why. Placing one of the engine-driven pumpswitches in the OFF position or pulling the fireemergency handle closes both the firewall and pressureline shutoff valves for that engine. But the pump con-tinues to operate whenever the engine is running, andit must therefore continue to be lubricated. Withoutan alternative means of receiving lubrication, thepump would heat up and fail in a very short period oftime.

pump was incorporated in the system’s plumbing forthe specific purpose of maintaining lubrication to thepump when the firewall and pressure line shutoffvalves are closed. The bypass loop routes case drainfluid back into the suction line and thereby providesthe necessary lubrication. A P/N 695903-l relief valvein the case drain line set to open at 22 psi ensures thathydraulic fluid will be forced into the bypass loopwhenever loss of pressure in the suction line caused bythe closing of the firewall shutoff valve allows the P/N695915-1 check valve to open.

This plumbing configuration is the only one ofthose found on Hercules aircraft that will keep theNYAB engine-driven hydraulic pump lubricated andwithin its temperature design limit when it is operatingand the firewall and pressure line shutoff valves areclosed.

There was one minor change to the NYAB plumb-ing at Lockheed serial number LAC 4182. The695903-l relief valve was replaced by an improvedrelief valve. P/N 695903-3 (Figure 2). The change inrelief valves did not affect the pump itself.

To avoid such a possibility, a bypass loop for each

Figure 2. The baseline configuration of LAC 4182 to LAC 4429; note relief valve change.

T O BOOSTERR E L I E F V A L V E

R E S E R V O I R

R E L I E F V A L V E

N O . 3 ENGI N O . 4 ENGID R I V E N P U

P R E S S U R EL I N E S O V

IREWALL

S U C T I O N

P R E S S U R EL I N E P R E S S U R E M A N I F O L D

Lockheed SERVICE NEWS Vl ON2

No other pump or plumbing configurations wereavailable on new Hercules aircraft until Lockheedserial number LAC 4430. Starting with this aircraft,the NYAB pump was superseded on new productionaircraft by a pump built by Vickers, Incorporated.This change was applicable to all new baselineHercules aircraft except those built for the U.S. AirForce. On U.S. Air Force C-130s built subsequent toLAC 4430, Lockheed installed either NYAB pumps orVickers pumps, depending upon which the Air Forcesupplied for installation at the time a particular air-craft was produced.

The P/N PV3-075-4 Vickers engine-drivenhydraulic pump is an in-line pump whose design issuch that it uses the fluid that has been forced into thecase drain line for internal lubrication. Tests showedthat with the firewall and pressure line shutoff valvesclosed, the use of a bypass loop caused the Vickerspump to generate an operating temperature that ex-ceeded the permissible value. The bypass loop wastherefore deleted from the plumbing configuration(Figure 3). The new arrangement allowed the Vickerspump to remain within safe temperature limits underall operating conditions.

Note that the 695903-3 relief valve remained in thecase drain line in this configuration. Tests performedat Lockheed later determined that a check valve couldbe installed in place of the 695903-3 relief valve, andthat a cost saving would result. The relief valve wastherefore deleted, and a P/N 1112-589978 check valveused in its place starting with Lockheed serial numberLAC 4459 (Figure 4).

With the change made at LAC 4459, there were atotal of four distinct hydraulic plumbing configura-tions that a Hercules aircraft operator could have:NYAB pump, bypass loop, and 695903-l relief valve(Figure 1); NYAB pump, bypass loop, and 695903-3relief valve (Figure 2); Vickers pump, no bypass loop,and 695903-3 relief valve (Figure 3); or Vickers pump,no bypass loop, and 1112-589978 check valve (Figure4).

Abex Pumps Introduced

At Lockheed serial number LAC 4653, engine-driven hydraulic pumps manufactured by AbexCorporation became the standard pumps installed onbaseline aircraft in place of the PV3-075-4 Vickers

Figure 3. At LAC 4430, Vickers pumps were introduced and the bypass loops deleted.

