Abstract:
A propeller blade retention system and method of manufacture are disclosed. Because of the design, a truly integral hub is able to house a set of variable pitch blades. Each hub socket establishes a substantially cylindrical interface with its respective blade, making the blade slidably receivable for installation. Each blade is allowed axial rotation, and held inside the socket by a set of angular contact bearings. A snap ring locks the blade against coming back out of the socket. An O-ring is provided in the interface to create a fluid seal. The hub alone accomplishes all of the required load-bearing and weather-seal functions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to aircraft. More specifically, the invention relates to the field of propeller and hub designs. 
     2. Description of the Related Art 
     Sophisticated blade retention systems are normally employed in accommodating variable pitch propeller arrangements for aircraft. This is because the system must accommodate the mechanical equipment necessary to rotate each blade on its longitudinal axis, while at the same time adequately secure each blade against the great tensile and rotational loads it must carry when in operation. 
     Each blade is normally retained inside a hub assembly. Ideally, any reductions in blade and/or hub weight is seen as a significant advance. But it is important that structural integrity not be compromised in these weight reduction pursuits. 
     SUMMARY 
     The present invention is defined by the claims below. Embodiments of the present invention include a propeller system. The system includes a hub. The hub has at least one socket having a substantially cylindrical internal surface. An adjustable-pitch blade is received in the hub. The blade has an airfoil portion and a base portion. A substantially cylindrical outer surface is formed on the base of the blade. Thus, the outer surface of the base portion of the blade is slidably receivable in the substantially cylindrical internal surface of the socket. 
     The blade is lockable against axial translation once installed, but otherwise axially slidable. Once installed, the blade is rotatable relative to its center axis. This enables pitch change in operation. 
     A sealing member is received in an interface between the substantially cylindrical outer surface of the bottom portion of the blade and the substantially cylindrical internal surface of the socket. This creates a fluid barrier between the inside and outside of the socket, while allowing for axial translation of the blade into the socket during installation, and also allowing for rotation of the blade to change pitch. 
     The system also includes an angular contact bearing arrangement. This arrangement includes a set of ball bearings which are housed within an inner race on the blade and an outer race on the hub. The outer diameter of the inner race is small enough to enable passage through the substantially cylindrical internal surface of the socket during installation. The outer race is made to have an inside diameter large enough that it does not interfere with the substantially cylindrical outer surface of the blade during installation. 
     This arrangement enables the hub to be truly integral, in that it is forged from the same integral material for added strength. 
     Similarly, the inner and outer races are also formed as substantially-integral parts that do not have to be installed in halves, or some other piecemeal fashion. 
     In embodiments, the substantially cylindrical outer surface exists on a collar provided on the base portion of the blade. 
     In embodiments, the sealing member is an O-ring which is received in an annular channel defined in the substantially cylindrical outer surface of the blade collar and seals against the substantially cylindrical internal surface of the socket. Alternatively, the O-ring could be received in an annular channel defined in the substantially cylindrical internal surface of the socket and seal against the substantially cylindrical outer surface of the collar. 
     In embodiments, the upper portion of the substantially cylindrical outer surface on the collar includes an annular groove which receives a snap ring which, when installed in the annular groove in the blade, prevents the blade from falling into the socket by holding the blade out, supported by a shim on the outside of the hub. Conversely, the snap ring contains the shim assembly in place, trapped against the hub within an angular notch defined by a surrounding upcrop. This arrangement of snap ring and shim takes up the slack in the installation of the blades, and prevents the balls of said angular contact bearing from escaping their installed positions. 
     In some embodiments, each of the: (i) outer diameter of the inner race, (ii) inner diameter of the outer race, (iii) substantially cylindrical internal surface of the socket, and (iv) substantially cylindrical outer surface of the bottom portion of the blade are substantially in line when viewed in cross section. 
     Also disclosed in embodiments is a method of assembling a propeller system including the steps of manufacturing an integral hub; causing a blade-receiving socket to be formed in the hub, the socket having a substantially cylindrical internal surface; producing a blade to have a base portion which has a substantially cylindrical outer surface which is receivable in and slidably mates with the substantially cylindrical internal surface of the socket; providing an angular contact bearing arrangement inside the socket, the bearing arrangement preventing the blade from coming out of the hub socket, while allowing for rotation on a center axis of the blade; including a locking mechanism to secure the blade against sliding into the hub after installation; and establishing a seal between the substantially cylindrical outer surface of the bottom portion of the blade and the substantially cylindrical internal surface of the socket. The hub, in embodiments, is made of forged metal construction. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein: 
         FIG. 1  is a perspective view of a single propeller blade before installation into the hub in a first embodiment; 
         FIG. 2  shows a sectional view taken in a plane taken from the axis of rotation for the propeller-blade-retention arrangement for the first embodiment; 
         FIG. 3  shows the bearing-race arrangement of the blade-retention mechanism with a removed portion showing the internals; 
         FIG. 4  shows an integral one-piece hub used for retaining the propeller blades; 
         FIG. 5  is an enlarged cross sectional view of a blade/hub interface for the first embodiment for a propeller-blade-retention system; and 
         FIG. 6  is an enlarged cross sectional view of an alternative second embodiment for a propeller-blade-retention system. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is a propeller system. More specifically, a system for securing propeller blades into a one-piece hub. One embodiment is disclosed in  FIGS. 1-5 , and a second embodiment is disclosed in  FIG. 6 . 
