Thrust producing unit with at least two rotor assemblies and a shrouding

Abstract

A thrust producing unit for producing thrust in a predetermined direction, comprising a shrouding and at least two rotor assemblies, wherein the shrouding defines an internal volume, and wherein a first rotor assembly of the at least two rotor assemblies defines a first rotor axis and a second rotor assembly of the at least two rotor assemblies defines a second rotor axis, the first and second rotor axes being one of: (i) coaxially arranged, and (ii) inclined by associated inclination angles with respect to the predetermined direction, the associated inclination angles being comprised in a range between 60 and +60, and preferably amounting to 0, and wherein the first rotor assembly is arranged outside of the internal volume of the shrouding.

Claims

1. A thrust producing unit for producing thrust in a predetermined direction, comprising: a shrouding and at least two rotor assemblies, wherein the shrouding defines an internal volume, and wherein a first rotor assembly of the at least two rotor assemblies defines a first rotor axis and a second rotor assembly of the at least two rotor assemblies defines a second rotor axis, wherein the first rotor axis is inclined by an associated first inclination angle with respect to the predetermined direction, the first inclination angle being longitudinal and in a range between +1 and +60, and the first rotor assembly being arranged outside of the internal volume of the shrouding and above the second rotor assembly that is arranged lower than the first rotor assembly; the second rotor assembly being arranged inside of the internal volume of the shrouding; the second rotor axis being inclined by an associated second inclination angle with respect to the predetermined direction, such that the second inclination angle is longitudinal and less than the range of the first inclination angle.

2. The thrust producing unit of claim 1, wherein the first rotor defines a first rotor plane and the second rotor assembly defines a second rotor plane and wherein D is a diameter of the second rotor assembly; and wherein a predetermined inter-planes distance between the first and second rotor planes is in a range between 0.01*D and 2*D.

3. The thrust producing unit of claim 1, wherein the shrouding comprises a leading edge and a trailing edge, wherein the first rotor assembly is adjacent the leading edge, and wherein the second rotor assembly is adjacent the trailing edge.

4. The thrust producing unit of claim 1, wherein the shrouding comprises a leading edge and a trailing edge, wherein the first rotor assembly is adjacent the leading edge.

5. The thrust producing unit of claim 1, wherein an additional shrouding is provided that accommodates the first rotor assembly.

6. The thrust producing unit of claim 5, wherein the shrouding and the additional shrouding exhibit each a height that is in a range between 0.04*D and 1*D, wherein D defines a diameter of the second rotor assembly.

7. The thrust producing unit of claim 5, wherein the shrouding and the additional shrouding are spaced apart from each other by an offset that is in a range between 0.01*D and 2*D, wherein D defines a diameter of the second rotor assembly.

8. The thrust producing unit of claim 5, wherein the additional shrouding comprises a leading edge that points away from the shrouding, wherein a predetermined leading plane distance between the leading edge and the rotor plane that is defined by the first rotor assembly is in a range between 1*D and 1*D, wherein D defines a diameter of the second rotor assembly, and wherein the first rotor assembly is arranged outside of the additional shrouding if the predetermined leading plane distance is in the range between 1*D and 0.

9. The thrust producing unit of claim 5, wherein each one of the first and second rotor assemblies defines an associated rotor plane, wherein a predetermined inter-planes distance between the associated rotor planes of the first and second rotor assemblies is in a range between 0.01*D and 2*D, wherein D defines a diameter of the second rotor assembly.

10. The thrust producing unit of claim 1, wherein each one of the first and second rotor assemblies defines an associated rotor plane, wherein a predetermined inter-planes distance between the associated rotor planes of the first and second rotor assemblies is in a range between 0.01*D and 2*D, wherein D defines a diameter of the second rotor assembly.

11. The thrust producing unit of claim 1, wherein the first rotor assembly comprises at least two rotor blades and the second rotor assembly comprises at least two rotor blades.

12. The thrust producing unit of claim 1, wherein the first rotor assembly is adapted to be rotated in a first rotation direction in operation and the second rotor assembly is adapted to be rotated in a second rotation direction in operation.

13. The thrust producing unit of claim 1, wherein the second inclination angle is generally equal to 0.

14. A multirotor aircraft comprising at least one thrust producing unit that is configured according to claim 1.

15. A thrust producing unit for an aircraft comprising: a shrouding defining an internal volume; a first rotor assembly disposed above the shrouding and having a first rotor axis being oriented at a first inclination angle with relative to a longitudinal direction, the first inclination angle in a range between +1 and +60; and a second rotor assembly disposed below the first rotor assembly inside the internal volume of the shrouding, the second rotor assembly having a second rotor axis oriented at a second inclination angle relative to the longitudinal axis being less than the range of the first inclination angle.

16. The thrust producing unit of claim 15, wherein the second inclination angle is generally equal to 0.

17. The thrust producing unit of claim 15, wherein the first rotor defines a first rotor plane and the second rotor assembly defines a second rotor plane and wherein D is a diameter of the second rotor assembly; and wherein a predetermined inter-planes distance between the first and second rotor planes is in a range between 0.01*D and 2*D.

18. The thrust producing unit of claim 15, wherein the shrouding comprises a leading edge and a trailing edge, wherein the first rotor assembly is adjacent the leading edge, and wherein the second rotor assembly is adjacent the trailing edge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are outlined by way of example in the following description with reference to the attached drawings. In these attached drawings, identical or identically functioning components and elements are labeled with identical reference numbers and characters and are, consequently, only described once in the following description.

