Def Stan 00-970 Part 7-2

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Text of Def Stan 00-970 Part 7-2

DEF STAN 00-970 PART 7/2 SECTION 2 Page 1 SECTION 2 STRUCTURAL STRENGTH AND DESIGN FOR FLIGHT CONTENTS LEAFLET 200STATIC STRENGTH AND DEFORMATION Leaflet 200/1Principles underlying the requirements Leaflet 200/2Static structural strength test loading sequence Leaflet 200/3General prototype tests Leaflet 200/4Strength of structures under conditions of heating and cooling LEAFLET 201FATIGUE Leaflet 201/1An acceptable procedure for estimating fatigue life LEAFLET 202MANOEUVRES Leaflet 202/1Definitions LEAFLET 203CONTROL SYSTEMS - MECHANICAL COMPONENTS Leaflet 203/0Reference page Leaflet 203/1Powered Flying Controls Leaflet 203/2Testing of Powered Flying Controls Leaflet 203/3Test Schedules for Powered Flying Controls Leaflet 203/4Fatigue Testing of Hydraulic Powered Flying Controls Leaflet 203/5Design Recommendations LEAFLET 204STRENGTH CONSIDERATIONS FOR AUTOMATIC CONTROL SYSTEMS Leaflet 204/1General requirements LEAFLET 205CARRIAGE OF UNDERSLUNG LOADS Leaflet 205/1General requirements Leaflet 205/2Definitions relating to underslung loads LEAFLET 206DESIGN TO RESIST BIRDSTRIKE DAMAGE DEF STAN 00-970 PART 7/2 SECTION 2 Page 2 LEAFLET 207ACTIVE CONTROL SYSTEMS Leaflet 207/1General requirements and Integration Aspects Leaflet 207/2System requirements Leaflet 207/3Control laws and software Leaflet 207/4Structural implications of ACS Leaflet 207/5Operational and piloting aspects Leaflet 207/6Airframe and system proving Leaflet 207/7Part time systems LEAFLET 208GUST LOADS LEAFLET 209RADOMES Leaflet 209/0Reference Page APPENDIX No 1STRUCTURAL STRENGTH AND DESIGN FOR FLIGHT FORMILITARY DERIVATIVES OF CIVIL ROTORCRAFT (Note:See relevant para of this Appendix for military derivativerequirements relating to particular Leaflets of Part 2) APPENDIX No 2U.S. MILITARY SPECIFICATIONS, STANDARDS AND HANDBOOKS *In preparation DEF STAN 00-970 PART 7/2 SECTION 2 LEAFLET 200 STATIC STRENGTH AND DEFORMATION 1DEFINITIONS 1.1ThisLeafletstatestherequirementsforstaticstrengthandfreedomfrom deformation which might adversely affect airworthiness, handling or maintenance. 1.2Therequirementsapplytoairframesandmechanicalcomponents,including undercarriages and systems. 1.3Criticaldesigncases,correspondingtothemostsevereauthoriseduseofthe rotorcraft,mustbeidentifiedandtheloadsassociatedwitheachcasemustbetraced through the structure. 1.4All Grade A details must be identified and for each of them an allowable stress or strength must be determined.This would normally be the appropriate allowable ultimate stressorstrengthdeterminedona'B'valuebasis.RefertoLeaflet400,para2.2for definition of Grade A details. 1.5Theallowableultimatestressesorloadsmustnotbeexceededatthedesign ultimate load, normally 1.5 times the maximum load in the design case (the design limit load). 1.6Thestructureasawholemustbetestedtothedesignultimateloadand supplementary evidence must be provided that 'B' values are not exceeded.It is, of course, forthedesignertodecidewhatmaterialallowables should be associated with his own design procedure in order that this requirement is satisfied. 1.7In addition, it must be shown that no detrimental deformations occur at loads of at least 75% of the design ultimate load. 1.8It must be shown that these proof and ultimate requirements can be satisfied under the most adverse loading and environmental conditions.For composites these conditions apply with the structure at the most adverse moisture level that is expected to occur during the life. 1.9Flightloadmeasurementsmustbemadeatanearlystagetoconfirmdesign assumptions. 1.10In service a programme of operational loads measurement must be maintained to ensure that any new critical loading actions, are identified so that appropriate action can be taken. 1.11Allcomplianceproceduresandjudgmentsaresubjecttotheapprovalofthe Rotorcraft Project Director (in conjunction with Airworthiness Division, RAE). 1.12Definitions are given in para 7. 1.13Advice on compliance with these requirements is given in Leaflets 200/1 to 200/4. Page 1 DEF STAN 00-970 PART 7/2 SECTION 2 2DESIGN CASES 2.1Forthepurposeofdesignandofdemonstrationofcompliancewiththedesign requirements, a limited number of discrete design cases are prescribed for which the loads and other conditions are specified.They are defined in the appropriate Leaflets of this publication. 2.2Theloadsassociatedwitheachcasemustbetracedthroughthestructurefar enoughtoensurethattherequirementsaresatisfiedeverywhere.Manyofthecases overlap,andthewholestructureneednotbe analysed for every one.When it can be shown that a particular case is covered by other more stringent requirements, it need not be considered any further. 2.3There may be cases that are more demanding of some designs than those defined in this publication.When such a case is identified it must be defined and then compliance with the requirements must be demonstrated in that case also. 3THE ULTIMATE STRENGTH AND PROOF REQUIREMENTS 3.1In general the ultimate factor shall be 1.5 and the proof factor shall be at least 1.125. In some particular design cases different values are required and they are given in the appropriate Leaflets of this publication. 