     Referring first to  FIG. 1 , a propeller blade  10  is comprised of carbon fiber composite materials. It is also possible, and is contemplated that other composite materials could be used instead, the use of such would also fall within embodiments of the current disclosures. Blade  10  has an airfoil portion  12  and a base. The base of the blade includes a cast plastic collar portion  16  which is received in a blade cup  18 . Inside the blade is a hollow tubular area  14 . In the disclosed embodiment, the blade is fixed in collar  16  using an integral loop  22  formed at the blade bottom. Loop  22  is formed around an internal ring  77  which enables the bottom of the blade to be secured. Although a loop/ring arrangement is used in the embodiments depicted, it should also be understood that other techniques of securing the blade within the collar could be used instead and still fall within the scope of embodiments contemplated herein. Collar  16  includes a snap-ring-receiving groove  55  and an O-ring receiving annular channel  53 . An annular inner race  32  is also fixed in place about the periphery as shown. A pin  20  at the bottom of blade  10  is what is used to change the pitch of the blade, as will be known to those skilled in the art. One skilled in the art will recognize that other systems, e.g., bevel gear arrangements, could be used instead and still work with the disclosed blade retention processes. 
       FIG. 2  shows blade  10  secured in a hub  50  after a snap ring  26  and a shim arrangement  24  have been installed. The figure is also helpful in showing the overall orientations of the various parts which will be further described in discussions regarding the other figures. 
       FIG. 3  shows the details for the bearings and races as they appear after a blade has already been installed in the hub. This figure shows the outer race  30  (which is press fit onto a surface  58  in a blade socket  54  in  FIG. 4 ) and an inner race  32  (which is fixed to the bottom of the blade  10  as shown in  FIG. 1 ). Even though the front portions of races  30  and  32  shown in  FIG. 3  are removed, it should be understood that they are actually of one piece ring-like construction. A plurality of angular contact ball bearings  38 , after installation, will be angularly sandwiched between the races  30  and  32  as shown in  FIG. 3 . Thus, outer race  30  bears on each ball bearing at a direction that is inward and down, whereas inner race  32  applies an opposing force on each ball bearing that is outward and up. Ball bearings used in this type of arrangement are sometimes referred to as “angular contact” ball bearings. It will be described later, that because these races are offset, they make the installation of the blade into a unitarily constructed hub possible in ways not before possible. Each ball bearing is a standard ball bearing of unitary construction. Although the ball bearings  38  are separate devices, they are all included in a stringer  40 . The stringer arrangement  40  includes separator portions  34  and a common spine  36 . The spine  36  serves to connect each of the separator portions  34  together so that the stringer assembly  40  is actually of unitary construction. 
     Shim arrangement  24  and snap ring  26  are snapped into the annular channels at a step in the installation process to secure the blade in a hub  50  in one of three sockets  54 . The hub and sockets are shown in  FIG. 4 . The hub is a forged and machined part of single-piece construction. Hub  50  also includes a front cylinder can opening  52 . The can is bolted to this and used to enclose a fluid reservoir which is used for hydraulic control purposes. The hub  50  is mounted on the aircraft at the rear of the hub at an engine/crank shaft mounting end  56 . Inside each of the three sockets  54 , there is a bearing surface  58 . This is where outer race  30  will be press fit as an initial step in securing each blade in the hub. 
     Reference back to  FIG. 2  which shows a view of one blade installed in the hub in cross section at the blade axis of rotation is helpful in understanding how the already-described components are used in the assembly process. The steps for executing that process will now be described. 