(2) FIG. 1 shows a perspective view of a multirotor aircraft with a plurality of thrust producing units not claimed by the present invention,

(3) FIG. 2 shows a top view of the multirotor aircraft of FIG. 1,

(4) FIG. 3 shows a side view of the multirotor aircraft of FIG. 1 and FIG. 2 in normal flight mode,

(5) FIG. 4 shows a front view of the multirotor aircraft of FIG. 3,

(6) FIG. 5 shows a perspective view of a thrust producing unit of the multirotor aircraft of FIG. 1 to FIG. 4,

(7) FIG. 6 shows a partly transparent side view of the thrust producing unit of FIG. 5,

(8) FIG. 7 shows a partly transparent side view of a thrust producing unit according to an embodiment of the present invention,

(9) FIG. 8 shows a partly transparent side view of a thrust producing unit according to another embodiment of the present invention,

(10) FIG. 9 shows a partly transparent side view of a thrust producing unit according to still another embodiment of the present invention,

(11) FIG. 10 shows a partly transparent side view of a thrust producing unit according to still another embodiment of the present invention,

(12) FIG. 11 shows a schematic view of a thrust producing unit according to still another embodiment of the present invention,

(13) FIG. 12 shows a side perspective view of an embodiment of multirotor aircraft as per the invention, in normal flight mode, and

(14) FIG. 13 shows a side perspective view of another embodiment of multirotor aircraft as per the invention, in normal flight mode.

DETAILED DESCRIPTION OF THE INVENTION

(15) FIG. 1 shows a multirotor aircraft 1 with an aircraft airframe 2. The aircraft airframe 2 defines a supporting structure that is also referred to hereinafter as the fuselage of the multirotor aircraft 1.

(16) The fuselage 2 has an extension in longitudinal direction 1a and an extension in lateral direction 1b and preferably defines an internal volume 2a that is at least adapted for transportation of passengers, so that the multirotor aircraft 1 as a whole is adapted for transportation of passengers. The internal volume 2a is preferably further adapted for accommodating operational and electrical equipment, such as e. g. an energy storage system that is required for operation of the multirotor aircraft 1.

(17) It should be noted that exemplary configurations of the internal volume 2a that are suitable for transportation of passengers, but also for accommodation of operational and electrical equipment, are readily available to the person skilled in the art and generally implemented to comply with applicable authority regulations and certification requirements regarding passenger transportation. Thus, as these configurations of the internal volume 2a as such are not part of the present invention, they are not described in detail for brevity and conciseness.

(18) According to one aspect, the multirotor aircraft 1 comprises a plurality of thrust producing units 3. Preferably, the plurality of thrust producing units 3 comprises at least two and preferentially four thrust producing units 3a, 3b, 3c, 3d. The thrust producing units 3a, 3b, 3c, 3d are embodied for producing thrust (9 in FIG. 3) in operation, such that the multirotor aircraft 1 is able to hover in the air as well as to fly in any forward or rearward direction.

(19) Preferably, the thrust producing units 3a, 3b, 3c, 3d are structurally connected to the fuselage 2. By way of example, this is achieved by means of a plurality of structural supports 4. More specifically, the thrust producing unit 3a is preferably connected to the fuselage 2 via a structural support 4a, the thrust producing unit 3b via a structural support 4b, the thrust producing unit 3c via a structural support 4c and the thrust producing unit 3d via a structural support 4d, wherein the structural supports 4a, 4b, 4c, 4d define the plurality of structural supports 4.

(20) Preferably, at least one of the thrust producing units 3a, 3b, 3c, 3d comprises an associated shrouding in order to improve underlying aerodynamics and to increase operational safety. By way of example, a plurality of shrouding units 6 is shown with four separate shroudings 6a, 6b, 6c, 6d. Illustratively, the shrouding 6a is associated with the thrust producing unit 3a, the shrouding 6b with the thrust producing unit 3b, the shrouding 6c with the thrust producing unit 3c and the shrouding 6d with the thrust producing unit 3d.

(21) The shroudings 6a, 6b, 6c, 6d can be made of a simple sheet metal. Alternatively, they may have a complex geometry, such as e. g. described below with reference to FIG. 5.

(22) Furthermore, the shroudings 6a, 6b, 6c, 6d can be connected to the fuselage 2 together with the structural supports 4a, 4b, 4c, 4d, in order to reinforce the connection between the thrust producing units 3a, 3b, 3c, 3d and the fuselage 2. Alternatively, only the shroudings 6a, 6b, 6c, 6d can be connected to the fuselage 2.

(23) According to one aspect, at least one and, preferably, each one of the thrust producing units 3a, 3b, 3c, 3d is equipped with at least two rotor assemblies. By way of example, the thrust producing unit 3a is equipped with two rotor assemblies 7a, 8a, the thrust producing unit 3b is equipped with two rotor assemblies 7b, 8b, the thrust producing unit 3c is equipped with two rotor assemblies 7c, 8c and the thrust producing unit 3d is equipped with two rotor assemblies 7d, 8d. The rotor assemblies 7a, 7b, 7c, 7d illustratively define a plurality of upper rotor assemblies 7 and the rotor assemblies 8a, 8b, 8c, 8d illustratively define a plurality of lower rotor assemblies 8.

(24) The plurality of upper and lower rotor assemblies 7, 8 is preferably connected to the plurality of structural supports 4 by means of a plurality of gearbox fairings 5. Illustratively, the upper and lower rotor assemblies 7a, 8a are connected to the structural support 4a by means of a gearbox fairing 5a, the upper and lower rotor assemblies 7b, 8b are connected to the structural support 4b by means of a gearbox fairing 5b, the upper and lower rotor assemblies 7c, 8c are connected to the structural support 4c by means of a gearbox fairing 5c and the upper and lower rotor assemblies 7d, 8d are connected to the structural support 4d by means of a gearbox fairing 5d.

(25) Preferably, each one of the upper rotor assemblies 7a, 7b, 7c, 7d defines an associated upper rotor plane (21 in FIG. 6) and each one of the lower rotor assemblies 8a, 8b, 8c, 8d defines an associated lower rotor plane (22 in FIG. 6). Preferably, the upper and lower rotor assemblies 7a, 7b, 7c, 7d, 8a, 8b, 8c, 8d define pairs of upper and lower rotor assemblies 7a, 8a; 7b, 8b; 7c, 8c; 7d, 8d that are accommodated in the shroudings 6a, 6b, 6c, 6d, respectively, so that the associated upper and lower rotor planes (21, 22 in FIG. 6) are located inside the shroudings 6a, 6b, 6c, 6d of the multirotor aircraft 1.

