WO2009112697A2

WO2009112697A2 - Method for drilling an acoustic part of an aircraft nacelle

Info

Publication number: WO2009112697A2
Application number: PCT/FR2009/000097
Authority: WO
Inventors: Benoît Barbe
Original assignee: Aircelle
Priority date: 2008-02-08
Filing date: 2009-01-28
Publication date: 2009-09-17
Also published as: FR2927271A1; WO2009112697A3; FR2927271B1

Abstract

The invention relates to a method for drilling an acoustic part of an aircraft nacelle (1) that comprises the following steps: A- selecting a utility surface of the acoustic part, wherein said utility surface is to be drilled; B- selecting a drilling means for drilling the utility surface; C- generating a movement pattern corresponding to the movement of the drilling means along two substantially coplanar and perpendicular directions; D- generating a drilling matrix by substantially perpendicularly projecting the movement pattern onto the utility surface; E- repeating step D on substantially the entire utility surface, thus defining a drilling frame; F- drilling the utility surface using the drilling means (30) following the drilling frame.

Description

Method of drilling an acoustic part of a nacelle of an aircraft

The invention particularly relates to a method of piercing an acoustic part of a nacelle of an aircraft. An aircraft is propelled by one or more propulsion units each comprising a turbojet engine housed in a tubular nacelle. Each propulsion unit is attached to the aircraft by a mast generally located under a wing or at the fuselage.

A nacelle generally has a structure comprising an air inlet upstream of the engine, a median section intended to surround a fan of the turbojet engine, a downstream section housing thrust reverser means and intended to surround the combustion chamber of the turbojet engine. The nacelle is furthermore generally terminated by an ejection nozzle whose outlet is situated downstream of the turbojet engine. Aircraft turbojets generate significant noise pollution. As a result, there is a strong demand to reduce this pollution, all the more so as the turbojets used become more and more powerful. The design of a nacelle surrounding a turbojet contributes to a large extent to the reduction of this noise pollution. To further improve the acoustic performance of aircraft, nacelles are equipped with acoustic panels to reduce the noise generated by the turbojet engine and vibration structures.

Acoustic panels are well known structures for absorbing these noises. These panels usually comprise one or more layers of honeycomb core structures (commonly called "honeycomb" structure). These layers are generally coated on their underside, that is to say not in contact with the air flow inside the nacelle, of a skin impermeable to air, called "full skin", and on their upper face, that is to say in contact with the air flow inside the nacelle, a skin permeable to air, called "acoustic skin" which has the particularity of to be perforated.

In the patent application FR 2,643,004, there is provided an acoustic skin piercing method in which the piercing tool is a plate having a plurality of piercing heads. The plate is positioned on the surface area of the acoustic panel before drilling this area. Namely, the operator positions the piercing tool on the area to be pierced so as to obtain the density of holes on the desired surface. In order for the piercing of the acoustic panel to be efficient, it is necessary for the piercing heads to pierce the surface substantially perpendicular to the zone to be pierced. Drilling areas with a high degree of curvature involves careful adjustment of the positioning of the plate.

The disadvantage of such a type of acoustic piercing is the duration too long, greater than two weeks, that requires the positioning and drilling phases. An object of the present invention is to optimize the acoustic piercing method in order to reduce the piercing time.

For this purpose, according to a first aspect, the subject of the invention is a method of drilling an acoustic part of a nacelle of an aircraft, comprising the steps in which:

A-select a useful surface of the acoustic piece, said useful surface being intended to be pierced;

B-selecting drilling means for piercing the useful surface; C is a displacement pattern corresponding to the displacement of the piercing means in two directions substantially coplanar and perpendicular;

D- a drilling die is produced by projecting the displacement pattern on the useful surface substantially perpendicularly; E-step D is repeated over substantially the entire useful area forming a piercing pattern;

F-pierce the useful surface through the piercing means following the piercing pattern.

The term "movement pattern" is understood here to mean a pattern, preferably immaterial, comprising a set of points in which the piercing means pierce an area of the acoustic surface along two substantially coplanar and substantially perpendicular directions. The displacement pattern thus obtained is therefore substantially plane.

