Patent Publication Number: US-2015078909-A1

Title: Rotor blade and structural system for coupling the rotor blade in a rotor hub

Description:
BACKGROUND 
     1. Technical Field 
     The present application relates to a rotor blade, as well as a structural system for coupling the rotor blade to a rotor hub. 
     2. Description of Related Art 
     Conventionally, rotor blades have been coupled to the rotor hub in a variety of ways. One conventional rotor blade attachment system involves attaching the rotor blade with two bolts oriented along a chordwise axis at the root end of the rotor blade. Another conventional rotor blade attachment system involves attaching the rotor blade with two bolts oriented along a spanwise axis at the root end of the rotor blade. Though significant improvements in rotor blade attachments have been made, significant room for improvement remains. 
     There is a need for an improved rotor blade, as well as an improved structural system for coupling the rotor blade to a rotor hub. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the embodiments of the present application are set forth in the appended claims. However, the embodiments themselves, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of a rotorcraft having a rotor blade, according to an example embodiment; 
         FIG. 2  is perspective view of the rotor hub, according to an example embodiment; 
         FIG. 3  is a top view of the rotor hub, according to an example embodiment; 
         FIG. 4  is a top view of the rotor hub, according to an example embodiment; 
         FIG. 5  is a top view of the rotor hub, according to an example embodiment; 
         FIG. 6  is a cross-sectional view of the rotor hub, taken from section lines  6 - 6  in  FIG. 5 , according to an example embodiment; 
         FIG. 7  is a perspective view of a rotor blade, according to an example embodiment; and 
         FIG. 8  is a partial perspective view of the rotor blade of  FIG. 7 , according to an example embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the apparatus and method are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. 
     Referring now to  FIG. 1  in the drawings, a rotorcraft  101  is illustrated. Rotorcraft  101  has a rotor system  103  with a plurality of rotor blades  105 . The pitch of each rotor blade  105  can be selectively controlled in order to selectively control direction, thrust, and lift of rotorcraft  101 . Rotorcraft  101  further includes a fuselage  107 , anti-torque system  109 , and an empennage  111 . Rotorcraft  101  further includes a landing gear system  113 , to provide ground support for the aircraft. It should be appreciated that rotorcraft  101  is merely illustrative of a variety of aircraft that can implement the embodiments disclosed herein. Other aircraft implementations can include hybrid aircraft, tilt rotor aircraft, unmanned aircraft, gyrocopters, and a variety of helicopter configurations, to name a few examples. 
     Referring to  FIGS. 2-6 , rotor hub  103  is illustrated in further detail. Rotor hub  103  includes a yoke  109  coupled to a mast  113 . Each rotor blade  105  is coupled to the yoke  115  with a grip  119 . An inboard portion of each grip  119  is secured within an opening of the yoke  115  with a centrifugal force bearing  135 . Grip  119  is a single continuous member having an upper extension  137  and a lower extension  139 . Rotor blade  105  is attached to the outboard portion of grip  119  with a unique arrangement of a first bolt  129 , a second bolt  131 , and a third bolt  133 . A pitch horn  123  is interposed between rotor blade  105  and the upper and lower extensions  137 ,  139  of grip  119 . A damper  121  is attached between yoke  115  and a damper attachment portion  141  of with pitch horn  123 . 
     During operation, dynamic forces act upon rotor blade  105  and associated components of rotor system  103 . Primary dynamic forces include a combination of centrifugal force loading in a centrifugal force direction  145 , a chordwise bending in a bending direction  147 , and a beamwise bending in a bending direction  149 . Such loading must be reacted by the attachment mechanism used to attach the rotor blade  105  to the grip  119 . Further, torsional loading about pitch change axis  143  can be experienced from aerodynamic loading as well as pitch change inputs from pitch horn  123 . Conventional two-bolt attachment arrangements have several shortcomings. For example, when the two bolts are arranged approximately spanwise, the torsional loading about pitch change axis  143  can induce bending along an axis formed by the two spanwise located bolts. In the conventional two-bolt arrangement wherein the two bolts are arrange approximately chordwise, the beam bending in direction  149  can induce bending along an axis formed by the two chordwise located bolts. In these conventional two-bolt arrangements, the two bolts must be sized in order to react the bending loads, which can add weight since a larger diameter bolt can increase edge distance requirements, bolt weight, and rotor blade structure at the root end. 
     In contrast to conventional two-bolt arrangements, the embodiments of the present disclosure include a three-bolt triangular pattern that collectively react the operation loads in such a manner so as to reduce the size of the bolts and corresponding attachment lugs in both the rotor blade  105  and grip  119 , thereby reducing the overall weight of rotor system  103  and increasing the useful load of the rotorcraft  101 . Further, the aerodynamic drag of the three-bolt pattern is actually less than two-bolt chordwise arrangement. Furthermore, utilizing more than three bolts can add unnecessary weight, and further add complexity to the manual rotor blade folding procedure. 
