Patent Publication Number: US-2022212550-A1

Title: Fuel Cell Protection System

Description:
BACKGROUND 
     Aircraft certification regulations ensure protection of aircraft fuel tanks and require that damage to fuel cells is minimize during a crash. Among other responsibilities, the United States Federal Aviation Administration (FAA) has established airworthiness standards for aircraft, such as airplanes and rotorcraft. The FAA also provides airworthiness approval for aircraft and aircraft component to certify that they conform to an approved design and are in a condition for safe operation. FAA regulations directed to airworthiness standards for transport rotorcraft require crash resistance for aircraft fuel systems. These standards are intended to minimize the hazard of fuel fires to occupants following an otherwise survivable impact, such as a crash landing. Additionally, FAA regulations require that fuel systems be capable of sustaining certain static and dynamic deceleration loads without structural damage to the fuel tanks or their components that could leak fuel to an ignition source. 
     One requirement for obtaining rotorcraft fuel system airworthiness approval is the successful completion of a drop test. The drop test requirements include: (1) a drop height of at least 50 feet; (2) a nondeforming drop impact surface; (3) fuel tanks filled with water to 80 percent of the normal full capacity or with fuel to the full capacity; (4) the fuel tank must be enclosed in a surrounding structure representative of the installation unless it can be established that the surrounding structure is free of projections or other design features likely to contribute to rupture of the tank; (5) the fuel tank must drop freely and impact in a horizontal position+/−10 degrees; and (6) after the drop test, there must be no leakage. External structures, such as cargo hooks or other protrusions on the belly of the aircraft, are a threat to fuel cell integrity during a crash. 
     SUMMARY 
     Embodiments are directed to systems and methods for minimizing damage to the fuel cells of an aircraft during a crash by providing an area for cargo hooks and other external accessories to fold into. The structure surrounding the cargo hook is allowed to damage and deflect, but the area for cargo hooks provides space between the damage and the fuel cells to capture puncture threats. 
     In an example embodiment, a fuel cell protection system comprises an aircraft fuselage having an inner surface and an outer surface, an attachment point mounted on the outer surface, an aircraft fuel cell spaced apart from the inner surface, and a plate positioned between the inner surface and the aircraft fuel system, the plate spaced apart from the inner surface to create a void space. The attachment point may be a cargo hook. The void space is configured to receive all or a portion of the cargo hook after a crash. The plate creating the void space may be a rigid material or may be a ballistic fabric material. 
     The fuel cell protection system may further comprise at least one sidewall coupled to one or more edges of the plate. The at least one sidewall is configured to hold the plate apart from the inner surface. The at least one sidewall is an integral part of the plate and is fixedly attached to the inner surface of the fuselage. Alternatively, a tab may be coupled to an edge of the at least one sidewall and is fixedly attached to the inner surface of the fuselage. 
     The fuel cell protection system may further comprise an aircraft structural beam attached to the fuselage inner surface, and a second tab coupled to at least one edge of the plate, wherein the second tab is fixedly attached to the structural beam. 
     In another example, a rotorcraft comprises a fuselage having an inner surface and an outer surface, a cargo hook is attached to the outer surface, a fuel tank having a plurality of interconnected fuel bags is spaced apart from the inner surface of the fuselage, and a fuel cell protection compartment between the inner surface and the fuel tank, wherein the fuel protection compartment is configured to receive all or a portion of the cargo hook after a crash. The fuel cell protection compartment is configured to prevent the cargo hook from damaging the fuel tank. The fuel cell protection compartment comprises a plate positioned between the inner surface and the fuel tank, wherein the plate is spaced apart from the inner surface to create a void space. The plate may be a rigid material or a ballistic fabric material. 
     The plate has at least one sidewall. The at least one sidewall is configured to hold the plate apart from the inner surface. The sidewall has a tab that is fixedly attached to the inner surface of the fuselage. The rotorcraft further comprises a structural beam attached to the inner surface of the fuselage. The plate has at least one edge, and a tab coupled to the at least one edge of the plate. The tab has a surface that is fixedly attached to the structural beam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIGS. 1A and 1B  are oblique views of an aircraft adapted for use with a fuel cell protection system according to this disclosure. 
