Single-blade aircraft rotor

Abstract

A rotorcraft rotor having a single blade (1), the blade (1) having a longitudinal pitch axis (LL) and being hingedly mounted about an axis (4) transverse to the axis of rotation of the rotor on the axis of rotation of the rotor, the wing system describing a cone when the angle of its pitch is non-zero, the rotor having a weight device (6) for balancing the resultant force (F8) of the horizontal component (F6) of the lift and the rotational drag (F7) acting on the blade, the device being mounted to rotate about its axis of rotation together with the wing system and generating a horizontal force (F9) applied to the axis of rotation of the rotor under the action of the centrifugal force experienced during the rotation of the wing system, contrary to the above result, the intensity of which depends on the position of one or more weights of the balancing device relative to the axis of rotation of the rotor.

Description

Technical Field

[0001] The present invention relates to a rotor for a rotary-wing aircraft having a single blade. Background Art

[0002] In the prior art, it is known that a rotor has only a single blade, which is balanced relative to the centrifugal force by a counterweight. Assuming that the pitch (pas) of the blade is zero and friction resistance is ignored, this balance is almost perfect. When it is desired to apply lift to the rotary wing by acting on the pitch of the blade, the problem is different, because in this case, the rotating blade describes a cone with its apex pointing downwards. Then the lift applied to the blade is inclined by a few degrees towards the axis of the cone. Thus, it has a vertical component compensated by the weight of the aircraft and a horizontal component that is directed towards the axis of the rotor and constitutes a rotational force around this axis. This force generates vibrations with a frequency equal to the rotational frequency and an amplitude that, at a constant rotational speed, depends on the cone angle described by the blade. This vibration is transmitted in an undesirable manner to the structure of the aircraft and quickly causes a significant amount of wear on the bearings of the rotor shaft and the rotating components within these bearings themselves.

[0003] A solution to this problem is described in document US 6,619,585. The general principle of these solutions is to move the center of mass of the rotor relative to its vertical axis of rotation according to the value of the angle at the apex of the cone described by the single blade. The mechanisms implemented act on the position of the counterweight, as also described in document US 2018222579, which proposes acting on the counterweight to adjust only the compensation of the centrifugal force, the application point of which on the single blade changes due to the above-mentioned cone shape. It has been observed that this action on the counterweight requires equipment that is difficult to implement.

[0004] Furthermore, the rotational resistance of the single blade is a disturbing force (effort parasite) that cannot be compensated by the rotational resistance of the counterweight of the single blade. This force perpendicular to the axis of the blade rotates around the axis of rotation and requires dynamic balancing to reduce or even eliminate the vibrations it generates in the bearings of the rotor.

[0005] Furthermore, this force combines with the above-mentioned force and increases the disturbing force of the imbalance, which is absorbed by the structure of the aircraft in an undesirable manner and increases the risk of a significant amount of wear quickly experienced by the bearings of the rotor shaft and the rotating components within these bearings themselves. Summary of the Invention

[0006] The present invention seeks to overcome these drawbacks by proposing a device for compensating the resultant of the disturbing forces formed by the horizontal component of the lift and the rotational resistance acting on the blade.

[0007] To this end, the present invention provides a rotor for a rotary-wing aircraft, the rotor having a single blade which has a longitudinal pitch axis and is articulated about an axis transverse to the axis of rotation of the rotor, the articulation being such that when the pitch angle of the blade is non-zero, the rotary wing describes a cone. The rotor has a balancing weight device for balancing the resultant of the rotational drag of the single blade and the horizontal component of the lift, the device being mounted to rotate with the rotary wing about its axis of rotation and, while the rotary wing is rotating, generating, under the action of the centrifugal force to which it is subjected, a horizontal force which is applied to the axis of rotation of the rotor and is opposite to the said resultant, the intensity of which depends on the position of one or more balancing weights (masselottes) of the balancing device relative to the axis of rotation of the rotor.

