PROPULSION SYSTEM ASSEMBLY

Abstract

A propulsion system assembly is provided including a driveshaft and a plurality of electric motor modules. The driveshaft is rotatably mounted to a casing about a drive axis, the driveshaft including a first shaft end and an opposite facing second shaft end. The plurality of electric motor modules are in axially stacked relationship with one another with respect to the drive axis to define an electric motor module stack, each electric motor module being configured for transmitting a torque to the driveshaft when coupled thereto independently of at least one other electric motor module. Each electric motor module includes a controllable clutch arrangement for selectively coupling and decoupling the respective electric motor module with respect to the driveshaft to respectively enable and disable transmission of torque between the respective electric motor module and the driveshaft.

Claims

1. Propulsion system assembly comprising: a driveshaft rotatably mounted to a casing about a drive axis, the driveshaft comprising a first shaft end and an opposite facing second shaft end; a plurality of electric motor modules in axially stacked relationship with one another with respect to the drive axis to define an electric motor module stack, said plurality being an integer greater than unity, each electric motor module being configured for transmitting a torque to the driveshaft when coupled thereto independently of at least one other said electric motor module; each electric motor module comprising a controllable clutch arrangement for selectively coupling and decoupling the respective electric motor module with respect to the driveshaft to respectively enable and disable transmission of torque between the respective electric motor module and the driveshaft.

2. The propulsion system assembly according to claim 1, wherein each said electric motor module comprises: a stator element; a rotor element rotatably mounted with respect to the stator element, and configured for being reversibly coupled to the drive shaft via the respective clutch arrangement.

3. The propulsion system assembly according to claim 1 or claim 2, wherein each electric motor module has a depth dimension parallel to the drive axis and a width dimension orthogonal to the drive axis, wherein said width dimension is greater than said depth dimension.

4. The propulsion system assembly according to claim 3, wherein a ratio of said width dimension to said depth dimension is between 5 and 20.

5. The propulsion system assembly according to claim 3, wherein a ratio of said width dimension to said depth dimension is greater than 10.

6. The propulsion system assembly according to any one of claims 1 to 5, wherein each said electrical motor module is design to generate the same torque under the same operating conditions as one another.

7. The propulsion system assembly according to any one of claims 1 to 6, wherein each said electrical motor module is design to generate a module design shaft power of 40 kW or more than 40 kW.

8. The propulsion system assembly according to any one of claims 1 to 7, wherein said propulsion system assembly is configured to provide a design shaft power using all said electric motor modules, wherein said design shaft power is greater than a required shaft power by a shaft power safety margin, wherein said shaft power safety margin is not less than a module design shaft power of at least one said electric motor module.

9. The propulsion system assembly according to any one of claims 1 to 8, wherein for each electric motor module, the respective clutch arrangement comprises an electromechanical clutch independently actuable with respect to the other said clutch arrangements.

10. The propulsion system assembly according to any one of claims 2 to 8, wherein for each electric motor module, the respective clutch arrangement comprises: a clutch rotor and a field coil concentrically provided on the rotor element, and an armature affixed to the driveshaft, wherein responsive to actuation of the respective clutch arrangement the clutch rotor frictionally abuts the armature driveshaft to enable transmission of said torque between the respective electric motor module and the driveshaft.

11. The propulsion system assembly according to any one of claims 1 to 10, wherein for each electric motor module, the respective clutch arrangement is actuable responsive to one or more of electric, electronic or digital signals.

12. The propulsion system assembly according to any one of claims 1 to 11, wherein for each electric motor module, the respective clutch arrangement is actuable responsive to the clutch arrangement being subjected to a rotational resistance from the respective electric motor module greater than a predetermined threshold.

13. The propulsion system assembly according to any one of claims 1 to 12, further comprising a first rotor element for aerodynamically generating a first thrust responsive to being turned about said drive axis by the propulsion system assembly.

14. The propulsion system assembly according to claim 13, wherein said first rotor element is affixed to said first shaft end.

15. The propulsion system assembly according to claim 13 or claim 14, wherein said first rotor element comprises any one of a propeller, ducted fan, unducted fan.

16. The propulsion system assembly according to any one of claims 1 to 12, further comprising a second rotor element for aerodynamically generating a second thrust responsive to being turned about said drive axis by the propulsion system assembly.

