Integrally damped composite aircraft floor panels

A sound-damping panel. The sound-damping panel includes a first face sheet. The sound-damping panel also includes a core connected to the first face sheet. The core has a honeycomb structure. Walls of the honeycomb structure are embedded with a viscoelastic material configured to dampen sound in a pre-selected frequency range. The sound-damping panel also includes a second face sheet connected to the core, the second face sheet opposite the first face sheet relative to the core.

BACKGROUND INFORMATION

The present disclosure relates to devices and methods for reducing noise inside vehicles, such as aircraft, and more particularly relate to integrally damped composite aircraft floor panels.

Current floor panels in aircraft have damping tiles attached to the underside of the panel. These damping tiles lower sound levels in the cabin of the aircraft. Similar panels may be used in other vehicles, such as automobiles, and may even be used in buildings in order to reduce noise inside a room or to prevent noise from leaving a room.

However, particularly in aircraft, weight is a serious consideration. Fuel can be one of the major operating expenses of operating an aircraft, and the heavier the plane is, the more fuel is used during operation. Therefore, techniques for reducing the weight of aircraft are usually desirable.

SUMMARY

The illustrative embodiments provide for a sound-damping panel. The sound-damping panel includes a first face sheet. The sound-damping panel also includes a core connected to the first face sheet. The core has a honeycomb structure. Walls of the honeycomb structure are embedded with a viscoelastic material configured to dampen sound in a pre-selected frequency range. The sound-damping panel also includes a second face sheet connected to the core, the second face sheet opposite the first face sheet relative to the core.

The illustrative embodiments also include a method of forming a sound-damping panel. The method includes fabricating a honeycomb core. The method also includes coating the honeycomb core with a viscoelastic fluid configured to dampen sound in a pre-selected frequency range. The method also includes thereafter curing the honeycomb core. The method also includes thereafter laying up a first face sheet on a first side of the honeycomb core and laying up a second face sheet on a second side of the honeycomb core, opposite the first side. In this manner, the sound-damping panel is formed.

The illustrative embodiments also include a method of forming a sound-damping panel. The method includes fabricating a honeycomb core. The method also includes pressing an elastomeric film into the honeycomb core. The elastomeric film is a material configured to dampen sound in a pre-selected frequency range. The method also includes thereafter curing the honeycomb core. The method also includes thereafter laying up a first face sheet on a first side of the honeycomb core and laying up a second face sheet on a second side of the honeycomb core, opposite the first side. In this manner, the sound-damping panel is formed.

DETAILED DESCRIPTION

The illustrative embodiments recognize and take into account that existing sound-damping panels include face sheets sandwiching a honeycomb core, plus one or more additional layers of sound-damping material. The illustrative embodiments also recognize and take into account that existing sound-damping panels are undesirably heavy and add excessive recurring cost for aircraft applications. For example, for typical floor panels in commercial aircraft, just the sound-damping layer or layers of the panels may weight a hundred pounds or more to an aircraft. The illustrative embodiments recognize and take into account that this extra weight significantly reduces fuel efficiency of the aircraft, thereby leading to higher costs of operating the aircraft. Recurring costs for the sound-damping material and installation costs degrade the aircraft profitability.

The illustrative embodiments address these and other issues by eliminating or greatly reducing the need for additional sound-damping layers in aircraft panels. In particular, the illustrative embodiments provide for integrating damping within the honeycomb structure of a penal. By avoiding or reducing additional sound-damping layers, the illustrative embodiments can both substantially reduce the weight of the aircraft, as well as maintain the same or better sound-damping properties of the aircraft panel.

The illustrative embodiments accomplish this advantage by placing a viscoelastic material inside the honeycomb, without sacrificing structural strength. This structure may be achieved through a liquid coating, embedding an elastomeric material, or some other fabrication technique.

The illustrative embodiments avoid use of a polypropylene core. Such a core material is sub-optimal structurally and would not be used in the aircraft floor, and possibly other portions of the aircraft.

The illustrative embodiments also do not rely on the face sheets for sound-damping, thereby further allowing different materials to be selected for the face sheets while still maintaining the desired acoustic properties of the panel. In turn, this advantage reduces aircraft weight, and accordingly, reduces both fuel and money required to operate the aircraft.

Thus, the illustrative embodiments provide for an apparatus that achieves acoustic damping in a crew cabin via honeycomb flooring panels integrated into the crew cabin which include embedded dampers consisting of liquid coating, foaming of an elastomeric, or some other fabrication technique. Said flooring does not use a polypropylene core, and does not rely on a face sheet for acoustic damping.