[0008] When the blade is rotating and providing lift, the action of the device is to apply to the axis of rotation of the rotor a force opposite to the resultant of the horizontal component of the lift and the drag to which the blade is subjected, the force being transmitted either directly to the axis or via the root of the axis. It will be understood that for a given rotational speed, the intensity of the force depends on the mass and position of one or more balancing weights and on the distance of one or more balancing weights from the axis of rotation. It should also be noted that the rotational speed, lift and drag of the rotary wing are interrelated. Thus, in order to obtain a given lift, the pitch angle of the single blade needs to be increased at a lower speed, for example at a speed lower than the nominal speed. For example, it may be appropriate to operate at a speed lower than the nominal speed during take-off and landing, in particular in order to limit the noise emitted by the rotary wing.

[0009] Several embodiments of the balancing device are possible. Each of them will be determined mainly according to the quality and fineness of the compensation desired.

[0010] Specifically, in certain applications of a single blade, it has an almost constant angle of attack (or blade pitch) practically throughout its operating period and has only two very short operating phases compared to that period. As an example, this applies to a vertical take-off aircraft that flies over a land area to be monitored or surveilled in an almost stationary manner. In this application, during these transient phases, the compensation for this disturbing force may not be perfect and the temporary presence of vibrations may thus be acceptable. The flyweights of the first embodiment of the device according to the invention will thus be permanently located at the end of an arm that extends parallel to the direction of the disturbing force to be compensated, the other end of the arm being fastened to the root of the single blade or to the rotor shaft. In this determined and fixed position, the centrifugal force experienced by the flyweights compensates only the above-mentioned resultant of the disturbing forces during the service period when the aircraft is hovering. In a variant of this embodiment, a movable flyweight may be provided between two positions, the first position on the arm corresponding to zero compensation, the flyweight being locked by a latch or the like which contracts once the blade reaches a certain pitch angle (e.g. 60% to 70% of its nominal blade angle) to allow it to reach, during the service period, for example when the load is approximately 90% of the maximum take-off weight (MTOW), a second position on said arm corresponding to a relatively effective compensation (approx. 85% of the resultant disturbing force). When the pitch angle of the blade returns below the above-mentioned threshold, a properly calibrated spring serves to return the flyweight from the second position to the first position.

[0011] In other applications, the single blade operates in a substantially variable state (the total pitch of the blade is variable and its rotational speed may also be variable), so the compensation needs to be continuously adjusted according to this changing state. This adjustment is then obtained by continuously adjusting the position of the flyweight along the above-mentioned arm parallel to the resultant of the disturbing forces.

[0012] After studying several relationships of the parameter variations to be considered for this continuous adjustment, it has been found that the square of the pitch of the blade seems to be a good variable based on which to servo-control the distance of the flyweight from the axis of the rotor in the direction defined above, which has been found to vary little according to the changing load.

[0013] It is important to note that this square-law relationship (i.e., a function of the square of the blade pitch) can balance this horizontal disturbing force well regardless of the load conditions of the aircraft. The compensation obtained exceeds 90% of the disturbing force.

[0014] It is then easy to conceive of one or more servo-control mechanisms to implement this varying relationship.

[0015] Thus, in another embodiment of the present invention, the flyweights of the mechanism are mounted to move in a direction extending obliquely relative to the longitudinal axis of a single blade near the axis of rotation of the rotor, wherein an actuator for moving it in the inclined direction is controlled in response to the square of the pitch angle of the single blade.

[0016] Thus, in a simple manner, the actuator may include a threaded rod having an inclined axis along the above-mentioned divergent direction, the flyweights cooperate with the rod in a screw and nut system, a motor, the motor is fixed to the screw to drive its rotation, and a motor control unit, the motor control unit continuously receives information related to the pitch angle of the blade as an input to appropriately control the motor. The mechanism may be associated with a flyweight return member, the flyweight return member acts in a direction opposite to the centrifugal force to adjust the driving force to be delivered. The threaded rod extends in the inclined direction so as to diverge from the leading edge of the single blade in front of it.

