GB2313871A

GB2313871A - Aircraft window noise attenuation

Info

Publication number: GB2313871A
Application number: GB9611923A
Authority: GB
Inventors: Anthony Furner
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1996-06-07
Filing date: 1996-06-07
Publication date: 1997-12-10
Also published as: GB9611923D0

Abstract

A noise attenuation arrangement and an aircraft fuselage including such an arrangement are provided in which a sealed double glazed resonator unit 1 is formed from spaced window panes 3, 4 having an air-tight peripheral seal 2. A vent tube 5 in the window seal 2 communicates a volume of air contained within the cavity 6 of the resonator unit with a space adjacent the unit for which noise attenuation is required, in the case of an aircraft, the cabin. The volume of air within the unit may be adjusted by varying the length of the tube 5 to tune the unit to frequencies of noise which the arrangement is designed to attenuate.

Description

NOISE ATTENUATION ARRANGEMENT This invention relates to noise attenuation and in particular to attenuation of noise in enclosures occupied by people. More particularly it relates to the attenuation of noise in passenger carrying vehicles with particular reference to aircraft.

Noise attenuation in any form of enclosure presents certain difficulties. The major difficulty is that effective noise attenuation to prevent noise being transmitted through or reflected off walls of enclosures usually involves the provision of heavyweight materials to absorb the noise, for example lead is an excellent sound damping medium.

When attempting to reduce noise levels in vehicles, particularly in aircraft, the use of such heavy materials can clearly present almost insuperable problems.

Certain types of lightweight material are more effective at noise attenuation than others. Nevertheless, as a general rule, the heavier the insulation material the more effective it is.

Certain types of aircraft, in particular propeller aircraft although turbine powered aircraft can also suffer in this respect, raise particular problems of noise attenuation for example owing to the passage of propeller blades in relatively close proximity to a fuselage skin of the aircraft. In areas of the aircraft nearest to the propellers quite severe low frequency noise of 50Hz-250Hz can occur inside the aircraft. Attempts to attenuate this noise using standard noise insulation materials inevitably result in considerable weight being added to the aircraft, even if only locally. Such weight increases can be either totally unacceptable or can reduce the aircraft range or reduce revenue earning capacity of the aircraft in particular circumstances.

Very often the noise to be attenuated is at a fixed frequency, for example the propeller blade passing frequency of a propeller driven aircraft. This will remain substantially constant even at different speeds of the aircraft and under different power loadings.

Resonating chambers of the Helmholtz variety with an enclosed volume of air in communication via a small passage with the air in which the noise is to be attenuated are known for motor vehicles. The resonating chambers however inevitably both add weight to the vehicle and take up space. For aircraft in particular the provision of such resonating chambers would not be practical where the skin of the aircraft fuselage were to be used as one wall thereof. This is because an inner wall of the chamber would need to be separately provided and attached to the fuselage skin. This would provide great stressing complications for the fuselage design, would add considerable expense to the manufacturing costs as well as giving a considerable weight penalty.

An improved arrangement for noise attenuation in passenger enclosures, in particular in vehicles, is therefore required.

According to one aspect of the present invention there is provided a noise attenuation arrangement for a walled enclosure, the arrangement comprising a resonator unit positionable in a said wall of the enclosure, the unit including a pair of window panes held in spaced apart relationship with each other by a seal extending peripherally around the panes, and a conduit, the panes and the seal defining a sealed cavity therein and the conduit extending between the cavity and an exterior of the unit whereby to connect the cavity with air in the enclosure.

A simple, lightweight and space efficient noise attenuator is thus provided.

The conduit may comprise a tube whose length and/or diameter may be adjusted to tune the resonator unit for different frequencies.

A tube of variable length may provide relatively fine tuning of resonating frequency for the arrangement.

