Abstract:
The invention provides a weight-reducing bearing assembly for rotary aircraft. An opposed tapered conical elastomeric flap bearing assembly for rotary aircraft includes an outer housing having an outer surface and an inner surface. The outer surface is configured to mechanically connect the bearing assembly to the attachment sections of the hub center body. The inner surface is configured to receive a pair of opposed taper conical bearing elements. An inboard bearing element and an outboard bearing element are located within the outer housing. The bearing elements are arranged in an opposed manner. An axial pre-load can be applied to the opposed bearing assembly wherein the resulting force couple bearing pre-load path is maintained entirely within the bearing assembly. Consequently, the weight of the main rotor hub is reduced increasing the efficiency of rotary flight.

Description:
RELATED APPLICATION  
         [0001]    This application incorporates by reference application titled “Installation of Internally preloaded Opposing Conical Elastomeric Bearing” invented by Neal Muylaert; attorney docket BOEI-1-1006.  
         FIELD OF THE INVENTION  
         [0002]    This invention relates generally to elastomeric bearings and specifically to opposed internally pre-loaded conical elastomeric bearings.  
         BACKGROUND OF THE INVENTION  
         [0003]    A key component of a helicopter is the main rotor hub. It provides attachment of the main rotor blades during operation. Rotational power is delivered to the main rotor hub to provide rotational velocity to the blades in order to create aerodynamic lift. The main rotor hub must allow for rotational motion of the blades in the vertical (flap), horizontal (lead-lag), and axial (pitch) directions near the blade root attachment with the hub to accommodate flight control authority and dynamic stability. Main rotor hub systems that accommodate these motions with discrete hinge mechanisms are referred to as fully articulated hubs. Through out the history of the helicopter, engineers have struggled to provide these rotational freedoms with bearing systems that can accommodate high frequency and high amplitude oscillatory motion under high trust loading created by the centrifugal force of the rotating blades. Elastomeric bearings have become an industry standard for accommodating flap-wise motion in articulated hub systems. These bearings are composed of elastomeric material that allows for shear compliance within the elastomer, and for rotational freedom while reacting radial centrifugal force in compression.  
           [0004]    Elastomeric conical bearings are commonly used in bearing assemblies for helicopter rotor systems to accommodate rotor motion. The bearing assemblies are axially preloaded to prevent the conical bearing elements from experiencing a resultant tensional load. Currently, mono-directional bearing elements are employed at each attachment site of the main rotor hub. FIG. 1 depicts a view of a prior art articulated hub assembly  20   a . The hub assembly  20   a  includes a tire bar  26  connected to a hub center body  22 . The tie bar  26  is connected to the center body  22  in a similar manner as disclosed in FIG. 1, however, the bearing assembly  30   a  is substantially different. The bearing assembly  30  includes a pair of conical bearing elements  52  contacting the journal  28  on the bearing&#39;s inner surface  52  and the outer bearing surface is contained within an outer housing  42   a . Each bearing element is a mono-directional single conical taper bearing having an elastomeric element  54  contained within. The conical bearings are arranged such that the apex of the conical elements extends radially outward from one another. The bearing arrangement yields a force couple that extends from one bearing to the other. The force couple yields a bearing pre-load path  43  extending through the hub center body  22 .  
           [0005]    The prior art design creates an extended force couple resulting in a bearing pre-load path extending through the main rotor hub center body. The hub center body must be designed to carry the extra loading. The extra design requirements add weight to the overall rotor hub reducing the aircraft&#39;s load capacity and fuel efficiency.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention provides a weight-reducing bearing assembly for rotary aircraft. An opposed tapered conical elastomeric flap bearing assembly for rotary aircraft includes an outer housing having an outer surface and an inner surface. The outer surface is configured to mechanically connect the bearing assembly to the attachment sections of the hub center body. The inner surface is configured to receive a pair of opposed taper conical bearing elements. An inboard bearing element and an outboard bearing element are located within the outer housing. The bearing elements are arranged in an opposed manner. An axial pre-load can be applied to the opposed bearing assembly wherein the resulting force couple bearing pre-load path is maintained entirely within the bearing assembly. Consequently, the weight of the main rotor hub is reduced increasing the efficiency of rotary flight.  
