GB2468484A

GB2468484A - An acoustic attenuation member for an aircraft

Info

Publication number: GB2468484A
Application number: GB0903999A
Authority: GB
Inventors: Julian Rishton; Ian Taylor
Original assignee: Aircelle Ltd
Current assignee: Safran Nacelles Ltd
Priority date: 2009-03-09
Filing date: 2009-03-09
Publication date: 2010-09-15
Also published as: WO2010103302A1; GB201115385D0; GB0903999D0; GB2480208A; EP2406786A1; CN102349101A; CA2754782A1

Abstract

An aircraft acoustic attenuation member comprises a cone fairing 10 having an inner thermal layer 24, an injection moulded cellular structure having an inwardly facing wall 28 and square cells 30, and an outer perforated skin 32. The cellular structure may include circular, rectangular or hexagonal cells 40, 42, 43 and the cross-sectional area of at least one cell may be different from that of at least one other cell.

Description

AIRCRAFT ACOUSTIC ATTENTUATION

The present invention relates to an aircraft acoustic attenuation member, an aircraft acoustic attenuation assembly, an aircraft engine core fairing and a method of forming an aircraft attenuation member.

Noise emitting from aircraft is a problem. The noise is at a peak during take off when engines are at full thrust. To alleviate the noise, core fairings are located around the engine with sound attenuation material being included.

An inner thermal and fire protection layer surrounds the engine. A middle layer surrounds the inner layer. The middle layer is formed by welding adjacent faces of metallic, such as aluminium, or paper based sheets at spaced locations. These locations subsequently form the contacting faces of the honeycomb. The moulded aluminium sheet is then pulled to expand to form the honeycomb.

The edges of the inner surface of the honeycomb are adhered to an inner layer. The edges of the outer layer are adhered to a 4-ply perforated outer layer.

The fabrication of the honeycomb and the attachment of the honeycomb to adjacent layers is a complicated and time consuming method. In addition, only the narrow edges of the honeycomb, equivalent to the thickness of the aluminium sheets, are available for bonding to adjacent layers. Accordingly, the bond is not as strong as would be desirable.

In addition, supports for the engine that come from the fan case have to pass through the honeycomb layer. Further, bolts have to pass through the layer. The honeycomb is extremely weak in the direction between the walls that form the honeycomb. Thus when the walls are disturbed by the supports and bolts, foaming adhesive is used to fill relevant cells of the honeycomb. Alternate strengthening method may also be used. The use of the resin is time consuming as the resin is not an easy material to work with. Furthermore, there is an associated weight penalty because cells are filled that are not needed to be filled to ensure that sufficient strength is present in the required areas and to ensure that parts passing at an angle through the layer have adequate support from the cells that they pass through.

Another problem with the aluminium honeycomb is that only a single depth is afforded and there are locations where greater depths are required for optimum sound attenuation.

It is an object of the present invention to attempt to overcome at least one of the above or other problems.

The present invention can be carried into practice in various ways but one embodiment will now be described by way of example and with reference to the accompanying drawing in which: Figure 1 is a perspective view of a core fairing; Figure 2 is a section of part of the core fairing in a direction around the fairing; Figure 3 is a plan view of the cellular structure alone used with the fairing; Figure 4 is a plan view of a cellular structure that has yet to be curved; Figure 5 is a side cross sectional view of a cellular structure affording an opening for a support for the engines to run through; Figure 6 is a view showing a fastener extending through the fairing; and Figure 7 is a view showing an attachment at the forward edge of the fairing.

As shown in Figure 1, the core fairing 10 is made up of six or more separate sections 12, 14, 16, 18, 20 and 22. Each segment has sound attenuation. Each segment is connected to adjacent segments or is able to move relative to an adjacent segment. There may be three fairings, for instance, located along the length of the engine.

As shown in Figures 2 and 3 the fairing section is formed with the conventional inner thermal protector and fire barrier 24, a middle layer 26 comprising an injection moulded cellular structure that includes an inwardly facing wall 28 with square cells 30 extending outwardly from the wall 28, and a conventional perforated outer skin 32.