[0017] The above applies regardless of the rotational speed of the rotor. In some cases, it may be useful to change the rotational speed, for example in order to reduce it relative to the nominal speed to reduce the noise emitted by the aircraft. Specifically, in order to obtain the same lift, it is appropriate to increase the pitch of the blade, and advantageously, the servo control relationship for the movement of the flyweights takes into account the increase in the pitch angle in order to appropriately compensate for the reduction in the rotational speed of the single blade.

[0018] Another embodiment of the present invention is also mentioned, which is applied to compensate the resultant force of the disturbing forces. It consists of at least a pair of flyweights rotating synchronously with the blade, and the angular position of each flyweight can be adjusted around the axis of the rotor shaft. It can be understood that by acting on the position of each flyweight first relative to the longitudinal axis of the blade and second relative to the position of another flyweight, an adjustable position and mass imbalance can be produced, and it will be subjected to a centrifugal force with adjustable intensity and direction, and this centrifugal force is opposite to the disturbing force to be compensated. Description of the Drawings

[0019] The present invention can be better understood through the following description and drawings. Referring to the drawings, in the drawings:

[0020] - Figure 1 is a schematic diagram showing the horizontal interference force experienced by a single blade (shown in outline) due to the lift of the rotor,

[0021] - Figure 2 is a schematic diagram seen from above, which shows the horizontal resultant force of the disturbing force caused by the lift and the disturbing force caused by the rotational resistance of the blade, and also shows the compensation principle according to the present invention,

[0022] - Figure 3Schematic diagram of an embodiment of a first compensation device according to the present invention,

[0023] - Figure 4 showing a variant applicable to small aircraft Figure 3 of,

[0024] - Figure 5 is a schematic diagram of a device showing a compensation device for controlling Figure 3 or Figure 4 of,

[0025] - Figure 6 is a schematic diagram of another embodiment of a vibration compensation device according to the present invention. Detailed description

[0026] In Figure 1 , a single blade 1 rotating counterclockwise R about the rotor axis ZZ and its counterweight 2 are shown. The rotor (or rotor shaft) 3 is driven by a motor 3a, and the blade 1 is freely hinged to the rotor shaft 3 about the transverse axis 4. The pitch of the blade 1 is non-zero, so that, as shown, the blade 1 describes a cone of angle A in a plane XX perpendicular to the axis ZZ of the rotor. If the pitch of the blade 1 were zero, this plane would contain the rotating blade 1.

[0027] The centrifugal forces F1 and F2 applied to the center of gravity 5 of the blade 1 and the center of gravity of the counterweight 2 are opposite and balanced, and the lift F3 has a vertical component F4 balanced by the lifting load F5. The lift applied to the counterweight 2 is not shown as it is negligible. It can be seen in this figure that the horizontal component F6 of the lift is directed towards the rotor 3 and is not compensated.

[0028] Figure 2 is a view from above of Figure 1 of, Figure 2 showing not only the above elements but also the rotational resistance on the blade 1, which is represented by F7, with the resistance on the counterweight 2 being neglected. The leading edge of the blade 1 is marked 1a.

[0029] Figure 2 shows that the horizontal force F8 generated by the combined action of the resistance F7 and the horizontal component F6 of the lift is unbalanced, resulting in disturbing vibrations in the structure of the aircraft where the rotor shaft 3 is mounted and its bearings.

[0030] The force F8 is directed along a direction D which is substantially constant and independent of the value of the load being lifted and thus independent of the collective pitch of the blade 1. By simulation, it has been found that the angle B by which the direction D is inclined with respect to the longitudinal pitch axis LL of the individual blade 1 is in the range of 65 degrees to 80 degrees, preferably in the range of 70 degrees to 75 degrees, and in this example is equal to 70 degrees. The intensity of this force depends on the pitch value of the blade 1, and calculations show that, as a good approximation, it depends on the square of the collective pitch, since the angle A is small (on the order of a few degrees, in the range of 2° to 5°).

[0031] Therefore, in order to compensate for the imbalance of the force F8, the device 6 of the present invention is shown in Figure 3 and is for generating a force F9 on the blade 1 which is opposite to the force F8. The device includes a flyweight 7 which is subjected to a centrifugal force during the rotation of the blade 1. It is mounted to move along a guide 8, one end 8a of which is fixed to the blade 1 near the rotor 3 at its shank. For example, the blade 1 has a U-shaped root 9 which is hinged to the rotor 3 about a transverse axis 4. Thus, the device 6 is advantageously received between the branches of the U-shaped root 9. The centrifugal force to which the flyweight 7 is subjected generates a force F9 along the direction of the guide.