3.2Until the design proof load is reached, no Grade A items shall sustain deformation detrimentaltosafety,andmovingpartsessentialtosafetyshallfunctionsatisfactorily.Afterremovalofthedesignproofloadnoeffectsofloadingshallremainthatmight reasonably cause the rotorcraft to be deemed unserviceable. 3.3Until the design ultimate load is exceeded, no Grade A item shall collapse, and the stress, load or strain at each detail shall not exceed the static allowable value. 4SUBSTANTIATION OF THE STATIC ALLOWABLE STRESS FOR GRADE ADETAILS 4.1All static allowable values must be based on nominal dimensions unless adverse tolerances significantly affect the strength. 4.2Theallowablemustbedeterminedunderthemostadverseloadingand environmental conditions arising in the critical design case for the detail in question. 4.3The derivation must be based upon a strength no greater than the 'B' value for the critical failure mode of the material from which the detail is made, using an acceptable method of structural analysis. 4.4Ingeneralthematerial'B'valueforeachmodeoffailureshouldbederivedin accordance with DEF STAN 00-932.Should this be impractical the value shall be based upon at least 15 coupons.These must be tested under the most adverse environmental conditions if these conditions significantly affect the strength. Page 2 DEF STAN 00-970 PART 7/2 SECTION 2 4.5When only 15 material coupons are used these must comprise at least 5 samples from each source of supply and at least 3 batches of material from each source.Similar representative samples must be used if larger numbers of coupons are tested. 4.6Exceptionally,itmaybeacceptabletoallocateallowablevaluestoindividual batches of material: in circumstances where the mean strength of the material varies from batch to batch, but the coefficient of variation (cv) (based on individual batches) remains reasonably constant, the 'B' value for a detail in a given batch of material must be reduced if the mean of the batch in question is lower than that of the batch on which the reference 'B' value is based in accordance with (paras 4.3 and 4.8).No increase in the reference 'B' value is permissible unless it can be shown that other failure modes do not thereby become significant. 4.7METHOD OF STRUCTURAL ANALYSIS 4.7.1Themethodofstructuralanalysismust be substantiated by test for each class of structural detail for which the method has not already been verified. 4.7.2Toverifytheanalysisatleastonespecimenrepresentingthedetailin questionmustbetestedunderthemostadverseloadingandenvironmental conditions specified for design.The value of strength so obtained must be reduced inordertoobtainanacceptableestimateofthe'B'valueforthetestspecimen (Table 1), and where appropriate a further allowance must be made for differences between the test specimen and the structural detail itself.The size of the reduction factor of Table 1 depends upon the failure mode that is observed, the variability associated with this failure mode and the number of coupons used in establishing that variability (paras 4.4 and 4.5).In general, the larger the sample of coupons upon which the variability is based the smaller the reduction factor. 4.7.3It is possible that the overall airframe static test adequately exercises some of the Grade 'A' details and a separate detail test may not be necessary.Indeed it may be difficult to apply the correct boundary conditions to the detail test. 5DEMONSTRATION OF COMPLIANCE WITH THE ULTIMATE STRENGTH AND PROOF REQUIREMENTS FOR COMPLETE STRUCTURES OR COMPONENTS 5.1Usuallycompliancemustbedemonstratedbytestingacompletestructureor component. Exceptionally such a test may be deemed unnecessary.In these circumstances an appropriate allowance must be made for the added uncertainties that are involved. 5.2Thetestprogrammeandtheresultsofthetestsmustbediscussedwiththe Rotorcraft Project Director (in conjunction with Airworthiness Division, RAE). 5.3To allow for the variability in strength between nominally identical items, a test factorappropriate to each test shall be determined from Table 2.The factors given in Table 2 correspond to a 'B'level of assurance normalised to the variability test factor of 1.0 that is customary for metal structures. Page 3 DEF STAN 00-970 PART 7/2 SECTION 2 6MEASUREMENT OF LOADS ON ROTORCRAFT STRUCTURES 6.1Measurementsoftheloadsandtemperaturesontherotorcraftstructureduring manoeuvresinflightandontheground,toanextenttobeagreedwiththeRotorcraft Project Director (in conjunction with Airworthiness Division, RAE), shall be made on one ormoreearlydevelopmentrotorcraftandonServicerotorcraftasrequiredbythe appropriate Leaflets of this publication. 7DEFINITIONS 7.1COUPON The simplest form of test specimen suitable for obtaining the properties of a materia


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