The panels of the illustrative embodiments are not limited to aircraft panels. The illustrative embodiments contemplate use of the panels described herein in any vehicle, including but not limited to automobiles, trucks, ships, tanks, helicopters. The illustrative embodiments also contemplate use of the panels described herein in buildings or rooms within buildings for sound proofing.

Attention is now turned to additional details regarding the design of sound-damping panels, especially those for use in aircraft. A common method for reducing noise from passenger floors into the aircraft cabin is through structural damping. The prior art damping designs are based on the principles described in D. Ross, E. E. Ungar, and E. M. Kerwin, Jr., in Structural Damping, The American Society of Mechanical Engineers, 1959. Essentially, a layer of material is added to a panel which is pre-selected to reduce acoustic frequencies in a pre-determined range.

The goal for vibration of the base panel is to induce strain energy into the viscoelastic material layer, which dissipates the vibration energy into heat. Lower vibration in the panel leads to lower noise radiated into the cabin. For a free-layer damper, the strain energy is introduced through extension of the viscoelastic. For a constrained layer damper, the strain energy is introduced through shear forces.

For aerospace applications, weight is important to the overall design. A constrained layer damper (CLD) is typically five times more weight efficient than the free-layer damper, so the use of CLD is much more common in aerospace applications.

Even with a weight-optimized design, there can be upwards of a hundred pounds of floor damping added to the airplane. Driving weight out of the detailed part design adds to the material cost. The CLD tends to be an expensive, highly engineered sandwich material with multiple constituent materials. Driving out weight also pushes the envelope on the robustness and durability of the parts, leading to more frequent inconsistencies and rework maintenance. Additionally, the reduced robustness also tends to dictate more, smaller parts for ease of installation, which results in higher labor cost.

One unique aspect of the illustrative embodiments is to drive the performance of the damping treatment into the build of the panel. This technique eliminates the issue of additional maintenance, automates the installation of noise control material, and utilizes an overall simpler design with lower material costs. This advantage would be true whether the viscoelastic material is integrated into the core or the face sheet of the sandwich panel. Nevertheless, the illustrative embodiments contemplate targeting mid-range acoustic frequencies to high-range acoustic frequencies (400 Hz-10,000 Hz). The illustrative embodiments also recognize and take into account that the strain energy in the sandwich structure transitions more and more to core as frequency increases. Thus, the illustrative embodiments contemplate incorporating the sound-damping material in the core itself. However, in other illustrative embodiments, the techniques described herein could be applied to one or more face sheets, or one or more additional layers for a given panel.

The improved sound-damping effects of the panels described herein have other benefits. For example, the improved performance of the panels described herein allow for reduction in noise control treatment in other areas of the aircraft cabin, such as acoustic blankets in the sidewall or damping treatment on the primary fuselage of the aircraft.

FIG. 1illustrates an aircraft, in accordance with an illustrative embodiment. Aircraft100is an example of an aircraft in which the sound-damping panels of the illustrative embodiments may be installed.

In this illustrative example, aircraft100has wing102and wing104attached to body106. Aircraft100includes engine108attached to wing102and engine110attached to wing104. Aircraft100could be any other aircraft, such as a prop aircraft, a helicopter, or some other moveable platform such as an automobile, a boat, or even a building.

A portion of body106is cut away to show a portion of the interior of aircraft100. As can be seen, the floor of the interior cabin is formed from floor panels, such as floor panel120. Floor panel120is a sound-damping panel, such as those described with respect toFIG. 2throughFIG. 7.

Note that while floor panel120is a sound-damping panel as described herein, not all floor panels need be of the sound-damping variety described herein. Likewise, panels other than those present in the floor may have the sound-damping structure described elsewhere herein. Further, some or all of body106of aircraft and aircraft interiors may be formed from a honeycomb structure having the sound-damping structure described elsewhere herein. Yet further, the sound-damping structures described herein may also apply to other types of vehicles or to buildings. Thus, the illustrative embodiments are not necessarily limited to floorboards within aircraft.

FIG. 2illustrates a honeycomb core of a sound-damping panel, in accordance with an illustrative embodiment. Honeycomb core200may be part of a sound-damping panel, such as floor panel120ofFIG. 1.

