Abstract:
An aircraft component includes a first segment having a first leading edge surface that extends to a first end of the first segment. The aircraft component also includes a second segment having a second leading edge surface that extends to a second end of the second segment. The second end is substantially adjacent to the first end of the first segment, and is connected to the first end. The first leading edge surface includes electrical resistance heating that extends to the first end of the first segment. In addition, the second leading edge surface includes electrical resistance heating that extends to the second end of the second segment. The electrical resistance heating is capable of providing ice protection heating immediately on either side of a juncture between the connected first and second ends.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to ice protection systems for aircraft, and more particularly relates to an ice protection system for selectively heating a leading edge surface of an aircraft component, including portions of the leading edge surface that are immediately adjacent to a structural joint in the aircraft component. 
     BACKGROUND 
     The leading edges of aircraft engine nacelles and other aircraft components are prone to ice buildup.  FIG. 1  shows a schematic representation of a typical high-speed jet engine assembly  10 . Air enters through inlet section  14 , between fan blade spinner  16  and an annular housing  18 , which constitutes the forward most section of a nacelle  20 , and includes nacelle inlet lip  21 . Hot, high-pressure propulsion gases pass through the compressor section  17  and the exhaust assembly (not shown) at the rear of the nacelle. An annular space or D-duct  30  is defined by bulkhead  28  and annular housing  18 . Bulkhead  28  separates D-duct  30  from the interior portion  31  of the inner barrel  12  of the nacelle. In flight, under certain temperature and humidity conditions, ice may form on the nacelle inlet lip  21 , which is the leading edge of the annular housing  18 , and on the fan blade spinner  16 . Accumulated ice can change the geometry of the inlet area between annular housing  18  and fan blade spinner  16 , and can adversely affect the quantity and flow path of intake air. In addition, pieces of ice may periodically break free from the nacelle  20  and/or spinner  16  and enter the engine  50 , potentially damaging fan and rotor blades  60  and other internal engine components. 
     Nacelles also serve an important role in addressing fan noise from the engines, which can be a prime source of overall aircraft noise. As is known to those skilled in the art, aircraft engine fan noise can be suppressed at the engine nacelle inlet  14  with a noise absorbing inner barrel liner  40 , which converts acoustic energy into heat. The liner  40  normally includes (as shown in  FIG. 6 ) a face skin  42  having a plurality of spaced openings or perforations  41 . The face skin  42  is supported by an open cell core  44  to provide structural support, and to provide a required separation between the porous face sheet  42  and a solid back skin  46 . The liner  40  also can include at least one septum  43  that divides each cell into sections, including an upper portion  45  and a lower portion  49 . The septum  43  can include a porous membrane or a solid membrane having at least one opening  47  to provide acoustic communication between the upper cell portion  45  and the lower cell portion  49 . This arrangement provides effective and widely accepted noise suppression characteristics. Aircraft engines with reduced noise signatures are mandated by government authorities, and often are specified by aircraft manufacturers, airlines and local communities. 
     U.S. patent application Ser. Nos. 11/276,344 and 11/733,628 (incorporated herein by reference in their entirety), describe graphite fabric heater elements embedded within the layers of a composite structure such as a nacelle inlet lip. The described composite structure includes a heater element integrally formed within a composite aircraft structure having a leading edge. The composite structure includes an open cell core, and a plurality of composite layers atop the core. The composite layers include perforations that extend through the composite layers (including the heater element layer) to the underlying open cell core. The graphite fabric heater elements can include a plurality of interwoven threads containing electrically conductive graphite fibers. Such a structure provides both ice protection and noise attenuation. 
     As shown in  FIG. 2 , a typical nacelle inlet lip  100  can be formed in two or more circumferentially extending lip sections  110 ,  112 ,  114  that are joined end-to-end. The sections  110 ,  112 ,  114  can be connected at spliced joints  115 ,  117 ,  119 . A detail of one typical prior art spliced joint  119  between the ends of two inlet lip segments  110 ,  112  is shown in  FIG. 3 . In this arrangement, the segments  110 ,  112  meet along a space  120 , which usually includes a narrow gap between the opposed ends of the segments  110 ,  112 . One end  126  of a first segment  110  is connected to an adjacent end  122  of a second segment  112  by a plurality of fasteners  121  that extend through the segments  110 ,  112  and connect to a backing plate or splice plate (not shown in  FIG. 3 ) that spans rear portions of the adjoined ends  122 ,  126  of the segments  110 ,  112  and the gap  120  therebetween, thus securing the ends  122 ,  126  in end-to-end relationship. As shown by dashed lines in  FIG. 3 , when the leading edges of the segments  110 ,  112  are provided with integral electrically powered ice protection heaters  123 ,  127 , the ends  125 ,  129  of the heaters nearest the gap  120  are spaced apart by a circumferential distance W 1 . The spacing W 1  is necessary in order that the metal fasteners  121  do not extend through or contact the electric heater elements  123 ,  127 . 