(26) According to one aspect, the multirotor aircraft 1 comprises an aircraft operating structure and a redundant security architecture. The aircraft operating structure is preferably adapted for operation of the multirotor aircraft 1 in failure-free operating mode and the redundant security architecture is preferably at least adapted for operation of the multirotor aircraft 1 in case of a failure of the aircraft operating structure. In particular, the redundant security architecture is provided to comply preferentially with applicable authority regulations and certification requirements regarding passenger transportation.

(27) Preferably, the aircraft operating structure comprises at least a first part of the upper and lower rotor assemblies 7a, 7b, 7c, 7d, 8a, 8b, 8c, 8d and the redundant security architecture comprises at least a second part of the upper and lower rotor assemblies 7a, 7b, 7c, 7d, 8a, 8b, 8c, 8d. Preferentially, a first one of the upper and lower rotor assemblies 7a, 8a, 7b, 8b, 7c, 8c, 7d, 8d of each thrust producing unit 3a, 3b, 3c, 3d is associated with the aircraft operating structure, while a second one is associated with the redundant security architecture. By way of example, the upper rotor assemblies 7a, 7b, 7c, 7d are associated with the aircraft operating structure and the lower rotor assemblies 8a, 8b, 8c, 8d are associated with the redundant security architecture. Thus, at least in case of a failure of the upper rotor assemblies 7a, 7b, 7c, 7d, the lower rotor assemblies 8a, 8b, 8c, 8d operate the multirotor aircraft 1 in order to avoid e. g. a crash thereof.

(28) It should, however, be noted that the above configuration, wherein the upper rotor assemblies 7a, 7b, 7c, 7d are associated with the aircraft operating structure and the lower rotor assemblies 8a, 8b, 8c, 8d are associated with the redundant security architecture, is merely described by way of example and not for limiting the invention thereto. Instead, alternative associations are likewise possible and contemplated. For instance, the rotor assemblies 7a, 7c, 8b, 8d can be associated with the aircraft operating structure, while the rotor assemblies 8a, 8c, 7b, 7d are associated with the redundant security architecture, and so on. As such alternative associations are readily available to the person skilled in the art, they are likewise contemplated and considered as being part of the present invention.

(29) FIG. 2 shows the multirotor aircraft 1 of FIG. 1 with the thrust producing units 3a, 3b, 3c, 3d that are connected to the fuselage 2. The thrust producing units 3a, 3b, 3c, 3d respectively comprise the upper and lower rotor assemblies 7a, 7b; 7b, 8b; 7c, 8c; 7d, 8d, which are preferably arranged in a side-by-side configuration with congruent rotor axes (12 in FIG. 3 and FIG. 4). Preferentially, the upper rotor assemblies 7a, 7b, 7c, 7d are arranged above the lower rotor assemblies 8a, 8b, 8c, 8d such that the upper and lower rotor assemblies 7a, 7b; 7b, 8b; 7c, 8c; 7d, 8d are stacked, i. e. arranged on top of each other with congruent rotor axes (12 in FIG. 3 and FIG. 4). However, alternative configurations are likewise contemplated, such as e. g. described below with reference to FIG. 11.

(30) As can further be seen from FIG. 2, the thrust producing units 3a, 3b, 3c, 3d are all exemplarily arranged laterally with respect to the fuselage 2, i. e. on the left or right side of the fuselage 2 seen in its longitudinal direction 1a. Illustratively, the left side corresponds to the lower side and the right side to the upper side of the fuselage 2 as shown in FIG. 2. Furthermore, the fuselage 2 is exemplarily embodied such that the laterally arranged thrust producing units 3a, 3b, 3c, 3d define at least approximately a trapezoidal shape.

(31) However, it should be noted that this exemplary arrangement is only described by way of example and other arrangements are also possible and likewise contemplated. For instance, two of the thrust producing units 3a, 3b, 3c, 3d can respectively be arranged at a front and rear section of the fuselage 2, and so on.

(32) FIG. 3 shows the multirotor aircraft 1 of FIG. 1 and FIG. 2 in an exemplary failure-free operating mode. In this exemplary failure-free operating mode, the plurality of thrust producing units 3 produce airstreams in a thrust producing airstream direction 9 by means of the plurality of upper and/or lower rotor assemblies 7, 8 that is suitable to lift the multirotor aircraft 1 off ground 10.

(33) Each one of the plurality of upper rotor assemblies 7 defines a first rotor axis and each one of the plurality of lower rotor assemblies 8 defines a second rotor axis. Preferably, the first and second rotor axes are respectively congruent, i. e. coaxially arranged, so that the plurality of upper and lower rotor assemblies 7, 8 define a plurality of coaxially arranged rotor axes 12. Illustratively, the upper and lower rotor assemblies 7c, 8c define first and second congruent rotor axes, which are commonly referred to as the rotor axis 12c, and the upper and lower rotor assemblies 7d, 8d define first and second congruent rotor axes, which are commonly referred to as the rotor axis 12d.

(34) Preferably, the plurality of thrust producing units 3 is inclined in the longitudinal direction 1a of the multirotor aircraft 1 by a plurality of longitudinal inclination angles 11 in order to increase the maneuverability of the multirotor aircraft 1 and to reduce an overall inclination in the longitudinal direction 1a of the multirotor aircraft 1 during forward flight. The plurality of longitudinal inclination angles 11 is illustratively defined between a vertical reference line 10a of the multirotor aircraft 1 and the plurality of coaxially arranged rotor axes 12. Preferably, a possible and realized number of the plurality of longitudinal inclination angles 11 depends on an underlying number of provided thrust producing units.

(35) More specifically, according to one aspect, at least one of the plurality of thrust producing units 3 is inclined in the longitudinal direction 1a of the multirotor aircraft 1 by a first longitudinal inclination angle defined between a vertical reference line 10a of the multirotor aircraft 1 and the first and second congruent rotor axes of this at least one of the plurality of thrust producing units 3. The first longitudinal inclination angle is preferably comprised in a range between 45 and +80, and preferentially amounts to 7.

