US3187820A

US3187820A - Propeller fan

Info

Publication number: US3187820A
Application number: US92227A
Authority: US
Inventors: Ralph P Maloof
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-02-28
Filing date: 1961-02-28
Publication date: 1965-06-08
Anticipated expiration: 1982-06-08

Description

June 8, 1965 R. P. MALOOF 3,137,820

PROPELLER FAN Filed Feb. 28, 1961 FIG. ,2.

INVENTOR. RALPH I? #44001? Aanvr United States Patent Ofitice 3,187,820 Patented June 8, 1965 3,187,829 PROPELLER FAN Ralph P. Maloof, Los Angeles, Calif. (5261 Whitsett Ave, North Hollywood, Caiif.) Filed Feb. 28, 1961, Ser. No. 92,227 1 Claim. (Cl. 170-46055) This invention relates to a propeller fan to be used for wind machines and exhausters and the like, and more particularly to a hub and blade structure that is particularly useful in such a propeller fan.

The forces present in a propeller fan are predictable and, generally, they are separable into two groups; one, steady loads and the other, fluctuating or vibratory loads. Steady loads are easily predictable and arise from centrifugal force, aerodynamic pressure diiferentials, and friction and these loads are easy to cope with. However, vibratory loads are more ditficult to cope with. The designer is aware that structural failures in rotating machines are frequently caused by fatigue of the materials which are subjected to alternating forces. One way of combatting fatigue failure is to make parts of high strength material and to increase the local section properties of the structure to a level that will diminish the intensity of the alternating stresses. Another Way to meet the fatigue problem is to provide auxiliary structure that will reinforce the affected parts. In this way an alternating stress is reduced. 1

Obviously, the two methods of fatigue design mentioned above necessarily incur unwanted complexity and expense. The invent-or prefers a third method, in accordance with the present invention, of meeting this fatigue problem. That is, by the removal of the path through which the alternating forces are transmitted. It is well known to fan designers that the major fatigue inducing factors appear as bending moments in the structure. Apparently, what is worse than a fluctuating unidirectional bending moment, is one that alternately changes direction or sense. Since these moments are usually maximum near the hub axis, one can take advantage of the relative unimportance of the hub or root section aerodynamics and such things as very thick airfoils or braces or vibration dampers can be applied here without serious loss of performance. Observing that the fan blade bending moments tend to disappear in a fan with blades that are leaned in the direction of the blade thrust, the inventor proposes to apply the counteracting'moment from centrifugal force against the said leaning or coning blade path to produce a bending moment opposite to that from blade thrust and equal to it. the blade root, on the average, is zero. However, variations from time to time in the aerodynamic environment of the fan causes oscillations in the blade bending moment, said oscillations appearing as alternating stress in the blade root structure.

It is an object of this invention to solve the problem of oscillating aerodynamic forces by providing a fan assembly and hub structure that does not permit bending moments to be transmitted in the plane of the blade or blades to be restrained by the hub and/ or blade root struc-' ture, regardless of the origin or degree of steadiness.

' It is another object of this invention to provide a blade and hub construction that takes advantage of blade deflection control provided by centrifugal forces.

It is another object of this invention to provide fan blades of good quality that can be formed by extrusion processes, or the like, from a variety of materials and including metals and plastics. An airfoil section, extruded in two parts, is connected in such a way as to form a light weight tubular blade and such as to accept the mounting blade root fitting, and said airfoil section is such as By so doing, the bending moment in a to accept accessible fasteners, all to the end that a simple and reliable and inexpensive propeller fan can be readily produced.

The various objects and features of this invention will be fully understood from the following detailed description of the typical preferred form and application thereof, throughout which description reference is made to the accompanying drawings, in which:

FIG. 1 is a perspective view of a propeller fan embodying the features of the present invention.

FIG. 2 is an enlarged detailed sectional view of the hub structure shown in FIG. 1.

