Air propeller blade pivot in the shape of a spherical cap

Abstract

A pivot for an air propeller blade, the pivot including a rotary support for mounting radially on a propeller hub while being suitable for pivoting about a pivot axis; and a blade support including a housing for receiving a blade root and at least one arm extending laterally relative to the pivot axis and carrying a flyweight forming a counterweight; the arm and its flyweight presenting the general geometrical shape of a spherical cap.

Claims

1. A pivot for an air propeller blade, the pivot comprising: a rotary support for mounting radially on a propeller hub while being suitable for pivoting about a pivot axis; and a blade support including a housing for receiving a blade root and an arm extending laterally relative to the pivot axis and carrying a flyweight forming a counterweight, wherein the arm and the flyweight present the general geometrical shape of a spherical cap facing the rotary support with a double curvature, the arm and the flyweight having a first section that is curved in a longitudinal plane defined by the pivot axis and a direction in which the arm extends, and having a second section that is curved in a transverse plane defined by the pivot axis and a direction in which the housing extends.

2. The pivot according to claim 1, wherein the arm and its flyweight have a section that is curved in a longitudinal plane and a section that is curved in a transverse plane.

3. The pivot according to claim 1, wherein each of the first and second sections presents a respective radius of curvature lying in the range 200 mm to 400 mm for a propeller blade of a turboprop having a single propeller, and lying in the range 700 mm to 900 mm for a propeller blade of a turboprop having two contrarotating propellers.

4. The pivot according to claim 1, wherein at least the blade support is made of organic matrix composite material.

5. The pivot according to claim 1, wherein the blade support comprises two opposite arms extending laterally relative to the pivot axis and each carrying a flyweight forming a counterweight.

6. The pivot according to claim 1, wherein the blade support arm is connected to the housing via a portion of curved profile.

7. The pivot according to claim 1, wherein the blade support arm is connected to the housing via a portion of rectilinear profile.

8. The pivot according to claim 1, wherein the blade support housing is a socket oriented in a direction that is substantially perpendicular to the arm.

9. An air propeller comprising a plurality of blades, each mounted in a pivot according to claim 1.

10. An aircraft turboprop including at least one propeller according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings, which show embodiments having no limiting character. In the figures:

(2) FIG. 1 is a diagrammatic view in longitudinal half-section of a turboprop having two unducted propellers to which the invention applies in particular;

(3) FIG. 2 is a diagrammatic view showing the operation of a propeller blade pivot;

(4) FIGS. 3 and 4 are perspective views of a propeller blade pivot in a first embodiment of the invention, seen respectively from above and from below;

(5) FIG. 5 is a longitudinal section view of the pivot of FIGS. 3 and 4;

(6) FIG. 6 is a cross-section view of the pivot of FIGS. 3 and 4;

(7) FIGS. 7 and 8 are perspective views of a propeller blade pivot in a second embodiment of the invention, seen respectively from above and from below; and

(8) FIG. 9 is a longitudinal section view of a propeller blade pivot in a third embodiment of the invention.

MORE DETAILED DESCRIPTION

(9) The invention applies to any aircraft turboprop having at least one propeller with variable pitch blades, and in particular it applies to airplane turboprops having two unducted contrarotating propellers, such as the turboprop shown in FIG. 1.

(10) Such a turboprop 10 is known and is therefore not described in detail. Typically, it comprises a longitudinal axis 12 and an annular nacelle 14 arranged coaxially about the longitudinal axis. The turboprop 10 also comprises, from upstream to downstream: a compressor 16; a combustion chamber 18; and a turbine 20 having two contrarotating rotors 22a and 22b, these various elements also being arranged coaxially around the longitudinal axis 12 of the turboprop.

(11) The turboprop 10 also has an upstream (or front) propeller 24a and a downstream (or rear) propeller 24b having fan blades 26 of adjustable pitch. More precisely, the fan blades 26 of each propeller 24a, 24b are mounted on respective rotary rings 28a, 28b centered on the longitudinal axis 12 of the turboprop. Each rotor 22a, 22b of the turbine 20 carries and drives in rotation a respective one of the rotary rings 28a, 28b having one of the propellers 24a, 24b mounted thereon. Alternatively, the propellers 24a, 24b could be driven in rotation by a single rotor of the turbine via stepdown gearing.

(12) The fan blades 26 of the two propellers 24a, 24b are of adjustable pitch, i.e. each of them can pivot about its longitudinal axis in order to adapt the orientation of its leading edge to the engine speed and/or to pilot controls.

(13) For this purpose, and as shown in FIG. 2, each fan blade 26 is mounted on a pivot 30 that is to be mounted radially on the corresponding rotary ring 28a, 28b while being suitable for pivoting in this orifice about a pivot axis Z of the pivot. Pivoting of the pivot 30 relative to the rotary ring 28a, 20b thus causes a change in the orientation of the leading edge of the corresponding fan blade. This pivoting is obtained by conventional actuator devices of hydraulic or electrical type.

(14) In the event of an engine failure, it is advantageous for each fan blade 26 to be capable of being feathered automatically, i.e. so as to have an angle of attack relative to the relative wind V.sub.R that is substantially zero. Furthermore, passive means are provided to keep the fan blades 26 feathered, even in the event of a failure of the actuator devices for pivoting the pivots 30. Specifically, the center of thrust L of each blade may be offset relative to the pivot axis Z of the pivot 30, thereby generating aerodynamic torque M.sub.A tending to cause the blade to pivot. In addition, inertia torque M.sub.i is also generated, as a result of the center of gravity G being offset relative to the pivot axis Z.

(15) In order to counter these torques M.sub.A and M.sub.i, and in order to keep the blade feathered, counterweight-forming flyweights 32 are typically mounted at the free ends of arms 34 that extend laterally relative to the pivot axis Z. These arms are oriented substantially perpendicularly to the pressure and suction sides of the blade 30 (angle ? lying in the range ?30? relative to a plane normal to the socket of the pivot receiving the blade root), in such a manner that when the propeller is rotating about its axis of rotation O, the centrifugal forces F.sub.C acting on the flyweights 32 tend to bring the main direction Y of the arms 34 into alignment with a tangential direction Y of the propeller, thereby countering the aerodynamic and inertia torques M.sub.A and M.sub.i and bringing the blade back into alignment with the direction of the relative wind V.sub.R.

(16) FIGS. 3 and 4 are perspective views of a propeller blade pivot 30 in a first embodiment of the invention.

(17) In this embodiment, the propeller blade pivot 30 comprises a rotary support 36 and a blade support 38. The rotary support 36 is in the form of a hollow cylinder centered on the pivot axis Z of the pivot. This rotary support 36 is for mounting radially on the respective rotary ring of the turboprop, while being capable of pivoting about the pivot axis Z.

(18) The blade support 38 comprises in particular a housing, e.g. a socket 40 in the form of a slot, that is for receiving a blade root, together with two opposite arms 34 (namely a pressure side arm 34a and a suction side arm 34b) extending laterally relative to the pivot axis Z from the socket.

(19) In the examples shown in the figures, the housing for the blade root is in the form of a slot. Naturally, it is possible to envisage other types of housing as a function of the selected application, and in particular a cylindrical housing when the blade root is cylindrical in shape.

(20) The arms 34 extend in a direction Y that is perpendicular to the pivot axis Z, and the socket 40 extends in a direction X that is perpendicular to the pivot axis Z and to the direction Y of the arms 34a, 34b. Furthermore, each arm carries a counterweight-forming flyweight 32 at its free end.

(21) In the invention, each arm 34a, 34b together with its flyweight 32 present the general geometrical shape of a spherical cap.

(22) The term shape of a spherical cap is used herein to mean that each arm and the flyweight that it carries present the shape of a portion of a sphere that has been truncated by a plane (other than a midplane).

(23) In other words, the arm and its flyweight present the shape of an inwardly-facing vault (i.e. facing towards the rotary support 36), with double curvature.

(24) Thus, and as shown in FIG. 5, which is a longitudinal section view of the pivot 30 (i.e. a view in a plane defined by the pivot axis Z and the direction Y of the arms 34), each arm 34a, 34b and its flyweight 32 presents a section that is curved with a first radius of curvature R.sub.c1.

(25) Likewise, FIG. 6 shows the propeller blade pivot of the first embodiment in a cross-section view, i.e. a view in a plane defined by the pivot axis Z and the direction X of the socket 40 (FIG. 6 is also a section view on plane VI-VI of FIG. 5).

(26) In this cross section plane, the suction side arm 34b and its flyweight 32 likewise present a section that is curved with a second radius of curvature R.sub.c2. Although not shown in the figures, the pressure side arm 32b and its flyweight also present a section that is curved in this cross section plane.

(27) For a pivot in which the distance between the centers of gravity of the flyweights 32 and the pivot axis Z lies in the range 100 mm to 300 mm, the radii of curvature R.sub.c1 and R.sub.c2 lie in the range 200 mm to 400 mm (for a turboprop propeller blade) and in the range 700 mm to 900 mm (for a propeller blade of a turboprop having two contrarotating propellers).

(28) It should be observed that when the pivot presents two arms provided with flyweights, the difference between the radial distances of the centers of gravity of the two flyweights relative to the pivot axis Z should be minimized.

(29) Furthermore, still with the presence of two arms, the radial positions of the flyweights should preferably be different in order to avoid any conflict during rotation of the pivots relative to one another. In other words, the radii of curvature R.sub.c1 are different for the pressure side arm 34a and for the suction side arm 34b of any given pivot.

(30) In the first embodiment, the two arms 34a and 34b of the blade support 36 are connected to the socket 40 by portions 42 of curved profile.

(31) The paths between the arms 34a, 34b and the central region of the pivot provided with the socket 40 are thus continuous, thereby better distributing the traction and compression stresses that are induced by the arms bending. In particular, the arms are connected to the socket and they also extend upstream and downstream therefrom, while conserving their double curvature (in the planes X-Z and Y-Z).

(32) As a result, if a composite material is used for making the blade support, the section of the composite material is maximized in the region where the stresses induced by bending of the arms are large.

(33) It should be observed that the arms could be elements that are added to the blade support, e.g. using assembly means of the bolting type or involving co-operation between male and female shapes.

(34) FIGS. 7 and 8 are perspective views of a propeller blade pivot 30 in a second embodiment of the invention.

(35) The pivot 30 differs from the above-described pivot in that the two arms 34a and 34b of the blade support 38 are connected to the socket 40 by portions 44 of rectilinear profile. In other words, the central region of the pivot having the socket 40 is truncated in comparison with the central region shown in FIGS. 5 and 6. Thus, compared with the above-described embodiment, the blade pivot 30 is of reduced weight.

(36) FIG. 9 is a longitudinal section view of a propeller blade pivot 30 in a third embodiment of the invention. In this embodiment, the blade support 38 has only one arm 34. The other characteristics are identical to those described with reference to either of the two above-described embodiments. In particular, the arm 34 and its flyweight 32 in this embodiment likewise present the general geometrical shape of a spherical cap.

(37) In an advantageous provision that is common to all of the described embodiments, at least the blade support (and possibly also the rotary support) is made of an organic matrix composite material.

(38) Typically, the organic matrix composite material that is used comprises fibers embedded in an organic matrix, and more specifically a polymeric matrix. The fibers may in particular be carbon fibers, glass fibers, polyamide fibers, or polyethylene fibers, etc. These fibers may be arranged in layers that are unidirectional, woven in two or three dimensions, and/or braided. They are embedded in an organic matrix, more specifically a polymeric matrix, which may be formed in particular by a thermosetting resin such as an epoxy resin, or by other thermosetting resins that are better adapted to high temperatures.

(39) Reference may be made to the French patent applications numbers 13/54427 and 13/54428 filed by the applicant on May 17, 2013, the content of which is incorporated herein by reference. Those patent applications describe various embodiments of a propeller blade pivot made at least in part out of an organic matrix composite material.