Abstract:
A windshield for a pressurized aircraft includes a single transparent unit that functions structurally to allow pressurization of the aircraft and to support the aircraft&#39;s fuselage in response to external loads. The windshield also functions operationally to provide the pilot with an unobstructed field of vision through an extended arc of more than two hundred degrees. For its manufacture, layers of the transparent unit are respectively bent along a straight center line to establish two curved portions that are symmetrical relative to a common plane. The layers are then laminated.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to cockpit windshields for aircraft. More particularly, the present invention pertains to aircraft cockpit windshields having a unitary construction. The present invention is particularly, but not exclusively, useful as a windshield for the cockpit of a pressurized aircraft that acts as a structural member for the fuselage and that surrounds the pilot to provide an unobstructed field of vision through an extended visual arc. 
       BACKGROUND OF THE INVENTION 
       [0002]    In addition to the obvious purpose of providing outside visibility for the crew, a cockpit windshield can, and sometimes must, perform several other functions. For one, the windshield may serve as a load bearing member that responds to external forces imposed on the aircraft, such as the forces that are exerted on the nose gear as the aircraft is landed. In this case, in order to withstand the landing forces, the windshield must be strong in compression, and be able to avoid buckling. For another, the windshield provides protection against objects that might impact against it, particularly in flight (e.g. bird strikes). Here, the windshield must have sufficient resilience and flexibility to deform and absorb the blow, and then return to its pre-impact configuration. Further, in the case of a pressurized aircraft, the windshield must be effectively incorporated into the wall of a pressure vessel (i.e. the cabin of the aircraft). 
         [0003]    Pressurized aircraft are designed with the objective of providing an environment that is compatible with normal human activity. In general, this requirement includes both oxygen and pressure considerations, and is typically referred to in terms of cabin pressure altitude. In context, normal atmospheric pressure, at sea level, is around fifteen pounds per square inch (15 psi). Clearly, aircraft can be flown without pressurization. According to Federal Aviation Regulations (FAR), however, oxygen requirements are imposed for flights above 12,500 feet (MSL). Accordingly, when aircraft are flown at high altitudes (i.e. at 12,500 feet and above) pressurization systems are frequently used to create cabin pressure altitudes that typically remain in a range of 5-10,000 feet (MSL). To do this, a differential pressure is established between the actual altitude of the aircraft (i.e. outside) and the cabin pressure altitude (i.e. inside). This differential is expressed in pounds per square inch, and can be more than 12 psid. Insofar as the cockpit windshield is concerned, a pressure differential of this magnitude (i.e. 12 psid) will exert a significant distributed force over the surface of the windshield that is proportional to its exposed area. Clearly, the windshield must be able to resist the forces that result from this pressure. 
         [0004]    In light of the above, it is an object of the present invention to provide a cockpit windshield for an aircraft that is of a unitary construction, and that will provide crew members in the cockpit with an unobstructed field of vision through an arc of about 220°. Another object of the present invention is to provide an aircraft windshield that will structurally respond to externally imposed forces on the aircraft (e.g. landing forces and bird strikes). Yet another object of the present invention is to provide a cockpit windshield, of unitary construction, that can be effectively incorporated as part of the pressure vessel for an aircraft cabin. Still another object of the present invention is to provide a cockpit windshield of unitary construction that is reliable for its intended purposes, is relatively easy to manufacture and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with the present invention, a cockpit windshield for an aircraft is manufactured and installed as a single transparent unit. Structurally, the windshield is made of various preformed layers that are laminated together to create the unit. Functionally, the windshield provides an extended and unobstructed field of vision for the crew, and it serves as a load-bearing member of the aircraft&#39;s fuselage. 
         [0006]    To manufacture a windshield in accordance with the present invention, five separate, flat layers are pre-cut to a substantially same, predetermined shape. Two of the layers are cut from a polycarbonate material (about ⅜ inch thick), two are cut from an acrylic material (about ⅛ inch thick), and the fifth layer is made from a Mylar® material (about 5/1000 inch thick) in which a metallic heating element (e.g. wires or foil sheet) has been embedded. Each of the flat layers is then transformed into a predetermined three-dimensional configuration. Preferably, this is done as a so-called “flat wrap.” 
         [0007]    In order to accomplish the flat wrap, a straight center line is identified for each layer. Specifically, this center line bifurcates the layer into substantially identical first and second portions. The layer is then positioned on a form and is bent around its center line. The result is a configuration for the layer wherein the first portion is symmetrical to the second portion. Preferably, the flat wrap is accomplished at a temperature that is in a range between 300-350 F°. After the flat wrap has been accomplished, the layer is formed as a continuous curve, without any compound curves. It is to be appreciated, however, that compound curves may be provided for the windshield, if desired. 
