US1532346A - Propeller - Google Patents

Description

April 7, 1925.

I. L. ROBERTS PROPELLER Filed Oct. 15, 1918 2.Sheets-Sheet 1 A ril 7, 1925.

' I. L. ROBERTS PROPELLER Filed on. 15, 1918 2 Sheets-Sheet 2 Patented Apr. 7, 1925.

ISAIAH I1. ROBERTS, OF

PATENT OFFICE.

uunva essence, ISLE or ruins, wnsr mums; Assrenoa on ONE-HALF T0 WILLIAM G. LIGHTENSTEIN, OF JERSEY CITY, NEW JERSEY.

. ZE'ROPELLER.

Application filed Getohcr 15, 1918." Serial No. 258,166.

To all 107mm it mag concern:

Be it known that I, ISAIAH L. Roennrs, av citizen of the United States, residing at Nueva Gerona, Isle of Pines, West Indies, have invented certain new and useful T111 provements in Propellers, of which the following is a specification. 7

My invention relates to a new and useful propeller for use in propelling ships or boats.

Heretofore all propellers known to me have blades which follow some uniform geometrical formula throughout their entire length and breadth as the screw or inclined plane. In order to get the highest efliciency from this form of propeller the blades must be made thick near the hub and comparatively thin in extension. H

If the blade is supported by a thick arm the support offers'a resistance instead of a help in operation. hen made wide enough to support the blade and thick enough to offer the minimum resistance to passing through the water it offers a large surface to the water when in motion and if the boat does not move forward in unison with the pitch of the propeller the action of all that portion of the propellerblade more orless distant from the hub then acts more or less as a churnor merely whirls the water and thus is consuming power uselessly, It is difficult to keep adjusted thespeed of such propeller to the forward movement of the boat so that high efficiency may be attained and if attained .under favorable engine power and clean boat surface these. conditions are difficult to maintain constantly in practice. Hence in practice owing to change of engine power and to fouling of hull or difference in speed owing to a light or heavy cargo which naturally varies the speed of the boat, propellers now made can notbe uniformly of equal efficiency in practice.

What has been said above is not so true of that portion of the blade from the center or midway out to the end. This portion of a propeller is really the working part and yields vastly more thrust or push to the vessel thanthe portion between the middle of the blade and the hub; so much so that if the blade is made of a uniform width and pitch the thrust increasesv as the square of the distance from the center of the circle described by said blade in turning. Further more, all bladed screw propellers known to me have the widest part of their blades 7 and near their centers and from thence taper moreor less to rounded points, thus losing or failing to secure propelling surface and supporting surface against slip at the most useful and advantageous point in the entire blade.

In all propellers there is a further loss of power due to slipping.

My invention has for its object the design of a propeller which avoids and overcomes to large extent the above'difliculties and increases the efiiciency orthrust of the propeller over a plain screw at all speeds of the boat or propeller.

In order to accomplish these results a radical departure has been made in the general design and construction of my propeller, a description of which follows wherein like letters refer to like parts'in the accompanying drawings in which:

Figure 1 is a plan view of a tar-med propeller;

Fig.2 is an elevation of Fig. 1;

Figs. 3, 4, 5' and 6 are sections on the planes AB, (I -D, EF, and G-'H, respectively indicated in Fig. l;

Fig. 7 is a plan view of a modified form;

Fig. 8 is an elevation of Fig. 7.

Referring to Fig. 1, the propeller is shown as consisting of four blades, 1, 2, 3 and 4, connected by curved arms 5, 6, 7 and S to a hub 9.

The arms 5, 6, 7 and 8 are not only formed on a curved axis, but their rearward or thrust surfaces are concaved or formed as warped surfaces, whose chords are 'set on pitch lines co-ordinating with pitch lines of the helicoidal blades. These concave surfaces are so shaped'in order that they may act as propelling surfaces tending of themselves to act as propellers as well as means for supporting the blades located at their outer ends. The arms 5, 6, 7 and 8 are made with tapering trailing edges, the surfaces 14 being inclined to the concave surfaces, the elements of these surfaces being indicated at 10, 11, 12 and 13 in Figs. 3 to 6.. The opposite or forward faces of :the arms are formed with surfaces as indicated in Figs. 3 to 6, the eifect of this construction being to facilitate the flow of water thereover.

The arms 5, 6, 7 and 8. as a whole are inclined to the longitudinal axial plane of the hub 20, and made th'i'n at their advancing edges sons to provide an easy entrance into the water, and the arms are axially curved into approsjmatcly semi-circular form, be cause the sharper the curve the less resistaiice is offered in revolving in the water. By the construction of the arms in the man ner described I provide with relatively small arms an adequate support for the blades which offer the least resistance in turning P lat the same time obtain additional propellingetiect with a an'inimum or obstruction to the passage of the water through the central portion of the propeller.

The concave arms 5, 6, 7, 8 terminate in blades 1, 2 3, r, rihose orking surfaces are circumferenti iy'e' tending portions of heiicoids, and both the inherandouter edges of these blades extend'along helice having the same pitch.