17. The propulsion system assembly according to claim 16, wherein said second rotor element is affixed to said second shaft end.

18. The propulsion system assembly according to claim 16 or claim 17, wherein said second rotor element comprises any one of a propeller, ducted fan, unducted fan.

19. The propulsion system assembly according to any one of claims 1 to 18, the casing comprising a first casing bracket affixed to a first said electric motor module that is closest to said first shaft end, and a second casing bracket affixed to a second said electric motor module that is closest to said second shaft end, said first casing bracket comprising a first bearing arrangement and said second casing bracket comprising a second bearing arrangement, the driveshaft being rotatably mounted with respect to said first bearing arrangement and said second bearing arrangement.

20. The propulsion system assembly according to any one of claims 1 to 19, wherein in said axially stacked relationship, each pair of axially adjacent said electric motor modules are fixedly connected to one another.

21. The propulsion system assembly according to any one of claims 1 to 20, wherein said electric motor modules are connected to the casing in fixed spatial relationship in said axially stacked relationship.

22. The propulsion system assembly according to any one of claims 1 to 21, wherein said casing comprises a plurality of spacer elements interconnecting each pair of axially adjacent electric motor modules in fixed spatial relationship in said axially stacked relationship.

23. The propulsion system assembly according to any one of claims 1 to 22, further comprising a housing member for enclosing therein at least said casing and said plurality of electric motor modules.

24. The propulsion system assembly according to claim 23, wherein said housing member is configured for pivoting about a pivot axis different from the drive axis.

25. The propulsion system assembly according to claim 24, wherein said pivot axis is orthogonal to the drive axis.

26. The propulsion system assembly according to any one of claims 1 to 25, further comprising a control system for controlling operation of each said electric motor module.

27. The propulsion system assembly according to claim 26, wherein said control system comprises a motor controller for each said electric motor module, each respective motor controller being configured for operating the respective said clutch arrangement, wherein to cause the respective said clutch arrangement to selectively couple and decouple the respective said electric motor module with respect to the driveshaft.

28. The propulsion system according to claim 27, wherein each said motor controller is configured for operating the respective said clutch arrangement to decouple the respective said electric motor module with respect to the driveshaft responsive to a detectable fault being detected in the respective said electric motor module.

29. The propulsion system according to claim 28, wherein said detectable fault comprises a significant reduction in the shaft power generated by the respective said electric motor module as compared with an expected shaft power level.

30. The propulsion system according to claim 28 or claim 29, comprising a detector for detecting said detectable fault, said detector being operatively connected to the control system.

31. The propulsion system according to claim 30, wherein said detector comprises at least one of Hall effect Sensors, Encoders, Resolvers.

32. The propulsion system according to any one of claims 27 to 31, wherein each said motor controller is configured for operating independently of at least one other said motor controller.

33. The propulsion system according to any one of claims 27 to 32, wherein said control system comprises a master controller for controlling operation of the plurality of said motor controllers corresponding to said plurality of electric motor modules.

34. An air vehicle comprising at least one propulsion system assembly as defined in any one of claims 1 to 33.

35. The air vehicle according to claim 34, wherein the air vehicle is a VTOL type air vehicle.

36. The air vehicle according to claim 34 or claim 35, wherein the air vehicle is a manned air vehicle.

37. The air vehicle according to claim 34 or claim 35, wherein the air vehicle is an unmanned air vehicle (UAV).

38. The air vehicle according to any one of claims 34 to 37, each said propulsion system assembly configured for selectively providing vertical thrust for vectored thrust flight and for selectively changing the thrust vector to provide horizontal thrust for aerodynamic flight.

39. The air vehicle according to claim 38, wherein at least one said propulsion system assembly is reversibly tiltable between a horizontal angular disposition for providing horizontal thrust and a vertical angular disposition for providing vertical thrust.

40. The air vehicle according to any one of claims 34 to 39, comprising three said propulsion system assemblies.

41. The air vehicle according to claim 34, wherein said three propulsion system assemblies are in triangular configuration when viewed in plan view.

