The vortex lattice method is applied to calculations of the aerodynamic characteristics of propellers. A blade of the propeller is divided into many trapezoidal panels, and each panel is represented by a spiral horse shoe vortex in which a bound vortex is placed on the 1/4chord line of the panel, and a pair of wake vortices is emitted from the both ends of the bound vortex. The circulation strength of these vortices can be obtained by the boundary conditions which describe the tangency

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... of the flow at 3/4-chord point. The forces acting on each panel are calculated by KUTTA-JOUKOWSKI theorem. Thrust, torque and efficiency of the propeller are obtained by summing up all forces. Although the flow is assumed to be inviscid and incompressible, the effect of displacement velocity, the effect of compressibility by PRANDTL-GLAUERT similarity rule and the effect of drag force introduced into the force calculations using experimental data are examined. Furthermore, utilizing the efficiency of each panel, total efficiency of propeller is improved by increasing or decreasing pitch angle of the blade. The following results are derived by these calculations. (1) The power coefficients agree well with the experimental values for the conventional type of propeller, however, for ATP theoretical values are larger than experimental results. (2) The efficiencies are larger than the experimental values for all types of propeller. Including