Patent Description:
Different kinds of liners or patches are known from <CIT> and <CIT>. Another patch is known from earlier European patent application <CIT> which relates to a smart repair patch and forms prior art according to Art. <NUM> (<NUM>) EPC.

<CIT> discloses a fuel tank structure, in particular an encapsulating method. The fuel tank design realizes a seal by injecting sealant into an injection channel between an upper upper cover plate and a frame of the fuel tank.

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.

In addition there is a general need for protective linings of (aircraft) parts to protect against - among other things - corrosion, impact damage or fracture.

It is the object of the invention to provide measures that allow protection of aircraft parts against adverse effects or conditions.

The object is achieved by the subject-matter of the independent claims. Advantageous embodiments are subject-matter of the dependent claims.

A method for protectively lining a part, preferably an aircraft part, the method comprising:.

Preferably, step b) comprises casting the self-curing potting sealant compound by pouring it out of a container, preferably via a spout, and/or by injecting it through a nozzle into the mold. Preferably, the nozzle atomizes the self-curing potting sealant and/or the nozzle has a bell shape that is getting arranged to cover a portion of the mold and the self-curing potting sealant is injected into the portion defined by the bell shaped nozzle.

Preferably, the part comprises a structural part of an aircraft and/or a tank wall and in step a) the mold is being prepared such that the structural part and/or the tank wall form a bottom side of the mold.

Preferably, the part comprises a structural part of an aircraft and in step a) the mold is being prepared such that the structural part wholly or partly forms a circumferential wall of the mold.

Preferably, the self-curing potting sealant compound has a viscosity greater than <NUM> pascal seconds (Pa s) up to and including <NUM> Pa s, preferably up to and including <NUM> Pa s, more preferably up to and including <NUM> Pa s.

Step b) comprises casting of a self-curing potting sealant compound that includes fibers or fiber material pieces. Alternatively or additionally, a fiber ply is being placed into the mold as a reinforcement layer, wherein the fiber ply is placed on the part or on top of uncured sealant.

Preferably, self-curing potting sealant compound is poured a second time into the mold, preferably on uncured sealant or a reinforcement layer.

The invention provides a protectively lined aircraft part obtainable by a preferred method. Preferably, the part is a tank wall for a fuel tank of an aircraft that encloses a tank volume for fuel.

The invention provides a fuel tank for an aircraft, the fuel tank comprising a tank wall obtainable by a preferred method or a preferred protectively lined aircraft part.

The invention provides an aircraft comprising a preferred protectively lined aircraft part or a preferred fuel tank.

The invention provides a self-curing potting sealant compound having a viscosity of greater than <NUM> pascal seconds (Pa s) up to and including <NUM> Pa s, preferably up to and including <NUM> Pa s, more preferably up to and including <NUM> Pa s. The invention provides a use of a preferred self-curing potting sealant compound in a method for manufacturing any of a preferred protectively lined aircraft part, a preferred fuel tank or an aircraft.

Currently sealants are applied via brush, roller, cartridges, spatula or Jurblami bells (special nozzles for cartridges that make a defined blob of sealant onto fasteners). The viscosity is around <NUM> pascal seconds (Pa s). This can be measured using a spindle viscometer. The sealant used herein is chosen such that it is castable. A suitable fluid-viscosity is preferably below <NUM> Pa s. It is also possible to add fibers (glass, aramid, polyester, etc.) to improve the mechanical performance of the final sealant.

The sealant compound can be quickly applied without adaption to a specific geometry and without rework (such as preformed linings). Fibers can be added after the potting process but before the sealant has cured or the tack free time has been reached. It is also possible to integrate fiber plies within the structure in the form of fiber-cut-outs/seals/etc. This can be done before, when the sealant is still liquid or even after curing of the sealant. It is also possible to manufacture multiple layers of plies in this manner. The fibers can be glass, aramid, polyester or other compounds (e.g. seals => fluorocarbon based).

The sealant potting compound is liquid enough to be able to flow within a specific predetermined area. In the context of aircraft this is preferably an area between two ribs/frames and stringers. The sealant can be applied on the inside and/or the outside of the aircraft, e.g. the fuel tank. The sealant potting compound can protect against impacts/defects and finally avoid leakages (fluid or gas). It also allows surface protection.

The invention provides a tank wall liner for a tank, preferably of an aircraft, the tank having a tank wall that encloses a tank volume, wherein the 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.

