WO2022171958A1

WO2022171958A1 - Vtol aircraft having four rotors in a cruciform arrangement, and associated method for managing an emergency landing

Info

Publication number: WO2022171958A1
Application number: PCT/FR2022/050237
Authority: WO
Inventors: Gaetan Alain Robert CHESNEAU
Original assignee: Safran
Priority date: 2021-02-15
Filing date: 2022-02-09
Publication date: 2022-08-18
Also published as: FR3119836A1; FR3119836B1

Abstract

VTOL aircraft having four rotors (10), each driving a propeller (14A, 14B, 14C, 14D), and comprising a control unit (18) for delivering a speed setpoint to each of the four rotors (12A, 12B, 12C, 12D), the four rotors being mounted on four arms (28A, 28B, 28C, 28D) defining two shafts in a cruciform arrangement supporting an aircraft airframe (30) intended to accommodate occupants, each of the two opposing rotors on a single shaft rotating in the same rotational direction, in which aircraft, in order to ensure a controlled emergency landing of the aircraft in the event of a rotor or propeller failure, without the airframe being rotated around the aircraft's yaw axis, the control unit (18) is configured to detect the fault and to generate zero speed setpoints for the faulty rotor or the rotor associated with the faulty propeller and the rotor diametrically opposite same and to simultaneously control a decoupling mechanism (32), decoupling the airframe from the two supporting shafts in a cruciform arrangement.

Description

VTOL AIRCRAFT WITH FOUR CROSS-ROTORS AND ASSOCIATED EMERGENCY LANDING MANAGEMENT METHOD

Technical area

The present invention relates to the general field of individual flying means of transport of the VTOL aircraft type (for “Vertical Take-Off and Landing”) and it relates more particularly to VTOLs with four rotors fixedly mounted on two cross-shaped axes.

Prior technique

Vertical takeoff and vertical landing are essential characteristics of VTOL aircraft, particularly in the context of urban evolutions of the logistics or passenger transport type, because they make it possible to avoid a take-off runway while being able to lay on restricted or even unprepared spaces.

Helicopters with a conventional configuration (a main rotor and a tail anti-torque rotor) have this characteristic with their main rotor, but this limits performance in the cruise phase with speeds not exceeding 300 km/h, in particular because of the Mach at the tip of the advancing blade (not horizontal). The vertical take-off constraint requires the generation of vertical thrust, whereas flight in airplane mode requires horizontal thrust. Since only one propeller rotor is available in this single-engine, main-rotor configuration, it is necessary to be able to tilt it through a swashplate mechanism to control pitch and roll motions. An anti-torque tail rotor stabilizes the attitude of the aircraft in yaw.

In the event of loss of the main rotor drive system, the autorotation speed allowed by this type of rotor allows the pilot to land even if this maneuver is not without risk for him. The pilot must apply an emergency landing procedure in autorotation followed by a flare phase landing flare in order to respect a certain trajectory during the descent.

Quadcopters (or quadrotors) which typically come in two different “+” or “x” configurations known as quad+ or quadx, make it possible to decouple the three movements of yaw, pitch, and roll with rotation speeds two-by-two opposed rotors. They consist of four rotors of smaller diameters to move a mass equivalent to that of a conventional helicopter (the lift being distributed over four points instead of just one in such a VTOL) and these four rotors do not need to be articulated or tilted around their axis of rotation to modify the attitude of the aircraft in nominal operation. Indeed, as is known, it is modified via the modification of the rotation speeds of the four rotors.

However, unlike conventional helicopters, an autorotation regime is not accessible in a quadricopter and the loss of the drive system of a rotor is therefore problematic because it almost systematically leads to the loss of the VTOL aircraft and therefore of the mission.

A first known solution to this problem is to make a redundancy of the propulsion system, thus effectively creating an octocopter. However, this solution, in addition to causing a significant increase in the onboard mass and therefore reducing flight performance, involves particularly complex management of the direction of rotation of these eight rotors, in particular when switching from nominal operation to degraded operation. following the loss of a rotor.

