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.
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).
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.
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.
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's fuselage.
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.”
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.
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.
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 (>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.
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°.
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:
Referring initially to
Referring now to
Dimensionally, each layer 22 defines a center line 24 that passes through a center point 26.
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
When considering
Turning now to
As shown in
In the manufacture of windshield 10,
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.).
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
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
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
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.