In 1966 it was shown that the maximum factor by which the amplitude of forced vibration of blades can increase due 10 mistuning is, with certain assumptions, 1/2(1+√N), where N is the number of blades in the row. This report gives a further investigation of the circumstances when this factor can be obtained. These are, small damping, and a relationship must hold between the mistuning distribution γ(s) and the interblade coupling function c(r), where r is the mode number. The mistuning distribution must be symmetrical about the blade on which maximum amplitude is to occur, s=0. The coupling function must be symmetrical about r=R, where R is the mode number of the excitation.
If the coupling is purely mechanical, additional conditions apply. The coupling function c(r) must consist of a number of identical symmetrical sub-strips. A 1976 result for mechanical coupling is amended.