     Another typical prior art spliced joint  419  between two adjoined inlet lip segments  410 ,  412  is shown in  FIGS. 4A and 4B . In this arrangement, a splice plate  424  is positioned on adjacent exterior faces of the segment ends  422 ,  426 , and across a gap  420  therebetween. A plurality of fasteners  421  extend through the splice plate  424  and the segment ends  422 ,  426 , thus securing the ends  422 ,  426  together in end-to-end relationship. As shown in  FIGS. 4A and 4B , integral electric heater elements  423 ,  427  can include a plurality of spaced electrically conductive bus strips  430  for use in establishing an electric potential across the heater elements  423 ,  427 . As also shown in  FIGS. 4A and 4B , the bus strips  430  can be connected to a voltage source by wires  433  that extend through the back sides of the inlet lip segments  410 ,  412 . Like the back-splice arrangement discussed above, the edges of heater elements  423 ,  427  that are nearest the gap  420  are necessarily spaced apart by a circumferential distance W 2  such that none of the metal fasteners  421  penetrate the heater elements  423 ,  427  or the bus strips  430 . 
     In some circumstances, the exterior surfaces of the inlet lip segments  110 ,  112  associated with the gaps W 1  and W 2  shown in  FIGS. 3-4B  may not be sufficiently heated by the nearest heater elements  123 ,  127  to prevent ice formation or to melt accumulated ice. Accordingly, these unheated gaps W 1 , W 2  can result in “cold spots” at the gaps  120  between adjoined inlet lip segments. As discussed above, ice accumulation on the surfaces of an aircraft&#39;s leading edges is undesirable, particularly on the leading edge of an aircraft engine nacelle. In addition, the spliced joints described above can substantially prevent effective acoustic treatment of the portions of the inlet lip segments associated with the gaps W 1 , W 2  because connecting hardware such splice plates, mechanical fasteners, and the like, can at least partially block acoustic perforations in the outer skin and/or the cells of an underlying cellular core, or otherwise interfere with optimal performance of the acoustic liner  40 . 
     Accordingly, there is a need for an ice protection system for an aircraft component&#39;s leading edge that includes heating elements that cover substantially the entire extent of the aircraft component&#39;s leading edge surface, including those portions of the component that are immediately adjacent to a structural joint between adjacent component segments. In addition, there is a need for such a system that also includes acoustic treatment of substantially the entire extent of the aircraft component&#39;s leading edge surface, including those portions of the component that are immediately adjacent to a structural joint between adjacent component segments. 
     SUMMARY 
     In one embodiment, an aircraft component can include a first segment having a first leading edge surface that extends to a first end of the first segment. The aircraft component can further include a second segment having a second leading edge surface that extends to a second end of the second segment. The second end can be substantially adjacent to the first end of the first segment. The first leading edge surface can include one or more electrical resistance heating elements that extend to the first end of the first segment, and the second leading edge surface can include one or more electrical resistance heating elements that extend to the second end of the second segment, thus providing electric heating immediately adjacent each side of a juncture between the first and second ends. 
     In another embodiment, a method of joining first and second aircraft components to form a leading edge of an aircraft surface can include providing a first component having a first exterior surface, a first end, and a first ice protection heater element immediately adjacent the first end. The method further can include providing a second component having a second exterior surface, a second end, and a second ice protection heater element immediately adjacent the second end. The first end of the first component can be joined to the second end of the second component such that the first and second exterior surfaces combine to form a substantially continuous and selectively heatable leading edge surface along a juncture between the first and second ends. 
     In a further embodiment, an ice protection heater for a leading edge of an aircraft component can include at least two segments joined end to end. The heater can include at least one substantially continuous conductive sheet having a heater portion and a first edge portion, wherein the heater portion and first edge portion intersect at an angle, such as at a right angle. At least a first bus strip can be connected to the first edge portion for supplying electric power to the ice protection heater. 