For fuel tanks a goal is to improve the failsafe capabilities of fuel tanks, preferably for aircraft. a tank wall liner for a tank, preferably of an aircraft.

One idea relates to a tank lined with a tank wall liner and an aircraft equipped with those apparatus. Another idea relates to manufacturing methods for the tank and the tank wall liner.

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, preferably for an aircraft, the tank comprising a tank wall that encloses a tank volume for fuel, preferably jet fuel, wherein a plurality of preferred 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.

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

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 a tank for an aircraft, the method comprising:.

The invention provides a method for manufacturing a tank wall liner, the method comprising:.

Preferably, the method comprises a step c) of laying a layer of fiber or textile material on the sealant layer cured in step b).

Preferably, the method comprises 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 forms the patches. The tank wall liners are preferably made in rectangular (including square), circular or ellipsoidal shapes and can be cut during installation 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.

In order to improve failsafe capabilities of fuel tanks (<NUM>), preferably for aircraft (<NUM>), and in particular with respect to mitigating the risk of fuel leakage even in case of mechanical damage to the tank, a tank wall liner (<NUM>) is proposed. The tank wall liner (<NUM>) comprises a liner body (<NUM>) made of a liner material. The liner material is a sealant or composite of sealant and fiber/textile materials. Multiple tank wall liners (<NUM>) are installed on the tank wall (<NUM>) and form a lining surface that seals the fuel in the tank (<NUM>) from the tank skin (<NUM>).

It should be noted that while the invention is described with respect to lining of a tank wall this serves only as an example. The ideas and measures disclosed herein are also applicable to different parts of an aircraft. 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 ribs <NUM>, the stringers <NUM> and the skin <NUM> are examples of structural parts. 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> may also be arranged so as to cover the ribs <NUM> and/or stringers <NUM> (not depicted). 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 installation 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.

Referring back to <FIG>, the tank wall <NUM>, the ribs <NUM> and stringers <NUM> collectively define a mold. Specifically the bottom portion <NUM> is arranged at the bottom side of the mold, whereas the ribs <NUM> and stringers <NUM> form a circumferential wall of the mold. In case the circumferential wall has any openings, they can be plugged with an appropriate piece of sealant or other member to prevent potting sealant compound from leaving the mold.

Subsequently, instead of placing tank wall liners <NUM>, a self-curing potting sealant compound is poured into the mold. The uncured sealant settles and can be self-levelling. It is also possible to use an appropriate tool to level the uncured sealant. In addition the sealant may include fibers or pieces of fiber materials. This method is particularly useful in such areas, where a large number of fasteners would require a complicated geometry of the tank wall liner <NUM>.

In a variant, a fiber ply is placed on the bottom portion <NUM>. The fiber ply is shaped to match the shape of the mold. Subsequently potting sealant compound is poured in the mold and before the sealant is fully cured another fiber ply may be placed on the almost cured sealant. Again potting sealant compound is poured into the mold. This process can be repeated several times until the desired height within the mold is reached.

With the above described methods the tank wall liner <NUM> is basically manufactured in-situ. The thickness of the tank wall liner <NUM> is preferably <NUM> to <NUM>. In a variant, seal caps can be put on fasteners <NUM> or sealant can be injected using a shaped nozzle to cover the fasteners <NUM> with sealant. Subsequently, the self-curing potting sealant compound is cast onto the covered fasteners <NUM>. It should be noted that the in-situ casting method of the tank wall liner <NUM> may be combined with the method of preparing different patches that are then introduced into the mold.

For example, referring to <FIG> a part of the self-curing main body <NUM> can be cast. The protrusions <NUM> are prepared separately as cured patches that are joined together by the reinforcement layer <NUM>. The protrusions <NUM> are introduced into the mold and the reinforcement layer <NUM> is laid on top of the cast sealant compound. Now the remaining potting sealant compound is cast onto the reinforcement layer <NUM> to form the remainder of the main body <NUM>, and the protrusions <NUM> are laid into the uncured sealant to be cured together with the main body <NUM>.

Claim 1:
A method for protectively lining a part, the method comprising:
a) preparing a mold that is defined on at least a bottom side by the part;
b) casting a self-curing potting sealant compound into the mold; and
c) levelling the sealant or letting the sealant self-level and letting the sealant cure in the mold,
characterized in that
d) step b) comprises casting of a self-curing potting sealant compound that includes fibers or fiber material pieces; and/or
e) a fiber ply is being placed into the mold as a reinforcement layer (<NUM>).