Fluid reaction surfaces (i.e. – impellers) – With weight-balancing means – Self-shifting or selectively adjustable mass
Reexamination Certificate
2001-04-23
2002-12-17
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With weight-balancing means
Self-shifting or selectively adjustable mass
C416S500000
Reexamination Certificate
active
06494680
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a rotorcraft rotor, particularly a helicopter main rotor, comprising a rotor head at which a hub intended to be driven in rotation about an axis of the rotor is connected to at least two rotor blades, the rotor also comprising a rotor head vibration suppressor also known as a rotor head resonator, that is to say a device for attenuating the vibrations generated by the movement of the rotationally driven rotor, the vibration suppressor being used at the rotor head to effectively counter the vibrations directly at the source where they are produced.
The desired effect is to improve the vibration comfort in the cabin of a helicopter by reducing the level of vibration in the cabin as far as possible using a rotor head vibration suppressor the weight and cost of which are as low as possible, the structure of which is as simple as possible, and which is economical to maintain, while at the same time being highly effective.
The level of vibration in the cabin of a helicopter depends chiefly on the dynamic excitation of the main rotor and on the dynamic response of the helicopter structure. The dynamic excitation of the rotor results from the aerodynamic loadings on the rotor blades and can be broken down into, on the one hand, a force in the plane of the rotor, or coplanar force, exerted in a plane perpendicular to the axis of rotation of the rotor, and, on the other hand, into a force said to be “vertical” because it is exerted along the axis of the rotor, and into a moment said to be “coplanar”, in a plane perpendicular to the axis of the rotor.
It is known that the frequencies of the “vertical” forces along the axis of the rotor in a rotating frame of reference are multiples of b&OHgr; where b is the number of rotor blades and &OHgr; is the angular speed of rotation of the rotor and that the frequencies of the coplanar moments applied to the rotor are (nb−1)&OHgr; or (nb+1 )&OHgr;, where n is an integer at least equal to 1.
For these reasons, known rotor head vibration suppressors, designed to reduce the dynamic excitation of the rotor, are essentially of two types, the first type relating to coplanar vibration suppressors for countering the forces in a plane perpendicular to the axis of the rotor, and the second type relating to “vertical” or “flap” vibration suppressors for attenuating forces and vibrations parallel to the axis of the rotor and generated by the flapping of the blades, and to counter the coplanar moments.
FR-A-2 733 483 and U.S. Pat. No. 5 639 214 have recently proposed that the well known coplanar vibration suppressors with at least one mass urged by at least one spring, or of the type known as “bifilar”, be replaced by pendular coplanar vibration suppressors comprising at least one pendular body mounted to oscillate on a support coaxial with the rotor mast and driven in rotation about the axis of the rotor, directly by the rotor head, and so that the pendular body can oscillate about an axis of pendular movement which is spaced away both from the center of inertia of the pendular body and from the axis of the rotor to which the axis of pendular movement is substantially parallel.
The pendular bodies of such pendular coplanar vibration suppressors therefore move in a plane parallel to the plane of the rotor, or even coincident with it, and their movements generate coplanar inertial forces which oppose the forces exerted in the plane of the rotor.
The “vertical” or “flap” vibration suppressors most commonly used are also pendular vibration suppressors comprising at least one pendulum for each rotor blade, that is to say at least two pendulums per rotor and each pendulum comprises at least one pendular body connected by at least one rigid arm to a support driven in rotation about the axis of the rotor and on which the pendulum is mounted to oscillate via a pivoting connection about an axis of pendular movement spaced away from the center of inertia of the pendulum and from the axis of the rotor. However, in these known “vertical” pendular vibration suppressors, the support is mounted transversely on or in the root of the corresponding blade or the connecting member, generally known as the cuff, connecting this blade to the hub, the axis of pendular movement then being substantially perpendicular to the longitudinal axis or pitch-change axis of the corresponding blade, which is an axis that is substantially radial with respect to the axis of the rotor, to which the axis of pendular movement may also be substantially perpendicular when the pitch of the corresponding blade is neutral.
Pendular vibration suppressors of the coplanar or vertical type have the advantage of being more lightweight than vibration suppressors of the other known types, because pendular vibration suppressors use centrifugal force as the force that returns the pendular bodies, which allows them to adapt to suit the variations in rotor rotational speed, and therefore makes them self-adapting or self-adjusting, if the influence of the speed of travel of the helicopter is neglected.
Furthermore, pendular “vertical” vibration suppressors, which oppose the vertical forces of the rotor and the coplanar moments, have the advantage that the pendulums mounted on the blades or on the flapping masses consisting of the blades with their cuffs that connect them to the hub, pivot about axes of pendular movement which are relatively distant from the center of the hub, which makes it possible to increase the maximum tuning frequency and the effectiveness of the pendulums.
These embodiments, known in particular from U.S. Pat. No. 4,239,456 and GB-2 123 371, do, however, have two major drawbacks. First of all, the blade pendulums are difficult to adjust because they are subjected to the changing pitch of the blades. Secondly, the presence of the pendulums on the blades increases the stresses along the blades, both in terms of drag and in terms of flapping, and for various rotor harmonics.
Hence, the blade pendulums affect the dynamic response of the blades and, more specifically, the stresses in the blades increase at the frequency to which the vibration suppressor is tuned, in particular, and at the harmonics of the rotor speed, in general.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to overcome these drawbacks of the known blade, or more generally, flapping mass, pendular vibration suppressors and to propose a “vertical” and pendular rotor head vibration suppressor, the operation and adjustment of which are not hampered by the pitch of the blades, which does not affect the dynamic response of the blades, does not introduce additional stress along the blades, and remains of a simple and economical structure, easy to maintain and of a limited mass while at the same time being highly effective, and which can be incorporated compactly into the rotor head.
To this end, the pendular “vertical” vibration suppressor equipping the rotorcraft rotor of the type described hereinabove is a vibration suppressor which comprises at least two pendulums, each of which comprises at least one pendular body connected by at least one rigid arm to said hub so that each pendulum rotates as one with said hub about the axis of the rotor, and mounted so as to oscillate with respect to said hub via a pivoting connection about an axis of pendular movement which is spaced from the center of inertia of the pendulum and from the axis of the rotor and is substantially perpendicular to a radial plane passing through the axis of the rotor and through the center of inertia of the corresponding pendulum without the possibility of the pendulum oscillating about an axis parallel to the axis of the rotor and concurrent with the axis of pendular movement so as to attenuate vibrations generated by the movement of the rotor, and is one wherein the mass and the inertia of each pendulum of a first group of at least two pendulums, and its lever arm between its center of inertia and the axis of pendular movement, and the radius of attachment between the axis of the pendular
Edgar Richard A.
Eurocopter
Look Edward K.
Piper Rudnick
LandOfFree
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