Aeronautics and astronautics – Aircraft – heavier-than-air – Helicopter or auto-rotating wing sustained – i.e. – gyroplanes
Reexamination Certificate
1998-11-02
2001-09-11
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Helicopter or auto-rotating wing sustained, i.e., gyroplanes
C244S017270, C244S075100, C188S379000, C248S564000
Reexamination Certificate
active
06286782
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for the reduction of vibrations of a structure, particularly a helicopter, as well as to a method for the reduction of vibrations of a structure, for example, tail-shake vibrations of a helicopter.
BACKGROUND
The air frame structures of helicopters are subject to significant vibrations. These are caused, for example, by air flow along the surface of the helicopter. In the case of so-called tail-shake vibrations, the rear end of the helicopter vibrates both in the vertical as well as in the horizontal directions. In particular, the first natural bending characteristics in the vertical and horizontal directions are responsible for cabin vibrations at the seat of the pilot and they greatly influence these vibrations. In order to reduce tail-shake vibrations, vibration dampers are conventionally utilized. These vibration dampers are essentially comprised of weights and springs.
In the conventional vibration dampers, the problem exists that great additional weight is necessary which significantly increases the total weight of the helicopter. In addition, these dampers require substantial space for their installation which is not always available at the location where they provide an optimal damping action. In addition, expensive fastening devices are necessary for the springs and the weights at various places in the helicopter.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to overcome the above disadvantages of the conventional damping devices and provide a damping device for the reduction of vibrations of a structure which has less weight and requires a minimum space and which can be easily produced and by which vibrations are effectively reduced.
Another object is to provide a method by which vibrations are reduced in structures, particularly in helicopters, both effectively and with savings in weight and space.
The above and further objects are achieved by a device according to the invention for the reduction of vibrations of a structure, particularly a helicopter, which comprises:
a spring system having an elastic wall structure defining a hollow body; and
a weighted vibration object which is attached in the hollow body; and
wherein at least one region of the wall structure is elastically deformable in the plane of its wall surface and has a spring stiffness, which is tuned to the frequency of vibration of the structure to be reduced.
It is possible in this way to support a weighted vibrating object in a simple way, so that in can produce elastic movements relative to its surrounding structure, such that the vibrating object is nevertheless supported permanently and stably. Such a spring structure saves space, can be easily produced, and makes possible a good connection to the structure, while providing a good adaptation to the vibrations to be reduced. Due to the configuration of the spring system as a hollow body, the vibrating object, for example, in the form of a block or cuboid structure, can be easily connected to the surrounding structure, so that the vibrations of the structure can be effectively reduced.
Advantageously, the elastic wall structure comprises a plurality of planar spring elements, which together form the hollow body. Preferably, each of the planar elements can be elastically deformed in its plane.
According to the invention, a battery, such as, a starter battery of the helicopter can be used as the vibrating object . In this way, the need for additional weight is eliminated. Advantageously, the device has two degrees of freedom of displacement, in order to reduce vibrations of the structure in two directions. In this way, the first natural bending frequency of the structure in the vertical and horizontal directions can be particularly reduced.
In the device, four spring elements can be arranged in such a way that two spring elements lie opposite each other in pairs. The spring stiffness of the spring elements of one pair preferably differs slightly from the spring stiffness of the spring elements of the other pair. In this way, vibrations of air frame structures with different frequencies in different directions can be effectively reduced. The weight M of the vibrating object may be between 10 and 50 kg, preferably between 20 and 30 kg, and particularly approximately 26 to 27 kg. This makes possible a good adaptation to the required frequencies to be damped. The spring system is preferably joined with the vibrating object by eight connections and advantageously it has eight other connections for attachment to the surrounding structure. The material and/or the length of the spring elements are preferably selected such that the stiffness and the spring path are adapted to the vibrations to be reduced. Therefore, an optimal adaptation and connection to the structure can be achieved by simple construction means.
Advantageously, the spring elements or wall structure are manufactured from a fiber composite material, for example, an isotropic or quasi-isotropic structure. This makes construction easy while providing high strength.
Advantageously, each of the spring elements is in the form of a flat, rectangular flat frame with a pair of first longitudinal elements or strips and a pair of first cross pieces, at least one of the first longitudinal elements being connected, preferably at its center, to a second cross piece which extends toward the outside. In this way, the individual spring elements can undergo elastic deformation in the plane of the frame. Each of the spring elements can have a second longitudinal element, which extends parallel to the first longitudinal elements and the first and second longitudinal elements are connected at their respective centers by the second cross piece. In this way, tensile and compressive stresses in the direction of the cross pieces are resisted at the centers of the longitudinal elements and lead to their elastic deformation. Preferably, the planar spring elements have a rectangular outer configuration, and they can be joined with the vibrating object at the first cross pieces. The connection of the spring elements to the surrounding structure is preferably made at the four outer comers of the spring elements.
According to a further aspect of the invention, a method is provided for the reduction of vibrations of a structure, particularly tail-shake vibrations of a helicopter, in which a battery of the helicopter is used as a vibration damper. Preferably, the battery is supported in a spring system, and the spring system is mounted, with the battery, at a location in the structure at which a first natural bending of the structure takes place.
According to the above further aspect of the invention, the method for the reduction of vibrations of a structure, includes the steps of:
supporting a weighted vibratable object in a spring system having two degrees of freedom of elastic deformation, the spring system being formed of planar spring elements, each of which can be deformed elastically in its plane;
fastening the spring system in a structure whose vibration is to be reduced, particularly a helicopter, at a location, at which vibratory motion of the structure occurs in two directions perpendicular to one another;
the spring system being aligned such that the elasticity of the spring elements operates in both directions of vibration of the structure.
In particular, tail-shake vibrations of helicopters can be effectively reduced by the method of the invention.
The spring system is preferably fastened in the helicopter at a place where the natural vibratory bending of the helicopter frame takes place in the horizontal and vertical directions. Vibrations with a frequency of 3 to 10 Hz, preferably 5 to 10Hz, and particularly, 5.6 Hz to 6.0 Hz are reduced according to the method.
REFERENCES:
patent: 3502290 (1970-03-01), Legrand et al.
patent: 3845917 (1974-11-01), Drees
patent: 4042070 (1977-08-01), Flannelly
patent: 4683520 (1987-07-01), Grassens et al.
patent: 5180147 (1993-01-01), Anderson et al.
patent: 5775472 (1998-07-01), Osterb
Bansemir Horst
Bongers Bernd
Barefoot Galen L.
Eurocopter Deutschland GmbH
Ladas & Parry
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