Cross-Reference to Related Applications

This patent appl ication is related to Italian Patent Application No . 102021000024506 filed on September 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 i s also configured to reduce the transmission of noise and of the vibrations produced by the propellers towards the cabin .

Patent US6132882A 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 claim 1 .

Brief Description of the Drawings

For a better understanding of the present invention, a preferred embodiment is described below, by way of nonlimiting example , with reference to the accompanying figures in which :

Figure 1 shows in simpli fied cros s-section an aircraft window reali zed according to the dictates of the present invention;

Figure 2 is a diagram showing the sound damping characteristics of the window of Figure 1 ;

Figures 3 and 4 show, in front view, a portion o f the window of Figure 1 .

Detailed Description of the Invention

Figure 1 denotes , as a whole , 1 an 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 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 .

Typically, the first and second elements of transparent material 2 , 3 are formed by weakly curved sheets made of acrylic or glass and have a thickness of about 2 . 5 cm; these elements 2 , 3 have perimeter edges 2c, 3c fixed to the fuselage ( shown schematically with hatching) with techniques of known type , e . g . by means of a very strong adhes ive glue and a series of rivets .

According to the present invention there is provided a first transparent sheet element 5 applied to a first face 6 of the first element of transparent material 2 facing the gap 4 and only a second transparent sheet element 7 applied to a first face 8 of the second element 3 facing the gap 4 .

The first transparent sheet element 5 covers a central area of the first face 6 and is spaced from the edges of the first face 6 so that the perimeter edges 2c of the first transparent element 2 are free of said first sheet element 5 ( see Figure 3 ) .

The second transparent sheet element 7 covers a central area of the second face 8 and is spaced from the perimeter edges of the second face 8 so that the perimeter edges 3c of the second transparent element 3 are free of said second sheet element 7 .

The first and second transparent sheet elements 5 , 6 are 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; i f they are subj ected 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 ; i f instead they are subj ected 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 layers 5 , 5a, ... 5n of viscoelastic material superimposed over one another ( indicated in the drawing with hatching) so as to obtain a layered structure applied to the first face 6 of the first element 2 facing the gap 4 and a second plurality m of transparent sheet layer 7 , 7a, ... 7m of vi scoelastic material superimposed over one another ( indicated in the drawing with hatching) so as to obtain a layered structure applied to the first face 8 of the second element 3 facing the gap 4 .

Preferably, the transparent sheet layers 5 , 5a, ... 5n belonging to the first layered structure have di f ferent 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 material 5 , 5a, ... 5n .

Furthermore , preferably the transparent sheet layers 7 , 7a, ... 7m belonging to the second layered structure have di f ferent 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 material 7 , 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 elements 5 and 7 dampen both the airborne vibrations (between the first element of transparent material 2 and the second element of transparent material 3 ) and the vibrations transmitted structurally ( from the structure of the aircraft directly to the second element of transparent material 3 ) 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 .

In Figure 2 in 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 160Hz 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

1 aircraft window

2 first element of transparent material

3 second element of transparent material

4 gap

5 first transparent sheet element

6 face

7 second transparent sheet element

8 face