FIG. 3 is an enlarged detail of the hub.

FIG. 4 is a cross-sectional enlargement of one of the fan blades and taken as indicated by line 4-4 on FIG. 1.

The fan illustrated and described is a propeller fan that is driven by a shaft S rotated by a prime mover 10 for the purpose of moving fluid axially of said shaft S. It is to be understood, however, that a reverse condition is contemplated wherein axially moving fluid rotates the fan to drive the shaft S, as will be apparent from the following description. As shown, the present invention involves a hub A, a blade B, a drive pin C and a clevis or yoke D. It is possible, in the broad sense, to embody the present invention in a single bladed propeller fan, however, in its preferred form it is embodied in a two bladed fan, in which case there is a pair of blades B and a pair of yokes D. .The invention is characterized by the single drive pin C that mounts one or a pair of blades B that pivot and lean forwardly into the fluid driven thereby.

The shaft S is shown as a round cylindrically shaped part that projects forwardly from the case of the prime mover 10. The prime mover 10 can be of any suitable type adapted to apply torque to the shaft S for rotating the same.

The hub A can vary in shape and is shown as an enlargement at the forward end of the shaft S. The hub A can be a separate part fixed to the shaft S and it is provided to carry the drive pin C and a blade positioning means E, later described.

It is preferred that there be two like diametrically opposite blades B, although a single blade B can be employed with a diametrically opposite counterbalance (not shown). The blades B are alike or identical units of construction characterized by a single cross-sectional configuration that makes for a light weight blade and for a durable mounting therefor. More specifically, it is highly desirable to have lightness in order to reduce centrifugal forces, together with a single cross-sectional configuration to retain a simple and relatively inexpensive blade and mounting construction. As shown, the blade B is' of uni-. form cross-sectional configuration and is fabricated of two elements, a leading edge 15 and a trailing edge 16. These two elements can be made by various methods, but preferably by extruding them of light weight metal such as aluminum or magnesium or alloy thereof.

The leading edge 15 has a rounded nose portion 14 fairing into a flat bottom 13 and it has a cam-bered top 12. The bottom 13 is provided with a keyshaped recess that is longitudinally dis-posed and coextensive with the element, preferably in the shape of a flat angularly disposed or undercut wall 17. The top His of substantial chord-wise extent, one-half or more, being characterized by a flat inwardly disposed wall 18 co-extensive with the element. The leading edge 15 is an extrusion, as it is shown, having relatively thin Walls and with a flat marginal portion 19 at its rearmost edge.

The trailing edge 16 has a tapered cross-section with converging top and

bottom faces

20 and 21, respectively. The edge element 16 is solid in section as it extends rearwardly from the rearmost marginal portion 19 of the leading edge, and it is characterized by a thin walled cross-section, or panel that extends from the bottom face 21 to merge with the bottom 13 of the leading edge 15; The said panel has an inwardly disposed wall 22 opposed to and parallel with the wall 18, and co-extensive with the length of the element. The foremost edge 23' of the panel 21 is shaped to have nesting engagement with the key-shaped recess or wall 17, while the marginal portion 19 of element 15 nests in a recess extending lengthwise of the element 16.

As a result of the very simple blade construction above described, lightness is obtained, utilizing light weight material and said tubular construction. Additionally, however, the opposed and parallel walls 18 and 22 are adapted to receive the tang 25 of the mounting yoke D, later. described. The tang 25 is characteristicaly fiat. and elongate and of a width to allow its extension into the tubular blade B, and with its two opposite faces in sliding engagement with the said faces 18 and 22. Thus, through fasteners 26 are projected through the assembly of parts, so as to be in double-shear at Walls 18 and 22. Also, the two

blade elements

15 and 16 are readily. fastened together by fasteners 29, each in single-shear. The tang 25 closes the inner end of the blade B, while a cap 30 closes the outer end, and it is significant that the blade assembly is accom- .plished withaccessible fasteners and without resort to socalled blind fasteners.

