US2212041A - Fan wheel - Google Patents

Description

Aug. 20, 1940. R. v. PFAUTSCH FAN WHEEL Filed June 8, 1939 2 She ets-Sheet 1 m a ma W4 Aug. 20, 1940.

R. V. PFAUTSCH FAN WHEEL Filed June 8, 1939' 2 Sheets-Sheet 2 AXIS 0E TATION OFFAN WHEEL R=.507 0 Y D=NORMAL DIAMETER OF FAN WHEEL M .m 3 m I P. n I m u I w m n 9 V9 5 0 M A r J m L 9 w -4 \Ww '1 is Q 16% 1.2 W LHM filo j Patented Aug. 20, 1940 UNITED STATES PATENT OFFICE FAN WHEEL Raymond V. Pfautsch, Chicago, 111., assignor to Ilg Electric Ventilating Company, Chicago, Ill., a corporation of Louisiana Application June 8, 1939, Serial No. 278,045 8 Claims. (01. 170-159) be emcient in operation but which, in addition,

shall operate very quietly. In fact, so important is the quietness of these devices that their acceptance and use depends largely upon the freedom from noise which characterizes the opera- 16 tion of the fan portion thereof.

The principal object of the present invention, therefore, is to produce a fan wheel which shall be extremely quiet in operation while at thesame time being reasonably efficient for its intended purpose. It is also an object of my invention to produce a fan wheel in accordance with the above stated principal object which shall be relatively simple in design and economical to manufacture. Other objects of my invention and the various advantages of my improved fan wheel will be made more apparent by reference to the accompanying drawings andthe following description of one preferred embodiment thereof. In the drawings- Figure 1 is a front or plan view of a three bladed fan wheel embodying the features of the present invention;

Figure 2 is a side elevational view of the fan wheel appearing in Figure 1, the'view being taken transversely of the axis of rotation of the fan wheel;

Figure 3 is a perspective view of the spider constituting a part of the fan wheel illustrated in Figures 1 and 2;

Figure 4 is a cross sectional view taken on the line 4-4 of Figure 1;

Figure 5 is a cross sectional view taken on the radial 55 of Figure 1;

Figure 6 is a front or plan view illustrating the geometric development of the outline of one of the individual blades of the fan wheel illustrated in Figures 1 and 2;

Figure 7 is a side elevational view illustrating the geometric development of the contour of one of the individual blades of the fan wheel illustrated in Figures 1 and 2; and

Figures 8 and 8 are geometric developments of the outer edge portion of the fan blade illustrated in Figures! and 5.

The fan wheel illustrated in the drawings includes three symmetrically positioned blades 9 each of which is riveted or otherwise securely attached to one of the blade mounting arms ll of a spider I3 which is illustrated particularly in Figure 3. The spider I 3 includes a hub i5 and a 5 reduced end portion IS on which is tightly fitted the hub ll of the three, symmetrically arranged blade mounting arms H which may conveniently comprise a unitary stamping, the projecting end of the reduced hub portion l5 being swaged over 10 as shown at I5" to lock the spider on the hub.

In order to provide the necessary angular displacement of the fan blades relative to the axis of rotation of the fan wheel, each of the blade mounting arms II is bent along a radial edge 15 as illustrated in Figure 3. The angle P thus formed between the forward surface of each of the blade supporting portions II and a plane normal to the axis of rotation of the fan wheel defines the angle of pitch of the blades. Under 20 ordinary circumstances, the angle of pitch of the blades will lie within the range of about 7 to 35 degrees. The hub I5 is drilled as illustrated at IT to receive the drive shaft of a fan motor or other driving means for the fan which may con- 25 veniently be provided with a suitable set screw l9 or other keying means.