42. Method for operating an air vehicle, comprising (a) providing a shaft power requirement for driving a desired rotor at desired operating conditions; (b) providing a propulsion system assembly as defined in any one of claims 1 to 33, wherein each said electric motor module is designed to provide a module shaft power output at said desired operating conditions, wherein said integer is chosen such that a shaft power output of the stack, defined as a product of said integer and said module shaft power output, matches or exceeds said shaft power requirement.

43. Method according to claim 42, comprising modifying said shaft power requirement and correspondingly modifying said integer by increasing or decreasing said plurality of said electric motor modules such that a modified product of said modified integer and said module shaft power output matches or exceeds said modified shaft power requirement.

44. Method according to claim 42 or claim 43, comprising adding additional said electric motor modules to said electric motor module stack to thereby increase said shaft power output of the thus modified propulsion system assembly as compared with the unmodified said propulsion system assembly.

45. Method according to claim 42 or claim 43, comprising removing at least one said electric motor modules from said electric motor module stack to thereby decrease said shaft power output of the thus modified propulsion system assembly as compared with the unmodified said propulsion system assembly.

46. Method according to any one of claims 42 to 45, comprising monitoring operation of each said electric motor module and operating the respective said clutch arrangement thereof to decouple the respective said electric motor module from the driveshaft responsive to a detectable fault being detected in operation of the respective said electric motor module.

47. Method according to any one of claims 42 to 46, wherein said shaft power requirement is determined for vectored thrust flight, and further comprising operating the propulsion system assembly in aerodynamic flight with a reduced number of electric motor modules coupled to the driveshaft, said reduced number being at least one less than said integer.

48. Method according to claim 47, wherein each said electric motor module of said reduced number of electric motor modules operates at maximum efficiency during said aerodynamic flight.

49. Method according to claim 47 or claim 48 wherein a ratio of said integer to said reduced number is between 5 and 10.

50. An electric motor module, comprising a stator element; a rotor element rotatably mounted with respect to the stator element, a controllable clutch arrangement for selectively coupling and decoupling the electric motor module with respect to a driveshaft to respectively enable and disable transmission of torque between the electric motor module and the driveshaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0100] FIG. 1 is an isometric view of a propulsion system assembly according to an example of the presently disclosed subject matter.

[0101] FIG. 2 is an isometric cross-sectional view of the example of FIG. 1.

[0102] FIG. 3 is an isometric exploded view of the example of FIG. 1.

[0103] FIG. 4(a) is side view of the example of FIG. 1; FIG. 4(b) is top view of the example of FIG. 1.

[0104] FIG. 5(a) schematically illustrates in side view an alternative variation of the example of FIG. 1 in horizontal thrust mode; FIG. 5(b) schematically illustrates in side view the example of FIG. 5(a) in vertical thrust mode.

[0105] FIG. 6(a) schematically illustrates in side view the example of FIG. 1 configured with a pusher propeller; FIG. 6(b) schematically illustrates in side view the example of FIG. 1 configured with a puller propeller; FIG. 6(c) schematically illustrates in side view an alternative variation of the example of FIG. 1 configured with a pusher propeller and a puller propeller.

[0106] FIG. 7 schematically illustrates a control system for the example of FIG. 1.

DETAILED DESCRIPTION

[0107] Referring to FIGS. 1 to 3, a propulsion system assembly according to a first example of the presently disclosed subject matter, generally designated 100, comprises a driveshaft 200, casing 300, and a plurality of electric motor modules (EMM) 400.

[0108] Referring to FIG. 2 in particular, each EMM 400 comprises in this example a first rotor 410 and a second rotor 420 sandwiching a stator 430 therebetween, and thus the first rotor 410 and the second rotor 420 are disposed one each on opposite facing sides of the stator 430.

[0109] The stator 430 is annular disc-shaped having a central opening 435, and includes a mounting ring 440 at the outer periphery thereof, the mounting ring 440 comprising a plurality of mounting points 442 as well as an electrical interface 444 including electrical inlet and/or outlet connection for providing electrical power to the EMM 400. The electrical interface 444 can also provide control inputs for controlling the EMM 400 and/or sensor outputs.

[0110] The first rotor 410 and the second rotor 420 are each disc-shaped having a respective central opening 415, 425 respectively, and are concentric with the stator 430, being co-axially aligned with the drive axis A of the driveshaft 200. Each one of said first rotor 410 and the second rotor 420 comprises a rotor mounting bracket, 411, 421 respectively, that inwardly project into the respective central opening 415, 425, and axially connect with one another via said central opening 435 to provide a rotor assembly 455.

