Abstract:
An easily removable and lightweight horizontal stabilizer configured to provide aerodynamic stability for a rotorcraft. The horizontal stabilizer comprising a spar removably coupled to a tailboom with a removable spar attachment means, the spar being located transversely through a tailboom opening and configured to provide structural support for at least a first horizontal airfoil and a second horizontal airfoil. The first and second horizontal airfoils are configured to fittingly receive the spar so that the spar fits at least partially inside the first and second horizontal airfoils. The first and second horizontal airfoils extend outboard from the tailboom to provide aerodynamic pitch stability.

Description:
TECHNICAL FIELD 
     The present application relates in general to the field of aerodynamic structures for rotorcraft; but more particularly, horizontal stabilizers for rotorcraft. 
     DESCRIPTION OF THE PRIOR ART 
     There are many different types of rotorcraft, including helicopters, tandem rotor helicopters, tiltrotor aircraft, four-rotor tiltrotor aircraft, tilt wing aircraft, and tail sitter aircraft. At least some of these aforementioned rotorcraft utilize horizontal stabilizers attached to a tailboom in order to provide aerodynamic stability during flight. Typically, a horizontal stabilizer will have one or more horizontal surfaces to aid in aerodynamic pitch stability. Additionally, a horizontal stabilizer may have one or more vertical surfaces to aid in aerodynamic yaw stability. It is often important for a rotorcraft to have the capability of reducing its overall volume for stowage reasons. For example, when transporting multiple rotorcraft in a cargo portion of a cargo plane, it is advantageous to convert the rotorcraft into a stowage configuration. In addition, it is also advantageous to be able to rapidly convert rotorcraft from a stowed configuration to an operable configuration, i.e. rapid deployment. 
     Referring to  FIG. 1 , a rotorcraft  101  is depicted with a conventional horizontal stabilizer  103  attached to a tailboom  109 . A forward end of tailboom  109  is attached to fuselage  119 . A tail rotor  121  is carried by an aft end of tailboom  109 . 
     Referring now to  FIG. 2 , conventional horizontal stabilizer  103  of rotorcraft  101  is shown in further detail. Horizontal structure  113  extends through an opening in tailboom  109  and is permanently attached to skin  111  of tailboom  109  with fasteners  107 . Endplates  115   a  and  115   b  are attached to horizontal structure  113  with a plurality of endplate fasteners  117   a  and  117   b . Folding mechanisms  105   a  and  105   b  provide a method of stowage for horizontal structure  113 . For horizontal stabilizer  103  to be in a stowable configuration, endplates  115   a  and  115   b  must be detached by removing fasteners  117   a  and  117   b . Then, because horizontal structure  113  is permanently attached to tailboom  109 , folding mechanism  105   a  and  105   b  must be used to allow the outboard portions of structure  113  to fold upward to a stowed position. 
     It is often desirable to create more efficient rotorcraft structure, thereby reducing the number of fasteners, reducing weight, and decreasing the amount of time it takes to stow and deploy an aircraft. There are many rotorcraft horizontal stabilizers known in the art; however, considerable room for improvement remains. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the system of the present application are set forth in the appended claims. However, the system itself, 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 with a prior art horizontal stabilizer; 
         FIG. 2  is a perspective view of the prior art horizontal stabilizer from the rotorcraft of  FIG. 1 ; 
         FIG. 3  is a side view of a rotorcraft having a horizontal stabilizer according the preferred embodiment of the present application; 
         FIG. 4  is a perspective view of the horizontal stabilizer from the aircraft in  FIG. 3 , according to the preferred embodiment of the present application; 
         FIG. 5  is a plan view of the horizontal stabilizer of  FIG. 4 , according to the preferred embodiment of the present application; 
         FIG. 6  is a partial cross-sectional view of the horizontal stabilizer, taken along the section lines VI-VI shown in  FIG. 5 , according to the preferred embodiment of the present application; 
         FIG. 7  is a partial cross-sectional view of the horizontal stabilizer, taken along the section lines VII-VII shown in  FIG. 6 , according to the preferred embodiment of the present application; 
         FIG. 8  is a bottom view of the horizontal stabilizer bonding strap shown in  FIG. 7 , according to the preferred embodiment of the present application; 
         FIG. 9  is a partial cross-sectional view of the horizontal stabilizer, taken along the lines IX-IX shown in  FIG. 6 , according to the preferred embodiment of the present application; 
         FIG. 10  is a bottom view of the horizontal stabilizer bonding strap shown in  FIG. 9 , according to the preferred embodiment of the present application; 
         FIG. 11  is a perspective view of the horizontal stabilizer of  FIG. 4 , according to the preferred embodiment of the present application; and 
         FIG. 12  is an exploded perspective view of the horizontal stabilizer of  FIG. 4 , removed from the rotorcraft, according to the preferred embodiment of the present application. 
