Patent Application
20180362142
This application claims the benefit of the European patent application No. 17382373.3 filed on Jun. 19, 2017, the entire disclosures of which are incorporated herein by way of reference.
The invention is related with a new structure that could replace typical sandwich panels, making use of a flexible layer to produce an inflatable structure.
The current solution to produce a structure that has big out-of-the-plane inertia, are honeycomb panels or panels stiffened with stringers. Bonded honeycomb sandwich construction has been a basic structural concept in the aerospace industry.
A honeycomb panel consists of two face sheets separated by a honeycomb core. The facings of the sandwich act similarly to the flanges of an I-beam, taking the bending loads, one facing in tension and the other in compression. Following the comparison, the honeycomb acts as the web of the I-beam, resisting the shear load and also separating the facings apart and increasing the stiffness. Finally, the core is adhesively joined to all the sandwich components, allowing them to act as one unit with high torsional rigidity.
Weight saving is one of the main drivers when using sandwich structures. However, there are several requirements that must be fulfilled by such structures:
The design of the sandwich structures should be optimized toward a minimum installation of elements or riveting of the structure in the areas with core. For this purpose, monolithic areas, potting compound or inserts can be used to create local structures for riveting and bolt installation.
The sandwich structures exposed to the airflow must conform to aerodynamic and structural tolerance requirements to minimize airflow perturbation and erosion.
The designer must consider the interface constraints, like room available for the component.
Water tightness inspection and non-destructive inspections and testing NDT/NDI of the structures has to be taken into account according to the classification of the structure.
On the other hand, these structures are difficult to produce by automated means due to the nature of the materials and the adjustments required in order to produce the sandwich. Thus, they are often produced manually and therefore with high associated costs.
The invention proposes a different way of having a structure able to carry out-of-the-plane loads, typically pressure, by using an inflatable panel made of flexible layer faces.
Some of the objectives for this concept, compared with the state of the art are mainly:
Weight saving.
Cost saving.
Water tight design.
Maintenance (easy to repair, replace, maintain).
The panel objects of the invention comprise:
an inflatable panel comprising two flexible face sheets and a core located between the two flexible face sheets, and
lateral joining members configured to be joined to the aircraft structure and coupled to the inflatable panel, the lateral joining members covering at least part of the linear contour of the two flexible face sheets and having a first part covering an edge portion adjacent to the contour of one of the face sheets and a second part covering an edge portion adjacent to the contour of the other face sheet.
Therefore, the faces of the inflatable panel are flexible layer faces and hence they can adapt to the interior pressure of the inflatable panel. The lateral joining members can cover part or the totality of the contour line of the flexible layer faces, i.e., the lateral joining members may surround totally or partially the inflatable panel. The lateral joining members comprise two parts:
a first part covering a portion of the external edge or outermost edge of one of the faces, i.e., the first part extending inwardly a portion from the contour of one of the faces, and
a second part covering a portion of the external edge or outermost edge of the other face, i.e., the second part also extending inwardly a portion from the contour of the other face.
Therefore, the edges of the inflatable panel are covered by the lateral joining members in both face sheets.
This invention can be used as an alternative to any sandwich panel, or even any panel stiffened with stringers, used in aircraft, such the ones used in belly fairings, trailing edge panels, access doors or other locations.
The above inflatable concept is valid for concave and convex surfaces under suction/pressure. The shape of the inflatable structure can be tailored to provide the concave/convex surface using, for instance, drop stitching technique in the core extending the drop stitch between both faces.
The way an inflatable panel works is the following:
By inflating the part up to a certain pressure (from 1 bar up to 5 bars), panel becomes stiff enough and is able to keep the shape to fulfill the requirements. The more pressure, the more stiffness, and smaller out of plane deformation. Also, the bigger the inflatable panel height, the bigger the panel stiffness.
A dedicated system is not needed to control inner pressure. Panel material is airtight so pressure will be kept.
Typical pressure values needed for inflation (1-3 bars), includes also the inner pressure variation due to in service temperature variation (−54° C. to 70° C.). That is, there is an inflation overpressure to compensate inner pressure decrease when being at high altitude due to low temperature.
The inflatable panel is intended to withstand out of the plane load, pressure/suction, and, depending on the attachment to the backup structure, will not carry any in-plane load. This is an advantage in some cases where typical sandwich panels take loads just by deformation compatibility with its supporting structure.
In case of damage, inner pressure will be lost, and therefore the stiffness. In that case, the claimed panel fulfills the same requirements as the sandwich panel it replaces due to the configuration of the lateral joining members.
To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. The drawings form an integral part of the description and illustrate preferred embodiments of the invention. The drawings comprise the following figures.
The core (4) of the inflatable panel (1) can be manufactured with or without drop stitching, depending on the requirements, i.e., the two face sheets (2, 3), named as inner and outer faces (2, 3) are joined or stitched by cords so the final external geometry is the required one. The inflatable panel (1) is made up of flexible sheets in the inner and outer faces (2, 3) and the drop stitching is the feature that gives and keeps the required external shape to the panel (1).
The contour frame (6), made of composite material or metal, is the part that connects the inflatable panel (1) and the supporting elements of the main structure of the aircraft.
The skin (7) is also attached to the contour frame (6), bonded or by any other mean, and can be bonded or not to the inflatable panel (1), depending on the requirements.
As an alternative to the embodiment shown in
The embodiments shown in
In case of inflatable panel (1) puncture or rupture, inner pressure will be lost, and the inflatable panel (1) will not keep the required shape, but it will not be lost, because it is attached to the main supporting structure of the aircraft by the two straps (12).
While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17382373.3 | Jun 2017 | EP | regional |