[0111] As best seen in FIG. 4(a) and FIG. 4(b), each EMM 400 is generally disc-shaped and has a depth dimension t (parallel to the drive axis A) and a width dimension W (orthogonal to the drive axis A). At least in the illustrated example, the width dimension W is greater than the depth dimension t, and while in the illustrated example, the ration R of the width dimension W to the depth dimension t is about 10, in alternative variations of this example the ratio R can have other suitable values, for example greater than 10, or within the range 5 to 20, for example.

[0112] In at least one implementation of this example, each EMM 400 can be a brushless coreless Axial-Flux motor, provided by Albus Technologies Ltd, of Israel, and/or an electric machine as disclosed in WO 2014/033715 or in WO 2014/033716 to Albus Technologies Ltd, for example.

[0113] Each EMM 400 comprises a respective controllable clutch arrangement 600 that is concentric with, and fixed to, the rotor assembly 415. The clutch arrangement 600 is configured for selectively coupling and decoupling the respective EMM 400 with respect to the driveshaft 200, enabling and disabling, respectively the transmission of torque/shaft power between the respective EMM 400 and the driveshaft 200, as will become clearer herein.

[0114] In this example, each clutch arrangement 600 is in the form of an electromechanical clutch 610 that is independently actuable with respect to the other clutch arrangements 600 of the other EMM 400 of the stack 450. Referring to FIG. 2 in particular, each clutch arrangement 600 comprises an armature 630 rotationally fixed to the driveshaft 200, and a clutch rotor 640 concentrically provided on the rotor assembly 455 and including a field coil (not shown). In response to actuation of the clutch arrangement 600, the clutch rotor 640 frictionally abuts the armature 630, and thus becomes mechanically connected to the driveshaft 200, thereby enabling transmission of torque/shaft power between the respective EMM 400 and the driveshaft 200. In this example, for each EMM 400, the respective clutch arrangement 600 is actuable responsive to one or more of electric, electronic or digital signals, as will become clearer herein. Thus, when the clutch arrangement is actuated, electrical current flows through the field coil, generating a magnetic field and magnetizing the clutch rotor 640, which in turn magnetically attracts the armature, abutting the armature to the clutch rotor 630 and generating friction. Thus, as the rotor assembly 455 spins about drive axis A, the drive shaft 200 becomes frictionally coupled via the armature, and thus shaft power is transmitted to the driveshaft 200 via the armature 630. The clutch arrangement 600 decouples the rotor assembly 455 from the driveshaft 200 when electrical current to the clutch arrangement 600 is stopped—the armature 630 is free to turn with the driveshaft 200, while the armature remains with the rotor assembly 455. Thus if a fault develops in the respective EMM 400 causing the EMM 400 to slow down or stop, the clutch arrangement 600 decouples that particular EMM 400 from the driveshaft 200, which is driven by the remaining EMM 400 of the stack 450.

[0115] In alternative variations of this example, other different clutch configurations can be used in place of the electromechanical clutch 610, for example an electromagnetic clutch arrangement or a mechanical clutch arrangement. For example, such a mechanical clutch arrangement can comprise a shaft clutch part rotationally fixed to the driveshaft 200, and a clutch rotor 640 concentrically provided on the rotor assembly 455, and including a release-type ball-detent type arrangement, in which spring loaded balls keep the shaft clutch part engaged with the shaft clutch part until the clutch arrangement is subjected to a torque overload, for example as a result of malfunction of the respective EMM 400 which for some reason is not developing torque and is now being rotated by the driveshaft. At torque overload conditions, the springs that abut the balls to one or another of the shaft clutch part engaged or the shaft clutch part becomes compressed, bringing the balls into disengagement with the other one of the shaft clutch part engaged or the shaft clutch part, respectively, allowing relative rotation between the driveshaft and the malfunctioning EMM 400.

[0116] In this example, the plurality of electric motor modules (EMM) 400 comprises four EMM 400 in axially stacked relationship with one another respect to the drive axis A, thereby defining an electric motor module stack (EMMS) 450. As will become clearer herein, in alternative variations of this example, or indeed in at least some implementations of this example, the EMMS 450 can have more than one EMM 400, i.e., two, three, five or more than five EMM 400, in axially stacked relationship with one another respect to the drive axis A.