     The three rotor blade attachment bolt arrangement includes the first bolt  129 , which is the most inboard of the three bolts, and lies upon a center spanwise plane of rotor blade  105 . The three rotor blade attachment bolt arrangement also includes the second bolt  131  and the third bolt  133  that are aligned along a chordwise plane, and offset from the first bolt  129  in an outboard spanwise direction by a distance D1. The second bolt  131  and the third bolt  133  are offset from the center spanwise plane by chordwise distances C1 and C2, respectively. In the example embodiment, C1 is equal to C2. 
     The combination and arrangement of the first bolt  129 , the second bolt  131 , and the third bolt  133  for attachment of the rotor blade  105  to grip  137  has unique advantages. First regarding the beam bending in direction  149 , if first bolt  129  weren&#39;t present, then second bolt  131  and third bolt  133  would be subject to relatively large bending forces from the beam bending in direction  149  due to the second bolt  131  and third bolt  133  being aligned in a chordwise direction. However, the presence of first bolt  129  acts to greatly reduce the bending forces on second bolt  131  and third bolt  133  by creating a heel/toe effect. Secondly regarding torsionally forces approximately about pitch change axis  143 , if either of second bolt  131  or third bolt  133  weren&#39;t present, then an input from pitch horn  123  or aerodynamic force, for example, would act to create relatively large bending forces about an axis formed between the first bolt  129  and either of the second bolt  131  or the third bold  133 . However, the presence of both second bolt  131  and third bolt  133 , in addition to first bolt  129 , acts to greatly reduce the bending forces by creating a heel/toe effect. 
     Further, by locating first bolt  129  inboard to the chordwise oriented second bolt  131  and third bolt  133 , the rotor blade  105  can taper down or become more narrow at the root end. The tapering of rotor blade  105  at the root end allows for clearance between the root end of rotor blade  105  and the damper attachment portion  141  of pitch horn. 
     Referring now also to  FIGS. 7 and 8 , rotor blade  105  is described in further detail. Rotor blade  105  can have a leading  701 , a trailing edge  703 , a root end  705  and a tip end  707 . It should be appreciated that rotor blade  105  can take on a wide variety of configurations. For example, rotor blade  105  can have a degree of built-in twist between root end  705  and tip end  707 . Describing another example, rotor blade  105  can have an anhedral tip, or any other desirable aerodynamic profile. Rotor blade  105  includes holes  709 ,  711 , and  713  which provide corresponding apertures for bolts  129 ,  131 , and  133 , respectively. Thus, the further disclosure herein regarding the location of bolts  129 ,  131 , and  133 , also applies to the location of holes  709 ,  711 , and  713  on rotor blade  105 . It should be appreciated that holes  709 ,  711 , and  713  can include bushings, or similar, located therein as a bearing surface for the shanks of bolts  129 ,  131 , and  133 . 
     Rotor blade  105  can include a forward taper  715  and an aft taper  717  that each taper toward a centerline axis of the rotor blade until joining at a rounded portion  719 . Rounded portion  719  can have a radius that is a function of a desired edge distance from hole  709 . 
     In  FIGS. 2-4 , first bolt  129  and third bolt  133  are illustrated as quick removable expandable bolts configured to be removed without the need for a tool. A pin can be removed from the lower portion, allowing the handle to be pivoted, which actuates a cam member allowing the bolt to be removed. Once the first bolt  129  and the third bolt  133  are removed, the rotor blade  105  is free to be rotated about second bolt  131 . It should be appreciated that some rotorcraft operators don&#39;t have a requirement for the folding of the rotor blades  105 ; as such, all of the first bolt  129 , the second bolt  131 , and the third bolt  133  can be conventional bolts. Furthermore,  FIGS. 5 and 6  illustrate all of the first bolt  129 , the second bolt  131 , and the third bolt  133  as conventional bolts. 
     The embodiments herein are illustrated with regard to a main rotor assembly on a rotorcraft; however, it should be appreciated that the embodiments may be adaptable to a tail rotor assembly. 
     The particular embodiments disclosed above are illustrative only, as the apparatus may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Modifications, additions, or omissions may be made to the apparatuses described herein without departing from the scope of the invention. The components of the apparatus may be integrated or separated. Moreover, the operations of the apparatus may be performed by more, fewer, or other components. 
     Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the application. Accordingly, the protection sought herein is as set forth in the claims below. 
     To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.