WO2013098736A2

WO2013098736A2 - A four-rotor helicopter

Info

Publication number: WO2013098736A2
Application number: PCT/IB2012/057589
Authority: WO
Inventors: Fabrizio GIULIETTI; Giulio AVANZINI
Original assignee: Alma Mater Studiorum - Universita' Di Bologna; Politecnico Di Torino
Priority date: 2011-12-29
Filing date: 2012-12-21
Publication date: 2013-07-04
Also published as: WO2013098736A3

Abstract

Described is a four-rotor helicopter (1) comprising: a frame (2), four rotors (3) equipped with propellers (8) and designed for generating a lift, the rotors (3) being connected to the frame in such a way as to be grouped in two pairs (4), the rotors (3) of each pair (4) being positioned diametrically opposite a corresponding operating axis (X, Y), for allowing a rotation of the helicopter about the corresponding operating axis (X, Y), the operating axes (X, Y) not being parallel to each other. According to a first aspect of the invention, the helicopter comprises actuator means (9) associated with the propellers (8) of at least one of the pairs of rotors for varying, relatively, the pitch, the rotors of the at least one pair being connected by a kinematic mechanism to a same motor (5), for being rotated at the same angular speed. According to another aspect of the invention, the helicopter comprises a plurality of drive elements (10) connected to the rotors for tilting them relative to the frame, each rotor (3) being tiltable relative to the frame (2) so as to vary the orientation of the axis of rotation of the corresponding propeller.

Description

DESCRIPTION

A FOUR-ROTOR HELICOPTER

Technical field

This invention relates to a four-rotor helicopter. Background art

Aircraft of this type are commonly used in particular as drones (commonly known as UAVs "unmanned aerial vehicles") due to their high manoeuvrability even in small spaces. More in detail, four-rotor helicopters of this type can be used for military activities such as, for example, reconnaissance and observation, or for civil purposes such as, for example, the search for survivors after natural disasters.

In the prior art, a four-rotor helicopter comprises a supporting frame for the rotors comprising, for example, a lattice comprising four coupling supports arranged in a "cross" shape.

The four rotors are connected to the frame, each at a respective support. The rotors are oriented parallel to a vertical axis of the frame, in such a way as to operate in conjunction with each other for creating a lift and allowing the operation of the aircraft. In detail, the aircraft is equipped with a front motor and a rear motor, positioned on the rolling axis. Two lateral motors are also positioned on the pitching axis, on opposite sides relative to the rolling axis. It should be noted that, in order to guarantee the stability of the aircraft, the rotors arranged in twos opposite each other rotate in opposite directions. Each rotor is coupled to a respective motor which is able to control the speed of rotation.

For this reason, the rotors can operate in conjunction with each other in such a way as to guarantee the manoeuvrability of the aircraft. More specifically, they guarantee to the aircraft the possibility of tilting about the pitching and rolling axes, as well as rotating about the yaw axis.

In detail, by increasing the revolutions of the front rotor and decreasing the revolutions of the rear rotor the aircraft is able to pull up, since the difference in rotation of the two rotors generates a torque about the pitching axis. If, on the other hand, the revs of the rear motor are increased and those of the front motor are decreased, the aircraft will tip its nose downwards, entering a dive.

In the same way, the two lateral motors can control the rolling of the aircraft by varying in a different way from each other the relative rotation speeds. The yaw is controlled in a similar manner, increasing the speed of the rotors with the direction of rotation opposite to that in which the aircraft is to be rotated and decreasing the revolutions of the rotors which rotate in the same direction as the desired yaw.

Lastly, it should be noted that these manoeuvres are sufficient to guarantee the complete mobility of the aircraft, since in order to move it along a predetermined direction it is sufficient to tilt it along that direction as described above, in such a way that the force produced by the rotors has a pulling component along the desired direction. In order to increase or decrease the flying altitude it is sufficient to increase or decrease, respectively, the speed of rotation of all the rotors simultaneously.

