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I'm trying to perform some flutter and dynamical (gust etc.) calculations with Nastran. It has been told to use a range up to 30 Hz for an aircraft I'm working with, but why the upper limit is so choosen 30 Hz? Why for some aircraft the range is up 60 Hz and for another one even up to 100 Hz? I suppose it depends on matirials used in a particular structure and/or a frequency range of presumed loads. I would be grateful if someone can explain how the frequency range of interest is exactly chosen. Thanks!

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You might want to try reviewing MIL-A-8870C AIRPLANE STRENGTH AND RIGIDITY VIBRATION, FLUTTER, AND DIVERGENCE. The CRJs were certified to this standard. Available here: http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-A/MIL-A-8870C_6746/ Just click the Download File button.

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  • $\begingroup$ Why would civilian aircraft be certified to military standards? $\endgroup$ – ROIMaison May 18 '18 at 7:32
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    $\begingroup$ Yes MIL-SPEC, MIL-PERF and Standards are used across the industry for all sorts of things in the civilian world of aerospace, because traditionally there was always a lot of overlap. Why reinvent the wheel? The old AN standard for aircraft hardware stands for Army/Navy. In the case of MIL-A-8870C, a manufacturer may choose to develop their own analysis for flutter margins, but they can also just use 8870 if they want. $\endgroup$ – John K May 18 '18 at 11:34
  • $\begingroup$ Ah, I always imagined MIL SPEC to be very different requirements (i.e. more or less stringent) than the commercial ones. $\endgroup$ – ROIMaison May 18 '18 at 12:04
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    $\begingroup$ One interesting change in the aerospace industry was a gradual switch from MIL-SPEC to MIL-PERF. MIL-SPEC components are built to a specific physical specification. Under MIL-PERF, a component only has to meet a performance standard. This allows commercial non-aerospace components to be used as long as they meet the PERF standard in performance. Example: around the turn of the century microprocessor makers stopped producing processors made to the old MIL-SPEC. Manufacturers started to use commercial components, allowable as long as they met MIL-PERF requirements. $\endgroup$ – John K May 18 '18 at 16:47

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