Vertical takeoff and landing aircraft

Abstract

Vertical takeoff and landing aircraft comprising: at least four pairs of contra-rotating propellers (10); drive units (21, 22, 23) to drive the propellers (11, 12) in rotation; a flight control unit to command the drive units (21, 22, 23) so as to obtain, for each propeller (11, 12), a target thrust; and a detection system to detect a failure of the drive units (21, 22, 23). Each pair of propellers (10) is equipped with three separately controllable drive units (21, 22, 23): a primary drive unit (21) for driving one of the propellers in the pair, and secondary and tertiary drive units (22, 23) for driving the other propeller. The secondary and tertiary drive units (22, 23) are arranged so that their drive torques are additive. (Figure 4)

Description

Title of the invention: Vertical takeoff and landing aircraft technical field

[0001] The invention relates to a vertical take-off and landing aircraft or "VTOL" aircraft (English acronym for "Vertical Take-off and Landing"). Background

[0002] Many VTOL aircraft configurations have been studied in the past. Examples of known configurations are described in patent document EP 3393904 B1 and in Publication 1: “Local controllability and attitude stabilization of multirotor UAVs: Validation on a coaxial octorotor” by Majd Saied et al (Robotics and Autonomous Systems 91 (2107) 128-138).

[0003] In Publication 1, according to the so-called coaxial counter-rotating octorotor configuration, the aircraft comprises: four pairs of counter-rotating propellers to provide lift to the aircraft; drive units to drive the propellers in rotation, each drive unit comprising an electric motor and its electronic control system; and a flight control unit to command the drive units so as to obtain, for each propeller, a target thrust.

[0004] Compared to other configurations, the coaxial, counter-rotating eight-rotor configuration offers advantages in terms of compactness. Furthermore, since the helical flow of the first rotor in a pair is corrected by the second, propulsive efficiency is improved. Such a configuration therefore makes it possible to obtain a maneuverable, stable aircraft well-suited for operations in confined areas. On the other hand, it is difficult to control the aircraft's behavior after the failure of one of the engine units or, worse, two engine units (see Table 10 of Publication 1).

[0005] The failure of one of the propulsion units has a direct and immediate impact on the aircraft's stability and creates a major safety risk. In the worst-case scenario, the aircraft risks rolling over and crashing. The problem becomes even more critical if two propulsion units fail simultaneously. The simultaneous failure of two propulsion units belonging to two pairs of propellers is referred to as a "double failure." While the simultaneous failure of three or more propulsion units is a highly improbable event, the occurrence of a double failure is considered sufficiently probable to warrant consideration in the aircraft design.This is therefore a critical point for airworthiness certification, particularly for certain categories of aircraft such as unmanned aerial vehicles or "UAVs" (English acronym for "Unmanned Aerial Vehicle") with a mass greater than 25kg when they have to fly over. urban areas or for VTOL aircraft intended for passenger transport.

[0006] There is therefore a need for a solution that allows for better control of the behavior of a multirotor aircraft with coaxial counter-rotating propellers in the event of a double failure. This solution must also be of relatively simple design and relatively limited mass, so as to guarantee a good level of aircraft performance, particularly in terms of payload and range. General presentation

[0007] A vertical takeoff and landing aircraft according to the invention comprises: at least four pairs of counter-rotating propellers to provide, at least in part, lift for the aircraft; drive units to rotate the propellers, each drive unit comprising an electric motor and its electronic control system; a flight control unit to command the drive units so as to obtain, for each propeller, a target thrust; and a detection system to detect a failure of the drive units. Each pair of propellers comprises an upper propeller and a lower propeller rotating in opposite directions around a propeller axis substantially parallel to the aircraft's yaw axis. The propeller pairs are arranged symmetrically with respect to the aircraft's roll and pitch axes. Each pair of propellers is equipped with three separately controllable drive units: a primary drive unit for driving one of the propellers (the single-engine propeller), and secondary and tertiary drive units for driving the other propeller (the twin-engine propeller). The secondary and tertiary drive units are arranged so that their engine torques are additive.

[0008] When a double failure is detected by the detection system, the flight control unit commands the secondary and tertiary drive units of at least two propellers, called compensating propellers, chosen from among the twin-engine propellers, to drive each of the compensating propellers by means of its secondary and tertiary drive units, so as to increase the thrust of each of the compensating propellers and compensate for the loss of thrust related to the failure of the two drive units.

