US2581873A - Fan blade and its formation - Google Patents

Description

Jan.8, 1952 w. E. MORRISON 2,581,873

' FAN BLADE AND ITS FORMATION Filed Dec. 17, 1947 I NVENTL'OR; WILLIAM E. MORRISON Patented Jan. 8, 1952 UNIT ED STATES G 'FF I 7 "$581,873 1 FAN' BL'ADEFAISD ITS'EOBMATIQN 'Wil1iam"E.Morrison, iTorrington, Connyassignor toTheTorringtonManufactmingfibg Torrington, Cnn.,'-a* corporation of Connecticut v- Applicationl-December 17, 1947,Senial 'No. .7;9 2,130

invention relatesstoj fan" bladesarid, their .formation, and more particularly to eertainim- .provemeni'ls in both 7 the sectional shaping .and plan, contour of the bladesof' propeller typ'ej'fans,

the,.,im provements' being ideally adapted to 7 fans "for relatively. highuair delivery or volume within relativelylow pressure ranges, .such as soecalleid -atticians. The present improvements are, however, broadly .a'daptedj'for ,use'in numerouslinstallations requiiinglbw,pressure; high volume air propellers. V

'Ihe ,greatlyj increasedrextent of .use of flarge .diameter ,propellers for ventilation Y purposes generally,and particularly in the vfield of .so-

called atticxf ans; has .directe'dmuch. experimental work to the end of providing .a more quiet and efficient type .of; fan for this purpose. vMany, .of the ,air,propell'ers heretoforeoffered to thetrade exhibit all lower efficiency in; this field of usage, than should be expec.tednin view vof experience wfix-ith V othfit propellers; in a. variety of other ,flelds. The presentinventionaccordingly has asamaior object, 'the improvement .of efliciency, of'jans-"for 'the' general purposes noted,,at1the same time realizing a more quiet, propeller.

7 Somewhat more particularlylstated, lthcpre'sent' improvements, objectively realize. a. more er,- iicientffan Lforilow pressure,i high volume work, by application of what'is herein fde'signatedgas .the inductiongprinciple hereinafter ,more .Zfiilly explained, V

illn'iurltheranceof the obi elct', last above .expresse ed, additional important ,objectivelfeatures of the .designincludelthe use of a relativelysmalllcenter fdiscl or spider. for the purpose ,of blade. mount ing; a design to, permit .a maximum, bladeengle, conducinjg" to large i open, passages of great area between the blades, and .a j relatively vnarrow blade ,roo'ti'pa'rtion, further conducing tolaisubstantial-section of air channel betweentheadjacentIblade rootyportions; inikeepina withijthe 'in'ducti'onitheory above noted.

A1 further and" highly importantaobjectwof the ,present improvementsis attained in animprove'd .bla'derfbrmation such that a propellerff'ormed 16f 'ithese' blades willexliibitahigh mefchanieal.efli-v ciency in the" low pressuregrange. of; its performance curve.

The "foregoing fan'drnumerous lothen objects will more clearly appear'jsfromlthe" fbllowingide- Claims. (01.1'170-1-159) tailed (descriptions of a; single; preferred. embofii- 'ment' ofilthe invention as lappliedetona propeller fan"for use". in various.ventilation-."fielda. forwexamplewasl, in .an attic; tan, of,,,36 "-.cliameter, the description .1heing. predicated .l on we gram of n. this size, and'ltype, andbest understood'iuwhen loonsi'd eredllnconnection with the. accompanyingidraw- .ingr in which:

' Fig.. 11 is ,a plan view o'fithe' pressure ,or delivery facevofflthe improvedpropellerifan and center disc, only two blaclesv being showniorlclearness, vone thereof being broken away;

Figi'zis .a'front, elevation of a'i:four""biade;fan with present improvements, being thegmost usual embodiment;

i Fig? 3"is a planview of, a" blade blank,;,with'the view taken ofi'thejpressureface of" the blad'ei'after blanking,.. butibeforejforming; henoej'in unpitched V relation;