         [0008]    Once the layers have been configured as disclosed above, an adhesive (e.g. polyurethane) is used to laminate the various layers together, to thereby create the single transparent unit. In this process, though not necessarily in the order presented here, the heating layer is bonded to one of the acrylic layers (hereinafter the outer layer). A first polycarbonate layer is then positioned against the outer layer, opposite the heating layer, and is bonded to the outer layer. A second polycarbonate layer is then bonded to the first layer. Finally, the remaining acrylic layer (hereinafter the inner layer) is bonded to the second polycarbonate layer. Together, these laminated layers create the transparent unit, with an edge. 
         [0009]    After the polyurethane adhesive has been applied between juxtaposed layers, a vacuum bag is installed along the edge of the unit. The vacuum bag is then activated to establish a pressure along the edge of the unit that is preferably below about twenty five inches of mercury. Next, the combined unit and vacuum bag are put into an autoclave. In the autoclave, the unit is subjected to a pressure greater than about fifty pounds per square inch (&gt;50 psi). This continues for about an hour. Also, during this time, the temperature inside the autoclave is maintained in a range between one hundred and eighty five degrees Fahrenheit and two hundred and sixty degrees Fahrenheit (185-260 F°). When the unit is removed from the autoclave, it is ready to be installed on the aircraft fuselage. 
         [0010]    For the installation of the cockpit windshield on the aircraft fuselage, carbon frames are respectively bonded to the first and second polycarbonate layers, along the edge of the unit. These carbon frames are then screwed or bolted onto the fuselage. When installed, the windshield provides the crew (pilot and copilot), when they are sitting in the cockpit of the aircraft, with an unobstructed field of vision that extends through an arc of approximately 220°. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0012]      FIG. 1  is a perspective view of an aircraft with a cockpit windshield of the present invention installed thereon; 
           [0013]      FIG. 1A  is an enlarged view of the cockpit windshield; 
           [0014]      FIG. 2  is a flat plan view of a layer configuration used for the manufacture of the windshield of the present invention; 
           [0015]      FIG. 3  is a side view of an aircraft incorporating the windshield of the present invention with portions broken away for clarity; and 
           [0016]      FIG. 4  is a cross sectional view of the windshield installation mechanism as seen along the line  4 - 4  in  FIG. 3 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring initially to  FIG. 1 , a single unitary cockpit windshield  10  is shown installed on an aircraft  12  in accordance with the present invention. As shown, the windshield  10  is installed as a single unit to effectively surround the cockpit of the fuselage  14 . For reference purposes, the aircraft  12  is shown to define a longitudinal axis  16  and an axis  18  that intersects the longitudinal axis  16 . Together, the intersecting axes  18  and  16  define a central plane  20  that bifurcates the aircraft  12  into symmetrical halves, relative to the central plane  20 . Also for reference purposes, an enlarged view of the cockpit portion of aircraft  12 , with an installed windshield  10 , is shown in  FIG. 1A . 
         [0018]    Referring now to  FIG. 2 , a template that is to be used in the manufacture of windshield  10  is shown as a layer  22 , in a two dimensional configuration. As intended for the present invention, various layers  22  of different materials are initially cut in the two dimensional configuration shown in  FIG. 2 . They are then each subsequently formed into a three dimensional configuration. The reconfigured layers  22  are then laminated together to create the windshield  10  shown in  FIG. 1A . 
         [0019]    Dimensionally, each layer  22  defines a center line  24  that passes through a center point  26 .  FIG. 2  also shows that the layer  22  establishes an arcuate distance “d” that extends between the center point  26  and an end point  28 . Similarly, a same distance “d” is established between the center point  26  and an end point  30 . Accordingly, when a layer  22  is folded along its center line  24 , each layer  22  is symmetrically bifurcated relative to the center line  24  into a first portion  32  and a second portion  34 , each of length “d”. 
         [0020]    In the manufacture of the windshield  10 , various materials are each configured like layer  22 . They are then preformed and laminated together to create the windshield  10 . The windshield  10  is then installed on the aircraft  12 . For this transformation, the relationship between the initial two dimensional configuration of layers  22 , and their final three dimensional configuration, when installed on the aircraft  12  as its windshield  10 , is best appreciated by cross referencing  FIG. 1A  with  FIG. 2 . 
         [0021]    When considering  FIG. 1A , together with  FIG. 2 , it will be appreciated that the windshield  10  is installed on the aircraft  12  with the center point  26  and the center line  24  both in the central plane  20 . Thus, the portions  32  and  34  of windshield  10  are symmetrical to each other, relative to the central plane  20 . Consequently, a pilot (not shown), when sifting in the cockpit of aircraft  12 , has an extended field of vision that is unobstructed from the end point  28  and through the center line  24  to the end point  30 . As a practical matter, this gives the pilot, and copilot, a full operational field of vision that extends through an arc of about 220°. 
         [0022]    Turning now to  FIG. 3 , the fuselage  14  of aircraft  12  is shown with portions broken away to reveal the cabin  36  of the aircraft  12 . As intended for the present invention, the cabin  36  is designed to withstand a pressure differential greater than approximately 10 psid. This will allow the aircraft  12  to fly at very high altitudes (e.g. 50,000 ft MSL). For this purpose, the cabin  36  must be sealed to act as a pressure vessel. 
