Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
1998-10-01
2001-05-01
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
Reexamination Certificate
active
06224014
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device for reducing the line noise inside a rotary-wing aircraft, especially a helicopter.
More specifically, it applies to the reducing of noise in the flight deck and/or the passenger cabin of said aircraft.
It is known that, in a rotary-wing aircraft of this type, the acoustic spectra defined in the range between 20 Hz and 20 kHz are the result of the superposition of noises of differing origins, which can be categorized into two different groups depending on their spectral characteristics, namely pure sounds, or line noises, and broadband noises.
As is known, pure sounds or line noise, in particular, arise, as appropriate:
at the characteristic frequencies of the aircraft drivetrain;
at the rotational frequencies of the rotor blades (main and tail rotor) and at the harmonics of these frequencies;
at the rotational frequencies of the turbine engine compressor blades; and/or
at the rotational frequencies of the fanblades of the fans that cool the main gearbox and/or electrical equipment, and at the harmonics of these frequencies,
whereas broadband noises include, in particular, and as appropriate:
the noise of the boundary layer developing on the fuselage;
the noise generated by the rotors;
the airflow noise from the air intakes and jet pipes;
the engine noise; and/or
the noise of the circuits for air-conditioning or heating of the flight deck or the passenger cabin.
All these noises are of course annoying to pilots and passengers.
Thus, there are various known solutions for reducing such noises inside a rotary-wing aircraft, especially a helicopter.
DESCRIPTION OF THE PRIOR ART
A first known solution is aimed at reducing the level of vibration or the radiation of sources of noise and/or of the fuselage. To do this, there are various physical actions that can be taken, in particular:
reducing the vibration of the structure and/or of mechanical components, by damping or modifying the stiffness or the mass;
attenuating the acoustic transmission, by deadening or modifying the stiffness or the mass;
a double-skin effect, by shrouding the target source;
acoustic absorption using fibrous or cellular material; and
acoustic absorption using Helmholtz resonators.
The first four physical actions mentioned above allow the overall noise level to be reduced in a broad range of frequencies, but they lead to a significant and highly disadvantageous increase in mass. Furthermore, the noise reduction obtained is not selective enough to cause the acoustic annoyance specific to pure sounds to disappear.
By contrast, the fifth and last physical action mentioned above does effectively allow the line noise to be reduced, but still only in a narrow band of frequencies defined by design.
This first abovementioned solution based on a passive treatment of the noise is therefore barely effective, especially for line noises generated by vibrational excitations.
A second known solution recommends that passive soundproofing be created in the form of lining panels mounted in the flight deck or in the passenger cabin. These panels are designed to suit the structural area to be treated and the spectrum of frequencies to be attenuated.
However, this second solution also has numerous drawbacks, and in particular:
a noise reduction that is limited especially at low frequencies;
a high increase in mass, which may be by several hundred kilograms in the case of a large-sized helicopter;
a not insignificant loss of space, especially when using thick panels with a view to increasing the acoustic absorption effect; and
acoustic leaks, particularly at the wiring lead-throughs and joints between the panels.
Thus, neither of these two known and aforementioned solutions is satisfactory in reducing the annoyance caused by the line noises.
It is also known that the existing and very great acoustic annoyance to passengers and crew is caused essentially by the line noises.
Thus, to reduce this acoustic annoyance, it is above all advisable to reduce said line noises. This is what the present invention sets out to achieve, another object of this invention being to overcome the aforementioned drawbacks.
SUMMARY OF THE INVENTION
To this end, the invention relates to a device of low mass, cost and bulk which allows an effective and significant reduction in noise, and more particularly line noise, inside a rotary-wing aircraft, especially a helicopter, it being possible in addition for said device to be applied to any type of rotary-wing aircraft, and for its action to be modified and adapted during flight to the prevailing flight conditions.
To this end, said device is noteworthy, according to the invention, in that it comprises:
at least one sensor for measuring the values of at least one vibrational and/or acoustic parameter representing a vibrational and/or acoustic effect of at least one source of noise of said aircraft;
at least one mechanical means that can be controlled and is capable of creating a force capable of reducing the vibrational and/or acoustic effect of said source of noise; and
a control unit for controlling said mechanical means on the basis of the values measured by said sensor.
Thus, by virtue of the invention, it becomes possible to adapt said noise-reduction device to the flight conditions by controlling said mechanical means.
In addition, owing to the low number of constituent parts, the device in accordance with the invention is not very bulky, not very heavy and not very expensive. Furthermore, as its constituent parts are independent of the aircraft, said device can be produced in the form of an optional “add-on extra” control unit which can be mounted on any type of rotary-wing aircraft.
Furthermore, said device is capable of reducing all the annoying line noise likely to exist, irrespective of its frequency, especially below
10
kHz.
According to the invention, said sensor or sensors are preferably accelerometers, strain gauges, special-purpose sensors capable of measuring a strain, a speed, an acceleration, a force or a displacement, or microphones, or alternatively a combination of these various means.
In the first three instances, each accelerometer, strain gauge or special-purpose sensor is preferably fixed to:
at least one engine fixing mount;
one or more bearing(s) in the aircraft drivetrain;
one or more bar(s) for fixing the main gearbox;
a mechanical suspension of said main gearbox;
the aircraft fuselage;
a device for fixing lining panels to the structure; or
a panel for lining the flight deck.
Furthermore, in the fourth instance, said microphone or microphones is or are advantageously installed at the point where it is mainly a reduction in noise that is to be obtained, mainly preferably close to the heads of the pilots and passengers or beneath the ceiling of the helicopter.
Furthermore, said mechanical means, which is preferably a piezoelectric actuator or a magnetostrictive actuator or an actuator using shape-memory materials, advantageously acts on:
one or more mount(s) for fixing said engine to the fuselage of the aircraft;
one or more bearing(s) in said drivetrain;
one or more bar(s) for fixing said main gearbox to the fuselage;
a mechanical suspension of said main gearbox;
the aircraft fuselage; or
a device for fixing lining panels.
Furthermore, said control unit advantageously uses reference values to determine the commands for controlling said mechanical means. As a preference, said reference values comprise at least some of the following values:
values measured by one or more accelerometer(s) arranged on:
a casing of a gearbox;
a bearing in the drivetrain;
a mount for fixing the engine to the fuselage;
a bar for fixing the main gearbox to the fuselage; and
a mechanical suspension of the main gearbox; and/or
values measured by one or more microphone(s) arranged in a cargo hold or in the compartment in which the main mechanical-power gearbox is located.
Furthermore, in a particularly advantageous embodiment of the invention, said device comprises P sensors Cp arranged at points Mp, P being a predefined integer and p b
Eurocopter
Jordan Charles T.
Marshall O'Toole Gerstein Murray & Borun
Palo Francis T.
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