[0009] The proposed solution therefore consists, for each pair of counter-rotating propellers, of providing one single-engine propeller and one dual-engine propeller, and of using, in the event of a double failure, at least two dual-engine propellers as compensating propellers. Thanks to the action of the compensating propellers, it is possible to control the aircraft's behavior in the event of a double failure, regardless of the configuration of the double failure.

[0010] By doubling the power of only one of the propellers in each pair, a good compromise is obtained between the desired safety and the aircraft's mass. It should be noted that another approach would consist of doubling the power of each of the two propellers of Each pair of counter-rotating propellers. This solution, known as a "full redundancy solution," would also address the problem of double failure of the propulsion units. However, it would have the drawback of increasing the aircraft's mass too significantly, making the compromise between safety and weight unsatisfactory.

[0011] The aforementioned features and advantages, as well as others, will become apparent from the detailed description that follows. This detailed description refers to the accompanying drawings. Brief description of the drawings

[0012] The accompanying drawings are schematic and not necessarily to scale; their primary purpose is to illustrate the principles of the invention. In these drawings, identical elements (or parts of elements) are identified by the same reference numerals from one figure (fig) to another. [Fig.1] This figure represents an example of a VTOL aircraft seen in profile. [Fig. 2] This figure shows the VTOL aircraft example from [Fig. 1] viewed from above. [Fig. 3] This figure schematically represents another example of a VTOL aircraft. [Fig. 4] This figure shows in detail an example of contra-rotating propellers with their drive units. [Fig.5] This figure represents the aircraft from [Fig.3] during a first example of a double failure. [Fig.6] This figure represents the aircraft from [Fig.3] during a second example of a double failure. [Fig.7] This figure represents the aircraft from [Fig.3] during a third example of a double failure. [Fig.8] This figure represents the aircraft from [Fig.3] during a fourth example of a double failure. Detailed description

[0013] Specific embodiments of the proposed aircraft are described in detail below, with reference to the example shown in the accompanying drawings. These embodiments illustrate the features and advantages of the invention. It should be noted, however, that the invention is not limited to these embodiments or to the example shown.

[0014] Generally, the multi-rotor VTOL aircraft comprises at least four pairs of counter-rotating propellers to provide, at least in part, lift to the aircraft; drive units to rotate the propellers, each drive unit comprising an electric motor and its electronic control system; a flight control unit to command the drive units so as to obtain, for each propeller, a target thrust; and a detection system to detect a de- failure of the drive units.

[0015] Figures 1 and 2 schematically represent an example of an aircraft 1 with four pairs of counter-rotating propellers 10. Figure 3 schematically represents another example of an aircraft 1 with eight pairs of counter-rotating propellers 10. However, the number of propeller pairs is not limited to these examples, and the aircraft may include 4, 5, 6, 7, 8, 9, 10, etc., pairs of propellers. When the aircraft 1 includes an odd number of propeller pairs 10, at least one of the propeller pairs 10 is arranged on the aircraft's roll axis X.

[0016] The roll axis X, pitch axis Y, and yaw axis Z of the aircraft are imaginary axes around which the aircraft rotates. These axes are oriented as follows: - the roll axis X, or longitudinal axis, is parallel to the line extending from the front part (e.g., the nose) to the rear part (e.g., the tail) of the aircraft, through the central body (e.g., the fuselage) of the aircraft, and passes through the center of mass of the aircraft; - The pitch axis Y, or lateral or transverse axis, is the axis perpendicular to the roll axis passing through the aircraft's center of mass. When the aircraft has a primary fixed wing, the pitch axis Y extends from one end of the primary fixed wing to the other end of that wing; and - the yaw axis Z, or vertical axis, passes through the center of mass G of the aircraft, from top to bottom, and is perpendicular to the other two axes X, Y.

[0017] These X, Y, Z axes are identified in the examples of figures 1 to 3. The front and the rear, like the upstream or the downstream, are defined with respect to the normal direction of advance of the aircraft, identified by the arrow of the X axis.

[0018] Figure 4 schematically represents, in detail, an example of a pair of counter-rotating propellers 10. The pair of propellers 10 comprises an upper propeller 11 and a lower propeller 12 rotating in opposite directions about a propeller axis A. The propeller axis A is substantially parallel to the yaw axis Z of the aircraft 1. The expression "substantially parallel" means that the propeller axis A may not be strictly parallel to the yaw axis Z and may form a slight angle (e.g., less than 10°) with the Z axis, provided that this angle does not prevent the effect that the pair of propellers 10 is intended to produce.