       FIG. 5  shows a close up cross-sectional view at the blade/hub interface  500 . More specifically, it can be seen that interface  500  is defined primarily between the substantially cylindrical outer surface of the blade collar  16  and a matching inner surface  502  of socket  54  of hub  50 , but also includes the opposing cylindrical surfaces  514  and  516  of outer race  30  and inner race  32 , respectively. Interface  500 , when viewed in cross section, is in a substantially straight line. This is because the diameter of the outside surfaces of collar  16  are substantially the same at all interface locations. This is true not only for the outer bearing cylindrical surface  510  which defined an annular groove  53  which is adapted to receive and contain a sealing member, in this embodiment, an O-ring  51 , but also for an outer diameter  516  for race  32 . It should be noted that because of the substantially cylindrical nature of interface  500 , inner race  32  and outer race  30  can pass each other despite their integral construction. Adequate sizing of the hub opening  52  allows installation of integral race  30 . The construction process of the blade makes it possible to install integral race  32  on the base of the blade. 
     A substantially cylindrical inside surface  502  of hub socket  54  is bored or otherwise formed at a diameter which is only slightly larger than the outside diameter of the blade collar  16 . This includes the inside diameter of surface  514  of race  30 . Because of this, the blade, along with sealing member  51 , will be slidably receivable in the blade socket before ball bearings  38  are installed. One way this differs from the traditional processes is that the sealing mechanics are installed simultaneously with the introduction of the blade. Conventionally, the fluid seals have had to be externally mounted after the blade was locked in place. The details regarding installation will be discussed in detail below. 
     It should be noted that although sealing member  51  is shown in the  FIGS. 5 and 6  embodiments as being an O-ring, that numerous other sealing members or systems, e.g., Chevron seals, radial-lip seals, could be used instead and still fall within the broad aspects of these disclosures. Additionally, although the annular channel used to receive O-ring  51  is shown in the drawings as being formed in the outer cylindrical surface  510  of the blade collar  16  such that it bears against the substantially cylindrical internal surface  502  of the socket, it should be understood that, alternatively, the annular receiving channel for O-ring  51  could be received in an annular channel defined in the substantially cylindrical internal surface  502  of the socket such that it bears against the substantially cylindrical outer surface  510  of the collar. 
     Also evident from this view of interface  500  is that the shim arrangement  24  includes both a shim body  506  and a carrier  504 . Shim arrangement  24  when installed is received by an annular notch  65  formed in the upper part of a hub socket (e.g., one of the plurality of sockets  54 ). Shim  506  is laterally retained by an inside surface of an upcrop portion  515 . Carrier  504  is sandwiched between the upper surface of shim  506  and the underside of snap ring  26 . Snap ring  26  is received in an annular groove  512  defined in the outer cylindrical surface  510  of the blade collar  16 . As those skilled in the art will recognize, the snap ring is substantially continuous, but open-ended. Much like with the common piston ring, the open-endedness of ring  26  provides it with the moderate flexibility necessary to snap it into groove  512 , but once installed it will prevent the blade from moving into the hub socket  54 , while the already-installed angular contact bearings  38  prevent movement out. Thus, the blade is effectively locked in place and cannot translate in any axial direction. It should also be understood that the locking arrangement might also be reversible from hub to blade or in some other fashion. Thus, the scope of the disclosed system and processes should not be limited to the arrangements disclosed unless otherwise specified in the claims. 
     The process of assembling the blades into the hub will now be discussed. First, looking at  FIG. 4 , the rear/engine end  56  of unitary hub  50  is secured on a tool (not shown) such that a first socket  62  of the plurality of sockets  54  is positioned downward as shown. Then, or before as a preliminary, outer race  30  is press fit onto bearing surface  58  for that particular socket  62 . Race  30  is able to be installed as an integral piece through hub opening  52 . After race  30  is in place, the user picks up a blade  10 . The snap ring  26  and shim arrangement  24  features are not yet in place on the device. (These features will later be installed into their ultimate reciprocating locations to lock the blade into position.) Snap ring  26  and shim carrier  504 , however, should be preloaded onto the blade by sliding it onto the airfoil portion so that it will be ready for installation later. 
     Grabbing the blade by its airfoil, the user then inserts the bottom base end (which includes collar  16 ) up through bottom socket  54  until inner race  32  has been translated to a position slightly past the final assembled and seated bearing position of outer race  30 . This presents an annular gap between races  30  and  32  into which the ball bearing string  40  can be inserted by the user alone or a partner. The positions of races  30  and  32  relative to one another, and the determination of whether the desired position has been achieved, can be seen by looking through front cylinder can opening  52  (see  FIG. 4 ). Before this, as a preliminary, the user or a partner will have already secured each of the ball bearings  38  into the stringer assembly  40 . That preliminary action presumed, the partner, will then, reaching though front opening  52 , string the ball bearings into the annular gap created between races  30  and  32  until all of the ball bearings have been installed, and spine  36  is pointing downward. Once so positioned, the blade can be released, causing ball bearings  38  in stringer  40  to be mashed between races  30  and  32  by the gravitational force of the blade, which is hanging down through socket  62 . 
