Patent Publication Number: US-2010112355-A1

Title: Aircraft Transparency

Description:
TECHNICAL FIELD 
     The present disclosed subject matter is related to aircraft, and in particular to aviation transparencies for applications such as windows and light covers for aircraft. 
     BACKGROUND 
     The aviation industry is always looking for lighter weight materials to increase fuel efficiency. Accordingly, aviation transparencies, such as windows, for both the cabin and the cockpit have gone from glass to lightweight polymeric materials. The polymeric materials for these polymeric windows are routinely subject to scratches. It is extremely difficult, and sometimes not possible, to “rub out” these scratches. As a result, a scratched window must be completely replaced, which occurs regularly. 
     Aircraft window replacement is time consuming, and expensive. The windows themselves are expensive, as well as parts associated therewith are expensive. Second, changing these windows is a further expense as it is labor intensive and must be performed by skilled personnel, as it requires the sidewalls of the cabin to be removed to access the windows for replacement. Additionally, there is downtime and thus loss of service while the window is being replaced. 
     Other lightweight polymeric materials are used in aircraft, to replace heavier glass. For example, a hybrid material including polycarbonate and acrylic has been used as a landing light lens. However, this material lacks desireable optical properties. 
     SUMMARY 
     The present disclosed subject matter improves on contemporary aviation transparencies, i.e., windows and landing light lenses, by providing a hybrid polymeric transparency for use in aircraft. This hybrid polymeric transparency possesses the requisite optical properties and impact resistance, that permit its use in aircraft as cockpit cabin windows landing light lenses, or in other applications. When the disclosed transparencies are used as aircraft windows, they are low-maintenance, as scratches can be polished out of the surface, allowing for minimal labor costs and minimal aircraft down time. Additionally, the disclosed transparencies are lighter in weight and tougher than conventional aviation transparencies. For example, by using polycarbonate layers, instead of acrylics, these polycarbonate layers being tougher than acrylics, thinner laminates may be used in the disclosed aircraft transparencies. This lighter weight contributes to fuel savings. 
     The present disclosed subject matter also provides methods for making aviation transparencies, such as aircraft windows with superior optical properties, over conventional aircraft windows, that are usable as both cockpit and cabin windows. For example, the windows are made by injection-compression molding techniques. These injection-compression molding techniques produce components for the windows with superior optics and lower residual stress, when compared to conventionally injection-molded components. 
     Another advantage to using an injection molding process is that it could enable the mounting features for the transparency, e.g., brackets, seals, etc., to be molded into the perimeter of the window. 
     An embodiment of the disclosed subject matter is directed to an aviation transparency. The aviation transparency includes a base, layer including a polycarbonate polymer, an upper layer including an acrylic polymer, and, an intermediate layer. The intermediate layer is a polymeric material for confining failures to the outer layer, and the intermediate layer is positioned between the base layer and the outer layer. The aviation transparency may be, for example, an aircraft window, such as a cockpit cabin window or a landing light lens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Attention is now directed to the drawings, where like numerals and characters indicate like or corresponding components. In the drawings: 
         FIG. 1  is a perspective view of an airplane, showing cockpit and cabin windows; 
         FIG. 2  is a cross sectional view of cabin windows in accordance with the disclosed subject matter, taken along line  2 - 2  of  FIG. 1 ; and, 
         FIG. 3  is a cross sectional view of cockpit windows in accordance with the disclosed subject matter, taken along line  3 - 3  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an aircraft  20 , with both cabin windows  22  and cockpit windows  24 . These components must exhibit optical properties, allowing both pilots and passengers sufficient visibility from inside the aircraft, as well as standards for impact resistance and light transmittance. The visibility and impact resistance standards are, for example, set by U.S. Department of Transportation, Federal Aviation Administration Standards. 
       FIGS. 2 and 3  show cross-sections of windows  30 ,  30 ′,  130 ,  130 ′, exemplary of the disclosed subject matter. Windows  30 ,  130  are suitable for use as cabin windows  22  (as shown in the cabin  22   a ), and windows  30 ′,  130 ′ are suitable for use as cockpit windows  24  (shown in the cockpit  24   a ). The windows  30 ,  30 ′ shown in  FIGS. 2 and 3  include three layers while the windows  130 ,  130 ′ of  FIGS. 2 and 3  include five layers. Windows  30  and  130  are similar in construction to windows  30 ′ and  130 ′, respectively, but differ in that they are shaped differently to accommodate placement in the cabin  22   a  and cockpit  24   a  of the aircraft  22 . While three and five layer structures are shown and described below, these constructions may include additional layers, adhesives, additives and the like, without departing from the disclosed three and five layer structures. 
     Turning specifically to  FIGS. 2 and 3 , the windows  30 ,  30 ′ include a base or base layer  44 , a laminate or intermediate layer  142 , and a top or outer layer  40 . The windows  30 ,  30 ′ are oriented in an aircraft  20  or other vehicle, such that the base layer  44  faces the inside of the cabin  22   a  while the outer layer  40  faces the outside or ambient environment  50  ( FIG. 1 ). 
     The base layer  44  is of a material such as a polycarbonate, and, for example, an optical grade polycarbonate, such as the polymer known as Polycarbonate GLX143, available from Exatec, a joint venture between Bayer and General Electric Plastics. The combination of the polycarbonate, acrylic and inner layer provides the windows  30 ,  30 ′ with the strength and impact resistance required by the aforementioned government regulations. The thickness may be approximately 0.115 inches to 0.265 inches, and may be, for example, a sheet of approximately 0.125 inches in thickness. 