Also, it is also known to stop the rotor opposite the failed rotor to allow the quadricopter to return to the ground without losing the mission. However, if this stopping of the opposite rotor makes it possible to stabilize the quadricopter in a horizontal plane, the necessarily reduced thrust force of the two rotors remaining in operation, by becoming less than the weight of the aircraft, will cause the VTOL to descend vertically until on the ground by rotating on itself (under the effect of the moment of rotation around its yaw axis which is created by the two remaining rotors which turn in the same direction of rotation, clockwise or counterclockwise depending on the rotor impacted), which cannot be envisaged, in particular when the cabin of the VTOL aircraft includes occupants, people or even animals.

Disclosure of Invention

The main purpose of the present invention is therefore to overcome these drawbacks by proposing a VTOL aircraft of the quadricopter type with fixed rotors capable of ensuring a controlled emergency landing in the event of failure of an engine or a propellant while eliminating all yaw movement such as to cause the occupants being transported to rotate during their descent to the ground. Another object is to allow the continuation of the mission despite this breakdown by allowing the aircraft to be reinserted into air traffic.

This object is achieved by a VTOL aircraft with four rotors each driving a propeller and comprising a control unit for delivering a speed setpoint to each of these four rotors, the four rotors being mounted on four arms defining two cross axes supporting a cell of the aircraft intended to receive the transported load, the two opposite rotors of the same axis each turning in the same direction of rotation, characterized in that, to ensure in the event of a fault in a rotor or a propeller, a controlled emergency landing of the aircraft without rotation of the cell around a yaw axis of the aircraft, the control unit is configured to detect the fault and to generate zero speed instructions on the rotor in fault or the rotor associated with the faulty propeller and that which is diametrically opposed to it, and simultaneously controlling a decoupling mechanism ensuring uncoupling of the cell from the two cross axes supporting it.

Thus, by uncoupling the cell from the arms supporting the rotors, it is possible to avoid its rotation during the descent of the aircraft and a soft landing is permitted, a guarantee of safety for the occupants transported.

Advantageously, the separation mechanism comprises a blocking finger actuated by an actuation system and selectively blocking the rotation of a central rotation shaft secured to the two cross axes. Preferably, said actuation system is a servomotor, the locking finger of which constitutes the motor shaft, or an electric motor actuating a worm in engagement with a rack integral with the locking finger.

Advantageously, the separation mechanism further comprises a first electric machine mounted on the central rotation shaft and preferably second and third electric machines articulated in rotation respectively on the pitch and roll axes of the aircraft, the first, second and third electric machines being advantageously machines operating on four quadrants.

The invention also relates to a method for managing an emergency landing in a VTOL aircraft with four rotors each driving a propeller and comprising a control unit for delivering a speed setpoint to each of these four rotors, the four rotors being mounted fixedly on four arms defining two cross axes supporting a cell of the aircraft intended to receive occupants, the two opposite rotors of the same axis each rotating in the same direction of rotation, process in which, in order to ensure in the event of a fault of a rotor or a propeller, a controlled emergency landing of the aircraft without rotation of the cell around a yaw axis of the aircraft, the defect is first detected and then simultaneously, it zero speed setpoints are generated on the faulty rotor or the rotor associated with the faulty propeller and the one diametrically opposed to it, and a decoupling mechanism is controlled ensuring uncoupling of the cell from the two axes e n cross supporting it.

Advantageously, the method also consists in controlling a first electric machine to deliver, via the rotation of a central shaft integral with the two cross axes, an anti-torque (AC) to the aircraft intended to cancel the resulting yaw moment of the rotor or propeller fault and preferably to control second and third electric machines for, after the uncoupling of the cell following the rotor or propeller fault, to follow and slave the inclination of the cell to the inclination of the two cross axes and therefore at the forward speed of the aircraft.