[0019] The direction of rotation of each propeller is represented by a double arrow in the figures. The pairs of propellers 10 are distributed symmetrically with respect to the roll X and pitch Y axes of the aircraft, and surround the central body (e.g., the fuselage) of the aircraft 1. Each pair of propellers can be connected, for example by means of a mounting arm 15 or any other connecting element, to the central body of the aircraft or to an intermediate element connected to the fuselage such as a fixed wing.

[0020] In the example of Figures 1 and 2, the aircraft 1 comprises a fuselage 2 forming the central body of the aircraft, a propulsion system 5 at the front of the fuselage 2, and four pairs of contra-rotating propellers 10. The aircraft 1 also comprises three wings wing: a canard-type forward wing 20 located at the front of aircraft 1; a main wing 30 located in the middle part of aircraft 1; and a tailplane 40 located at the rear of aircraft 1. The main wing 30 is formed of a pair of wings 32 (i.e. a right wing and a left wing) joined together above the fuselage 2.

[0021] The four pairs of propellers 10 are distributed symmetrically on either side of the main wing 30 and on either side of the fuselage 2. In other words, two pairs of propellers 10 are located on the right side of the fuselage 2, on either side (i.e., forward and backward) of the right wing 32, and two pairs of propellers 10 are located on the left side of the fuselage, on either side (i.e., forward and backward) of the left wing 32. In this example, each pair of propellers 10 is structurally connected, i.e., is fixedly attached, to the main wing 30. Together, the four pairs of propellers 10 and the wing 20, 20, 30 provide lift for the aircraft.

[0022] In the example of [Fig.3], the aircraft 1 comprises a central body 3 around which the pairs of propellers 10 are distributed. The pairs of propellers 10 are distributed symmetrically with respect to the roll X and pitch Y axes of the aircraft 1. Thus, there are two pairs of propellers 10 in each of the front right, front left, rear right and rear left sectors of the aircraft.

[0023] In certain embodiments and in the examples of Figures 1 to 3, the upper propellers 11 symmetrical with respect to the roll axis X rotate in opposite directions, the upper propellers 11 symmetrical with respect to the pitch axis Y rotate in opposite directions, the lower propellers 12 symmetrical with respect to the roll axis X rotate in opposite directions, and the lower propellers 12 symmetrical with respect to the pitch axis Y rotate in opposite directions. Thus, in the example of [Fig. 2], the upper propellers 11 of the forward right and aft left sectors rotate in the same direction.

[0024] As illustrated in [Fig. 4], each pair of propellers 10 is equipped with three separately controllable drive units, namely a primary drive unit 21 for driving one of the propellers, referred to as the single-engine propeller, and secondary drive units 22 and tertiary drive units 23 for driving the other propeller, referred to as the twin-engine propeller. The secondary drive units 22 and tertiary drive units 23 are arranged so that their engine torques are additive. In other words, if in a flight configuration propeller 11 needs to provide thrust requiring a significant torque that only one of the drive units 22, 23 can provide, starting the second drive unit increases the total engine torque to obtain the required thrust. In the example of [Fig.4], the upper propeller 11 is the double-engine propeller and the lower propeller 12 is the single-engine propeller, but the reverse configuration is possible.It should be noted that the use of the ordinal adjectives "primary", "secondary" and "tertiary" is not intended to imply or create an order of operation of the . motor units. The use of these adjectives simply serves to distinguish the motor units from one another.

[0025] Each drive unit 21, 22, 23 comprises an electric motor and its electronic control system. Each drive unit 21, 22, 23 may also comprise an electronic power supply system and, in particular, an inverter. The drive units 21, 22, 23 may be powered by different types of electrical energy sources, such as an energy storage system (batteries, hydrogen), an energy generation system (thermal, hydrogen), or a mixed (hybrid) system. When there are several electrical energy sources on board, the outputs of the electrical energy sources may be summed before being distributed to the drive units. The drive units 21, 22, 23 may be powered independently.

[0026] Aircraft 1 includes a detection system for detecting a failure of each of the drive units 21, 22, 23. Failure means a defect or malfunction of the drive unit, whether that defect or malfunction originates from the electric motor, its electronic control system, or its electronic power supply system. In this application, a propeller with a faulty drive unit is referred to as a "faulty propeller".

