Patent Description:
Aircraft nacelle structures for turbine engines typically include acoustic panels which include, for example, a back skin and a perforated top skin with a core material sandwiched there between. In some cases, the acoustic panel may be formed during manufacturing with an undesirable void between the top skin and the core, or the top skin may delaminate from the core material while in service, or the top skin may otherwise be damaged. Existing repair techniques involve removing and then replacing a portion of the top skin with a patch which overlaps the existing top skin. Perforations may be formed on the patch, but the perforations do not line up between the patch and the existing top skin in the overlap area, such that the acoustic properties of the acoustic panel are diminished in the overlap area.

<CIT> discloses a method according to the preamble of claim <NUM>.

A method of repairing an acoustic panel for an aircraft may comprise coupling a fiberglass ply to the acoustic panel; creating dimples in the fiberglass ply using a differential pressure, wherein the dimples are located within first perforations in the acoustic panel; coupling the fiberglass ply to a replacement patch; and drilling second perforations in the replacement patch.

In various embodiments, a perforated maskant may be coupled to the replacement patch. Third perforations may be blasted in the replacement patch. The dimples may be sanded off the fiberglass ply. The second perforations may be drilled at locations of the dimples. The second perforations may be aligned with the first perforations. The replacement patch may be bonded to the acoustic panel. The replacement patch may comprise a core portion, a ramp portion, and an overlap portion. Third perforations may be blasted in the core portion, and wherein the second perforations are drilled in the ramp portion and the overlap portion.

A method of repairing an acoustic panel may comprise removing a damaged section of the acoustic panel; laying up a plurality of composite plies into a replacement patch on a bond tool; coupling a maskant to the replacement patch; blasting first perforations in a core portion of the replacement patch; placing a fiberglass ply on the acoustic panel; creating dimples in the fiberglass ply corresponding to second perforations in a top skin of the acoustic panel; transferring the fiberglass ply to the replacement patch; sanding off the dimples; drilling third perforations in a ramp section of the replacement patch; and coupling the replacement patch to the acoustic panel.

In various embodiments, the acoustic panel and the fiberglass ply may be placed in a bag, and a vacuum may be created within the bag. The dimples may be created using a pressure differential. Fourth perforations may be drilled in an overlap portion of the replacement patch. The third perforations may be aligned with the second perforations. The replacement patch may comprise a core portion, a ramp portion, and an overlap portion.

The method of repairing an acoustic panel according to the invention comprises removing a damaged portion of a perforated skin on the acoustic panel; forming a patch to fit in place of the damaged portion, wherein the patch comprises an overlap area with the perforated skin; perforating the patch to match a perforation pattern on the perforated skin; aligning the patch on the acoustic panel such that first perforations in the patch are aligned with second perforations in the perforated skin; and bonding the patch to the acoustic panel.

A fiberglass ply is coupled to the acoustic panel. Dimples in the fiberglass ply are created using a differential pressure, wherein the dimples are located within the second perforations. The fiberglass ply may be coupled to the patch. The dimples may be sanded.

The detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical, chemical and mechanical changes may be made without departing from the scope of the inventions. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented.

Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option.

Referring to <FIG>, a nacelle <NUM> for a gas turbine engine is illustrated according to various embodiments. Nacelle <NUM> may comprise an inlet <NUM>, a fan cowl <NUM>, and a thrust reverser <NUM>. Nacelle <NUM> may be coupled to a pylon <NUM>, which may mount the nacelle <NUM> to an aircraft wing or aircraft body. Thrust reverser <NUM> may comprise an inner fixed structure ("IFS") <NUM>, an outer fixed structure ("OFS"), and a translating sleeve <NUM>. Bypass air from an engine fan may flow in a generally annular bypass air duct defined between the IFS <NUM> and the translating sleeve <NUM>. Portions of the inner fixed structure <NUM>, the translating sleeve <NUM>, and the inlet <NUM> may be commonly formed using acoustic panels.

