The method of determining the stresses in rotating disks and cylinders is given in various engineering textbooks. For a disk of varying thickness the form of the differential equation derived in the stress analysis is such that it can only be conveniently applied to disks of particular section, and even then the solution involves tedious arithmetical computation. This method can be applied to disks of practical section by approximating to the section as far as possible by one or more sections of soluble shape. Where the approximation involves more than one section, the method becomes exceedingly cumbersome owing to the number of constants introduced and the laborious arithmetic required in their evaluation. The absence of a ready method of determining stresses in disks of different shape is a decided disadvantage when considering the stresses in fan rotors. The running speeds of fans are frequently such that they impose high stresses in the rotors, and it would be useful to have some method of assessing rapidly the effect on stress both of modifications in the design stage and later of wear in service. A simple method of determining to a fairly close approximation the hoop stresses in rotors containing a central hole is given in this paper. It is shown by applying the method to cases capable of solution by the more exact method that, subject to certain limitations, the likely error in the maximum hoop stress is an overestimate by the approximate method of about 5 per cent.

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