US1940318A - Fan blade - Google Patents

Description

Dec. 19, 1933. H. F. MORSE 18' mu sums Filed Dec." 20. 1932 2 Shuts-Shut 1 Inventor:

Harold F. Morse,

by His Attorney.

19, 1933. H. F. MORSE 1,940,318

FAN BLADE Filed Dec. 20, 1932 2 Shuts-Shut 2 InVentor:

Harold F Morse.

His Attorney.

Patented Dec. 19, 1933 PATENT OFFICE FAN BLADE Harold F. Morse, .Southport, Conn, assignor to General Electric Company, a corporation of New York Application December 20, 1932 Serial No. 648,073,

4 Claims.

My invention relates to fan blades and more particularly to fan blades of the propeller type.

An object of my invention is to provide a fan blade with directional characteristics so that i it may be mounted on a hub to propel the air in a desired direction either perpendicular to the plane of rotation of the fan or at any other angle thereto.

Another object of my invention is to provide an improved ian blade which will move a relatively large volume of air at a comparatively low velocity.

Another object of my invention is to provide a fan blade which maybe so mounted on the hub as to take air in from either side of the fan as desired and will move a relatively large volume of air.

Fans have heretofore been provided with blades which direct the air from the fan in an axial direction, the intake for the air being from the rear of the fan. Fans 0! this type characteristically move the air in the form of a funnel, the air column being of relatively large diameter bebind the fan and being reduced in diameter to as about 60% of the diameter of the fan a short distance in front of it. This small diameter air column in front of the fan reduces the emciency of the fan as it is necessary to increase the velocity imparted to the air in order to increase the 80 volumetric output of the fan for a given diameter of the fan. Attempts have been made to increase the diameter of the air column in front of a the fan to improve its efllciency. Most of these attempts have resulted in a slight increase of this '85 diameter which has increased the efficiency by a small amount. The high velocity which has been characteristic of this type of fan has been found objectionable by virtue of the fact that the air is propelled a considerable distance from the fan and one within its range can feel the motion of the air. Also, when fans of this type are used in offices the high velocity of air propelled a considerable distance from the fan is objectionable because it will blow papers and light objects from a desk or table unless they are weighted down.

By my improved fan blade I am able to increase the diameter 0! the column of air projected by the fan so that it may be even considerably greater than the diameter of the fan to thereby increase the efficiency of the fan so that a large volume of air may be moved without imparting a high velocity to it. Also, my improved fan blades may be so mounted as to direct the air radially or axially or at a diverging angle between those two limiting positions.

What I consider to be novel and my invention will be better understood by reference to the following specification and appended claims when 50 considered in connection with the accompanying drawings.

In the drawings, Fig. 1 is a plan view or a tan with the blades mounted to propel the air radially; Fig. 2 is a side view of the fan of Fig. 1; 05 Fig. 3 is a plan view of a fan with blades mounted to propel the air axially; Fig. 4 is a side view of the fan of Fig. 3; Fig. 5 is a perspective view of an electric light fixture with a fan mounted centrally of the canopy; Fig. 6 is a plan view of a fan with the blades mounted to propel the air in a diverging column; Fig. '7 is a side view of the fan of Fig. 6.

Referring to the drawings, Figs. 1 and 2, blades 10 are secured to arms 11 of the hub 12 by means of screws 13. Blades 10 of Fig. 1 are mounted to propel the air radially from the fan. The center line of the blade is mounted at an angle approximately 30 with respect to the path of travel of the blade, i. e. the center line of the blade extends go at an angle of about 30 with respect to a tangent to the circle drawn from the axis of rotation at the point the blade is secured to arm 11. Thus the pitch of the blades is 30. This pitch angle may be varied depending upon the amount of air it is desired to move and upon the load to be placed upon the motor driving the fan. It has been found that the maximum efllciency is obtained when the blade is mounted at a pitch angle between 20 and 30, the exact angle for maximum efliciency depending upon the size of the blades and the diameter of the fan. With the blades mounted in this position the air propelled radially is taken in about equally from both sides of the fan. As best indicated in Fig. 2, the blade may be inclined at an angle to the plane of rotation. This inclination is determined by whether a larger portion of the air is taken in from one side of the fan or the other. As a general rule, the motor and supporting mechanism located on one side of the fan will so obstruct the passage of air as to somewhat reduce the amount of air taken in at that side of the fan. To fully utilize the amount of air which may be taken in from the other side of the Ian it will be inclined so that the intake end of the fan is directed toward the side of maximum input. In Fig. 2 it will be seen that the blade is inclined with the input end directed toward the face of the fan. The amount of this inclination varies with the amount of the with an inclination of the center line of the blade' of the order of 8 to the plane of rotation of the fan. Blade 10 is in theshape of a longitudinal section of a frustrum of a cone, the large end of the blade being the input end and the small endthe output end. Thus, the blade sides converge from the input to the output end of the blade, or, in other words, the radius of curvature decreases from the input to the output end of the blade. The converging sides correspond to the direction of the flow of air as it is propelled by the blades. As the air increases in velocity the cross sectional area of the column of air decreases in proportion to the increase of velocity. For a maximum efliciency the ratio of the input area of the blade to the output area should be equal to the inverse ratio of the velocity of the air entering the blade to the velocity of the air leaving the blade. The air entering the blade has an initial velocity imparted to it by the movement of the air propelled by the fan which creates a partial vacuum. This ratio varies with a number of factors includingthe size of the blade, the speed of the fan, and the diameter of the fan. For a fan speed of 1000 R. P. M. a fan diameter of 12 inches, and a blade of relative size, as shown in the drawings, it has been found that a ratio of input area to output area of the blade of 3:1 is satisfactory. For slower speeds the size of the blade would be increased and likewise the ratio of the input area and the output area would be increased.