         FIG. 2  is an isometric view of a fuel tank receiving assembly for use with a fuel cell protection system in accordance with embodiments of the present disclosure. 
         FIG. 3  is an isometric view of a fuel tank for use with a fuel cell protection system in accordance with embodiments of the present disclosure. 
         FIGS. 4A-4D  are various views illustrating a fuel cell protection system according to an example embodiment. 
         FIGS. 5A-5B  are oblique views illustrating an alternative fuel cell protection system according to another example embodiment. 
     
    
    
     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. 
     DETAILED DESCRIPTION 
     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. 
     Referring to  FIGS. 1A-1B , a rotorcraft  100  is schematically illustrated. Rotorcraft  100  has a rotor system  101  with a plurality of rotor blades  102 . The pitch of rotor blades  102  can be collectively and cyclically manipulated to selectively control direction, thrust, and lift of rotorcraft  100 . Rotorcraft  100  includes a fuselage  103 , an anti-torque system  104  and an empennage  105 . Rotorcraft  100  has a landing gear system  106  to provide ground support for the aircraft. Located within a lower portion of fuselage  103 , rotorcraft  100  includes a fuel tank receiving assembly  107  that supports and contains a fuel system  108  including a fuel tank  109 . Liquid fuel is contained within fuel tank  109  that is used to power one or more engines that drive rotor system  101  and anti-torque system  104 . One or more cargo hooks  110  are mounted on a belly or underside  111  of the fuselage of aircraft  100 . Cargo hooks  110  allow the transport of external loads during flight. 
     It should be appreciated that rotorcraft  100  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. It should be appreciated that even though aircraft are particularly well suited to implement the embodiments of the present disclosure, non-aircraft vehicles and devices can also implement the embodiments. 
       FIG. 2  depicts a fuel tank receiving assembly  107  is illustrated. Fuel tank receiving assembly  107  may be fully or partially integral with fuselage  103  of rotorcraft  100  or may be independent of but secured to fuselage  103  of rotorcraft  100 . In the illustrated embodiment, rotorcraft bulkhead  201  forms an aft portion of fuel tank receiving assembly  107  and rotorcraft bulkhead  202  forms a forward portion of fuel tank receiving assembly  107 . Rotorcraft bulkhead  201  and rotorcraft bulkhead  202  may be formed from a metal such as aluminum, composite, or other suitable material. Fuel tank receiving assembly  107  includes a frame structure  203  that may be a unitary frame structure or may be formed from a plurality of frame elements. Frame structure  203  may be formed from a metal such as aluminum, polymer, composite, or other suitable material. Frame structure  203  supports a plurality of a panel members including side panel members  204 ,  205  of a forward portion of fuel tank receiving assembly  107 , side panel members  206 ,  207  of a middle portion of fuel tank receiving assembly  107  and side panel members  208 ,  209  of an aft portion of fuel tank receiving assembly  107 . Frame structure  203  also supports lateral panel  2100  between the middle and aft portions of fuel tank receiving assembly  107  and panel  211  between the forward and middle portions of fuel tank receiving assembly  107 . Frame structure  203  further supports longitudinal panel  212  between right and left sections of the forward portion of fuel tank receiving assembly  107 . 