N O . 3 ENGIN

D R I V E N P U M P .

VICKERS

N O . 4 ENGID R I V E N P U M P ,

P/N PV3-075-4

P R E S S U R EL I N E S O V FIREWALL

S U C T I O N

PRESSUREL I N E P R E S S U R E M A N I F O L D

C A S ED R A I N

N O . 3 ENGIN N O . 4 ENGI

D R I V E N D R I V E N

P I N PV3-075-4

P I N PV3-075-VICKERS VICKERS

P R E S S U R EL I N E S O V

FIREWALL

r

S U C T I O NL I N E

1

L I N E P R E S S U R E M A N I F O L D

IFigure 4. The baseline configuration of LAC 4458 to LAC 4652 I ne valves nave oeen rep laced

check valves.

pumps (Figure 5). The P/N 66039 Abex pump con-tains a thermal off-stroke feature which allows it to beused in any of the four hydraulic plumbing configura-tions we have previously described. It can be used withor without a bypass loop, and with either a relief valveor check valve in the case drain line. The baseline con-figuration starting with LAC 4653 and presently ineffect uses the 66039 Abex pump, no bypass loop, anda 1112-589978 check valve in the case drain line.

pumps. But there is another possibility.

If a repeat customer originally bought Hercules air-craft equipped with NYAB pumps, Abex pumps withbypass loops and 695903-3 relief valves would beinstalled on the subsequent aircraft purchase (Figure6). This would provide the customer with a Herculesfleet in which NYAB or Abex pumps could be usedinterchangeably.

Note that once again this change pertained only tothose airplanes being built for operators other than theU.S. Air Force. Lockheed continued to install NYABor Vickers pumps on U.S. Air Force C-130s until afiscal year 1982 contract provided for the use of Abexpumps on aircraft designated for the U.S. Air ReserveForces.

A customer buying Hercules aircraft today mightthink that his aircraft would automatically come withthe baseline configuration; i.e., Abex pumps, nobypass loops, and 1112-589978 check valves. Hewould be right if he had never bought a Herculesbefore, or if he had bought Hercules airlifterspreviously that were equipped with Vickers or Abex

Lockheed SERVICE NEWS VlON2

by

Other Pumps

We have already mentioned that U.S. Air ForceC-130s were originally equipped with NYAB orVickers pumps prior to the fiscal year 1982 AirReserve Forces buy. The Air Force went one stepfurther and procured a number of modified Vickerspumps with the part number PV3-075-4A as replace-ment parts. Some C-130s in the Air Force inventorywill therefore be equipped with this pump. Thedifference between the PV3-075-4A Vickers pump andthe PV3-075-4 model that was installed on baselineHercules aircraft between LAC 4430 and LAC 4652are relatively minor. The -4A pump has a displace-ment of 0.60 cubic inch per revolution and will deliver

6

T O B O O S T E RP/N 11 1 2 - 5 8 9 9 7 8 C H E C K V A L V E

R E S E R V O I R

PIN 1 1 1 2 - 5 8 9 9 7 8C H E C K V A L V E S E

AIN

N O . 3 ENGINE-D R I V E N P U M P . 1 A E E X

N O . 4 ENGIND R I V E N P U M P

P R E S S U R EL I N E S O V FIREWALL

S U C T I O NL I N E

PRESSURELINE P R E S S U R E M A N I F O L D

Flgure 5

I he Abex pump was introduced at Hercules alrcratf LAC 4653 No changes were required inbasic system design.

approximately 8.6 gallons per minute. The -4 Vickerspump has a displacement of 0.75 inch per revolutionand delivers approximately 10.7 gallons per minute.

