MIL-STD-810D Downloaded from https://www.everyspec.com I 19 July 1983 ,., ,,, . , , : . . m I I . i I 20 f-l fz 2000 . Frequency.(Hz) ,. ,., ...’ .,, .. i. ., FIGURE 514.3-33. ti~ested vabutlOn test levels fOr eauimmk . . . . ed n external st~ried on et aircraft. ,1-3.2.9 .. 7C - Assembled exter~ Complex v stor~. periodic waveforms characterize the service vibrati’op,etivironmenten,cotictered by assembled stores externally carried,on helicopters,,,Unlike ‘storescarried on fixed-wing aircraft, externally mounted helicopter.stores receive little aerodynamic excitation, particularly when compared with the rotor-induced vibration.
Thus, most of”the vibratory energy r,eache?the equipment.through the attachment,points between the aircraft and the store. Some excitation,. however, is added along the entire etore struoture due to,periodic rotor-. induced.pressure fluctuations. The result is a complex’response, unique to the particular aircraft-store configuration. Therefore, realistic testing depends almoat totally upon the use of in-flight vibratiOn’measurements! This environment is simulated by exposing the test item to a low-level broadband random spectrum with discrete vibration,peaks at the frequencies and first three “fundamentalsof the aircraft main rotor .(sourc,edwell tes,tintT.,- see paragraph I-4.2.2). ,.
14Aa2L . As stated above, because o~ the 9trong dependency Of the vibration level on the aircraft-store combination, the use of measured data . taken on the store ifx+elf ia recommended for setting the”1evels. The resultirii I teat spectrum shall include exposure based upon the source dwell concepts of I-4.2.2. The suggested vibration conditions from table 514.3-IV qd. figure 514.3-28 can be used for initial testing prior to acquisition of field data. b. I . &d&&k The test duration shall be developed ‘from,flighttest data. Exposure”periods shall be developed by constructing h life cycle based on the measured flight environment, equipment Iife requirements and airoraft mission profiles.
If flight test data are not available, then test durationa can be selected from information provided in I-3.2.12. t@THOD 514;3 19 July’1983 514.3-52