Referring to <FIG>, an acoustic panel <NUM> is illustrated according to various embodiments. The acoustic panel <NUM> may comprise perforations <NUM>, and could be used to form portions of a nacelle for an aircraft engine, as described above. The acoustic panel <NUM> may comprise a core <NUM>, positioned between a first skin <NUM> and a second skin <NUM>. The core <NUM> may have walls extending generally in a normal direction from the first skin to the second skin that form a plurality of cells <NUM>. The cells <NUM> may be hexagonal in shape and are then commonly referred to as honeycomb core. In various embodiments, however, the cells <NUM> could have any of a number of different geometries. Core walls could be made from various metals such as titanium or aluminum, or composites, or hardened paper or other plastics, according to the particular application and material properties. Adjacent core walls may be bonded to each other with glue or may be welded, or other methods may be used to join core walls together to form the cellular structure. The first skin <NUM>, core <NUM>, and second skin <NUM> combine to form closed cells that may become resonator chambers when one of the skins is perforated and work to attenuate acoustic waves, such as noise from an aircraft engine, in a known fashion. The first and second skins <NUM>, <NUM> may be formed of laminar plies of fiber reinforcement joined together with a matrix. The fibers may be carbon, glass, aramid or other known types. The matrix may be thermoset polymers such as epoxies, thermoplastics, and other known materials. The acoustic panel <NUM> is formed by joining together the first skin <NUM>, second skin <NUM>, and core <NUM>, which may be done with adhesive, co-curing, mechanical fastening, or through other means. In the case of an adhesively bonded acoustic panel, the edges of the core walls adjacent to each skin are bonded thereto to form a rigid, high strength structure.

In various embodiments, a portion of the first skin <NUM> may not be fully attached to the core <NUM> during manufacture of the acoustic panel <NUM>, or the portion may delaminate from the core <NUM>, resulting in a void, or the first skin <NUM> may become damaged during operation. It may be desirable to repair the first skin <NUM> by replacing a portion of the first skin <NUM> with a patch.

Referring to <FIG>, a schematic cross-section view of an acoustic panel <NUM> with a damaged portion of a perforated top skin <NUM> removed is illustrated according to various embodiments. The damaged portion may be cut with a continuously sloped ramp portion <NUM> between the top of the top skin <NUM> and the core section <NUM> where the top skin <NUM> is completely removed. However, in various embodiments, the damaged portion may be cut with a stepped profile. In various embodiments, the acoustic panel <NUM> may be curved in two or three dimensions. The curved shape may make it difficult to align perforations <NUM> between the remaining top skin and a replacement patch.

Referring to <FIG>, a schematic cross-section view of a replacement patch <NUM> is illustrated according to various embodiments. The replacement patch <NUM> may comprise a plurality of composite plies. The plies may be laid up on a bond tool which matches the shape of the component which is being repaired. The replacement patch <NUM> may comprise a core portion <NUM> which is configured to be placed directly over the core of an acoustic panel where the original top skin is completely removed. The replacement patch <NUM> may comprise a ramp portion <NUM> which is configured to be placed where the original top skin is partially removed. The replacement patch <NUM> may comprise an overlap portion <NUM> which is configured to be placed over the original top skin.

Referring to <FIG>, a maskant <NUM> may be coupled to the replacement patch <NUM>. The maskant <NUM> may be a polymeric material. The maskant <NUM> may comprise a plurality of apertures <NUM> matching a perforation pattern of an acoustic panel. A tape <NUM> may be coupled to the replacement patch <NUM> or the maskant <NUM> over the ramp portion <NUM> and the overlap portion <NUM>.

Referring to <FIG>, perforations <NUM> may be created in the core portion <NUM> with a blasting process. An abrasive material may be blasted at the replacement patch <NUM>. In various embodiments, the abrasive material may comprise aluminum oxide, silicon carbide, or any other suitable abrasive material. The maskant <NUM> and the tape <NUM> may prevent the abrasive material from removing material from the replacement patch <NUM>, other than through the apertures <NUM> in the maskant <NUM>. The blasting may create the perforations <NUM> in the core portion <NUM>.

Referring to <FIG>, an uncured fiberglass ply <NUM> may be coupled to the acoustic panel <NUM>. In various embodiments, a single ply may be used. However, in various embodiments, a plurality of plies may be used.