In accordance with the present invention, the'single drive pin C is provided to mount the blade or blades B for driving connection with the hub A. The pin C is a straight cylindrical pin and it is disposed on an axis that intersects the hub axis at right angles. As shown, there is a-transverse bore 35 that passes through the hub A to receive the pin C, and to have driving engagement to turn the pin.

The yoke D of the present invention is the mounting element for the blade B, there being an identical yoke for each of the two blades. Due to the pivotal mounting on the axis of the single pin C, the blades B are permitted to flap or to lean forwardly toward the flow of fluid driven thereby. Further, centrifugal force operates on the blades B so as to extend them radially from the hub A. It is this resultant combination of moments, that is,

thrust counteracted by centrifugal force, that establishes the stable position of the blades B'relative to the shaft S without benefit of a rigid connection therebteween. The advantage is that the root sections of :blades B are not required to endure large bending stresses, since none exist. Consequently, stresses are steady and relatively reduced,, making a minimum but reliable structure feasible.

The yoke D is a clevis-shaped element having a pair of depending legs 36 and37.. The leading leg 66 is closer to the mean radial a of the structure while the trailing leg 37 is farther removed therefrom. The said legs have aligned

bores

38 and 39 adapted to receive thepin C. The legs are joinedby a head 40 that spans between the legs and which carries the radially projecting tang 25, above described. The tang 25 is suitably pitched, as circumstances require, and it is positioned so that the center of gravity or gravitational axis of the blade B (indicated as CG) is rearward, ortoward the trailing edge, of the radial extending at right angles from the shaft S. Thus, there is a moment whereby the Weight of the blade B can be equal to and neutralize the transmission of torque to the blade B from the hub A, this being accomplished by operation at an optimum predetermined. speed of rotation.

In order to limit flapping or leaning of the blades B opening cavity or recess.

4 the positioning means E is provided and which is incorporated in cooperating parts of the hub Afand yoke D. In accordance with the invention, the yoke D is shellshaped with depending side walls 45 defining an inwardly the hub A at the side of the pin C and on the radial a. The said lug 44 enters the said recess in the yoke D, with suitable clearance,and is engageable with the opposite side walls 45. The lug may be equipped with a resilient bumper 43 to snub excessive movement of the blades.

Another feature of the invention is that the yokes D are identical while still advantageously providing offset mounting of the two blades, respectively. 'As driving forces are applied to the pin C, in order to rotate the blades B, centrifugal forces acting on the rearwardly oifset center of gravity of the blades causes a counteracting moment to be developed and which opposes the moment caused by driving forces through the pin. As a result and at a predetermined speed of rotation and development of power, the two said moments neutralize bending in the pin C, to the endthat the pin C is subjected only to shear forces at the

legs

36 and 37. 7

Having described only atypical preferred form an application of my invention, I do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to myself any modifications or variations that may appear to those skilled in the art and fall within the scope of the following claim:

Having described my invention, I claim:

A structure of the character described and comprising a pair of diametrically opposite aerodynamic blades projecting on spaced parallel gravitational axes transverse to the axis of a supporting rotating shaft and including, a drive pin on an axis disposed normally through and intersecting the axis of the shaft, a yoke, carrying each blade and each yoke pivotally mounted on said drive pin,

said gravitational axes thereof intersecting said drive pin at right angles and disposed axially along the axes of said drive pin at diametrically opposite points displaced radial-- ly from the axis of the supporting rotating shaft and means limiting pivotal movement of each yoke relative to the other and comprising diametrically opposite lugs projecting radially from the shaft and each engageable with a wall on a yoke.

References Cited by the Examiner V UNITED STATES PATENTS EDGAR W. GEOGHEGAN, Primary Examiner.

EMILE PAUL, ABRAM BLUM, JULIUS E. WEST,

Examiners.

A stop lug 44 is provided on.