     
    
    
     While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the system to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present application as defined by the appended claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the system of the present application are described below. In the interest of clarity, not all features of an actual implementation are 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. 
     The system of the present application represents a horizontal stabilizer for a rotorcraft and a rotorcraft incorporating the horizontal stabilizer. The horizontal stabilizer of the present application allows for improved rotorcraft functionality. It should also be appreciated that for this application, the term “left” is synonymous with the term “first” and the term “right” is synonymous with the term “second.” 
     Referring to  FIG. 3 , a rotorcraft  201  is depicted having a tailboom  209  connected to a fuselage  231 . A tail rotor  233  is operably associated with tailboom  209  for providing a means for torque control. A horizontal stabilizer  203  is attached to tailboom  209  in order to provide aerodynamic stability to rotorcraft  201  during flight. 
     Referring now to  FIG. 4 , horizontal stabilizer  203  is shown in greater detail. Horizontal stabilizer  203  comprises a left horizontal airfoil  213   a , a right horizontal airfoil  213   b , and a spar  205 . In the preferred embodiment, horizontal stabilizer  203  further comprises a left endplate  215   a  and a right endplate  215   b . Endplates  215   a  and  215   b  are coupled to airfoils  213   a  and  213   b  with endplate fasteners  211   a  and  211   b , respectively. Left and right endplates  215   a  and  215   b  provide aerodynamic yaw stability; however, it should be appreciated that the system of the present application fully contemplates horizontal stabilizer  203  without endplates  215   a  and  215   b . In the preferred embodiment, horizontal stabilizer  203  also comprises leading edge slats  217   a  and  217   b  attached to the forward portions of left horizontal airfoil  213   a  and right horizontal airfoil  213   b , respectively. Slats  217   a  and  217   b  are meant to optimize desired airflow characteristics of stabilizer  203  at different angle of attacks; however, it should be appreciated that the system of the present application fully contemplates horizontal stabilizer  203  without slats  217   a  and  217   b.    
     Referring now to  FIG. 5 , which is a plan view of horizontal airfoils  213   a  and  213   b  coupled to spar  205 , and spar  205  coupled to tailboom  209 . Left horizontal airfoil  213   a  is coupled to spar  205  with at least one removable airfoil attachment fastener  219   a . Similarly, right horizontal airfoil  213   b  is attached to spar  205  with at least one removable airfoil attachment fastener  219   b . Fasteners  219   a  and  219   b  may be a wide variety of removable fasteners; such as, bolts, screws, and other hardware. It should be appreciated that permanent fasteners, such as rivets, are not preferred. Removal of permanent fasteners typically requires destruction of the permanent fastener, requires a time consuming process, and poses a risk of harmful effects upon surrounding structure. As shown in  FIG. 5 , the preferred embodiment utilizes two removable airfoil attachment fasteners  219   a  on the left side, and two removable airfoil attachment fasteners  219   b  on the right side; however, it is contemplated that other rotorcraft applications may require fewer or greater number of removable fasteners to attach left and right airfoils  213   a  and  213   b  to spar  205 . 