As can be seen inFIG. 2, honeycomb core200is composed of interconnected walls, such as walls forming cell202, which form a hexagonal pattern between which are defined interstices, such as interstice204. Note that the size and period of the interstices may vary. In some illustrative embodiments, differently sized hexagons may be present in the same honeycomb core. The illustrative embodiments are not limited to hexagonal shapes. The shape of the cells may be rectangular, diamond, circular, or any other suitable shape.

In an illustrative embodiment, suitable materials for forming honeycomb core200may be metal (such as but not limited to aluminum) or fiber reinforced composite—typically an aramid (such as but not limited to Kevlar or Nomex) fiber in a resin matrix. These honeycomb structures can be used in other types of aircraft structures, such as but not limited to crew bunk modules, partitions, wing-to-body fairing panels, ceiling panels, and others.

FIG. 3illustrates an apparatus for performing coating by dipping a honeycomb core, in accordance with an illustrative embodiment. Apparatus300is an example of an apparatus that may be used to modify a honeycomb core, such as honeycomb core200ofFIG. 2to serve as an integrally damped composite aircraft floor panel, such as floor panel120ofFIG. 1, or any other suitable sound-damping panel as described elsewhere herein.

Apparatus300includes vat302which contains elastomeric fluid or viscoelastic fluid. Apparatus300also includes arm304which may be operated robotically using a power supply and a controller, or which may be operated manually. Arm304holds workpiece306, which may be a honeycomb structure such as those described above. Whether automated or manually controlled, arm304dips workpiece306into vat302, thereby immersing workpiece306into the elastomeric fluid. In this manner, workpiece306is coated.

The elastomeric fluid composition may be varied, though the material is selected for properties which will reduce pre-determined frequency ranges of acoustic energy. Some examples include thermoplastic polyurethanes or polyalkenes.

Still other variations are possible. Therefore, the illustrative embodiments described with respect toFIG. 3do not necessarily limit the other illustrative embodiments described herein.

FIG. 4illustrates an apparatus for pressing an elastomeric film into a honeycomb core, in accordance with an illustrative embodiment. Apparatus400is an example of an apparatus that may be used to modify a honeycomb core, such as honeycomb core200ofFIG. 2to serve as an integrally damped composite aircraft floor panel, such as floor panel120ofFIG. 1, or any other suitable sound-damping panel as described elsewhere herein.

Apparatus400includes pressure plate402which is actuated either by robotic arm404, a hydraulic press, by manual operation, or by some other machine. When actuated, pressure plate402presses viscoelastic film406into honeycomb structure408. Thus, material of viscoelastic film406, shown for example at area410, is pressed into the interstices of honeycomb structure408.

The elastomeric film composition may be varied, though the material is selected for properties which will reduce pre-determined frequency ranges of acoustic energy. Some examples include natural or synthetic rubbers and cured thermoplastic polyurethanes.

Still other variations are possible. Therefore, the illustrative embodiments described with respect toFIG. 4do not necessarily limit the other illustrative embodiments described herein.

FIG. 5illustrates a close-up perspective of certain cells of the honeycomb core shown inFIG. 4, in accordance with an illustrative embodiment. Honeycomb structure500is a close-up perspective of honeycomb structure408ofFIG. 4, particularly where the elastomeric film406has been pressed into the interstices of honeycomb structure500. Walls502of honeycomb structure500are pointed out for reference.

The interstices between walls are filled with the material of elastomeric film406ofFIG. 4. However, additional processing may be performed at this point. Additional curing, which may be either at elevated temperature or at room temperature, may be applied to honeycomb structure500.

Still other variations are possible. Therefore, the illustrative embodiments described with respect toFIG. 5do not necessarily limit the other illustrative embodiments described herein.

FIG. 6illustrates a sound-damping panel, in accordance with an illustrative embodiment. Sound-damping panel600is a variation of apparatus400shown inFIG. 4, or the other sound-damping panels described herein.

Sound-damping panel600includes first face sheet602. Sound-damping panel600also includes core604connected to first face sheet602. Core604has a honeycomb structure. Walls606of the honeycomb structure are embedded with a viscoelastic material configured to dampen sound in a pre-selected frequency range. Sound-damping panel600also includes second face sheet608connected to core604. Second face sheet608is disposed opposite of first face sheet602relative to core604.

The illustrative embodiments described with respect toFIG. 6may be varied. For example, sound-damping panel600may be a floor board for installation in an aircraft. In another illustrative embodiment, walls606of the honeycomb structure may be coated with the viscoelastic material. However, in a different illustrative embodiment, walls606of the honeycomb structure may be infused with the viscoelastic material.

