IT is usual when presenting a paper of this nature to start off with an ex cathedra pronouncement that the results of recent research and past experience now make it possible, for critical speeds to be calculated in advance with a degree of accuracy sufficient for practical purposes. I make no such assertion. What I have done is to formulate an analytical solution of the problem of coupled engine crankshaft torsional and airscrew blade flexural vibrations in which the assumptions made, in order to render the problem soluble, are not unreasonable. I fully realize that anyone disposed to be critical will find much to criticize. But I think I can say that my work has elucidated much that was hitherto obscure and that my results may enable designers to ensure better provision against possible trouble. The data and conditions of the problem are by no means precise, and no exact solution seems possible or likely to be forthcoming, either from practical experiment or from theoretical treatment.
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