Referring to Figs. 3 and 4, it will be seen that the blades 10 are mounted to propel the air axially. The center line of the blade, as better indicated in Fig. 4, is 30 to the tangent of a circle drawn from the axis through the fan blade. This is the pitch angle and is the same as the pitch angle of the blades of Figs. 1 and 2. The blade is inclined at an angle to a line perpendicular to the arm 11 with the input end directed outwardly from the center of the fan. This inclination is to fully utilize the available air which may be taken in by the blades. With the blades mounted in this position much of the .air of necessity enters the blades from their outer side. The greater the diameter of the fan the lesser inclination is necessary. The air propelled by this fan is taken from the rear and propelled in a cylindrical column axially of the fan. With the blades mounted in this position there is some contraction in the column of air in front of the fan. This contraction may be overcome by mounting the blades to propel the air in a slightly diverging column. The shape of these blades is the same as the shape of the blades shown in Figs. 1 and 2.

In Fig. 5, a specific application of this fan is shown to a ceiling mounted ,unit. The fan is connected to an electric motor 14 which is mounted centrally of a canopy 15 to which is secured electric lamps 16. The electric motor and canopy are adapted to be. supported on a fixture stud, not shown, in the usual manner by means of a strap 17. Blades 10 of Fig. 5 are mounted to propel the air in a diverging column as better indicatedinFigs.6and7inwhichthisfanis shown. Blades 10 are secured to mil with the plane of the center line of the blade at an angle less than 90 to the plane of rotation of the fan. The center line of the blade is substantially to the tangent of a circle drawn from the axis of the fan as a center and intersecting the point at which the blades 10 are secured to the arms 11. Thus the pitch angle of the blade is the same as the pitch angle of the blades-shown in Figs. 1

constriction but, in general, it will be relatively and 3. The angle of'inclination of the plane of 'the center line of the blade with respect to the plane of rotation determines the angle of divergence of the column of air projected by the fan. In Fig. l where the angle of this plane is the air is propelled radially by the fan. When this angle is slightly less than 90 the column of air is projected at a wide angle of divergence by the fan. The air is taken in proportionately from both sides of the fan depending upon this angle of divergence. As the deviation of the angle of this plane from the 90 angle increases the divergence angle decreases and the amount taken in from the front of the fan likewise decreases. A point is reached as this diverging angle is decreased at which the amount of air taken in from the front of the fan becomes negligible due to an intersection of the column of air in front of the fan. This column of air intersects even though the air is projected at a diverging angle due to the fact that themovingcolumnofairentrainsthe stillair through which it is moving on either side of the cone of air, also, the air decreasing in velocity expands or increases in the area it occupies. Thus the diverging column of air increases in cross sectional area at increased distances from the fan. In Fig. 5 the openings 18 are provided to permit the air to be projected by the fan and the positioning of these openings depends upon the angle at which the air is projected by the fan. Openings 19 on the lower side of the canopy 15 are provided to permit air to be taken in from the front of the fan. As better indicated in Fig. 7 the input end of the blade is inclined at an angle toward the rear of the fan, this angle being about 10 in the plane of rotation of the fan and the positioning of the blades without the necessity of directing vanes. Also, the fan blade increases the efficiency of the fan by reducing the necessary velocity to obtain the volumetric output desired.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1; In a fan, a hub with radially extending arms, and a plurality of blades secured to the ends of the arms, each blade of the form of a longitudinal section of a frustrum of a cone and mounted at an angle of about30 to a tangent to the circular path described by the rotating blade with the larger end of the blade leading in the direction of rotation.

2. In a fan, a hub with radially extending arms, and a plurality ofblades secured to the ends of the arms, each blade of the form of a longitudinal section of a frustrum of a cone and mounted at an angle of about 30 to a tangent to the circular path described by the rotating blade with the larger end of the blade leading in the direction of rotation and extending behind in the direction of the air movement across the blade.

3. In a fan, a hub with radially extending arms, and a plurality of blades secured to the endsof the arms, each blade of circular arcuate shape with a decreasing radius of curvature from the input to the output end and mounted at an angle of about 30 to a tangent to the circular input to the output end and mounted at an angle between and to a tangent to the, circular path described by the rotating blade with the input end leading in the direction of rotation and extending behind the output end in the direction of air movement.

HAROLD I". MORSE.

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