As pointed out above, the prior art aircraft is extremely manoeuvrable, however it disadvantageously requires the installation of four motors which are operated varying the number of revolutions. Consequently, the aircraft is heavy and inefficient from the propulsive point of view.

Moreover, since all four motors are required for the correct operation of the aircraft, the reliability is affected, since the fault of one motor is sufficient to compromise the operation of the helicopter.

Moreover, it should be noted that, even though the aircraft is manoeuvrable, it is necessary to vary the alignment in order to move it. This could make it unsuitable in applications for observing a fixed target, since it would be necessary to lose the target from sight in order to move it. Aim of the invention

In this context, the technical purpose which forms the basis of this invention is to propose a four-rotor helicopter which overcomes the above mentioned drawbacks of the prior art.

More specifically, the aim of this invention is to provide a four-rotor helicopter having a particularly light structure and particularly efficient in terms of output.

A further aim of the invention is to provide a four-rotor helicopter in which the control of the alignment is particularly precise and efficient.

Another aim of the invention is to provide a particularly reliable four-rotor helicopter.

The technical purpose indicated and the aims specified are achieved by a four-rotor helicopter comprising the technical features described in one or more of the appended claims.

More specifically, the four-rotor helicopter according to this invention comprises a frame and four rotors equipped with propellers and designed for generating a lift.

The rotors are connected to the frame in such a way as to be grouped in two pairs; the rotors of each pair are positioned diametrically opposite a corresponding operating axis, for allowing a rotation of the helicopter about the corresponding operating axis.

These operating axes are not parallel to each other, and they are preferably perpendicular to each other.

According to this invention, the helicopter comprises actuator means associated with the propellers of at least one of the pairs of rotors for varying the pitch, the rotors of the at least one pair are connected by a kinematic mechanism to a same motor, for being rotated at the same angular speed.

Preferably, the helicopter according to this invention comprises a single motor designed to rotate all the rotors, that is, all propellers about the corresponding axes of rotation. Thus, all the rotors are connected by a kinematic mechanism to the motor for being rotated at the same angular speed.

For this reason, the actuator means are preferably designed for varying the pitch of the propellers of both the groups of propellers (that is, the groups of rotors), relative to each other.

More specifically, the actuator means are designed for varying the pitch of the propellers of a group independently from the pitch of the propellers of the other group.

Preferably, the helicopter according to this invention comprises a unit for controlling the alignment of the helicopter.

The control unit is designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and is connected to the actuator means, for controlling them as a function of the drive signal.

In this way, the alignment is controlled by varying the pitch of the propellers, which can thereby be rotated by a same motor, preferably at a constant speed.

This allows an increase in the efficiency of the propulsion and the lightness of the helicopter.

Preferably, each rotor can be tilted relative to the frame.

In light of this, the helicopter comprises, for each rotor, a corresponding drive element, for tilting it relative to the frame and relative to the other rotors, automatically with respect to the other rotors.

This allows the alignment of the helicopter to be maintained even in the event of a fault to one of the rotors, with a consequent increase in the reliability of the four-rotor helicopter.

In light of this, the unit for controlling the alignment of the aircraft is designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and it is connected to the drive elements of the rotors for controlling them (that is, for controlling the tilting) as a function of the drive signal. For this reason, this invention also provides a process for controlling the alignment of the four-rotor helicopter.

According to this invention, the process comprises the following steps:

- moving the rotors of at least one of the pairs for rotating the propellers at the same speed;

- varying the pitch of one of the propellers (of the pair of rotors) relative to the other, for rotating the helicopter about the operating axis corresponding to the at least one pair of rotors.

Preferably, the process also comprises a step of tilting the axis of rotation of the rotors.

Brief description of the drawings

Further features and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, non-limiting, embodiment of a four-rotor helicopter as illustrated in the accompanying drawings, in which:

- Figure 1 is a schematic perspective view of a four-rotor helicopter according to this invention;

- Figure 2 is a schematic cross-section of a detail of the helicopter of Figure 1.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes a four-rotor helicopter according to this invention.