A. propeller inad'e in the form shown in the drawii'igs and described above yields a much higher eiiiciency than any other lcnown to me. The arms yield aproportional return of thrust for the powcr appliedto them as do the terminal blades and have greater resistance to slip thanplain 'arms'or'a helix. Their form and the ejecting ottheavater to the rear in lines directly opposed to the progress ofthe boat; causes an equal straight thrust at all times.

The rear termination of the concavity of the arms pointing directly rearward 'produces a greater "efficiency than can be "ob tained if the Water is ejected-at "any angle to the line traversed the boat in its-progress. The convexity 01" the opposite side to the concavity produces a suction when the arm is rotating and-this'suctioh is in front of the arms and in thedir'ection the boat is traveiing and materiallyadds to the thrust. The curve'o'f said'arm 'in anarc ofa'circle minimizes the resistance to the passageor rotary n'iovemeiit thereof throu 'gli'the Water. The concavity further gre'atly strengthens the-arms and necessnates less metal in eonstruction. The angular projections '-at'10, 11, l2, l3 rearward on the arms shownflad'd strength to the arms andheing'tap'e'red to 'a sharp angle rearwardly tend 'to prevent "cavi ating at high speeds.

The blades in area greatly ex'ce'edtheir respective arms or support-s. Th'e'objectof making said vanes of'such is two-fold. The propelling force of any pr'opeller is greatest at its greatest distance from the center of the hub, areaffor' area' thereof, c'ons 'h'n'ed;'also the quantity or area of crosssec ion of water out tlirough in revolving is greatest and as the \v'ater' is theiibutm'ent against Which the propeller gets its thrust it is ii'np'o'rtant to secure as large an abutment as possible. v

IIoexact rule canjhere be-"giveinfor the percentage of area oi 'these blades toihc tage may however be varied for conditions of use. In the case of towing, Where the speed *of the boat is slow and a strong pull is required blades of larger area may he used, While on high speed boats blades of smaller area may be used to advantage. The greater the area the less Willbe' the slip.

The high 'cfiiciency of v a propeller constructed asabove described is due to several factors which include (1) the form and arrangement of the arms, whereby there is aiiorded easy passage'of thewater'through the cent a1 portion of the propeller, as the boat advances, with the lowest resistance to or disturbance of this central column of Water; '(2) the i ac-tthat the arms though relatively small yetexert considerable thrust operative; because of the form of the c0ncavity, 'to'forcethe' water straight back; 3) the relatively large area of blade surface located at the greatest possible distance from the axis, whereby slip is lessened to a high degree; and (4:) theexact curvatureiot the edgesofthe blades to the curve of the spiral through which they travel 'in rotating,

This large area ofblade and "arm surface Working effectively againstthe Water, as an abutment, further obviates, to a large de 'gree, the necessity for nice adjustment of thepitch-ofthe propeller blades to thelines or 'speed of the particular'vesselon which the p'ropell'er'is to be used, and the efficiency of the-propeller is maintained Within a Wide range ofv'ariation of speed of travelof the boat or of variation in the rate of rotation otthe propeller.

it "will be noted, furt-her; that'the major portion of the area of the propellerislocated' at its'outer or peripheral part and preferably beyond an imaginary cylindrical surface having a radius of about live eighths that of the propeller as a Whole. The blades lie approximately between two limiting cylindrical; surfaces or'in cylinders co-axi'al with the' propeller. The diameter of the -propeller, as herein shown and described is 1'6 inches and the pitch is'22' inches, which may however be Ina'de greater or less a'cc0rding' to the speed at Which the boat is designed to go. r-is the rearWard concave Warped surfaces of the propeller arms havethe same pitch as the Working blade surfaces and these surfaces merge into each other, the propeller as a Whole closely "approaches the-ideal condition of a sc'rewivcrlizing into the water as into-a solid nut. Th-isideaI c'on'ditio'n'is more closely approximated because of the particular construction of the arm portions,

5 manner, but has the advantage that there is less liability of the blades catching in ropes or weeds.

In the form shown in Figs. 7 and 8, the arm-portions 5 6 7 8 are of the same construction and arrangement as the arms 5, 6, 7 and 8; but the blades 1, 2, 3*, P are extended, as shown, to one side only of the arm, the area of the blades being however substantially the same as that of the blades shown in Fig. 1.

lVhile I have shown a e-bla-de propeller obviously any different number of blades may be used as conditions of use may require. Nor is my invention limited to strictly helicoidal surfaces for the working surfaces of the arms and the blades, as slight variations from this form may be made without departure from the spirit of my invention.

1. A propeller comprising a plurality of ciflcumferentially and axially extending heliooidal blades and arms lying in substantially the same radial plane connecting the blades to the shaft, said arms having concaved propelling surfaces Whose cords are set 1 on pitch lines co-ordinating with the pitch lines of the heliooidal blades.

2. Propeller according to claim 4; in which the arms are axially curved, their convex edges pointing in the direction-of rotation.

3. Propeller according to claim 4 in which the concave propelling surface of each arm is defined by progressively varying radii of curvature, the radius being shortest adj acent the hub and longest adjacent the line of union with the blade.

In testimony whereof I afiix my signature.

ISAIAH L. ROBERTS.

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