US1107101A - Propeller. - Google Patents

Description

C. A. PARSONS.

PROPELLBR. APPLIOATIQN FILED JULY 26, 1913.

Patented Aug. 11 1914.

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ATTORNEYS G. A. PARSONS.

PROPELLBR.

APPLICATION FILED JULY 25, 1913. l

Patented Aug. 11, 191

2 SHEETS-SHEET 2.

iNVENTQR CHARLES ALGERNON PARSONS, OF NEWCASTLE-UPON-TYNE, ENGLAND.

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Specification of Letters Patent.

Patented Aug. 11, 1914.

Application filed July 25, 1913. Serial No. 781,202.

To all whom it may concern:

Be it known that I, CHARLEs ALGERNON PAnsoNs, a subject of the King of Great Britain and Ireland, residing at Heaton Works, Newcastle-upon-Tyne, in the county of Northumberland, England, have invented certain new and useful Improvements in and Relating to Propellers, of which the following is a specification.

This invention relates to improvements in propellers and particularly to propellers designed for propulsion of modern high speed vessels.

It is well known that in order to carry the thrust necessary for such high speed vessels it is essential that the projected blade area of the propeller shall represent from 50 per cent. to 90 per' cent. of the disk area of the propeller. Such propellers, however, are less efficient at all the low speeds than the propellers with narrower blades of the typ usual in former years. A

The object of the present invention is to provide a propeller of improved form which, when applied. to the modern conditions for high speed vessels shall give a greatly increased efficiency. This object is attained by giving the leading edges of the propeller blades a Scimitar or thrown-back configuration, and combining this configuration with a sufliciently large blade thrust area of from 50 per cent. to 90 per cent. of the disk area as above described. Scimitar blades have been previously proposed, but without success, and my invention requires a large thrustarea in addition to the specially shaped edge. A. ropeller according to this invention there ore has blades of large area and a leading edge to each blade so shaped as regards the whole or the outer part only thereof that the component of the velocity of entry of the edge or of the-outer part thereof into the surrounding medium in the direction normalto the edge is approximately constant. It is generally advisable that this constant velocity shall be kept small especially over the outer edge of the blade, and should not exceed one-third of the peripheral velocity of thetip of the blade. I have found by experiment that one of the chief causes of loss in cavitation is the formationof vortex spirals produced by the flow of water from the pressure to the suction side over the outer portions of a propellerblade. These spirals form a sink of energy drawn from the propeller blade -which energy is absorbed by the eddying motion of the fluid upon theextinction of such vortices. The shape of the leading edge of a propeller blade is therefore of great importance in regard to the efliciency of a propeller. I have further found by experiment that the shaping of the whole or the outerpart of the leading edge of a propeller blade in the foregoing manner owing to the more gradual cutting of the edge through the fluid which is thereby obtained, diminishes the formation of such spirals and the consequent loss of energy.

Referring now to the accompanying drawings :-Figure 1 illustrates a method of. setting out the projection of the edge. Fig. 2 shows the projected view, and expanded view of one blade, of a propeller constructed in accordance with the invention. Fig. 3 shows a plan view, Fig. 4 a longitudinal section through the boss and one of the blades, and Fig. 5 sections of the blade on various radii of the propeller shown in Fig. 2.

The value of the constant component of the velocity of the blade normal to the leading edge may be chosen to suit the conditions of the case, but generally it is preferred to make this not more than one-third of the tip speed of the propeller. The constant component of the velocity into the surroundin medium in the direction normal to the edge of' the blade is the product of the velocity in a helical direction of. any point on the curve multiplied by the cosine of the angle a which the true curve makes with the perpendicular from that point to the axis of the propeller. The value of cos a can be ex pressed in terms of the tangent of the projected angle 1), and the value of the component is then given by the expression,

the projected curve shown in-Fig. 1 and any of the lines 0 P. By these means the value of g5 for any point on the curve is easily calculated for which purpose the foregoing expression may be rewritten.

A sufiiciently close approximation to the curve of the leading edge of the blade may be obtained by neglecting the slip S in which case the following simplified expression may be used.

(11" by 'r' the value of is-obtained in terms of by dividing 1' at any point, and the value of in terms of r can be deduced therefrom by integration. The curve of the projected leading edge is plotted as shown in Fig. 1 by the intersection of a series of equidistant concentric circles with radii drawn for the corresponding values of determined as above.

The extreme diameter of the propeller, pitch ratio, projected surface ratio, diameter of the boss and number of blades can be varied as desired and are determinable in the usual way, as for propellers of normal shape. The curve of the leading edge having been determined as above, the trailing edge can be drawn by striking 'a fair curve from the tip ofthe propeller t0 the boss in such amanner as to give the necessary projected area to suit the thrust and speed for which the propeller is designed.

A three-bladed propeller in accordance with this invention is shown in Figs. 2 to 5 of the accompanying drawings,Fig. 2 showing a projected view of the three blades on a plane at right angles to the axis of rotation also an expanded view of the upper blade indicated by-dotted lines. This propeller has a uniform pitch equal to its dlameter, and in Fig. 3 the plan of one blade is shown, together with the projections of the pitch helices which would betraced upon the surfaces indicated by the semi-circles numbered 1 to 8 in Fig). 2. Fig. 4 shows a section through the oss together with a section through one of the blades upon a line drawn from the boss to the tip approximately through the middle of the blade. A side View of the upper blade is also shown in projection.

In Fig. 5 the true sections of the blade upon surfaces indicated by the semi-circles 2 to 8 of Fig. 2 are shown, the sections being numbered to correspond with the surfaces upon which theyare taken.

The formation of blade as hercinbefore described induces a more regular stream line motion of the fluid around the blade, and thus diminishes its resistance as a body moving through the fluid. Such a propeller has a considerably improved efiiciency at'high speeds, and high thrusts with which cavitation usually occurs, but I also find that this improvement is obtained at low speeds and small thrusts at which no cavitation occurs.

With a propeller blade constructed in the foregoing manner a line drawn approximately through the middle of the blade slopes back in a projected view at a large angle from the radius, and this median line in the projected view may be approximately an equi-angular spiral. The shape of the blade may be modified for the sake of strength in the portions near the boss without appreciably affecting the ellicicney of the propeller, provided that the leading edge is substantially shaped in the above manner at its outer portion, where the peripheral velocity is high. Also other modifications may be made, for instance, the propeller may be of uniform or varying pitch, or its generating line may be inclined backward or forward to the axis of the propeller.

Having now fully described and ascertained my invention and in what manner the same is to be performed, I declare that what I claim is A propeller having blades of large area and a leading edge to each blade so shaped as regards the whole or the outer part only thereof that the component of the velocity of entry of the edge or of the outer part thereof into the surrounding medium in the direction normal to the edge isv approximately constant, substantiall as described.

In testimon whereof I a x my signature in presence 0 two witnesses.

CHARLES ALGERNON PARSONS.

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