           [0007]    The proposed invention provides a unique flap bearing arrangement by localizing the pre-load within each flap bearing assembly and, thus, eliminates the necessity for the transfer of the pre-load through the hub structure. The elimination of bearing pre-load through the hub structure can significantly reduce weight of the rotor hub assembly. Many components, including the bearing attachment flanges on the hub center body as well as the bearing housings can be configured to accommodate only the design flight and static loads without having to carry the off axis bearing pre-loads. The unique design of the instant invention yields an approximate 6%-10% weight reduction in the main rotor hub assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings.  
         [0009]    [0009]FIG. 1 is a partially sectional isolated plan view of a prior art bearing assembly;  
         [0010]    [0010]FIG. 2 is an isometric view of an articulated hub assembly;  
         [0011]    [0011]FIG. 3 is a partially sectional isolated plan view of a bearing assembly of the instant invention;  
         [0012]    [0012]FIG. 4 is an exploded isometric view of the bearing assembly;  
         [0013]    [0013]FIG. 5 is an isometric view of the bearing assembly;  
         [0014]    [0014]FIG. 6 is an alternative isometric view of the bearing assembly;  
         [0015]    [0015]FIG. 7 is a partial sectional view of the bearing assembly; and  
         [0016]    [0016]FIG. 8 is a partial sectional view of the bearing assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 2 depicts a fully articulated hub assembly  20  that includes a pre-loaded, opposed flap bearing assembly  30  that maintains a force couple bearing pre-load path entirely within the flat bearing assembly  30 . The hub assembly  20  includes a plurality of rotor assemblies  24  radially attached to a hub center body  22 . The articulated hub assembly  20  is designed to allow and to control the flap, pitch and lead-lag motion of an aircraft rotor.  
         [0018]    In a presently preferred embodiment, the rotor assembly  24  includes a tie bar  26 . However, any other rotor attachment structure or assembly is considered within the scope of the invention. The tie bar  26  is a substantially cylindrical shaped element having a pair of radially opposed journals  28  at an end. Each journal is designed to receive the flap bearing assembly  30 . The bearing assembly  30  extends over the journal  28  attaching itself to the journal  28 . The tie bar  26  and bearing assembly  30  combination attach the rotor assembly  24  to the hub center body  22 .  
         [0019]    The flap bearing assembly  30  includes an inboard bearing element  32  and an outboard bearing element  34  contained within an outer housing  42  to form the bearing assembly  30 . The outer surface of the outer housing  42  is configured to attach the bearing assembly to another structure, for example, the main rotor hub 22 . In a presently preferred embodiment, the outer housing  42  includes two pair of radially extending bearing flanges  36  configured to mate with a hub yolk  38  of the hub center body  22 . However, any other structure or arrangement for attaching the bearing assembly to the rotor hub located on the outer housing  42  is considered within the scope of this invention, for example, a single pair of projections or molding the outer housing to the hub. A plurality of flange bores  60  align with yolk bores  40  allowing fasteners (not shown) to rigidly attach the structures.  
         [0020]    [0020]FIG. 3 depicts an isolated view of the hub assembly  20   b  of the instant invention. The tie bar  26  is attached to the hub assembly  20   b  via a pair of bearing assemblies  30   b  attached to the hub yolk  22  by attachment lug  58 . The bearing assemblies  30   b  extend over and contact each respective journal  28 . Each bearing assembly  30  includes a mated set of opposed, taper conical elastomeric bearing elements,  32  and  34 , enclosed within an outer housing  42   b . When preloaded in the axial direction, the opposed bearing assembly  30   b  limits the force couple to each individual bearing assembly  30   b . According to the invention, the force couple is not passed through the hub center body. The force couple yields a bearing pre-load path  43   b  that remains entirely within each respective bearing assembly  30   b.    
         [0021]    [0021]FIG. 4 depicts an exploded view of the flap bearing assembly  30   b . The bearing assembly  30  includes an outboard bearing element  34  and an inboard bearing element  32  disposed within an outer housing  42   b . The outer housing  42  includes a first section  45  and a second section  47 .  
         [0022]    The first section  45  includes a pair of radially extending flange sections  36 . The flange sections  36  are configured to align with the hub yolk  38  (FIG. 1). An inner surface of the first section is shaped to receive the inboard bearing element  32 . More specifically, an outer surface of the inboard bearing element  32  is bonded to the inner surface of the outer housing  42   b  in the first section  45 . The bonding method is suitably any commonly known bonding method used in the art.  
         [0023]    Disposed inside and adjacent the outer surface of the inboard bearing element  32  is an elastomeric element  54 . The composition of the elastomeric element  54  can be any of the commonly employed elastomeric compositions, and is variable based upon the loading requirements of the employment environment. For example, an elastomeric element with a plurality of metal laminates is considered within the scope of this invention.  