In yet another illustrative embodiment, only the first face sheet, the core, and the second face sheet are present in the sound-damping panel. In this manner, a sound-damping layer in the sound-damping panel is avoided. Thus, the illustrative embodiments may produce the desired sound-damping effects without the added weight of additional sound-damping layers. The total weight savings may be between about 20% to 50% reduction in weight per panel. The total cost savings may be between about 40% to 60% per panel. Accordingly, the illustrative embodiments provide for a significant advance over the known art and significant fuel and cost savings to operating an aircraft.

In still another illustrative embodiment, core604is free of polypropylene. In yet another illustrative embodiment, first face sheet602and second face sheet608may be free of the viscoelastic material. Thus, again, the illustrative embodiments may produce the desired sound-damping effects without the added weight of additional sound-damping layers. Accordingly, the illustrative embodiments provide for a significant advance over the known art and significant fuel and cost savings to operating an aircraft.

Still other variations are possible. Therefore, the illustrative embodiments described with respect toFIG. 6do not necessarily limit the other illustrative embodiments described herein.

FIG. 7illustrates a method of forming a sound-damping panel, in accordance with an illustrative embodiment. Method700may be a variation of the methods described elsewhere herein, such as the forming technique described with respect toFIG. 3throughFIG. 4. Operations shown with dashed boxes are optional.

Method700includes fabricating a honeycomb core (operation702). The term “fabricating” contemplates both actively fabricating or making the honeycomb structure, as well as simply providing the honeycomb structure. Method700also includes coating the honeycomb core with a viscoelastic fluid configured to dampen sound in a pre-selected frequency range, wherein a viscoelastic coating is formed (operation704). This coating may be a structural resin which effectively mimics a constrained damping layer. A structural resin would be applied after the viscoelastic fluid is cured. Then the resin would mimic a constrained damping layer. Otherwise, as is described elsewhere herein, the coating is unconstrained.

Method700also includes thereafter curing the viscoelastic coating (operation706). Method700also includes thereafter laying up a first face sheet on a first side of the honeycomb core and laying up a second face sheet on a second side of the honeycomb core, opposite the first side, whereby the sound-damping panel is formed (operation710). In one illustrative embodiment, the method may terminate thereafter.

Method700may be varied. For example, coating at operation704may include using a coating technique comprising translating the honeycomb core through a flow of the viscoelastic fluid. In another example, coating at operation704may include coating comprising dipping the honeycomb core in the viscoelastic fluid.

Method700may also have additional operations. For example, optionally, method700also includes, prior to curing the honeycomb core, blowing air through cells of the honeycomb structure to clear interstices of the cells of the viscoelastic fluid (operation706). In a variation, curing at operation708comprises curing at room temperature. Curing could also be performed at an elevated temperature.

Still other variations are possible. For example, method700also may include, after curing but prior to laying up the first face sheet, preparing a surface of the honeycomb core (operation710). In another example, method700also includes, after laying up the first face sheet and the second face sheet, performing a second curing process on the sound-damping panel (operation714).

Method700may also be exclusive. Thus, for example, after performing only fabricating, coating, curing, and laying up the first face sheet and the second face sheet, formation of the sound-damping panel is complete. In this manner, no additional layers are added to the sound-damping panel. The resulting sound-damping panel weighs less than conventional sound-damping panels, which do require additional layers of damping material.

Still other variations are possible. Therefore, the illustrative embodiments described with respect toFIG. 7do not necessarily limit the other illustrative embodiments described herein.

FIG. 8illustrates a method of forming a sound-damping panel, in accordance with an illustrative embodiment. Method800may be a variation of the methods described elsewhere herein, such as the forming technique described with respect toFIG. 3throughFIG. 4, as well asFIG. 7. Operations shown with dashed boxes are optional.

Method800includes fabricating a honeycomb core (operation802). The term “fabricating” contemplates both actively fabricating or making the honeycomb structure, as well as simply providing the honeycomb structure. Method800also includes pressing an elastomeric film into the honeycomb core, the elastomeric film comprising a material configured to dampen sound in a pre-selected frequency range (operation804). Method800also includes thereafter curing the elastomeric film (operation806). Method800also includes thereafter laying up a first face sheet on a first side of the honeycomb core and laying up a second face sheet on a second side of the honeycomb core, opposite the first side, whereby the sound-damping panel is formed (operation810). In one illustrative embodiment, the method may terminate thereafter.

