A rim-driven electric thruster

Abstract

A rim-driven electric thruster 10 for vehicle propulsion is provided. There is a stator 12 defining a nacelle with an inlet and an outlet, a circumferential rotation channel 44 formed in the stator 12

Description

The present invention relates to a rim-driven electric thruster for providing propulsion for a vehicle. The invention further relates to a method of providing an efficient aircraft drive system, to a vehicle comprising such a rim-driven electric thruster, and to a method of 5 manufacturing an efficient aircraft drive system. An aircraft is typically propelled by a system including a motor coupled to an assembly of blades by a shaft, which rotates when driven by the motor to drive the blades and generate thrust. These blades may be open to the air as in an aircraft propeller or enclosed in a duct or nacelle. 10 Conventional ducted rotor thruster systems house the blades in an aerodynamic ring with a small gap between the blades and the duct, providing increased efficiency due to reduced drag. Air circulating around the blade tips is a substantial source of efficiency LO losses and noise, so a very small gap between the blades and the duct is important to CM minimise these effects, increasing manufacturing difficulty. 15 In these systems, the motor is also typically housed in the duct, which blocks a portion of the airflow and further reduces efficiency. Additionally, because of the high power 1— concentrated in a single central motor, active cooling is needed to prevent overheating. Finally, driving the blades of the rotor with a rotating shaft necessitates a mechanical gearbox, which is a prominent source of noise and increases the risk of mechanical 20 failure. The present invention seeks to provide a solution which obviates or overcomes the above-mentioned deficiencies by providing a rim-driven electric thruster which, compared to existing thrusters for vehicle propulsion, is more efficient, quieter, requires no active cooling, and is and less prone to mechanical failure due to fewer complex parts. 25 According to a first aspect of the invention, there is provided a rim-driven electric thruster for vehicle propulsion, the rim-driven electric thruster comprising: a stator defining a nacelle with an inlet and an outlet, a circumferential rotation channel being formed in the stator, and the stator including a plurality of coreless windings arranged around the circumferential rotation channel, the stator comprising a plurality of winding supports 30 around which the plurality of windings is wound; a rotor comprising; an outer rim portion positioned radially outwards of a centre of the rotor, the outer rim portion having a plurality of circumferentially spaced rim members defining a plurality of magnet receivers therebetween; a plurality of magnets, each of the plurality of magnets being engaged with a said one of the plurality of magnet receivers such that the plurality of magnets and the plurality of rim members form an outer perimeter having a continuous or substantially 5 continuous surface; and a plurality of rotor blades extending from the outer rim portion towards the centre of the rotor; the rotor being positioned in the stator such that the plurality of magnets is received in the rotation channel in-use to permit rim-driven operation of the rotor; and further comprising at least one stator blade attached to an inner surface of the nacelle. There is a central hub positioned at the centre of the rotor 10 connected with each of the plurality of rotor blades, and the central hub is or is substantially annular, wherein each of the plurality of winding supports has a complementarily shaped rotor-facing surface to the outer perimeter of the rotor. 15 CXI Conventional thruster systems have many issues such as efficiency losses from air flow around rotor blades, loud operation, susceptibility to overheating, and vulnerability to mechanical failure. The present invention provides a rim-driven electric thruster which is more efficient, quieter, requires no active cooling, and is less prone to mechanical failure. This is achieved by the provision of the coreless windings in the stator which are positioned about the magnets of the rotor. A central hub provides a means to hold the plurality of rotor blades centrally. Holding the 20 plurality of blades near a centre of the rotor as opposed to at the rim reduces wear on the system, since the speed of each of the plurality of blades decreases towards the centre of the rotor. The annular hub has the advantage of increasing the airflow through the nacelle, increasing the efficiency of the rim-driven electric thruster. 25 Winding supports can help maintain the shape of each of the plurality of windings, and winding the windings directly around the winding supports is a convenient method to install the windings. The complementary shaping advantageously minimises the air gap between the stator and the rotor, which increases the efficiency of the rim-driven thruster by increasing the 30 strength of the electromagnetic interactions between the windings and the magnets. Optionally, the stator may comprise a rotor support with which the central hub of the rotor is rotatably engageable. Such a rotor support provides structural integrity for the central hub, increasing the stability of the system which helps to reduce deformation of the rotor. Each of the plurality of magnets may have a cylindrical or substantially cylindrical shape. Cylindrical magnets are a convenient choice because of their ease of manufacture, and 5 potentially ease of installation into the rotor itself, for example using an axle or pin system. Optionally, each of the plurality of magnets may have an arcuate outer surface and a receiver-contact surface which is complementarily shaped to an outward-facing surface of each of the plurality of magnet receivers. Each of the plurality of magnets having an arcuate outer surface means the plurality of 10 windings can capture a large portion of the flux around the circumference of the magnets, increasing efficiency. The receiver-contact surface being complementarily shaped to an outward-facing surface of each of the plurality of magnet receivers advantageously allows the plurality of magnets to be engaged flush with the plurality of magnet receivers. LO One or more stator blades within the nacelle can direct part of the airflow, reducing 15 efficiency losses from air flowing around the circumference of the nacelle. Optionally, the at least one stator blade may be rotatable about a radial axis of the stator. This advantageously allows the stator blades to be adjusted, providing more control over 1— airflow direction which allows for the further reduction of circumferential airflow, increasing efficiency. 