Referring to <FIG>, the acoustic panel <NUM> and the fiberglass ply <NUM> may be vacuum bagged, and a pressure differential may force the fiberglass ply <NUM> to droop into the perforations <NUM> in the ramp portion <NUM> and the overlap portion <NUM>, creating dimples <NUM> within the perforations <NUM>.

Referring to <FIG>, the fiberglass ply <NUM> may be removed from the acoustic panel and coupled to the replacement patch <NUM>. The dimples <NUM> corresponding to the perforations in the acoustic panel may remain present as raised bubbles relative to the flat portions of the fiberglass ply <NUM>.

Referring to <FIG>, the fiberglass ply <NUM> may be sanded. The sanding may remove the dimples <NUM> from the fiberglass ply <NUM>. The fiberglass ply <NUM> may be left with apertures <NUM> where the dimples were formerly located which correspond to the perforations in the acoustic panel. Thus, the fiberglass ply <NUM> may provide a perforation template matching the acoustic panel.

Referring to <FIG>, perforations <NUM>, <NUM> may be drilled in the ramp section <NUM> and the overlap section <NUM> of the replacement patch. The perforations <NUM>, <NUM> may be drilled through the apertures <NUM> in the fiberglass ply <NUM>. Thus, the perforations <NUM>, <NUM> may match the perforation pattern of the acoustic panel. In various embodiments, the perforations <NUM>, <NUM> may be laser drilled or drilled with a mechanical drill.

Referring to <FIG>, a repaired acoustic panel <NUM> is illustrated according to various embodiments. The replacement patch <NUM> may be bonded to the acoustic panel <NUM>. The perforations <NUM>, <NUM> in the ramp section <NUM> and the overlap section <NUM> of the replacement patch <NUM> may align with the perforations <NUM> in the acoustic panel <NUM>. One or more pins may be inserted through the perforations <NUM>, <NUM>, <NUM> to keep the replacement patch <NUM> in place during curing. An adhesive may be placed on the replacement patch <NUM> and/or the acoustic panel <NUM> between the replacement patch <NUM> and the acoustic panel <NUM>. The acoustic panel <NUM> with the replacement patch <NUM> may be cured in an autoclave. The repaired acoustic panel <NUM> may then be ready for operational use.

Referring to <FIG>, a flowchart <NUM> of a process for repairing an acoustic panel is illustrated according to various embodiments. Damage may be detected in an acoustic panel. The damaged section may be removed from the acoustic panel (step <NUM>). A replacement patch may be laid up using a bond tool matching the shape of the acoustic panel (step <NUM>). A perforated maskant may be coupled to the replacement patch (step <NUM>). Perforations may be blasted in the replacement patch (step <NUM>). The perforations may match the perforations in the maskant. A fiberglass ply may be coupled to the acoustic panel (step <NUM>). The acoustic panel may be enclosed in a vacuum bag, such that the fiberglass ply droops into perforations in the acoustic panel, forming dimples in the fiberglass ply (step <NUM>). The fiberglass ply may be removed from the acoustic panel and coupled to the replacement patch (step <NUM>). The dimples in the fiberglass ply may be sanded off (step <NUM>). Perforations may be drilled in the ramp section and overlap section of the replacement patch according to the pattern of the fiberglass ply (step <NUM>). The replacement patch may be aligned with the acoustic panel and bonded to the acoustic panel (step <NUM>).

Claim 1:
A method of repairing an acoustic panel comprising:
removing a damaged portion of a perforated skin on an acoustic panel (<NUM>);
forming a patch (<NUM>) to fit in place of the damaged portion, wherein the patch (<NUM>) comprises an overlap area with the perforated skin;
perforating the patch (<NUM>) to match a perforation pattern on the perforated skin;
aligning the patch (<NUM>) on the acoustic panel (<NUM>) such that first perforations (<NUM>) in the patch (<NUM>) are aligned with second perforations (<NUM>) in the perforated skin; and
bonding the patch (<NUM>) to the acoustic panel (<NUM>); characterized in that the method further comprises:
coupling a fiberglass ply (<NUM>) to the acoustic panel (<NUM>); and
creating dimples (<NUM>) in the fiberglass ply (<NUM>) using a differential pressure, wherein the dimples (<NUM>) are located within the second perforations (<NUM>).