[0027] The detection system may include one or more sensors such as temperature probes, engine speed sensors, torque sensors, sensors for measuring various engine currents and / or its electronic circuitry, sensors for measuring leakage currents, partial discharge currents, or any other measurement enabling a health diagnosis (i.e., a condition diagnosis) of the engine unit. The detection system may also use measurements and / or estimation of one or more aircraft parameters and / or flight conditions.

[0028] When a simultaneous failure of two power units, or double failure, is detected by the detection system, the flight control unit commands the secondary and tertiary power units of at least two propellers, called compensating propellers, chosen from among the twin-engine propellers, to drive each of the compensating propellers by means of its secondary and tertiary power units, so as to increase the thrust of each of the compensating propellers and compensate for the loss of thrust related to the shutdown of the two failing power units.

[0029] In certain embodiments, the thrust of each of the compensating propellers is increased beyond the maximum thrust that would be available if the compensating propeller were driven solely by its secondary drive unit 22 or by its tertiary drive unit 23. In other words, the secondary and tertiary drive units, when actuated together, make it possible to obtain a thrust, called "compensating thrust," greater than the thrust that can be obtained with only one of the two drive units 22, 23. Thus, the secondary drive unit 22 is not not sized to obtain, on its own, said compensating thrust. The same applies to the tertiary engine unit 23. This makes it possible to reduce the size and mass of these engine units 22, 23 which, typically, are designed (or selected off-the-shelf) only to ensure the nominal flight thrust.

[0030] In certain embodiments, for each pair of propellers 11, 12 operating normally, the drive units 21, 22 and / or 23 are controlled so that the resisting torques of each of the propellers 11, 12 cancel each other out. The pair of propellers 11, 12 is thus torque-balanced so as not to create a yaw moment.

[0031] In certain embodiments, the secondary drive units 22 and tertiary drive units 23 are identical in terms of motor torque. This choice allows for symmetrical handling of failures in each of these drive units 22, 23.

[0032] In certain embodiments, the upper propellers 11, symmetrical with respect to the roll X and pitch Y axes, rotate in opposite directions, and the lower propellers 12, symmetrical with respect to the roll X and pitch Y axes, rotate in opposite directions. This cancels the yaw moments produced by all the upper propellers and the yaw moments produced by all the lower propellers. Control of the aircraft via the central flight control unit is then facilitated.

[0033] In some embodiments, the flight control unit may be centralized. In some embodiments, the flight control unit is part of the aircraft's flight control system, or "FCS" (Flight Control System), this system being based on the control of one or more aircraft state parameters and / or measurements and / or estimation of one or more aircraft parameters and / or flight conditions to one or more control devices. This flight control system is further equipped with a control reconfiguration function. The flight control system also has a pilot alert function indicating the detection of one or more faults (defects or failures) and the control reconfiguration and its impact on the mission.Preferably, the flight control system includes a pilot assistance function that suggests an optimal trajectory to the pilot and provides assistance in managing the trajectory following control failure and reconfiguration.

[0034] In certain embodiments, the flight control unit defines a compensation strategy, or compensation logic, based on the number of simultaneous failures to be considered. This compensation strategy can be defined from a table dealing with all possible failure cases and proposing a compensation strategy (optimized or not) for each case. The compensation strategy can also be obtained by an embedded optimization algorithm operating in real time. The compensation strategy can be used by the reconfiguration function. Configuration of flight control system commands. The reconfiguration function will adapt the piloting laws and servo gains according to the selected compensation strategy, piloting mode and flight configuration (speed, altitude, etc.).

[0035] Figures 5 to 8 illustrate various possible double failure scenarios. These figures schematically represent the aircraft example in [Fig. 3]. The direction of rotation of propellers 11, 12 is the same as in [Fig. 3]. The single-engine propellers are the lower propellers 12 and the dual-engine propellers are the upper propellers 11, as in the example in [Fig. 4]. However, the single-engine propellers could be the upper propellers and the dual-engine propellers could be the lower propellers, without affecting the explanations that follow. The letters "D", "C" and "E" are used on these figures following the propeller number (e.g. 11C, 11D, 12D, 12E) to designate, respectively, faulty propellers ("D"), compensating propellers ("C") and non-faulty propellers that have been voluntarily stopped ("E").The aircraft's roll axis (X) and pitch axis (Y) define four sectors: a forward right sector (FR), a forward left sector (FL), a rear right sector (RR), and a rear left sector (RL). Several compensation strategies are defined below with reference to these figures.