Preferably, to prevent the airframe from rotating around the yaw axis and allow the aircraft to land without the airframe rotating or continue its mission, the control of the first electric machine is adapted to respectively make it possible to reduce gradually and in a coordinated manner each of the rotation speeds of the two rotors remaining in operation or make it possible to increase the rotation speeds of these two rotors in order to stop the descent or even ensure an ascent for the continuation of the mission in this degraded mode.

Advantageously, the continuation of the mission is conditioned on a zero rate of rotation and on a zero linear speed around and along the axes of yaw, pitch and roll.

Brief description of the drawings

Other characteristics and advantages of the present invention will become apparent from the description given below, with reference to the appended drawings which illustrate an example of embodiment devoid of any limiting character and on which:

[Fig. 1] Figure 1 is a block diagram of the electrical architecture of a quadricopter,

[Fig. 2] FIG. 2 very schematically illustrates an example of a quadricopter according to the invention,

[Fig. 3] figure 3 illustrates a first embodiment of a decoupling assembly implemented in the quadricopter of figure 2,

[Fig. 4A] FIG. 4A illustrates a view from above of the forces brought into play during hovering flight without rotation of a quadricopter according to the invention,

[Fig. 4B] FIG. 4B illustrates a front or side view of the forces brought into play during hovering flight without rotation of a quadricopter according to the invention,

[Fig. 5A] FIG. 5A shows an operating step of the emergency landing management method of the invention,

[Fig. 5B] FIG. 5B shows an operating step of the emergency landing management method of the invention,

[Fig. 6A] FIG. 6A illustrates a top view of the forces brought into play in the event of a breakdown of a quadricopter according to the invention, [Fig. 6B] FIG. 6B illustrates in front or side view the forces brought into play in the event of a breakdown of a quadricopter according to the invention,

[Fig. 7] FIG. 7 illustrates a second embodiment of a decoupling assembly according to the invention, and

[Fig. 8] FIG. 8 represents in the form of a state diagram the various functional configurations in which the quadricopter according to the invention may be found.

Description of embodiments

FIG. 1 schematically shows the electrical architecture of a VTOL aircraft of the quadricopter type 10 comprising four thrusters (horizontal propellers 12A to 12D) each connected to an electric drive motor (or rotor) 14A to 14D whose rotation is controlled via one or more power converters 16 by a control unit 18 of the dedicated controller type which delivers the speed setpoints for these motors. This control unit is connected to a memory module 20 comprising in particular a map of the grounds flown over, an input/output module 22 in connection with various sensors (not shown) of physical data or images and necessary for the flight of the aircraft (position, altitude, external temperature and pressure, on-board mass, wind speed, etc.) such as the control of the four engines (engine speed and temperature for example) and a transmission/reception module 24 for in particular the exchange of this data via a 24A radio frequency antenna with ground stations. One or more batteries 26 are also provided for powering the various elements of the aircraft. Depending on the area overflown and the surrounding obstacles, different piloting strategies (control laws) can of course be implemented at the level of the flight controller 18.

Figure 2 schematically illustrates such a quadricopter with four arms 26A,

26B, 26C, 26D (forming two cross axes) supporting a cell or cabin 28 and which can perform vertical takeoffs and landings (along the so-called yaw z axis) as well as horizontal movements (along the so-called roll x axes where does it say pitch) in cruising speed at variable speeds depending on the respective speeds of its four thrusters 12A, 12C and 12B, 12D. It can also operate a stationary flight, that is to say remained motionless without rotation in a given attitude (position and altitude). The four arms supporting the engines and the propellers generally placed at the ends of the cross form what is known as an aircraft support structure which is connected to the airframe of the aircraft by an appropriate decoupling assembly 30 shown in more detail in Figure 3.