     In an additional embodiment, an aircraft component can include a first segment having a first exterior surface, a first end, and a first electric heater element having a first edge proximate to the first end. The aircraft component can further include a second segment having a second exterior surface, a second end, and a second electric heater element having a second edge proximate to the second end. The second end can be configured to be joined to the first end such that the first external surface and the second external surface combine to form at least a portion of a substantially continuous leading edge surface. A first bus bar can be connected to the first edge of the first heater element, and a second bus bar can be connected to the second edge of the second heater element. The first and second bus bars can be disposed between the first end and the second end when the first end is joined to the second end. 
     These and other aspects and features of the invention will be understood from a reading of the following detailed description together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a typical high-speed jet engine assembly. 
         FIG. 2  is a front perspective view of a nacelle inlet lip formed in three segments. 
         FIG. 3  is a front perspective view of a conventional back-spliced joint between adjoined inlet lip segments. 
         FIG. 4A  is a front elevation view of a conventional front-spliced joint between adjoined inlet lip segments. 
         FIG. 4B  is a cross-sectional view of the front-spliced joint shown in  FIG. 4A  taken along line  4 B- 4 B in  FIG. 4A . 
         FIG. 5A  is a front perspective view of a joint between two ends of adjacent inlet segments with ice protection according to the invention. 
         FIG. 5B  is a rear elevation view of the joint between two ends of adjacent inlet segments with ice protection as shown in  FIG. 5A . 
         FIG. 5C  is a cross sectional view of the joint between two ends of adjacent nacelle inlet lip segments with ice protection as shown in  FIGS. 5A and 5B , taken along line  5 C- 5 C in  FIGS. 2  and line  5 C- 5 C in  FIG. 5B . 
         FIG. 6  is a perspective view of an acoustically treated portion of a prior art aircraft component. 
         FIG. 7  is a cross-sectional view of an inlet lip joint according to the invention showing inlet lip segments with both ice protection and acoustic treatment. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 5A-5C  show one embodiment of an ice protection heater system according to the invention as applied to a multi-segment nacelle inlet lip  200 , for example. As shown in  FIG. 5A , a nacelle inlet lip  200  includes a first inlet lip segment  110  having a first end  226  joined to a second end  222  of a second inlet lip segment  112  along a joint  211 . The joint  211  can include a narrow gap  220  between the segment ends  222 ,  226 . The first inlet lip segment  110  can include a first embedded heating element  227  adjacent to the first end  226 , and the second inlet lip segment  112  can include a second embedded heating element  223  adjacent to the second end  222 . As shown in  FIG. 5A , the joined inlet lip segments  110 ,  112  can form a substantially continuous exterior surface in the region immediately adjacent to the joint  211  and gap  220 .  FIGS. 5B and 5C  show details of one embodiment of the joint  211 . 
     As shown in  FIGS. 5B and 5C , the first end  222  of the first inlet lip segment  110  can include an outermost layer  287 , a heater element layer  223 , a cellular core  245 , one or more bus strips  230 , and one or more first backing layers  292 . The core  245  can be a metallic or non-metallic honeycomb structure, for example. In the embodiment shown in  FIGS. 5B and 5C , the core  245  and the backing layers  292  combine to form a rearwardly extending first flange  293 . Similarly, the second end  226  of the second inlet lip segment  112  can include a second outermost layer  283 , a second heater element layer  227 , a second cellular core  244 , one or more bus strips  230 , and one or more second backing layers  290 . Also similarly, the second core  244  and second backing layers can combine to form a rearwardly extending second flange  291 . The various cores and layers can be bonded together within each inlet lip segment  110 ,  112  to form a unitary structure using known composite materials and composite forming and bonding techniques. One or more additional outermost or backing layers can be provided for additional strength, to provide electrical insulation between electrically conductive portions of the structure, or for any other purpose. The respective thicknesses of the various layers shown in  FIG. 5C  are exaggerated for purposes of illustration. 