(36) Illustratively, the thrust producing unit 3c of the plurality of thrust producing units 3 is inclined by a first longitudinal inclination angle 11a defined between the vertical reference line 10a and the rotor axis 12c, wherein the first longitudinal inclination angle 11a is preferably comprised in a range between 45 and +80, and preferentially amounts to 7. However, it should be noted that the thrust producing unit 3a of the plurality of thrust producing units 3 of FIG. 1 and FIG. 2 is preferably also inclined by the first longitudinal inclination angle 11a.

(37) According to one aspect, at least one of the plurality of thrust producing units 3 is inclined in the longitudinal direction 1a of the multirotor aircraft 1 by a second longitudinal inclination angle defined between the vertical reference line 10a and the first and second congruent rotor axes of this at least one of the plurality of thrust producing units 3. The second longitudinal inclination angle is preferably also comprised in a range between 45 and +80, and preferentially amounts to 7.

(38) Illustratively, the thrust producing unit 3d of the plurality of thrust producing units 3 is inclined by a second longitudinal inclination angle 11b defined between the vertical reference line 10a and the rotor axis 12d, wherein the second longitudinal inclination angle 11b is preferably comprised in a range between 45 and +80, and preferentially amounts to 7. However, it should be noted that the thrust producing unit 3b of the plurality of thrust producing units 3 of FIG. 1 and FIG. 2 is preferably also inclined by the second longitudinal inclination angle 11b.

(39) FIG. 4 shows the multirotor aircraft 1 with the fuselage 2 of FIG. 3, which illustratively comprises a width 2b. The latter is defined as a maximum distance measured orthogonally to the longitudinal direction 1a of the multirotor aircraft 1 between the respective outmost left hand and right hand side surfaces of the fuselage 2.

(40) According to FIG. 3, the multirotor aircraft 1 is shown in the exemplary failure-free operating mode, wherein the plurality of thrust producing units 3 produce airstreams in the thrust producing airstream direction 9 by means of the plurality of upper and lower rotor assemblies 7, 8. The upper and lower rotor assemblies 7c, 8c define the rotor axis 12c and the upper and lower rotor assemblies 7d, 8d define the rotor axis 12d.

(41) Furthermore, the upper and lower rotor assemblies 7a, 8a exemplarily define first and second congruent rotor axes, which are commonly referred to as the rotor axis 12a, and the upper and lower rotor assemblies 7b, 8b define first and second congruent rotor axes, which are commonly referred to as the rotor axis 12b. It should be noted that the rotor axes 12a, 12b, 12c, 12d are preferably implemented as described in order to reduce the overall complexity, system weight as well as geometrical size of the multirotor aircraft 1.

(42) Preferably, the plurality of thrust producing units 3 is inclined in the lateral direction 1b of the multirotor aircraft 1 by a plurality of lateral inclination angles 13 in order to provide reduced gust sensitivity and to increase the maneuverability of the multirotor aircraft 1. The plurality of lateral inclination angles 13 is illustratively defined between the vertical reference line 10a of the multirotor aircraft 1 and the plurality of coaxially arranged rotor axes 12. Preferably, a possible and realized number of the plurality of lateral inclination angles 13 depends on an underlying number of provided thrust producing units.

(43) More specifically, according to one aspect, at least one of the plurality of thrust producing units 3 is inclined in the lateral direction 1b of the multirotor aircraft 1 by a first lateral inclination angle defined between the vertical reference line 10a of the multirotor aircraft 1 and the first and second congruent rotor axes of this at least one of the plurality of thrust producing units 3. The first lateral inclination angle is preferably comprised in a range between 45 and +80, and preferentially amounts to 5.

(44) Illustratively, the thrust producing unit 3a of the plurality of thrust producing units 3 is inclined by a first lateral inclination angle 13a defined between the vertical reference line 10a and the rotor axis 12a, wherein the first lateral inclination angle 13a is preferably comprised in a range between 45 and +80, and preferentially amounts to 5. However, it should be noted that the thrust producing unit 3c of the plurality of thrust producing units 3 of FIG. 1 and FIG. 2 is preferably also inclined by the first lateral inclination angle 13a.

(45) According to one aspect, at least one of the plurality of thrust producing units 3 is inclined in the lateral direction 1b of the multirotor aircraft 1 by a second lateral inclination angle defined between the vertical reference line 10a of the multirotor aircraft 1 and the first and second congruent rotor axes of this at least one of the plurality of thrust producing units 3. The second lateral inclination angle is preferably comprised in a range between 45 and +80, and preferentially amounts to 5.

(46) Illustratively, the thrust producing unit 3b of the plurality of thrust producing units 3 is inclined by a second lateral inclination angle 13b defined between the vertical reference line 10a and the rotor axis 12b, wherein the second lateral inclination angle 13b is preferably comprised in a range between 45 and +80, and preferentially amounts to 5. However, it should be noted that the thrust producing unit 3d of the plurality of thrust producing units 3 of FIG. 1 and FIG. 2 is preferably also inclined by the second lateral inclination angle 13b.

(47) FIG. 5 shows the thrust producing unit 3d of the preceding figures, with its upper rotor assembly 7d, its lower rotor assembly 8d, its gearbox fairing 5d and its shrouding 6d for further illustrating an exemplary configuration thereof. It should, however, be noted that the thrust producing units 3a, 3b, 3c of the preceding figures preferably comprise similar configurations, so that the thrust producing unit 3d is only described representative for all thrust producing units 3a, 3b, 3c, 3d, for brevity and conciseness.

(48) Illustratively, the shrouding 6d has an inner surface 20a and an outer surface 20b with an outer diameter 20f. The shrouding 6d exemplarily further defines a leading edge 20d and a trailing edge 20e. Preferably, an internal volume 20c is defined between the inner surface 20a, the outer surface 20b, the leading edge 20d and the trailing edge 20e. This inner volume 20c can e. g. be used as storage volume for a battery system of the multirotor aircraft 1 of the preceding figures.

(49) The shrouding 6d can be made of a simple pressed, bended metal sheet such that the inner and outer surfaces 20a, 20b are substantially parallel to each other, i. e. feature an almost constant distance with respect to each other. However, it may as well have a complex geometry. Illustratively, the shrouding 6d accommodates the upper rotor assembly 7d and the lower rotor assembly 8d.