This assembly 30 comprises a central rotation shaft 32 integral with the support structure and fixed vertically in the middle of the cross to be connected to the cell 28 via a pivot connection 34. This central shaft is driven in rotation under the control of the processing unit 18 by an electric machine 36 mounted at the end of the shaft and operational in the 4 dials, that is to say operating both as a motor and as a generator and rotating in one direction to the other. A locking finger 38 makes it possible to make the cell and the support structure mechanically integral via the pivot connection 34. More precisely, the locking finger 38 is mechanically linked to a rack 40 engaged with a worm screw 42 driven for a motor under the control of the processing unit and mechanically fixed to the cell via the pivot connection 34. Of course, this endless screw and rack system could be replaced by a servomotor, the motor shaft of which then constitutes the finger of blockage.

FIGS. 4A and 4B illustrate stationary flight without rotation in which the sum F of the thrust forces exactly balances the total weight (empty weight of the cell included plus transported load) of the aircraft P (the wind being assumed to be zero). It can be noted that in this equilibrium configuration, the speeds of rotation V (and torques C) of the four rotors are identical and each have a thrust force F _I2A , F _I 2 _B , F12 F i2 _D equal to a quarter of the weight total. The two by two opposed propellers 12A, 12C and 12B, 12D (those whose support arms are aligned) rotate in the same direction and the adjacent propellers (for example 12A, 12B and 12C, 12D whose arms 26A, 26B and 26C, 26D are placed at 90° to each other) rotate in opposite directions. According to the invention, it is proposed to allow by the appropriate decoupling assembly 30 a decoupling of the cell (the cabin 28 which accommodates the transported load) of this support structure in the event of engine failure via the release of the finger of blocking 38 ensuring their connection in rotation and simultaneously controlling the rate of rotation of the support structure (which will rotate around the yaw axis) with respect to the cell which must remain fixed without rotation around this z axis, thanks to the use of the electric machine 36 to, by creating an anti-torque adapted to the rotation of the support structure, cancel a rate of rotation of the cell measured by a gyroscope of an inertial unit (one of the sensors not illustrated in Figure 1) of the aircraft. Indeed, so that the cell does not have time to rotate around its yaw axis (in particular for the comfort of the occupant), it is assumed that the uncoupling of the cell with the support structure will be instantaneous (which requires a very fast actuation system) and that there is no wind. Concerning this second point, the aerodynamic shape of the cell with an additional empennage should make it possible to improve the control of the attitudes of the cell with wind in this transitional phase which must remain as short as possible. The support structure therefore becomes a rotary wing in autorotation in the event of a motor or rotor failure, while the electrical machine at the interface of the two elements becomes an anti-torque device.

In vertical (take-off and landing), horizontal or stationary flight, the locking finger is engaged and the support structure and the cell are mechanically secured to each other and evolve together, a rotation of the structure causing a rotation of the cell. In this standard flight configuration, the electrical machine is not activated and the performance of the aircraft in terms of speed, flight duration or energy consumption in cruise flight will be only slightly degraded compared to a Standard VTOL without module 30.

On the other hand, in the event of failure of one of the engines (at the level of the rotor or the propeller) from a situation in hover or in vertical flight (climb or descent), the uncoupling of the cell will make it possible to create via the machine electric an anti ^¬ torque which will cancel the rotational movement around the yaw axis of the levitation structure by creating a yaw moment without a change in pitch or roll attitude. This control of the anti-torque by controlling the electric machine by avoiding the rotation of the cell on itself makes it possible to ensure the boarding of a crew and passengers. But it also obviously proves useful for controlling an aircraft over its entire mission whether it is more generally transporting any living being or whether it is simply intended for logistics.

