Fluid reaction surfaces (i.e. – impellers) – Sustained ancillary movement of rotary working member – Lead-lag type rotor blade movement
Reexamination Certificate
1999-05-12
2001-03-20
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Sustained ancillary movement of rotary working member
Lead-lag type rotor blade movement
C416S13400R
Reexamination Certificate
active
06203277
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns rotorcraft rotors, in particular helicopter rotors, that include a dual plate hub with two plates associated with a tubular pylon and a blade pitch control device comprising a pitch rod operating a pitch lever for each rotor blade.
BACKGROUND OF THE INVENTION
The invention relates more particularly to a so-called “articulated” rotorcraft rotor as described in FR 2 456 034, FR 2 516 891 and FR 2 671 049.
The above patents disclose a rotorcraft rotor, such as a helicopter main rotor or tail rotor, which comprises:
a tubular pylon adapted to be driven in rotation about its axis, which is the rotation axis of the rotor, from its foot,
a hub attached to the pylon by a flared base and comprising two annular plates substantially radial to the rotor axis and spaced from each other along the rotor axis so that relative to the pylon one is an axially inside plate and the other is an axially outside plate,
at least two blades each of which has its root connected to the hub by retaining and articulation means retained between said plates of the hub and enabling relative angular movement of the blade at least in pitch about a longitudinal blade pitch change axis and controlled by displacement by a pitch rod of a pitch lever attached to the blade root.
Compared to articulated rotors with a single plate hub, as described in FR 2 427 251, or with an integrated tubular pylon-hub, as described in FR 2 584 996, dual plate hub articulated rotors of the type referred to above have the advantage of improved resistance to centrifugal forces and to shear forces and static and dynamic flapping and drag bending moments for substantially the same overall size, mass and aerodynamic drag.
Like the single plate hub or integrated tubular pylon-hub rotors described in FR 2 427 251 and FR 2 584 996, respectively, the dual plate hub articulated rotors described in FR 2 456 034, FR 2 516 891 and FR 2 671 049 can be equipped with pitch control devices entirely external to the pylon-hub assembly, generally in the case of main rotors, or entirely internal to the tubular pylon and to the hub connection base, generally in the case of tail rotors, or partly internal to the tubular pylon and external to the hub, with a collective pitch control plate usually called the spider plate axially external of the hub, in the particular case of tail rotors.
In pitch control devices entirely external to the pylon-hub assembly the pitch lever of each blade is articulated to one end of a pitch rod external to the base connecting the tubular pylon to the hub and the other end of which is articulated to a pitch control plate that surrounds the rotor pylon, with which this plate is constrained to rotate and around which this plate is mobile at least in the axial direction.
In the case of a main rotor this pitch control plate is generally the rotating plate of a set of cyclic plates in which the rotating plate is rotatably mounted on a non-rotating plate that can be moved in axial translation and inclined in any direction about the axis of the rotor by controls operated by the pilot.
The above pitch control devices are too complex, with too large an overall size around the rotor pylon and too high a mass to be economically transposed to controlling the collective pitch of the blades of a tail rotor, for which all that is required is to move the rotating pitch control plate axially.
For this reason pitch control devices for tail rotors internal to the pylon-hub assembly have been proposed that include a pitch control plate that rotates with the rotor and slides axially inside the base connecting the pylon to the hub, being articulated, for each blade, to a pitch rod that is also internal of the assembly and is itself articulated to a pitch lever on a radial inner armature of the means for retaining each blade on the hub and articulating it thereto, so that the pitch lever is also inside the pylon-hub assembly.
This complicates the structure of the radially inner armature and increases its overall size and its mass, and therefore its cost, as well as increasing the eccentricity of flapping of the rotor and its aerodynamic drag.
What is more, placing the pitch rods inside the pylon-hub assembly complicates maintenance and makes it more costly, in that checking the pitch rod ball joints for play is complicated, as is any work to be carried out on the ball joints in order to replace them.
What is more, the dimensions and therefore the mass and the drag of a tail rotor of the above kind with internal pitch control are further increased if the dimensions of the spherical laminated thrust bearing included in the means for retaining each blade on and articulating it to the hub of an articulated rotor of the above kind must be increased to increase the service life of those units, which accentuates the drawbacks associated with the use of internal pitch controls.
The problem to which the invention is directed is that of remedying the aforementioned disadvantages and proposing an articulated rotor of the type described hereinabove equipped with a pitch control device that is better suited to the various requirements of the art than the prior art devices, in particular for tail rotors.
OBJECT AND SUMMARY OF THE INVENTION
The aim of the invention is therefore to propose a rotor of the type described hereinabove in which the means for retaining the blades on and articulating them to the hub can be dimensioned as required in terms of service life without excessively increasing the eccentricity of the rotor and are combined with a pitch control device which is simple to maintain, in particular in respect of the pitch rod joints, combined with a reduction in mass and aerodynamic drag compared to the prior art.
To this end, in a rotorcraft rotor in accordance with the invention of the type described hereinabove and disclosed in particular in FR 2 671 049 the base has lateral openings through which pass arms of a pitch control plate constrained to rotate with the hub and mobile at least axially in the base, the end of each arm, outside the base, being articulated to one end of a pitch rod articulated at the other end to the pitch lever of a respective rotor blade.
The resulting structure has many advantages: installing the pitch rods outside the pylon and the hub connecting base simplifies maintenance by greatly simplifying checking the rod ball joints for play and replacing them. The radially inner armature of the spherical laminated thrust bearings does not have to support the pitch lever, which can conventionally project laterally from the leading edge or the trailing edge of the blade root, radially outside the hub, and the external position of the pitch rods also significantly reduces the eccentricity of the rotor. Note finally that the external pitch rods of the rotor of the invention are less heavily loaded by centrifugal forces and control forces than prior art internal pitch rods.
To summarize, installing the pitch rods outside the pylon in the rotor of the invention is a significant improvement in terms of mass, aerodynamic drag and direct maintenance costs compared to rotors with the same general architecture but equipped either with internal pitch rods or with a spider plate disposed axially outside the hub and moved axially by means disposed inside the tubular pylon, in which case the pitch rod is replaced by a linkage partly accommodated in the pylon-hub and comprising, externally thereof, a small connecting rod between the pitch lever of each blade and a spider plate arm.
To retain adequate stiffness and adequate strength at the base connecting the tubular pylon to the hub, it is advantageous if the number of lateral openings in the base is equal to the number of blades and each opening has an arm of the pitch control plate passing through it, the openings being equi-angularly distributed in the circumferential direction on the base and each opening being offset in the circumferential direction relative to the retaining and articulation means of the corresponding blade, on the same side of th
Legendre Philippe Maurice Rene
Rampal Etienne Jean
Eurocopter
Look Edward K.
Piper Marbury Rudnick & Wolfe
Rodriguez Hermes
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