Abstract:
A window assembly is provided to prevent the migration of the window seal. The window assembly includes an outer window pane, an inner window pane and a seal. The outer window pane having a geometric feature configured to become parallel relative to another structure while the outer window pane rotates from a first position to a second position. The window assembly may further include a stiffening ring and a clamping ring which act to further secure the window seal in the desired position.

Description:
BACKGROUND 
   1. Field of the Invention 
   This invention relates generally to aircraft windows and specifically the prevention of window fogging. 
   2. Background of the Invention 
   Throughout the history of commercial aviation, airlines have experienced fogging, or the formation of condensation, on passenger windows on their aircraft. 
   There are numerous potential causes of fogging on passenger windows. One such cause of severe fogging on passenger windows has been found to be displaced seals in areas around the window edge. Generally, the rubber seal that normally surrounds the inner and outer acrylic panes of an aircraft window have been found to move, or ‘migrate’, off the edges of the panes. 
     FIG. 1A , is an illustration of a typical aircraft window  100  with a normal seal  102   a  within gap  104  between outer window pane  108  and surrounding aircraft structure. In contrast,  FIG. 1B  is an illustration of window  100  with a ‘migrated’ seal  102   b  within gap  104 . 
   Once window seal  102   a  has moved away from its intended position, migrated seal  102   b  may no longer function properly. This condition can result in pressure leaking through gap  104  and/or external moisture entering window cavity  106 , both of which can result in undesirable condensation forming in the cavity during routine operation of the aircraft. 
   The traditional solution for preventing window seal  102   a  from moving away from its intended position would be to make the edge of seal  102   a  thicker. This solution, however, is not weight effective. 
   Accordingly, what is needed is a device that properly retains the seal in the gap between the edge of outer window pane and the surrounding window frame structure in the most weight-effective manner possible. 
   SUMMARY OF THE INVENTION 
   The present invention includes features designed into components of a window assembly that act together to prevent window seal movement. 
   Certain features of the present invention are designed into components of the window assembly and act to physically restrain the window seal around its edge. 
   Other features are designed into the edge shape of the window outer pane to prevent it from applying a ‘walking’ force to the seal as it rotates caused by cyclic pressure loads during aircraft operation. 
   The combination of physical restraint of the window seal and change in shape of outer pane act together to ensure that the window seal cannot move or migrate off the edge of the window panes. 
   In one aspect of the present invention a window assembly is provided which includes an outer window pane, an inner window pane and a seal. The outer window pane includes a geometric feature configured to become parallel relative to another structure while rotating from a first position to a second position. 
   In another aspect of the present invention, a window assembly is provided which includes an outer window pane; an inner window pane; and a seal assembly. The seal assembly further includes a seal configured to physically restrain outer edges of the outer window pane and the inner window pane. The seal assembly also includes a stiffening ring made integral with the seal; and a clamping ring configured to restrain the seal about the outer and inner window panes. 
   The invention described herein provides solution to the seal movement problem in a weight efficient method, which is of critical consideration in design of aircraft components. In one embodiment of the present invention, a weight savings of more than 10 lbs. per aircraft may be realized over a more traditional solution of adding material at the edge of the window seal. 
   Additional advantages, objects, and features of the invention will be set forth in part in the detailed description which follows. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide further understanding of the invention, illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures: 
       FIGS. 1A and 1B  are simplified cross-sectional views of a typical aircraft window assembly; 
       FIG. 2  is a simplified cross-sectional view of a window assembly with features to prevent window seal movement in accordance with an embodiment of the present invention; 
       FIG. 3  is a simplified cross-sectional view of a window seal in accordance with an embodiment of the present invention; and 
       FIG. 4  is a simplified cross-sectional view of a window pane design in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Seal movement is typically caused by a combination of three main external influences on aircraft windows. 
   The first is the cyclic flexing of the acrylic panes from aircraft pressurization loads. As the panes flex outward at the center, the outer edges rotate, creating a back-and-forth motion with every pressurization cycle of the aircraft that when combined with the angle created between the edge and window frame can effectively ‘walk’ the seal off the edge of the panes. 
   The second is vibration caused by engines and flight loads during normal operation of the aircraft. Vibration causes the window panes, seal and surrounding structure to vibrate at their respective resonant frequencies. Over long periods of time, with the shape and mounting method of modern passenger windows, this resonance can directly result in movement of the seal on the edge of the window. 
   The third is external hydrodynamic forces impinging upon the seal at the edge of the window, the main source of which can be from pressure washers that may be used to clean the aircraft exterior or de-icing fluids applied during the winter season. 