To do this, and as shown in FIG. 5A, a fault is first identified at the level of an engine or a propeller (in this case 12B), for example by a measurement of an engine speed inconsistent with the speed setpoint delivered by the control unit, then, once this identification has been confirmed, on the one hand to the simultaneous sending then the maintenance of a zero speed setpoint to the motor supplying the faulty rotor and to the diametrically opposed motor (in this case 12D - see FIG. 5B) and on the other hand to a disengagement of the locking finger 38 ensuring the mechanical connection in rotation between the support structure and the cell. The cell which has become free to rotate will evolve independently of the support structure which will turn on itself under the effect of the two rotors remaining in operation and it is the adequate control of the electric machine (production of the necessary torque) which will fix the relative rotation rate of one with respect to the other with the aim of canceling the rotation movement of the cell in the very short transient phase between the detection of the fault and the release of the finger. In addition, it is to the cell that the rest legs of the aircraft are connected which will come into contact with the ground during landing and which therefore must not turn on themselves around the yaw axis. .

Thus, and as shown in FIG. 6A, in a hovering or vertical flight situation (climb or descent), the detection of such a failure will lead to the stopping of the rotation of two of the four rotors opposed two by two in order to create a yaw moment (torque C) without pitching or rolling but with a reduction in the thrust force. This thrust force F becoming less than the weight of the aircraft P (see FIG. 6B), this will result for the quadricopter in a vertical descent at a determined rate of descent which, if the actuation of the locking finger is simultaneous, c 'is say fast enough (in practice from 10 to 100 milliseconds) following the detection of the failure, will take place without causing the cell to rotate around the yaw axis (z axis), the electrical machine creating on the rotation shaft 32 an anti-torque (AC) opposing the yaw moment created by the rotors remaining in operation on the support structure, to stabilize in hovering flight.

With this strategy, the quadricopter will be able to descend vertically without the cell rotating around the yaw axis. It is then possible either to increase the rotation speeds of the rotors remaining in operation to stop the descent or even go up again and the control of the electric machine will then be adapted accordingly to avoid the cell rotating around the axis of yaw, or to reduce progressively and in a coordinated manner each of the rotation speeds of these rotors by adapting the control of the electric machine. The attitude in pitch, in roll and in yaw will remain unchanged as the aircraft approaches the ground and the aircraft will eventually land without turning on itself in contact with the ground making it possible to deposit the transported occupants without difficulty.

This ability to stop the fall and climb back to altitude will allow this aircraft to fit into air traffic while being robust to engine failure. Moreover, by analogy with twin-engine helicopters, it will be able to allow a crew to continue its mission in the event of engine failure if the control of the electric machine is adapted to operate beyond a vertical trajectory.

More particularly, in a complementary embodiment illustrated in FIG. 7, the cabin is not only made mobile in rotation along its yaw axis by the first electric machine 36 but also articulated in rotation on its pitch and roll axes and slaved according to the inclination of the plane of the support structure according to the desired forward speed in a given direction by second and third electric machines 44, 46 also controlled from the processing unit 18. All three connections pivot thus formed forms what can be called an articulated stabilization nacelle 48 allowing the cell to be mechanically suspended from the support structure. In this embodiment, in forward flight, the inclination of the cell is slaved to the inclination of the plane of the support structure and therefore to the forward speed. This allows the occupants of the cell to be in a comfortable flight situation with always a view of the direction of travel as in horizontal flight.

In the event of engine failure and if the mission is abandoned (with emergency landing priority), the same process as in vertical flight without an airframe can be operated with an additional step which consists in repositioning the plane of the structure of lift horizontally as quickly as possible to better manage the descent. If, on the other hand, the mission must continue (flight over the sea), a piloting mode is possible where the support structure would turn on itself in one direction and where the yaw joint would be piloted to have a rate of zero rotation of the airframe to allow forward flight. The reversal of the direction of rotation of one of the rotors still operational could also be carried out to finish the mission without impacting the attitude of the cell. With a longitudinal repositioning of the front of the cell according to the axis of the still operating rotors, the bi-rotor obtained could behave like a tandem helicopter with two counter-rotating rotors. The management of the forward and backward rotation speeds via the second and third electric machines would make it possible to tilt the aircraft forwards or backwards to engage in forward or backward flight.