The inner layer 24 may be attached to the wall 28 of the middle layer by mechanical fixings or by bonding. The outer layer may be attached to the free ends of the walls defining the cells by mechanical fixings or bonding.

In use, sound from the engine is partly absorbed with the cells 30.

The middle layer is able to be injection moulded from plastics such as PEEK, PBI (polybenzimdazole) or other injection moulded material as the thermal barrier inner layer shields the middle layer from most of the heat such that the maximum temperature that the middle layer will experience is 180°C.

In Figures 1 and 2 the thickness of the walls at the cells 30 is 1mm and the distance between opposed walls of the cells is 18mm. The height of the cells is 50mm. However, it will be appreciated that any of these dimensions can be varied.

Furthermore, it is possible for the wall 28 to be formed on the outer wall with the open ends of the cells facing inwardly. In this alternative embodiment the inner walls of the cells may be attached to the barrier layer 24. Further, the wall 28 may be formed with perforations in which case the skin 32 may not be required.

Whilst the middle layer 26 has been described as having a wall 28 in any of the embodiments referred to herein, it is possible that the wall may extend over part of the extent of the layer or that the wall 28 may be omitted.

Most of the fairing does not experience significant loads. However, in some instances it is necessary to apply loads to the fairing. Figure 3 shows the junction of four of the walls that define the cells herein formed with an opening 34. The walls extending from that opening are thickened over part of their extent as indicated by arrow 36 to provide reinforcement. In addition the inner wall 28 is thickened as shown by arrow 38. Accordingly, a fastener such as a bolt can be passed through the opening 34 and the inner and outer walls with the middle layer being designed to provide the optimum support. As the middle layer is injection moulded there is no need to modify a uniformly formed honeycomb layer by adding resin and then drilling through the resin, for instance in order to accommodate a bolt.

In Figures 2 and 3 the cells are shown as being of square cross section. However, the cells may have any cross section. For instance, as shown in Figure 4 the cells may be circular cells 40, rectangular cells 42, hexagonal cells 43, or there may be a combination of any such formed cells. In this way the sound absorption features of the middle layer may be optimised.

In any of the embodiments described the moulding may be a substantially planar moulding which may subsequently be made into a curved member or an arc. Alternatively the moulding may be in the form of a curve or arc.

Figure 5 is a cross section of the middle layer where a pipe has to cross the middle layer at an angle. The layer can be formed with a channel 44 with the walls of the channel being thicker than the walls of the cells. Again with the moulded inner layer there is no need to fabricate such a channel from the conventional honeycomb structure such as by filling a certain number of cells with the foamed glue, waiting for the glue to dry and then drilling the channel.

Although not shown herein, whilst the depth of the middle section is shown as constant it is possible for the depth to vary. For instance, some cells may have a greater depth than others. The depth change may be a step change. Alternatively, the change may be in the form of a straight line or a curved line in the direction of depth change.

Figure 6 shows a bracket 46 that is attached to the fairing. The fairing has a hollow insert 48 pushed through with a flange 50 at the insert bearing against one side and with a threaded washer 52 holding the insert in place. A bolt 54 extends through the insert and the bracket 46 with a nut 56 holding the bracket in place. The walls 58 of the middle layer may be thicker in the region of the insert.

Figure 7 shows a bracket 60 being fastened to a spigot 62 towards the end of the fairing 66. The spigot is connected to the forwards end by being rotated to cooperate with a nut 64 on the inner side of a wall 67. It is possible that the wall 67 or the wall and the nut could be moulded with the middle section. Again no fabrication will be required to provide the means to attach the spigot.

