Downloaded from https://www.everyspec.com MIL-STD-81OD. J 19 July 1983 b. ~st dllrati~. The test duration for thisprocedure should be based upon the mechanical setup.of the test equipment, the packaging state of the test,item; and.the desired results of the exposure. A duration of 30 minutes is recommended where several test”items are placed”on a steel package tester bed .and,, allowed to ‘collidewith each other as well as the restraints of the t,estequipment. A duration of 3 hours is recommended where the test item is placed upon a plywood package tester bed and allowed only to collide with the restraints of the,test equipment. ,., . c. .ff.est. setuQ.
The differences in the methods for simulating this environment:are associated‘with the test setup. The setup uses a package tester as.depicted in figure 514.3-24. The fixturing required is as shown and will not secure the item to.t“hebed of the package tester. A vertical impact wall and sideboards as depioted’in figure 514.3-24 shall be implaced to contain the test items on the bed of the packa”getester. The test is intended to simulate the unrestrained collision of the test item with the bed and aidea of the transport vehicle as well ,aswith other cargo. ,.. , .,, . ,,.
For the 30-minute test, the bed “of the package tester shall be covered with a plate of cold-rolled steel 3/16 to 3/8 inch thick. Several test items shall be placed within the enclosure created by the vertical wall and sideboards. The total free space surrounding each test item placed on the’table’of the package tester will be“at leaat 5.o8 cm (2 inches) between the teat item and the opposing sideboards,and any other teat item. All loading configurations (i.e., test items laid horizceitallyor stood on end vertically) deemed practical shall be included in the placement of the test items on the package tester to evaluate the item integrity. ,... :,. .:, ..
.,, For the th,ree-hourtest, the ‘constraintfences are constructed of suitable wood and,are sized for a single test item. The fences shall be positioned so that the horizontal motion”of the test item is limited ‘tonot more than two inches. The bed of the package tester shall be covered with a sheet of 1/2 inch plywood suitably secured by nailing. .,: In both!methods, the test item(s) is placed on the bed of the teat equipment secured in its transit case combination or ak ‘otberwiaeprepared for loQse- cargo fie~d transportation. The test item shall not ‘beoperated during vibration:““ ... APPLICATION VIBRATION I-3.2.4 ~euorv Proueher aircraft.
Service vibration frequency spectra for equipment installed in propeller aircraft consist of a broadband background with superimposed narrowband ‘spikes: The ‘backgroundspectrum results from various random”sources (see 1-3.2.5)”with many periodic (not pure sinusoidal) components due,to the rotating elements (engines, gearboxes, shafts, etc.) aaaociated with turb?props. The spikes are produced by passage of pressure fields rotating with the propeller bl”ade~; These occur in relatively narrowbands centered on the propeller passage frequency (number of blades multiplied by the propeller rpm) and harmonics.
The spectrum for equipment mounted directly on turbine engines is similar to tbe propeller aircraft spectrum except the primary spike frequency is the rotational speed of the rotor(s). 19 July 1983 514.3-31 MSTHOD 514’.3