Thus the emergency landing method of the invention making it possible to bring the VTOL aircraft back to the ground without harming its occupants comprises the following steps:

• Detect the loss of an engine (rotor) or thruster (propeller),

• Generate zero speed instructions on this motor and the one diametrically opposed to it and simultaneously disengage the locking pin,

• Generate speed instructions adapted to a desired rate of descent for the two motors remaining in operation and provide by the electric machine the anti-torque necessary to cancel the rotational movement of the cell around the yaw axis , Where • Stabilize the loss of altitude by re-accelerating in a coordinated manner the two motors remaining in operation and supply by the electric machine the anti ^¬ torque necessary to cancel the rotational movement of the cell around the yaw axis .

FIG. 8 represents in the form of a state diagram the different functional configurations in which the quadricopter can thus find itself.

Immediately after switching on and a certain number of initialization steps managed during state 50 “Start”, the quadricopter is in state 52 “Landed”, with the motors ready to start. The sending of a command by the pilot (if he is at the controls of the aircraft) or the remote pilot (if he has remote control) causes the start of the engines and the takeoff of the quadricopter which is then in the state 54 "Take off" from which two main modes of operation are possible.

In a first piloting mode, state 56 “Hovering flight”, the piloting of the quadricopter is operated automatically by implementing the autonomous system for stabilization in hovering flight. This autopilot mode is activated in particular at the end of the take-off phase, as soon as the pilot releases his controls, or in the event of interruption of the radio link between the aircraft and the VTOL in the event of a remotely piloted command.

In the other piloting mode, state 58 “Piloted flight”, the piloting of the quadricopter is operated directly by the pilot or remote pilot, by means of a combination of signals emitted by the inclination detector of the device and/or commands available on the ground station.

The "Piloted flight" or "Hovering flight" state ends by passing to a landing state 60 "Landing", following the pressing of a specific command on the aircraft or in the event of on-board energy reserve weak (here the battery). Switching to this state produces a reduction in engine rotation speed and a coherent reduction in altitude. When contact with the ground has been detected, the state is again state 52 “Landed”. The quadricopter also includes a state 62 "Stationary piloted transition", to allow the quadricopter to pass from the state 58 of movement in piloted flight, where it moves with a non-zero inclination and therefore a horizontal speed which can be relatively high, up to the state 56 of vertical levitation in hovering flight where it will be immobile and maintained in this fixed position by the automatic piloting and stabilization system. This stopping procedure will be carried out in a minimum time and without horizontal speed reversal.

It also includes a state 64 "Piloted stationary transition", to allow the VTOL to pass the vertical levitation state 56 where it will be immobile and maintained in this fixed position by the automatic piloting and stabilization system in the state of movement. 58, where it moves with a non-zero inclination and therefore a horizontal speed which can be relatively high.

Finally, state 66 “Fault management” corresponds to an emergency state in the event of an anomaly being detected. It causes the default launch of the quadricopter emergency landing process described above. This failure state can be reached from any of the states previously described (illustrated by the dotted arrows), in particular in the event of failure of the distributed propulsion system (blockage of an engine or loss of a rotor). The purpose of this process is to stabilize the loss of altitude. Once the loss has stabilized, the pilot or remote pilot from a ground station can choose to continue the mission in this degraded mode and therefore not land immediately. This choice is advantageously made via a simple man-machine interface, easy to access and within easy reach like a push button near or on the control interfaces. For example, by default, button released, the emergency landing procedure is engaged. If the pilot or remote pilot presses the button and the conditions for continuing the mission are met: measurement of the stabilization of the attitude of the aircraft (absence of cell rotation rate on the 3 yaw axes , pitch and roll) and measurement of the absence of movement (zero linear speed along the 3 axes of the cell) by a state estimator internal to the flight controller, the emergency landing procedure is abandoned and the pilot can continue the mission in degraded mode with a reduced guidance/piloting capability identical to that available to make the emergency landing.