[0117] In this example, all the EMM 400 in the EMMS 450 are essentially identical to one another, and each EMM 400 is designed to provide the same torque and same module design shaft power (DSP) for the EMM 400 as the other EMM 400. For example, the module design shaft power for each EMM 400 can be 40 kW or more than 40 kW. In other examples, the module design shaft power for each EMM 400 can be less than 40 kW, for example 10 kW, 15 kW, 20 kW, 25 kW, 30 kW, or 35 kW, or any power level in-between these values.

[0118] Each EMM 400 is configured for transmitting torque/shaft power to the driveshaft 200, when coupled thereto via the respective clutch arrangement 600, independently of at least one other EMM 400 or independently of operation of all the other EMM 400 of the stack 450.

[0119] The driveshaft 200 is rotatably mounted to the casing 300 about drive axis A. The driveshaft comprises a first shaft end 210 and a second shaft end 220, the first shaft end 210 and the second shaft end 220 being at opposite longitudinal ends of the driveshaft 200.

[0120] Referring also to FIG. 3, the casing 300 comprises a first casing bracket 310 affixed to one longitudinal end of the stack 450, and a second casing bracket 320 affixed to the opposed longitudinal end of the stack 450. More particularly, the first casing bracket 310 affixed to the EMM 400 that is closest to said first shaft end 210, and the second casing bracket 320 is affixed to the EMM 400 that is closest to the second shaft end 220.

[0121] The first casing bracket 310 comprises a first bearing arrangement 315, and radial arms 316 outwardly project therefrom to an outer base element 317 which is fixed to the uppermost EMM 400 as seen in FIG. 3.

[0122] The second casing bracket 320 comprises a second bearing arrangement 325, and radial arms 326 outwardly project therefrom to an outer base element 327 which is fixed to the lowermost EMM 400 as seen in FIG. 3.

[0123] The driveshaft 200 is rotatably mounted with respect to the first bearing arrangement 315 and the second bearing arrangement 325.

[0124] In the aforementioned axially stacked relationship, each pair of axially adjacent EMM 400 are fixedly connected to one another via the casing 300. For this purpose, the casing 300 further comprises a plurality of spacer elements 340 interconnecting each pair of axially adjacent EMM 400 in a fixed spatial relationship in stack 450.

[0125] While in this example, the stack 450 is exposed to the external environment, in alternative variations of this example, and referring to FIG. 5(a) and FIG. 5(b), the propulsion system assembly 100 comprises a housing member 120 for enclosing therein at least the casing 300 and stack 450. In the illustrated example, the housing member 120 is configured for pivoting about a pivot axis B different from the drive axis A; in particular, in this example the pivot axis B is orthogonal to the drive axis A, and thus in one mode of operation the example illustrated in FIG. 5(a) and FIG. 5(b) can be used for generating a vertical thrust and a horizontal thrust, respectively, as the housing 120 together with the propulsion system assembly 100 is pivoted 90° about pivot axis B.

[0126] The propulsion system assembly 100 further comprises a first rotor element 700 for aerodynamically generating a thrust T1 responsive to being turned about the drive axis A by the EMM 400 of the propulsion system assembly 100. The first rotor element 700 is affixed to the first shaft end 210. While in this example the first rotor element 700 is in the form of a propeller, other forms of rotor can be provided in alternative variations of this example, for example a ducted fan or an unducted fan.

[0127] Referring to FIGS. 6(a) and 6(b), the rotor element 700 can be configured as a pusher propeller or a puller propeller, respectively, for example.

[0128] In yet other alternative variations of these examples, and referring to FIG. 6(c), the propulsion system assembly 100 further comprises a second rotor element 750 for aerodynamically generating a second thrust T2 in the same direction as, and concurrently with, thrust T1, responsive to being turned about the drive axis A by the EMM 400 of the propulsion system assembly 100, and thus the second rotor element 750 is affixed to the second shaft end 220. The second rotor element 750 can comprise any one of a propeller, ducted fan, unducted fan, for example.