"Rig; '4 11s a fragmentary section the location of which; ina'forrned'lblade, is. alone 1ine?4 4.;of -'73)- F;ig;.1'5 "is a ffurther 1 section, "and" being fragmentary nature, ifthisi'section"'being' located,

Fig. 6 is a fragmentary "sectional view, the

location of which in aiormedbladeglisindicated fFigf "l is a transverse section taken on-a' curved 1 plane; parallel to" but-somewhat 'inwardlrof the peripheral edge of the'blade; the location-there'- of beingli'designatedi'by line Y 1 11 of 1', this If gure including, in clotted ;lines,y"an' edgevportion of .the center disc "in ordertto" portray, 'iiiat- -grammatically;"the pitch of" the blade;

Referring 'now by characters "of"re'ference "to the "drawin the propellerifan' is comprised of a selected, small plurality of blades. formed ofgza suitable sheet, material, ,such as, "sheet steel "or aluminum, "the blades being attached at equiiangular "intervalsto andgabout a" spider :of any suitable "form, exemplified in the present (dis- Jc'losure ,as ,a ,planar, center disc' 1,0. iThelblades are mountedlto provide a pitch angle oflitheprtier of i5ffdegrees lin the example shown. The disc 10 j,isc-ap.ertured, at III .ffor a. .hub .Lor: ..dther' suitable. shaft lmounting element j (notalshownl'l. ,The number, of bl'a'deslis: oicourse optionalmthere .usually; being two, 'ithree, or ;-four in avian-of, the

general ttype illustrated ;.and for the. fields ofincluded herein since it constitutes per se, the subject of a copending application Serial No. 711,273, filed November 21, 1946, by this applicant. It may be noted, however, that the tabs l3 and I4 are bent along lines 2| and 22 so that the body of each tab lies outwardly from and at a distinct angle to the face or faces of the center disc; and each tab forms therewith, a short tubular passage 23 adjacent the center disc and directed toward the medial region of the root portion of the blade.

Proceeding now to a description of the nature, contour and formation of the body of the blade til proper, it should be noted that the apparent difference in blade width between Figs. 1 and 3, is due to the relatively high pitch preferably imparted to the blade in mounting same on the center disc, and derived by the angularity and leading edge 24, through a rounded corner 25,

which would otherwise appear as an apex, merges into a widely arcuately formed peripheral margin 26' which is or ,may be of substantially regular curvature although possibly deviating to a very minor extent from a regular curve. The line or edge 26 is brought inwardly in a rounded corner 2'1, thence merging into the trailing margin or edge 30 of the blade. The edge 30 is approximately radial and is shown as being straight.

CItiwill appear that if the lines 30 and 24 were to be continued inwardly they would intersect in or near-the axis of revolution, or perhaps slightly outwardly thereof. It will be obvious to those involved with the design of propeller blades that the rounded cornering 25 and 21, as is of itself well known, conduces to quietness of operation. ,Butfor such elimination of true apices, the blade in plan would generally resemble a triangle modified by rounding of one side such as 24, shown asbeing a uniformly curved line on a radius of 14 inches, and the base such as 26. If the blade be considered as an uppermost blade, such triangle-or quasi-triangle would be viewed in inverted'frelation, and by reason of the root portion should be considered as further modified in that itis' frustrate in what becomes the root portion of the blade. This shaping, as will appear from the drawing, results in an unusually narrow root -portion which conduces to the provision of a maximum path of air ingress in the regions of the blade roots, and over the periphery of the center, disc, The proportions of the blade as viewedflin' plan or outline, are further such that the blade width in or just inwardly of its pe ripher preferably substantially equals or even exceeds the length of its active surface on a radius drawn from the center of revolution. Thus the fan is of a distinctly wide blade type. i