More specifically, the helicopter 1 comprises a frame 2. The frame can comprise, as shown in Figure 1 , four arms 2a arranged in a "cross" shape.

The helicopter 1 also comprises four rotors 3, each connected to the frame

2 and acting at least along a vertical direction for creating a lift. More specifically, in the preferred embodiment, each rotor 3 is connected to the end of a respective arm 2a. The rotors 3 are grouped together in two pairs

4. Each rotor 3 of each pair 4 is opposite the other rotor 3 of the same pair 4 relative to a respective operating axis X, Y, in such a way as to rotate the frame 2 about the operating axis X, Y. More specifically, the operating axes are positioned transversely and preferably perpendicularly to each other. More in detail, two rotors 3 are positioned at opposite ends of the frame 2 along a first operating axis "X", whilst the other two rotors 3 are positioned at the opposite end of the frame 2 along a second operating axis Ύ". By way of an example, the first operating axis "X" can be defined as the pitching axis of the helicopter 1. Similarly, the second operating axis "Y" can be considered to be the rolling axis of the four-rotor helicopter 1. Advantageously, the helicopter 1 comprises a number of motors 5 less than the number of rotors 3. For this reason, at least one motor 5 is connected by a kinematic mechanism to more than one rotor 3. More specifically, in the preferred embodiment of this invention, the helicopter 1 comprises a single motor 5 which is connected by a kinematic mechanism to all the rotors 3. The single motor 5 is preferably located at the intersection between the arms 2a of the frame 2.

The helicopter 1 also comprises drive means 6 acting between the motor 5 and the rotors 3, in such a way as to transfer the motion from the motor 5 to the rotors 3.

More specifically, the drive means 6 comprise four kinematic drive mechanisms 7 each positioned between the motor 5 and a respective rotor 3. Advantageously, the drive means 6 move all the rotors 3 with the same rotation speed.

In the example partly illustrated in the drawings, the motor 5 is connected to a pinion, which engages with four gear wheels (one for each arm 2a). Each arm 2a is equipped with a drive system having a belt 61 trained round pulleys; of these, a first pulley (not illustrated) is keyed on a spindle fixed to a corresponding gear wheel (and thus positioned in a central body of the helicopter, close to the motor 5), whilst the other pulley, labelled 62 in Figure 2, is positioned at the end of a corresponding arm 2a.

Preferably, the belts 61 are housed inside the corresponding arms 2a. In this way, the rotation of the motor 5 is transmitted to the four pulleys 62 corresponding to the four rotors 3.

Each of the pulleys 62 is connected by a kinematic mechanism to a corresponding propeller 8 for transmitting the rotary movement to them. The above-mentioned rotors 3 each comprise a propeller 8 having a variable pitch. More specifically, each propeller 8 comprises a plurality of blades 11 (preferably two blades 11).

To allow the pitch of the propellers 8 to be varied the helicopter 1 comprises actuator means 9 associated with them to vary the tilting of the blades 11. The actuator means 9 allow the pitch of the respective propellers 8 to be effectively acted on, in such a way as to vary the lift produced by each rotor 3.

With regard to the actuator means 9, an embodiment is shown in Figure 2. According to the embodiment illustrated, the actuator means 9 (for each propeller 3) comprise the following.

The propeller 8 is connected to a shaft 91 rotatable about a relative axis A'.

A pin 92 is fixed to the free end of the shaft 91 , perpendicularly to the axis A' of the shaft 91.

Corresponding blades 11 are rotatably coupled at the opposite ends of the pin 92 (in the example illustrated and described here there are two blades, but a similar technical solution could be adopted for a different number of blades).

A movable unit 93 is coupled to the shaft 91 in such a way as to translate along it (and if necessary rotate).

A bushing 94 is coupled to the movable unit 93 in such a way that the movable unit 93 is free to rotate relative to the bushing 94, but is movable as one with it along the axis A' of the shaft 91.

In other words, an axial movement of the bushing 94 along the axis A' of the shaft 91 causes a corresponding axial movement of the movable unit 93, whilst a movement of the movable unit 93 about the axis A' does not cause a corresponding rotation of the bushing 94.

