Patent Description:
Different kinds of liners or patches are known from <CIT> and <CIT>. Another patch is known from unpublished German patent application <CIT> which relates to a smart repair patch. Different aircraft fuel tanks with tank liners in form of bladders or partial bladders are known from <CIT>, <CIT>, and <CIT>.

Due to increasing consciousness for the environmental impact of air travel, the requirements for fuel safety as it relates to environmental damage also increases. Thus, there exists a need for improved fuel tanks that are able to mitigate the risk of fuel leakage even in case of mechanical damage to the tank. In other words, the fuel tanks failsafe capabilities shall be improved.

It is the object of the invention to provide measures that improve the failsafe capabilities of fuel tanks, preferably for aircraft.

For achieving such object, the invention provides a fuel tank having the features of claim <NUM>. A further aspect of the invention is defined by the manufacturing method for the fuel tank according to claim <NUM>. Advantageous embodiments are subject-matters of the dependent claims.

The invention provides a fuel tank for an aircraft with a plurality of tank wall liners. The fuel tank has a tank wall that encloses a tank volume. Each tank wall liner comprises a liner body made of a liner material, the liner body comprising a mounting surface configured to be installed facing a tank wall and at least one sealing surface configured to be installed facing another tank wall liner, wherein the liner material includes a cured sealant that is suitable for jet fuel.

Preferably, the liner material includes at least one reinforcement layer made of a textile or fiber material.

Preferably, the reinforcement layer is arranged entirely within the cured sealant or wherein the reinforcement layer protrudes from at least one sealing surface.

Preferably, the reinforcement layer is arranged in a thickness direction of the liner body in any or one of the following portions: in the lower third, the medium third, or the upper third of the liner body.

Preferably, the liner body comprises a plurality of cut-outs or through-holes that are suitable for accommodating fasteners of the tank.

Preferably, the cut-outs or through-holes are only into or through the cured sealant or both the cured sealant and the reinforcement layer.

The invention provides a tank for an aircraft, the tank comprising the tank wall that encloses the tank volume for fuel, namely jet fuel, wherein the plurality of tank wall liners are mounted to the tank wall on the inside of the tank volume so as to form a lined tank wall portion that is configured to seal the tank wall from the jet fuel.

Preferably, the tank wall forms a fuselage section, preferably an aft fuselage section, of a fuselage of an aircraft.

Preferably, the tank wall liners are adhesively bonded to the tank wall, preferably with a sealant.

According to the invention, the tank wall comprises a frame structure and a skin that is supported by the frame structure, wherein the tank wall liners are mounted to the skin between the frame structure.

Preferably, the frame structure comprises a plurality of ribs and stringers, wherein a pair of ribs and stringers form a contoured area, and the tank wall liner is shaped to match the contoured area.

Preferably, laterally adjacent tank wall liners form a joint that is sealed with sealant.

The invention provides an aircraft comprising a preferred tank.

The invention provides a method for manufacturing the tank for an aircraft according to any of the aforementioned embodiments, the method comprising:.

A method for manufacturing the tank wall liners of the fuel tank may comprise:.

The method for manufacturing the tank wall liners may comprise a step c) of laying a layer of fiber or textile material on the sealant layer cured in step b).

The method may also comprise a step d) of applying another layer of sealant on the fiber or textile layer and performing step b) on that layer.

Preferably, the steps b) to d) are repeated until a predetermined number of fiber or textile layers are embedded between sealant layers.

The tank wall liners allow for enhanced protection against fuel leakages. The tank wall liners (also called sealing patches) can be made of a sealant that is generally used in aviation. Typical examples are polysulfide or polythioether based sealants. In another embodiment the patches may also be made from fluoroelastomeric materials. The patches may be reinforced using textiles or fibers, e.g. glass fibers, polyester fibers or aramid fibers. The tank wall liners can be separately manufactured and subsequently installed on the inside of a corresponding tank. This also allows retrofitting of tanks that are already in service. The tank wall liners are preferably bonded to the tank wall with a self curing sealant, that may be of the same type or the same sealant that formes the patches. The tank wall liners are preferably made in rectangular (including square), circular or ellipsoidal shapes and can be cut during installtion to fit the specific location in the tank.