The improved operation of the fan wheel of my invention results from the novel outline and contour of the fan blades. The outer convex 30 peripheral edge A of each of the blades 9 is in the form of an are having a radius substantially equal to one-half the normal or effective diameter of the fan wheel, and the blades 9 are so supported upon the mounting arms I I of the spider l3 that the entire peripheral edge of each blade will be as nearly as possible at a constant distance from the axis of rotation of the fan wheel at all times. The leading edge B of the blade is sharply concaved and is defined by a complex 40 curve described by four diiferent radii, as illustrated in Figure 6. The arcuate convex peripheral edge A and the concave leading edge B intersect to form a sharply tapering pointed tip portion 2|, and the investigations which I have 45 made show very definitely that it is necessary that the tip portion 2| shall be made as sharp as possible, consistent with safe operation of the fan, and shall be located at the periphery or maximum circumference of rotation of the fan ;wheel. The trailing edge D of the blade is sharply convex and is in the form of a complex curve defined by two differing radii as illustrated in Figure 6.

The surface portion F of each of the blades 55 is defined by the peripheral intermediate the leading edge B and the dot and dash line 25 (Figure 6) is flat, .and in the assembled fan wheel this flat portion is held in contact, as by rivets 22, with the forward surface of the cooperating blade mounting arms II. The peripheral edge surface portion G (which edge A, the outward part of the dot and dash line 25, and the dash line 21) and the trailing edge surface portion H (which is defined by the trailing edge D, the straight part of the dot and dash line 25, and the dash line 21) of each of the blades are curved in the direction of air movement, the amount of curvature increasing uniformly in a rearward direction from the tip 2| along the entire peripheral edge A and preferably along at least the greater portion of the trailing edge D. It might be said, therefore, that each of the blades of the fan wheel of the present invention comprises a member having an arcuate peripheral edge A, a sharply concave leading edge B, a sharply convex trailing edge D, a flat portion F of substantial area extending rearwardly from the leading edge, and angularly disposed relative to the plane of rotation of the fan wheel, and curved edge portions G and H disposed between the fiat portion F, and the peripheral and trailing edges, the amount of curvature of these edge portions constantly increasing from the tip of the blade to at least the mid point T of the trailing edge D.

The exact geometric development of the contour and outline of the blades 9 is illustrated in Figures 4 to 8 and 8 To facilitate a better understanding of these views, the peripheral and trailing edges A and D of the blade have been arbitrarily divided into twenty-six numbered sections of equal length, and the locations of the centers of the radii used in describing the complex curves of the leading and trailing edges A and D have been laid out on the basis of the effective radius of the fan wheel which is equal to 0.507D, where D is the normal diameter of the fan wheel.

The uniformly increasing curvature of the forwardly curving peripheral and trailing edge portions G and H of the blade is illustrated particularly in Figures 7, 8, and 8 In these figures, each of the various numbered ordinates 29 is representative of the forward displacement of the peripheral edge A and the trailing edge D of the blade relative to the plane of the flat portion F of the blade at the corresponding numbered point along those edges.

In the particular design illustrated in the drawings, the total forward displacement of the peripheral and trailing edges A and D increases uniformly from the tip of the blade to the heel portion of the blade at a rate equal to approximately l (see Figures 8 and 8). For fan wheels utilizing a standard number of blades, that is, two to twelve, this increase should be at a rate not less than 3% and not more than 7%. Preferably, the curvature of the edge portions G and H is arcuate in planes normal to the peripheral and trailing edges A and D of the fan wheel as illustrated at 3| in Figures 4 and 5, the radius X being selected to produce a smooth curve tangent to the flat section F.

While most quiet operation of the fan is obtained when forward displacement or curvature of the peripheral edge portion G and the trailing edge portion H increases uniformly from the tip of the fan, i. e. the point of intersection of the leading and peripheral edges B and A to the heel portion of the blade, practical considerations in the manufacture of fans, particularly those of the smaller type, usually require that the trailing edge adjacent the hub shall be cut away as at 33 so, as not to project beyond the hub. Tests indicate, however, that this uniformly increasing forward displacement or curvature of the peripheral and trailing edge portions should be continued at least to ing edge portion, the point T of Figures *1, 5 and 8. At the point T the distance between the forwardly curved edge of the blade and the plane of the flat portion F of the blade is equal to about one-tenth of the effective radius R of the blade. If the increasing forward displacement and curvature is continued at least to the point T, substantially all of the advantages of the invention will be accomplished, although a slight increase in the amount of air delivered by the fan wheel and a slight decrease in the amount of noise produced during the operation of the fan wheel will result if the increased curvature is extended over the entire trailing edge.

