Variable pitch propeller

Claim 1

An automatic variable pitch variable diameter marine propeller comprising: a central hub defining rotation axis, said central hub having three exhaust ports extending longitudinally therethrough, three radial bores interdigitated with said ports, each of said radial bores receiving one of three propeller blade shafts, and three guide pin bores each receiving one of three guide pins, each of said guide pin bores being parallel to said propeller rotation axis and intersecting perpendicularly with a said radial bore; three propeller blades, each of said blades comprising a said blade shaft and a blade portion, said blade shaft being attached to said blade portion at one end and extending away from said blade portion into a said radial bore, said blade shaft being capable of rotation within said radial bore about an axis of pitch rotation, said axis of pitch rotation being normal to said axis of propeller rotation, said blade shaft having a helical groove in its periphery to receive a said guide pin, said blade portion being configured and attached to said blade shaft such that force due to water pressure on said blade portion defines a center of pressure which is located remote from the axis of pitch rotation; each of said guide pins passing through a said guide pin bore and being recieved by said helical groove wherein, said helical groove defines pitch of the associated said propeller blade by controlling its rotation within said radial bore about its axis of pitch rotation; and synchronization means to synchronize the varying pitches of the propeller blades, comprising a ring rotatably mounted on said central hub, and attachment means locating said propeller blades relative to the ring; wherein said rotation of said propeller blade shaft in said radial bore about said axis of pitch rotation to change the pitch of its propeller blade is accompanied by a change in diameter of said propeller, said changes in pitch and diameter are restricted by the limited rotation of said blade shaft within said radial bore defined by the length of the helical groove and the interaction of said guide pin therewith; centrifugal force acting on said propeller blades due to rotation of said propeller about said propeller rotation axis tends to move propeller blades radially outwardly, to increase propeller diameter, said increased diameter being controlled by said guide pins interacting with said helical groove and resulting in an accompanying increase in pitch of said propeller blade, said force due to water pressure on said propeller blades, when said propeller is rotating about said propeller rotation axis, acting at said center of pressure tends to cause said propeller blade to rotate within said radial bore about said axis of pitch rotation, to tend to cause propeller blades to move inwardly, to decrease propeller diameter, toward said central hub as controlled by said guide pins interacting with said helical groove with an accompanying decrease in pitch of said propeller blades; forces tending to increase pitch and diameter resulting from centrifugal force are opposed by forces tending to reduce pitch and diameter resulting from force due to water pressure acting on said propeller blades such that when these pitch and diameter changing forces are balanced against each other a desired propeller pitch and diameter for existing operating conditions is produced.