However, the useful surface to be pierced generally comprises more or less curved parts. The piercing means must pierce the useful surface on both sides substantially perpendicularly if not the drilling would not allow to obtain holes substantially perpendicular to the useful surface. The acoustic panel thus obtained would not absorb the noise effectively.

By "substantially perpendicular" is meant here that the element for piercing the acoustic surface pierces the acoustic surface at an angle of between 80 ° and 100 °, or between 85 ° and 95 °. The angle is measured relative to the local tangent of the area to be pierced and the perpendicular to said tangent.

Therefore, the displacement pattern is projected substantially perpendicularly on the useful surface. As a result, the resulting drilling die comprises a set of points in which the drilling means concretely penetrate the useful surface, in particular the curved portions having a strong curvature.

In order to carry out the drilling on the whole of the useful surface, the drilling pattern is carried out which comprises all the points of the useful surface intended to be concretely drilled when drilling the acoustic piece.

Thus, the drilling method has a time advantage over those of the prior art insofar as it determines in advance the optimal positioning of holes according to the desired hole density, for example. In particular, the step of positioning the displacement patterns on the useful surface is performed according to the portions of the useful surface having a radius of curvature more or less important. It is no longer necessary to seek optimal positioning manually as is the case in the prior art.

Thus, for example, the piercing time is decreased to less than 2 days, or even 12 hours.

Moreover, thanks to the method of the invention, it is possible to optimize the density of holes on the useful surface according to the desired effect. Thus, it is possible in particular to obtain the maximum number of holes for good acoustic attenuation of the acoustic panel while maintaining mechanical rigidity. Thus, it is possible to choose the number of holes and to distribute the holes so as to achieve an acceptable acoustic loss. In addition, the method of the invention makes it easier to manage the change of drilling means when necessary. or when the piercing means are too worn to pierce properly.

In another aspect, it is also possible to determine the displacement pattern and thus the drilling pattern so as to meet the kinematic constraints related to the drilling means. In fact, the method of the invention makes it possible to minimize the trajectory of the piercing means and thus to reduce the duration of the piercing of the acoustic piece by taking into account the bulk and the limited rotational and axial displacement of the piercing means. In addition, the method according to the invention makes it possible to respect the dimensional constraints of the acoustic piece and to choose the drilling means most suitable for drilling.

According to other features of the invention, the structure of the invention comprises one or more of the following optional features considered alone or according to all the possible combinations:

step E comprises the steps in which: E1. a limit curve defining the useful surface to be pierced is determined; E2. determining a starting curve substantially corresponding to the intersection of the useful surface and a plane containing the main axis of the acoustic piece;

E3. the guidelines of the matrices are determined by substantially aligning the center of the various piercing matrices along the starting curve, substantially joining said matrix to one another along said starting curve, and substantially intersecting the useful surface and the cross-section. transverse to the main axis of the acoustic piece passing through the center of the drilling dies; E4. the center of the various matrices is aligned substantially on each guide line of the matrices up to the limit curve of the useful surface, so that the distance between the adjacent ends of two consecutive drilling matrices is substantially equal to a predetermined distance;

E5. the piercing pattern is determined by partially deactivating the piercing matrices lying outside the limit curve, thereby providing an optimum piercing pattern while reducing the time required to obtain the piercing pattern; - The drilling pattern is determined by performing a first half-drilling pattern according to step E4 between the starting curve and the limit curve, the second peening half-frame being the symmetrical frame of the first half-drilling frame. relative to the starting curve, which makes it possible not to make the weft frame on the whole of the useful surface and thus to save drilling time;

the predetermined distance is less than approximately 10 ^'7 m, which makes it possible to obtain a desired optimal hole density on the useful surface;

the displacement pattern is produced by moving the piercing means by a first step along the length of said piercing means and by a second step along the width of said piercing means, which makes it possible to produce movement patterns according to repeated and simple geometric figures which simplifies the implementation of the invention;

the first and second steps are substantially equal, which simplifies the implementation of step C;

- The drilling means comprise plates amounting between 1 and 21 piercing heads, which allows to drill the useful surface, including the curved areas in an optimal time;

the piercing means comprise plates having a different number of piercing heads, which makes it possible to adapt to the profile of the useful surface, in particular that of the curved zones;

the piercing heads are spaced apart by a number substantially equal to a multiple of the first step or the second pitch, which makes it possible to obtain a regular piercing; step E5 comprises a step where at least one piercing head is broken.

