Abstract
Expressions for the vibratory pressure field produced by an operating counterrotating propeller system are developed in terms of first and second blade harmonics of the individual propellers. It is found that the pressure signal due to a counterrotating propeller can be obtained from the summation of the pressure fields of its two components as though the two propellers operate as separate units, since their mutual interference has been found to contribute little to the total vibratory pressure signal in the near field. This study indicates that the counterrotating propeller system has vibratory characteristics much superior to an equivalent single propeller having the number of blades of one of its components, delivering the same thrust at the same RPM at optimum conditions. A study of the interference effects by means of a two-dimensional analogue indicates that the effect of the forward propeller on the aft is much greater than the effect of the aft propeller on the forward propeller.
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