Over considerably thegreater part of the area of its pressure or forward face each fan blade is of nearly flat, or of concave aspect, with the exception of a minor portion hereinafter noted in the trailing area of the blade. For consideration of blade formation, specifically its various sectional shapes, it may be considered as divided into three areas as viewed on its pressure or forward face. Thedirection of rotation is indicated by the large arrow near the periphery of the complete blade of Fig. 1. Thus the curved leading margin 24 together with a part of the peripheral edge 26 and a forming line AB, bounds a quasi-triangular leading area A-25-B. The line AB, located at an angle of 20 degrees to a radius through point B, may be considered as the median of a channel directed from the root region near point A outwardly to the periphery of the blade at B. On the leading side of the line AB, the pressure face of the fan is concave on forwardly projecting radii, and on the trailing side of line AB, as will be described, there is a large practically flat area ABC, which may be very slightly curved on very large forward radii. In the area of which line AB is a trailing boundary line, there is a forming curvature on forward radii, these radii being approximately, but without restriction, of the order of fourteen inches. Thus the area A-25-B constitutes a portion of the wall of a cylinder of that radius, and merges gradually and smoothly into the area ABC. This formation results in a channel on the forward face of the blade which slopes in the direction of air flow as will appear, from the blade root about point A, and thence extends toward the peripheral region in the general direction of air movement across the blade when the fan is in motion.

In the preferred construction as shown, a second preferably rectilinear forming line is indicated at CB, located at 16 degrees to the radius through point B, the lines AB and CB being of converging trend toward the periphery of the blade, as will be noted. The generally triangular space between forming lines AB and CB constitutes an intermediate, approximately fiat triangular area or zone. The formation curvature of the area just beyond line CB, is preferably, for best results, in a typical fan blade of 36" diam eter, on forwardly projected radii of the order of ten inches. Thus it will now appear that the area bounded by BCD constitutes a portion of a cylinder having a radius of ten inches, and that the area ABC merges smoothly and gradually into BCD. This part cylindrical formation constitutes a channel from the region of point C to the periphery, and which slopes opposite the general direction of air movement across the blade when in motion.

The third forming line CD which is somewhat shorter, by reason of its location, than the two described, lies at an angle preferably of the order of 30 degrees to the line CB, and bounds a channel presentedon the back or intake face of the blade, resulting in a similar convexity presented on the pressure face of the fan. The relation between the ten inch positive curvature of area BCD, and the last noted negative curvature characterizing the area D-2'l-C on backward radii, best appears from the section of Fig. 6. The backward radii on which the latter area is formed, are preferably of the order of six inches. Thus the area D-Z'I-C constitutes a portion of a cylinder of this radius. It will now have appeared that the several groups of forward and backward radii, as described, may be considered as ranged parallel to the forming lines, with those of each group considered as being in a row tangent to a circle on the axis of propeller revolution.

It will now have appeared that the concave region bounded by lines CB and CD consists of a relatively inverted triangular area which may be considered a trailing portion of the blade, and that the line CD taken with the trailing extremity of peripheral edge 26, and trailing edge 30'.

trail n :directionirom.theileadin dger-24- h are: 1 ;F gz .1 to takeira ranexamp e f aicircular-arceconce iawith h xis; of: rota: tion. Fi bein a;,..section l view: takenalon the..said.arc-;.. By. ref en e Q a; '7 t w ll b ob: served: that thepitch: n les a e p o e s greater-at the followingfiones; spacedin the'traile 'ing directionz the;zone immediately'yadjacentthe leading. ed e; the-zone midw y t een-t leading edge. 24.1.and1the line BA, the zone betweenthelinesBA andBC, the zone midway betweenthe linesBC andDQ, ndtheizone immediately adjacent and 1. at; the leading; side of the D9,, Thepitch anglessimilarly'increaseprogres: sivelyrxalong: each other arcconcentricwith the axis; rotation and-.beyondor spaced. outwardly from the root areas From the foregoing description it will be observedthatthe forwardly curved leading area 3.2! of thebladeis preferably a cylindrical section which is tangent alongthe line AB to the central area 32. The line AB intersects a radial line through the center of the blade at a substantial angle with its outer. end at the periphery and with its inner end'at the leading edge. The forwardly curved area 33 of the blade is preferably a cylindrical section which is tangent along the line CB to the central area 32. The line CB intersectsthesaidradial line through the center of the blade at an opposite substantial angle with its outer end at-t-he periphery and with its-inner endat the trailing edge.- The central area 32 is preferably triangular and is also preferably flat orsubstantially flat.