(50) According to one aspect, the upper rotor assembly 7d comprises at least two and, illustratively, three rotor blades 18a, 18b, 18c for producing thrust in operation. Similarly, the lower rotor assembly 8d preferably also comprises at least two and, illustratively, three rotor blades 19a, 19b, 19c for producing thrust in operation.

(51) Furthermore, preferably at least one first engine 14a is provided for driving the rotor blades 18a, 18b, 18c, i. e. the upper rotor assembly 7d in operation and at least one second engine 14b is provided for driving the rotor blades 19a, 19b, 19c, i. e. the lower rotor assembly 8d in operation. The at least one first engine 14a is preferably associated with the aircraft operating structure described above with reference to FIG. 1, and the at least one second engine 14b is preferably associated with the redundant security architecture described above with reference to FIG. 1. Illustratively, the at least one first and second engines 14a, 14b are arranged inside of and, thus, encompassed by the gearbox fairing 5d.

(52) It should be noted that optionally one or more gearboxes can be introduced between the at least one first and second engines 14a, 14b and the rotor blades 18a, 18b, 18c respectively 19a, 19b, 19c. By such an optional introduction of one or more gearboxes, an operating efficiency of the at least one first and second engines 14a, 14b can be increased since their rotational speed is increased.

(53) It should further be noted that the at least one first and second engines 14a, 14b can be implemented by any suitable engine that is capable of producing torque in operation, such as a turbine, diesel engine, Otto-motor, electrical engine and so on, and that can be connected to the rotor blades 18a, 18b, 18c respectively 19a, 19b, 19c for rotating these rotor blades 18a, 18b, 18c respectively 19a, 19b, 19c, i. e. the upper and lower rotor assemblies 7d respectively 8d, in operation. However, as such engines are well-known to the person skilled in the art they are not described in greater detail for brevity and conciseness.

(54) Preferably, the upper rotor assembly 7d is adapted to be rotated in a first rotation direction 15 in operation. Similarly, the lower rotor assembly 8d is adapted to be rotated in a second rotation direction 16 in operation. Illustratively, the first and second rotation directions 15, 16 are preferably opposed to each other.

(55) According to one aspect, at least the upper rotor assembly 7d and, more specifically, its rotor blades 18a, 18b, 18c, are provided with an optional pitch variation 17. Similarly, the lower rotor assembly 8d, i. e. its rotor blades 19a, 19b, 19c, are preferably also provided with such an optional pitch variation. In this case, control of the produced airstream in the thrust producing airstream direction 9 of FIG. 3 and FIG. 4 can either be achieved in operation by means of pitch variation, by means of RPM variation or by means of a combination of pitch and RPM variation.

(56) In contrast thereto, if the upper and lower rotor assemblies 7d, 8d are not provided with such an optional pitch variation, e. g. if the rotor blades 18a, 18b, 18c respectively 19a, 19b, 19c are implemented as fixed pitch blades, control of the produced airstream in the thrust producing airstream direction 9 of FIG. 3 and FIG. 4 in operation by means of pitch variation cannot by performed. In this case, only RPM variation can be used for control of the airstream in the thrust producing airstream direction 9 of FIG. 3 and FIG. 4 that is produced by the upper and lower rotor assembly 7d, 8d in operation.

(57) According to one aspect, each one of the upper and lower rotor assemblies 7d, 8d is individually sized and comprises a diameter that ranges from 0.05 to 6 times of the fuselage width 2b of FIG. 4, which is designated as W hereinafter for simplicity. In other words, the diameter of each one of the upper and lower rotor assemblies 7d, 8d preferably ranges from 0.05*W to 6*W, and preferentially amounts to 1.5*W.

(58) FIG. 6 shows a schematic view of the thrust producing unit 3d of FIG. 5 with the upper and lower rotor assemblies 7d, 8d, which are arranged inside of the shrouding 6d, and which preferably define separated rotor planes 21, 22 in order to reach a required safety level and a satisfying flight mechanical behaviour. Illustratively, the rotor planes 21, 22 are arranged on top of each other. Preferably, a predetermined distance between the rotor planes 21, 22 is comprised in a range between 0.01*D and 2*D, and preferably amounts to 0.17*D, wherein D defines a diameter of the second rotor assembly 8d.

(59) The upper and lower rotor assemblies 7d, 8d are driven in operation by the at least one first and second engines 14a, 14b, respectively, which are arranged in the gearbox fairing 5d. As described above, the upper and lower rotor assemblies 7d, 8d preferably rotate around the rotor axis 12d that is commonly defined by a first rotor axis associated with the upper rotor assembly 7d and a second rotor axis 8d associated with the lower rotor assembly 8d.

(60) According to one aspect of the present invention, these first and second rotor axes can be inclined by associated inclination angles 21a, 22a. The latter are preferably comprised in a range between 60 and +60, and preferentially amount to 0.

(61) If, however, the associated inclination angles 21a, 22a are selected such that the rotor planes 21, 22 intersect, the upper and lower rotor assemblies 7d, 8d are intermeshing in operation. This may be allowable to actively rotate the at least one first and second engines 14a, 14b about the corresponding rotor planes 21, 22 in order to vary an underlying direction, i. e. thrust vector 23. Alternatively, the rotor axis 12d as such can be inclined by one of the associated inclination angles 21a, 22a.

(62) In operation of the thrust producing unit 3d, rotation of the upper and lower rotor assemblies 7d, 8d around the rotor axis 12d generates an air inflow 23a and an air outflow 23b through the rotor planes 21, 22. The air inflow 23a and the air outflow 23b themselves produce thrust and further produce an additional thrust by acting on the shrouding 6d. This will lead to a total thrust illustrated by a thrust vector 23, which will allow the multirotor aircraft 1 of FIG. 1 to FIG. 4 to be lifted. It should be noted that at the same thrust level, a respective amount of power needed by the at least one first and second engines 14a, 14b driving the upper and lower rotor assemblies 7d, 8d will be significantly lower than the power needed to drive the upper and lower rotor assemblies 7d, 8d without the shrouding 6d.

