Fluid reaction surfaces (i.e. – impellers) – Articulated – resiliently mounted or self-shifting impeller... – Nonmetallic resilient mounting
Reexamination Certificate
1999-11-12
2001-09-11
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Articulated, resiliently mounted or self-shifting impeller...
Nonmetallic resilient mounting
C416S248000
Reexamination Certificate
active
06287076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rotor blades, particularly those intended for a shrouded antitorque tail rotor (fenestron™—registered trademark of the French company EUROPCOPTER) for a helicopter. It relates more specifically to the device for attaching such a blade to the hub of said rotor.
2. Description of the Related Art
It is known that antitorque tail rotor blades for helicopters are generally set by their root into the hub of said rotor, by means of two bearings which are separated from one another along the length of said root. They are also attached near the center of the hub by members which are elastically deformable in terms of torsion, which allow the angle of incidence to be varied while at the same time withstanding the centrifugal force which is exerted on the blades as they rotate.
These members which are elastically deformable in terms of torsion are either metallic (for example a bundle of superimposed leaves made of stainless steel) or made of a fiber-resin composite (it then being possible for each elastic member to be an extension of a blade, itself made of composite), depending on the design of said blades.
Whatever the design of these members which are elastically deformable in terms of torsion, these members constitute critical elements of said rotors because they experience high tensile stresses under the action of centrifugal force and, above all, because they experience high torsional fatigue loads for controlling the incidence, and so, in order to reduce the torsional stresses and extend the life of said members, these members have to be made as long as possible, although this increases the radial size of the rotor hub.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome these drawbacks by allowing a rotor of this kind to be produced with a small radial size, while at the same time eliminating any risk of breakage of the members which are elastically deformable in terms of torsion.
To this end, according to the invention, the rotor blade, particularly for the antitorque tail rotor of a helicopter, comprising:
a blade root mounted so that it can rotate in the hub of said rotor, so as to allow said blade to rotate about its pitch axis; and
means of attaching said blade root to said rotor hub, including a member which is elastically deformable in terms of torsion about said pitch axis, is noteworthy in that:
said blade root is hollow and open at its internal end;
said member which is elastically deformable in terms of torsion consists of an elastic stop housed in said blade root and is capable of acting as a limited-action ball joint centered on said pitch axis; and
a rigid tie rod connects said elastic stop to said rotor hub.
Thus, such an elastic stop eliminates any danger of breakage through torsional fatigue. It can be robustly engineered and can offer a long service life without appreciable wear and without ever leading to sudden fatigue failure.
Furthermore, an elastic stop of this kind is particularly compact and therefore takes up a small amount of space, especially radially with respect to the rotor.
However, in order to reduce the radial size of the rotor still further, it is advantageous, said elastic stop having, in the known way, a number of laminated elements made of elastomer arranged between two armatures, for:
said elastic stop to be arranged inside said blade root in such a way that one of its armatures, known as the outer armature, is on the same side as the profiled part of said blade, while the other of said armatures, known as the inner armature, is on the same side as the axis of the rotor;
said elastic stop to have a central recess which is coaxial with said pitch axis;
said rigid tie rod to pass with clearance through said central recess and its outer end, which is on the same side as said profiled part of the blade, to be secured to the outer armature of said elastic stop; and
the inner armature of said elastic stop, through which said tie rod passes with clearance, to be secured to the inner end of the blade root which is on the same side as the axis of the rotor.
Thus, the small size of the elastic stop and of the tie rod makes it possible to greatly reduce the diameter of the rotor hub supporting the bearings in which the blades are supported, and this leads to an improvement in the thrust performance and, above all, to a reduction in the mass of the hub, and of the support for the gearbox (which drives the rotation of said rotor) which is in line with and behind said hub.
Said elastic stop may be spherical, that is to say that its laminated elastomer elements are then spherical and centered on said pitch axis. However, given the small excursion of said elastic stop, it may be conical, that is to say that its laminated elements are also conical and centered on said pitch axis.
Furthermore, it is advantageous to provide a ball joint-type support, centered on said pitch axis, between the outer end of said tie rod and the outer end of said blade root.
Thus, by creating this kind of support for the outer end of the tie rod inside said blade root, said tie rod can be immobilized and the elastic stop, loaded axially with centrifugal force, is subjected only to the torsion which corresponds to the variations in incidence.
Moreover, by virtue of this support, it becomes possible to use just one bearing, arranged at the outer end of said blade root, for articulating said blade root to the hub. This is because, in rotation, the flapping movements of the blade are small (less than 1°) and the corresponding deformations of the elastic stop lead to very small movements. Furthermore, when stationary, the flapping movements of the blade are limited by contact between the inner armature of the elastic stop and said tie rod.
It will be readily understood that omitting one blade bearing—compared with the prior art—appreciably lightens and simplifies the rotor hub which may, for example, then be made by pressing, like a saucepan. Furthermore, omitting one bearing eliminates the majority of the control efforts, which majority results from the friction in the bearings which are highly loaded because of the way the blade is fitted. It is therefore no longer necessary to use servocontrol, without this entailing having to resort to heavy balancing masses on the blades. This too constitutes a simplification and a reduction in weight. Thus, by virtue of the present invention, the means of attaching the blades are simpler, more compact, more dependable and less expensive than those of the prior art.
The figures of the appended drawing will make it easy to understand how the invention may be achieved. In these figures, identical references denote similar elements.
REFERENCES:
patent: 4244677 (1981-01-01), Noehren et al.
patent: 4273511 (1981-06-01), Mouille et al.
patent: 4886419 (1989-12-01), McCafferty
patent: 5330322 (1994-07-01), Aubry
patent: 5478204 (1995-12-01), Desjardins et al.
patent: 0331791 (1989-09-01), None
patent: 1593008 (1970-05-01), None
patent: 8002407 (1980-11-01), None
patent: 0549455 (1993-06-01), None
PCT International Search Report dated Jun. 24, 1999.
Look Edward K.
Nguyen Ninh
Stevens Davis Miller & Mosher LLP
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