When themain portion of the blade is formed with two cylindrical sections such as 3| and 33 which are tangent to an intermediate flat sectionsuch asr,32 narrower at the periphery than atthe, root, the concavity of the mainportion isidifierent along difierent arcuate lines concentric with the axis of rotation. The extent of concavity decreases progressively from the peripherytothe-root region. For instance, a concentric arcuateline near the periphery intersects only ayery narrow. portion of the flat area 32 andthe, degree of concavity is substantiaL, A concentric arcuate line substantially nearer the center intersects a much wider portion of the fiat area .32 and the degree of concavity along the last said line is.considerably less. A concentric arcuate line through the points A and C intersectsonly the flat area 32 and there is no concavity.

The rearward curved trailing portion 34 joins the forward curved area 33 alongthe forming orpjuncture-line CD. The outer end of the said line at D is substantially spaced in the trailing directionjrom a radial line through the center of; the blade, that from-a radialline through the-poin B... The line, extends.,-eenera11y inward iromthenointfl and" the :inner end ofthelineeat C:is located; at the. trailing-i edge: and 'isi-substan; tiallyspaced; from the blade periphery. Then .1 tion:3.4.sis.bo.unded;in partby an arc such:-as;-2] which is tangent .to the arcuate peripheral-ledge 26- and is also tangent to theradial trailingiedge 30;

The particular 'blade formation as; described has resulted frominnumerable experiments; fole lowed .by-and including usual determ-inationsaof air stream-movements, as by: smoke streams.:and stroboscopic observation, and. it may. bezhere noted that the efiiciency of the fan in compari-.-- son with a uniformly concave blade, is -materially increased by addition of 'thechannelling of the area 3|. Similarly,- advantages are ofiered' by the channelling characterizing the area 33;-however, a greatly improved performance is-noted upon the introduction ofboth'of these features of formation, and still further by the reversely curved trailing lip-34 resulting from the backward radii as described, the latter particularly'serving to minimize, in fact-virtually to prevent ina moderate'speed fan; the-adverse effect sometim'esvdescribed as a-tip-vo-rtexor-eddy.- I

In presenting applicantstheory-as -to opera.- tion of a fanconstructed and formed asrdescribed; it should first-bencted that-the -design throughout is predicated upon what isherein for brevity-and aptness, referred to as the "air induction principle. Fundamental *in thistheory of operation is theuseof acenter'discor-spider of a relatively small -area, h ence if'circulaizof a diameter which bears'a low proportionto the diameter-of the fancircle. It hasbeen proven'as a result of applicants experiments that a propeller-with a minimum centerobstruction-exhibits a relatively higher mechanical efliciency at low delivery pressures than comparable pro: pellers with larger center discs or the like, Further, the provision, one example of which has been heretofore, described, of a maximum practical open area around the hub region, has. been shown to give a high mechanical efiicienc'y through the low pressure range of the perform: ance curve of the propeller. This range ashore: tofore implied,"is1th'at over which ventilatingand attic ,fans willusually operate. Applicantsb: lief as .to thereasonsjor or explanation, oimthe high efficiency attained at low pressures is that the high-velocity tubular or annular tream emanating from approximatelyLthe outer onee thirdgof thefagbla'des, resultsin apressure. drop or cavitation which effect is believed towbe-greattg estionthefrontzcenter ofthe fan. Itnow follows that, assuming the root regions of the blades-to. be mutually well spaced, and thecenter ofr-the whole propeller of relatively open design the higher pressureairon the intakeiside of theifan will be'induced ordrawn through such open area into the, low pressure ,zone centrally of thepressure face, andwill thereupon augment the volume, of'air positively im filled by the faster moving outer part, of the propeller. It is applicantsizbee. lief that such portion of. the air delivery,.,namee ly, that part which isinduced-by "flow into and about 1 its center region, is attained with; virtually little. increasein power requirement, inasmuch as the'energy necessary forsuchinductiomhas theretofore ibeenexpended in the development of the, ;velocity of j the stream impelled by -the. outer.- most one-third (for example) of the-fan circle. It is felt thatthis theory accounts for the rise -in' mechanical. efficiency oi the propeller; It -is iii keeping with this principle that the center disc I is kept small, and blade angle is preferably at a maximum to provide greatest open area between the blades, which effect is further. augmented by minimizing the width of the blade root regions.

