Patent Application
20080078876
Prior Art
A composite resin window frame 1 is depicted in
Prior Art
Prior Art
Prior Art
The present invention recognizes that the airplane fuselage skin can be utilized to carry the loads associated with stresses induced by skin-piercing apertures in the fuselage, where the composite resin window frame carries the transparency and its associated load. The subject composite window frame design allows for a composite fuselage barrel to function effectively without the necessity for conventional strength enhancement, such as that provided in prior window frame designs utilizing the up-standing reinforcement leg discussed previously. The composite window frame relies on the strength of the composite fuselage skin and associated stringers to bear the necessary loads while retaining the window transparencies in place.
Stress and compression analyses confirmed that the present composite resin window frame design achieved successful results without resorting to the use of a conventional, strength-enhancing upstanding leg, thereby benefiting from both weight and cost savings. Furthermore, it will be recognized that the advantages provided by the subject composite resin window frame assembly would apply equally well to other apertures in the fuselage of an airplane. Another benefit of manufacturing the subject composite resin frame is that there is no need to scallop the fuselage skin for installation.
The composite resin window frame and assembly may be fabricated in accordance with the following procedures and several different material and manufacturing options may be utilized or combined. The manufacturing process described for the composite resin frame is not limited to any single composite manufacturing method, rather, any number of approaches can be used.
A composite window frame of the present design may be made of either thermosetting or thermoplastic resin. Also, many different reinforcing fibers can be used in the resin matrix including glass and carbon fibers or combinations of these or other fibers used to reinforce the composite matrix.
In accordance with conventional composite resin manufacturing techniques, the selected resin and reinforcing fibers can be combined ahead of time, as in a so-called prepreg hand lay-up process. Other suitable methods include hot drape forming, tape lamination, fabrication with sheet molding compound, tow or slit tape placement, resin transfer molding, liquid resin infusion, resin film infusion, bulk resin infusion and reinforced thermal plastic lamination. Alternatively, the resin and fibers can be combined during molding operations such as resin infusion, resin injection molding, compression molding or resin transfer molding. Those skilled in the art will recognize that the method of the invention may be readily modified to incorporate pre-fabricated inserts, metallic inserts, and inserts comprising metal/composite hybrid structures.
The manufacturing methods described above may be enhanced by utilizing stress analysis techniques to design, refine and fabricate a variety of suitable composite resin window frames for use in combination with a composite fuselage, thereby providing stronger window frames while saving weight and cost. Since the composite resin window frame relies on the strength of the composite fuselage skin and associated stringers to distribute the shear loads adequately while still retaining the window, the load stays in the composite skin.
A typical composite window frame of the present design will have a generally oval shape. Overall dimensions across the frame are about 55-60 cm in the long dimension and have a narrower dimension of about 35-40 cm. The composite frame has a width of about 5-6 cm in the region depicted by position i-i in
In one embodiment of the manufacturing process useful for producing the subject composite window frame, prepreg material is selected and cut to size for a particular part configuration, placed in a cure tool of desired shape and dimension and cured using heat and pressure.
An alternative method of fabrication involves tow prepreg or slit tape placement using an advanced fiber placement head which positions the prepreg in the molding tool and thereafter cures the resin composite using heat and pressure.
Another alternative method of fabrication involves resin transfer molding utilizing a dry fiber braid and resin. The braid is placed in a matched die tool; the resin is then injected into the tool and cured using heat and pressure. Another alternative method of fabrication involves liquid resin infusion wherein dry fiber braid is placed in the part tool; the braid is infused with the resin and cured using heat and pressure. In a vacuum-assisted resin infusing method, dry woven graphite is preformed and positioned over inexpensive aluminum tooling prior to curing the frame.
Other alternative methods include liquid film infusion and bulk resin infusion wherein dry fiber braid is placed in the part tool, the braid is infused with the resin film and cured using heat and pressure.
A method of reinforced thermal plastic lamination involves cutting a thermal plastic prepreg blank to appropriate size, heating the blank in an oven, forming the hot blank in a press, cooling the part and removing it from the press. Alternatively, cut plies can be stacked and placed on a consolidation tool. Consolidation can then be accomplished with heat and pressure, as in an autoclave or press method.
The following examples illustrate the invention and are not intended to limit the general applicability of the subject method.
A composite window frame of the present invention was made by compression molding the frame in a molding tool. The molding tool produced a composite window frame having the shape and dimensions of the frame depicted in
Another composite resin window frame part of similar size and shape was fabricated using an intermediate modulus compression molding material, Toray BMS 8-276 carbon fiber epoxy prepreg tape material in accordance with the manufacturer's instructions. After molding, curing and cooling, another composite resin window frame of the present invention was thereby produced.
Composite resin window frames made in accordance with the foregoing examples were converted into window frame assemblies by combining each of the frames with acrylic transparencies by means of clips and a rubber seal and installing the combined assemblies in composite fuselage apertures of sufficient size to receive and complete an integrated frame-window-fuselage assembly. Stress and load analyses confirmed that the frames carried and transmitted the loads satisfactorily to the surrounding fuselage skin structure.