[0032] The guide 8 extends in the direction D which is inclined at an angle B with respect to the axis, this angle B corresponding to the angle formed by the resultant force F8 of the horizontal component F6 of the lift force F3 and the rotational resistance F7 of the blade 1 with respect to this direction. This eliminates or at least significantly reduces the rotational vibrations and stresses to which the rotor shaft 3 is subjected.

[0033] Figure 3 The embodiment schematically shown in is particularly applicable to an aircraft mainly used for hovering flight. The lift of the rotor is constant and the force F8 is also constant. The mass of the flyweight 7 is determined such that it correctly compensates for the force F8 when it is in its extreme position 8b along the guide 8 next to the leading edge 1a of the blade 1. It should be noted that in the case where the flyweight 7 is not controlled by the pitch angle of the blade 1, the flyweight 7 is released from a position close to the rotor axis towards its position close to the leading edge of the blade 1 by the calibrated spring 10 "yielding", or more generally, when the latch of the flyweight 7 contracts at the nominal rotational speed of the blade 1, the spring 10 serves to return the flyweight 7.

[0034] In Figure 4 it can be seen that there are most of the elements described with reference to Figure 3 and they have the same reference numerals.

[0035] Then, the device for compensating for the disturbing force acts directly on the rotor shaft 3 while rotating with the individual blade, the guide 8 being a radial rod extending in the direction D and fixed to a bearing which is constrained to rotate with the rotor shaft 3.

[0036] Determine the mass of the flyweight 7 so that, when it is in the position at the end of the guide 8, particularly towards the leading edge 1a of the blade 1, it generates a force F9 that correctly compensates the force F8.

[0037] This construction is advantageous for small machines that pursue simplicity.

[0038] In this case, once the rotational speed of the rotor 3 reaches, for example, 30% of the nominal rotational speed, the pitch angle of the blade 1 advantageously reaches its maximum value.

[0039] For an aircraft that varies between operating flight and cruise flight, the lift varies from one flight to another because the pitch of the blade 1 also varies. Then it is necessary to have a device that adapts to the variation of the force F8, and it should be mentioned again that the force F8 varies according to the square of the pitch angle of the blade 1.

[0040] In this case and as Figure 5 shown, the movement of the flyweight 7 along the guide 8 is servo-controlled by a control unit 11 for controlling the motor 12, which rotates the guide 8, which is, for example, a screw, then the flyweight 7 is a nut that is prevented from rotating and cooperates with the screw as in a screw-nut system. In this case, the spring 13 serves to relieve the load on the motor, particularly in the rotational direction that causes an increase in the centrifugal force experienced by the flyweight.

[0041] In an embodiment not shown, the motor can form the flyweight itself, which cooperates with the guide 8 via a suitable drive system. The flyweight can also include a battery for powering the motor.

[0042] The control unit of the motor receives as input a signal "a" corresponding to the instantaneous value of the pitch angle of the blade 1 (the value averaged over one revolution or a given time length), and in a more refined version of the device, it also receives a signal "v" delivered by one or more accelerometers or vibration sensors 14 on the structure of the receiving rotor. Then the control unit 11 acts on the motor 12 in the direction that minimizes the signal "v". The device 14 is located in a known manner on a structural element close to the rotor shaft or on the rotor shaft itself.