Lockheed has approved the use of another Vickers-built pump, one which up to this time has not beeninstalled on any new Hercules aircraft. The VickersP/N PV3-075-16 engine-driven hydraulic pump incor-porates a thermal off-stroke feature like the Abexpump. This allows it to operate in any of the plumbingconfigurations that we have previously discussed; thatis, with or without a bypass loop, and with a reliefvalve or a check valve in the case drain line. At thistime, the U.S. Air Force is modifying some Vickers-4A pumps to the -16 configuration; some new -16Vickers units are also being procured as spares.

:he

It can be seen from the foregoing discussion that asfar as the engine-driven pumps are concerned, the nor-mal hydraulic system plumbing configurations foundon Hercules aircraft offer considerable latitude interms of interchangeability. Briefly stated, theconditions governing the interchangeability of engine-driven hydraulic pumps are as follows: Always use abypass loop and 695903-3 relief valve with any NYABpump. Omit the bypass loop with a Vickers -4 or -4Apump and use either a 695903-3 relief valve or a1112-589978 check valve in the case drain line. Finally,any of the standard plumbing configurations can beused with the 66039 Abex pump or the -16 Vickerspump. The table below shows this same informationin graphic form.

P U M P B Y P A S S L O O P P I N 6 9 5 9 0 3 - 3R E L I E F V A L V E

O R P/N 1112-589978C H E C K V A L V E

NYAB Y E S R E L I E F V A L V E

V I C K E R S - 4 NO E I T H E RV I C K E R S - 4 A NO E I T H E RV I C K E R S - 1 6 O P T I O N A L EITHER

A B E X O P T I O N A L E I T H E R

7 Lockheed SERVICE NEWS Vl ON2

TO S O O S T ER E S E R V O I R

P/N 6 9 5 9 0 3 - 3R E L I E F V A L V E

6 9 5 9 1 5 - 1

N O . 3 ENGIND R I V E N P U M P ,A B E X

N O . 4 ENGID R I V E N P U M P ,

P R E S S U R EL I N E S O V FIREWALL

L I N E P R E S S U R E M A N I F O L D

Figure 6. System plumbing configured for use with either NYAB or Abex pumps.

Operational Notes

We would like to mention here that there are twocharacteristics that the flight crew will notice if aNYAB engine-driven hydraulic pump is replaced witha -4 or -4A Vickers pump (with the appropriateplumbing change), a -16 Vickers pump, or an Abexpump.

First, the NYAB pump is of a design often referredto as a “check valve” type pump. It will allow suctionboost pump pressure (approximately 100 psi) to flowthrough a static engine-driven pump to operate theflight controls, albeit at a very reduced rate. TheVickers and Abex pumps, which are commonly refer-red to as “in-line” type pumps, will not allow suctionboost pump pressure to flow through a static engine-driven pump.

Second, if the flight crew turns off the suction boostpump, the output pressure of a rotating NYABengine-driven pump will drop, as evidenced on theaffected system’s pressure gage. The primary reasonfor the pressure drop is that a compensator is refer-enced to the pressure in the suction line; if suction line

Lockheed SERVICE NEWS Vl ON2 8

pressure is reduced, output pressure drops. The com-pensators on Vickers and Abex pumps are referencedto case pressure and are therefore theoretically insen-sitive to suction line pressure. There will neverthelessbe a very slight drop in pressure on the gage withVickers or Abex pumps when the suction boost pumpis not operating. This pressure drop is causedprimarily by a slight reduction in case drain pressurewhen suction pressure is switched off.

The C-130A

We have not up to this point made any mention ofthe engine-driven hydraulic pumps of the C-130A. Thereason is that the interchangeability of pumps on theA-model Hercules aircraft is not governed by theinternal lubricating characteristics of the pumpthemselves. C-130As, originally equipped with NYABpumps, have a bypass valve connecting the pressureand suction lines (Figure 7). The bypass valve willopen to allow lubricating flow through the pumpanytime the engine-driven pump switch is placed toOFF or the fire emergency handle is pulled. Thisplumbing configuration never changes, regardless ofthe type of replacement pump that might later beinstalled.