For best results, in a three-blade fan the combined area of the flat portion F, the peripheral edge portion G, and the trailing edge portion H of each individual blade should be substantially less than one-third of the total normal effective area of the fan wheel, which area is equal to the area of a circle having a diameter equal to the normal or effective diameter of the fan wheel. In the particular design illustrated in the drawings, the total area of each fan blade is equal to approximately 26% of the total effective area of the fan, and tests indicate that for a threebladed construction the individual blade area should lie within the range of 22% to 29% of the total effective area of the fan wheel.

As has been indicated above, the design principles of the present invention are applicable to the design of fan blades or fan wheels having from two to about twelve blades. In fan wheels having from two to twelve blades, the area of each blade should be somewhat less than times the total effective circular area of the fan wheel, where N is the number of blades, and tests indicate that most satisfactory results are obtained if the area of the individual blades is equal to about 71% to 78% of the total blade area divided by the number of blades. In the design of blades for fan wheels having more than three blades, the various radii of Figure 6 will necessarily have to be modified to conform to the design principles disclosed.

It should be noted that the leading tip portion 2| of each of the blades is (1) sharply pointed, (2) located at the periphery or maximum circumference of rotation of the fan wheel, and (3) disposed approximately ahead of the central blade radius (indicated by the straight portion of the line 25 in Fig. 6) or the line about which the bladeis turned to determine the blade pitch. These are important features of the blade design of the present invention. The approximate 90 lead of the blade tip reduces the pitch or entrance angle of that portion of the blade to almost zero, with accompanying reduction in blade noise, and tests show that this reduction in blade noise is further augmented to a very substantial extent by the sharply pointed form of the blade and by the locating of the tip at the miximum circumference of rotation of the fan wheel.

While best results are obtained if the peripheral the mid point of the trailconcave leading edge which intersects said arcuedge portion G is curved in the direction of air movement throughout its entire length, some benefit over the prior art arrangements will result even when forward curving of the peripheral edge section is not carried completely to the tip of the blade. Althoughthis blade form is not recommended, it maybe used when economy of manufacture is a primary consideration.

In the foregoing I have disclosed the features of a new and improved type of fan blade and fan wheel which will operate much more quietly than the prior art structures delivering the same amount of air. Moreover, fan wheels constructed in accordance with my invention will be found to deliver as much or more air per unit of input power as the prior art arrangements. It will be evident to those skilled in the art that various sizes and types of fan wheels may be developed in accordance with theprinciples disclosed herein, and accordingly it is my desire that the accompanying claims shall be accorded the broadest reasonable construction consistent with the terms thereof and the prior art.

I claim the following as my invention:

1. In a fan wheel, a plurality of blades each of which has an arcuate peripheral edge disposed throughout its length at a uniform distance from the axis of rotation of said fan wheel, a sharply ate peripheraledge to produce a sharply pointed blade tip located at the periphery of said fan wheel, a sharply convex trailing edge, a flat portion adjacent said leading edge and angularly disposed relative to the plane of rotation of said fan wheel, and edge portions curved in the direction of air movement extending from said flat portion to said peripheral and said trailing edges.

-2. In a fan .wheel, a plurality of blades each of which has a curved convex peripheral edge, a sharply concave leading edge which intersects said peripheral edge to produce a sharply pointed blade tip, a sharply convex trailing edge, a fiat portion of substantial area extending rearwardly from said leading edge and angularly disposed relative to the plane of rotation of said fan wheel, and edge portions curved in the direction of air movement extending from said flat portion to said peripheral and said trailing edges, the curvature of said edge portions increasing at a uniform rate along at least a substantial portion of the length of said peripheral edge and said trailing edge.