[0043] Finally, referring to Figure 6, showing another embodiment of the compensation device of the present invention. It includes at least a pair of flyweights 15 and 16, each flyweight being carried by the free end of a respective arm 17 and 18, the other end of the arm being fixed to a respective ring 19 (only one ring is shown in the drawing), the axis of which coincides with the axis of the rotor shaft 3. Each ring is angularly positioned relative to the axis of rotation of the rotor 3 and thus relative to the longitudinal axis of the blade 1. It can be understood that the position occupied by each flyweight relative to the blade 1 and the angular spacing between the flyweights define the direction D1 and the intensity of the resultant force F10 of the centrifugal forces experienced by the flyweights (this direction is the bisector of the angle formed by the two arms 17 and 18, and when the flyweights are radially opposite, the intensity of the resultant force F10 is zero). As described above, the positioning of each flyweight is controlled by appropriate servo control means, for example in response to a change in the pitch of the blade 1, such that the compensation can be adjusted according to changes in the flight conditions.

[0044] Of course, the present invention is not limited to the described embodiments, but encompasses any variant falling within the scope of the present invention defined by the claims.

[0045] Thus, if it is necessary to compensate for a disturbing force, the intensity of which would otherwise require the installation of unduly large flyweights, then providing another pair of flyweights such as flyweights 15 and 16 does not go beyond the scope of the present invention.

[0046] In accordance with the same principle, it is also not beyond the scope of the present invention to provide compensation for disturbing forces on the rotor, where the counterweight is a short blade which, when rotating, also has a horizontal lift component, but this component is directed towards the end of the blade, and a horizontal drag component which combines with the horizontal lift component to produce a disturbing force along the blade / counterweight which is opposite to the disturbing force present in the direction of a single blade. Thus, due to all the forces involved being combined (the horizontal components of lift and drag) and due to the geometry of the rotor (the above-mentioned coning being flattened), the mass of the flyweights of the flyweight balancing device of the present invention is smaller.

Claims

1. A rotor for an aircraft with a rotor having a single blade (1), the blade having a longitudinal pitch axis (LL) and being hingedly mounted on a rotation axis for rotating the rotor, the hinge being about an axis (4) transverse to the rotation axis. When the rotor is rotating and the pitch angle of the rotor is non-zero, the rotor describes a cone. The rotor is characterized in that the rotor has a balance weight device (6) for balancing the resultant force (F8) of the horizontal component of the lift force (F6) and the rotational resistance (F7) of the blade. The balance weight device is mounted to rotate with the rotor about its rotation axis and generates a compensating force (F9) under the action of the centrifugal force it experiences while the rotor is rotating. The compensating force is horizontal and is applied to the rotation axis of the rotor and is opposite to the resultant force. The intensity of the compensating force depends on the position of one or more weights of the balance weight device relative to the rotation axis of the rotor.

2. The rotor according to claim 1, characterized in that, the balance weight device only has a first balance weight (7), the first balance weight being carried by a first arm (8). One end (8a) of the first arm (8) is fixed to the root of the blade (1), the root extending in front of the longitudinal pitch axis (LL) in the rotational direction of the blade and being inclined at an angle (B) relative to the longitudinal pitch axis, the angle (B) corresponding to the angle formed by the resultant force (F8) relative to the longitudinal pitch axis.

3. The rotor according to claim 2, characterized in that, the first balance weight (7) is fastened to the first arm (8) at a determined position such that the compensating force (F9) obtained at this position compensates the resultant force only for the nominal pitch angle of the single blade.

4. The rotor according to claim 2, characterized in that, the position of the first balance weight (7) is adjustable along the first arm (8).

5. The rotor according to any one of claims 2 to 4, characterized in that, the axis of the first arm (8) intersects the axis of the rotation axis of the rotor.

6. The rotor according to any one of claims 2 to 4, characterized in that, the above angle (B) is in the range of 65 degrees to 80 degrees.

7. The rotor according to claim 6, characterized in that, the above angle (B) is in the range of 70 degrees to 75 degrees.

8. The rotor according to claim 4, characterized in that, the first balance weight (7) is coupled to a control member (11), the control member being used to control the movement of the weight along the first arm to be proportional to the square of the pitch angle of the single blade (1).

9. The rotor according to claim 1, characterized in that, The balance weight device (6) includes at least a pair of second balance weights (15, 16), the second balance weights being arranged at the free ends of corresponding second arms (17, 18), the second arms (17, 18) rotating synchronously with the blades, and the angular positions of the second arms being adjustable about the axis of rotation of the rotor.

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