Fluid reaction surfaces (i.e. – impellers) – Radially extensible or retractible rotor working member
Patent
1996-11-18
2000-11-28
Kwon, John
Fluid reaction surfaces (i.e., impellers)
Radially extensible or retractible rotor working member
416142, F04D 2926
Patent
active
061526932
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a folding propeller having a hub and at least two propeller blades which are pivotally mounted in the hub about pivot axes extending radially outwardly from a central area in the hub, said blades being pivotable about their pivot axes between unfolded, radially protruding operating positions in which the propeller during rotation propels the ship through the water, and one passive position in which the shaft does not rotate, and in which the blades extend axially rearwardly in extension of the hub, said blades being adapted to pass each other in said passive position.
The folding propellers used in practice are unique in presenting a very low water resistance when a sailing ship sails forwardly with the engine stopped. The folding propellers have blades which are mounted pivotally in the hub in such a manner that they are unfolded by the centrifugal force to an active position in which the propeller drives the ship through the water when the shaft rotates, and are folded together by the water pressure to a passive position with minimal water resistance when the ship is under sail with the engine stopped, in which position the blades extend rearwardly in extension of the hub.
The folding propeller may be designed with the correct pitch distribution, but the blade weight must be carefully adapted to be able to keep the propeller open when sailing astern. The most popular folding propellers have just two blades, which makes it difficult to obtain a sufficiently large blade area and thus thrust for larger vessels, since the blades will hereby be excessively big and heavy.
U.S. Pat. No. 4,364,711 discloses a two-bladed folding propeller of the type mentioned in the opening paragraph, in which the blades in said passive position extend axially away from the hub with the front side edge of one blade positioned opposite the rear side edge of the other blade, and vice verse, as is also the case in the conventionally used two-bladed folding propellers when the blades are folded together in the passive position. In the propellers of the US document the hub is rotatably mounted on the shaft, so that a transmission mechanism arranged in the hub causes the blade to unfold when the propeller shaft begins to rotate.
In contrast to the propeller known from the above-mentioned US patent Specification, the folding propellers used in practice do not have the front edge of the blade, but the rear edge as the leading one when sailing astern, causing the propellers used in practice to work with reduced efficiency.
Accordingly, there is need for a folding propeller which, in engine propelled navigation, may have the front edge of the blades as the leading one, no matter whether the ship sails ahead or astern, which has the correct pitch distribution and automatically assumes stable positions with an optimum propeller efficiency under the action of the hydrodynamic forces and the centrifugal force.
The novel folding propeller of the invention is characterized in that, in said passive position, all the blades extend axially away from the hub with the same side edge of the two side edges of the blades facing each other.
In said passive position, the blades, seen in a radial section, thus extend in directions radially outwards from the axis of rotation in such a manner that the blade cross-sections divide a circle into angles of equal sizes between them.
Where a two-bladed propeller is involved, the blade cross-sections extend radially outwards to their respective sides from the axis of rotation and preferably extend in extension of each other and thereby divide a circle into two angles of 180.degree..
Where a propeller having three blades is involved, the angles will be 120.degree., in case of four blades they will be 90.degree., and so for.
A special advantage of the invention is that it is possible to provide a folding propeller having three or more blades which is sufficiently compact for it to be used in practice.
In case of navigation ahead as well as astern the folding propeller of the invention may have
REFERENCES:
patent: D141235 (1945-05-01), Birsh
patent: 3589647 (1971-06-01), Burkham
patent: 4364711 (1982-12-01), Brandt et al.
patent: 4768927 (1988-09-01), Munk
patent: 4801243 (1989-01-01), Norton
Ehrenskjold Sune
Olsen Steen Christian
Gori marine as
Kwon John
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