US3635590A - Propeller - Google Patents

Abstract

A marine propeller having a convex shape on the blade rearward surface extending from the blade leading edge and terminating intermediate the blade leading edge and trailing edge, and a substantially planar forward blade surface, whereby the major portion of thrust from the blade is derived from the convex rearward surface of the blade.

Description

O 1 United States Patent 1 1 39035150 Phillips Jan. 1, 1197 54] PROPELLER 3,333,817 21/!967 Rhomberg ..416/242 Inventor: Adrian Phillips, 14 Deer Park Crescent 3,514,215 5/1970 wllllams ...4l6/242 onfamacanada FOREIGN PATENTS 0R APPLICATIONS [221 Filed 1970 383,040 12/1907 France ..4l6/242 [211 App]. No.: 11,382 1,183,498 1/1959 France ..4l6/223 521 11.5.01 ..416/223,4l6/242,4l6/243 g Z '59 T Mb 51 Int. Cl ..B63h 11/26 m 1 [58] Field of Search ..4l6/242, 237, 223, 243, 234,

416/235 ABSTRACT A marine propeller having a convex shape on the blade rear- [56] References Cted ward surface extending from the blade leading edge and ter- UNITED STATES PATENTS minating intermediate the blade leading edge and trailing edge, and a substantially planar forward blade surface, 1,068,946 7/1913 Taylor X whereby the major portion of thrust from the blade is derived 1 1 1 8/1933 Ostfia at from the convex rearward surface ofthe blade. 2,161,932 6/1939 Peters0n..... 416/235 2,236,494 3/1941 Albers 416/223 6 Claims, 4 Drawing Figures DIRECTION OF ROTATION PATENTEDJAIHB m 3.635590 PITCH LINE FIG. 1

( PRIOR ART) VESSEL VELOCITY Vv DIRECTION OF BLADE VELOCITY v5 DECREASE-ID ROTATION PRESSURE 1 v 14 FIG. 2

PRIOR ART) i INCREASED PRESSURE E -E I DIRECTION OF K ROTAT'ON 8 DECREASED PRESSURE INCREASED PRESSURE FIG. 4

- .\'Vi;l"-- 7 7R ADRIAN PHILLIPS Agent PROPELLER BACKGROUND OF THE INVENTION This invention relates to marine propellers and is particularly directed to an improved marine propeller blade.

The design of conventional marine propellers is based on aerodynamic principles whereby the face, or rearward surface of each propeller blade is usually flat in section and the for ward surface is convex in section, providing the blade with a positive camber. In operation, rotation of a marine propeller about its hub causes the propeller blades to move through the water at a pitch angle relative to the plane of rotation of the propeller resulting in the generation of a positive pressure on the flat rearward surface of the blade and a negative pressure over the forward surface of the blade, the latter negative pressure providing about two-thirds of the thrust obtained. The propeller blade usually is evenly cambered between the leading and trailing edges in order to reduce peak levels of negative pressure over the forward convex surface.

A number of major problems arise from the application of these principles to marine propeller design. The pressure drop induced over the upper forward surface of the blades promotes cavitation, particularly at blade speeds of above 30 feet per second. This cavitation can and often does result in blade damage, turbulence and drag, and undesirable vibratron.

The down-wash caused at the trailing edges of the blades by the convex contour of the forward blade surface results in an induced angle of attack of the blades relative to the direction of flow of the water medium. This induced angle of attack produces a drag component which acts in opposition to the torque provided to the propeller shaft to impede rotation of the propeller through the water medium.

Efforts have been made to reduce extremes of negative pressure created on the convex forward blade surface such as by increasing the length of the transverse chord of the blade to produce a more gradual rate of camber. However, the resulting increased blade surface area has been found to augment blade surface drag, particularly at higher blade velocities.

SUMMARY OF THE INVENTION I have found surprisingly that the foregoing disadvantages inherent in conventional marine blade design can be substantially minimized by providing to the blade rearward surface, taken in transverse cross section, a convex shape commencing at the leading edge thereof and terminating intermediate the leading edge and the trailing edge, preferably terminating about one-third of the chord length from the leading edge, whereupon the blade assumes a planar shape extending to the trailing edge, and an upper forward surface substantially planar in shape, preferably having a slightly convex shape at the leading edge extending back a short distance from the said leading edge. This blade design has been found to provide generation of an increased positive pressure on the convex rearward surface and a relatively slight negative pressure over the forward substantially planar surface whereby the major portion of the resultant thrust is derived from the said positive pressure.

It is a principal object of the present invention therefore to provide a marine blade design producing the major portion of thrust from positive pressure exerted by the rearward surface of the blades on water, instead of utilizing negative pressure on the forward surface of the blades, thereby minimizing cavitation.

It is another object of the invention to provide a marine propeller having a blade shape which provides maximum water displacement in a restricted zone in proximity to and coextensive with the leading edge of the propeller blades, thereby permitting increase of the area of planar surface desirable for streamlining water flow in order to reduce turbulence due to trailing edge vortices normally inherent in conventional blade design. This substantial elimination of trailing edge vortices is effective in minimizing the induced angle of attack, and consequently minimizing induced drag.

