Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 “TABLE520.0-11. om vibration test crlt.sma . . for aircraft eauirmenk. mLAwxAr Use table 514.3-III with these‘modifications: K = 6.8 x 10-9 for aockpit panel equipment and equipment attached to structure”‘ in compartments adjacent to external surfaces that are smooth, free from discontinuities”. K . 3.5 x IO-8 for equipment’attached”to structure in compartment adjacent to or immediately aft of external surfaces having discontinuitieg (cavities, chines, blade antennaa, speed brakes, etc.) and equipment in wings, pylons, stabilizer, and fuselage aft of trailing edge wing root.
If Mach number ‘ignot in the range of 0.85 to 0.95 the calculated levels caribe reduced by 5 dB. For propeller aircraft and helicopters, use appropriate tables in method 514.3 of MIL-STD-810. For these segments with the same vibration spectrum shape, the fcllowing ., analysis can be used to reduce the number of vibration test levels. The discussion is in terms of the suggested spectrum shapes for jet, rotary wing “cr’ propeller aircraft of method 514 of MIL-STD-810. For test purposes a WO vibration level for each mission segment can be determined using the altitude and Mach number plots for each mission.
(Note:‘ For test purposes the larger of WO due to aerodynamic or WO due to jet engine noise is utilized at any point in time in the mission.) The maximum WO value that occurs in each missicn shall be identified. All segments of the missicn that have Wo values within three dB of the maximum shall be considered, for test purposes, ae having a constant Wo value determined using the value of WOMAX -3 LiB. All segments of the missicn that have dynamic pressure valuea between WO~x -3 dB and WOMAx -6 dB shall be considered for test purpcses as WOMAx having a ccnstant Wo value determined using the value cf WOMAx -4.5 dB.
This prccess of identifying three-dB bands of dymmic pressure values, over which WO is considered to be a constant and whcse value is determined by using the dynamic pressure values of the band’s midpoint, is continued until the calculated WO value is less than O .001. Fcr test purpcses, segments cf the mission with calculated values of WO less than 0.001 can be set equal to 0.001 unless the test facility can contrcl below this test level. The value.of W1 reflects the changes in aerodynamic flow field around the aircraft.
A cruise W1 value reflects normal angle of attack flight, while a maneuver W, value reflects highly separated flew conditions which induce intense low-frequency aircraft vibration. M2THOD 520.0 19 July 1983 520.0-10