Downloaded from https://www.everyspec.com MIL-STD-81OC 4 b. Jet engine noise impinging on aircraft structure. c. Gun blast pressure impinging on,aircraft structure from high speed repetitive firing of installed guns~ d. General aircraft motions caused by such factors as minway roughness,” Ianding, and gusts. The tests outlined in this procedure consider all of these environments and require design to the most severe of these. These tests are preferred I for use with equipment in jet aircraft in lieu of the sinusoidal tests of procedure I, table 514.2-II, figure 514.2-2, except for jet engine mounted I equipment. For equipment mounted directly to aircraft jet engines, use procedure 1.
To dete~ine an equipment specific random vibration test, compute functional and endurance,test levels for aerodynamic induced and for jet engine induced vibration from table 514.2-11A and figure 514.2-2A. Use’the more severe of the two functional levels as the equipment’s func- tional test, and the more severe of the, two endurance levels (on an equal time, T, basis) for the equipment’s endurance test. ,, 4.6.2.1 Performance of test. The individiialequipment test item shall be subjected to broadband random vibration excitation. The power spectral density tolerances of applied vibration shal1 be according to 4.5.2. The test item shal1 be attached to the vibration exciter according to 4.2.
Equipment hard mounted in service shall be,hard mounted to the test fixture. Equipment isolated in service shall use service isolators when mounted on - the test fixture. If service isolators cannot be made available during the qualification test, isolators shall be provided with characteristicssuch that the isolator/equipmentresonant frequencies shall be between 20 Hz and 45 Hz with resonant amplification ratio between 3 and 5. Vibration shall be applied sequentially along each of the three orthogonal axes of the test item. Two test levels are required, a functional level and an endurance level.
For,each axis, one half of the functional test shall be conducted first, then the endurance test, followed by the second half of the func- tional test. The equipment shall perform according to the equipment specificationoperating requirements in accordance with General Requirements, 3.2 during the functional testing. The acceleration power spectral density (G2/Hz) of applied vibration, as measured on the test fixture at mounting’ points of the test item, shall be according to table 514.2-11A and figure 514.2-2A. The functional and endurance test time durations and other test conditions shall be determined from the test level.equations and other parameter.valbesfrom table 514.2-11A.
METHOD 514.2 514.2-8