The invention relates to an aircraft wing according to the preamble of claim 1 .

Such an aircraft wing is well known, and it is also well known that aircraft represent a notable source of aircraft noise , not only during takeof f and landing, but also during cruise flight . The noise may come from the airfoil itsel f generated by a turbulent boundary layer especially on a flap surface in the trailing edge region, but also from interaction noise due to the proximity between the wing and an exhaust flow from engines , or impinging vortices from propellers .

It is known to apply acoustic liners or open cell permeable structures in the trailing edge region of the aircraft wing to combat noise . However such liners and structures are ef fective only in one particular stage of flight , and are ineffective or possibly even counterproductive in other flight phases .

US2015/ 0259060 discloses for purposes of noise reduction an orthotropic lattice structure interconnecting porous surfaces of a flap connectable to an aircraft wing with internal lattice structured perforations to equali ze a steady pressure field on the flap surfaces adj acent to the end and to reduce the amplitude of the fluctuations in the flow field near the flap end . The global communication that exists within all of the perforations provides a mechanism to lessen the pressure gradients experienced by the end portion of the flap . In addition to having di f fusive ef fects ( di f fusing the incoming flow) , the three-dimensional orthogonal lattice structure is also reactive ( acoustic wave phase distortion) due to the interconnection of the perforations .

US2009/ 0261204 discloses an aircraft wing provided with a trailing edge region, wherein the trailing edge region is provided with a noise attenuation structure , which noise attenuation structure at least comprises two micro perforated plates adj acent to each other in combination that are both in an upper region of the trailing edge , and that are slidable with respect to each other for aligning and/or misaligning the micro perforations of the two adj acent micro perforated plates with respect to each other . The noise attenuation structure of this document can be provided on an upper region and on a lower region, that is on opposite sides of an aircraft wing, wherein both noise attenuation structures can be in communication with each other .

It is an obj ect of the invention to provide a low- noise aircraft wing .

Accordingly an aircraft wing is proposed with the features of one or more of the appended claims .

In a first aspect of the invention the trailing edge region is delimited by a trailing edge , wherein a density of the micro perforations in the respective micro perforated plates increases towards the trailing edge . In this way an optimi zed permeability can be achieved with respect to a surface pressure distribution on the flap, and avoids a sudden change in impedance between solid and permeable surfaces of the aircraft wing so as to minimi ze possible losses in performance due to li ft decrease . Accordingly the distribution of the micro perforations in the respective micro perforated plates is varied in order to answer to speci fic needs in particular parts of the trailing edge region of the aircraft wing .

Suitably a relative position of at least one of the second micro perforated plate and the third micro perforated plate is controllable with an actuator that is arranged to slide the at least one of the second micro perforated plate and the third micro perforated plate with respect to each other .

Preferably the micro perforations of the second micro perforated plate and the micro perforations of the third micro perforated plate are attuned to each other so as to arrange that the second micro perforated plate and the third micro perforated plate are able to occupy a first position wherein the micro perforations of the second micro perforated plate and the micro perforations of the third micro perforated plate are misaligned, and a second position wherein the micro perforations of the second micro perforated plate and the micro perforations of the third micro perforated plate are aligned, as well as any position between the first position and the second position .

Accordingly the aircraft wing of the invention preferably provides the following options : 1 . The micro perforations of the second and third micro perforated plates are misaligned, providing no permeability through any of the honeycomb channels . The noise attenuation structure of the aircraft wing of the invention then operates as an acoustic liner . This mode can be activated when the flaps are fully retracted during the cruise phase of the flight .

2 . Some of the micro perforations of the second and third micro perforated plates are aligned, providing permeability through some of the honeycomb channels . This provides a hybrid noise attenuation structure of the aircraft wing of the invention, between the acoustic liner option 1 , and the following option 3 of a fully permeable structure . This mode can be activated when the flaps are partially deployed during takeof f .

3 . The micro perforations of the second and third micro perforated plates are all aligned, providing permeability through all of the honeycomb channels . The noise attenuation structure is fully permeable , and this mode can be activated when the flaps are fully deployed during the approach phase .