Whilst the present invention has been described as being a noise attenuator it will be appreciated that the honeycomb type structure will also act as a strengthener.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS: 1. An aircraft acoustic attenuation member comprising a plurality of cells characterised in that the cells are moulded and are integrally formed.
2. A member as claimed in claim 1 in which each cell includes at least one opening.
3. A member as claimed in claim 1 or 2 in which the member includes an integrally formed connecting member extending across adjacent cells.
4. A member as claimed in claim 3 in which the connecting member is located at an end region of adjacent cells.
5. A member as claimed in claim 3 or 4 in which the connecting member completely covers adjacent cells.
6. A member as claimed in claim 5 in which the connecting member comprises a sheet.
7. A member as claimed in claim 6 in which the sheet includes perforations.
8. A member as claimed in claim 6 or 7 in which the sheet, in use, is curved to face outwardly with respect to the acoustic source.
9. A member as claimed in claim 6 or 7 in which the sheet is arranged, in use, to face inwardly with respect to an acoustic source.
10. A member as claimed in any preceding claim in which the attenuation member is flexible.
11. A member as claimed in any preceding claim in which the attenuation member is formed as a flat member.
12. A member as claimed in any preceding claim in which the flat member is arranged, in use, to be bent.
13. A member as claimed in any preceding claim in which the cross sectional area of at least one cell is different from at least one other cell.
14. A member as claimed in any preceding claim in which the shape of one cell is different from the shape of at least one other cell.
15. A member as claimed in any preceding claim in which the depth of at least one cell is different from the depth of at least on adjacent cell.
16. A member as claimed in claim 15 in which the depth changes is a step change.
17. A member as claimed in claim 15 or 16 in which the depth change is a linear change whereby the height of the cell walls in the direction of change increased at a constant rate.
18. A member as claimed in claims 15 to 17 in which the depth change is a non-linear change whereby the height of the cell walls in the direction of change alters at a varying rate.
19. A member as claimed in any preceding claim in which the attenuation member includes a through-channel extending from one side to the other at an inclined angle with respect to the general extent of the attenuation member.
20. A member as claimed in claim 19 in which the thickness of the at least part of the wall that defines the channel is greater than the thickness of the wall that defines a cell.
21. A member as claimed in any preceding claim in which the thickness of a cell wall is less than 5mm or less than 3mm or more than 0.2mm or more than 0.5mm and is preferably between 0.75mm and 1.5mm.
22. A member as claimed in any preceding claim in which the depth of a cell is preferably less than 100mm or less than 80mm or more than 20mm or more than 30mm and is preferably between 40mm and 60mm.
23. A member as claimed in any preceding claim in which the cross sectional area of a cell is preferably less than 1000mm2 or less than 750mm2 or less than 500mm2 or more than 100mm2 or more than 200mm2 and is preferably between 300mm2 and 350mm2.
24. A member as claimed in any preceding claim in which the ratio of the depth of the cell to the cross sectional area of a cell is preferably less than 1:50 or less than 1:40 or less than 1:30 or more than 1:5 or more than 1:10 and is preferably between 1:15 and 1:25.
25. A member as claimed in any preceding claim in which the member includes an integrally formed attachment means whereby, in use, the attenuation member can be attached to another part.
26. A member as claimed in claim 25 in which the attachment means extends from one side to the other.
27. A member as claimed in claim 26 in which the attachment means comprises a hole extending through the junction of at least two cells.
28. A member as claimed in claim 27 in which the walls of the cells are of increased thickness in the region of the hole.
29. A member as claimed in claim 27 or 28 in which the sheet is of increased thickness in the region of the hole.
30. A member as claimed in claims 25 to 29 in which the attachment means is located on an end of the member.
31. A member as claimed in claim 30 in which the attachment means includes a plate having an opening.
32. An aircraft acoustic attenuation assembly including an aircraft attenuation member as claimed in any preceding claim having a heat shield located between what, in use, will be the acoustic source and the attenuation member.
33. An aircraft engine cone fairing including a plurality of assemblies as claimed in claim 32.
34. A method of forming an aircraft attenuation member having a plurality of cells characterised in that the cells are integrally formed by moulding.
35. A method as claimed in claim 33 in which the cells are integrally formed by injection moulding.
36. A method as claimed in claim 33 or 34 in which the member is flexed into a curve after injection moulding.
37. A method as claimed in any of claIms 33 to 35 when the member is as claImed in anyof claIms I to 31.