Claims

[Claim 1] VTOL aircraft with four rotors (10) each driving a propeller (14A, 14B, 14C, 14D) and comprising a control unit (18) for delivering a speed setpoint to each of these four rotors (12A, 12B ,

12C, 12D), the four rotors being mounted on four arms (28A, 28B, 28C, 28D) defining two cross axes supporting a cell (30) of the aircraft intended to receive the transported load, the two opposite rotors the same axis each rotating in the same direction of rotation, characterized in that, in the event of a rotor or propeller failure, a controlled emergency landing of the aircraft without rotation of the airframe around a yaw axis of the aircraft, the control unit (18) is configured to detect the fault and to generate zero speed instructions on the faulty rotor or the rotor associated with the faulty propeller and the one which is diametrically opposed to it, and simultaneously control a decoupling mechanism (32) ensuring a decoupling of the cell from the two cross axes supporting it.

[Claim 2] Four-rotor VTOL aircraft according to claim 1, characterized in that the separation mechanism comprises a locking finger (38) actuated by an actuating system (40, 42) and selectively blocking the rotation of a central rotation shaft (32) secured to the two cross axes.

[Claim 3] Four-rotor VTOL aircraft according to Claim 2, characterized in that the said actuation system is a servomotor, the locking finger of which constitutes the motor shaft, or an electric motor actuating a worm screw (42) in engagement with a rack (40) integral with the locking pin.

[Claim 4] A four-rotor VTOL aircraft according to claim 2, characterized in that the separation mechanism further comprises a first electrical machine (36) mounted on the central rotation shaft (32).

[Claim 5] A four-rotor VTOL aircraft according to claim 4, characterized in that the separation mechanism further comprises second (44) and third (46) electric machines articulated in rotation respectively on the pitch and roll axes of the aircraft.

[Claim 6] A four-rotor VTOL aircraft according to claim 4 or claim 5, characterized in that the first, second and third (46) electrical machines are four-quadrant machines.

[Claim 7] Method for managing an emergency landing in a VTOL aircraft with four rotors (10) each driving a propeller (14A, 14B, 14C, 14D) and comprising a control unit (18) for delivering a speed at each of these four rotors (12A, 12B, 12C, 12D), the four rotors being fixedly mounted on four arms (28A, 28B, 28C, 28D) defining two cross axes supporting a cell (30) of the aircraft intended to receive occupants, the two opposite rotors of the same axis each turning in the same direction of rotation, process in which, in the event of a fault in a rotor or a propeller, a controlled emergency landing of the aircraft without rotation of the cell around a yaw axis of the aircraft, the fault is first detected and then simultaneously, zero speed instructions are generated on the faulty rotor or the associated rotor to the faulty propeller and the one diametrically opposed to it, and a cutting mechanism is controlled lage (32) ensuring a disconnection of the cell from the two cross axes supporting it.

[Claim 8] Method according to claim 7, characterized in that a first electric machine (36) is also controlled to deliver, via the rotation of a central shaft (32) integral with the two cross axes, an anti -torque (AC) to the aircraft intended to cancel the yawing moment resulting from the rotor or propeller failure.

[Claim 9] Method according to claim 8, characterized in that in order to prevent the cell from rotating around the yaw axis and to allow the aircraft to land without the cell rotating on itself or continue its mission, the control of the first electric machine (36) is adapted to respectively make it possible to reduce gradually and in a coordinated manner each of the rotation speeds of the two remaining rotors in operation or make it possible to increase the rotation speeds of these two rotors in order to stop the descent or even to ensure an ascent for the continuation of the mission in this degraded mode.

[Claim 10] Method according to claim 9, characterized in that the continuation of the mission is conditioned on a zero rate of rotation and at a zero linear speed around and along the axes of yaw, pitch and roll.

[Claim 11] Method according to claim 8, characterized in that second (44) and third (46) electrical machines are also controlled for, after the uncoupling of the cell following a fault in the rotor or the propeller , follow and slave the inclination of the cell to the inclination of the two cross axes and therefore to the forward speed of the aircraft.