I Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1963 I-3.2.2.4 ~en tal stresses. The second step is to determine environmental stresses include vibration, temperature, supplemental cooli”ng, humidity, altitude, and electrical stresses.. Test levels for each stress are determined from mission profile information’in the manner described in I-3.2.2.5 thru I-3.2.2.9. Other information, such as engine rpm or data on the aircraft’s environinentalcontrol system (ECS) may also be needed. TABLE’520.0-1. Examvle u ih t ation ratea of on Drofilea. Percent Utl ~ .1.
Ground Attack, Training .40 Ground Attack, Combat 20 Defdnsive Maneuvers 20 Search and Rescue 10 Functional Check Training Cycle 2 Since the first three missions, as a group, total 80 percent of the utilization rate, then these three mission profiles would be selected for combined environment testing. If any of the other missions are determined to include extreme or sustained environmental conditionsnot encountered in the first three missions, then those missions containing these extreme or sustained conditions and adding the most diversity to the test cycle also should be selected.
If the first mission selected is utilized twice ae !nuchas the other two missions,’then Mission 1 should be run twice as much per cycle. I-3.2.2.5 ~ stress. Random vibration shall be applied to all equipment items designated for jet aircraft installation. Random vibration or sine superimposed on random vibration should be used for all equipments designated for propeller aircraft. Vibration of an appropriate level and spectrum shape shall be applied continuously during mission profile simulation in”the test cycle.
Unless measured data exist, it is recommended that the appropriate tables and figures of method 514 of MIL-STD-810 be used to determine vibration conditions except as modified in table 520.0-11. Short duration vibration events and those that occur infrequently need not be included in the test cycle. These eventa include firing of onboard guns, general aircraft motion, and shock of hard landings. These events may be tested separately using the appropriate MIL-STD-8.1Otest method..
The vibration stresses to be considered for the test cycle are those due to both attached and separated aerodynamic airflow along the vehicle’s external surfaces, jet engine noise, or pressure pulses from propeller or helicopter blades on the aircraft structure. The vibration spectrum and level can be determined for each miaaion segment by careful use of measured data. Guidance written below shall be applied in those cases. In many instancea, measured flight data are not available for the specifiic aircraft, equipment location in the aircraft,.or flight phases.
In such cases, there are several analytical technique for vibration spectrum and level prediction that can be ue.edto determine vibration test conditions (ref.’a). t43THOD“520.0‘ 19‘July 1983 520.0-8