According to a second aspect, the invention relates to a computer program product comprising one or more instruction sequences accessible to a central unit and, when a sequence is executed by the central unit, the central unit performing at at least one of steps A to F of the process of the invention.

The method of the invention is therefore advantageously automatable executable by means of the computer program product of the invention, which makes it possible to shorten the drilling time. According to a preferred embodiment, the central unit performs all the steps of the method of the invention which makes it possible to automate all the steps and to significantly reduce the piercing time. Furthermore, it is also possible to control the execution of one or more steps of the method of the invention.

According to another aspect, the invention also relates to a digital medium comprising one or more sequences of instructions of the computer program product according to the invention and readable by a central unit. Thus, it is possible to separate the drilling development phases by implementing steps A to E of the method of the invention and to proceed with the execution of the drilling step F either at a convenient time or at a location different from the place of implementation of Steps A to E.

According to yet another aspect, the subject of the invention is a nacelle for a turbojet engine of an aircraft that can be obtained according to the method of the invention.

The invention will be better understood on reading the nonlimiting description which follows, with reference to the appended figures.

- Figure 1 is a schematic representation in longitudinal section of a first embodiment of a nacelle according to the invention; FIG. 2 is a cross-section of an embodiment of an acoustic piece used in the method of the invention;

FIG. 3 is a partial schematic view of the embodiment of FIG. 2; FIG. 4 is a partial schematic view of an embodiment of a piercing means used in the method of the invention;

Figure 5 is a partial schematic representation of a piercing means employed in the method of the present invention; FIG. 6 is a partial schematic representation of a variant of FIG. 5;

FIG. 7 is a schematic representation of an embodiment of a displacement pattern employed in the method of the invention;

FIG. 8 is a schematic representation of an embodiment of a piercing matrix employed in the method of the invention;

FIGS. 9 to 13 show an embodiment of step E of the method of the invention.

According to the embodiment shown in FIG. 1, a nacelle 1 according to the invention comprises an upstream air inlet structure 2, a median structure 3 surrounding a fan 4 of a turbojet engine 5, and a downstream structure. The downstream structure comprises, in a manner known per se, an external structure 6, called OFS, housing thrust reverser means 7, and an internal structure 9, called IFS. The nacelle 1 according to the invention is attached downstream via any appropriate means, including connecting rods, to a suspension mast, not shown, for the attachment of the nacelle 1 under an aircraft wing. The outer structure 6 and the inner structure 9 also define an annular flow channel 8.

The internal structure 9 is intended to cover a downstream portion 11 of the turbojet engine extending downstream of the fan.

Parts of the nacelle 1 of the invention need to be arranged to reduce the noise generated by the turbojet engine 5. For this, said parts comprise one or more acoustic panels. According to an embodiment of acoustic panel shown in Figure 2, the acoustic panel 20 has several layers. The layer 22 is composed of a skin intended to be mounted on the nacelle on the side of the air flow present in the annular flow channel 8. This skin is perforated with a multitude of holes 24 of small diameters, typically included between 1, 7 and 1, 9 mm. The holes are spaced so that the ratio of the perforated surface to the total area comprising the holes allows the desired noise to be absorbed (see FIG. 3). On this hood is a second layer 26 generally consisting of a honeycomb core structure, typically made of a light alloy, such as aluminum.

On this second layer is a third layer 28, namely a non-perforated solid skin intended to close the absorbent cellular cells of the second layer 26.

These three layers 22, 26 and 28 are in particular fixed to each other by gluing.

The perforated and solid skins can be made either of light metal alloy of aluminum type or of a material based on fibers (carbon, glass, boron or aramid).

The method of the invention is applied to a skin intended to be used in the layer 22 in order to produce series of perforations.