     Frame structure  203  supports lower panels  213 ,  214  in the forward portion of fuel tank receiving assembly  107 , lower panel  215  in the middle portion of fuel tank receiving assembly  107  and a lower panel  216  in the aft portion of fuel tank receiving assembly  107 . The various panels may be formed from a metal such as aluminum, polymer, composite, or other suitable material and may be attached to, coupled to or integral with frame structure  203 . The various panels include openings to allow fluid lines or other systems to pass through one or more panels or entirely through fuel tank receiving assembly  107 . Even though fuel tank receiving assembly  107  has been described as having frame and panel construction, it should be understood by those skilled in the art that fuel tank receiving assembly  107  could be constructed in any number of different manners including, but not limited to, as a single unitary assembly, as multiple unitary subassemblies such as a front subassembly, a middle subassembly, and an aft subassembly, or in another suitable manner. Likewise, portions of fuel tank receiving assembly  107  could alternatively be formed by sections of keel beams connected to or integral with fuselage  103  of rotorcraft  100  such as a pair of side keel beams and a central keel beam each of which extends in the longitudinal direction of fuel tank receiving assembly  107 . Regardless of the specific manner of construction, important features of fuel tank receiving assembly  107  include being sized and shaped to operably receive and contain fuel tank  109  therein. 
     Referring now to  FIG. 3  in the drawings, a fuel tank  109  is illustrated. In the illustrated embodiment, fuel tank  109  is depicted as having six interconnected fuel bags including forward bags  301 ,  302 , feed bags  303 ,  304 , middle bag  305  and aft bag  306 . Also, as illustrated, the height of middle bag  305  and aft bag  306  may be greater than that of forward bags  301 ,  302  and feed bags  303 ,  304 . The volume of fuel that may be stored in fuel tank  109  will depend on the particular implementation but will typically be on the order of several hundred to a thousand gallons. Even though fuel tank  109  has been described as having a particular number of fuel bags in a particular configuration, it should be understood by those skilled in the art that fuel tank  109  could have any number of fuel bags both less than or greater than six and the fuel bags could be arranged in any manner of different configurations depending upon the particular implementation. Although the term fuel bag is used in the example embodiment, it will be understood that the fuel protection system disclosed herein may be used with any flexible or rigid fuel cell manufactured of any material. 
     Lower panels  213 - 216  may form underside  111  ( FIG. 1B ) of aircraft  100  or may be adjacent to underside  111 . During a crash, cargo hooks  110  on underside  111  may puncture, deform, or otherwise damage underside  111 . As a result, lower panels  213 - 216  of fuel tank receiving assembly  107  may be damaged and may in turn puncture, tear, split, or otherwise damage fuel bags  301 - 306  of fuel tank  109 . Such damage would make it possible for the fuel bags  301 - 306  to leak fluid during and following a crash impact, thereby creating a post-crash fire risk. 
       FIGS. 4A-4D  depict cargo hooks  401  mounted on the exterior face of underside belly skin  402  of an aircraft. Cargo hooks  401  may be positioned under or in line with keel beam  403 , such as an I-beam. A backbone  404  or other reinforcement structure may provide a mounting structure for each cargo hook  401 . The cargo hooks  401  are secured to the aircraft to transfer the weight of any associated payload (e.g., any item vertically supported by the hooks  401 ) to the aircraft. The cargo hooks  401  are located vertically below the fuselage skin  402 , and below fuel tanks  405 ,  406 . With the cargo hook  401  being located below the tanks  405 ,  406 , the hooks  401  may be forced upward and into the space occupied by the fuel tanks  405 ,  406  during a crash. 
     Intrusions into the fuel tanks  405 ,  406  by cargo hooks  401  during a crash or impact are prevented by creating a protected area  407 ,  408  for the cargo hooks  401  to fold into during a crash. This protected area  407 ,  408  allows the surrounding structure to damage and deflect, while leaving some space between the damaged underside  402  and the fuel bags  405 ,  406  to capture puncture threats. The protected areas  407 ,  408  are created by a structure  409 ,  410 , respectively, that encloses the protected areas  407 ,  408  entirely or in part. Structure  409 ,  410  creates a space or void  407 ,  408  between belly skin  402  and fuel bags  405 ,  406 . The structure  409 ,  410  may be constructed of a rigid material, such as an aluminum, polymer, composite, or other material. Alternatively, structure  409 ,  410  may be created using flexible materials or ballistic fabric, such as Kevlar® or other strong synthetic polymer. 