The bushing 94 is connected by a kinematic mechanism 95 to a corresponding arm 2a.

The kinematic mechanism 95 comprises an actuator (preferably a tie rod), and it is designed for controlling the translation of the bushing 94 along the axis A' of the shaft 91.

The movable unit 93 is connected (for example by means of articulated arms 96) to the blades 11 , in such a way that a movement of the movable unit 93 along the axis A' of the shaft 91 causes a rotation of the blades 1 (in opposite directions) about the axis B defined by the pin 92.

It should be noted that the axis B is in turn rotatable about the axis A'. For each rotor 3, the actuators of the respective kinematic mechanism 95 can be driven independently (using controls positioned in the pilot's cabin and preferably using an electronic control unit).

It should be noted that, according to a first aspect of the invention, each rotor 3, in particular each propeller 8, lies on a respective fixed plane relative to the frame 2.

Alternatively, each rotor 3 lies on a respective plane which can be tilted relative to the frame 2 so as to exert a longitudinal and/or transversal thrust force. Advantageously, in this way the aerodynamic force resulting from the movement of the rotor 3 can be directed along a direction other than the vertical, thereby having a component lying on a horizontal plane. This is possible without modifying the alignment of the aircraft 1.

More specifically, each rotor 3 comprises a respective drive element 10 which is able to vary the inclination of the above-mentioned plane.

The drive elements 10 (only partly illustrated in the Figure 2) are described below, for a single rotor 3 (since they are similar for the other rotors 3), in one embodiment of the invention.

A spindle 101 is rotated about a relative axis A, using the drive means 6. In the example illustrated, the spindle 101 is fixed to the pulley 62.

The shaft 91 which rotates the propeller 8 about the relative axis A' can be tilted relative to the spindle 101 , in such a way that the axis A and the axis A' form an angle relative to each other.

For that purpose, between the spindle 101 and the shaft 91 there is a ball joint (for example a bearing, that is, a sliding or plain bearing), or a cardan joint or other joints designed to transfer the rotary movement between a first shaft and a second shaft tilted relative to the first.

The ball joint is not illustrated, being perse known.

Moreover, the drive element 10 comprises a kinematic mechanism connected to the shaft 91 for tilting it by an angle relative to a predetermined reference, for example, from the axis A of the spindle 101 or from the arm 2a.

For example, the kinematic mechanism comprises one or more arms of variable length (for example, a jack or a telescopic arm connected to an actuator) having a first end hinged to a bushing rotatably coupled to the shaft 91 and a second end hinged to a runner slidably coupled to a circular guide positioned outside the bushing to surround it.

In this way, acting on an actuator designed to move the runner along the guide and on the actuator designed to vary the length of the variable length arm, the axis A' of the shaft 91 is moved inside a cone having substantially as the vertex the joint defined by the ball joint connecting between the shaft 91 and the spindle 101 and lateral surface tangential to the guide.

The embodiment of the drive element 10 can be replaced by other known systems and it may be modified (for example, the guide can have different shapes, other than circular).

It should be noted that, in the example described above, the plane in which the rotor 3 lies is perpendicular to the axis A' of the corresponding shaft 91.

It should be noted that the helicopter 1 comprises a control unit 1 1 for coordinating the actuator means 9 in such a way as to guarantee a complete control of the aircraft. Preferably, the control unit is connected to the actuators of the drive elements 10 (designed to vary the plane on which the rotors 3 lie); moreover, preferably, the control unit is connected to the actuator means 9 (designed to vary the pitch of the propellers 8).