The tank wall liners preferably have a thickness of <NUM> to <NUM>, more preferably a thickness of <NUM> to <NUM>. The liner may have a length of <NUM> to <NUM>, more preferably a length of <NUM> to <NUM>. The liner may have a width of <NUM> to <NUM>, preferably of <NUM> to <NUM>.

The tank wall liners may be formed as plates or plate-like elements. The tank wall liners can also have one or more legs, when viewed in a cross-section. The legs may protrude perpendicularly from the main part to preferably form a U-shape. The main part and/or the one or more legs may include or exclude a reinforcement layer, as desired by the application.

Embodiments of the invention are described in more detail with reference to the accompanying schematic drawings that are listed below.

Referring to <FIG>, an aircraft <NUM> has a fuselage <NUM> and a pair of wings <NUM> attached to the fuselage <NUM>. The aircraft <NUM> also includes a plurality of engines <NUM> that are attached to the wings <NUM>. The fuselage <NUM> has an aft section <NUM> that includes horizontal and vertical tail plane and an additional fuel tank <NUM>. The additional fuel tank <NUM> includes jet fuel for the engines <NUM> and therefore allows a range extension compared to conventional airplanes.

<FIG> depicts the fuel tank <NUM> in more detail. In general, the fuel tank <NUM> is configured in the usual manner. The fuel tank <NUM> includes a tank wall <NUM>. The tank wall <NUM> encloses and thereby defines a tank volume for the jet fuel.

The tank wall <NUM> is on the one hand formed by a part of the fuselage <NUM> and additional wall portions <NUM>. The tank wall <NUM> comprises a plurality of ribs <NUM> and stringers <NUM> which support a skin <NUM>. The skin <NUM> is may be made of light weight metal or fiber reinforced composite materials.

The ribs <NUM> and stringers <NUM> define mostly rectangular zones in which the skin <NUM> is accessible from the inside of the fuel tank <NUM>. In addition, a man-hole portion <NUM> may be formed in the tank wall <NUM> to allow access for maintenance.

As depicted in <FIG>, a plurality of tank wall liners <NUM> are arranged so as to cover the skin <NUM>. The tank wall liners <NUM> are preferably arranged on a bottom portion <NUM> of the tank wall <NUM>. The bottom portion <NUM> roughly includes those sections of the tank wall <NUM> that face the ground and may be impacted by debris from or contact the runway during take-off. It should be noted that the tank wall liners <NUM> may also cover up to the entire inner surface of the tank wall <NUM>.

<FIG> depict different embodiments of the tank wall liner <NUM> in more detail from the top (left) and in a cross-section (right).

In <FIG>, the tank wall liner <NUM> comprises a liner body <NUM>. The liner body <NUM> has a roughly rectangular shape, that is preferably fitted to the grid defined by the ribs <NUM> and stringers <NUM>. The liner body <NUM> may also have a different shape, for example a shape that fits the man-hole portion <NUM> or other portions. The liner body <NUM> is roughly plate-like and has a thickness of a couple of mm.

The liner body <NUM> includes a mounting surface <NUM>. The mounting surface <NUM> is arranged so that it can face the tank wall <NUM> and be bonded thereto. In addition, the liner body <NUM> includes a plurality of sealing surfaces <NUM>.

The sealing surfaces <NUM> are arranged such that in an installed position they can face another sealing surface of another tank wall liner <NUM>. The sealing surfaces <NUM> are arranged on a circumferential portion of the tank wall liner <NUM>.

The liner body <NUM> may have a plurality of cut-outs <NUM> that can accommodate fasteners <NUM> of the tank wall <NUM>, i.e. of the ribs <NUM> and/or stringers <NUM>.

The liner body <NUM> is made of a liner material that consists entirely of a cured sealant <NUM>.

Subsequently, the further embodiments of the tank wall liner <NUM> are only described insofar as they differ from the previously described embodiment(s).