The method of the invention comprises the steps in which: A- a useful surface of the acoustic piece is selected, said useful surface being intended to be pierced;

B-selecting drilling means for piercing the useful surface;

C is a displacement pattern corresponding to the displacement of the piercing means in two directions substantially coplanar and perpendicular;

D- a drilling die is produced by projecting the displacement pattern on the useful surface substantially perpendicularly;

E-step D is repeated over substantially the entire useful area forming a piercing pattern;

The method of the invention advantageously makes it possible to determine the location of the holes where the piercing means pierce, before drilling the useful surface. Thus, it is possible to adjust the hole density to the desired density or maximum acceptable acoustic loss.

Typically, an acoustic part has a number of holes of between 300,000 and 700,000 holes, or even about 500,000 holes. Thus, before drilling, it is possible to modify or correct the drilling frame if the latter does not correspond to the constraints imposed.

More particularly, step A of the method of the invention comprises the selection of a useful surface of the acoustic piece, said useful surface being intended to be pierced.

By "useful surface" is meant here a surface intended to be pierced and thus to provide an acoustic role in the nacelle. Such a surface is different from the surfaces intended to be solid which allow for example to ensure good mechanical strength or to receive fixing means.

In general, the acoustic loss is equal to about 2%.

Step B of the method of the invention comprises the selection of piercing means for piercing the useful surface.

The piercing means are, for example, plates comprising piercing heads, a nozzle for jet of water, an abrasive jet or a laser or any other suitable means known to those skilled in the art.

According to one embodiment, the piercing means are not all of the same nature. That is, said piercing means may for example comprise plates mounting piercing heads as well as a nozzle for water jet and / or a laser.

According to a preferred embodiment shown in FIG. 4, the piercing means 30 comprise plates 32 that mount 9 piercing heads. A piercing head is constituted, for example, of a spindle or drill bit. Nevertheless, in general, the plates can mount at least 3 drilling heads, preferably between 1 and 21 drilling heads, in particular between 9 and 21 drilling heads.

The plates 32 may be substantially flat or have a radius of curvature to adapt to the profile of the more or less curved areas of the useful surface. Indeed, it is important that the piercing means 30 pierce the useful surface substantially perpendicular to the latter so that the resulting acoustic panel can satisfactorily absorb the noise generated by the turbojet engine.

As shown in FIGS. 5 and 6, a piercing zone 37 may be sufficiently convex so that a portion of said zone 37 is not pierced by the piercing heads 35 and 36 located at the ends of the plate 32. In these cases, the piercing plate 32 must be chosen so as to completely and not partially pierce the useful surface.

Likewise, a piercing zone 38 may be concave enough so that part of said zone 38 is not pierced at an angle sufficiently close to 90 ° by the piercing heads 35 and 36 located at the ends of the plate 32. in this case, the noise is not trapped correctly over the entire surface of the acoustic piece when the nacelle comprising the part thus pierced is used in an aircraft in operation. In the two cases presented above, when the zone to be drilled has a greater curvature than those of the neighboring zones, it is possible to reduce the number of piercing heads by breaking the number of suitable heads and / or by selecting a plate having the right number of piercing heads. According to a preferred embodiment, the piercing means comprise plates having a different number of piercing heads.

The plates 32 may have any geometric shape known to those skilled in the art that is adapted to perform the drilling. By way of non-limiting example, there may be mentioned a rectangular, square, trapezoidal or diamond shape.

Step C of the method of the invention comprises the production of a displacement pattern 40 corresponding to the displacement of the piercing means 30 in a first direction 42 and a second direction 44 which are substantially coplanar and perpendicular (see FIG. 7). Interestingly, the displacement pattern 40 indicates the points at which the piercing means must drill on a substantially planar surface. According to a preferred embodiment, the displacement pattern 40 is produced by moving the piercing means 30 by a first step 46 along the first direction 42 and by a second step 48 along the second direction 44. Preferably, the first direction 42 is substantially parallel to the length 50 of said piercing means and the second direction 44 is substantially parallel to the width 52 of the piercing means.

Thus, the elementary displacement of the piercing means 30 corresponding to the displacement along the first 46 and second 48 steps may represent any geometric shape known to those skilled in the art. Interestingly but not limitatively, the geometric shape shown is a rhombus, square or rectangle.

The length of the first 46 and second 48 steps typically depend on the shape of the acoustic piece, including the useful surface to drill.

According to a preferred embodiment, the first 46 and second 48 steps are equal, which simplifies the implementation of step C of the method of the invention.