T O B O O S T E RR E S E R V O I R

0 . 1 E N G I N E - N O . 3 E N G I N E -D R I V E N P U M P D R I V E N P U M P

S U C T I O N FIREWALLL I N E SOV

P R E S S U R E L I N E P R E S S U R E M A N I F O L DL

Figure 7. C-l 30A plumbing configuration; note bypass valves

We hope that this short history of the engine-driven that we have laid out here are followed whenever ahydraulic pumps used in Hercules aircraft has cleared pump is to be replaced, there should never be anyup any confusion you might have had concerning their worry about installing a pump in an aircraft with theapplication and interchangeability. If the guidelines wrong plumbing configuration.

An incident occurred recently aboard a Herculesaircraft on a military training mission that could havehad serious consequences for both the aircraft and itscrew.

After a paradrop, the aft cargo door switch was leftin the neutral position and the emergency manualrelease cable was used to close the cargo door. Unfor-tunately, air had become trapped in the associatedhydraulic lines and the heavy door dropped suddenlyand with considerable force. This applied excessivestress to the structure supporting the upper end of thecargo door actuating cylinder at FS 968, causing it tofracture.

In itself, this would not have resulted in anythingmore serious than an inoperable door system. But thebleed valve on the actuating cylinder snagged one ofthe elevator control cables that run beneath it as itdropped, causing the aircraft to assume a nose-downattitude. The aircraft did not prove uncontrollable,however, and landed safely.

To avoid any possible repetition of this type ofproblem, Lockheed engineering recommends that twoactions be taken by Hercules aircraft operators. First,if there is a bleed valve on the aft cargo door actuatingcylinder of any of your aircraft, it should be replacedwith a bleed plug. Lockheed engineering will soon

9 Lockheed SERVICE NEWS Vl ON2

Aft cargo door actuator. Note the protruding bleedvalve.

issue Service Bulletins SB 82-532 and 382-29-6, “BleedPlugs - Aft Cargo Door - Bleed Valve Replacement,”which describes replacement of the bleed valve. Thebleed plug, which is used in place of the bleed valve onall current production Hercules, is too short to foulthe elevator cables should the aft cargo door actuatingcylinder become loose for any reason.

The second recommendation is that Hercules air-craft operators who have not accomplished ServiceBulletins SB 82-299 or 382-093, “Doors - Installationof Snubber and Attaching Structure on the Aft CargoDoor,” do so as soon as possible. These servicebulletins install a snubber on the aft cargo door whichwill prevent the door from dropping too rapidly whenit is allowed to close of its own weight.

Many Hercules aircraft are equipped with four typeF-2B 20-man life rafts stowed in four compartmentsbuilt into the upper surface of the center wing section.From time to time, Lockheed receives a report of aninadvertent deployment of a life raft during flight.Such incidents are cause for concern that goes beyondthe value of the lost equipment. A life raft released in-

to the slipstream can damage or foul empennagesurfaces on its way aft.

It is clear that most cases of inadvertent life raftdeployment come about because a life raft becomespartially inflated and forces open the life raft com-partment access door. What is less clear is just how

Lockheed SERVICE NEWS VlON2 10

"SHUT"(valve losed)

valveVENT"open)

Figure 1. Vent valve positions.

this partial inflation occurs. Lockheed engineering has position.long suspected that the majority of these unscheduled

The raft appeared to have been properly

life raft deployments occur either because the raft wasevacuated and installed, except for the valve position,

incompletely evacuated prior to installation, orbut the access door clearly showed signs of damage.

because the P/N 9153 vent valve on rafts so equippedEach time the aircraft went to altitude, the air trappedin the raft expanded, pushing on the door latches.

has been left in the closed position. Figure 1 illustrates How long the raft had been installed could not bethe appearance of the vent valve in both the closed determined,(SHUT) and open (VENT) positions.

but loss of the l i fe raft appearedimminent because of bending of the door latches.