Moreover, the control unit is connected to control instruments accessible to the pilot and, if necessary, to a plurality of sensors (being per se known in the field of helicopters), for allowing the pilot to control the alignment of the helicopter, that is, for converting the pitching, rolling, yaw and translation commands along the three axes controlled by the actuators (and, if necessary, for defining an automatic piloting system which is able to give similar commands automatically relative to the inputs by the pilot). According to another aspect, the invention provides a four-rotor helicopter 1 comprising:

- a frame (2);

- four rotors 3 equipped with propellers 8 and designed for generating a lift, the rotors 3 being connected to the frame in such a way as to be grouped in two pairs 4, the rotors 3 of each pair 4 being positioned diametrically opposite a corresponding operating axis X, Y, for allowing a rotation of the helicopter about the corresponding operating axis X, Y, the operating axes X, Y not being parallel to each other;

- a plurality of drive elements 10 connected to the rotors for tilting them relative to the frame, each rotor 3 being tiltable relative to the frame 2 so as to vary the orientation of the axis of rotation of the corresponding propeller.

Preferably, each drive element 10 comprises a shaft 91 rotating about an axis A' and connected to a spindle 101 rotating about an axis A by means of a joint designed to allow a tilting of the shaft 91 relative to the spindle 101 , the shaft 91 being connected to the corresponding propeller 8 and being coupled to a kinematic mechanism designed for tilting the shaft 91 relative to the spindle 101.

Preferably the helicopter comprises a unit for controlling the alignment of the helicopter, designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and connected to the drive elements 10 of the rotors 3 for controlling them as a function of the drive signal, maintaining the alignment even in the event of a fault to one of the four rotors 3.

Preferably, the drive elements 10 are designed for tilting the axis of rotation of each rotor 3 independently from the orientation of the axes of rotation of the other rotors 3.

Preferably, the helicopter comprises actuator means 9 associated with the propellers 8 of at least one of the pairs of rotors 3 for varying, relatively, the pitch, the rotors of the at least one pair being connected by a kinematic mechanism to a same motor 5, for being rotated at the same angular speed.

Preferably, all the rotors 3 are connected by a kinematic mechanism to the same motor 5 for being rotated at the same angular speed, the actuator means 9 being designed for varying the pitch of the propellers 8 of both the groups 4, relative to each other.

Preferably, wherein the actuator means 9 are designed for varying the pitch of the propellers 8 of each of the groups 4 independently from the pitch of the propellers of the other group.

Preferably, the actuator means 9, for each rotor 3, comprise a movable unit 93 slidable along an axis A' of rotation of a propeller 8 of the rotor 3, wherein the propeller 8 comprises a pin 92 rotating about the axis A' and a pair of blades 11 rotatably coupled to the pin 92 so as to rotate about an axis B defined by the pin 92 and transversal to the axis A', the movable unit 93 being connected by a kinematic mechanism to the blades 1 , in such a way that a movement of the movable unit along the axis A' generates a corresponding rotation of the blades 11 about the axis B.

Preferably, the helicopter comprises four belts 61 wound on corresponding pairs of pulleys, each pair of pulleys having a first pulley connected to the motor 5 and a second pulley connected by a kinematic mechanism to a propeller 8 of the corresponding rotor 3.

Preferably, the helicopter comprises a unit for controlling the alignment of the aircraft, designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and connected to the actuator means 9 for controlling them as a function of the drive signal.

The invention also provides a process for controlling the alignment of a four-rotor helicopter 1 , having four rotors 3 connected to the frame in such a way as to be grouped in two pairs 4, the rotors 3 of each pair 4 being positioned diametrically opposite a corresponding operating axis X, Y, for allowing a rotation of the helicopter about the corresponding operating axis X, Y, the operating axes X, Y not being parallel to each other.

According to the further embodiment, the process comprises a step of tilting the axis of rotation of the rotors 3.

Preferably, the process also comprises the following steps:

- moving of the rotors 3 of at least one of the pairs 4 for rotating the propellers 8 at the same speed;

- varying the pitch of one of the propellers 8 relative to the other, for rotating the helicopter about the operating axis corresponding to the at least one pair of rotors 3.

The invention achieves the set aims. By interfacing a single motor with more than one rotor it is possible to reduce the number of motors on the aircraft. Consequently, it is possible to mount motors with larger dimensions, which are more efficient and lighter for the same overall power. In this way, the four-rotor helicopter is able to guarantee higher levels of performance.