         [0023]    As shown in  FIG. 3 , the cabin  36  (i.e. pressure vessel) includes a substantially cylindrical shaped body section  38  that is closed by an aft bulkhead  40  at its tail end. At its nose end, the body section  38  of cabin  36  is integrated with a forward bulkhead  42 . Further, the body section  38  is formed with an extension  44  that establishes a gap  46  which is created between the extension  44  and the forward bulkhead  42 . In accordance with the present invention, the windshield  10  is installed in this gap  46 . Importantly, when so installed, the windshield  10  structurally functions as a part of the wall of the cabin  36  (pressure vessel). Thus, as a structural part of a pressure vessel, the windshield  10  must be capable of withstanding various forces, in addition to its more obvious function of providing a field of vision for the crew (pilot and copilot) of the aircraft  12 . 
         [0024]    In the manufacture of windshield  10 ,  FIG. 4  indicates that six separate components are involved. These are: a first polycarbonate layer  48 , a second polycarbonate layer  50 , an acrylic outer layer  52 , an acrylic inner layer  54 , a heating layer  56 , and an intermediate layer  58 . In their relationship to each other, the intermediate layer  58  is positioned between the first and second polycarbonate layers  48  and  50 . The acrylic outer layer  52  is positioned against the first polycarbonate layer  48 , opposite the intermediate layer  58  and, similarly, the acrylic inner layer  54  is positioned against the second polycarbonate layer  50 . The heating layer  56  is then positioned against the acrylic outer layer  52 . 
         [0025]    For purposes of the present invention, the heating layer  56  is preferably made of a Mylar® material, with a metal foil or wires embedded therein to provide the necessary heating capability. Also, the intermediate layer  58  is preferably made of a polyurethane. Dimensionally, the polycarbonate layers  48  and  50  are each preferably about ⅜ inch thick. On the other hand, the acrylic outer layer  52 , the acrylic inner layer  54 , and the heating layer  56  are each preferably about one hundredth of an inch thick (0.01 in.). The intermediate layer  58  will be about five hundredths of an inch thick (0.05 in.). 
         [0026]    As mentioned above, each of theses layers  48 ,  50 ,  52 ,  54 ,  56  and  58  all generally conform to a template layer  22 . More specifically, as will be appreciated by the skilled artisan, each layer  48 ,  50 ,  52 ,  54 ,  56  and  58  will vary slightly in their dimensions, depending on their respective bending radius. Further, the layers  48 ,  50 ,  52  and  54  are individually preformed. The remaining layers  56  and  58  are sufficiently thin to be bent into shape without being preformed. Specifically, the preforming of layers  48 ,  50 ,  52  and  54  is accomplished as a so-called “flat wrap” wherein each layer is individually bent about its respective center line  24 . As intended for the present invention, this “flat wrap” is preferably accomplished at a temperature in a range between three hundred and three hundred and fifty degrees Fahrenheit (300-350 F°). The result of the “flat wrap” is that each of the layers  48 ,  50 ,  52 ,  54 ,  56  and  58  are shaped as shown for the windshield  10  in  FIG. 1A . 
         [0027]    For the transformation of layers  22  into the windshield  10 , the preformed layers are prepared with an adhesive (not shown) placed between juxtaposed layers  22  (i.e. the layers  48 ,  50 ,  52 ,  54 ,  56  and  58 ). The combination of layers  22  are then juxtaposed as described above to establish a common edge  60  (see  FIG. 2 ). Next, a vacuum bag (not shown) is installed along the edge  60  of the unit (i.e. the combination of layers  22 ). With the vacuum bag installed, a vacuum of approximately twenty three inches of mercury is drawn to help compress the layers  22  (i.e. the layers  48 ,  50 ,  52 ,  54  and  56 ) together. The unit (layers  48 ,  50 ,  52 ,  54  and  56 ) with the installed vacuum bag is then placed in an autoclave and is subjected to a pressure greater than about fifty pounds per square inch (&gt;50 psi). This autoclaving continues for about one hour. During this period of time, the temperature inside the autoclave is maintained at a temperature in a range between one hundred and eighty five and two hundred and sixty degrees Fahrenheit (185-260 F°). When taken from the autoclave, the windshield  10  has been constructed and is ready for installation. 
         [0028]    In order to install the windshield  10  onto the aircraft  12 , a carbon frame  62  is bonded to the first polycarbonate layer  48  by any means well known in the pertinent art. Similarly, a carbon frame  64  is bonded to the second polycarbonate layer  50 . The carbon frames  62  and  64  are then affixed to the fuselage  14  of aircraft  12 . Preferably this is done using a nut  66  and bolt  68  substantially as shown in  FIG. 4 . 
         [0029]    While the particular Unitary One-Piece Windshield as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.