EP4054934A1

EP4054934A1 - Single-blade aircraft rotor

Info

Publication number: EP4054934A1
Application number: EP20800149.5A
Authority: EP
Inventors: Jean-Michel Simon; Louis Chemouni
Original assignee: Innostar; Hutchinson SA
Current assignee: Innostar; Hutchinson SA
Priority date: 2019-11-04
Filing date: 2020-11-04
Publication date: 2022-09-14
Also published as: WO2021089616A1; US20220388641A1; FR3102751A1; CN114641430A; US11987347B2

Abstract

Rotary wing aircraft rotor provided with a single blade (1) which has a longitudinal pitch axis (LL) and is hingedly mounted on the rotating shaft of the rotor about an axis (4) transverse to said rotating shaft, the wing system depicting a cone when the angle of its pitch is not zero, the rotor having a weighted device (6) for balancing the result (F8) of the horizontal component (F6) of the lifting force and the rotational drag force (F7) acting on the blade, the device being mounted so as to rotate with the wing system about its rotational shaft and generating, under the effect of the centrifugal force to which it is subjected when the wing system rotates, a horizontal force (F9) which is applied to the rotational shaft of the rotor, counter to the aforementioned result, with an intensity depending on the position of the weight(s) of the balancing device relative to the rotational shaft of the rotor.

Description

SINGLE BLADE AIRCRAFT ROTOR

The present invention relates to a single blade rotary wing aircraft rotor.

BACKGROUND OF THE INVENTION

It is known from the state of the art of rotors having only one blade, balanced with respect to the cen trifugal force by a counterweight. This equilibrium is almost by fact - except for a friction drag - when the pitch of the blade is zero. The question is different when one seeks to give lift to the rotary airfoil by acting on the pitch of the blade because in this case, the rotating blade describes a cone whose tip is turned downwards. The lift force exerted on the blade is then inclined a few degrees towards the axis of the cone. It therefore has a vertical component which is compensated by the weight of the aircraft and a horizontal component, directed towards the axis of the rotor and which constitutes a rotating force around this axis. This force generates a vibration of frequency equal to that of the rotation and of amplitude which depends, at constant speed of rotation, on the angle of the cone described by the blade. This vibration is transmitted to the structure of the apparatus in an undesirable manner and is a cause of significant and rapid wear of the rotating members in the bearings of the rotor-mast and of these bearings themselves.

Solutions to this problem have been described in 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 as a function of 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 in document US 2018222579 which proposes to act on the counterweight to adjust the compensation of the centrifugal force alone, the point of application of which on the single-blade has varied from made of the aforesaid taper. It has been noted that this action on the counterweight requires means that are difficult to implement. Furthermore, the rotational drag of the single-blade is a parasitic force which is not compensated for by the rotational drag of the counterweight of the single-blade. This force, perpendicular to the axis of the blade, rotates around the axis of rotation and needs to be dynamically balanced in order to reduce if not eliminate the vibration that it generates at the level of the bearings of the rotor.

Also this force is it composed with the preceding one and adds to the unbalanced parasitic force which is received by the structure of the apparatus in an undesirable manner and reinforces the risks of important and rapid wear of the rotating members in the bearings of the rotor mast and of these bearings themselves.

AIM OF THE INVENTION The invention intends to alleviate these drawbacks by providing a device for compensating this resultant of the parasitic forces formed by the horizontal component of the lift force and of the rotational drag exerted on the blade. DISCLOSURE OF THE INVENTION

To this end, the invention relates to an aircraft rotor with rotary airfoil, equipped with a single-blade with a longitudinal pitch axis, mounted articulated on the rotation shaft of the rotor about a transverse axis. to this rotation shaft, said airfoil describing a cone when the angle of its pitch is not zero. The rotor has a counterweight device (s) for balancing the resultant of the horizontal component of the lift force and the rotational drag force of the single-blade, mounted to rotate with the airfoil around its shaft. rotation and generating, under the effect of the centrifugal force to which it is subjected during the rotation of the airfoil, a horizontal force, applied to the rotation shaft of the rotor, opposite to the aforesaid resultant, with a function intensity of the position of the weight (s) of the balancing device with respect to the rotation shaft of the rotor. The effect of this device is to exert on the shaft of rotation of the rotor, when the blade is rotating and is load-bearing, a force opposite to the resultant of the horizontal component of the lift force and the drag force. that this blade undergoes, either transmitted by the root of the blade to this tree, or transmitted directly to this tree. It will be understood that the intensity of this force depends on the mass and on the position of the weight (s) and on its distance (s) from the axis of rotation, for a given speed of rotation. It should also be noted that the speed of rotation, the lift and the drag of the airfoil are linked. Thus, to obtain a given lift, the pitch angle of the single blade is all the greater the lower the speed, for example lower than the nominal speed. For example on take-off and landing, it may indeed be useful to operate at nominal speed, in particular to limit the noise emitted by the airfoil.