[0036] In certain embodiments, according to a first compensation strategy, when the two failing drive units are two primary drive units driving, respectively, two single-motor propellers rotating in opposite directions, the compensating propellers comprise the two dual-motor propellers belonging, respectively, to the two pairs of propellers to which the two single-motor propellers belong. In other words, the failing single-motor propellers and the compensating dual-motor propellers belong to the same propeller pairs.

[0037] This first compensation strategy is illustrated by the example in [Fig. 5]. In this example, the single-engine failure propellers are designated 12D and marked with a cross. In the example, the failure propellers 12D are located in the front right sector FR and front left sector FL, respectively, but they could be located in other sectors or both in the same sector. The single-engine failure propellers 12D rotate in opposite directions. In such a case of a double failure, the proposed compensation strategy consists of shutting down the drive units 21 of the failure propellers 12D and using the dual-engine propellers designated 1 IC as compensating propellers. In normal operation, these compensating propellers 1 IC can be driven by a single drive unit, for example, the secondary drive unit 22.In the event of a double failure, the tertiary drive units 23 are activated so that each compensating propeller 1 IC is driven not only by its secondary drive unit 22 but also by its drive unit. tertiary 23. Thus, the thrust of each compensating propeller 1 IC can be increased to compensate for the thrust loss due to the failure of the propellers 12D. Alternatively, in normal operation, the compensating propellers 11C can be driven by their two secondary 22 and tertiary 23 drive units, these drive units producing a nominal torque lower than their maximum available torque. In the event of a double failure, the secondary and tertiary drive units 22, 23 are controlled to produce their maximum available torque (or a torque strictly greater than their nominal torque and less than or equal to their maximum available torque). Thus, the thrust of each compensating propeller 1 IC can be increased to compensate for the thrust loss due to the failure of the propellers 12D.

[0038] In certain embodiments, according to a second compensation strategy, when the two faulty drive units are two primary drive units belonging to two adjacent sectors and driving, respectively, first and second single-engine propellers rotating in the same direction, the flight control unit commands the shutdown of the two faulty drive units and the two primary drive units located, respectively, in the two adjacent sectors and driving the two single-engine propellers symmetrical to the first and second single-engine propellers with respect to the roll axis X or pitch axis Y. In this case, the compensating propellers comprise the four twin-engine propellers belonging, respectively, to the pairs of propellers of which the stopped drive units are part.

[0039] This second compensation strategy is illustrated by the example in [Fig. 6]. In this example, the failed single-engine propellers 12D are located in the forward right sector FR and forward left sector FL, but they could be located in other adjacent sectors (e.g., sectors RL and FL, sectors RL and RR, or sectors RR and FR). The failed single-engine propellers 12D rotate in the same direction. In such a case of double failure, the proposed compensation strategy consists of stopping the failed propellers 12D but also stopping the single-engine propellers 12E, which are located in the two adjacent sectors FL and FR and are symmetrical to the two single-engine propellers 12D with respect to the roll axis X. The compensation strategy also consists of using the four twin-engine propellers 11C as compensating propellers.These compensating propellers 11C are the twin-engine propellers belonging to the same propeller pairs as propellers 12D and 12E. In normal operation, the compensating propellers 1 IC can be driven by a single drive unit, for example, the secondary drive unit 22. In the event of a double failure, the tertiary drive units 23 are actuated so that each compensating propeller 1 IC is driven not only by its secondary drive unit 22 but also by its tertiary drive unit 23. Thus, the thrust of each compensating propeller 1 IC can be increased to compensate for the loss of power. Thrust related to the stopping of propellers 12D and 12E. Alternatively, in normal operation, the compensating propellers 1 IC can be driven by their two secondary drive units 22 and tertiary drive units 23, these drive units producing a nominal torque lower than their maximum available torque. In the event of a double failure, the secondary and tertiary drive units 22 and 23 are controlled to produce their maximum available torque (or a torque strictly greater than their nominal torque and less than or equal to their maximum available torque). Thus, the thrust of each compensating propeller 1 IC can be increased to compensate for the loss of thrust related to the stopping of propellers 12D and 12E.

