US2587247A - Twin blade mounting for fans and propellers - Google Patents

Description

E. M. TURNER TWIN BLADE MOUNTING FOR FANS AND PROPELLERS Filed May 28, 1948 Feb. 26, 1952 INVENTOJE:

Z11.Turnr OF P 747/0 d wm Patented Feb. 26, 1952 UNITED STATES PATNT orrlcs v Estey Turner, Arcadia, Calif.

Application May 28, 1948, Serial N0. 29,816

6 Claims.

This invention relates to variable pitch air impellers and has particular reference to improvements in the mounting of the blades of such impellers.

In airplane propellers and circulating fans, single blades are ordinarily used and it has become common practice in order to provide more efficient air flow control for particular purposes to mount the blades for axial rotation on the impeller hub thereby to vary the pitch of the impeller during operation thereof. In performing the operation of rotating the blades to vary the pitch in the single blade impellers, it is found that certain forces, commonly known as the centrifugal torque, exert pressure against such single fan blades to, urge axial rotation of the blades into neutral position. It is furthermore found that the pressure in this manner exerted increases as the speed of rotation of the impeller in creases.

It is largely for the purpose of overcoming or balancing these forces that twin blades have been introduced for use in air impellers and it is the object of the present invention to devise the most efficient manner of mounting and relatively arranging the units of such twin blades.

In mounting the units of twin blades in parallel spaced relation to each other and having their leading edges rectangularly aligned, it has been found that while theoretically the twin blade is more efilcient than the single blade, this advantage is largely sacrificed by the relative positions of the units, the reason being that the front unit of the blade blankets the rear unit to such an extent that it substantially destroys the utility thereof. It is in view of this condition the further object of the invention to arrange the units of the blade in such staggered relation to each other that the front unit of the blade is set back a considerable distance relative to the rear unit. When so. arranged, it is found that the front unit acts as a booster for the rear unit, resulting in an increase in efficiency as high as 40% at certain blade pitches, as has been determined by numerous wind tunnel tests and by a series of small propeller tests.

Further study and a great number of tests have taught me that the relative angle of incidence of the blade units is an important factor in the efficiency of the impeller and it is an additional object of the invention so to arrange the angle of incidence of the units that the greatest efficiency of each particular blade assembly is obtained.

These and other objects of the invention are hereinafter fully described and drawings are hereto annexed in which a preferred form of the invention is illustrated.

In the drawings:

Fig. 1 is a front view, partly in section, of a twin blade combination embodying the invention as it appears when the blade is turned into neutral position;

Fig. 2 is a plan view of the lower portion of the blade and blade supporting members illustrated in Fig. 1, as they appear when removed from the impeller hub thereof.

Fig. 3 is a schematic view which is added more clearly to illustrate the relative position of the blade units to each other.

As indicated in Fig. l, a twin blade composed of units 1, 2 is mounted on a propeller hub 3. A stem 3 projects radially from the hub and the outer end of this stem is threaded to receive a nut 5 by means of which the blade units are clamped in position on the stem. As usual in practice, this stem is rotatable by suitable, wellknown external means to vary the pitch angle of the twin blade assembly to suit operating'condi tions. And it should be understood that there is one of these stems for each propeller blade. The units of the blade are made from thin sheet metal, the inner ends of which are shown rigidly secured to brackets 6, 1, which are centrally perforated to seat'on the stem 4. As best shown in Figs. 2 and 3, each blade unit is slightly transversely curved, such curving having been found more efficient than the conventional flat blade. It is important to note that the portion of these brackets to which the blade units are secured do not extend the entire distance across the blade unit, but that the center portion thereof is removed, leaving legs from the ends of which lugs 6 5, and l l rise perpendicularly. These lu s are merely wide enough to retain suflicient strength to support the blade units. The purpose of so shaping the brackets is to obtain as nearly as possible a perfectly balanced condition. If the portion between the lugs at the ends of the brackets had not been removed, it would be necessary, in order to obtain a balanced condition, to place similar panels between the lugs of adjacent legs of the two brackets, as indicated at 8 and 9 in dotted outline in Fig. 2. It may be suggested that the blade units I, 2 show a similar unbalanced condition and there is no doubt but that, if the central portion of the blade units were similarly removed, a more perfectly balanced assembly would be obtained, but it has not yet been found commercialy practical to produce such four unit blade and, in the present state of development, it becomes necessary to stay within the limits prescribed by accepted manufacturing methods.

As suggested above, Fig. 3 is added for the purpose of more clearly showing the relation of the blade units to each other, to the direction of the air flow and to the direction of rotation of the impeller. Experience and numerous tests have proved to me that the distance between the units of the twin blade holds a certain fixed relation to the width of the blade units and it has been my experience that most satisfactory results have been obtained where the width of the units is about twice the distance between the units. As above stated, it is necessary to set the leading edge of the front unit 2 back relative to the direction of propeller rotation a considerable distance behind the leading edge of the rear unit I in order to permit the leading edge of the rear unit first to act upon the air and to impart motion thereto, concurrently to create a partial vacuum on the back surface of this blade unit. The distance that the leading edge of the front unit is set back should be at least equal to one fourth of the distance between the units.