Moreover, since the rotors can be oriented relative to the frame it is no longer necessary to vary the alignment of the aircraft in order to translate it. It is therefore possible to pursue a target by always keeping a fixed alignment relative it.

Claims

1. A four-rotor helicopter (1) comprising:

- a frame (2),

- four rotors (3) equipped with propellers (8) and designed for generating a lift, the rotors (3) being connected to the frame in such a way as to be grouped in two pairs (4), the rotors (3) of each pair (4) being positioned diametrically opposite a corresponding operating axis (X, Y), for allowing a rotation of the helicopter about the corresponding operating axis (X, Y), the operating axes (X, Y) not being parallel to each other,

characterised in that it comprises actuator means (9) associated with the propellers (8) of at least one of the pairs of rotors for varying, relatively, the pitch, the rotors of the at least one pair being connected by a kinematic mechanism to a same motor (5), for being rotated at the same angular speed.

2. The four-rotor helicopter (1) according to claim 1 , wherein all the rotors (3) are connected by a kinematic mechanism to the same motor (5) for being rotated at the same angular speed, the actuator means (9) being designed for varying the pitch of the propellers (8) of both the groups (4), relative to each other.

3. The four-rotor helicopter (1) according to claim 1 or 2, comprising four belts (61) wound on corresponding pairs of pulleys, each pair of pulleys having a first pulley connected to the motor (5) and a second pulley connected by a kinematic mechanism to a propeller (8) of the corresponding rotor (3).

4. The four-rotor helicopter (1) according to any of the foregoing claims, wherein the actuator means (9), for each rotor (3), comprise a movable unit (93) slidable along an axis (Α') of rotation of a propeller (8) of the rotor (3), wherein the propeller (8) comprises a pin (92) rotating about the axis (Α') and a pair of blades (11) rotatably coupled to the pin (92) so as to rotate about an axis (B) defined by the pin (92) and transversal to the axis (Α'), the movable unit (93) being connected by a kinematic mechanism to the blades (11), in such a way that a movement of the movable unit along the axis (Α') generates a corresponding rotation of the blades (11) about the axis (B).

5. The four-rotor helicopter (1) according to any of the foregoing claims, comprising a unit for controlling the alignment of the aircraft, designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and connected to the actuator means (9) for controlling them as a function of the drive signal.

6. The four-rotor helicopter (1) according to claim 2, wherein the actuator means (9) are designed for varying the pitch of the propellers (8) of each of the groups (4) independently from the pitch of the propellers of the other group.

7. The four-rotor helicopter (1) according to any of the foregoing claims, wherein each rotor (3) is tiltable relative to the frame (2), the helicopter (1) comprising a plurality of drive elements (10) connected to corresponding rotors for tilting them relative to the frame.

8. The four-rotor helicopter(l) according to claim 7, wherein each drive element (10) comprises a shaft (91) rotating about an axis (Α') and connected to a spindle (101) rotating about an axis (A) by means of a joint designed to allow a tilting of the shaft (91) relative to the spindle (101), the shaft (91) being connected to the corresponding propeller (8) and being coupled to a kinematic mechanism designed for tilting the shaft (91) relative to the spindle (101).

9. The four-rotor helicopter (1) according to claim 8 or 9, comprising a unit for controlling the alignment of the helicopter, designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and connected to the drive elements (10) of the rotors (3) for controlling them as a function of the drive signal, maintaining the alignment even in the event of a fault to one of the four rotors (3).

10. A process for controlling the alignment of a four-rotor helicopter (1), having four rotors (3) connected to the frame in such a way as to be grouped in two pairs (4), the rotors (3) of each pair (4) being positioned diametrically opposite a corresponding operating axis (X, Y), for allowing a rotation of the helicopter about the corresponding operating axis (X, Y), the operating axes (X, Y) not being parallel to each other,

characterised in that it comprises the following steps:

- moving of the rotors (3) of at least one of the pairs (4) for rotating the propellers (8) at the same speed;

- varying the pitch of one of the propellers (8) relative to the other, for rotating the helicopter about the operating axis corresponding to the at least one pair of rotors (3).