[0040] In certain embodiments, according to a third compensation strategy, when the two failing drive units are a primary drive unit and a secondary drive unit driving, respectively, a first single-engine propeller and a first dual-engine propeller, the flight control unit commands: the shutdown of the failing primary drive unit; the shutdown of a primary drive unit driving a second single-engine propeller symmetrical to the first single-engine propeller with respect to the roll axis X or pitch axis Y; and the shutdown of the first dual-engine propeller to compensate for the loss of thrust due to the failure of the secondary drive unit. According to this third compensation strategy, the compensating propellers comprise the two dual-engine propellers belonging, respectively, to the two pairs of propellers of which the first and second single-engine propellers are a part.

[0041] This third compensation strategy is illustrated by the examples in Figures 7 and 8. In the example in [Fig. 7], the failed single-engine and twin-engine propellers 12D, 11D are located in the same sector, namely the forward left sector FL. In such a case of a double failure, the proposed compensation strategy consists of stopping the failed single-engine propeller 12D and the single-engine propeller 12E, which is symmetrical to the first single-engine propeller with respect to the roll axis X. The proposed compensation strategy also consists of energizing the tertiary drive unit 23 of the failed twin-engine propeller 11D to compensate for the loss of thrust due to the failure of the secondary drive unit 22 of this propeller 11D. According to this third compensation strategy, the compensating propellers 11C include the two twin-engine propellers belonging to the same propeller pairs as the single-engine propellers 12D and 12E.In normal operation, the compensating propellers 11C can be driven by a single drive unit, for example the secondary drive unit 22. In the event of a double failure, the tertiary drive units 23 are actuated so that each compensating propeller 1IC is driven not only by its secondary drive unit 22 but also by its tertiary drive unit 23. Thus, the thrust of each compensating propeller 1IC can be increased so as to. to compensate for the thrust loss due to the shutdown of propellers 12D and 12E. Alternatively, in normal operation, the compensating propellers 1 IC can be driven by their two secondary drive units 22 and tertiary drive units 23, these drive units producing a nominal torque lower than their maximum available torque. In the event of a double failure, the secondary and tertiary drive units 22 and 23 are controlled to produce their maximum available torque (or a torque strictly greater than their nominal torque and less than or equal to their maximum available torque). Thus, the thrust of each compensating propeller 1 IC can be increased to compensate for the thrust loss due to the shutdown of propellers 12D and 12E.

[0042] In certain embodiments, the propellers of the apparatus and their drive units are designed to produce a nominal thrust (Tnom) and a maximum compensating thrust (Tmax). This variation in thrust can be obtained by varying the rotational speed of the propellers and / or their pitch. The maximum thrust (Tmax) is calculated based on the number of multiple failures that the system must manage. The nominal thrust (Tnom) and the maximum compensating thrust (Tmax) of each propeller correspond, respectively, to a nominal torque (Qnom) and a maximum torque (Qmax) required by the propeller.

[0043] In certain embodiments, each of the drive units (i.e., each of the motors) of the twin-engine propellers is sized to produce a nominal torque (Qnom / 2) that represents half of the nominal torque (Qnom) required by the propeller, and a maximum torque (Qmax / 2) that represents half of the maximum torque (Qmax) required by the propeller. In such cases, both drive units are subjected to the nominal torque (Qnom) required by the propeller during normal operation, and both are subjected to the maximum torque (Qmax) required by the propeller during compensation. Furthermore, the maximum torque (Qmax / 2) is greater than or equal to the nominal torque (Qnom) required by the propeller, so that in the event of a failure and shutdown of one of the two drive units, the other drive unit alone can produce the nominal torque (Qnom) required by the propeller.Using a gearbox between the common shaft of the drive unit motors and the propeller shaft can allow for better adaptation of the motor characteristics to the required specifications.

[0044] The embodiments described in this presentation are given by way of illustration and not limitation, a person skilled in the art being able to easily, in view of this presentation, modify these embodiments, or consider others, while remaining within the scope of the invention.

[0045] In particular, a person skilled in the art will easily be able to consider variants comprising only some of the features of the embodiments described above, if those features alone are sufficient to provide one of the advantages of the invention. Furthermore, the various features of these embodiments can be used alone or combined. When combined, these features can be used as described above or otherwise, the invention not being limited to the specific combinations described herein. In particular, unless otherwise specified, a feature described in relation to one embodiment can be applied analogously to another embodiment.