It is very important that the vent valve be left in theopen (VENT) position once the life rafts are installedin their compartments. The porosity of the life raftmaterial will not permit the raft to remain evaucatedindefinitely, and venting of the raft is thereforerequired to avoid expansion at altitude. Also, if thevent is left closed, any leakage from the CO2 cylindersused to inflate the rafts for use cannot escape to theatmosphere and will enter the raft itself.

In an effort to reduce the chance that a vent valvewill be left in the closed position after installation ofthe rafts in their compartments, Lockheed has added adecal (Figure 2) to the life raft access doors on newproduction airplanes which shows the proper position-ing of the vent valve. The Lockheed part number ofthe decal is 3319712-1, and it is installed in a space onthe access doors next to the existing decals whichdescribe how to fold the life raft.

For detailed information on life raft handling pro-cedures, see the applicable maintenance manuals foryour airplane and T.O. 14S-1-102/TM5-4220-202-14for the raft. Also see an in-depth article on life raftswhich was presented in Vol. 6, No. 1 of LockheedService News (January-March 1979). This articledescribes air evacuation, installation, and rigging pro-cedures and precautions.

Additional evidence has recently come to lightwhich tends to underscore the role that improper posi-tioning of the vent valve plays in these life raftincidents. During a recent investigation of an inadver-tent life raft deployment on a C-130H, the life raftcompartments of several in-service Hercules aircraftwere inspected at random. In one airplane, a life raftwas discovered with the vent valve in the closed

Figure 2. Part number 3319712-I decal incorporated on production Hercules aircraft LAC 4917 and up.

Lockheed SERVICE NEWS VlON2

The design of the Hercules aircraft main landinggear is straightforward and its operating cyclerelatively simple, especially when compared with theconsiderably more complicated mechanical cyclesrequired to accomplish gear retraction and extensionon many other large aircraft. This functional simpli-city helps ensure that the components of the systemwill be able to provide long service and dependableperformance under a wide variety of operational con-ditions. It should be remembered, however, that everymechanical system is built with certain “normal”operational parameters in mind. Unusually heavy ser-vice or severe climatic conditions impose stresses thattend to shorten component life and precipitate specialmaintenance problems. The Hercules main landinggear is not immune from such effects.

Recently, a military operator whose Hercules air-craft were in virtually continuous operation carryingheavy loads into areas where extreme weather condi-tions prevailed noted a significant increase indiscrepancies involving excessive axial play in theMLG upper bumper stop assemblies. Some of theballscrew assemblies had only recently been installedand were apparently in good condition otherwise.

Investigation determined that in each of the casesthe ring spring assembly had jammed, whichaccounted for the excessive axial clearance. The exactcause of the condition was more difficult to pinpoint,but it appears that heavy loads, harsh climatic condi-

12

tions, and inadequate lubrication all played a part. Inany event, it proved possible to repair most of theaffected upper bumper stops, using a simplified pro-cedure which did not require removing them from theairplane. This resulted in a considerable saving in bothdowntime and expense. The particular aircraftinvolved happened to be equipped with Western Gearballscrew assemblies, but since the Calco ballscrewsare essentially similar in construction and function, adiscussion of the procedures that can be used torestore jammed ring spring assemblies to serviceshould be helpful to all Hercules aircraft operators.

Whenever excessive axial clearance is discovered ina MLG upper bumper stop, the possibility that ajammed ring spring assembly may be the cause shouldbe considered. A worthwhile initial step is to try tofree it without disassembly. Look for a lubrication fit-ting on the upper bumper stop housing. If one is pro-vided, pump MIL-G-81322 grease into the bumperstop with a grease gun. Then give the bumper stop asharp blow or two with a rubber or leather mallet. Ifthis frees the spring and the excessive axial play disap-pears, no further action is required other than periodiclubrication with MIL-G-81322 grease.