In the case where the piercing means 30 comprise plates 32 mounting piercing heads 34 as represented in FIG. 4, the displacement pattern 40 is divided into as many zones 54 as the plate 32 has piercing heads 34. Thus, in the particular case where the plate 32 has 9 drilling heads 34, the displacement pattern 40 is divided into 9 zones 54. In the case where the plate 32 comprises 9 drilling heads 34, each drilling head 34 can perform About 100 points per zone 54. In particular, each head 34 performs about 10 first steps 46 and 10 second step 48.

In general, a piercing head 34 performs in particular between 30 and 200 points per zone 54, or even between 50 and 100 points per zone 54.

The center 56 of each zone corresponds to the position of the piercing head 34 at rest without effecting elementary displacement.

According to a preferred embodiment, the centers 56 are spaced apart by a number substantially equal to a multiple of the first step 46 or the second step 48.

Step D of the method of the invention comprises producing a drilling die by projecting the displacement pattern on the useful surface substantially perpendicularly.

The term "substantially perpendicular" projection is here understood to mean the projection of the displacement pattern 40 substantially plane over the useful surface in a direction substantially perpendicular to the tangent 61 of said useful surface. In particular, the tangent 61 generally corresponds to that of the tangent passing through the center 62 of the central zone of the displacement pattern 40 (see FIG. 8). The angle α between the axis of the projection 63 and the tangent 61 is in particular between 80 ° and 100 °, or even between 85 ° and 95 °. The ends 64 and 66 of the displacement pattern are projected substantially perpendicular to the useful surface at the ends 68 and 70.

As a result, the piercing die 60 substantially matches the profile of the area of the usable surface on which the movement pattern 40 is projected. The drilling die 60 comprises more or less curved parts so that it is necessary to determine the locations on the profile of said parts which are intended to be physically pierced by the piercing means 30. Generally, in the case where the drilling means comprise plates 32 mounting drill heads 34, the size and the shape of the drilling plate 32, in particular the number of drilling heads 34, are chosen so that the projection of the ends 64 and 66 remains substantially perpendicular. Thus, the drilling of the surface at the ends 68 and 70 is substantially perpendicular which ensures the achievement of effective holes in the acoustic absorption.

Step E of the process of the invention comprises repeating step D over substantially the entire useful area by forming a piercing pattern. According to a preferred embodiment represented in FIGS. 9 to 13, step E comprises the following steps E1 to E5.

In step E1, a limit curve 80 defining the useful surface 82 to be pierced is determined. The limit curve 80 corresponds to a curve beyond which the surface is not intended to be pierced because the acoustic part in this zone does not fulfill an acoustic absorption function.

In step E2, a starting curve 84 is determined, corresponding substantially to the intersection of the useful surface 82 and a plane 86 containing the main axis 88 of the acoustic piece. This starting curve can be positioned so as to be substantially a symmetry axis for the limit curve 80 or an axis separating a substantially equivalent number of drilling dies 60.

In step E3, the guidelines 90 of the dies are determined by substantially aligning the center 92 of the different drilling dies 60 along the starting curve 84, by substantially sealing said dies 60 with each other along said initial curve. 84, and intersecting substantially the effective area 82 and the cross section to the main axis 88 of the acoustic piece through the center 92 of the drilling dies.

According to one embodiment, the centers 92 of the drilling dies are aligned by positioning the center 62 of the displacement patterns 40 on the useful surface 82.

In general, a first piercing die 60 is positioned on the starting curve 84 and a second piercing matrix 60 is positioned on said curve 84. Namely, the centers 92 of the piercing matrices 60 are aligned by positioning the center 62. displacement patterns 40 on the working surface 82 at the starting curve 84. Thus, having placed the first drilling die 60 on the starting curve 84, the center 62 is positioned of another movement pattern 40 substantially on the starting curve 84 so that the piercing matrix 60 resulting from the perpendicular projection of this pattern 40, as exposed in step C, ensures a spacing between the ends of the two piercing matrices 60 less than 10 ^"7 m. It should be noted that the spacing between two consecutive drilling matrices depends on the curvature of the effective area of the surface 82 is performed suriaquelle projection substantially perpendicula In fact, the greater the curvature of the zone, the greater the distance between the two matrices.