11. The process according to claim 10, comprising a step of tilting the axis of rotation of the rotors (3).

12. A four-rotor helicopter (1) comprising:

- a frame (2),

characterised in that it comprises a plurality of drive elements (10) connected to the rotors for tilting them relative to the frame, each rotor (3) being tiltable relative to the frame (2) so as to vary the orientation of the axis of rotation of the corresponding propeller.

13. The four-rotor helicopter( ) according to claim 12, wherein each drive element (10) comprises a shaft (91) rotating about an axis (Α') and connected to a spindle (101) rotating about an axis (A) by means of a joint designed to allow a tilting of the shaft (91) relative to the spindle (101), the shaft (91) being connected to the corresponding propeller (8) and being coupled to a kinematic mechanism designed for tilting the shaft (91) relative to the spindle (101).

14. The four-rotor helicopter (1) according to claim 12 or 13, comprising a unit for controlling the alignment of the helicopter, designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and connected to the drive elements (10) of the rotors (3) for controlling them as a function of the drive signal, maintaining the alignment even in the event of a fault to one of the four rotors (3).

5. The four-rotor helicopter (1) according to any one of claims 12 to 14, wherein the drive elements (10) are designed for tilting the axis of rotation of each rotor (3) independently from the orientation of the axes of rotation of the other rotors (3).

16. The four-rotor helicopter (1) according to any one of claims 12 to 15, comprising actuator means (9) associated with the propellers (8) of at least one of the pairs of rotors (3) for varying, relatively, the pitch, the rotors of the at least one pair being connected by a kinematic mechanism to a same motor (5), for being rotated at the same angular speed.

17. The four-rotor helicopter (1) according to claim 16, wherein all the rotors (3) are connected by a kinematic mechanism to the same motor (5) for being rotated at the same angular speed, the actuator means (9) being designed for varying the pitch of the propellers (8) of both the groups (4), relative to each other.

18. The four-rotor helicopter (1) according to claim 17, wherein the actuator means (9) are designed for varying the pitch of the propellers (8) of each of the groups (4) independently from the pitch of the propellers of the other group.

19. The four-rotor helicopter (1) according to claim 17 or 18, wherein the actuator means (9), for each rotor (3), comprise a movable unit (93) slidable along an axis (Α') of rotation of a propeller (8) of the rotor (3), wherein the propeller (8) comprises a pin (92) rotating about the axis (Α') and a pair of blades (11) rotatably coupled to the pin (92) so as to rotate about an axis (B) defined by the pin (92) and transversal to the axis (Α'), the movable unit (93) being connected by a kinematic mechanism to the blades (11), in such a way that a movement of the movable unit along the axis (Α') generates a corresponding rotation of the blades (11) about the axis (B).

20. The four-rotor helicopter (1) according to any one of claims 16 to 19, comprising four belts (61) wound on corresponding pairs of pulleys, each pair of pulleys having a first pulley connected to the motor (5) and a second pulley connected by a kinematic mechanism to a propeller (8) of the corresponding rotor (3).

21. The four-rotor helicopter (1) according to any one of claims 16 to 20, comprising a unit for controlling the alignment of the aircraft, designed to receive a drive signal, representing the commands given by the pilot for giving a desired alignment to the aircraft, and connected to the actuator means (9) for controlling them as a function of the drive signal.

22. A process for controlling the alignment of a four-rotor helicopter (1), having four rotors (3) connected to the frame in such a way as to be grouped in two pairs (4), the rotors (3) of each pair (4) being positioned diametrically opposite a corresponding operating axis (X, Y), for allowing a rotation of the helicopter about the corresponding operating axis (X, Y), the operating axes (X, Y) not being parallel to each other,

characterised in that it comprises a step of tilting the axis of rotation of the rotors (3).

23. The process according to claim 22, comprising the following steps: - moving of the rotors (3) of at least one of the pairs (4) for rotating the propellers (8) at the same speed;