Patent Application
20180105240
The present invention relates generally to marine propellers and, specifically, relates to a metallic hub and blade assembly with composite blades.
Marine propellers have traditionally been cast or forged of metal and the hub and blades were formed as a single unitary part. This design provided strength and reliability that the blades would not come loose from the hub. Disadvantages include that if the blade struck a foreign object, enormous forces could be transmitted through the metal blade and hub to the drive shaft, possibly bending it or damaging its mounting. Also the blades are heavy. Damage to even one blade required replacement of the entire assembly because the blades and hub formed a single piece.
Molded plastic propellers were developed. U.S. Pat. No. 4,930,987 discloses marine propeller blades including, at their roots, a root portion that slides axially into a re-entrant cavity that extends axially in the hub. End caps prevent axial removal of the blade roots from the hub. This makes it possible to replace an individual damaged blade, and the hubs are interchangeable from ship to ship, although the blades may vary slightly. All of the parts are injection molded of a high-strength fiber-reinforced plastic.
It is desirable to provide marine propeller assemblies with light-weight blades securely attached to metallic hubs.
A marine propeller blade includes a composite propeller blade with an axially extending composite blade root with a dovetail wound in a partial spiral or helix around a centerline. The dovetail tapers down in width between clockwise and counter-clockwise dovetail sides of the dovetail from a dovetail bottom in a radially outwardly direction away from the centerline. The composite propeller blade may include a blade suction or forward side and a pressure or aft side extending from the blade root to a blade tip.
A marine propeller includes a metallic hub and blade assembly with composite blades having axially extending composite blade roots mounted in axially extending hub slots in a metallic hub. Axially extending wedges are disposed within the hub slots circumferentially between the blade roots and one of clockwise slot sides and counter-clockwise slot sides and the wedges abut the blade roots and one of the clockwise slot sides and counter-clockwise slot sides. A radial retention means may be used for radially retaining and securing the wedges in the hub slots such as bolts engaging the wedges and screwed into threaded holes in the hub at a slot bottom of the hub slot.
Each blade root may include a dovetail wound in a partial spiral or helix around the centerline and the dovetail tapers down in width between circumferentially spaced apart clockwise and counter-clockwise dovetail sides of the dovetail in a radially outwardly direction away from the centerline.
Each wedge may taper down in width between clockwise and counter-clockwise wedge sides in a radially inwardly direction from a wedge outer surface towards the axis or centerline of the hub and the dovetails and the wedges may be wound in partial spirals or helixes around the centerline. A first one of the clockwise and counter-clockwise wedge sides may abut and be flush and conformal with a first one of the counter-clockwise dovetail sides respectively, a second one of the clockwise and counter-clockwise wedge sides may abut and be flush and conformal with a second one of the counter-clockwise dovetail sides respectively, an obtuse dovetail angle may extend between a second one of counter-clockwise slot sides and a slot bottom of the hub slot, and an acute dovetail angle may extend between a first one of the counter-clockwise slot sides and the slot bottom of the hub slot. The hub slots being wound in partial spirals or helixes around the centerline.
Each composite propeller blade may include a blade suction or forward side and a pressure or aft side and a blade tip representing a maximum reach of the composite propeller blade from the centerline and separating leading and trailing edges of the blade.
A marine propeller metallic hub may include hub slots axially extending through a metallic hub for receiving blade roots of blades and the hub slots being wound in partial spirals or helixes around a centerline of the hub. The hub slots may include circumferentially spaced apart counter-clockwise slot sides and a slot bottom therebetween, an obtuse dovetail angle extending between a second one of the counter-clockwise slot sides and the slot bottom, and an acute dovetail angle extending between a first one of the counter-clockwise slot sides and the slot bottom. The metallic hub being conical or cylindrical.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is described in the following detailed description taken in conjunction with the accompanying drawings in which:
Illustrated schematically in
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The dovetail 26 has a radially inner or dovetail bottom 36 which is complimentary and conformal with the slot bottom 38 of the hub slot 20. An acute dovetail angle 54 extends between one side of the hub slot 20, illustrated herein as clockwise slot side 50 and the slot bottom 38 of the hub slot 20. The same angle extends between the clockwise dovetail side 30 and the dovetail bottom 36 of the dovetail 26. This helps radially retain the dovetail 26 of the blade root 18 in the hub slot 20. The dovetail 26 illustrated herein includes the same acute dovetail angle 54 between the clockwise and counter-clockwise dovetail sides 30, 32 and the dovetail bottom 36 of the dovetail 26.
The wedge 22 is characterized by slanted circumferentially spaced apart axially extending clockwise and counter-clockwise wedge sides 60, 62. The wedge 22 includes a wedge outer surface 58 from which the wedge 22 tapers down in width W between the clockwise and counter-clockwise wedge sides 60, 62 in a radially inwardly direction towards the axis or centerline 48 of the hub 28. A first wedge side, illustrated herein as the clockwise wedge side 60, abuts and is flush and conformal with the counter-clockwise side 32 of the dovetail 26. An obtuse dovetail angle 56 extends between a counter-clockwise slot side 52 and the slot bottom 38 of the hub slot 20. A second wedge side, illustrated herein as the counter-clockwise wedge side 62, abuts and is flush and conformal with the counter-clockwise slot side 52 of the dovetail 26.
The hub 28 and the hub outer surface 40 of the hub 28 may be cylindrical. In such a case, the hub outer surface 40 would have a constant diameter D from the upstream or forward end 42 to the downstream or aft end 44. The blade roots 18, hub slots 20, and wedges 22 would wind around the centerline 48 in helixes less than 1 full turn which is 360 degrees and extend axially from the upstream or forward end 42 to the downstream or aft end 44.
While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims.