Thus, the drilling dies 60 substantially centered on the starting curve 84 are also substantially joined.

In step E4, the center 92 of the different matrices is aligned substantially on each guideline 90 up to the limit curve 80 of the useful surface, so that the distance d between the adjacent ends of two consecutive drilling matrices is substantially equal to a predetermined distance.

According to an embodiment shown in FIG. 11, the centers 92 of the drilling dies are aligned by positioning the center 104 of the central zone of the displacement patterns 106 on the useful surface 82. Thus, having placed the first drilling die 107 on a guideline 90, the center 110 of the central zone of another displacement pattern 108 is positioned substantially on this guideline 90 so that the piercing matrix 109 resulting from the perpendicular projection of this pattern 108, as exposed during step C, ensures a distance d between the two ends 112 and 114 less than the predetermined distance. As long as the distance d is not less than this predetermined distance, positioning of the center 110 of the displacement pattern 108 is continued.

Preferably, the predetermined distance is less than about ^{10 -7} m. Such a value of the predetermined distance makes it possible to obtain the desired optimum hole density while maintaining good mechanical rigidity.

According to a preferred embodiment that is not shown, the drilling pattern is determined by performing a first half-drilling pattern according to step E4 between the starting curve 84 and the limiting curve 80, the second half-drilling frame being the symmetrical weft of the first half-weft of drilling relative to the starting curve 84. Thus, it is not necessary to make the drilling pattern on the entire useful surface 82 which reduces the time required for the formation of the drilling frame. According to one embodiment, the positioning of the piercing matrices 60 on a guideline 90 is stopped when the desired number of piercing matrices 60 is reached, when the last piercing matrix 60 placed intersects the limit curve 80 or when it It is no longer possible to place other piercing matrices 60 on the guideline 90. In step E5, the piercing frame 120 is determined by partially deactivating the piercing matrices 122 lying outside the limit curve 80. Thus, the surface 124 situated outside the limit curve 82 is not pierced by the piercing means 30. In the case where the piercing means 30 are plates 32 mounted with piercing heads 34, it is possible either to to break the number of suitable drilling heads 34 or to select a plate 32 having an adequate number of piercing heads 34. It should also be noted that the method of the invention makes it possible to determine the number maximum of piercing heads to break. Indeed, the fact of breaking a piercing head 34 and the fact of changing the plate 32 extends the duration of the piercing of the acoustic piece.

Step F of the method of the invention comprises drilling the useful surface 82 via the piercing means 30 following the drilling pattern 120. To do this, the surface of the acoustic piece to be pierced is oriented in such a way that substantially perpendicular to the piercing means 30. By the method of the invention, it is possible to minimize the trajectory of the piercing means 30 and thus to optimize the piercing time. For some reasons of space, it is possible to reverse the direction of the drilling means 30 at an angle substantially equal to 180 °.

The piercing means 30 start the physical piercing of the acoustic piece on a piercing die 60 of the piercing frame 120. Said piercing die 60 is selected so that the overall movement of the piercing means 30 is minimal and optimal in the case where the piercing means 30 must be modified or changed.

On said selected drilling die 60, the piercing means 30 pierce the corresponding zone, for example zones 54, along the first step 46 and the second step 48. When the piercing means 30 have finished piercing the zone delimited by the piercing die 60, they stop drilling and move to another piercing die 60 adjacent to the first piercing die 60. The piercing means 30 pierce the area delimited by said adjacent die 60 as indicated upper. The drilling means 60 recommence for all the matrices 60 of the drilling frame 120.

According to one aspect of the invention, the method of the invention can also be realized or executed using a computer program product comprising one or more instruction sequences accessible to a central unit and, when a sequence is executed by the central unit, the central unit performing at least one of steps A to F of the method of the invention.

Thus, at least one of the steps of the method of the invention is automated using the product of the invention.

According to a preferred embodiment, the central unit performs all the steps of the method of the invention, in particular the steps E1 to E5. In this case, advantageously, the implementation of the method of the invention lasts less than three days, especially less than 48 hours.

Any type of language can be used for the product of the invention.