         [0024]    Positioned on an inner surface of the elastomeric element  54  is an inner race of the inboard bearing element  62 . The inner race  62  includes a distal section  63  and a proximal section  65 . The outer surface of the inner race  62  is tapered in the direction of the inner bearing element  32 . The inner surface of the proximal section  65  forms an axial bore  44  therethrough. The bore  44  is sized to receive the journal  28  through an open end  55  and extends into the distal section  63 . The axial bore  44  terminates at an inner race closed end plate  53  located in the distal section  63 . An outer surface of the distal section is substantially cylindrically shaped and configured to receive an inner race of the outboard bearing  64 .  
         [0025]    The outboard bearing element  34  is also a taper conical elastomeric bearing wherein the taper is in an opposing direction to the inboard bearing element  32 . The outer surface  66  is configured to bond with the inner surface of the second section  47  of the outer housing  42   b . The inner race has an open end to receive the outer distal section  63  of the inboard bearing inner race  62 . At another end of the inner race of the outboard bearing  64  is an outer plate  56 . Sandwiched between the outer race  66  and inner race  64  is another elastomeric element  54 .  
         [0026]    The outer plate and the inner race closed end plate  63  have a plurality of aligned bores extending therethrough. A tie bar attachment bore  46  is centrally disposed through each to receive a tie bar attachment lug (not shown). The tie bar attachment lug maintains the bearing assemblies  30  connection with the tie bar  26 . Further, a plurality of coupler bores  48  area disposed through the respective surfaces. Each coupler bore receives a coupler lug  49  (FIG. 6) to maintain the spatial integrity between the inboard and outboard bearing elements. Further, a plurality of dowel bores extend through the respective plates, each bore receiving alignment dowels (not shown) extending from the journal end  29  (FIG. 1).  
         [0027]    [0027]FIG. 5 depicts an assembled view of the flap bearing assembly  30 . The inboard bearing element  32  and the outboard bearing element  34  are coupled via a friction fit between the respective elements and the bearing coupler lugs  49 . More specifically, the inner race of the outboard bearing  64  and the inner race of the inboard bearing  62  are frictionally mated upon insertion of the outboard bearing element  34 . Additionally, the outer race of the outboard bearing  66  is bonded to the inner surface of the outer housing  42 . Consequently, the outer housing  42  encompasses both the inboard bearing element and the outboard bearing in a single unitary assembly.  
         [0028]    [0028]FIG. 6 depicts the assembled flap bearing assembly  30 . The bearing assembly includes an outer housing  42  surrounding the inner and outer bearing elements  32  and  34 . The outboard bearing assembly  34  is pressure fit into the inboard bearing element  32  and then bonded between the outer race of the outboard baring  66  and an inner surface of the inboard bearing.  
         [0029]    As discussed above, bearing coupler lugs  49  are disposed through the bearing coupler bores  48  connecting the outboard bearing element to the inboard bearing element. Additionally, a tie bar attachment bore is axially located through the respective bearing elements and is in alignment with a respective bore in the journal end  29  (see FIG. 1). An attachment lug  58  (not shown) is disposed through the tie bar attachment bore  46  and mechanically fastened to the journal end  29 . Consequently, a bearing integrity redundancy is created by to the two separate coupling structures.  
         [0030]    The bearing assembly  30  is axially pre-loaded. In the preferred embodiment, a bearing assembly  30  axial pre-load of 8500-15,000 lb. range is desired. The pre-load helps to prevent the elastomeric elements of the bearing assembly  30  from tensional loading during operating conditions. However, any other pre-load is considered within the scope of this invention. The axial pre-load can be applied through the coupler lugs  49 , the tie bar attachment lug (not shown) or combinations thereof.  
         [0031]    [0031]FIGS. 7 and 8 depict an isolated view of the opposed conical elastomeric bearings with and without pre-loading, FIG. 7, and with pre-loading, FIG. 8. A bearing gap  82  is located between the respective inboard and outboard bearing elements,  32  and  34  respectfully, prior to any axial pre-loading. As the axial pre-load is applied the bearing elements,  32  and  34 , are brought together. The inner races,  62  and  64 , frictionally engage one another and any space, or bearing gap  82 , between the bearing elements,  32  and  34  is removed. The bearing elements,  32  and  34 , combine within the bearing assembly  30  to carry the flap-wise motion of the rotor assembly  24 .  
         [0032]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.