AIRCRAFT WINDOW

An aircraft window configured to reduce the intensity of vibrations transmitted from outside the aircraft to inside the aircraft cabin comprising: a first element of transparent material (2) arranged, in use, facing the outside of the aircraft; a second element of transparent material (3) arranged, in use, facing the cabin; a gap (4) that separates the first and second elements of transparent material-(2,3) which are arranged facing and spaced apart from one another, a first transparent sheet element (5) applied to a first face of the first element (2) facing the gap; and at least one second transparent sheet element-(7) applied to a second face of the second element-(3) facing the gap. The first and second transparent sheet elements (5,7) are made of transparent viscoelastic material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to Italian Patent Application No. 102021000024506 filed on Sep. 23, 2021, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an aircraft window.

BACKGROUND OF THE INVENTION

The structure of an aircraft passenger window generically comprises: a first element of transparent material arranged, in use, facing the outside of the aircraft; a second element of transparent material arranged, in use, facing the cabin; and a gap that separates the first and second elements of transparent material which are arranged facing and spaced apart from one another.

The window not only separates the outside of the aircraft from the inside in a gas-tight manner, thus allowing the cabin to be pressurised, but is also configured to reduce the transmission of noise and of the vibrations produced by the propellers towards the cabin.

U.S. Pat. No. 6,132,882A describes a transparent wall that can be used in an aircraft window comprising (a) a first rigid layer formed by a material selected from the group consisting of glass and plastic; (b) a second rigid layer formed by a material selected from the group consisting of glass and plastic; (c) a layer of anti-vibration material comprising a viscoelastic material placed between the first rigid layer and the second rigid layer; and (d) a first flexible plastic layer placed between the first rigid layer and the layer of anti-vibration material.

Patent EP1928732B1 describes an aircraft window comprising: a first inner layer of transparent material; a second outer layer of transparent material parallel to the first layer of transparent material and separated from it by a hollow gap; a rubber gasket securing the first and second layers at a depth within the rubber gasket; and a window frame, wherein the window frame wraps around the rubber gasket and encloses the rubber gasket around an entire perimeter of the rubber gasket.

Aim of the present invention is to realise an aircraft window that achieves a high damping of the noise and vibrations transmitted from outside the aircraft towards the cabin.

SUMMARY OF THE INVENTION

The above-mentioned aim is achieved by the present invention in that it relates to an aircraft window of the type described in claim1.

DETAILED DESCRIPTION OF THE INVENTION

FIG.1denotes, as a whole,1an aircraft passenger window configured to reduce the intensity of noise and of vibrations transmitted from outside the aircraft to inside the aircraft cabin comprising:a first element of transparent material2arranged, in use, facing the outside of the aircraft;a second element of transparent material3arranged, in use, facing the cabin;a gap4that separates the first and second elements of transparent material2,3which are arranged facing and spaced apart from one another.

Typically, the first and second elements of transparent material2,3are formed by weakly curved sheets made of acrylic or glass and have a thickness of about 2.5 cm; these elements2,3have perimeter edges2c,3cfixed to the fuselage (shown schematically with hatching) with techniques of known type, e.g. by means of a very strong adhesive glue and a series of rivets.

According to the present invention there is provided a first transparent sheet element5applied to a first face6of the first element of transparent material2facing the gap4and only a second transparent sheet element7applied to a first face8of the second element3facing the gap4.

The first transparent sheet element5covers a central area of the first face6and is spaced from the edges of the first face6so that the perimeter edges2cof the first transparent element2are free of said first sheet element5(seeFIG.3).

The second transparent sheet element7covers a central5area of the second face8and is spaced from the perimeter edges of the second face8so that the perimeter edges3cof the second transparent element3are free of said second sheet element7.

The first and second transparent sheet elements5,6are made of transparent viscoelastic material.

As is well known, purely viscous materials respond to a tangential stress exhibiting a behaviour consistent with Newton's law, that is, by giving rise to a tangential strain within themselves equal to the product of the speed of deformation and viscosity; if they are subjected to a normal stress, they do not oppose in any way.

The elastic materials respond to a normal stress exhibiting a behaviour consistent with Hooke's law, that is, by giving rise within them a normal strain equal to the product of Young's modulus and deformation (expressed in terms of percentage elongation) and returning to their original state when these stresses cease; if instead they are subjected to a tangential stress, they do not oppose in any way.

Viscoelastic materials oppose both tangential stresses and normal stresses, thus generating both tangential strains and normal strains within them.

Examples of viscoelastic materials are some amorphous polymers, some semi-crystalline polymers and some biopolymers.

Other examples are the thermosetting polymers, which at an appropriate temperature behave like a viscous fluid, and the polymers in a rubbery state such as the elastomer.

In particular, the viscoelastic material may belong to the family of acrylic polymer materials and is provided with a silicone coating film.

Preferably, the first and second transparent elements may comprise a first plurality n of transparent sheet layers5,5a, . . .5nof viscoelastic material superimposed over one another (indicated in the drawing with hatching) so as to obtain a layered structure applied to the first face6of the first element2facing the gap4and a second plurality m of transparent sheet layer7,7a, . . .7mof viscoelastic material superimposed over one another (indicated in the drawing with hatching) so as to obtain a layered structure applied to the first face8of the second element3facing the gap4.

Preferably, the transparent sheet layers5,5a, . . .5nbelonging to the first layered structure have different thicknesses from one another.

The thicknesses vary from one tenth of a millimetre to one millimetre and the elements may preferably have the same dimension as the one underneath or smaller dimensions to facilitate the passage of light through the window. The application is carried out through the adhesive property of the transparent elements of viscoelastic material5,5a, . . .5n.

Furthermore, preferably the transparent sheet layers7,7a, . . .7mbelonging to the second layered structure have different thicknesses from one another.

The thicknesses vary from one tenth of a millimetre to one millimetre and the elements may preferably have the same dimension as the one underneath or smaller dimensions to facilitate the passage of light through the window. The application is carried out through the adhesive property of the transparent elements of viscoelastic material7,7a, . . .7m.

The window shown above solves the problem of vibration and noise transmission by providing one or more layers of varying thickness of viscoelastic material, each of which is applied internally to the transparent elements of which the pre-existing window configuration is composed.

The two viscoelastic elements5and7dampen both the airborne vibrations (between the first element of transparent material2and the second element of transparent material3) and the vibrations transmitted structurally (from the structure of the aircraft directly to the second element of transparent material3) obtaining a high overall damping performance.

This leads to acoustic performances that, at least up to 800 Hz, are advantageous compared to the solutions proposed by the prior art.

InFIG.2in fact it can be seen that the loss of sound transmission (also called Insulating Power-Transmission Loss), represented by a measurement in dB of the ratio between the incident sound power and the power transmitted through a dividing element hit by an acoustic wavefront, is maintained between 20 and about 30 dB in the range 160 Hz and 800 Hz which corresponds to both the multiple rotation frequencies of many turboprop engines, and to a portion of the frequencies of the noise generated by the turbulent aerodynamic flows on the fuselage. The line indicated with a non-continuous stroke indicates the performance of a window made according to the present invention (Window UP with viscoelastic) while the curve indicated with a solid stroke indicates the performance of a window made according to the known art (Window UP without viscoelastic).

NUMBERS

1aircraft window2first element of transparent material3second element of transparent material4gap5first transparent sheet element6face7second transparent sheet element8face