     The first and second flanges  293 ,  291  on rear portions of the ends  222 ,  226  of the inlet lip segments strengthen and stiffen the segments  110 ,  112 , particularly at their ends  222 ,  226 . As shown in  FIG. 5C , a splice plate  224  can extend between the flanges  293 ,  291 , and across the interstitial gap  220  therebetween. In  FIGS. 5B and 5C , the width of the interstitial gap  220  is exaggerated for illustration purposes. Preferably, the gap  220  is not larger than about 0.1 inch, and preferably, not larger than about 0.06 inch. In one embodiment, the gap  220  can have a nominal width of about 0.03 inch. The splice plate  224  can be connected to each flange  293 ,  291  by a plurality of removable mechanical fasteners  221 , such as by a plurality of blind rivets, or the like. As shown in  FIG. 5C , the fasteners  221  can extend through the splice plate  224 , through the backing layers  292 ,  290 , and through the back skins  246 ,  247  on the cellular cores  245 ,  244 , thus securely connecting the ends  222 ,  226  of the inlet lip segments  110 ,  112  together. As also shown in  FIG. 5C , because the splice plate  224 , backing layers  292 ,  290 , and back skins  246 ,  247  are positioned behind and away from the heating elements  223 ,  227 , the fasteners  221  can be arranged such that none of the fasteners  221  penetrates or contacts any portion of the electrically conductive heating elements  223 ,  227 . As shown in  FIG. 5B , the bus strips  230  can be positioned between the fasteners  221 , such that the fasteners  221  also do not penetrate or contact any portion of the electrically conductive bus strips  230 . The bus strips  230  can be connected to an aircraft electric power supply, such as one or more batteries, an aircraft engine, an auxiliary power unit (APU), or a combination thereof. 
     As shown in  FIG. 5C , the first heating element  223  can include a first leading edge portion  296 , and a first recessed portion  297 . In this embodiment, the first leading edge portion  296  and the first recessed portion  297  can be substantially orthogonal to each other, though the heater portions  296 ,  297  also can be configured at other angular orientations. Similarly, the second heating element  227  can include a second leading edge portion  298 , and a second recessed portion  299 . In this embodiment, the second leading edge portion  298  and the second recessed portion  299  also can be substantially orthogonal to each other, though the heater portions  298 ,  299  also can be configured at other angular configurations. Because the recessed portions  297 ,  299  of the heating elements  223 ,  227  extend into the interstitial gap  220  between the segments  110 ,  112 , the adjoined leading edge portions  296 ,  298  of the heating elements  223 ,  227  can extend to the edges of the gap  220 . Each of the heating elements  223 ,  227  generally extends along at least a portion of an outer face of an inlet lip segment  110 ,  112 , and further extends around a corner of an inlet lip segment  110 ,  112 , such that a portion of each heater element  223 ,  227  extends along an edge surface of a segment  110 ,  112 . Each of the bus strips  230  can include a front end  230   a  that is in contact with one of the recessed portions  297 ,  299  of the heating elements  223 ,  227  within the gap  220 , and an opposed rear end  230   b  that is positioned away from the gap  220  and the splice plate  224 , thereby permitting connection to an electrical power source. As shown in  FIG. 5C , wires  233  or another electrical supply means can be connected to the rear ends  230   b  of the bus strips  230  for applying voltages across the heating elements  223 ,  227 . The bus strips  230  can be covered by an electrically insulating coating, or another insulating material. As shown in  FIG. 5C , the heating elements  223 ,  227  extend to the opposed edges of the gap  220 , and the recessed portions  297 ,  299  extend into the gap  220 . Accordingly, when electric power is supplied to the heating elements  223 ,  227 , the heat generated by the heating elements  223 ,  227  can effectively prevent and/or eliminate ice formation within the gap  220  and at and along the adjoined ends  222 ,  226  of the inlet lip segments  110 ,  112 . 
       FIG. 7  shows one alternative embodiment of the invention. In this embodiment, an ice protection heater system according to the invention again is applied to a multi-segment nacelle inlet lip  300 . As shown in  FIG. 7 , a nacelle inlet lip  300  includes a first inlet lip segment  310  having a first end  322  joined to a second inlet lip segment  312  at its second end  326 . A narrow gap  320  may exist between the segment ends  322 ,  326 . As shown in  FIG. 7 , the first inlet lip segment  310  can include a first embedded heating element  323  that is adjacent to the first end  322 ,. and the second inlet lip segment  312  can include a second embedded heating element  327  that is adjacent to the second end  326 . 
     The first end  322  of the first inlet lip segment  310  can include at least one first outermost layer  387 , a first heater element layer  323 , a first cellular core  345 , one or more bus strips  330 , and one or more first backing layers  392 . Similarly, the second end  326  of the second inlet lip segment  312  can include at least one second outermost layer  383 , a second heater element layer  327 , a second cellular core  344 , one or more bus strips  330 , and one or more second backing layers  390 . The cores and layers of each inlet lip segment  310 ,  312  can be bonded together to form a unitary structure using known composite materials and composite forming and bonding techniques. As discussed in more detail below, the outermost layers  387 ,  383  and heater elements  323 ,  327  can be perforated. 
     As shown in  FIG. 7 , a splice plate  324  can extend between the first and second ends  322 ,  326  and across the interstitial gap  320  therebetween. In  FIG. 7 , the width of the interstitial gap  320  is exaggerated for ease of illustration. Preferably, the gap  320  is not larger than about 0.1 inch, and preferably is not larger than about 0.06 inch. In one embodiment, the gap  320  has a nominal width of about 0.03 inch. The splice plate  324  can be connected to an interior portion of each of the first and second ends  322 ,  326  by a plurality of mechanical fasteners  321 , such as by a plurality of blind rivets, or the like. The fasteners  321  can extend through the splice plate  324 , through the backing layers  392 ,  390 , and through the back skins  346 ,  347  on the cellular cores  345 ,  344 , thus securely connecting the ends  322 ,  326  of the inlet lip segments  310 ,  312  together. Like the embodiment shown in  FIG. 5C , the fasteners  321  can be arranged such that none of the fasteners penetrates or contacts any portion of the electrically conductive heating elements  323 ,  327 . In addition, the bus strips  330  can be positioned between the fasteners  321  such that none of the fasteners  321  penetrates or contacts any portion of the electrically conductive bus strips  330 . 
     As shown in  FIG. 7 , the first heating element  323  can include a first leading edge portion  396 , and a first recessed portion  397 . In this embodiment, the first leading edge portion  396  and the first recessed portion  397  are substantially orthogonal to each other, though the portions  396 ,  397  can be configured and arranged at substantially any angle. Similarly, the second heating element  327  can include a second leading edge portion  398 , and a second recessed portion  399 . In this embodiment, the second leading edge portion  398  and the second recessed portion  399  also are substantially orthogonal to each other, though the portions  398 ,  399  can be configured and arranged at substantially any angle. Because the recessed portions  397 ,  399  of the heating elements  323 ,  327  extend within the interstitial gap  320  between the segments  310 ,  312 , the leading edge portions  396 ,  398  of the heating elements  323 ,  327  extend to and around the edges of the gap  320 . As shown in  FIG. 7 , each of the bus strips  330  can include a front end portion  330   a  that is in electrical contact with one of the recessed portions  397 ,  399  of the heating elements  323 ,  227 , and an opposed rear end portion  330   b  that extends away from the gap  320  and the splice plate  324 . Wires  333  or another electric supply means can be connected to the rear portions  330   b  of the bus strips  330  for connecting the bus strips  330  to an electric power source. Any exposed portions of the bus strips  330  can be covered by an electrically insulating coating or other insulating material. As shown in  FIG. 7 , the heating elements  323 ,  327  extend to the opposed edges of the gap  320 , and the recessed portions  397 ,  399  extend into the gap  320 . Accordingly, when electric power is supplied to the heating elements  323 ,  327 , the heat generated by the heating elements  323 ,  327  can effectively prevent and/or eliminate ice formation within the gap  320  and at and along the adjoined ends  322 ,  326  of the inlet lip segments  310 ,  312 . 
     As shown in  FIG. 7 , a first plurality of openings  301  can extend through the first outer layer(s)  387  and the first heating element layer  323  of the first lip segment  310  to the underlying first cellular core  345 . Similarly, a second plurality of openings  303  can extend through the second outer layer(s)  383  and the second heating element layer  327  of the second lip segment  312  to the underlying second cellular core  344 . Thus, the first and second pluralities of openings  301 ,  303  can provide acoustic communication pathways to the open cells of the underlying cores  344 ,  345 . Accordingly, the inlet lip  300  can include both ice protection and acoustic treatment that each extend to the ends  322 ,  326  of the adjoined segments  310 ,  312  and to the edges of the gap  320 . 
     The embodiments described above are intended to describe and illustrate various features and aspects of an ice protection system according to the invention. Persons of ordinary skill in the art will recognize that certain changes or modifications can be made to the specifically described embodiments without departing from the invention. For example, though the invention has been specifically described with respect to the leading edges of an aircraft engine nacelle inlet lip, the invention also can be applied to other segmented aircraft components that may be prone to ice formation and accumulation, such as an aircraft&#39;s wings, or the like. All such changes and modifications are intended to be within the scope of the appended claims.