The Wide divergence between lateral blade margins conduces to a high air velocity in the peripheral region, at the same time obstructing no more than necessary, the induced central stream of air. The extreme divergence of leading. and trailingmargins presents the advantages of wide-blade fans, including quietness of operation.

, By way of. explanation of the advantages of the general formation of the blade as to its varying concavity and location of forming lines, it may be noted that the relatively large forward radii characterizing, the area 3|, give the effect of a substantially constant pitch to the leading area of the'blade, and thus minimize drag losses on the outer portion thereof. Further, such forming results in the channelled section extending outwardly of the axis in the direction of rotation, thischannelbeing of material aid in imparting a centrifugal effect to the induced air entering the blade, causing it definitely to rise on the blade. Such outward component of air motion persists until its'radial force component is neutralized by the atmospheric pressure about the blade periphery, acting to impel the air into the low pressure zone created by axial velocity of the de scribed tubular air stream.

As heretofore briefly noted, the channel beyond the forming line CB, being in area 33, and on a somewhat lesser radius than the leading area 3|, provides additional axial velocity to the flow resulting from the actual air contact with the blade. This channel is sloped oppositely to that of area 3|, and thus imparts a centripetal effect to the air, somewhat compensating the centrifugal action of area 3|, and coacts with the air pressure about the periphery in forming and maintaining the tubular character of the fan stream. 1

The backwardly formed trailing area is an added feature of design for best results, and permits'a smooth takeoff of the positively axially impelled air stream, and prevents all but a negli gible minimum of turbulence loss or tip vortex,

otherwise resulting in the recognized blade tip r drag.

Tests indicate'that the outer diameter of the annular or tubular velocity ring is substantially the same as the fan diameter, since the effect of ambient air pressure thereabout, serves thus to limit the outer diameter of this high velocity cylinder. Theinduction theory heretofore described is upheld by the shape and pattern of the eificiency curve-of propellers constructed substantiall as described; such curve shows the highest efiiciency in the region of zero static pressure and decreases only very little as static pressure is slightly increased, then diminishes rapidly with successive-increases in static pressure. It is not intended that a propeller designed as described will exhibit high efficiency against high pressures, this being inherently inconsistent with the theory of a centrally induced flow, it being possible to attain such flow only within a low range of workingpressures. It will, however, appear that a fan designed in keeping with the theory discussed, will realize the many advantages of propellers characterized by, wide blades with ofi-i radial channelling, and will serve fully to attain each of the several'objects hereinabove expressly stated and others implied from the structural description of a selected exemplary embodiment.

Although the invention has been described by specific reference to a single propeller of commercial type, the specification should not be understood in any limiting sense, inasmuch as numerous variants are possible within thescope of the appended claims. 7

I claim as my invention:

1. The combination in a fan, of a rotatable hub and a plurality of similar blades securedthereto at substantial pitch angles each of which blades is of uniform thickness, the main portion of each blade beyond the root area thereof being generally concave at the pressure or forward side thereof and the leading and trailing areas of the said main portion beyond the said root area being forwardly curved sections tangent to a plane having a substantial pitch angle, thesaid leading forwardly curved section being tangent tothe said plane along a line which intersects a radial line through the center of the blade at a substantial angle with its outer end at the periphery and with its inner end at the leading edge of the blade and the said trailing forwardly curved section bein tangent to the saidplane along a line which intersects the said radial line at a substantial angle with its outer' end at the periphery and with its inner end terminating at the trailing edge of the blade.

2. The combination in a fan, of a rotatable hub and a plurality of similar blades secured thereto at substantial pitch angles each of which blades is of uniform thickness, the main portion of each-blade including a substantially'fiat triangular central section located at a substantial pitch angle and having'its base at the root area of the blade andthe said main portion of the blade also including two cylindrical sections at the leading and trailing sides of the triangular central section, which cylindrical sections are curved in the pressure 01' forward direc; tion, the said leading cylindrical section being tangent to the said central section along the leading edge thereof and the said trailing cylindrical section being tangent to the said central section along the trailing edge thereof.