If the above steps do not succeed in unjamming thespring, the upper bumper stop stop can be partiallydisassembled for inspection and possible on-the-aircraft repair of the ring spring assembly. The follow-ing upper bumper stop ring spring separation pro-

Lockheed SERVICE NEWS VlON2

cedures in effect combine information now foundpiecemeal in several technical manuals.

Western Gear Procedure

Install a ground safety lock on one ballscrew oneach side of the airplane and on the nose landing gear.Install a main landing gear strut lock on the strut thatis being worked on and jack the aircraft. Remove theinsulation blanket located on the inside of the cargocompartment at the MLG wheel well to gain access tothe vertical torque shaft access door (Figure 1). Aftertaking off the door, disconnect the vertical torqueshaft by removing the four bolts on the torque shaftcoupling assembly. Then remove the pillow block andshims by taking out the four bolts that attach it to thefuselage structure. Use a standard gear puller to com-press the parts in the upper bumper stop housing, andremove the bumper stop retainer ring from the top ofthe upper bumper stop housing (Figure 2) with a pairof external snap-ring pliers. Now lower the upperbumper stop housing. Be careful: Jammed ring springelements can separate spontaneously and forcefullywithout warning; stay alert to the possibility and keepfingers and tools clear.

When the ring spring assembly is exposed, check tosee if the spring elements are still stuck together. Ifthey are, you should be able to separate them bylightly tapping on the outer ring with a mallet. Oncethe elements are freed, examine them for corrosion,scored surfaces, nicks, chipped mating surfaces, andbroken parts. Serious damage will require that the ringspring assembly be replaced, which should be done inthe shop after removal of the ballscrew assembly fromthe airplane.

Minor damage can be much easier to correct. Ifcorrosion is only minor and there are no signs of per-manent physical damage, the only repair that will benecessary is to clean all grease from the matingsurfaces of the ring spring elements and remove anycorrosion with emery cloth. Avoid “polishing” the

Figure I. Remove the access door to reach thevertical torque shaft and the upper bumper stop.

elements, and protect the other parts of the ballscrewassembly from falling debris while you work.

Before reinstalling the ring spring assembly,lubricate the elements of the ring spring assemblyliberally with MIL-G-81322 grease. Insert the ringspring elements, the spacer, and the bearing into theupper bumper stop housing. Press the upper bumperstop housing upward on the ballscrew with a standardgear puller and install the bumper stop retainer ring.Rotate the ring in its groove on the bumper stophousing to ensure positive seating.

Reinstall the original pillow block and shims, andreconnect the torque shaft and the ballscrew. Be sureto install all of the coupling bolts head-down andsafety-wire all four castellated nuts.

Next, synchronize the ballscrews as outlined in theappropriate landing gear maintenance manual. Thenreinstall the vertical torque shaft access door and theinsulation blanket. Remove the main landing gear

Figure 2. Exploded view of the Western Gear upper bumper stop.

BUMPER STOPRING SPRING, OUTER

LUBRICATION

RING RING SPRING FITTINGRETAINER RING

i O-RING UPPER BUMPER/

STOP HOUSING

Lockheed SERVICE NEWS Vl ON2 13

THRUSTBEARING

OUTER

BUMPER

STOP NUT

STOP HOUSINGRACE

RING SPRING

Figure 3. Exploded view of the Calco upper bumper stop.

strut lock and the ground safety locks and perform anoperational check of the MLG in accordance with thelanding gear maintenance manual. The repair is nowcomplete. Reinstall the nose landing gear groundsafety lock, lower the airplane, and remove the jacks.

Calco Procedure

The steps required to free a jammed ring springassembly in a Calco upper bumper stop are in manyways similar to those used for Western Gear units.There are, however, some differences in design detailsbetween the two units and these are reflected in thisrepair procedure.

Install a ground safety lock on one ballscrew oneach side of the airplane and on the nose landing gear.Install a main landing gear strut lock on the strut thatis being worked on and jack the aircraft.

