I Downloaded from https://www.everyspec.com J41L-STD-8”1 OD ‘:19-July.1983 b. Test dur@.m. Test durations should be developed from flight measurement or field data. Refer to appendix 1 for guidanoe,in developing test durations from field data. If field data are not available for development of the,test duratione, then the.test levels of table 514.3-III and guidance .. dia~ussed in I-4.3, I-4.6, 14.7, I-4.8, and I-4.9 apply. These levels represent’maximum actual operating conditions and are functional test levels. ., The requirements of paragraph I-3.2.12 also apply. c,.‘“~st setw. See’test setup”criteria, paragraph I-4.11. .., .. ., I-3~2.6 krv 6 - Htionter aircraft/~. .: .,..,,.
Helicopter vibration iS ~: characterized by broadband random with superimposed strong vibration peaks, as depicted in figure 514.3-28. ,... These peaks’are generated by the rOtatinS ., components ih the helicopter, such as the main an~ “tailrotors, engines and .. . ...... gear meshing. The operating speeds of these oomponents under flight conditions” are:essentially constant, varying by only about five Percent. , -. The’relative levels of these peaks differ thruout the helicopter, depending on. the’proximity of the sources, geometry of the aircraft, and location of the test item. Thus, the need for measured data is especially acute.
‘ An obvious requirement for helicopter equipment design is to avoid ? match or near match between an item’s–resona’ntfrequencies’and ‘theexcitation‘frequenciesat the installment location. The major peaks in the helicopter vibration spectrum are usual1y associated.with the main rotor. However, each.type of helicopter will have different sources within-different areas of each aircraft. Since tbe vibration environment is dominated by discrete frequency peaks, it is logical to use some of these,freq~encies for exposure in the laboratory test. Normally about four.frequencies are.ctiosen.for”.the t“e’its.For)equipmeritmouritedon engines, refer to paragraph I-3.2.4.
For equipment exposed to gunfire, refer e to method 519. a. -t leve~. For the reasons stated above, the test levels for equipment installed in helicopters should be derived from field measurements. When measured data are not available, the test levels can be selected from table 514.3-IV. These levels are’an attempt at enveloping potential worst- caae environments. They do not represent environments‘underwhich vibration- sensitive equipment should be expected to perform to specification. Costs for many devices are a strong function of the performance requi~ed in a particular vibration environment.
Consequently,.performance vibration levels”should be ., tailored to particular application” and are not appropriate for a general standard. For testiru?rnmDoses’,the aircraft can be divided into-three zones, -.. . shown in figure 514.3-29.,’All equipment locations included:in a vertical projection of the”main rotor disc should use the source frequericiegof the main rotor for the values of L 1, L2, L3, and L4 at frequencies F1, F2, F3, sridF4. For equipment that will be located in the horizontal projection of the tail: rotor disc, use the source frequencies of the tail rotor as the values of L1, L2, L3, and L4.
The ‘fundamentalmain and tail rotor source.frequencies; F1,, for a few helicopters are given in tab+e 514.3-V. All equipment located on drive train components such .as..gearboxes and .driveshafts Should use the ; .. source frequencies of that drive tra”incomponent (i.e., gear mesh frequencies, shaft rotational speeds). ,, , ; ,,,.j-i ,.:. ,, ,.. b. Test durati.m. Test durations shall be derived from the field measurements and actual flight characteristics and ,durations. ... .,. . t, ,... ,:..+. .s,’~’.‘,, .-.. .. . !, . !.. .NETHOD,514:3 -:19” July,1983 514’:3-40