Using two specific arrangements, the operation of a unique class of variable diameter propellers intended for vertical take-off and high-speed (>300 knots) cruise is analyzed and tested experimentally. The freely rotating hub of propellers in this group, subject to opposing torques due to the blades' centrifugal forces and in-plane aerodynamic drags, causes the blades to extend and retract as a result of changes in the latter, achieved here by changing blade pitch. Steady-state analysis and model tests show there are pitch thresholds in which no transition takes place when the propeller is operating at its minimum and maximum diameters. Preliminary dynamical analysis indicates that little or no power beyond rated is consumed during transition; that retraction occurs mainly by the transfer of energy to the airstream and extension by the use of available shaft power, which is momentarily in excess.
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