..-. --- n.. . CUL-SIV-OIUU Downloaded from https://www.everyspec.com 19 July 1983 The scaling of vibration test conditions from data measured on another aircr,?ft,at a different equipment location, or for a different flight condition has to be done with extreme care because of the numerous nonlinear relationships involved and the limited amount of data being utilized. For example, maneuver-induced vibration conditions generally cannot be predicted from cruise vibration data. A more prudent approach ia to utilize th,elinear dynamic pressure models in method 514. (.
In all casea, measured flight vibration should be in acceleration power spectral density (PSD) format based on one-third octave analysis or 20 Hz or narrower constant-bandwidth analysis. Experience has shown that the use of a standardized vibratiorispectrum ehape and,the modified levels of method 514.of MIL-STD-810 yield as good ,resultsin terms of equipment deficiencies as the use cf the highly shaped vibration spectra (ref. b). Because of the nature of vibration,control equipment, it is difficult to change vibration level and spectrum shape in a continuous, smooth manner.
Therefore, tbe mission profile has to be divided into segments over which it will be assumed that the vibration level and spectrum ahape is constant for test purposes. 1-3.2-2.6 E@@mL&w- The thermal stresses that internally-carried, avionics equipment experiences during a mission are dependent upon the ambient conditions, flight conditions, and,the performance of the ECS. For the purposes of this test, the ambient outside air conditions shall be as ‘shownin table 520.0-111 for the hot, warm moist, and cold day environments. Hot and cold ambient environments of table 520.0-111 are based on the 20 percent worldwide clizuiticextreme envelopes from MIL-STD-21OB, tables XXII and XIII.
The warm moist environment is based on the tropical environment shown in table v of MIL-STD-21OA. These temperatures values are to be used as the ambient conditions for thermodynamic analyses for the development of the mission profile“test conditions. The ground soak temperatu~es in each mission are not necessarily related to measured data. The values shown in table 520.0-111 are extreme conditions that have been,used in Previous programs tc accelerate time and reduce”time between transitions from mission to another.
The specific environmental teat conditions for any teat item are dependent on the type of cooling for the,compartment in which the equipment is to be located (air-conditionedor ram-air,cooled). Avionics equipment systems that consist of more than one black box may require different environmental test conditions for each black box. (For.example, when bcxes are in different aii’crift compartments.) For the common case of a two-black-box system where one box is cooled by supplemental air or fluid and the other box is ambiently cooled, botb boxes can be tested in,one chamber as long as appropriate vibration and altitude simulation for each box can be achieved.
The thermal stimulation would be realistic ,sincethe ambient-cooled box would respond to the ambient temperature simulation while the box that required supplemental cooling would > be primarily responsive to the supplemental cooling air or fluid. METHOD 520.0 ,. 19 July 1983 520.0-9