     Referring now to  FIG. 6 , which is a cross-sectional view, taken along section lines VI-VI in  FIG. 5 . Spar  205  is coupled to tailboom  209  with spar lug pins  207   a  and  207   b . Spar  205  is located transverse and through tailboom  209 . The inboard edges of horizontal airfoils  213   a  and  213   b  are located adjacent to an outer skin of tailboom  209 . Spar  205  and horizontal airfoils  213   a  and  213   b  are preferably made of carbon fiber and bismaleimide (BMI) resin, and formed in a resin transfer molding (RTM) process. The RTM process allows the inner and outer surfaces of spar  205  and horizontal airfoils  213   a  and  213   b  to be tooled, thereby providing closely controlled tolerances between spar  205  and horizontal airfoils  213   a  and  213   b . As such, the closely controlled tolerances between spar  205  and horizontal airfoils  213   a  and  213   b  provide an efficient structural load path between airfoils  213   a  and  213   b , and tailboom  209 . Load (or forces) acting upon airfoils  213   a  and  213   b  translate into spar  205  through structural contact between spar  205  and airfoils  213   a  and  213   b ; and further through airfoil attachment fasteners  219   a  and  219   b . Further, load (or forces) acting upon spar  205  translate into an attachment structure  235  of tailboom  209  (as best shown in  FIGS. 7 and 9 ), via spar lug pin  207   a  and  207   b . It is important to note that the primary structural load path does not go through a skin of tailboom  209 , rather directly into the internal structure of tailboom  209 . The fatigue life and corrosion life of tailboom  209  and horizontal stabilizer  203  are increased by utilizing a minimum number of fasteners and by providing the efficient structural load path as described herein. It should be noted that even though it is preferable for spar  205  and horizontal airfoils  213   a  and  213   b  to be manufactured of carbon fiber and bismaleimide (BMI) resin through a resin transfer molding (RTM) process; spar  205  and horizontal airfoils  213   a  and  213   b  may also be manufactured out of a metal, such as aluminum, through a machining process. In addition, spar  205  and horizontal airfoils  213   a  and  213   b  may also be manufactured from other composite materials and processes. 
     Referring now to  FIGS. 7 and 9 , which are cross-sectional views looking inboard, taken along section lines VII-VII and IX-IX in  FIG. 6 , respectively. Though spar  205  is shown having generally rectangular cross section, rounded corners, and a hollow interior, spar  205  may also be of other cross section shapes such as oval, circular, square, or that of an I-beam. Spar lug pins  207   a  and  207   b  allow for rapid removal and installation of spar  205  to and from tailboom  209 .  FIGS. 7 and 9  also depict weatherproof seals  229   a  and  229   b  between inboard edges of horizontal airfoils  213   a  and  213   b  and outer skin of tailboom  209 , respectively. As shown in  FIGS. 7 and 9 , lug pins  207   a  and  207   b  each extend generally in a forward and aft direction, and engage spar  205  with attachment structure  235  of tailboom  209 . Attachment structure  235  is configured to provide a primary structural path between spar  205  and tailboom  209 . It should be appreciated that bushings, washers, cotter pins, safety wire, nuts and other associated hardware may be used with lug pins  207   a  and  207   b  in order to provide an appropriate structural connection between spar  205  and attachment structure  235  of tailboom  209 . Left bonding strap  225   a  and right bonding strap  225   b  are connected between tailboom  209  and horizontal airfoils  213   a  and  213   b , respectively. 