     This configuration prevents the rupture or puncture of fuel bags  405 ,  406  in response to an impact that forces underside  402  and/or belly-carried accessories, such as cargo hooks  401 , in an upward direction. During a crash, cargo hooks  401  may penetrate belly skin  402  and enter protected areas  407 ,  408 . Alternatively, cargo hooks  401  may deform belly skin  402  upward and into protected areas  407 ,  408 . In either case, the cargo hooks  401  are not allowed to penetrate fuel bags  405 ,  406 , which prevents the fuel bags  405 ,  406  from leaking fluid during and following a crash impact, thereby minimizing post-crash conflagration risk. Even if cargo hooks  401  or belly skin  402  are able to penetrate structure  409 ,  410  and impact fuel bags  405 ,  406 , the additional structure  409 ,  410  will absorb some of the energy in the cargo hooks  401  or belly skin  402  and will minimize any damage to fuel bags  405 ,  406 . 
     While cargo hooks  401  are shown as conventional cargo hooks, it will be understood that in other embodiments, the hook system may comprise any other hook or device suitable for facilitating the hanging or mounting of a payload, rail, tank, or other accessory. Additionally, in other embodiments, the protected areas  407 ,  408  formed by structures  409 ,  410  are not limited to the underside of an aircraft. The protected areas  407 ,  408  but can be deployed in any other compartment in an aircraft or other vehicle that requires extra protection for fuel cells. 
     As noted above, structures  409 ,  410  may be any appropriate material to form the protected areas  407 ,  408 . The size and shape of the protected areas  407 ,  408  created by structures  409 ,  410  may generally have a box or channel shape. 
       FIGS. 5A and 5B  illustrate a fuel cell protection system  500  according to an example embodiment. Plate  501  is generally parallel to fuselage skin  502 . Plate  501  is spaced apart from fuselage skin  502  by one or more sidewalls  503 . The dimensions and size of plate  501  are selected to entirely cover the region  504  that may be impacted, penetrated, or deformed by an external hook or other accessory. The region  504  may be selected based upon all possible crash modes, which may include lateral as well as vertical motion so that the external hook may bend forward, back, or sideways on impact. 
     A tab  505  on sidewall  503  is attached to fuselage skin  502 . Tab  505  may be attached or bonded to fuselage skin  502  using any appropriate method, such as an adhesive, weld, rivet, or other fasteners. At least one wall  503  is attached to one edge of plate  501 . One or more other edges of plate  501  have a tab  506  that is attached to beam  507 , reinforcement structure  508 , or mounting structure  509 . Tab  506  may be attached using any appropriate method, such as an adhesive, weld, rivet, or other fasteners. In other embodiments, tab  506  may be attached to fuselage skin  502 . In further embodiments, plate  501  is held spaced apart from fuselage skin by two or more sidewalls  503  with or without tabs  505  and without connection directly to beam  507 , reinforcement structure  508 , or mounting structure  509 . 
     Generally, fuel cells (not shown) are positioned above plate  501 , and a cargo hook or external accessory (not shown) is located vertically below fuselage skin  502  under region  504 . During a crash or impact against the underside of fuselage skin  502 , the cargo hook could be forced upward and into the space occupied by the fuel cell. However, such intrusions into the fuel tanks are prevented by plate  501 , which creates a void or space  510  that allows the cargo hook and fuselage skin  502  to be forced in an upward direction without hitting the fuel cells. The open space  510  may be configured to accept all or a portion of the cargo hook. Alternatively, the cargo hook and fuselage skin  502  may be forced upward and into plate  501 , which may be moved further upward; however, plate  501  would distribute and absorb the force of any such upward movement thereby preventing catastrophic damage to the fuel cells. 
     Although plate  501  is shown as having a rectangular shape in the embodiment illustrated herein, it will be understood that plate  501  may have any appropriate shape as required to create a void space  510  having sufficient dimensions to receive all or a portion of a cargo hook upon deformation following a crash impact. In addition to cargo hooks, the void space  510  may be adapted to receive all or a portion of an attachment point, mounting device, suspension system, rail, bracket, or other device connected to the belly of a helicopter. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.