Referring to <FIG>, the liner body <NUM> includes a reinforcement layer <NUM> that is made of fiber or textile material. Preferably, the reinforcement layer <NUM> is made of glass or aramid fibers. Thus, the liner material in this embodiment is a fiber reinforced material. As depicted in <FIG>, the reinforcement layer <NUM> is entirely enclosed within the cured sealant. Preferably, the reinforcement layer is arranged in the upper third of the liner body <NUM> along the thickness direction. The distance from the sealing surface <NUM> to the reinforcement layer <NUM> is about <NUM> to <NUM>.

Referring to <FIG>, the liner body <NUM> is almost identical to the embodiment of <FIG>. However, here the distance from the sealing surface <NUM> to the reinforcement layer <NUM> is about <NUM> to <NUM>.

Referring to <FIG>, the liner body <NUM> is similar to the embodiment of <FIG>, but it could also be configured like the embodiments of <FIG>. This embodiment includes a plurality of through-holes <NUM> that are arranged such that they go through the sealant and the reinforcement layer <NUM>.

Referring to <FIG>, the liner body <NUM> is again similar to the previous embodiments, with the distinction that the reinforcement layer <NUM> protrudes from the sealing surface <NUM>. This embodiment may also be made with through-holes <NUM> similar to the previous embodiment of <FIG>.

Referring to <FIG>, the liner body <NUM> comprises a plurality of protrusions <NUM> that protrude from the inner surface <NUM>. The inner surface <NUM> is opposite the mounting surface <NUM>. When viewed in a cross-section the reinforcement layer <NUM> is embedded in the protrusions <NUM> and the main body <NUM>.

It should be noted that in other variants that are not explicitly depicted, the reinforcement layer <NUM> may be arranged in the center third or the bottom third of the main body <NUM>. Alternatively or additionally, there could be more than one reinforcement layer.

Subsequently, installation of the tank wall liners <NUM> is described in more detail. Initially, a wet self-curing sealant is applied to the self-curing tank wall <NUM> or rather the portions that should be lined, e.g. the bottom portion <NUM>. Then a tank wall liner <NUM> is arranged on the sealant, pressed on and left to cure. This process is repeated until the entire desired portion, such as the bottom portion <NUM>, is covered with the tank wall liners <NUM> and forms a lining surface without gaps for the jet fuel. Depending on the configuration of the tank wall liner <NUM>, the ribs <NUM> and/or stringers <NUM> may also be covered with sealant. It is also possible to form the protruding reinforcement layer <NUM> (<FIG>) around different structures within the tank volume and fix them with sealant.

The tank wall liners <NUM> may be manufactured in different ways. In one embodiment, a self-curing sealant is applied to a form that corresponds to the desired shape. After curing the tank wall liner <NUM> is ready. In another embodiment, a reinforcement layer is put on top of the cured sealant and another layer of sealant is applied. This can be repeated multiple times, until the desired configuration of the tank wall liner <NUM> is achieved.

Claim 1:
A fuel tank (<NUM>) for an aircraft (<NUM>), the fuel tank (<NUM>) comprising a tank wall (<NUM>) that encloses a tank volume for jet fuel, and a plurality of tank wall liners (<NUM>), wherein each tank wall liner (<NUM>) comprises a liner body (<NUM>) made of a liner material, the liner body (<NUM>) comprising a mounting surface (<NUM>) configured to be installed facing a tank wall (<NUM>) and at least one sealing surface (<NUM>) configured to be installed facing another tank wall liner (<NUM>), wherein the liner material includes a cured sealant (<NUM>) that is suitable for jet fuel, wherein the plurality of tank wall liners (<NUM>) are mounted to the tank wall (<NUM>) on the inside of the tank volume so as to form a lined tank wall portion that is configured to seal the tank wall (<NUM>) from the jet fuel, wherein the tank wall (<NUM>) comprises a frame structure and a skin (<NUM>) that is supported by the frame structure (<NUM>, <NUM>), characterized in that the tank wall liners (<NUM>) are mounted to the skin (<NUM>) between the frame structure (<NUM>,<NUM>).