Abstract:

ESDU 89047 gives simple semi-empirical methods for estimating the forces and moments on single or contra-rotating propellers inclined at angles up to 20 degrees with the local flow. The results are given graphically as derivatives with respect to the local flow angle, and that must be separately evaluated if forces and moments are required. The graphical data are plotted as functions of thrust coefficient (from 0 to maximum likely) and advance ratio from 0 to 3, for a range of values of solidity from 0.05 to 0.5. The data apply strictly to six-bladed propellers, but the results are found to be insensitive to the number of blades between 2 and 10. For cases where the solidity is unknown an approximate relationship is given to derive values from the total activity factor. Comparisons with test data extracted from the literature suggest the force derivatives are predicted to within 15 per cent and moments to within 40 per cent, but it is felt those are conservative assessments due to the test difficulties of measuring the small forces and moments. A detailed worked example illustrates the use of the data. A computer program of the method is provided as ESDUpac A8947.