Several embodiments of this balancing device are possible. Each of them will be primarily determined on the basis of the quality and finesse of the compensation that one wishes to obtain.

Indeed, in certain uses of a single-blade, it has an angle of attack (or not of the blade) practically constant over almost all of its operating speed and has only two very transient operating phases. short compared to this diet. This is the case, for example, with vertical take-off aircraft which fly in a quasi-stationary manner over a land area to be monitored or controlled. In this application, it is possible to tolerate that, during these transient phases, there is an imperfect compensation for this parasitic force and therefore to accept the existence of temporary vibrations. The weight of a first embodiment of the device according to the invention will then be permanently disposed at the end of an arm oriented parallel to the direction of the parasitic force to be compensated, fixed by its other end to the root of the single blade or the rotor shaft. In this determined fixed position, the centrifugal force which it undergoes does not exactly compensate for the aforementioned resultant of the parasitic forces in the service regime relating to the hovering flight of the aircraft. In a variant of this embodiment, it is possible to provide a flyweight movable between two positions, a first position on the arm corresponding to zero compensation, locked by a latch or the like which is erased when a certain pitch angle of the blade is reached (for example 60-70% of the nominal pitch angle) to allow it to reach a second position on the said arm corresponding to a relatively effective compensation (about 85% of the resultant of the parasitic forces) during operating speed, for example with a payload of approximately 90% of the maximum take-off load (MTOW). A suitably calibrated spring makes it possible to return the weight from the second position to the first when the pitch angle of the blade passes below the aforementioned threshold.

In other uses, the single-blade operates under an essentially variable speed (the collective pitch of the blade being variable as can also the speed of rotation) and the compensation must be permanently adjusted according to the variations. of this diet. This adjustment is then obtained by continuously adjusting the position of the weight along the aforesaid arm, parallel to the direction of the resultant of the parasitic forces.

After having researched several laws of variation of the parameters to be taken into consideration to achieve this continuous adjustment, it appeared that the square of the pitch of the blade is a good variable for controlling the distance of the weight to the axis of rotation of the blade. rotor in the direction defined above, a direction which was found to vary little according to the load. It is important to note that this parabolic law (function of the square of the pitch of the blade) allows good balancing of this horizontal parasitic force whatever the load conditions of the aircraft. The compensation obtained is greater than 90% of the para-site effort.

It is then easy to design one or more control mechanisms to implement this law of variation.

Consequently, in another embodiment of the invention, the weight of the mechanism is mounted movably along the direction, obliquely on the longitudinal axis of the single-blade in the vicinity of the axis of rotation of the rotor while an actuator for its displacement along this oblique direction is controlled in response to the square of the pitch angle of the single blade.

Thus, in a simple manner, this actuator comprises a threaded rod with an oblique axis in the divergent direction indicated above with which the weight cooperates in the manner of a screw-nut system, a motor, wedged on the screw for its operation in rotation and a motor control unit, receiving as input continuous information relating to the pitch angle of the blade to provide an appropriate motor command. We can add to this mechanism a return member of the weight, the effect of which is opposite to that of the centrifugal force to regulate the motor force to be supplied. The direction of this threaded rod will be inclined so as to diverge from the leading edge of the single-blade, in front of it.

The above is verified independently of the value of the speed of rotation of the airfoil. In certain cases, it may be useful to vary the speed of rotation, for example to reduce it compared to the nominal speed in order to reduce the noise emitted by the apparatus. In fact, to obtain identical lift, the pitch of the blade should be increased and, interestingly, this increase in the pitch angle is taken into account by the law of slaving the displacement of the flyweight to favorably compensate. the decrease in the speed of rotation of the single-blade. Another embodiment of the invention will also be mentioned in its application to the compensation of the resultant of parasitic forces. It consists of at least one pair of weights which rotates in synchronism with the blade and each of which weights are adjustable in angular position around the axis of the rotor shaft. It is understood that by acting on the position of each weight relative, on the one hand to the longitudinal axis of the blade and, on the other hand to the position of the other weight, it is possible to create an unbalance of position and of adjustable mass which will be subjected to a centrifugal force, of intensity and direction adjustable accordingly, which will be in opposition with the parasitic force to be compensated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood during the description and the drawings given below. Reference will be made to the figures in which:

- Figure 1 is a diagram illustrating the horizontal horizontal force undergone by a single-blade, shown in profile, resulting from the lift of the wing,

FIG. 2 is a diagram illustrating, seen from above, the horizontal resultant of the parasitic force due to the lift with that due to the rotational drag of the blade and the principle of compensation according to the invention, - the FIG. 3 is the diagram of an exemplary embodiment of a first compensation device according to the invention,