Referring further to Fig. 3, it is noticed that the pitch angle, which is the mean'angle of incidence of the twin blade relative to the direction -of rotation thereof corresponds to the various positions taken by the blade during operating conditions and it is important to note that the angle of incidence of the front unit 2 of the twin blade is greater than that of the rear unit I. I have found that this increased angle of incidence of the front unit has a controlling effect on the vacuum formed on the rear unit of the twin blade and also imparts increasing velocity to the air stream which has been set in motion by the leading edge of the rear blade unit. In other words, I have found that the front unit of the blade, on account of its increased angle of incidence, acts as a booster resulting in an increase in efficiency as high as 40% at certain pitch angles of the blade. This result, as stated, has been definitely determined by numerous wind tunnel tests and by a series of other impeller tests conducted by me over a long period of time. Once the correct angle of incidence has been fixed, the two supports may be positively locked in position against relative rotation by means of a screw or pin I0.

I am aware that staggering of blade units in a twin blade propeller has been proposed but, in such devices as have come to my notice, I have found that the front unit of the blade has been given an advance stagger and the rear unit has been set back relative to the front unit. Such arrangement has been found completely impractical and has resulted in a definite loss of efficiency, as has been conclusively indicated in wind tunnel tests. The relative positions of the blade units of the present device is therefore of utmost importance.

It was above stated that the distance between the units of the twin blade should be approximately one-half the width of the blade units. Such relative proportioning has also been found most efficient in reducing the effect of the centrifugal torque on the blade during operation thereof and to result in easier adjustment of the blades to change the pitch angle during operation thereof.

I claim:

l. The combination with an impeller hub having a stem radially projecting therefrom, of a twin blade support comprising two brackets, each bracket including a bifurcated base perforated at the apex thereof for engagement with said stem, the base having legs extending from the bifurcation thereof andhaving lugs perpendicularly rising from the ends of the legs for supporting one of the units of the blade, means for clamping said brackets in position on the stem, and means for clamping the twin blade units in position on the lugs of the brackets.

2. The combination with an impeller hub having a stem radially projecting therefrom, of a twin blade support comprising two brackets, each bracket including a bifurcated base perforated at the apex thereof for engagement with said stem, the bracket having legs extending from the bifurcation thereof and having lugs perpendicularly rising from the ends of the legs for supporting one of the units of the blade, means for clamping said brackets in position on the stem, and means for clamping the twin blade units in position on the lugs of the brackets, the length of the legs of each bracket and the position of the lugs of the brackets relative to the bracket centers being proportioned to space one unit a predetermined distance away from the other unit.

3. The combination with an impeller hub hav ing a stern radially projecting therefrom, 'of a twin blade support comprising two brackets, each bracket including a bifurcated base perforated at the apex thereof for engagement with said stem, the bracket having legs extending from the bifurcation thereof and having lugs perpendicularly rising from the ends of the legs for supporting one of the units of the blade, means for clamping said brackets in position on the stem, and means for clamping the twin blade units in position on the lugs of the brackets, the brackets being rotatable on the stem to bring the units into correct angular relation to each other.

4. The combination with an impeller hub having a stem radially projecting therefrom, of a twin blade support comprising two brackets, each bracket including a bifurcated base perforated at the apex thereof for engagement with said stem, the brackets having legs extending from the bifurcation thereof and having lugs perpendicularly rising from the ends of the legs for supporting one of the units of the blade, means for clamping said brackets in position on the stern, and means for clamping the twin blade units in position on the lugs of the brackets, the legs of each bracket, the

positions of the lugs of the brackets relative to the bracket centers being proportioned to spaceone unit a predetermined distance away from the other unit, the brackets being rotatable on the stem to bring the units into correct angularrelation to each other, and means for locking the brackets against relative rotation. v

v 5. The combination with an impeller hub having a stem radially extending therefrom and curved twin blade units mountable on said stem, of a support comprising two brackets, each bracket including a bifurcated base perforated at the apex thereof for engagement with said stem, the bracket having legs extending from the bifurcation thereof and having lugs perpendicularly rising from the ends of the legs for supporting one of the blade units, the lugs being curved to fit the curvature of the unit they support, means for clamping the units in position on the lugs, and means for clamping the brackets in position on said stem.

6. The combination with an impeller hub having a stem radially extending therefrom and curved twin blade units mountable on said stem, of a support comprising two brackets, each rising from the ends of the legs for supporting 5 one of the blade units, the lugs being curved to fit the curvature of the unit they support, means for clamping the units in position on the lugs, the length of the legs of each bracket and the position of the lugs of the brackets relative to w the bracket centers bein proportioned to space one unit a predetermined distance away from the other unit, means for clamping the brackets in position on said stem, the brackets being rotatable on the stem to bring the units into correct 15 angular relation to each other, and means for locking the correctly set brackets againstrelative rotation.

ESTEY M. TURNER.

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

UNITED STATES PATENTS Number Name Date 10,474 Leach Jan. 31, 1854 1,021,822 Broussouse Apr. 2, 1912 1,098,306 Trautmann May 26, 1914 1,243,885 Smyth Oct. 23, 1917 1,355,462 Francis Oct. 12, 1920 1,463,441 Pike July 31, 1923 1,813,877 Gunn July 7, 1931 1,864,492 Krasnodmsky June 21, 1932 2,279,190 Wilkinson Apr. 7, 1942 2,344,266 Reissner Mar. 14, 1944

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