US2011672A - Screw propeller - Google Patents

Description

Aug. 20, v1935. A, BARKER SCREW` PROPELLER Filed April 25, 1934 Patented Aug. 20,V l1935 .Q OFFICE SCREW PROPELLER Auriolarker, Thornleigh, near Sydney,

' New South Wales, Australia Application April 25, 1934, Serial No. 722,389 In Australia June 7, 1933 "This invention relates'toV screw propellers; it

. isI equally applicable to airplane propellers, ships 1 peller.

4propellers, air propeller fans, and circulating propellersffor various iiuids.

According to this invention the pitch of a screw propeller is made 1.5708, that is to say, for one revolution the advance of the propeller due to its mean helix is, equal to 1.5708 times the diameter of the propeller measured lover the extreme ends of the blades; the mean angle of the blades at the extreme ends describes a helix which in one revolution of the propx-ller advances 1.5708 times the diameter of the pro- Further, the mean radial centre line of each blade describes a right helicoid, the angle of the blade with respect to the axis of *rotation at any diameter being such that the advance at that'diameter will be equal to the Ladvance at the extreme diameter.` A propeller so designed operates with aminimum lossand creates minimum disturbance in axial direction in` the'iiuid in which it runs, and the losses due tov centrifugal displacementY of the fluid in which the propeller works are reduced to a minimum.

Both faces of the blades form oblique helicoids, situated equally on both sides of the right heliccid representing the pitch of the propeller.

This arrangement if schemed as above described, would result in blades of unnecessary thickness at the tips; thetip thickness is obviated by reducing the thickness of the blades in steps the reduction beingsuch that the cross sectional L area of the blade atv any point is not reduced bev y low that necessary to provide strength to with- Y the plane of revolution.' 50

.slip caused partly by excessive thickness of the blades at the root, where the thickness of the Vblades is usually greatest, and partly is a consequence of the tilting back of the blades from Back tilting of the blades of a screw propeller results in the imparting of movement to the iiuid in which the propeller is yoperating and owing to the progression of the propeller this radially moving iiuid is met by the blades where tilted backwards.

'I'his disturbing condition iS. avoided in the present invention because of the relative thinness of the blades at the root, small axial length of the propeller, and elimination of tilt of the blades.

A stillfurther object of this invention is to provide a' propeller made in axial sections, and "5 these sections assembled so that the axial length -of the propeuer can be varied with facility.

In the accompanying drawingz y Fig. 1 showsan elementary section of apropeller according to this invention. Figs. 2, 3, 4, 10 and 5 illustrate graphically themethod of determining the correct angle and major cross sectional area of the blades atthefend 2l and at the steps marked 22, I8 and I6, respectively in Fig; 1, l5

Fig. 6 shows a propeller in which three of the units shown in Fig. lare assembled in close contact so that the contacting blades form a. continuous helical surface. In Fig. 1, l'l is a boss or hub, ,I2 being Vthe rshaft bore `and I3 20 the keyway. The blades i4 and la extend outwardly and oppositely from the hub. Two blades -are shown, butthree blades orfour blades spaced symmetrically may be fitted. The root portions` Ofeach blade l5 on bothsides -is helically angled 25 with respect to the axis ofthe hub in such a manner as to produce in one revolution an adi Vance equal 1.5708 `times the extreme diameter of the propeller. The sides of the blade root Vportions l5 and 15a lie along lines drawn radi- 30 ally from and normal to the axis of rotation, or the centre line of bore l2. The radial sides l5 and 15a diverge from the axis at a relatively great angle and at the points i6 and Ia the blade sides are stepped inwardly, reducing the 35 thickness of the blade aty that point to the smallest practicable dimension consistent with .the necessary strength, and thereafter again expand radially outwards along sides l1 and lla, until a thickness of blade is reached at which it is de- 4.0

sirable to again step it inwardly, as shown at I8 and 18a. This progression goes on in stages on the sections marked I9 and 20, the mean pitch at each step and intermediately being such that the advance in one revolution is equal to 45 1.5708 times the diameter of the propeller. The number of stages whereat the thickness of the blade is reduced will vary with the diameter of the propeller, and is not confined to the four stages shown.