3. In a fan wheel, a plurality of blades each of which has an arcuate convex peripheral edge disposed throughout its length at a uniform distance from the axis of rotation of said fan wheel, a sharply concave leading edge which intersects said peripheral edge to produce a sharply pointed blade tip located at the periphery of said fan wheel, a sharply convex trailing edge, a flat portion of substantial area extending rearwardly from said leading edge and angularly disposed relative to the plane of rotation of said fan wheel, and edge portions curved in the direction of air movement extending from said fiat portion to said peripheral and said trailing edges, the curvature and displacement of said edge portions relative to the plane of said flat portion increasing at a uniform rate from the tip of the blade to at least approximately the mid point of said trailing edge.

4. In a fan wheel, a plurality of blades each of which has an arcuate convex peripheral edge, a 1

sharply concave leading edge which intersects said peripheral edge to produce a sharply pointed blade tip, a sharply convex trailingedge, a

said edge portions being arcuate in planes normal to said peripheral and said trailing edges, and the displacement of said peripheral edge and said trailing edge portions relative to the plane of said flat portion increasing uniformly along at least a substantial portion of the length of said peripheral edge and said trailing edge.

5. In a fan wheel, a plurality of blades each of which has an arcuate peripheral edge disposed throughout its length at a uniform distance from the axis of rotation of said fan wheel, a sharply concave leading edge which intersects said peripheral edge to produce a sharply pointed blade tip located at the periphery of said fan wheel, a sharply convex trailing edge, a flat portion of substantial area extending rearwardly from said leading edge and angularly disposed relative to the plane of rotation of said wheel, and edge portions curved in the direction of air mdvement extending from said flat portion to said peripheral and said trailing edges, said edge portions being arcuate in planes normal to said peripheral and said trailing edges, and the displacement of said peripheral edge and said trailing edge with respect to the plane of said flat portion increasing uniformly at a rate within the range of 3 to 7 per cent along at least a substantial portion of the length of said peripheral edge and said trailing edge.

6. In a fan wheel, a plurality of blades each of which has an arcuate peripheral edge disposed throughout its length at a uniforin distance from the axis of rotation of said fan wheel, a sharply concave leading edge which intersects said peripheral edge to produce a sharply pointed blade tip located at the periphery of said fan wheel, a flat portion of substantial area extending rearwardly from said leading edge and angularly disposed relative to the plane of rotation of said wheel, and edge portions curved in the direction of air movement extending from said flat portion to said peripheral and said trailing edges, said edge portions being arcuate in planes normal to said peripheral and said trailing edges, and the displacement of said peripheral edge and said trailing edge with respect to said flat portion increasing uniformly from the tip of the blade to at least approximately the mid point of said trailing edge at a rate within the range of 3 to 7 per cent.

7. In a fan wheel, a plurality of blades each of which has an arcuate peripheral edge disposed throughout its length at a uniform distance from the axis of rotation of said fan wheel, a sharply concave leading edge which intersects said arcuate peripheral edge to produce a sharply pointed blade tip located at the periphery of said fan wheel, a sharply convex trailing edge, a flat portion adjacent said leading edge and angularly disposed relative to the plane of rotation of said fan wheel, edge portions curved in the direction of air movement extending from said flat portion to said peripheral and said trailing edges, and support means for said blades so arranged that each of said blade tips is disposed approximately ahead of the central radius of the blade of which it constitutes a part.

8. In a fan wheel, a plurality of blades each of which has an arcuate peripheral edge disposed throughout its length at a uniform distance from the axis of rotation of said fan wheel, a sharply concave leading edge which intersects said arouate peripheral edge to produce a sharply pointed blade tip located at the periphery of said tan wheel, a sharply convex trailing edge, a fiat portion of substantial area extending rearwardly of said leading edge and angularly disposed rela- 10 tive to the plane of rotation of said fan wheel,

edge portions curred in the direction of air movement extending from said flat portion to said peripheral and said trailing edges, the curvature of said edge portions increasing at a uniform rate along, at least, a substantial portion of the length of said peripheral edge and said trailing edge. and support means for said blades so arranged that each of said blade tips is disposed approximately 90 ahead of the central radius or the blade of which it constitutes a part.

RAYMOND V. PFAUTSCH.

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