Another object of the invention is the provision of a marine propeller providing improved propulsion efficiency.

BRIEF DESCRIPTION OF THE DRAWING These and other objects of the invention and the manner in which they can be attained will become apparent from the fol lowing detailed description of the drawings, in which:

FIG. 1 is a transverse section of a conventional marine propeller;

FIG. 2 is a graphical illustration of pressure distribution about the blade shown in FIG. 1, as the blade is pivoted through a water medium about a propeller hub;

FIG. 3 is a transverse section of a propeller blade of the present invention; and

FIG. 4 is a graphical illustration of pressure distribution about the propeller blade shown in FIG. 3, as the blade is pivoted through a water medium about a propeller hub.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference to FIG. 1 of the drawing, the conventional marine blade shown is arranged at a pitch angle P relative to the direction of rotation of the blade measured from the blade pitch line which is coincident with the chord line formed by the rearward surface 10 of the blade. It will be understood that the vectors indicated relate blade velocity V,,, in the direction of rotation of the propeller, to the vessel velocity V,, subte nding an angle [3 and hypotenuse V, for relative water velocity. The angle or indicates the blade angle of attack.

FIG. 2 shows the sectional area of decreased pressure coextensive with the convex forward surface 14 of the blade illustrated in FIG. 1. Two-thirds of the total lift affecting the blade is derived from the said negative pressure, resulting in undesirable characteristics such as cavitation and turbulence inherent in conventional blade design.

FIG. 3 illustrates the blade section of my invention in which the cord line indicated connects the blade trailing edge 18 to the blade leading edge 20. The pitch line coincides with the flat portion 24 of the rearward surface of the blade aft of convex portion 26 which commences at the leading edge 20 and terminates at a longitudinal line designated by numeral 28. Convex surface 26 is shown to extend back from the leading edge approximately one-third of the chord length. The length of the convex surface portion 26 can be varied as desired, it being preferable to maintain a relatively long planar portion 24, i.e., at least one-half of the chord length, to minimize turbulence and trailing edge vortices. The radius of curvature of convex portion 26 can be varied for particular propeller applications, depending primarily on the thickness ratio of the blade section.

The forward surface of the blade is substantially planar, having a flat portion 30 and a slightly convex portion 32 in proximity to leading edge 20. Forward surface portion 32 is joined to convex rearward surface 26 by a rounded leading edge. It will be understood that the forward surface can be flat with no convex portions such as designated by numeral 32.

FIG. 4 illustrates the relatively small area of decreased pressure on the forward surface of the blade and the relatively large area of increased pressure coextensive with the convex rearward surface portion 26 of the blade. As the majority of thrust is provided by this increased pressure, i.e., positive pressure, cavitation due to negative pressure is reduced. The flat surface portions 24 and 30 of the blade permit the negative and positive pressures to return to static pressure in a uniform manner from the trailing edge 18 of the blade, thereby minimizing turbulence and trailing edge vortices.

What I claim as new and desire to protect by Letters Patent of the United States is:

I. A marine propeller blade having a leading edge and a trailing edge and a rearward high pressure working surface and a forward surface, comprising: said blade rearward surface having a convex shape commencing at the leading edge of the blade and terminating intermediate the leading edge and trailing edge, whereupon the rearward surface assumes a one-third of the chord length between the leading edge and the trailing edge thereof. 1

5, A marine propeller blade as claimed in claim 1 whereby the major portion of thrust provided by the blade moving through water is produced by positive pressure exerted by the blade rearward surface on the water.

6. A marine propeller blade as claimed in claim 4 whereby the major portion of thrust provided by the blade moving through water is produced by positive pressure exerted by the blade rearward surface on the water.

Claims (6)

1. A marine propeller blade having a leading edge and a trailing edge and a rearward high pressure working surface and a forward surface, comprising: said blade rearward surface having a convex shape commencing at the leading edge of the blade and terminating intermediate the leading edge and trailing edge, whereupon the rearward surface assumes a planar shape extending at least onehalf of the chord length to the trailing edge, and said blade forward surface having a substantially planar shape between the said leading edge and trailing edge.

2. A marine propeller blade as claimed in claim 1 in which said leading edge is rounded.

3. A marine propeller blade as claimed in claim 2 in which the blade forward surface is slightly convex at the leading edge.

4. A marine propeller blade as claimed in claim 3 in which the rearward surface has a convex shape for approximately one-third of the chord length between the leading edge and the trailing edge thereof.

5. A marine propeller blade as claimed in claim 1 whereby the major portion of thrust provided by the blade moving through water is produced by positive pressure exerted by the blade rearward surface on the water.

6. A marine propeller blade as claimed in claim 4 whereby the major portion of thrust provided by the blade moving through water is produced by positive pressure exerted by the blade rearward surface on the water.

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