MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)TABLE 4-4. LIST OF TOP TENREPLACEMENT PARTS BY MAN-HOURSTO REPLACEM113 Family(Ligh Combat Vehicle)Track ShoeEngineEngine OilTransmissionRubber CushionRoad WheelSprocketFinal DriveTransmission OilBatteryM915 Series(Heavy Tactical Truck)Engine ValveInsertSealDecreasing TireMan-Hours SpringTransmissionGasketFuel FilterOil FilterAir FilterFor combat vehicles, track is usually the number onemaintenance burden. An accessible location for breakingand joining track is essential if the time to perform trackmaintenance is to be minimized. For all tank-automotiveequipment, engine oil and filter change also is a significantcontributor to total maintenance time. In general,the maintainability engineer should place emphasis onthose items in Table 4-4 since they are the top contributorsto the maintenance burden. Tasks such as replacingthe gearshaft are performed more often than replacing theengine valve, but they do not add as much to the totalmaintenance burden.4-6.5.4 Performance and/or DesignConsiderationsBecause tank-automotive equipment is mobile, it issubject to dynamic stress and strain. To maintain vehicleintegrity regarding stress and strain calculations, accessibilitymust be considered during design and not as anafterthought. For example, rectangular hull access panelshave maximum stress at the corners (Fig. 4-34). Theoptimum solution from a stress consideration is a circularaccess hole. However, this shape access may be totallyimpractical from the viewpoint of production, i.e., cuttingor machining difficulties. A reinforced edge around theperimeter of the rectangular access may serve to strengthenthe hull and prevent cracking. The use of the accessFigure 4-34.Corner Stress Cracksplate in the first place, however, may degrade ballisticprotection. The goal is to conduct the appropriate accessibilityperformance trade-offs to arrive at the optimumsystem design.4-6.6 ARMY MARINE EQUIPMENTThe accessibility of marine components that may requiremaintenance is affected by fouling, i.e., the growth ofanimals and plants on the surfaces of submerged objects.A principal source of trouble is the fouling in pipes andconduits used to conduct water inside ships. For example,fouling may prevent closure of an isolation valve thatmust be closed to access a failed component. Fouling canmake underwater structural repairs difficult or impossible.Consequently, more ships will require dry-dock facilities,i.e., making dry docks less available.Fouling is controlled primarily by the selection ofappropriate materials of construction and the use of protectivecoatings such as paint. The common antifoulingpaints contain copper, mercury, or arsenic compounds invarious combinations; concentrations of about 1 milligramper liter are effective in reducing fouling. Diisobutylphenol and chlorophenarsamine are consideredvery effective in combatting fouling. As a preventive measure,pipes and conduits should be made of bronze orother copper alloys because these materials are the leastlikely to foul.4-6.7 AIRCRAFT (Refs. 4 and 5)Aircraft components that require maintenance shouldbe easily accessible. However, the designer should considerthe expected frequency of maintenance to determinethe degree of accessibility and to insure that the effortexpended to provide accessibility is warranted.4-6.7.1 General Inspection and AccessRequirementsThe aircraft designer should provide every possibleconvenience for performing periodic inspections andreplacements of functional components in a minimumperiod of time and for decreasing possible in-flighthazards. Some design recommendations that merit considerationfollow:1. Do not use doors that are welded or riveted tothe airframe, panels, or other accesses requiring the removalof permanently attached structures.2. Provide doors or access panels in the fuselage.airfoils, nacelles, control surfaces, and any location nototherwise accessible from the interior for the inspectionand servicing of actuators, controls, jack screws, pulleys,cables, guides, electric junction boxes, the Pitot-staticsystem, fuel tanks and system, boost pumps, and similaritems.3. Uniquely mark all removable inspection andaccess doors or otherwise identify their locations to expe-4-24