- Figure 4 is an alternative embodiment of Figure 3 suitable for small aircraft, - Figure 5 is a diagram of an example of means implemented for the control of the compensation device of Figure 3 or the figure 4,

- Figure 6 is a diagram of another embodiment of the vibration compensation device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION In Figure 1, there is shown a single blade 1 rotating R counterclockwise around the rotor axis ZZ with its counterweight 2. The rotor (or rotor shaft) 3 is driven by a motor 3a and the blade 1 is articulated freely on the rotor shaft 3 around a transverse axis 4. The pitch of this blade 1 is not zero so that, as shown, the blade 1 describes a cone of angle A on the plane XX perpendicular to the ZZ axis of the rotor, plane which would contain the rotating blade 1 if the pitch of the blade 1 were zero. Applied to the center of gravity 5 of the blade 1 and to that of the counterweight 2, the centrifugal forces Fl and F2 are opposed and balanced. The lift force F3 has a vertical component F4 balanced by the lifted load F5. The lift applied to the counterweight 2, which is negligible, has not been shown. 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.

In FIG. 2, which is a top view of FIG. 1, in addition to the elements already represented, the rotational drag of the blade 1 will be illustrated by F7 while neglecting that applied to the counterweight 2. The leading edge of the blade 1 is noted la.

Figure 2 shows that the horizontal force F8, resulting from the composition of the drag F7 and the horizontal component F6 of the lift is not balanced, which results in the creation of para-site vibrations at the level of the 'embedding and bearings of the rotor shaft 3 in the structure of the aircraft.

The force F8 is oriented along a direction D which is substantially constant whatever the value of the load lifted, therefore whatever the collective pitch of the blade 1. By simulation, it was found that this direction D is inclined. on the longitudinal axis of pitch LL of the single blade 1 at an angle B of between 65 and 80 degrees, preferably between 70 and 75 degrees, here 70 degrees. The intensity of this force depends on the value of the pitch of the blade 1 and the calculations show that it depends, in good approximation, on the value of the square of this collective pitch since the angle A is small (of the order of a few - 2 to 5 - degrees). So, to compensate for the imbalance of this force

F8, a device 6 according to the invention is shown in FIG. 3 which generates on the blade 1 a force F9 opposite to the force F8. This device comprises a weight 7 which undergoes 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 integral with the blade 1, at its root, at most near the rotor 3. For example, the blade 1 has a root in the form of a stirrup 9 which is articulated to the rotor 3 around the transverse axis 4. The device 6 is therefore advantageously housed between the branches of this stirrup 9. The cen trifugal force undergone by the weight 7 gives rise to the force F9 in the direction of the guide.

The guide 8 extends along a direction D inclined on the axis of an angle B corresponding to that formed on this direction by the resultant F8 of the horizontal component F6 of the lift force F3 and of the force of drag F7 of rotation of the blade 1. This results in an elimination or at least a significant reduction in the vibrations and rotating stresses to which the rotor shaft 3 is subjected. The embodiment shown schematically in this FIG. 3 is especially suited to aircraft whose primary speed is hovering. The lift of the canopy is constant and the force F8 is also constant. The mass of the weight 7 is calculated so that, in its position at the end 8b of the guide 8 on the leading edge 1a side of the blade 1, it correctly compensates for the force F8. It will be noted that in the case of a weight 7 not controlled by the pitch angle of the blade 1, the weight 7 is released from a position close to the rotor axis towards its position close to the leading edge of the blade. blade 1 when the spring 10 is calibrated

"Gives way" or, more generally, when a lock in the flyweight 7 is erased at the nominal speed of rotation of the blade 1, the spring 10 serving to return this mass-buckle ?.

In Figure 4 we find most of the elements described with reference to Figure 3 with the same references.

The parasitic force compensation device then acts directly on the rotor shaft 3 while rotating with the single blade, the guide 8 being a radial rod of direction D integral with a bearing fixed in rotation on the rotor shaft 3.

The mass of the weight 7 is calculated so that, in its position at the end of the guide 8, here towards the leading edge 1a of the blade 1, it generates a force F9 which correctly compensates for the force F8. This arrangement is interesting on small machines where simplicity is sought.

The pitch angle of the blade 1 will advantageously, in this case, be brought to its maximum value as soon as the speed of rotation of the rotor 3 has reached 30% (for example) of the nominal speed of rotation.

In the case of an aircraft intended to experience variable speeds between hovering flight and cruising flight, the lift varies from one speed to another because the pitch of the blade 1 also varies. It is then a question of having a device which adapts to the variations of the force F8, which we recall that it varies due to the square of the pitch angle of the blade 1.

In this case illustrated by FIG. 5, the movement of the weight 7 along the guide 8 is controlled by a control unit 11 of a motor 12 which rotates the guide.