Claims

Demands

1. Vertical takeoff and landing aircraft comprising: at least four pairs of contra-rotating propellers (10) to provide, at least in part, lift for the aircraft (1); drive units (21, 22, 23) to drive the propellers (11, 12) in rotation, each drive unit comprising an electric motor and its electronic control system; a flight control unit to command the propulsion units (21, 22, 23) so as to obtain, for each propeller (11, 12), a target thrust; and a detection system to detect a failure of the drive units (21, 22, 23), in which each pair of propellers (10) comprises an upper propeller (11) and a lower propeller (12) rotating in opposite directions about a propeller axis (A) substantially parallel to the yaw axis (Z) of the aircraft (1), in which the pairs of propellers (10) are distributed symmetrically with respect to the roll (X) and pitch (Y) axes of the aircraft (1), in which each pair of propellers (10) is equipped with three separately controllable drive units (21, 22, 23), namely a primary drive unit (21) for driving one of the propellers, referred to as the single-engine propeller, and secondary and tertiary drive units (22, 23) for driving the other propeller, referred to as the twin-engine propeller, the secondary and tertiary drive units (22, 23) being arranged such that that their motor torques are additive, in which, when a simultaneous failure of two motor units (21, 22, 23) belonging, respectively,When two pairs of propellers (10) are detected by the detection system, the flight control unit commands the secondary and tertiary drive units (22, 23) of at least two propellers, called compensating propellers (11C), chosen from among the twin-engine propellers, to drive each of the compensating propellers (11C) by means of its secondary and tertiary drive units (22, 23), so as to increase the thrust of each of the compensating propellers (1 IC) and compensate for the loss of thrust due to the failure of the two drive units.

2. Aircraft according to claim 1, wherein the thrust of each of the compensating propellers (1 IC) is increased beyond the thrust maximum that would be available if the compensating propeller (11C) was driven only by its secondary drive unit (22) or its tertiary drive unit (23).

3. Aircraft according to claim 1 or 2, wherein the secondary (22) and tertiary (23) drive units are identical in terms of drive torque.

4. Aircraft according to any one of claims 1 to 3, wherein, where the two faulty power units are two primary power units (21) driving, respectively, two single-engine propellers (12D) rotating in opposite directions, the compensating propellers (11C) comprise the two twin-engine propellers belonging, respectively, to the two pairs of propellers (10) of which the two single-engine propellers (12D) are a part.

5. Aircraft according to any one of claims 1 to 4, wherein the roll (X) and pitch (Y) axes of the aircraft define between them four sectors (FL,FR, RL, RR), and wherein, when the two faulty drive units are two primary drive units (21) belonging to two adjacent sectors and driving, respectively, first and second single-engine propellers (12D) rotating in the same direction, the flight control unit commands: the stopping of the two faulty drive units and of the two primary drive units located, respectively, in the two adjacent sectors and driving the two single-engine propellers (12E) symmetrical to the first and second single-engine propeller (12D) with respect to the roll (X) or pitch (Y) axis;and in which the compensating propellers (11C) comprise the four twin-engine propellers belonging, respectively, to the pairs of propellers (10) of which the stopped drive units are a part.;

6. Aircraft according to any one of claims 1 to 5, wherein, when the two faulty propulsion units are a primary propulsion unit and a secondary propulsion unit driving, respectively, a first single-engine propeller (12D) and a first twin-engine propeller (11D), the flight control unit commands: the shutdown of the faulty primary propulsion unit; the shutdown of the primary propulsion unit driving a second single-engine propeller (12E) symmetrical to the first single-engine propeller (12D) with respect to the roll (X) or pitch (Y) axis; the tertiary propulsion unit (23) of the first twin-engine propeller (11D) to compensate for the loss of thrust due to failure of the secondary power unit, and in which the compensating propellers include the two twin-engine propellers (11C) belonging, respectively, to the two pairs of propellers (10) of which the first and second single-engine propellers (12D, 12E) are part.

7. Aircraft according to any one of claims 1 to 6, wherein, for each pair of propellers (10) operating normally, the drive units (21, 22, 23) are controlled so that the resisting torques of each of the propellers (11, 12) cancel each other out.

8. Aircraft according to any one of claims 1 to 7, wherein the upper propellers (11) symmetrical with respect to the roll (X) and pitch (Y) axes rotate in opposite directions, and wherein the lower propellers (12) symmetrical with respect to the roll (X) and pitch (Y) axes rotate in opposite directions.

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