In a preferred embodiment on top of the third micro perforated plate a smooth acoustically permeable surface layer is provided . This surface layer can be c with a high form drag coef ficient , for maintaining aerodynamic performance of the aircraft wing, as well as mitigating possible additional surface roughness .

The invention wi ll hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of an aircraft with an aircraft wing according to the invention that is not limiting as to the appended claims .

In the drawing :

- figure 1 shows an aircraft with an aircraft wing of the invention in a top view and a side view; -figure 2 shows an exploded view of a noise attenuation structure as applied in the trailing edge region of the aircraft wing of the invention; and

-figure 3 shows different modes of application of the noise attenuation structure of figure 2.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Figure 1 shows an aircraft with an aircraft wing 1 provided with a trailing edge region 2. Usually the aircraft wing 1 supports an engine 3.

According to the invention the trailing edge region 2 is provided with a noise attenuation structure which is shown in an exploded view in figure 2. The noise attenuation structure as shown in figure 2 comprises in combination, looking in an upwards direction: a first micro perforated plate 2.1 with micro perforations, a structure 2.2 with open channels, a second micro perforated plate 2.3 with micro perforations, and a third micro perforated plate 2.4 with micro perforations, wherein the open channels of the structure 2.2 connect micro perforations of the first micro perforated plate 2.1 with micro perforations of the second micro perforated plate 2.3. Further at least one of the second micro perforated plate 2.3 and the third micro perforated plate 2.4 is slidable with respect to the other as symbolized by the arrows A, for aligning and/or misaligning the micro perforations of the second micro perforated plate 2.3 and the third micro perforated plate 2.4 with respect to each other.

Preferably the open structure 2.2 is a honeycomb structure, but this is not essential.

Accordingly a relative position of at least one of the second micro perforated plate 2.3 and the third micro perforated plate 2.4 is controllable with an actuator (not shown - but clear to the skilled person) that is arranged to slide the at least one of the second micro perforated plate 2.3 and the third micro perforated plate 2.4 with respect to each other.

It is further observed that preferably the micro perforations of the second micro perforated plate 2.3 and the micro perforations of the third micro perforated plate 2.4 are attuned to each other so as to arrange that the second micro perforated plate 2.3 and the third micro perforated plate 2.4 are able to occupy a first position wherein the micro perforations of the second micro perforated plate 2.3 and the micro perforations of the third micro perforated plate 2.4 are misaligned, and a second position wherein the micro perforations of the second micro perforated plate 2.3 and the micro perforations of the third micro perforated plate 2.4 are aligned, as well as any position between the first position and the second position.

Accordingly figure 3 shows the following options:

Mode 1. The micro perforations of the second and third micro perforated plates 2.3, 2.4 are misaligned, providing no permeability through any of the honeycomb channels. The noise attenuation structure of the aircraft wing of the invention then operates as an acoustic liner. This mode 1 can be activated when the flaps are fully retracted during the cruise phase of the flight .

Mode 2. Some of the micro perforations of the second and third micro perforated plates 2.3, 2.4 are aligned, providing permeability through some of the honeycomb channels. This provides a hybrid noise attenuation structure of the aircraft wing of the invention, between the acoustic liner option mode 1, and the following mode option 3 representing a fully permeable structure. This mode 2 can be activated when the flaps are partially deployed during takeoff.

Mode 3. The micro perforations of the second and third micro perforated plates 2.3, 2.4 are all aligned, providing permeability through all of the honeycomb channels. The noise attenuation structure is fully permeable, and this mode 3 can be activated when the flaps are fully deployed during the approach phase .

It is further remarked that the trailing edge region 2 is delimited by a trailing edge, wherein a density of the micro perforations in the respective micro perforated plates 2.1, 2.3, 2.4 increases towards the trailing edge. Finally it is remarked with reference to figure 2 that on top of the third micro perforated plate 2 . 4 preferably a smooth acoustically permeable surface layer 2 . 5 is provided .

Although the invention has been discussed in the fore- going with reference to an exemplary embodiment of an aircraft wing of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention . The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith . On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment . The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment .