Method for modifying the collective and cyclic blade pitch of a turbomachine propeller

Abstract

The present description relates to a method for modifying a collective pitch and a cyclic pitch of blades (2) for a propeller (1) of a turbomachine, comprising the following steps: - translation of a plate assembly (10) along a propeller axis (R) so as to modify the collective pitch of the blades (2), - modification of the inclination of the plate assembly (10) with respect to a plane normal to the propeller axis (R) so as to modify the cyclic pitch of the blades (2), in which the translation and the modification of the inclination of the plate assembly (10) are obtained by actuation of a cylinder (20) mounted on the plate assembly (10) between a first stroke corresponding to a minimum collective pitch (Col_min) and a minimum cyclic pitch (Cyc_min), and a second stroke corresponding to a maximum collective pitch (Col_max) and a minimum cyclic pitch (Cyc_max). Figure for the abridged version: Fig. 4

Description

Title of the invention: Method for modifying the collective and cyclic blade pitch of a turbomachine propeller technical field

[0001] The present exposition relates to the general technical field of aircraft equipped with a turbomachine including a propeller, and more particularly to a method allowing the collective and cyclic pitching of the propeller blades. STATE OF THE ART

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0006] One of the approaches identified to improve the propulsive efficiency of aircraft engines, reduce their fuel consumption and the noise generated by the propulsion module, is to increase the bypass ratio (or BPR), which corresponds to the The ratio of the secondary airflow mass flow rate to the primary airflow mass flow rate. However, improving the bypass ratio generally also implies an increase in the diameter of the propulsion module, and consequently, in the external dimensions of the propulsion system. This results in an increase in the mass, fuel consumption, and drag of the propulsion system, as well as more difficult integration within the aircraft. Furthermore, engines with a high bypass ratio are subject to a mechanical stress known as "IP" (Infrared Pressure), which is predominant and must be taken into account in the engine's sizing and design.

[0007] In the context of this description, the term "turbomachine" refers to all gas turbine devices that produce the thrust necessary for the propulsion of an aircraft, particularly an airplane, by reaction to the high-speed ejection of gas, primarily by the propeller. The term "propeller" refers to a fan rotor, for example, a shrouded or unshrouded fan rotor.

[0008] In particular, the airflow inlet to the blades of a turbomachine propeller may have an angle of incidence with respect to the axis of rotation of the blades. This angle of incidence results notably from predictable phases, such as the aircraft's angle of attack during takeoff, climb, or descent. Figure 1a illustrates, for example, an aircraft in cruise at a stabilized altitude, with the airflow F inlet to the propeller blades directed along the axis of rotation R of the propeller. Figure 1b represents an aircraft in climb, with the airflow F comprising a longitudinal component directed along the axis of rotation R of propeller 1 and a transverse component in a plane perpendicular to the axis of rotation R of propeller 1. The blades of propeller 1 are then subjected to an airflow distribution that is not homogeneous during their rotation, which generates asymmetrical thrust on the blades.The thrust then includes a longitudinal component, but also a transverse component corresponding to parasitic forces directed in a plane normal perpendicular to the axis of rotation R of the propeller 1. In addition to the loss of thrust caused, these parasitic forces generate parasitic moments, called "IP moment" in the aeronautical field, applied to the blades.

[0009] IP moments are critical to the mass of the blade structure and all the components that transmit forces to the aircraft. An increase in IP moments therefore leads to an increase in the mass of these components. Furthermore, significant IP moments are likely to increase wear and thus reduce the service life of the propeller and the components securing the turbomachine to the aircraft, necessitating more frequent maintenance and component replacement. IP moments have an impact on ducted architectures such as turbofans, particularly when their bypass ratio is high, despite some flow straightening by the nacelle. IP moments are particularly critical for the propeller structure and the optimization of its operation for unducted architectures, such as turboprops, or "open rotors" or "unducted fans," which allow for a higher bypass ratio compared to conventional turbofans. IP moments are also critical for buried turbomachinery, as a thrust asymmetry is likely to appear between the enclosed and free-swimming parts of the propeller.

[0010] Systems for controlling the collective pitch of the blades are known, capable of modifying the pitch of all the propeller blades identically and simultaneously. However, these systems do not allow for the reduction of the IP moments resulting from a non-homogeneous distribution of airflow over the blades.

[0011] Existing cyclic pitch control systems for propeller blades, particularly in the field of helicopters, are capable of imposing a pitch on each propeller blade that varies cyclically according to its angular position during rotation. The resulting thrust differential allows for adjusting the flight direction to control the helicopter. However, these systems are not suited to the constraints, needs, and architectures encountered in other aircraft, such as airplanes.

[0012] French patent document FR 2 997 138 describes a system for controlling the cyclic pitch of propeller blades by modifying the inclination of a component articulated on the blades by means of three servovalves. The pitch is determined by pre-established laws in order to reduce losses caused by obstacles known in advance. This system therefore requires prior knowledge and simulation of flow inhomogeneities and does not allow for real-time adaptation of the cyclic pitch of the blades according to the phases encountered by the aircraft during flight. Furthermore, the system enabling control of the cyclic pitch of the blades, particularly with the three additional servovalves, results in a significant increase in the mass and size of the turbomachine.

[0013] French patent FR 3 101 664 describes a system for controlling the cyclic pitch of propeller blades. The cyclic pitch is achieved by moving several actuators using a cyclic pitch control that is calculated in response to measurements taken by force sensors, based on the forces encountered by the aircraft during flight. However, the system enabling cyclic pitch requires the implementation of an additional control loop, dedicated sensors, and additional actuators, resulting in a significant increase in the complexity, mass, and size of the turbomachine. GENERAL STATEMENT

[0014] One object of the present application is to remedy the aforementioned drawbacks, by proposing a method for modifying a collective pitch and a cyclic pitch of blades for a propeller of a turbomachine, which is simplified and has a reduced impact on the mass and size of the turbomachine.

[0015] Another objective of the present application is to propose a method for modifying a collective pitch and a cyclic pitch of blades which makes it possible to reduce in real time during flight the IP moments generated on the blades.

[0016] To this end, the application is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft.

[0017] The application relates to a method for modifying a collective pitch and a cyclic pitch of blades for a turbomachine propeller, comprising the following steps: - translation of a plate assembly along a propeller axis in order to modify the collective pitch of the blades, - modification of the inclination of the entire swashplate relative to a plane normal to the propeller axis so as to modify the cyclic pitch of the blades, in which the translation and the modification of the inclination of the entire swashplate are obtained by actuation of a cylinder mounted on the entire swashplate between a first stroke corresponding to a minimum collective pitch and a minimum cyclic pitch, and a second stroke corresponding to a maximum collective pitch and a minimum cyclic pitch.

[0018] The first stroke may correspond to a minimum cylinder stroke and the second stroke may correspond to a maximum cylinder stroke.

[0019] An actuation of the cylinder between the first stroke and the second stroke can lead to a progressive increase in the collective and cyclic stall according to a linear correlation relationship between the collective and cyclic stall.

[0020] An actuation of the cylinder between the first stroke and the second stroke can lead to an increase in collective and cyclic stall according to a non-linear correlation relationship between collective and cyclic stall.

[0021] An actuation of the cylinder between the first stroke and an intermediate stroke between the first stroke and the second stroke can lead to an increase in collective stall without an increase in cyclic stall.

[0022] An actuation of the cylinder between the intermediate stroke and the second stroke can lead to an increase in cyclic stalling, with or without an increase in collective stalling.

[0023] The actuator can be actuated according to a phase of flight of the aircraft. For example, the actuator can be actuated until it reaches the first stroke when the aircraft is During a descent phase, the actuator can be actuated to its second stroke when the aircraft is in a takeoff or climb phase. The actuator can also be actuated to its intermediate stroke when the aircraft is in a cruise phase. DESCRIPTION OF THE FIGURES

[0024] Fig. 1a, already commented on, represents a schematic view of an aircraft during a stabilized flight phase.

[0025] Fig. 1b, already commented on, represents a schematic view of an aircraft during a climb phase.

[0026] Fig. 2a represents a schematic side view of a collective and cyclic blade leveling system according to one embodiment, the entire slab assembly being non-inclined.

[0027] Fig. 2b represents a schematic front view of blades of a propeller according to one embodiment, the blades having zero cyclic pitch.

[0028] Fig. 3a represents a schematic side view of a collective and cyclic blade leveling system according to one embodiment, the entire slab being inclined.

[0029] Fig. 3b represents a schematic front view of blades of a propeller according to one embodiment, the blades having a non-zero cyclic pitch.

[0030] Fig. 4 represents a schematic side view of a collective and cyclic blade pitching system according to a first embodiment.

[0031] Fig. 5 represents a schematic side view of a collective and cyclic blade pitching system according to a second embodiment.

[0032] Fig. 6 represents a correlated modification law of the collective pitch and the cyclic pitch of blades according to an embodiment.

[0033] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION Preliminary definitions

[0034] In the following description, upstream and downstream are defined with respect to the normal flow direction of the fluid through the operating turbomachine. Thus, an airflow passes through the turbomachine from upstream to downstream. The turbomachine extends around a longitudinal axis. A radial axis is an axis perpendicular to and passing through the longitudinal axis. A circumferential axis is an axis perpendicular to and not passing through the longitudinal axis. A longitudinal, radial, or circumferential direction corresponds to the direction of the longitudinal, radial, or circumferential axis, respectively. The longitudinal, radial, and circumferential directions are orthogonal to each other. The terms internal and external, respectively, are used with reference to a radial direction such that the internal part or face of an element is closer to the longitudinal axis than the external part or face of the same element.

[0035] The turbomachine may be a turbojet or a turboprop, more particularly an open-rotor or unducted-fan type turbojet. The term "propeller 1" is used to designate, for example, a turbofan fan propeller 1, a turboprop propeller 1, or an open-rotor propeller 1. The propeller 1 may be a wheel comprising a plurality of blades 2 that rotate about a propeller axis R and extend around the propeller axis R. The propeller axis R may correspond to the longitudinal axis of the turbomachine. The turbomachine includes a propeller shaft 3 adapted to drive the propeller 1 in rotation about the propeller axis R. The propeller shaft 3 may extend along the longitudinal axis of the turbomachine. A stator reference frame of the turbomachine is a reference frame in which the blades 2 of the propeller 1 are rotating during the operation of the turbomachine.A rotor frame of the turbomachine is a frame of reference in which the blades 2 of the propeller 1 are fixed during the operation of the turbomachine.

[0036] The turbomachine may include at least one compressor, a combustion chamber, a turbine, and an exhaust nozzle. For example, the turbomachine may be a twin-spool, twin-flow turbojet engine comprising, from upstream to downstream, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, and a low-pressure turbine. The high-pressure turbine drives the high-pressure compressor via a high-pressure shaft, and the low-pressure turbine drives the low-pressure compressor via a low-pressure shaft. The low-pressure turbine may also drive the fan either directly via the low-pressure shaft, which then corresponds to the propeller shaft 3, or via a reduction gear disposed between the low-pressure turbine and the fan.The gearbox is driven in rotation by the low-pressure shaft and drives the propeller shaft 3, which is then separate from the low-pressure shaft. The high-pressure and low-pressure shafts can be co-rotating or counter-rotating. During turbomachine operation, an airflow passes through the fan and then splits into a primary flow Fp and a secondary flow. The primary flow Fp flows in a primary flow channel and passes through the compressors, the combustion chamber, and the turbines, while the secondary flow flows in a secondary flow channel that is concentric with the primary flow channel and radially bounded outwards by the nacelle.

[0037] By pitching system, we mean a collective and cyclic pitching system for the blades 2 of a propeller 1 of a turbomachine. A blade axis P corresponds to an axis extending between an inner radial end and an outer radial end of blade 2. The pitch of a blade 2, or pitch angle, corresponds to the angle formed between the chord of blade 2 and the axis of rotation of the propeller 1 in which blade 2 is mounted. The chord of blade 2 is an abstract geometric segment extending, at a given height of the airfoil, i.e., at a given position along the blade axis P, between the leading edge and the trailing edge of blade 2. A low pitch, or large pitch, corresponds to the pitch of a blade 2 whose chord is generally aligned with the axis of rotation of propeller 1. A high pitch, or small pitch, corresponds to the pitch of a blade 2 whose chord has a large angle with respect to the propeller axis R. A change in the pitch of a blade 2 corresponds to a pivoting of the blade 2 around the blade axis P.

[0038] A collective pitch corresponds to a pitch common to all the blades 2 of the propeller 1. A collective pitch system is configured to modify the pitch of the blades 2 of the propeller 1, simultaneously and identically for each blade 2 of the propeller 1.

[0039] A cyclic pitch corresponds to a pitch specific to each blade 2 of the propeller 1, the pitch varying according to the angular position of the blade 2 around the propeller axis R. The cyclic pitch of the blades 2 can, in particular, be different for two adjacent blades 2. A cyclic pitch system is configured to adjust the cyclic pitch of each blade 2 of the propeller 1 during the rotation of the propeller 1 around the propeller axis R. Shimming system and shimming method

[0040] A collective and cyclic blade pitching system 2 for a propeller 1 of a turbomachine is illustrated by way of non-limiting example in Figures 4 to 5. The propeller 1 comprises a set of blades 2 that rotate about a propeller axis R. The pitching system comprises: - a plate assembly 10 that can be moved in translation along the propeller axis R so as to modify a collective pitch of the blades 2, the plate assembly 10 also being tiltable with respect to a plane normal to the propeller axis R so as to modify a cyclic pitch of the blades 2, - a cylinder 20 configured to move the entire platform assembly 10 in translation along the propeller axis R, and - a tilting system 30 which cooperates mechanically with the plate assembly 10 and is configured to tilt the plate assembly 10 relative to the plane normal to the propeller axis R, the actuation of the cylinder 20 mechanically triggering the tilting of the plate assembly 10 by means of the tilting system 30.

[0041] A method for modifying the collective pitch and cyclic pitch of blades 2 for a propeller 1 of a turbomachine includes the following steps: - translation of a plate assembly 10 along a propeller axis R so as to modify the collective pitch of the blades 2, - modification of the inclination of the plate assembly 10 with respect to a plane normal to the propeller axis R so as to modify the cyclic pitch of the blades 2.

[0042] The translation and the modification of the inclination of the entire plate 10 are obtained by actuation of a cylinder 20 mounted on the entire plate 10 between a first stroke corresponding to a minimum collective setting Col_min and a minimum cyclic setting Cyc_min, and a second stroke corresponding to a maximum collective setting Col_max and a minimum cyclic setting Cyc_max.

[0043] The pitch control system described above, as well as the pitch modification method described above, allows for both collective and cyclic pitch control to be applied to the blades 2 of the propeller 1. The collective and cyclic pitch control of the blades 2 are correlated to each other so as to balance the forces exerted by the airflow on the blades 2, thereby reducing parasitic forces due to a non-homogeneous airflow distribution. Thus, the aerodynamic moments IP generated on the blades 2 of the propeller 1 can be reduced. The pitch control system and the pitch modification method therefore enable a reduction in mass and a decrease in wear on the structures bearing the moments IP, such as the blades 2 or the parts ensuring the transmission of forces to the aircraft.

[0044] The tilting system 30 mechanically modifies the tilt of the plate assembly 10 relative to the normal plane according to the position of the plate assembly 10 along the propeller axis R. Thus, the tilting system 30 allows a mechanical and passive coupling of the collective and cyclic pitching, the cyclic pitching being imposed by the collective pitching. Indeed, the movement of the entire swashplate assembly 10 by the actuator 20 along the propeller axis R modifies the collective pitch of the blades 2 and mechanically triggers, via the tilting system 30, a change in the tilt of the entire swashplate assembly 10, the tilt modifying the cyclic pitch of the blades 2. This mechanical correlation makes it possible to manage the collective and cyclic pitch of the blades 2 by means of a simplified pitching system, which does not require additional servo control or control loop compared to a system that would only manage the collective pitch of the blades 2.The shimming system therefore offers reduced mass and size, and improved reliability compared to current collective and cyclic shimming systems. Similarly, the shimming method allows for modification of both collective and cyclic shimming using a single cylinder 20, without the need for additional servo control or control loops.

[0045] The pitching system and the pitching modification method allow, in particular, real-time compensation during the operation of propeller 1 of predictable IP moments, i.e., IP moments due to the aircraft's angle of attack. during a mission in flight phases for which a certain collective calibration is imposed, such as takeoff and climb phases with angle of attack.

[0046] The pitching system and the pitching modification method also allow unidirectional compensation of the IP moments exerted in a principal direction of forces, which corresponds for example to the direction of the blade axis P. Thus, the thrust asymmetry between the upward blades 2 and the downward blades 2 is compensated, which makes it possible to compensate the maximum IP moments, which are the most significant for the turbomachine.

[0047] More specifically, certain flight phases, such as the aircraft's angle-of-attack phases during takeoff or climb, cruise, descent, or approach, are predictable during a mission. These predictable phases are associated with predetermined collective pitch ranges. For example, a descent phase typically corresponds to low collective pitch values, i.e., large pitch steps; a cruise phase typically corresponds to collective pitch values ​​slightly higher than a descent phase; and a takeoff or climb phase with an angle of attack typically corresponds to collective pitch values ​​higher than the descent and cruise phases, i.e., small pitch steps.

[0048] However, these predictable phases, which correspond to different collective pitch settings, also present different IP moment compensation requirements. In particular, during the aircraft's angle-of-attack phases during takeoff or climb, the downward-moving blade 2 of propeller 1 experiences greater stress than the upward-moving blade 2, resulting in a thrust asymmetry between the upward and downward blades 2. This thrust asymmetry notably generates a yaw moment around the axis of blade P, as the IP moments are directed primarily along a principal direction of force corresponding to the axis of blade P. Thus, a takeoff or climb phase with an angle of attack generates high IP moments due to the aircraft's low speed and high angle of attack. Conversely, a descent phase generates low IP moments due to the aircraft's very low speed.Finally, a cruise phase generates low IP moments due to the high speed and low angle of attack of the aircraft.

[0049] Correlating the cyclic pitch with the collective pitch allows for optimization of the compensation of IP moments and the efficiency of the turbomachine. In fact, during predictable phases generating high IP moments that correspond to certain collective pitch values, a non-zero cyclic pitch can be imposed on the blades 2, so that the pitch of the blades 2 varies according to their angular position, in particular depending on whether the blade 2 is rising or falling, in order to compensate for, or even cancel out, the IP moments, particularly in the principal direction of forces. The [Fig. 3b] illustrates a non-limiting example of blades 2 of a propeller 1 exhibiting a non-zero cyclic pitch. Conversely, during predictable phases generating low IP moments, which correspond to other collective pitch values, a low or even zero cyclic pitch can be imposed on the blades 2. [Fig. 2b] illustrates a non-limiting example of blades 2 of a propeller 1 exhibiting a zero cyclic pitch. Tray set

[0050] The plate assembly 10, illustrated by way of non-limiting example in [Fig.4], is movable in translation along the helix axis R and tiltable with respect to the normal plane perpendicular to the helix axis R.

[0051] A zero inclination of the swashplate assembly 10 corresponds to a zero cyclic pitch of the propeller blades 2 of the propeller 1. A non-zero inclination of the swashplate assembly 10 with respect to the normal plane corresponds to a non-zero cyclic pitch of the propeller blades 2 of the propeller 1. The greater the inclination of the swashplate assembly 10 with respect to the normal plane, the greater the cyclic pitch of the propeller blades 2 of the propeller 1; that is, the greater the amplitude of the pitch variation of a blade 2 during its rotation around the propeller axis R. For example, the closer the swashplate assembly 10 is to the propeller 1, the greater the collective pitch.

[0052] The plate assembly 10 comprises at least one plate 11, 12. This at least one plate 11, 12 may be annular and disposed around the helix axis R, and may have rotational symmetry about the helix axis R. Thus, an inclination of the plate assembly 10 with respect to the normal plane results in an opposite displacement of the same magnitude of two diametrically opposite points of the plate 11, 12 of the plate assembly 10. The plate 11, 12 may have a substantially disc-like shape. A through cavity is provided in the plate 11, 12 so as to accommodate the propeller shaft 3, as illustrated in [Fig. 4].

[0053] The tray assembly 10 may include:

[0054] - a stator plate 11 mounted integrally with the cylinder 20 in translation along the axis propeller R,

[0055] - a rotor plate 12 mounted integrally with the rotor plate 12 inclined relative to the normal plan, and

[0056] - a rotational guide bearing 13 of the rotor plate 12 relative to the stator plate 11.

[0057] The stator plate 11 is fixedly mounted in the stator housing. The rotor plate 12 is mounted to rotate freely about the propeller axis R, and is driven in rotation about the propeller axis R during the operation of the propeller 1, the rotor plate 12 following the rotation of the blades 2 of the propeller 1. The stator plate 11 and the rotor plate 12 are independent in rotation about the propeller axis R thanks to the rotational guide bearing 13. The stator plate 11 and the rotor plate 12 are fixed in tilt by With respect to the normal plane, an inclination of the stator plate 11 results in an identical inclination of the rotor plate 12. Thus, when the rotor plate 12 is driven to rotate around the propeller axis R during the operation of the propeller 1, the stator plate 11 remains fixed in the stator frame. Conversely, an inclination of the rotor plate 12 with respect to the normal plane results in a corresponding inclination of the stator plate 11 with respect to the normal plane.

[0058] The rotor plate 12 and the stator plate 11 can be mounted fixed together in translation along the propeller axis R.

[0059] A rotational guide bearing 13 can be mounted between the rotor plate 12 and the stator plate 11. The rotational guide bearing 13 allows the forces to be transferred from the stator frame, in which the cylinder 20 and the stator plate 11 are located, to the rotor frame, in which the rotor plate 12 and the propeller blades 2 are located. The rotational guide bearing 13 can be a roller bearing or a double ball bearing with opposed angular contact. The rotational guide bearing 13 can comprise a rotor face integral with the rotating rotor plate 12, a stator face integral with the stator plate 11, and a bearing mounted between the two faces to isolate the two rotating faces. The rotational guide bearing 13 can be installed, in particular, at the level of recesses formed in each of the rotor plate 12 and the stator plate 11.Two rotation guide bearings 13 can be mounted between the rotor plate 12 and the stator plate 11, on either side of the propeller shaft R. Shimming ring

[0060] The shimming system may include a shimming ring 14 disposed around the propeller shaft R. The shimming ring 14 is mounted integrally with the cylinder 20 and the plate assembly 10 in translation along the propeller shaft R. The shimming ring 14 has an external face 141 adapted to cooperate by complementary shape with an internal face 111 of the stator plate 11, and where applicable with an internal face of the rotor plate 12, so as to guide a change in inclination of the plate assembly 10.

[0061] The shim ring 14 is mounted movable in translation along the propeller axis R to ensure the collective shimage of the blades 2, for example by means of rollers configured to allow sliding of the shim ring 14 on the propeller shaft 3 and rotation of the propeller shaft 3 relative to the shim ring 14, or by means of an annular bearing support of the intermediate housing of the turbomachine disposed around the propeller shaft 3 by means of at least one roller bearing.

[0062] The shim ring 14 can be mounted as a unit of the cylinder 20 and the stator plate 11. For example, the shim ring 14 can be mounted directly on the stator plate 11, with at least one connecting rod 142 being fixed to both the cylinder 20 and the stator plate 11. Alternatively, the shim ring 14 can be mounted on the cylinder 20 by means of at least one connecting rod 142 fixed to both the cylinder 20 and the shim ring 14, for example via pivot or ball joint connections.

[0063] The external face 141 of the shim ring 14 can be an annular convex face forming a ball joint, the internal face 111 of the stator plate 11 being concave and of complementary dimensions to the convex external face 141 of the shim ring 14. Thus, the external face 141 of the shim ring 14 guides a change in inclination of the plate assembly 10. Articulation system

[0064] Each blade 2 is thus pivotally mounted around the blade axis P on the propeller hub 1, so as to allow its pitch to be adjusted. More specifically, the root of each of the blades 2 can be mounted on the propeller hub 1 via a bearing.

[0065] The articulation system 40 articulates the plate assembly 10 relative to the blades 2, so that a translation of the plate assembly 10 along the propeller axis R results in a change in the collective pitch of the blades 2 and an inclination of the plate assembly 10 relative to the normal plane results in a change in the cyclic pitch of the blades 2.

[0066] The articulation system 40, illustrated by way of non-limiting example in [Fig. 2a] and [Fig. 3a], may include at least one connecting rod 401 linking the swashplate assembly 10 to a blade 2, and at least one pivot joint 402 linking the connecting rod 401 to the blade 2. More particularly, the articulation system 40 can articulate the rotor swashplate 12 relative to the blades 2. When the propeller 1 rotates, the blades 2 drive the swashplate assembly 10 in rotation about the propeller axis R via their respective pivot joints 402 and connecting rods 401. Alternatively, the articulation system 40 can allow the swashplate assembly 10 to be articulated on the blades 2 in any other conceivable configuration.

[0067] The articulation system 40 may include a set of connecting rods 401. Each connecting rod 401 is articulated at its distal end to an associated blade 2, for example via a pivot joint 402, and at its proximal end to the swashplate assembly 10, more specifically to the rotor swashplate 12. The connecting rods 401 are mounted to rotate freely around the propeller axis R. The movement of a connecting rod 401 causes the blade 2 to rotate, thereby changing its pitch. Thus, an inclination of the swashplate assembly 10, and therefore of the rotor swashplate 12, causes a cyclical movement of the connecting rods 401, which cyclically changes the pitch of the blades 2. In other words, a connecting rod 401 can be moved so as to rotate the blade 2 around a pivot depending on whether the connecting rod 401 is pulled or pushed by the swashplate assembly 10. When the blade 2 rotates around the pivot, its pitch is changed accordingly. Thus, an inclination of the entire platform 10 conditions the movement of the connecting rods 401..

[0068] More specifically, the connecting rods 401 can be distributed around the substantially circular outer circumference of the rotor plate 12, the arrangement of the connecting rods 401 corresponding substantially to the arrangement of the blades 2. Thus, an inclination of the outer plate with respect to the normal plane causes a corresponding inclination of the substantially circular outer circumference of the rotor plate 12, which results in an opposite and identical displacement of the proximal ends of two diametrically opposed connecting rods 401 on the outer circumference of the rotor plate 12. Therefore, the two blades 2 associated with the two diametrically opposed connecting rods 401 undergo an opposite and identical change in their pitch. The blades 2 of this system thus exhibit a continuously and cyclically variable pitch during a rotation of the blade 2.In other words, at each predefined angular position around the propeller axis R, the blades 2 take, during their successive passage through these predefined angular positions during the rotation of the propeller 1, a pitch associated with each of these predefined angular positions, as illustrated as an example in figure 4b. Jack

[0069] The cylinder 20 allows the entire plate assembly 10 to be moved in translation along the propeller axis R. Any other suitable means of movement for moving the entire plate assembly 10 in translation along the propeller axis R can be used instead of a cylinder 20.

[0070] The cylinder 20 can extend parallel to the propeller axis R. The cylinder 20 can be a hydraulic cylinder supplied with pressurized oil via its own supply line.

[0071] The cylinder 20 can be configured to move between a first cylinder stroke 20 corresponding to a minimum collective adjustment Col_min and a minimum cyclic adjustment Cyc_min, with minimal compensation for any IP moments, and a second cylinder stroke 20 corresponding to a maximum collective adjustment Col_max and a minimum cyclic adjustment Cyc_max, with maximum compensation for IP moments. The minimum collective adjustment Col_min can be zero. The minimum cyclic adjustment Cyc_min can be zero. The maximum collective adjustment Col_max is strictly positive. The minimum cyclic adjustment Cyc_max is strictly positive.

[0072] The first stroke of cylinder 20 may correspond to a stroke greater than or equal to a minimum stroke of cylinder 20. The second stroke of cylinder 20 may correspond to a stroke less than or equal to a maximum stroke of cylinder 20.

[0073] The minimum collective trim Col_min may correspond to the minimum operational collective trim Col_min encountered in flight, for example during an aircraft descent phase. The maximum collective trim Col_max may correspond to the collective trim The maximum operational cyclic pitch (Col_max) encountered in flight, for example during takeoff or climb, is determined by the maximum cyclic pitch (Cyc_max). The minimum cyclic pitch (Cyc_max) can be predetermined to optimize the compensation of IP moments during takeoff or climb, when the need for IP moment compensation is high. Therefore, the 30° tilt system is designed to generate a higher cyclic pitch, and thus greater IP moment compensation, during takeoff and climb phases at an angle of attack, which correspond to higher collective pitches, compared to descent phases, which correspond to lower collective pitches. The 30° tilt system is thus adapted to increase the cyclic pitch of the two blades as the collective pitch of the two blades increases.

[0074] The plate assembly 10 can be located along the propeller axis R in a position further away from the blades 2 of the propeller 1 for the first stroke of cylinder 20 than for the second stroke of cylinder 20, a displacement of the cylinder 20 between the first stroke and the second stroke bringing the plate assembly 10 closer to the blades 2 of the propeller 1.

[0075] The plate assembly 10 is mounted fixed in translation along the propeller axis R of the cylinder 20, in particular the sliding rod 201 of the cylinder 20. The stroke of the cylinder 20 therefore conditions the position and the collective pitch of the blades 2, and also conditions the cyclic pitch of the blades 2 due to the presence of the tilting system 30.

[0076] The cylinder 20 may include a fixed cylinder in the stator frame, for example mounted on a propeller shaft bearing support housing 3, and a sliding rod 201 capable of being moved in translation along the propeller axis R by means of a cylinder actuator 20 so as to achieve the different cylinder strokes 20. For example, in the first cylinder stroke 20, the sliding rod 201 may be fully retracted, the swashplate assembly 10 being in its furthest position relative to the blades 2. In the second cylinder stroke 20, the sliding rod 201 may be fully extended, the swashplate assembly 10 being in its closest position relative to the blades 2.The collective and cyclic pitch of the blades 2 can increase, regularly or irregularly, as the stroke of the cylinder 20 is increased, i.e. as the sliding rod 201 of the cylinder 20 is extended and the plate assembly 10 is brought closer to the blades 2.

[0077] In particular, the sliding rod 201 of the cylinder 20 can be mounted on the shim ring 14 or on the stator plate 11, in particular by means of at least one connecting rod fixed at a proximal end to the sliding rod 201 and at a distal end to the shim ring 14 or to the stator plate 11, for example by means of two such connecting rods arranged on either side of the propeller shaft 3.

[0078] The cylinder 20 can be arranged around the propeller shaft 3, a through cavity being provided in the cylinder 20 so as to accommodate the propeller shaft 3, as illustrated in [Fig. 4]. Alternatively, the cylinder 20 can be arranged on one side of the propeller shaft 3 and be connected to the swashplate assembly 10 by at least one connecting rod.

[0079] The cylinder 20 may also have an intermediate stroke included, or even strictly included, between the first stroke of cylinder 20 and the second stroke of cylinder 20. The tilting system 30 can be adapted to maintain a zero tilt of the entire platform 10 when the stroke of the cylinder 20 is less than the intermediate stroke, and to modify the tilt of the entire platform 10, according to any conceivable evolution, when the stroke of the cylinder 20 is greater than the intermediate stroke.

[0080] The intermediate stroke of cylinder 20 can correspond to a collective pitch setting representative of a cruise regime. The intermediate stroke of cylinder 20 corresponds to an intermediate collective pitch setting Col_int, which may or may not be strictly between the minimum collective pitch setting Col_min and the maximum collective pitch setting Col_max, and to an intermediate cyclic pitch setting Cyc_int, which may or may not be strictly between the minimum cyclic pitch setting Cyc_min and the minimum cyclic pitch setting Cyc_max. The intermediate collective pitch setting Col_int may be strictly positive and correspond to the operational collective pitch setting encountered in flight during a cruise phase of the aircraft.The intermediate cyclic timing Cyc_int can be predetermined to optimize IP moment compensation and fuel consumption; for example, it can be zero because during the cruise phase, the need for IP moment compensation is low and the turbomachine's fuel consumption must be particularly optimized. Tilting system

[0081] The tilting system 30 may include any system enabling a mechanical correlation of the position of the plate assembly 10 along the propeller axis R with a tilt of the plate assembly 10 around the normal plane.

[0082] In a first embodiment, illustrated by way of non-limiting example in [Fig.4], the tilting system 30 includes a guide cam 31 and the plate assembly 10 includes a guided element 15, the guided element 15 being configured to cooperate with an inner face 311 of the guide cam 31 so that a translation of the plate assembly 10 along the helix axis R has the effect of tilting the plate assembly 10 with respect to the plane normal to the helix axis R.

[0083] The guide cam 31 is fixed in the stator frame of the turbomachine. The inner face 311 of the guide cam 31 may include a guide rail adapted to modify the inclination of the plate assembly 10 by moving the guided element 15 of the stator plate 11 in the guide rail when the cylinder is actuation 20. The guided element 15 can be, for example, an external end, for example an external protrusion, of the stator plate 11. Alternatively, the guided element 15 can be a roller attached and fixed to the stator plate 11, in particular to the external end of the stator plate 11. The protrusion or the roller are each adapted to be engaged in the guide rail of the guide cam 31. The guide cam 31 can prevent the guided element 15, which is in the guide rail, from advancing as much as the rest of the stator plate 11 when the stroke of the cylinder 20 is greater than the intermediate stroke.

[0084] The inner face 311 of the guide cam 31 can have any shape adapted to guide a change in the inclination of the swashplate assembly 10 as a function of the stroke of the cylinder 20. The convexity of the guide cam 31 can be fixed or variable. Thus, the guide cam 31 allows for a wide variety of correlation relationships between the collective pitch and the cyclic pitch of the blades 2.

[0085] The inner face 311 of the guide cam 31 may have a flat downstream portion substantially parallel to the propeller axis R, so that the inclination of the entire swashplate remains zero during a progressive increase in the stroke of the cylinder 20 up to the intermediate stroke. The inner face 311 of the guide cam 31 may have a concave upstream portion adapted to progressively incline the stator swashplate 11 when the stroke of the cylinder 20 is greater than the intermediate stroke. Thus, the correlation between the collective pitch and the cyclic pitch is non-linear, which makes it possible to compensate for the IP moments only in the phases that require it; that is, the cyclic pitch of the blades 2 is increased only when the collective pitch is greater than the intermediate collective pitch Col_int.

[0086] Alternatively, the inner face 311 of the guide cam 31 can be fully concave, so as to progressively increase the inclination of the plate assembly 10, and therefore the cyclic timing, during a progressive increase in the collective timing.

[0087] Alternatively, the inner face 311 of the guide cam 31 can form, particularly at its upstream end, a stop adapted to retain the guided element 15 of the stator plate 11 when the stroke of the cylinder 20 is greater than the intermediate stroke. An increase in the stroke of the cylinder 20 beyond the intermediate stroke then does not cause an increase in the collective pitch of the blades 2, but only an increase in the cyclic pitch of the blades 2 through the tilting of the plate assembly 10.

[0088] The rotor plate 12 can be configured so as not to come into contact with the guide cam 31, regardless of the stroke of the cylinder 20. Thus, regardless of the stroke of the cylinder 20, the rotor plate 12 can rotate freely about its axis of rotation. For example, a radial dimension of the rotor plate 12 can be smaller than a radial dimension of the stator plate 11, so that the stator plate 11 can be guided in the guide rail without the rotor plate 12 coming into contact with the guide rail.

[0089] The tilting system 30 may include a second guide cam 31 radially opposed to the first guide cam 31 with respect to the propeller axis R. Each guide cam 31 may have the configuration described above. The stator plate 11 includes a second guided element 15, which is adapted to be guided by the guide rail of the second guide cam 31 when the cylinder 20 is actuation.

[0090] In a second embodiment, illustrated by way of non-limiting example in [Fig. 5], the tilting system 30 includes a stop 32, the swashplate assembly 10 being adapted to be retained by the stop 32 when a stroke of the actuator 20 exceeds the intermediate stroke. The stop 32 enables a non-linear correlation between the collective pitch and the cyclic pitch of the blades 2. The arrangement of the stop 32 can be chosen so as to impose a tilt on the swashplate assembly 10 only beyond the intermediate stroke of the actuator 20, which can correspond to an intermediate collective pitch Col_int encountered during cruise flight. Thus, the low IP moments encountered during cruise are not overcompensated, and the turbomachine's efficiency is optimized during cruise.

[0091] The shim stop 32 is fixed in a stator reference frame of the turbomachine. The shim stop 32 can be fixed to any static element of the turbomachine, including the body of the cylinder 20. The shim stop 32 can be adapted to retain one end of the plate assembly 10, for example one end of the stator plate 11, when the stroke of the cylinder 20 is greater than the intermediate stroke.

[0092] The shim ring 14 can then be mounted directly on the stator plate 11, with the connecting rod 142 fixed to both the cylinder 20 and the stator plate 11. The tilting system 30 may further include a stop rod 321 having a distal end 323 fixed to the plate assembly 10, in particular fixed to the stator plate 11, and a proximal end 324 arranged to abut against the shim stop 32 when the stroke of the cylinder 20 is greater than or equal to the intermediate stroke. The stop stop 32 may include a chamber having an opening adapted to allow the rod of the stop rod 321 to pass through and to retain the proximal end of the stop rod 321 within the chamber.

[0093] As long as the stroke of cylinder 20 is less than the intermediate stroke, the stop link 321 moves freely along the propeller axis R, and an increase in the stroke of cylinder 20 only causes a displacement of the entire slab assembly 10 along the propeller axis R but does not cause a change in the inclination of the entire slab assembly relative to the normal plane. Thus, only the collective alignment the blades 2 is increased during an increase in the stroke of the cylinder 20 between the first stroke and the intermediate stroke, the cyclic pitch being unchanged, for example being zero corresponding to a zero inclination of the plate assembly 10 with respect to the normal plane.

[0094] When the stroke of the cylinder 20 is equal to the intermediate stroke, the stop rod 321 comes to rest against the shim stop 32, which retains the end of the swashplate assembly 10 to which the stop rod 321 is fixed, while the other end of the swashplate assembly 10 remains free to be moved by the cylinder 20, resulting in an inclination of the swashplate assembly 10 relative to the normal plane. Thus, only the cyclic pitch of the blades 2 is increased when the stroke of the cylinder 20 increases between the intermediate stroke and the second stroke, the collective pitch remaining unchanged.

[0095] The tilting system 30 may further include a return spring 322 adapted to return the swashplate assembly 10 to a position of zero tilt relative to the normal plane. The return spring 322 is fixed in a stator frame of the turbomachine. Thus, when the stroke of the actuator 20 is between the first stroke and the intermediate stroke, the swashplate assembly 10, if it was tilted due to a previous actuator stroke 20 greater than the intermediate stroke, is righted by the return spring 322 so that the cyclic pitch of the blades 2 returns to zero and remains zero for any actuator stroke 20 between the first stroke and the intermediate stroke.

[0096] Correlation relationship between collective calibration and cyclic calibration

[0097] The method for modifying the collective pitch and cyclic pitch can result in a correlated modification of the collective pitch and cyclic pitch of the propeller blades 2 of the propeller 1 according to a predetermined correlation relationship between the collective pitch and the cyclic pitch, the correlation relationship being established by means of a mechanical tilting system 30 as described above. The correlation relationship characterizes a cyclic pitch value as a function of a collective pitch value. The collective pitch corresponds to the x-axis and the cyclic pitch corresponds to the y-axis. The correlation relationship is characterized by a curve that passes through a first point corresponding to the first stroke of the actuator 20 with the minimum collective pitch Col_min and the minimum cyclic pitch Cyc_min, and a second point corresponding to the second stroke of the actuator 20 with the maximum collective pitch Col_max and the minimum cyclic pitch Cyc_max.The movement of the cylinder 20 between the first stroke and the second stroke causes a translational movement of the plate assembly 10 along the propeller axis R and a change in the inclination of the plate assembly 10 relative to the normal plane, the plate assembly 10 being inclined as a function of the translational movement of the assembly. platform 10 by means of the mechanical tilting system 30. Two examples of correlation relationships are illustrated by way of non-limiting example in [Fig.6].

[0098] The correlation relationship curve can take any conceivable shape to connect the first and second points with any conceivable cyclical calibration evolution. For example, the correlation relationship can be a straight line, an increasing curved line, or a strictly increasing line. The slope of the curve can be fixed, corresponding to a linear relationship, or variable, corresponding to a non-linear relationship in which the growth rate of the correlation relationship can vary between the first and second points. For example, the slope of the curve can be zero at one point on the curve and strictly positive at another, the curve can be convex, etc.

[0099] In a first embodiment, actuation of the cylinder 20 between the first and second strokes results in a progressive increase in the collective and cyclic pitch of the blades 2 according to a linear correlation between the collective and cyclic pitch. The correlation relationship is then a straight line passing through the first and second points and having a constant slope. Curve a) illustrated in [Fig. 6] constitutes an example of this first embodiment, with the minimum cyclic pitch Cyc_min being zero. Either the first and second points are predefined and the slope of the line results from them, or the slope of the line and one of the first and second points is predefined, and the other of the first and second points results from them.The tilting system 30 is adapted to gradually tilt the swashplate assembly 10 as the stroke of the cylinder 20 gradually transitions from the first stroke to the second stroke, i.e., as the swashplate assembly 10 is gradually moved translationally along the propeller axis R, thus progressively changing the collective pitch and cyclic pitch of the blades 2. For example, a gradual movement of the swashplate assembly 10 along the propeller axis R that gradually increases the collective pitch can also gradually increase the cyclic pitch. This first embodiment can be achieved, for example, by means of a guide cam 31 as described above, the inner face 311 of the guide cam 31 being concave.

[0100] In a second embodiment, an actuation of the cylinder 20 between the first and second strokes results in an increase in the collective and cyclic pitch of the blades 2 according to a non-linear correlation relationship between the collective and cyclic pitch. For example, the correlation relationship could be an increasing curved line with a variable slope, a convex curved line, etc.

[0101] In this second embodiment, an actuation of the cylinder 20 between the first stroke and the intermediate stroke between the first and second strokes can lead to an increase in the collective adjustment without an increase in the cyclic adjustment, and an actuation of the cylinder 20 between the intermediate and second strokes can lead to an increase in the cyclic adjustment, with or without an increase in the collective adjustment. The correlation relationship then passes through a third point corresponding to the intermediate stroke of cylinder 20 with the intermediate collective adjustment Col_int and the intermediate cyclic adjustment Cyc_int.Thus, the correlation relationship has a zero slope for a collective adjustment between the minimum collective adjustment Col_min and the intermediate collective adjustment Col_int, that is, when the stroke of cylinder 20 is between the first stroke and the intermediate stroke, and a strictly positive slope, fixed or variable, for a collective adjustment between the intermediate collective adjustment Col_int and the maximum collective adjustment Col_max, that is, when the stroke of cylinder 20 is between the intermediate stroke and the second stroke. The correlation relationship curve therefore has an inflection point or break point at the intermediate collective adjustment Col_int obtained for the intermediate stroke of cylinder 20.In particular, the correlation relation can correspond to a piecewise linear function, or a sigmoid, or a curve parallel to the x-axis for a collective calibration between the minimum collective calibration Col_min and the intermediate collective calibration Col_int, and then parallel to the y-axis when the collective calibration is equal to the intermediate collective calibration Col_int. Curve b) illustrated in [Fig. 6] constitutes an example of this second embodiment, the minimum cyclic calibration Cyc_min and the intermediate cyclic calibration Cyc_int being nuis.

[0102] The intermediate collective pitch Col_int can correspond to an operational collective pitch encountered in flight, for example, during cruise. The intermediate cyclic pitch Cyc_int can be zero. Such a correlation relationship makes it possible to maintain a zero cyclic pitch for cruise, during which the IP moments are low, while compensating for the IP moments during flight phases such as takeoff or climb, during which the IP moments are high and the collective pitch is greater than the cruise collective pitch. Thus, the turbomachine's fuel consumption and the compensation of IP moments are optimized.

[0103] This second embodiment can be obtained by means of a guide cam 31 as described above, the inner face 311 of the guide cam 31 having a flat downstream portion and a concave upstream portion, the intermediate collective adjustment Col_int then being strictly between the maximum collective adjustment Col_max and the minimum collective adjustment Col_min. This second embodiment can be obtained by the adjustment stop 32 as described above, in which case the Intermediate collective setting Col_int is equal to the maximum collective setting Col_max and only the cyclic setting is increased, from the minimum cyclic setting Cyc_min to the minimum cyclic setting Cyc_max, when the stroke of cylinder 20 is increased between the intermediate stroke and the second stroke.

[0104] The actuator 20 can be actuated according to a flight phase of the aircraft. The actuator 20 can be actuated to its first stroke when the aircraft is in a descent phase, and to its second stroke when the aircraft is in a takeoff or climb phase. The actuator 20 can also be actuated to its intermediate stroke when the aircraft is in a cruise phase. Thus, the actuation of an actuator 20 is carried out in such a way as to control a collective and cyclic pitch adjustment of the turbine blades 2 according to a flight phase of the aircraft. Propeller, turbomachine and aircraft

[0105] A turbomachine propeller section 1 may include a propeller 1 comprising a set of blades 2 rotatable about a propeller axis R and a collective and cyclic pitching system for the blades 2 of the propeller 1 as described above. The propeller 1 is provided with a set of blades 2 rotatable about the propeller axis R. The propeller 1 may be a shrouded or unshrouded propeller. The blades of the propeller 1 may be made entirely or partially of composite material.

[0106] A turbomachine may include a propeller section 1 as described above. The turbomachine may be a ducted turbomachine, such as a high bypass ratio turbofan, or an unducted turbomachine, such as a turboprop, an "open rotor" or an "unducted fan".

[0107] An aircraft may include at least one turbomachine as described above. For example, an aircraft may include at least one turbomachine per wing, each wing being equipped with the same number of turbomachines.

[0108] Although the present description has been made with reference to specific embodiments, it is clear that modifications and changes can be made to these examples without departing from their general scope. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. It is also clear that all the features described with reference to a process are transferable, alone or in combination, to a system, and conversely, all the features described with reference to a system are transferable, alone or in combination, to a process.

Claims

Demands

1. A method for modifying a collective pitch and a cyclic pitch of blades (2) for a propeller (1) of a turbomachine, comprising the following steps: - translation of a swashplate assembly (10) along a propeller axis (R) so as to modify the collective pitch of the blades (2), - modification of the inclination of the swashplate assembly (10) with respect to a plane normal to the propeller axis (R) so as to modify the cyclic pitch of the blades (2), in which the translation and the modification of the inclination of the swashplate assembly (10) are obtained by actuation of a cylinder (20) mounted on the swashplate assembly (10) between a first stroke corresponding to a minimum collective pitch (Col_min) and a minimum cyclic pitch (Cyc_min), and a second stroke corresponding to a maximum collective pitch (Col_max) and a minimum cyclic pitch (Cyc_max).

2. Method of modifying the collective and cyclic timing according to claim 1, wherein the first stroke corresponds to a minimum stroke of cylinder (20) and the second stroke corresponds to a maximum stroke of cylinder (20).

3. A method for modifying the collective and cyclic timing according to claim 1 or claim 2, wherein an actuation of the cylinder (20) between the first stroke and the second stroke results in a progressive increase in the collective and cyclic timing according to a linear correlation relationship between the collective and cyclic timing.

4. A method for modifying the collective and cyclic timing according to claim 1 or claim 2, wherein an actuation of the cylinder (20) between the first stroke and the second stroke results in an increase in the collective and cyclic timing according to a non-linear correlation relationship between the collective and cyclic timing.

5. A method for modifying the collective and cyclic timing according to claim 4, wherein an actuation of the cylinder (20) between the first stroke and an intermediate stroke between the first and second strokes results in an increase in the collective timing without an increase in the cyclic timing, and in which an actuation of the cylinder (20) between the intermediate stroke and the second stroke results in an increase in the cyclic stall, with or without an increase in the collective stall.

6. A method of modifying the collective trim and cyclic trim according to any one of claims 1 to 5 wherein the cylinder (20) is actuated according to a flight phase of the aircraft, wherein the cylinder (20) is actuated until it reaches the first stroke when the aircraft is in a descent phase, and wherein the cylinder (20) is actuated until it reaches the second stroke when the aircraft is in a takeoff or climb phase.

7. A method of modifying the collective trim and cyclic trim according to claim 5, wherein the cylinder (20) is further actuated until it reaches the intermediate stroke when the aircraft is in a cruise phase.

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