[0129] Referring to FIG. 7, the propulsion system assembly 100 further comprises a control system 800 for controlling operation of each EMM 400. The control system 800 comprises a motor controller 810 for each EMM 400. Each respective motor controller 810 is configured for operating the respective clutch arrangement 600, to cause the respective clutch arrangement 600 to selectively couple or decouple the respective EMM 400 with respect to the driveshaft 200, according to predetermined criteria. In this example, such criteria include decoupling the respective EMM 400 with respect to the driveshaft 200 responsive to a detectable fault being detected in the respective EMM 400. For example, such a detectable fault can comprise a significant reduction in the shaft power generated by the respective EMM 400, as compared with an expected or nominal shaft power level. The control system 800 comprises a detector 830 (only shown for one EMM 400) for detecting such a detectable fault using suitable decision-making algorithms, the detector 830 being operatively connected to the control system 800, in particular to the respective motor controller 810.

[0130] Such decision-making algorithms can provide control outputs, based on input received from one or more known sensors, for controlling operation of the respective EMM 400. Such sensors can include, for example, one or more of Hall effect Sensors, Encoders, Resolvers, or combination of part or all of these. Additionally or alternatively, such sensors can include temperature sensors. The sensors are configured for providing the required data at a sufficiently high frequencies that are high enough to detect abnormal behavior of the respective EMM 400, and thus analyzing the data from those sensors by the respective motor controller 810 can indicating a problem in a specific EMM 400. Accordingly, the respective malfunctioning EMM 400 can be stopped, while concurrently allowing the other EMM 400 in the stack 450 to continue rotating the driveshaft at the required RPM. In at least some examples, this can require designing the propulsion system assembly 100 so that the power requirements for the total number of EMM 400 will allow less than this number of EMM 400 (for example one less) to supply adequate power for the air vehicle (in which the propulsion system assembly 100 is installed) in all the stages of aerodynamic flight, as well in all stages of vectored flight for cases in which the air vehicle is a VTOL air vehicle.

[0131] Each motor controller 810 is configured for operating independently of at least one other motor controller 810, and in this example independently of all the other motor controllers 810 of the control system 800.

[0132] The control system 800 also comprises a master controller 850 for controlling operation of the plurality of motor controllers 810, corresponding to the plurality of EMM 400. Essentially, the master controller 850 operates to monitor the behavior of all the EMM 400, to analyze the performance of each EMM 400, to analyze the operation of each motor controller 810, and to compare the performance and operation of all the EMM 400. The master controller 850 further operates to determine, from the information gathered in this manner, whether any particular EMM 400 in the stack 450 is behaving in a different or abnormal manner from the other EMM 400 in the stack 450. In such a case the master controller 850 can operate to stop or start EMM 400 directly, even if the respective motor controller 810 fails. In such cases where one EMM 400 no longer generates torque and is decoupled from the driveshaft 200, the remaining coupled EMM 400 compensate for the decoupled EMM 400 and will attempt to meet the required RPM for the driveshaft, wherein each respective motor controller 810 will operate to increase the demand for current and thus enable the coupled EMM 400 to operate at an increased power rating to develop the required shaft power.

[0133] For example, if a malfunction causes a particular EMM 400 to run at a higher RPM than the other EMM 400 in the stack, the motor controller 810 will attempt to match the RPM to that of the other EMM 400, and if not possible then will shut down the particular EMM 400, and the respective clutch arrangement 600 decouples the malfunctioning EMM 400 from the driveshaft.

[0134] For example, if a malfunction causes particular EMM 400 to run at a lower RPM than the other EMM 400 in the stack, the motor controller 810 or the master controller 850 will attempt to match the RPM to that of the other EMM 400, and if not possible then will shut down the particular EMM 400, and the respective clutch arrangement 600 decouples the malfunctioning EMM 400 from the driveshaft. Alternatively, even if the respective motor controller 810 fails, and/or the master controller 850 fails, the clutch arrangement 600 will automatically decouple the malfunctioning EMM 400 from the driveshaft 200 when the RPM is sufficiently lower than that of the driveshaft 200.

[0135] Thus, for example, the control system 800 can be operated to monitor operation of each EMM 400 and to actuate each the respective clutch arrangement 600 to selectively decouple the respective EMM 400 from the driveshaft 200 responsive to a detectable fault being detected in operation of the respective EMM 200.