Method800may be varied. For example, method800also may include performing a second cure process after laying up the first face sheet and the second face sheet (operation812). In yet another example, method800also may include, after curing but prior to laying up the first face sheet, preparing a surface of the honeycomb core (operation808). Again, preparing may include sanding, etching, cutting, or other methods of preparing a surface for further processing.

In another illustrative embodiment, after performing only fabricating, pressing, curing, and laying up the first face sheet and the second face sheet, formation of the sound-damping panel is complete. In this manner, no additional layers are added to the sound-damping panel. The resulting sound-damping panel weighs less than conventional sound-damping panels, which do require additional layers of damping material.

Still other variations are possible. Therefore, the illustrative embodiments described with respect toFIG. 8do not necessarily limit the other illustrative embodiments described herein.

Illustrative embodiments of the disclosure may be described in the context of aircraft manufacturing and service method900as shown inFIG. 9and aircraft1000as shown inFIG. 10. However, the illustrative embodiments described herein are applicable to any machine or vehicle that uses an exhaust system or exhaust pipe, including but not limited to automobiles and generators. The techniques described herein may be used to manufacture aircraft1000using aircraft manufacturing and service method900. The techniques described with respect toFIG. 9andFIG. 10may take advantage of the inspections systems, devices, and methods described with respect toFIG. 1throughFIG. 8.

Turning first toFIG. 9, an illustration of an aircraft manufacturing and service method is depicted in accordance with an illustrative embodiment. During pre-production, aircraft manufacturing and service method900may include specification and design902of aircraft1000inFIG. 10and material procurement904.

During production, component and subassembly manufacturing906and system integration908of aircraft1000inFIG. 10takes place. Thereafter, aircraft1000inFIG. 10may go through certification and delivery910in order to be placed in service912. While in service912by a customer, aircraft1000inFIG. 10is scheduled for routine maintenance and service914, which may include modification, reconfiguration, refurbishment, and other maintenance or service.

With reference now toFIG. 10, an illustration of an aircraft is depicted in which an illustrative embodiment may be implemented. In this example, aircraft1000is produced by aircraft manufacturing and service method900inFIG. 9and may include airframe1002with plurality of systems1004and interior1006. Examples of systems1004include one or more of propulsion system1008, electrical system1010, hydraulic system1012, and environmental system1014. Any number of other systems may be included. Although an aerospace example is shown, different illustrative embodiments may be applied to other industries, such as the automotive industry.

Apparatuses and methods embodied herein may be employed during at least one of the stages of aircraft manufacturing and service method900inFIG. 9.

In one illustrative example, components or subassemblies produced in component and subassembly manufacturing906inFIG. 9may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft1000is in service912inFIG. 9. As yet another example, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during production stages, such as component and subassembly manufacturing906and system integration908inFIG. 9. One or more apparatus embodiments, method embodiments, or a combination thereof may be utilized while aircraft1000is in service912and/or during maintenance and service914inFIG. 9. The use of a number of the different illustrative embodiments may substantially expedite the assembly of and/or reduce the cost of aircraft1000.

The illustrative embodiments described herein with respect toFIG. 2throughFIG. 8use examples where one coating is applied to the honeycomb structure. However, the illustrative embodiments also contemplate multiple coating and cure cycles to increase the thickness of the elastomeric sound-damping material included in the honeycomb structure. The illustrative embodiments contemplate still other variations, such as that described with respect toFIG. 11.

FIG. 11is an illustration of a portion of a sound-damping panel, in accordance with an illustrative embodiment. Sound-damping panel1100may be a variation of the panels described with respect toFIG. 2throughFIG. 6.

Sound-damping panel1100is a honeycomb structure including one or more face sheets and a honeycomb core. Sound-damping panel1100includes core cell wall1102and face sheet1104. A second face sheet, opposite of face sheet1104, may be present, but is not shown inFIG. 11. Elastomeric coating1106is disposed on core cell wall1102. However, elastomeric coating1106does not extend on or past resin fillet1108.

Resin fillet1108is a portion of resin that is used to secure face sheet1104to core cell wall1102. Resin fillet1108extends on both sides of core cell wall1102, as shown inFIG. 11. By preventing elastomeric coating1106from impinging on resin fillet1108, the mechanical and structural performance of sound-damping panel1100can be maintained to a degree greater than if elastomeric coating1106had impinged on resin fillet1108. Compromising the fillet integrity with the elastomer could degrade performance of the panel or undesirable over-deign of the face sheets and/or core.