8 which is for example a screw, the weight 7 then being a nut fixed in rotation, cooperating with the screw like a screw-nut system. The function of the spring 13 in this case is to relieve the force of the motor, in particular in the direction of rotation which produces an increase in the centrifugal force undergone by the weight. In an embodiment not shown, the motor can constitute the flyweight itself cooperating with the guide 8 according to an appropriate kinematic chain. This flyweight can also include the engine supply battery. The engine control unit receives as input the signal "a" corresponding to the instantaneous value of the pitch angle of the blade 1 (value averaged over a given revolution or space of time) and, in a more elaborate version of the positive, the signal “v” emitted by one or more accelerometers or vibration sensors 14 at the level of the structure receiving the rotor. The control unit 11 will then act on the motor 12 in the direction of minimizing the signal “v”. The device 14 is, in a known manner, located either on a structural element close to the rotor mast or on the rotor mast itself.

Finally, with reference to FIG. 6, another embodiment of the compensation device according to the invention has been shown. It comprises at least one pair of massager 15 and 16 each carried by the free end of an arm 17 and 18, the other end being integral with a ring 19 (the figure shows only one only) of axis con fused with that of the rotor shaft 3. Each ring is angularly indexable with respect to the axis of rotation of the rotor 3 and therefore with respect to the longitudinal axis of the blade 1. We understand than the position indexed with respect to the blade

1 of each weight and their angular spacing defines the direction DI (this is the bisector of the angle formed by the two arms 17 and 18) of the resultant F10 of the centrifugal forces undergone by the weights and the intensity of this resultant (this resultant F10 is zero when the weights are diametrically opposed). A control of the indexing of each flyweight by an appropriate servo device, for example to the variation of the pitch of the blade 1, as mentioned above, makes it possible to adjust the compensation as a function of the variations in speed. flight of the device. Of course, the invention is not limited to the embodiments described and encompasses any variant falling within the scope of the invention as defined by the claims. Thus, it is not departing from the scope of the invention to provide another pair of weights such as those 15 and 16 if it is necessary to compensate for parasitic forces, the intensity of which would require the fitting of excessively high weights. voluminous. It is also not departing from the scope of the invention to ensure, on the same principles, compensation for the parasitic forces of a wing in which the counterweight is a short blade which, in rotation, also has a component. of the horizontal lift force but directed towards the end of the blade and a horizontal drag component which is composed with this horizontal component of the lift force to generate a parasitic force along the blade / counterweight opposite to the parasitic force existing in the direction of the single blade. It follows, due to the composition of all the forces in play (the horizontal components of the lift and drag) and the geometry of the rotary airfoil (taper described more flattened) that the weights of the balancing device Weights according to the invention will be of lower masses.

Claims

1. Rotor of a rotary wing aircraft equipped with a single blade (1) with a longitudinal pitch axis (LL), mounted articulated on the rotation shaft of the rotor about a transverse axis (4) to this rotation shaft, said airfoil describing a cone when the angle of its pitch is not zero, characterized in that it has a device (6) with weight (s) for balancing the resultant (F8) of the horizontal component (F6) of the lift force and the rotational drag force (F7) of the blade, mounted rotating with the airfoil around its rotating shaft and generating, under the effect of the centrifugal force at which it is subjected during the rotation of the airfoil, a horizontal force (F9), applied to the rotation shaft of the rotor, opposite to the aforesaid resultant, with an intensity depending on the position of the flyweight (s) ) of the balancing device with respect to the rotation shaft of the rotor.

2. Rotor according to claim 1, characterized in that the device comprises only one counterweight (7) for balancing carried by an arm (8), one end (8a) of which is integral with the root of the blade (1 ) which extends in front of said longitudinal pitch axis (LL) in the direction of rotation of the blade and is inclined at an angle (B) on this axis, corresponding to that formed on said axis by said resultant (F8) .

3. Rotor according to claim 2, characterized in that the weight (7) is fixed to this arm (8) in a determined position so that the compensation force (F9) obtained in this position does not exactly compensate for the aforesaid resultant that for a nominal pitch angle of the single blade.

4. Rotor according to claim 2, characterized in that the weight (7) is adjustable in position along the arm (8).

5. Rotor according to one of claims 2 to 4, characterized in that the axis of the arm (8) passes through the axis of the shaft of rotation of the rotor (3).

6. Rotor according to one of claims 2 to 5, characterized in that the aforesaid angle (B) is between 65 and 80 degrees and preferably 70 and 75 degrees.

7. Rotor according to claim 4, characterized in that the weight (7) is coupled to a control member (11) of its displacement along the arm, proportional to the square of the pitch angle of the single-blade. (1).

8. Rotor according to claim 1, characterized in that the device (6) with balancing weights comprises at least one pair of weights (15,16), each disposed at the free end of an arm (17,18 ) which rotates in synchro nism with the blade and which is adjustable in angular position around the axis of the rotor shaft (3).