   This invention includes features designed into components of the window assembly that act together to prevent seal movement caused by, for example, the external influences previously described. 
   As illustrated in  FIG. 2 , window assembly  200  in accordance with an embodiment of the present invention includes an outer pane  202 , an inner pane  204 , and window seal assembly  206 . Window seal assembly  206  further includes a seal  208 , an integral stiffening ring  210  and a clamping ring  212 . 
   The remaining components of window assembly  200  may include all the components necessary to mount window panes  202  and  204  and seal assembly  206  to an aircraft, for example, window frame  214  and window retention clip  216 , all of which are known to those of ordinary skill in the art. 
   Window assembly  200  includes features designed into components of window assembly  200  in accordance with embodiments of the present invention. The features rely upon mechanical engineering principles to prevent seal movement. 
   Referring now to  FIGS. 2 and 3 , window seal assembly  206  includes a change to the shape of window seal  102   a  ( FIG. 1 ) to create window seal  208 , and the addition of integral stiffening ring  210  and clamping ring  212  in accordance with an embodiment of the present invention. 
   Window seal  208  includes a first portion  302 , configured to match the contour of an outer window pane, such as that described in detail below. Window seal  208  also includes a second portion  304  defining a cut-out or channel configured to receive integral stiffening ring  210  as described in detail below. A third portion  306  of seal  208  is configured to extend around a portion of inner pane  204  to contact additional surface area thereon and to contact clamping ring  212 . In this configuration, seal  208  is advantageously configured to physically restrain window seal  208  around outer edges of outer pane  202  and inner pane  204 . 
   In accordance with an embodiment of the present invention, integral stiffening ring  210  may be embedded in the periphery of window seal  208  in cutout portion  304 . Stiffening ring  210  acts to physically restrain window seal  208  to keep seal  208  in constant contact with outer and inner window panes  202  and  204  at edges  308  and  310 . Stiffening ring  210  may be made of any suitable material, such as a material that has more stiffness than the seal material and which can provide stiffness to seal  208  to increase resistance to the forces that cause seal movement. Stiffening ring  210  may be either bonded or molded into seal  208 , or alternatively, may be a separate component positioned in cutout portion  304  of seal  208  during the window assembling process. 
   Clamping ring  212  is a ring configured to surround the external periphery of the window seal and acts to physically restrain window seal  208 , or alternatively window seal  208  and stiffening ring  210 , in position against the inner and outer window panes. In one embodiment, clamping ring  212  has an L-shaped cross section. One leg of the L-shaped cross section contacts seal  208  adjacent to third portion  306 , while the other leg extends to cutout portion  304 . 
   Clamping ring  212  may be made from any suitable material, such as a material that has more stiffness than the window seal material, and that achieves a significant increase in stiffness from the L-shaped configuration. 
     FIG. 4  is a simplified illustration of a feature  218  ( FIG. 2 ) of outer window pane  202  which contacts the portion of seal  208  present in gap  104 . Feature  218  includes a reconfigured edge portion designed to prevent the detrimental affects of the cyclic flexing of outer window pane  202  caused by aircraft pressurization loads. As illustrated in  FIG. 4 , as outer window pane  202  flexes outward at the center, the outer edge  218  rotates from a normal position shown in solid to a deflected position shown dashed. The movement is a back-and-forth motion occurring with every pressurization cycle of the aircraft. 
   Feature  218  that when combined with the angle created between feature  218  and the aircraft window frame can effectively prevent the back-and-forth movement from creating a force on seal  208  that can cause outward seal movement. For example, as in  FIG. 1A , typical window designs use an outer window pane  108  with an edge geometry that results in the edge being parallel to the window frame when outer window pane  108  is in an undeflected state, such as when the aircraft is on the ground. As this typical outer window pane  108  is deflected from pressurization loads, for example, while airborne at cruising altitude, outer pane  108  rotates at the edge, which causes an outward acting force to be applied to seal  102   a , which typically results in seal movement. 
   As shown in  FIG. 4 , the geometry of feature  218  in accordance with an embodiment of the present invention is designed such that in the normal or undeflected position edge  402  of outer window pane  202  in gap  104  is at an angle or not parallel to edge  404  of window frame  406 . As shown in dashed lines, the geometry of edge  402  of outer window pane  202  becomes substantially parallel to edge  404  of window frame  406  when outer window pane  202  has rotated to its maximum deflected state. In the parallel position, the application of any outward force on the portion of seal  208  in gap  104  is substantially reduced or eliminated. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.