     Referring now to  FIGS. 8 and 10 , which are bottom views of bonding straps  225   a  and  225   b , respectively. Left bonding strap  225   a  and right bonding strap  225   b  provide lightning strike bonding paths between tailboom  209  and horizontal airfoils  213   a  and  213   b , respectively. However, it should be appreciated that bonding straps  225   a  and  225   b  may not be required in all installations of horizontal stabilizer  203  on rotorcraft  201 ; in addition, other forms of lightning strike protection may be used to replace or supplement bonding straps  225   a  and  225   b . Bonding strap  225   a  is coupled to tailboom  209  and horizontal airfoil  213   a . Bonding strap fasteners  227   a  removably attach bonding strap  225   a  to airfoil  213   a . Similarly, bonding strap  225   b  is coupled to tailboom  209  and horizontal airfoil  213   b . Similarly, bonding strap fasteners  227   b  removably attach bonding strap  225   b  to airfoil  213   b . As such, bonding strap fasteners  227   a  and  227   b  should be unfastened to facilitate removal of horizontal airfoils  213   a  and  213   b  from rotorcraft  201 . Fasteners  227   a  and  227   b  may be a wide variety of removable fasteners; such as, bolts, screws, and other hardware. 
     Referring now to  FIGS. 11 and 12 , in which  FIG. 11  illustrates horizontal stabilizer  203  assembled, but the remainder of rotorcraft  201  is not shown in order to provide for improved clarity. In  FIG. 12 , horizontal stabilizer is  203  is illustrated in an exploded view for improved clarity of installation and removal of horizontal stabilizer  203  from tailboom  209 . Horizontal stabilizer  203  is configured for rapid removal and installation, to and from rotorcraft  201 . In the preferred embodiment, removal of horizontal stabilizer  203  occurs during the process of converting rotorcraft  201  into a stowed configuration. Similarly, installation of horizontal stabilizer  203  occurs when converting rotorcraft  201  into an operable configuration. Removal of left horizontal airfoil  213   a , as well as endplate  215   a , entails removal of removable airfoil attachment fasteners  219   a  and bonding strap fasteners  227   a . After which, stabilizer  213   a  can then be slid in an outboard direction  223   a  away from tailboom  209 . Similarly, removal of right horizontal airfoil  213   b , as well as endplate  215   b , entails removal of removable airfoil attachment fasteners  219   b  and bonding strap fasteners  227   b . After which, stabilizer  213   b  can then be slid in an outboard direction  223   b  away from tailboom  209 . During this process, it may be necessary to disconnect any electrical harnesses, or other systems related hardware, that may be routed through tailboom  209  and into horizontal stabilizer  203 . Removal of spar  205  entails removal of spar lug pins  207   a  and  207   b  (shown best in  FIGS. 7 and 9 ), and then sliding spar  205  out of a tailboom opening  221  in either outboard direction  223   a  or outboard direction  223   b . It should be noted that it is not required to remove endplates  211   a  and  211   b  from horizontal airfoils  213   a  and  213   b , respectively, in order to remove horizontal stabilizer  203  from rotorcraft  201 . Installation of horizontal stabilizer  203  is the reverse process of removal of horizontal stabilizer  203 , as previously described. For purposes of this application, removal of horizontal stabilizer  203  is equivalent to stowing of horizontal stabilizer  203 , and installation of horizontal stabilizer  203  is equivalent to deployment of horizontal stabilizer  203 . It should also be noted that tailboom opening  221  can be only large enough for spar  205  to enter tailboom  209 . Opening  221  should be too small for horizontal airfoils  213   a  and  213   b  to enter tailboom  209 ; as such, this improved structural efficiency allows for enhanced performance of rotorcraft  201 . 
     The system of the present application provides significant advantages, including: (1) providing a easily stowable horizontal stabilizer without a heavy folding mechanism; (2) reducing horizontal stabilizer fastener part count so as to decrease labor and maintenance costs, increasing fatigue life, decreasing weight, and reducing likelihood of corrosion; (3) decreasing the amount of time and labor required between horizontal stabilizer stowage and deployment; (4) reducing the size of the opening required within the tailboom so as to improve structural characteristics; and (5) improving rotorcraft performance. 
     It is apparent that a system with significant advantages has been described and illustrated. Although the system of the present application is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.