(63) However, during forward flight or upon occurrence of essentially horizontal wind gusts, an airstream in an exemplary free airstream direction 23c acts on the shrouding 6d, i. e. on its outer surface 20b. This leads to undesirable drag in the direction 23c on the thrust producing unit 3d and, thus, on the multirotor aircraft 1 of FIG. 1 to FIG. 4, which is disadvantageous for a respective power consumption of the multirotor aircraft 1.

(64) FIG. 7 shows the thrust producing unit 3d of the invention, which is configured to produce thrust in direction of the thrust vector 23 and includes at least the two rotor assemblies 7d, 8d, and the shrouding 6d, which illustratively defines the internal volume 20c, the leading edge 20d and the trailing edge 20e according to FIG. 5. Each one of the at least two rotor assemblies 7d, 8d defines its associated rotor plane 21 resp. 22. Furthermore, each one of the at least two rotor assemblies 7d, 8d defines its associated rotor axis 12d.

(65) By way of example, the rotor axes 12d of the at least two rotor assemblies 7d, 8d are arranged coaxially. Alternatively, they can be inclined by associated inclination angles 21a, 22a with respect to the direction of the thrust vector 23. The associated inclination angles 21a, 22a are preferably comprised in a range between 60 and +60, and preferentially amount to 0.

(66) The first rotor assembly 7d is preferably provided for operating in a failure-free operating mode of the thrust producing unit 3d and the second rotor assembly 8d is preferably provided for operating at least in case of a failure of the first rotor assembly 7d. However, it should be noted that the first rotor assembly 7d must not necessarily be provided for operating in the failure-free operating mode of the thrust producing unit 3d and the second rotor assembly 8d must not necessarily be provided for operating at least in case of the failure of the first rotor assembly 7d. Instead, the second rotor assembly 8d can be configured for operating in the failure-free operating mode of the thrust producing unit 3d and the first rotor assembly 7d can be configured for operating at least in case of the failure of the second rotor assembly 8d. Furthermore, the first and second rotor assemblies 7d, 8d can be configured for operating together in the failure-free operating mode, etc.

(67) According to one aspect and in contrast to the embodiment of the thrust producing unit 3d described above with reference to FIG. 5 and FIG. 6, however, the shrouding 6d now preferably accommodates at most one of the at least two rotor assemblies 7d, 8d. More specifically, preferably at least one of the at least two rotor assemblies 7d, 8d and, illustratively, the first rotor assembly 7d is arranged outside of the internal volume 20c of the shrouding 6d. Preferentially, the first rotor assembly 7d is facing the leading edge 20d of the shrouding 6d. Furthermore, according to one aspect, the second rotor assembly 8d is arranged inside of the internal volume 20c of the shrouding 6d.

(68) FIG. 8 shows the thrust producing unit 3d of FIG. 7, which is configured to produce thrust in direction of the thrust vector 23 and includes at least the two rotor assemblies 7d, 8d, and the shrouding 6d, which illustratively defines the internal volume 20c, the leading edge 20d and the trailing edge 20e, and which illustratively exhibits the outer diameter 20f. Each one of the at least two rotor assemblies 7d, 8d defines its associated rotor plane resp. 22. Furthermore, each one of the at least two rotor assemblies 7d, 8d defines its associated rotor axis 12d, both of which are exemplarily arranged coaxially. Moreover, the second rotor assembly 8d is arranged inside of the internal volume 20c of the shrouding 6d.

(69) According to one aspect and in contrast to the embodiment of the thrust producing unit 3d described above with reference to FIG. 7, however, now an additional shrouding 6e is provided. Preferably, the additional shrouding 6e accommodates the first rotor assembly 7d.

(70) Illustratively, the additional shrouding 6e also defines a leading edge and a trailing edge. For brevity and simplicity, similar to the shrouding 6d the leading edge of the additional shrouding is labelled with the reference sign 20d and the trailing edge of the additional shrouding 6e is labelled with the reference sign 20e. Illustratively, the trailing edge 20e of the additional shrouding 6e faces the leading edge 20d of the shrouding 6d.

(71) According to one aspect, a predetermined distance 24 between the associated rotor planes 21, 22 of the first and second rotor assemblies 21, 22 is comprised in a range between 0.01*D and 2*D, and preferentially amounts to 0.17*D, wherein D defines a diameter of the second rotor assembly 8d. Preferably, the shrouding 6d and the additional shrouding 6e are spaced apart from each other by an offset 25 that is comprised in a range between 0.01*D and 2*D. The offset 25 preferentially amounts to 0.17*D.

(72) A distance 26 between the leading edge 20d of the additional shrouding 6e and the rotor plane 21 that is defined by the first rotor assembly 7d is preferably comprised in a range between 1*D and 1*D. Preferentially, the distance 26 amounts to 0.08*D. It should be noted that the first rotor assembly 7d will be arranged outside of the additional shrouding 6e and preferably faces the leading edge 20d if the distance 26 is comprised in the range between 1*D and 0. Preferably, the shrouding 6d and the additional shrouding 6e exhibit each a height 27a resp. 27b that is comprised in a range between 0.04*D and 1*D.

(73) According to one aspect, the outer diameter 20f of the shrouding 6d is smaller than a diameter of at least one of the at least two rotor assemblies 7d, 8d, e. g. a diameter 28 of the second rotor assembly 8d. It should, however, be noted that this feature is not illustrated in FIG. 8, but readily understandable by the person skilled in the art when being viewed in conjunction with FIG. 7 or, in particular, FIG. 9.

(74) It should be noted that in the configurations of the thrust producing unit 3d as illustrated in FIG. 8 and FIG. 7, a respective undesirable drag in forward flight, as described above with reference to FIG. 6, is reduced and the thrust generated by the shrouding 6d resp. the additional shrouding 6e, other non-rotating elements of the thrust producing unit 3d, which adds to the thrust generated by at least two assemblies 7d, 8d, as well as rotating elements thereof, increase a respective efficiency of the thrust producing unit 3d, which is defined as T*Vi/PTOT, with T being the thrust generated by one of the at least two rotor assemblies 7d, 8d, Vi its induced velocity and PTOT the required total power of the thrust producing unit 3d.