Fig. 2 is a projected view of the end 2| of the blade shown in Fig. 1, the angle being derived as follows: 3| is la centre line parallel to the axis of rotation, 32 and 33 are two lines equal to 0.0375 times Athe outside diameter of the pro- 55 peller,v and 'parallel` toy 3j.; and at such distances trom 3lv as to form withfportions of 7the upper The' thickness of the. blade at line 32; dra'WngV/lines andUatsaid distances from 32 andfparallelfto' 32, and intersecting yline "35 at 4IA and @2. From these intersections", lines 43'and 44 are drawn parallel VVandequal tothe` f diagonal; these lines 43 ande@ y.rneetlline 34p atr points 45 and 45, and the`rh0rnbid fi5-46-4l;42 represents the'projectediarea and y. angle of the extreme endjof the blade 2li1 -inf Fig.'l.` Fromtheextreme end 2l inFig.1,1,'-the faces@` of section A2i) are. tapered helically, .cont/1ergingj finWards' until Aa point 22 is reachedwlieregcal-y Icula't'on showsthat thermateral'hasl been-re'- .ducediyinfrellective strength to. av safe'low limit. `The'lpitchf angle at 20L-is"then'ascertainedi by calculation, and'lad out'at. 55; 3,.b'etWee`nf vparallellinesz55 andG-M-'equ'al to .lines-.32 A'and 33 Fig. 2.y Oneach sidepof lines 55 and 56 at dis-r fltances and58v equal to distances Sland 30,

FigfZfar drawn lines Aand 6'0parallelto 55.

On abasethus deterniined-by the intersectiony 0f.lines59 anollr with line. 52 Va rhomboid is In thegfsarnef. Way thv Ydimensions of step :i8

'Fig'.Y 1. .are'fderivedV iny Fi.4.` 52 4irs-"a .diagonal ascertained uby Ycalculation of "the `angle' at.A i3,

L about. Whichvr described"V Aon an equal .,base, landbetween. .the samel parallels a rhomboid Y @56E-56, which representsfthe majorcross f .between the same .parallels abouta diagonali I;

` g Which-representsthe anglea'ncl` niajonc'ross secl tional area of 1the-b1 ade rat-,.thegstep.-l6;.Fig. 1.

- I In the same mannerfthe pitch'an'gle atA any K 45 'diameter having `been calculatedg-themajfr are@V secure by.` Letters/Paramus.-

divided!intmstepped'lsections. Y. n f AURIOLBRKER- at' anystep 'canfbe ascertained bi1-'constructing i a rhomboid about such 'diagonal having aheight of 0.0375 timest'he diameter, and: abase of half that amount. j y

If it be desired to increase the axial length "ofethe propeller, theniat anystepin the blade the v pertinentr rhomboid 'would' still ,have a lbase f 0.0375 times'the .diameter of the proithaheight to correspond tothe desired-'axial lengthy" The area oftherhomboid at any vmajor section .is equal to '.(DEr

lWhere.Dstheextreme of the ypropeller con- `'cerneol and-Eis 0.0375. A z

Fig.6 showsa propeller in which sectionsv 237i!) 82,:-and'83 are assembled Vtogether tof increase nthe iax'u'il"length of ,theprbpeller, Lthe sections having-their several keyways 85 vcut incorrect relationtopermitpfthe assembly oifthe sections yin an unbroken helix. l 'Any'nunjber of section-s Ymay be usedr in the v.as s'erribly of. a' propeller acverasing to'. 'my invention.; but; it.' is'fmmc that v j eighth ,of .thediametery 'of the' propeller.v

what` I Claim as :my'j invention ya essere fr0 ,y 111A. .propeuer in Vwhich themadag have a conf stant"pitch'iriu the form ofga riglfitv helicoid, and the" faces of the bladesa'rein the orrns'pof 'oblique .rient helic'oidyf y the` facesiof'theblades are in.' the forms of oblique 'helicoids, equally.disposedfoneithe side ofthe fl'ght'Q-helicoi'd and-.divided into stepped sections.` .3J-A'. propeller in 'Which'the blades have a'constant'pitchfin'thejforrn of .a Vvright helicoid and .a pitchfratioof'1.5708Qandrthe faces of the' blades y are. p in'r fthe -fforms fof oblique" heliccidsj; equally disposed Von* "eithersidelof the.v right helicoicL. and

neuen-nds; equallyV disposeq'ori either side of. the

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