     Now that the bearings have been installed, the blade cannot escape outward away from the hub. Next, the blade is locked against falling into the hub by installing the shim arrangement  24  and snap ring  26 . To do this, the shim arrangement is first brought into position into the annular notch  65  (See  FIGS. 4 and 5 ) which is defined in the hub. Next, snap ring  26 , which as described above was preloaded onto the blade over the airfoil section, is snapped into annular groove  512  which goes around the upper outside portion of collar  16 . This secures the first blade against moving axially into the hub socket thereby locking stringer  40  and balls  38  in the assembly even when the propeller is turned over on the mount. 
     Once the first blade is installed, the user will be able to rotate the hub around on the tool (not shown) so that another of sockets  54  is pointed down. At that time, a second blade is selected and the same procedures discussed above are repeated to install it in the second socket. Finally, these same processes are used to install the third blade in the third remaining socket to complete the blade attachments. One skilled in the art will recognize that these same general processes could be followed to install and then retain blades in hubs adapted to hold two or more blades. 
     Once all three blades have been attached, the control components are installed using known techniques. Then, a nose can  37  is installed over the front cylinder can opening  52 , and other known procedures are instituted to complete the installation process. 
     Once installed, each blade  10  is able to rotate about its longitudinal axis for variable pitch when pin  20  is acted on by an actuator mechanism  21  (see  FIG. 2 ) in which pin  20  is received. The angular contact roller bearings  38  existing between inner and outer races  32  and  30  enable this rotation. As this rotation occurs, the mated relations between the outer cylindrical surface  510  of collar  16  inside of the cylindrical internal surface  502  of the hub socket provide the dynamic stability necessary and react the bending loads from the blade. 
     In other embodiments of the invention, an additional set of roller bearings are provided between the outer cylindrical surface of the collar  16  and the inside surfaces of socket  54  in hub  50  to reduce friction and increase the load-bearing capacity. 
     Because of the system disclosed, races  30  and  32  and hub  50  that are each of unitary construction. Conventionally, artisans have had to use two part races and/or two or more part hubs to accomplish these objectives. The unitary nature of the device herein, however, enables drastic reduction in weight, which is critical to aircraft performance and highly desirable. Further, the design and assembly processes disclosed herein enable the use of a truly integral hub. Some conventional designs, e.g., U.S. Pat. No. 4,921,403 issued to Poucher et al., require clamping sealing rings which are bolted onto the upper portion of the hub socket and are necessarily removable because of assembly requirements. Here, however, the hub is completely integral while still enabling blade installation. This reduces the number of potential leak paths available for the control and lubrication fluids existing in the hub dramatically improving the overall quality of the hub-to-blade seal. 
     An alternative embodiment for a blade/hub interface  600  is shown in  FIG. 6 . Like the earlier embodiment, the assembly has a collar  616  which includes an O-ring  651  in an annular groove. Unlike the  FIG. 5  embodiment, this embodiment includes a plurality of outboard roller bearings  602  which are embedded into an annular slot  606  in collar  616  and which engage the inner surfaces of an outer bearing race  604 . It will be recalled that the  FIG. 5  embodiment simply allowed for rotation between outer surface  510  of blade collar  16  and inner surface  502  of the hub socket. While the system of  FIG. 5  might be most desirable for light aircraft propeller assemblies, the frictional resistance created by the assembly might be too great for use with larger aircraft propellers. Because of this, the roller  602  and outer bearing  604  arrangement of  FIG. 6  creates an interface  600  which offers less frictional resistance and greater load-bearing capacity. Another difference is that collar  616  is able to be constructed of metal rather than the plastic described for collar  16 . Because of this, the collar  616  is able to be integral with the blade angular contact bearing race  632 . 
     In terms of installation, the  FIG. 6  embodiment also allows for the same installation processes discussed for the  FIG. 5  embodiment. This is because roller bearings  602  are embedded in an annular channel defined in collar  616 . Even though bearings  602  extend out to the extent necessary to engage outer bearing  604 , they do not extend out so far that the blade collar, once loaded with bearings, will not fit through the cylindrical cavity defined by internal surfaces  608 ,  610 , and  612 . Similarly, the external cylindrical surfaces of the blade collar, e.g., surface  616 , are also created such that they do not interfere with the blade being axially slidable into the collar. Thus, this arrangement enables the same assembly processes discussed above, as well as enabling the use of integral races and a truly integral hub. 
     Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described.