More fundamental tuning may be achieved by provision of seals of variable depth measured in a direction substantially normal to the planes of the window panes into which panes of the double glazed window may be inserted to form the sealed unit. By this means different volumes of air may be enclosed within the resonator by the expedient of varying the gap between adjacent window panes thereof.

The seal or seals may also be adapted to extend by a variable distance in a direction substantially parallel with the planes of the window panes into the volume of air between the two panes of the window, further to provide adjustment of resonating frequency of the arrangement.

It will be appreciated that, with careful design of the arrangement of the invention a resonator unit of the desired frequency may be provided for a vehicle, for example an aircraft already provided with double glazing, substantially without any increase of weight to the structure of the aircraft at all.

According to a second aspect of the invention there is provided an aircraft fuselage incorporating a series of noise attenuation arrangements according to the first aspect of the invention fitted to a skin of the fuselage.

The invention will now be described by way of example with reference to the accompanying drawings of which:- Figure 1 is an isometric view of a noise -attenuation arrangement according to the invention in the form of an aircraft cabin window resonator, Figure 2 is a vertical section through a window resonator similar to that shown in Figure 1, Figure 3 is a vertical section through a window resonator installed in an aircraft cabin wall, and Figure 4 is a isometric ghosted view of an aircraft centre fuselage according to the invention.

Referring to the drawings, a noise attenuation arrangement according to the invention comprises a sealed double glazed resonator unit 1 having a circular or ovoid window seal 2 into which is set an outer structural window pane 3 and an inner structural window pane 4 (see figures 1 and 2). The window seal 2 forms an air-tight seal with both window panes 3 and 4. A conduit in the form of a vent tube 5 defines a passageway in communication with air adjacent the inner structural window pane 4.

A cavity 6 whose volume may be altered is enclosed within the window panes 3 and 4 and the window seal 2. It will be appreciated that by either increasing or reducing the separation between the window panes 3 and 4 and/or by extending the window seal more or less between the window panes the volume of the cavity 6 may be enlarged or decreased for tuning the resonator. In addition, for finer frequency tuning the length and/or diameter of the vent tube 5 may be reduced or increased.

Turning now to figures 3 and 4, figure 3 shows in section a resonator arrangement according to the invention installed in the fuselage of an aircraft. Like parts of the arrangement have been given like reference numerals throughout for ease of understanding. The arrangement of the invention is shown installed in a fuselage structure comprising a skin 7 and mounting bracketry 8 and retained by a spring clip 9. A window reveal 10 surrounds the arrangement and forms a frame for the arrangement.

Within the fuselage structure 7, 8 is carried a furnishing panel 11 of plastics material into which is set, via fasteners 12, a scratch panel/third window 13.

It will be seen that the cavity 6 within the resonator of the invention is in communication with an interior of a cabin 14 of the aircraft defined inside the fuselage structure 7, 8. Referring to figure 4 entries 15 to the vent tubes 5 may be seen underneath each cabin window/double glazed unit 1 of the fuselage 16.

It will be appreciated from figure 4 how each resonator unit 1 comprises one of a series of such units distributed along fuselage 16 whereby to provide a noise attenuation arrangement effective along the length of the cabin 14.

Claims

1. A noise attenuation arrangement for a walled enclosure, the arrangement comprising a resonator unit positionable in a said wall of the enclosure, the unit including a pair of window panes held in spaced apart relationship with each other by a seal extending peripherally around the panes, and a conduit, the panes and the seal defining a sealed cavity therein and the conduit extending between the cavity and an exterior of the unit whereby to connect the cavity with air in the enclosure.

2. A noise attenuation arrangement as in claim 1 in which the conduit comprises a tube whose length is adjustable to tune the resonator unit for different frequencies.

3. An aircraft fuselage incorporating at least one noise attenuation arrangement according to claim 1 or 2 fitted to a skin of the fuselage.

4. A noise attenuation arrangement substantially as herein described with reference to the accompanying drawings.

5. An aircraft fuselage substantially as herein described with reference to the accompanying drawings.