(75) FIG. 9 shows the thrust producing unit 3d of FIG. 7, which is configured to produce thrust in direction of the thrust vector 23 and includes at least the two rotor assemblies 7d, 8d, and the shrouding 6d, which illustratively defines the internal volume 20c, the leading edge 20d and the trailing edge 20e. Each one of the at least two rotor assemblies 7d, 8d defines its associated rotor plane 21 resp. 22. Furthermore, each one of the at least two rotor assemblies 7d, 8d defines its associated rotor axis 12d, both of which are exemplarily arranged coaxially. Moreover, the first rotor assembly 7d is arranged outside of the internal volume 20c of the shrouding 6d and faces the leading edge 20d of the shrouding 6d.

(76) According to one aspect and in contrast to the embodiment of the thrust producing unit 3d described above with reference to FIG. 7, however, now the shrouding 6d is arranged in-between the first rotor assembly 7d and the second rotor assembly 8d without accommodating one of the first and second rotor assemblies 7d, 8d. In other words, the second rotor assembly 8d is now also arranged outside of the internal volume 20c of the shrouding 6d. Preferentially, the second rotor assembly 8d is facing the trailing edge 20e of the shrouding 6d. Furthermore, as described above, the outer diameter (20f in FIG. 8) of the shrouding 6d can be smaller than a diameter of at least one of the at least two rotor assemblies 7d, 8d.

(77) FIG. 10 shows the thrust producing unit 3d of FIG. 8, which is configured to produce thrust in direction of the thrust vector 23 and includes at least the two rotor assemblies 7d, 8d, as well as the shrouding 6d with its associated internal volume 20c. Each one of the at least two rotor assemblies 7d, 8d defines its associated rotor plane 21 resp. 22.

(78) According to one aspect and in contrast to the embodiment of the thrust producing unit 3d described above with reference to FIG. 8, however, now the thrust producing unit 3d further comprises at least one upper intermediate rotor assembly 29 that defines an associated rotor plane 30 and/or at least one lower intermediate rotor assembly 31 that defines an associated rotor plane 32. The associated rotor plane 30, 32 are illustratively arranged in-between the rotor planes 21, 22.

(79) Accordingly, the at least one upper and/or lower intermediate rotor assemblies 29, 31 and the at least two rotor assemblies 7d, 8d define at least four separate rotor planes 30, 32, 21, 22. This allows to further increase a provided safety level and a satisfying flight mechanical behaviour.

(80) It should be noted that all upper and lower rotor assemblies 7d, 29; 8d, 31 are illustratively accommodated in the shrouding 6d, i. e. inside of its internal volume 20c. However, alternatively, only the lower rotor assemblies 8d, 31 can be accommodated in the shrouding 6d, while the upper rotor assemblies 7d, 29 are accommodated in the additional shrouding 6e of FIG. 8. Still alternatively, the two rotor assemblies 7d, 8d can be arranged as illustrated in FIG. 9 outside of the shrouding 6d, while only the upper and lower intermediate rotor assemblies 29, 31 are accommodated in the shrouding 6d. Still alternatively, only the lower rotor assemblies 8d, 31 can be accommodated in the shrouding 6d, while the upper rotor assemblies 7d, 29 are arranged outside of the shrouding 6d according to FIG. 7.

(81) FIG. 11 shows a schematic view of the thrust producing unit 3d of FIG. 5 with the upper and lower rotor assemblies 7d, 8d, which preferably define the separated rotor planes 21, 22. The upper and lower rotor assemblies 7d, 8d are driven in operation by the at least one first and second engines 14a, 14b. The at least one first engine 14a is preferably adapted to rotate the upper rotor assembly 7d around a first, upper rotor axis 33 and the at least one second engine 14b is preferably adapted to rotate the lower rotor assembly 8d around a second, lower rotor axis 34.

(82) In contrast to FIG. 5, however, the first and second rotor axes 33, 34 are spaced apart, i. e. distanced from each other by a predetermined rotor axis displacement 35. This displacement 35 can be directed in the longitudinal direction 1a of the multirotor aircraft 1 of the preceding figures and/or in its lateral direction 1b.

(83) FIG. 12 shows a side perspective view of an embodiment of multirotor aircraft 1 as per the invention, in normal flight mode. Unless otherwise stated, the references used below refer to similar elements and structures from previous embodiments.

(84) The multirotor aircraft 1 of FIG. 12 has at least one front thrust producing unit 3a, 3c and at least one rear thrust producing unit 3b, 3d. On FIG. 12 all the at least one front and at least one rear thrust producing units 3a, 3c, 3b, 3d have at least one respective shrouding 6a, 6c, 6b, and 6d.

(85) Illustratively, multirotor aircraft 1 has a plurality of front and rear thrust producing units 3a, 3c, 3b, 3d. Illustratively, the multirotor aircraft 1 has an equal mount of thrust producing units e.g. 3c, 3d on a star side and of thrust producing units e.g. 3a, 3b on a board side, laterally the longitudinal direction 1a of the multirotor aircraft 1.

(86) In a given thrust producing units 3a, 3c, 3b, 3d, are provided upper and lower rotor assemblies 7d, 8d. The upper and lower rotor assemblies 7d, 8d respectively have a first rotor axis 21a and a second rotor axis 34.

(87) On FIG. 12, the first rotor axis 21a is inclined by an associated first inclination angle 21a with respect to the predetermined direction 23 of the thrust. Illustratively, the rotor planes 21, 22 arranged on top of each other are as well inclined one relative the other, in a given thrust producing units 3a, 3c, 3b, 3d, by a complementary angle respective to the associated first inclination angle 21a.

(88) FIG. 12 shows thrust producing units 3a, 3c, 3b, 3d each with the upper and lower rotor assemblies 7d, 8d, which define the separated rotor planes 21, 22.