It is not necessary to detach the pillow block fromthe fuselage structure to gain access to the ring springassembly. Remove the safety wire, the screw, and keyfrom the upper bumper stop nut (Figure 3). Use astrap wrench to keep the upper bumper stop housingfrom rotating, and screw the upper bumper stop nutout of the housing. Now lower the ring springassembly, the thrust races, and the thrust bearing. Becareful: If the ring spring elements are jammed, theycan separate spontaneously and with great force; useappropriate precautionary measures.

Note the condition of the upper bumper stopO-rings. If they appear to be deteriorated, theballscrew assembly should be removed for inspectionof the O-rings.

Inspect the ring spring assembly to determine if thespring elements are still jammed. If they are, tap theouter ring lightly with a mallet to free them. After theelements are separated, check them for corrosion,scored surfaces, nicks, chipped mating surfaces, andbroken parts. If any significant damage is present, the

ring spring assembly must be replaced, which shouldbe done in the shop after removal of the ballscrewfrom the airplane.

In cases where only minor corrosion is found, theonly repair required will be to clean the matingsurfaces of the ring spring elements carefully andremove any corrosion with emery cloth. Don’t“polish” the elements, and protect the other parts ofthe ballscrew assembly from any foreign particles thatmay become loosened while you work.

Begin assembly by applying a liberal coat of MIL-G-81322 grease to the thrust bearing, thrust races, andthe ring spring elements. Coat the threads of thebumper stop nut with MIL-T-5544 anti-seizecompound. Install the thrust races, thrust bearing,and ring spring assembly into the upper bumper stophousing and screw the upper bumper stop nut onfinger tight.

Now tighten the nut to a value of 250 inch-pounds.Further tighten the nut to align the locking slots on thenut and on the housing, but do not exceed 400 inch-pounds of torque. After the slots are aligned, installthe key and the screw and safety wire the screw.

Next, remove the MLG strut lock and the groundsafety locks from the landing gears. Perform anoperational check of the landing gear in accordancewith the landing gear maintenance manual. The repairis now complete. Install the nose landing gear groundsafety lock; then lower the airplane and remove thejacks.

While we don’t suggest that the steps we havediscussed here will take care of all of your ballscrewproblems, the information we have presented shouldprove helpful in many situations. When a jammed ringspring is all that keeps a Hercules aircraft mainlanding gear from performing as it should, it is bothquicker and less expensive to repair it than to requisi-tion and install an entire new ballscrew assembly.

14 Lockheed SERVICE NEWS VlON2

by A.D. Wing, Service Representative

1 . M E A S U R E

2 . S A N D

& C L E A N

RUBBER

3 . A P P L Y A D H E S I V E

A N D R U B B E R

4 . F I N I S H E D

S A N D -P A P E R

A L C O H O L

BOSTIC

A D H E S I V E

The leading edges of the blade-type UHF and VHFantennas located on the lower part of the Hercules air-craft fuselage are often gradually eroded by sand,gravel, and other solid particles tossed up by the pro-pellers and nose wheels during landings and groundoperations. Ice crystals and hail encountered in flightcan also cause significant wear and tear on thesesurfaces.

A simple but effective approach to protecting theleading edge of an antenna of this type is to glue on astrip of rubber cut from an old inner tube. The rubberstrip should be large enough to overlap 3/4 inch to 1inch on each side of the antenna leading edge, and itshould be long enough to run the full length of theantenna. Both the antenna and the rubber strip need tobe prepared for adhesion by roughening the surfacesthat will be in contact. Use medium-grade sandpaper forthis purpose, and then clean the surfaces with solvent.Alcohol is a good choice because it leaves no residue.

Any strong adhesive can be used to cement the rub-ber strip to the antenna leading edge. One recommendedbrand is Bostic No. 1096, used with Boscodur No. 9accelerator. Be sure to follow the manufacturer’sinstructions carefully to ensure maximum adhesion anddurability.

Lockheed SERVICE NEWS Vl ON2 15