     Polycarbonates are suitable as the base layer  44 , as they are easily worked molded and thermoformed. The base layer  44  of polycarbonate is produced by injection-compression molding processes, and results in transparency that provides optical properties sufficient for cockpit and cabin windows. The resultant material also provides the necessary impact strength. Additionally, injection-compression molding allows for mounting structures, for example, brackets and seals to be molded onto the perimeter of the window  30 ,  30 ′ when it is finished, as detailed below. 
     The laminate or laminate layer  142  is, for example, of Polyvinyl butyral (PVB) resin, in a thin layer, film or sheet. This laminate layer  142  provides bonding between the base layer  44  and the top or outer layer  40 , along with optical clarity, free of distortion. It is also tough and ductile, to confine cracks and other defects in the surrounding layers  40 ,  44 , from passing through the laminate  30 . The laminate layer  142  may be a PVB film, of materials such as Butacite®, Saflex®, S-Lec® and Trosifol®. Alternately, the laminate of the laminate or intermediate layer  142  may be a urethane. The laminate layer  142  may be of a thickness approximately 0.025 inches to 0.175 inches, e.g., 1 inch thick in an embodiment. 
     The top or outer layer  40  is, for example, of a Polymethyl Methacrylate (PMMA) (methyl 2-methylpropenoate), or other acrylic. The PMMA may be, for example, Polycast®, Plexiglas®, Perspex®, Plazcryl®, Acrylite®, Acrylplast®, Altuglas®, or Lucite®, or other acrylic. It is made, for example, by a casting process, and provides a surface from which scratches can be removed by polishing. The PMMA or other acrylic is also ultraviolet (UV) light resistant. The top or outer layer  40  may be of a thickness approximately 0.344 inches to 0.490 inches, e.g., 0.417 inches in an embodiment. 
     The windows  30 ,  30 ′ are manufactured by the following exemplary process. Initially, the polycarbonate base layer  44  and PMMA outer layer  40  are injection-compression molded as shells with corresponding configurations, so as to have nesting geometries. This molding as well as other processing steps are performed, for example, in a clean room. The PMMA layer  40  is placed on a tool and the nesting surface, opposite the tool, is coated with a primer, for example, an optically clear adhesion promoter. 
     After assembly the materials will be cured based on known standards, such as glass transition temperatures, as established by the manufacturers of the material and available in Material Specification Sheets from the respective manufacturers. 
     A thin precut sheet of PVB (that forms the laminate or intermediate layer  142 ) is placed onto the primed surface of the PMMA layer  40 . A primer coating, for example, an optically clear adhesive, is placed onto the nesting surface of the polycarbonate base layer  44 . 
     The now coated polycarbonate base layer  44  is placed into contact with the thin sheet of PVB (the laminate or intermediate layer  142 ) that covers the PMMA layer  40 , to form an uncured product with three layers with flush edges. 
     The three layers are then cured, by being vacuum bagged in an autoclave. The vacuum bagging process is employed, as it allows for high temperature curing at elevated pressures, in oxygen-free environments. 
     Attention is now directed to alternate windows  130 ,  130 ′, that are suitable for use as cabin  22  and cockpit  24  windows. The windows  130 ,  130 ′ are formed of five layers  140 ,  142   a ,  142   b ,  144   a ,  144   b.    
     The base layer  140  is similar in construction and materials to the base layer  44  detailed above. This base layer  140  is contacted on both sides by a laminate or laminate layer  142   a ,  142   b , similar to the laminate layer  142  detailed above. Top or outer layers  144   a ,  144   b  are over the respective laminate layers  142   a ,  142   b . These top or outer layers  144   a ,  144   b  are in accordance with the top or outer layer  40 , as detailed above. 
     The windows  130 ,  130 ′ are manufactured by the following exemplary process. Initially, the polycarbonate base layer  140  and both PMMA outer layers  144   a ,  144   b  are injection-compression molded as shells with corresponding configurations, so as to have nesting geometries. This molding as well as other processing steps are performed, for example, in a clean room. One PMMA layer  144   a  is placed on a tool and the nesting surface, opposite the tool, is coated with a primer, for example, an optically clear adhesion promoter. 
     A thin precut sheet of PVB (forming a laminate or intermediate layer  142   a ) is placed onto the adhesive coated surface of the PMMA layer  144   a . A primer coating, for example, an optically clear adhesion promoter, is placed onto the nesting surface of the polycarbonate base layer  140 . The now coated polycarbonate base layer  140  is placed into contact with the thin sheet of PVB (forming the laminate or intermediate layer  142   a ) that covers the PMMA layer  144   a , to form a product with three layers. 
     The polycarbonate base layer  140 , at the non-coated surface, is now coated with the aforementioned primer coating. A second thin precut sheet of PVB (forming a laminate or intermediate layer  142   b ) is placed onto the adhesive coated surface. The other PMMA layer  144   b  is now coated with primer, as detailed above, and placed into contact with the exposed sheet of PVB (forming a laminate or intermediate layer  142   b ). A five layer uncured product with flush edges has been made. The five layer product is cured, by being vacuum bagged in an autoclave, as detailed above, to produce the resultant window  130 ,  130 ′. 
     There has been shown and described at least one preferred embodiment of a transparency for use with aircraft. It is apparent to those skilled in the art, however, that many changes, variations, modifications, and other uses and applications for the apparatus and its components are possible, and also such changes, variations, modifications, and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is limited only by the claims which follow.