The term "computer program" here refers to any type of action and / or method of a computer or computer system or similar information device that is capable of manipulating and / or transforming the data reopresented as physical and / or electronic quantities in the computer system memory to other similar data representing physical quantities stored in the computer system memory or present in transmission or dispatching devices. The product of the invention can be implemented with any type of computer program.

According to another aspect of the invention, a digital medium comprises one or more sequences of instructions of the computer program product according to the invention and readable by a central unit.

Examples of digital media include any type of disk including diskettes of the "floppy" type, optical disks, CD-ROMs, magneto-optical disks, ROMs ("Read-Only Memories"), RAMs ( "random access memories"), electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards or any other medium capable of storing electronic instructions and being coupled to a computer.

It is understood that the present invention is not limited to the embodiments shown but includes any other mode that may be suitable for the invention.

Claims

1. A method of drilling an acoustic part of a nacelle (1) of an aircraft, comprising the steps in which: A- a useful surface (82) of the acoustic piece is selected, said useful surface (82) being intended to be pierced;

B- drilling means (30) are selected for piercing the useful surface (82);

C is a movement pattern (40; 106; 108) corresponding to the displacement of the piercing means (30) in two directions (42, 44) substantially coplanar and perpendicular;

D- a piercing die (60; 107; 109; 122) is made by projecting the displacement pattern (40; 106; 108) on the usable surface (82) substantially perpendicularly; E-step D is repeated over substantially the entire usable area (82) forming a piercing frame (120);

F- the useful surface (82) is drilled through the piercing means (30) following the piercing pattern (120).

2. Method according to the preceding claim, wherein step E comprises the steps in which:

E1. a limit curve (80) defining the useful surface (82) to be drilled is determined;

E2. determining a starting curve (84) substantially corresponding to the intersection of the usable area (82) and a plane (86) containing the main axis (88) of the acoustic piece;

E3. the guidelines (90) of the dies are determined by substantially aligning the center (92) of the different dies (60;

107; 109; 122) along the starting curve (84), substantially joining said die (60; 107; 109; 122) to each other along said starting curve (84), and substantially intersecting the useful surface (82) and cross-sectional to the main axis (88) of the acoustic piece through the center (92) of the piercing dies (60;

107; 109; 122); E4. the center (92) of the various dies (60;

107; 109; 122) on each guideline (90) of the matrices up to the limiting curve (80) of the effective area (82) so that the distance (d) between the adjacent ends (112; 114) of two consecutive piercing matrices (107; 109) is substantially equal to a predetermined distance; E5. the piercing frame (120) is determined by partially deactivating the piercing dies (122) lying outside the limit curve (80).

3. Method according to the preceding claim wherein the drilling frame is determined by performing a first half-drilling frame according to step E4 between the starting curve (84) and the limit curve (80), the second half-frame. of peening being the symmetrical weft of the first half-weft of drilling relative to the starting curve (84).

4. Method according to claim 2 or 3, characterized in that the predetermined distance is less than about 10 ^'7 m.

A method according to any one of the preceding claims, wherein the displacement pattern (40; 106; 108) is achieved by moving the piercing means (30) a first pitch (46) along the length (50). said piercing means (30) and a second pitch (48) along the width (52) of said piercing means (30).

6. Method according to the preceding claim, wherein the first (46) and second (48) steps are substantially equal.

7. Method according to any one of the preceding claims, wherein the piercing means (30) comprise plates (32) amounting between 1 and 21 piercing heads (34).

8. Method according to the preceding claim, wherein the piercing means (30) comprise plates (32) having a different number of piercing heads (34).

9. The method of claim 7 or 8, wherein the piercing heads (34) are spaced a number substantially equal to a multiple of the first step (46) or the second step (48).

The method of any one of claims 7 to 9, wherein step E5 comprises a step where at least one piercing head (34) is broken.

11. Computer program product comprising one or more instruction sequences accessible to a central unit and, when a sequence is executed by the central unit, the central unit performing at least one of steps A to F of the method according to claim 1.

12. Product according to the preceding claim, characterized in that the central unit performs all the steps of the method of any one of claims 2 to 10.

13. Digital medium comprising one or more sequences of instructions of the computer program product according to claim 11 or 12 and readable by a central unit.