3. The combination in'a fan, of a rotatable hub and a plurality of similar blades secured thereto at substantial pitch angles each of which blades is of uniform thickness'and has an arcuate peripheral edge substantially concentric with the axis of rotation, each blade comp-rising a main portion and also comp-rising a. trailing portion which is curved in the intake or rearward direction, the 'said'main po'rtion of each blade beyond the root area thereof being generally concave at the forward'side and the leading and trailing areas of the said main portion beyond the root area being forwardly curved substantially cylindrical sections tangent to a plane having a substantial pitch angle, the said leading cylindrical section being tangent to the said plane along a line which intersects a radial line through the center of the blade at a substantial angle with its outer end at the periphery and with its inner end at the leading edge of the blade and the said trailing cylindrical section being tangent to the said plane along a line which intersects the said radial line at a substantial angle with its outer end at the periphery and with its inner end at thetrailing edge of the blade, and the said rearward curved trailing portion of each blade joining the said main portion along a substantially straight juncture line which extends generally inward from an intersection point located at the said peripheral edge of the blade and substantially spaced in the trailing direction from a radial line through the center of the blade and which terminates at a second intersection point located at tile said trailing edge of the blade and substantially spaced from the blade periphery.

4. Thecombination in a fan, of a rotatable hub and a plurality of similar blades secured thereto at substantial pitch angles each of which blades is of uniform thickness and has an arouate peripheral edge substantially concentric with the axis of rotation, each blade comprising a main portion and also comprising a trailing portion curved in the intake or rearwarddirection and bounded in part by an arc of substantially uniform convex curvature tangent to the said arcuate-peripheral edge and also tangent to the trailing; edge of the blade, the said rearward curved trailing portion of each, blade joining the said main portion along a substantially straight juncture line which extends generally inward from an intersection point located at the said peripheral edge of the blade and substantially spaced in the trailing direction from a radial line through the center of the. blade "and which terminates at a second intersection point locatedat the trailing edge of the blade and substantially spaced from the blade periphery.

5. The combination in a fan, of a rotatable hub and a plurality of similar blades secured thereto at substantial pitch angles each of which blades is of uniform thickness and has an arm-- ate peripheral edge substantially concentric with the axis of rotation, each blade comprising a main portion which is concave at the pressure or forward side thereof and also comprising a rearward curved trailing portion, the said main portion of each blade beyond the root area thereof being so formed that the pitch angles along each circular arc concentric with the axis of rotation progressively increase in the trailing 10 direction from the leading edge thereof to the said trailing portion and, the said main portion beyond the root area thereofbeing also so formed that its concavity along suc'cessive circular arcs concentric with the axisfof rotation progressively increases from the said' 'oot area to the periphery, and the said rearigvard curved trailing portion of each blade joining the said main portion along a substantially-straight juncture line which extends generally; inward from an intersection point located at the said peripheral edge of the blade and substantially spaced in the trailing direction from'i'a' radial line through the center of the bladeand which terminates at a second intersection jjpoint located at the said trailing edge of the blade and substantially spaced from the blade periphery.

WILLIAM E. MORRISON.

REFERENCES CITED The following references are of record in the file of this patent:

UN ITED STATES PATENTS Number Name Date 328,549 Viggers Oct. 20, 1885 505,902 Leslie Oct. 3, 1893 1,370,284 Carlson Mar. 1, 1921 1,506,947 Miller Sept. 2, 1924 1,508,086 Crawford Sept. 9, 1924 1,688,462 Oswald May 1, 1928 1,806,345 Halvorsen May 19, 1931 2,023,111 Alsing Dec. 3, 1935 2,031,466 C'riqui Feb. 18, 1936 2,056,547 Weber Oct. 6, 1936 2,148,555 Hicks Feb. 28, 1939 2,212,041 Pfautch Aug. 20, 1940 2,370,652 Frisbie Mar. 6, 1945 2,390,804 McLean Dec. 11, 1945 FOREIGN PATENTS Number Country Date 485,041 Great Britain May 13, 1939

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