Patent Application
20090277996
The present invention relates to wing and empennage leading edge structure, comprising an outer shell suitable to define a front portion of an airfoil, said outer shell being made of a bent plate of a fiber-reinforced resin composite material.
Wings and empennage (both vertical and horizontal) are primary structures that are normally dimensioned in terms of stiffness and strength according to the aerodynamic loads to which they can be subjected during flight and/or landing (or take-off) steps.
A particular mention should be made of the requirements to be met by the leading edges of these structures: in these cases, this structure is generally defined and dimensioned by the resistance to possible bird strike during the flight and landing (or take-off) steps.
The so-called bird strike testing is regulated according to FAR 25.631 and sets forth that: when an aircraft impacts with a bird of a defined weight and at a set velocity, following this condition no damage shall occur to the primary structures such as to affect the aircraft safe landing at the nearest airport. As the leading edge is the first structural element which is most likely to be subjected to this kind of impact in cruise conditions, this structure must accordingly comply with the above-defined regulation.
Obviously, besides the above requisite, the leading edge requires to be suitably dimensioned such as to withstand the aerodynamic loads applied thereto.
The above-mentioned structures are usually designed and manufactured such as to prevent the leading edge from being perforated, and thus avoiding possible damages to the structure at the back, or, when perforation is expected, they are designed such that the damage is locally limited.
Traditionally, wing structures are made of aluminum (generally, shells are a few mm thick) reinforced with transversal elements, which have the main task of shaping the profile. A typical example is C-27J Spartan leading edge structure.
Other feasible solutions are, for example, those used in ATR 42-72 regional aircrafts, in which the leading edge is made of double-sandwich glass fiber, or Airbus A380, which has a vertical leading edge of Glare® (a glass fiber/aluminum laminate), and a wing leading edge of a thermoplastic material, or still in Boeing aircrafts of last generation, in which the leading edge of the horizontal empennage is a sandwich of fiber glass with a thin outer aluminum layer, or finally in Airbus A400M, in which the fixed wing leading edge is of an aluminum-carbon fiber mixed structure.
In general terms, accordingly, the materials used for known structures can be metal (aluminum), hybrid (Glare®) or sandwich (glass fiber and honeycomb, carbon fiber and honeycomb) materials, and are used to manufacture a configuration with a single primary bearing element (shell).
The object of the present invention is to provide an alternative to known solutions, which has advantages both in terms of structural configuration and in terms of materials and processes used.
The object of the present invention is thus a leading edge structure of the type defined at the beginning, further comprising
Preferred embodiments of the invention are as defined in the depending claims.
A further object of the present invention is also a method for manufacturing a leading edge structure according to the invention, comprising the following steps:
A preferred, though non limiting, embodiment of the invention will be now described, with reference to the annexed drawings in which:
It should be noted that the figures relate to various configurations of the structure being the object of this patent (number, shape and position of the cross elements) such as to point out the flexibility thereof relative to the various applications provided herein (in terms of position, size, processes, materials).
In
In the following description, the terms “front”, “outer” and “inner” will be used. The term “front” is obviously related to the aircraft movement direction, whereas the terms “outer” and “inner” are general references to a condition in which the leading edge structure is assembled to the remaining wing structure or empennage, whereby the “inner” elements result to be closed within the wing structure or empennage.
The leading edge structure 1 comprises an outer shell 2 suitable to define a front portion of a airfoil. This outer shell 2 is formed by a bent plate of a fiber-reinforced thermoplastic resin composite material. Examples of this material comprise, but are not limited thereto, PPS (Polyphenylene sulphide), PEEK (Polyether-etherketone), PEKK (Polyether ketone ketone) that may be either previously impregnated or infused with short, long fibers or fabrics or mats of carbon or glass fibers, and optionally stiffened with metal strands.
The structure 1 further comprises an inner shell 3 having a convex profile oriented in the same direction as the profile of outer shell 2. In other words, the convexity of the inner shell 3 is oriented in the same direction (i.e. forwards) as the convexity of the outer shell 2.
The inner shell 3 is also formed by a bent plate of fiber-reinforced thermoplastic resin composite material. As examples of this material, reference should be made to what has been described above for the outer shell 2.
The inner shell 3 is bonded to the outer shell 2 at the longitudinal edges 4 thereof. This bonding is simply obtained by means of the thermoplastic resin of the material of the two shells 2, 3. Thereby, an optimum continuity is obtained between these shells at the mutual bonding areas.
The structure 1 further comprises one or more reinforcing elements 5 transversally extending such as to connect the outer shell 2 and inner shell 3 to each other. Each of these reinforcing elements 5 is formed by a piece of fiber-reinforced resin composite material. Preferably, it is a thermoplastic resin, but it may also be a thermosetting resin, e.g. an epoxy resin. As examples of reinforced thermoplastic resin, reference should be made to what has been described above for the outer shell 2.
Each of the reinforcing elements 5 is fixed at opposite ends to the outer shell 2 and inner shell 3, respectively. This fixing is obtained, for example by means of bolting or bonding. When the resin of the reinforcing elements 5 is also a thermoplastic resin, the bonding is advantageously obtained by means of the thermoplastic resin of the material of the two shells 2, 3. Thereby, an optimum continuity is obtained between each reinforcing element and the outer shell on the one side, and between each reinforcing element and the inner shell, on the other side.
The above-described structure is based on a progressive shock-absorption concept, by providing several successive walls being suitably spaced from each other, and supported to one another, such that the impact energy is gradually distributed throughout the penetration step following the impact. The impact substantially takes place against the first shell which absorbs an energy aliquot, while in the meantime the reinforcing elements transmit a portion of this energy to the inner shell. Upon breaking of the outer shell the part of the bird passing therethrough (with a considerably lessened impact energy) is stopped by the inner shell.
According to a preferred manufacturing process, the structure 1 is manufactured by means of a matched moulding process. Each of the parts, i.e. the outer shell 2, the inner shell 3 and the reinforcement elements 5 is manufactured separately by means of matched moulding, at such a temperature as to cause the softening of the resin composing the material of these parts.
After these parts are cooled, they are then assembled to each other, and welded at mutual contact points (e.g., by laser, induction, infrared techniques, etc.), such as to provide an intimate connection therebetween.
Preferably, when large sized components are used, the structure 1 is manufactured in single separated modules, each of which comprises an outer shell 2, an inner shell 3, and at least one cross-connecting element 5. In
As illustrated in
As illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| TO2008A000333 | May 2008 | IT | national |
