Patent Application
20190176992
An aircraft may include heated floor panels to mitigate the effects of cold underfloor temperatures and to help maintain a comfortable cabin temperature. The floor panels are typically supported by an aircraft structure arranged, for example, in a grid-like pattern. The floor panels have structural integrity sufficient to support the weight of people and objects resting on the panels. A metal cover sheet typically forms the top surface of the panel to protect the underlying layers from punctures from high heels, chips from dropped objects, scratches from dragged luggage and/or other floor-traffic related hazards. Some type of floor covering (e.g., carpeting, tiling) is typically placed over the panels for comfort and/or appearance. A heated floor panel can include a weight-supporting layer and a heating layer. The floor panel can also include an insulating layer to prevent heat from exiting the aircraft compartment.
The heating layer of the heated floor panels can be placed just under the metal sheet or near the top surface of the floor. This makes the heating elements of the floor panels susceptible to damage (mechanical or due to fluid intrusion) during installation, maintenance or general use. To address this issue, additional protective layers can be placed over the heating layer. However, such layers can reduce thermal conductivity to from the heating layer to the panel surface, thus requiring a greater power input to achieve the desired panel temperature.
A composite sandwich structure for heating an environment includes a first core layer made from a first cellular material and having a first thickness, and a second core layer made from a second cellular material and having a second thickness less than the first thickness. The structure further includes a heating layer having a thermoelectric heating element and disposed between the first and second core layers. The first core layer is positioned between the heating layer and the environment.
The present invention is directed to a composite sandwich panel, and more specifically, to a heated floor panel having an asymmetric core structure. The core structure includes two core layers surrounding a heating layer. The upper core layer is thinner than the lower core layer, which facilitates heat transfer to the panel surface while providing impact protection to the heating layer.
Heating layer 12 can include a thermoelectric heating element (not shown). The heating element can be a resistive heating element formed, for example, from a metallic material, Positive Temperature Control (PTC) ceramic, PTC polymer, or carbon allotrope material. The heating element can be arranged as an etched foil, wire, or printed-ink element. Other suitable heating elements are contemplated herein. Heating layer 12 can be used to control the temperature of surface 26 of panel 10, which can be installed, for example, in an aircraft cabin or cockpit. In certain embodiments, the heating element can extend across the entire area of heating layer 12. In other embodiments, the heating element can be inset some distance from the edges of heating layer 12 in order to protect the element from fluid spills along or damage at the edges of panel 10.
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In an exemplary embodiment, t2 can be 50% to 60% of t1. In such an embodiment, heating layer 12 can sufficiently heat upper cover sheet 24 and environment E, while requiring less power than if t2 and t1 were equal. The layers above heating layer 12 (on the side of environment E), meanwhile, experience similar impact stresses to equal-thickness models, while the stresses on heating layer 12 are slightly greater. In other embodiments, t2 can be anywhere from 20% to 80% of t1. The variation in t2 can be based on, for example, heating requirements and power of the heating element, or the impact/puncture risk from environment E.
Lower structural layer 18 and upper structural layer 20 surround heating layer 16 to secure it at the center of panel 10. Structural layers 18 and 20 can be formed from a material that is not electrically conductive. For example, layers 18 and 20 can be a pre-impregnated material, such as a carbon fiber or fiberglass with a resin system such as epoxy, polyurethane, phenolic, cyanate ester, bismaleimide, or other appropriate resins. The resin system in structural layers 18 and 20 can additionally contain short or chopped fibers. Each of structural layers 18 and 20 can include a single ply, or a plurality of plies, depending on, for example, the material chosen to form the structural layers, or the robustness of heating layer 16.
Cover sheets 22 and 24 are the outermost layers of panel 10. Lower cover sheet 22 provides structural support to panel 10 on a side of substrate S. Upper cover sheet 24 provides structural support to panel 10 on the side of panel 10 exposed to environment E, which can be, for example, an aircraft cabin, cockpit, or other compartment. Cover sheets 22 and 24 are relatively stiffer than core layers 14 and 16 (having a higher value of elastic modulus E). Cover sheets 22 and 24 can be formed from a composite material, such as a pre-impregnated carbon fiber, fiberglass, Kevlar®, or combinations thereof. Other suitable reinforced polymer matrix materials are contemplated herein. In some embodiments, cover sheets 22 and 24 can be formed from the same material, while in other embodiments, cover sheets 22 and 24 can be formed from different materials.
Under normal loading, cover sheets 22 and 24 function similar to the flanges of an I-beam, whereby lower cover sheet 22 is in tension and upper cover sheet 24 is in compression. Core layers 14 and 16 function similar to the web of an I-beam by evenly spacing cover sheets 22 and 24. That is, the arrangement of core layers 14 and 16 between cover sheets 22 and 24 gives panel 10 a bending stiffness. Bending stiffness can be increased, for example, by spacing cover sheets 22 and 24 father apart. Therefore, the bending stiffness of panel 10 is generally proportional to core thickness T.
The disclosed sandwich panel having an asymmetric core structure maximizes both the heating of the floor panel surface, the structural integrity of the panel, and the protection of the embedded heating element. The sandwich panel can optionally include adhesives between any of the disclosed layers, or within the layers themselves, in order to solidify the panel structure. Other means of attachment are contemplated herein. In addition to aerospace applications, the disclosed sandwich panel can be used in maritime, railroad, and automotive applications, as well as the construction industry.
Discussion of Possible Embodiments
The following are non-exclusive descriptions of possible embodiments of the present invention.
A composite sandwich structure for heating an environment includes a first core layer made from a first cellular material and having a first thickness, and a second core layer made from a second cellular material and having a second thickness less than the first thickness. The structure further includes a heating layer having a thermoelectric heating element and disposed between the first and second core layers. The first core layer is positioned between the heating layer and the environment.
The structure of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
The above structure can further include a first structural layer disposed between the heating layer and the first core layer, and a second structural layer disposed between the heating layer and the second core layer.
In any of the above structures, the first and second structural layers can be formed from a composite fabric pre-impregnated with a resin.
In any of the above structures, the resin can include an epoxy, a polyurethane, a phenolic resin, a cyanate ester, a bismaleimide, or combinations thereof.
Any of the above structures can further include a first cover sheet abutting the first core layer on a side opposite the first structural layer, and a second cover sheet abutting the second core layer on a side opposite the second structural layer.
In any of the above structures, a bending stiffness of the structure can be proportional to a sum of the first thickness and the second thickness.
In any of the above structures, the first and second cover sheets can be formed from a reinforced polymer material.
In any of the above structures, the first cover sheet can abut the environment.
In any of the above structures, the first and second cover sheets can have higher elastic moduli than the first and second core structures.
In any of the above structures, the first and second core layers can form an asymmetric core structure having a core thickness.
In any of the above structures, the second thickness can range from 20% to 80% of the first thickness.
In any of the above structures, the second thickness can range from 50% to 60% of the first thickness.
In any of the above structures, the second thickness can range from 0.05 in (1.27 mm) to 0.25 in (6.35 mm).
In any of the above structures, the first or second cellular material can be a honeycomb material.
In any of the above structures, the first or second cellular material can be a foam material.
In any of the above structures, the first and second cellular material can be the same.
In any of the above structures, the heating element can include a metallic material, PTC ceramic, PTC polymer, or carbon allotrope material.
In any of the above structures, the structure can be an aircraft floor panel.
In any of the above structures, the environment can be an aircraft compartment.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
