§29.931 Shafting critical speed

(a) The critical speeds of any shaft ing m ust be det ermined by dem onstration except that analytical m ethods m ay be used i f rel iable methods of analysis are available for the particular design. (b) If any critical speed lies with in, o r clo se to, t he operat ing ranges for idling, power-on, and autorotative conditions, the stresses o ccurring at that sp eed m ust b e with in safe lim its. Th is must be shown by tests. (c) If anal ytical m ethods are used and show that no critical sp eed lies with in th e p ermissible operating ranges, t he m argins bet ween the calculated critical speeds and th e lim its o f th e allowable operating ranges m ust be adequat e t o allow for possible vari ations bet ween t he computed and actual values.