[0136] The above example of the propulsion system assembly 100 can be used, by itself or in addition to other propulsion system assemblies 100 and/or other propulsion units, to power an air vehicle (e.g., a fixed wing air vehicle or a rotary wing air vehicle, for example a helicopter), or indeed other types of vehicles, including for example any one of: a hovercraft, land vehicle, sea surface vehicle, undersea vehicle. For example, the air vehicle can be a conventional air vehicle or a VTOL type air vehicle, and furthermore, the air vehicle can be a manned air vehicle or an unmanned air vehicle (UAV).

[0137] For example the air vehicle can be configured with three tiltable propulsion system assemblies 100 in triangular configuration in plan view.

[0138] The design aggregate shaft power generated by the propulsion system assembly 100 is essentially the sum of the module design shaft powers generated by each of the EMM 400 (minus some losses as a result of coupling the EMM 400 to the driveshaft 200). Thus, to meet the requirement of providing a particular design aggregate shaft power, the propulsion system assembly 100 comprises at least the appropriate number of EMM 400 which together can provide or exceed this design aggregate shaft power. In this example, the stack 450 comprises at least one additional EMM 400 than is required to provide the design aggregate shaft power, so as to provide a safety margin in case correspondingly one or more EMM 400 fail, so that the remaining operating EMM 400 can together provide the design aggregate shaft power. At the same time, it is to be noted that by disengaging the EMM 400 that develop a fault, the driveshaft does not turn the malfunctioning EMM 400, and thus there are no significant power losses that would otherwise be incurred for turning the malfunctioning EMM 400.

[0139] It is also readily evident that the propulsion system assembly 100 provides a very versatile propulsion system that can be modified for different air vehicles and even for different mission requirements for the same air vehicle.

[0140] For example, starting with propulsion system assembly 100 including a particular number of EMM 400 developing a particular a design aggregate shaft power, such a propulsion system assembly 100 can be modified when the design aggregate shaft power needs to be modified. For example, if the design aggregate shaft power needs to be increased or decreased, the number of EMM 400 provided in the stack 450 is correspondingly increased or decreased. Thus the sum of the module design shaft powers of the new number of EMM 400 matches or exceeds the modified design aggregate shaft requirement.

[0141] Thus, by adding additional EMM 400 to the stack 450, the shaft power output of the thus modified propulsion system assembly 100 is increased as compared with the unmodified said propulsion system assembly 100. Conversely, by removing at least one EMM 400 from stack 450 thereby decreases the shaft power output of the thus modified propulsion system assembly 100 as compared with the unmodified propulsion system assembly 100.

[0142] In this manner, the power output of the propulsion system assembly 100 can be changed dramatically in a simple manner, and optimizes every time the weight of the propulsion system assembly 100 by not having to carry additional engine weight when less power output is required.

[0143] According to an aspect of the presently disclosed subject matter, the propulsion system assembly 100 provides a very versatile propulsion system that can be modified for different power requirements of the air vehicle even during a particular mission while operating at maximum efficiency.

[0144] For example, starting with propulsion system assembly 100 including a fixed number of EMM 400 developing a particular a design aggregate shaft power, this aggregate shaft power can be chosen as that required for vectored thrust flight while operating all the EMM 400 of the stack 450 at maximum efficiency. Operation of such a propulsion system assembly 100 can be modified when the design aggregate shaft power needs to be changed. For example, the design aggregate shaft power needs to be significantly decreased when in aerodynamic flight such as for example cruising. In such a case, the number of EMM 400 in the stack 450 that are coupled to the driveshaft is correspondingly decreased, such that the sum of the module design shaft powers (each corresponding to maximum efficiency) of the EMM 400 that remained coupled to the driveshaft 200 matches or exceeds the modified design aggregate shaft requirement for aerodynamic flight.

[0145] In the method claims that follow, alphanumeric characters and Roman numerals used to designate claim steps are provided for convenience only and do not imply any particular order of performing the steps.

[0146] Finally, it should be noted that the word “comprising” as used throughout the appended claims is to be interpreted to mean “including but not limited to”.

[0147] While there has been shown and disclosed examples in accordance with the presently disclosed subject matter, it will be appreciated that many changes may be made therein without departing from the spirit of the presently disclosed subject matter.