(89) FIG. 12 shows the first inclination angle 21a being longitudinal and comprised in a range between +1 and +60. The first rotor 7d assembly is arranged outside of the internal volume of the shrouding;

(90) The second rotor assembly 8d is arranged inside of the internal volume 20c of the corresponding shrouding 6d. Also, the second rotor assembly 8d is inclined by an associated second inclination angle 22a with respect to the predetermined direction 23. The second inclination angle 22a of FIG. 12 is in a range inferior to the range of the first inclination angle 21a.

(91) Generally speaking, the second rotor axis 22d is inclined by an associated second inclination angle 22a with respect to the predetermined direction 23, such that the second inclination angle 22a is in a range which is inferior to the range of the first inclination angle 21a. In the embodiment of FIG. 12, with respect to the predetermined direction, the second inclination angle is null thus equals 0.

(92) FIG. 13 shows another embodiment of multirotor aircraft 1 as per the invention, which is slightly similar to the one of FIG. 12. Thus, unless otherwise stated, the references used below refer to similar elements and structures from previous embodiments.

(93) The multirotor aircraft 1 of FIG. 13 has at least one front thrust producing unit 3a, 3c and at least one rear thrust producing unit 3b, 3d. On FIG. 13 only the at least one front thrust producing unit 3b, 3d has at least one respective shrouding 6b, 6d. The second rotor assembly 8d in the at least one front thrust producing unit 3b, 3d is arranged inside of the internal volume 20c of the corresponding shrouding 6d. The first rotor assembly 7d in the at least one front thrust producing unit 3b, 3d is arranged outside of the internal volume 20c.

(94) Illustratively, multirotor aircraft 1 has a plurality of front and rear thrust producing units 3a, 3c, 3b, 3d. On FIG. 13, the multirotor aircraft 1 has an equal mount of thrust producing units e.g. 3c, 3d on a star side and of thrust producing units e.g. 3a, 3b on a board side, laterally the longitudinal direction 1a of the multirotor aircraft 1.

(95) In this embodiment, the front thrust producing units 3b, 3d have at least one respective shrouding 6b, 6d. More remarkably, on FIG. 13, all the rear thrust producing units 3a, 3c have both upper and lower rotor assemblies 7d, 8d that are depraved of shrouding, i.e. such that both rotor planes 21, 22 of the upper and lower rotor assemblies 7d, 8d are not surrounded but by the fuselage 2a.

(96) As per on FIG. 12, the first rotor axis 21a of all front and rear thrust producing units 3a, 3c, 3b, 3d are respectively inclined by an associated first inclination angle 21a with respect to the predetermined direction 23 of the thrust. FIG. 13 shows the first inclination angle 21a being longitudinal and comprised in a range between +1 and +60. Also, the second rotor assembly 8d is inclined by an associated second inclination angle 22a with respect to the predetermined direction 23. The second inclination angle 22a of FIG. 13 is in a range inferior to the range of the first inclination angle 21a, for instance amounts about 0. In the example of FIG. 12 or 13, the angular value of the first inclination angle 21a amounts for instance between 5 and 30, preferably between 10 and 20, more preferably about 15, e.g. 17.

(97) Finally, it should be noted that modifications of the above described aspects of the present invention are also considered as being part of the claimed invention.

REFERENCE LIST

(98) 1 Multirotor aircraft

(99) 1a Aircraft longitudinal direction

(100) 1b Aircraft lateral direction

(101) 2 Aircraft airframe

(102) 2a Aircraft airframe internal volume

(103) 2b Aircraft airframe width

(104) 3 Thrust producing units

(105) 3a, 3b, 3c, 3d Thrust producing unit

(106) 4 Thrust producing units structural supports

(107) 4a, 4b, 4c, 4d Thrust producing unit structural support

(108) 5 Gearbox fairings

(109) 5a, 5b, 5c, 5d Gearbox fairing

(110) 6 Shrouding units

(111) 6a, 6b, 6c, 6d, 6e Shrouding

(112) 7 Upper rotor assemblies

(113) 7a, 7b, 7c, 7d Upper rotor assembly

(114) 8 Lower rotor assemblies

(115) 8a, 8b, 8c, 8d Lower rotor assembly

(116) 9 Thrust producing airstream direction

(117) 10 Ground

(118) 10a Vertical resp. perpendicular reference line

(119) 11 Longitudinal inclination angles

(120) 11a, 11b Longitudinal inclination angle

(121) 12 Rotor axes

(122) 12a, 12b, 12c, 12d Rotor axis

(123) 13 Lateral inclination angles

(124) 13a, 13b Lateral inclination angle

(125) 14a Upper rotor assembly engine

(126) 14b Lower rotor assembly engine

(127) 15 Upper rotor assembly rotation direction

(128) 16 Lower rotor assembly rotation direction

(129) 17 Pitch variation

(130) 18a, 18b, 18c Upper rotor assembly rotor blade

(131) 19a, 19b, 19c Lower rotor assembly rotor blade

(132) 20a Shrouding inner surface

(133) 20b Shrouding outer surface

(134) 20c Shrouding internal volume

(135) 20d Shrouding leading edge

(136) 20e Shrouding trailing edge

(137) 20f Shrouding outer diameter

(138) 21 Upper rotor assembly rotor plane

(139) 21a Upper plane inclination angle

(140) 22 Lower rotor assembly rotor plane

(141) 22a Lower plane inclination angle

(142) 23 Thrust vector

(143) 23a Airstream inflow direction

(144) 23b Airstream outflow direction

(145) 23c Free airstream flow direction

(146) 24 Distance between rotor planes

(147) 25 Upper and lower shrouding offset distance

(148) 26 Distance between leading edge and rotor plane

(149) 27a, 27b Shrouding heights

(150) 28 Rotor assembly diameter

(151) 29 Upper intermediate rotor assembly

(152) 30 Upper intermediate rotor assembly rotor plane

(153) 31 Lower intermediate rotor assembly

(154) 32 Lower intermediate rotor assembly rotor plane

(155) 33 Upper rotor assembly rotor axis

(156) 34 Lower rotor assembly rotor axis

(157) 35 Rotor axis displacement