20 Optionally, each of the plurality of winding supports may be or substantially be an elliptic paraboloid shape or a saddle shape. This allows for easy installation of elliptic or paraboloid coreless windings, by winding each of the windings around each of the winding supports. Preferably, each of the plurality of winding supports may be provided as an individual 25 component receivably engageable with a main stator body of the stator. This modularisation simplifies the construction of the rim-driven electric thruster, as the winding supports can be separately manufactured and then received within a main stator body of the stator. Optionally, each of the plurality of windings may have or substantially have an elliptic 30 paraboloid shape or a saddle shape. Each of the windings having an elliptic paraboloid or saddle shape increases the amount of magnetic flux that can be captured from the plurality of magnets, increasing the efficiency of the rim-driven electric thruster. Optionally, the plurality of windings may collectively form a toroidal winding in the stator. 5 The windings collectively forming a toroidal winding in the stator means that electromagnetic interactions with the magnets can occur around the entire circumference of the stator, distributing power load which helps with keeping the system cool and stable. Preferably, at least one of the plurality of rotor blades may include a serrated edge portion. This edge structure reduces the noise of the rotor in use and provides a better 10 aerodynamic performance. Preferably, at least one of the plurality of rotor blades may have a twisted aerodynamic profile. LO A twisted aerodynamic profile provides a more equal distribution of lift by compensating CM for the difference in speed along the length of one of the plurality of rotor blades in-use. 15 Optionally, the plurality of magnets may be arranged such that a polarity of adjacent magnets alternates in a circumferential direction of the outer rim portion. In other words, north poles of adjacent magnets face one another, and south poles of adjacent magnets 1— face one another. This may be deemed a quasi-Halbach type of magnetic configuration. Arranging the magnets in this way means that a large portion of the magnetic flux can 20 be captured by the plurality of windings. Preferably, each of the plurality of windings may be a polyphase winding, most preferably a three-phase winding. Suitably configured polyphase windings produce a rotating magnetic field, which can be used to drive the rotor. 25 Optionally a plurality of said rotors may be provided, with the stator having a complementary number of circumferential rotation channels therein. Having a plurality of rotors allows for a greater amount of thrust to be produced by the rim-driven electric thruster. According to a second aspect of the invention, there is provided a vehicle comprising a rim-driven electric thruster in accordance with the first aspect of the invention. Optionally, this vehicle may be an aircraft. A rim-driven electric thruster provides means of generating thrust for an aircraft, or 5 indeed other vehicle, that is more efficient, quieter, requires no active cooling, and is less prone to mechanical failure than existing aircraft thrusters, for example. Optionally, the rim-driven electric thruster may be integrated within the vehicle. Having the rim-driven electric thruster integrated within the vehicle may provide aerodynamic benefits, reducing drag and increasing efficiency. 10 Optionally, the rim-driven electric thruster may be pivotably or movably mounted to an outer surface of the vehicle to permit alteration of a direction of thrust provided by the rim-driven electric thruster. 15 This allows the direction of thrust to be altered, enabling a direction of travel of the vehicle to be altered. According to a third aspect of the invention, there is provided a method of providing an efficient aircraft drive system, the method comprising the steps of: a] providing a vehicle in accordance with the second aspect of the invention; and b] providing a drive current to the plurality of windings to provide a rimless drive for the rim-driven electric thruster. Existing aircraft drive systems have many issues such as efficiency losses from air flow 20 around rotor blades, loud operation, susceptibility to overheating, and vulnerability to mechanical failure. The present invention provides a method for providing an efficient aircraft drive system which is more efficient, quieter, requires no active cooling, and is less prone to mechanical failure. The invention will now be more particularly described, by way of example only, with 25 reference to the accompanying drawings, in which: Figure 1 shows a front isometric view of a first embodiment of a rim-driven electric thruster in accordance with the first aspect of the invention; Figure 2 shows a rear isometric view of a portion of the rim-driven electric thruster of Figure 1, wherein a plurality of stator blades is present; Figure 3 shows a front isometric view of a rotor of the rim-driven electric thruster of Figure 1; Figure 4 shows a front isometric view of the rim-driven electric thruster of Figure 1, wherein the stator is shown in cross section and the winding supports are omitted; 5 Figure 5 shows a front isometric view of the rim-driven electric thruster of Figure 1, wherein the rim-driven thruster is shown in cross section; Figure 6 shows an isometric view of a winding support and a portion of an outer perimeter of the rim-driven electric thruster of Figure 1; Figure 7 shows an isometric view of a coreless winding and a winding support of 10 the rim-driven electric thruster of Figure 1; Figure 8 shows an enlarged view from the side of a portion of the outer rim of Figure 1, including a plurality of magnets, with magnetic field lines and polarities indicated; Figure 9 shows an isometric view of a second embodiment of a partially-15 constructed rotor of a rim-driven electric thruster in accordance with the first aspect of the invention; Figure 10 shows an enlarged isometric view of the rotor of Figure 9, including more magnets; Figure 11 shows an isometric representation of the rotor of Figure 10, including 20 a circumferential rotation channel formed by a winding support of the stator of the rim-driven electric thruster; Figure 12 shows a first embodiment of a vehicle including two rim-driven electric thrusters in accordance with the second aspect of the invention; and Figure 13 shows a lower view of a second embodiment of a vehicle including 25 eight integrated rim-driven electric thrusters in accordance with the second aspect of the invention. Referring to Figure 1, there is shown a rim-driven electric thruster, referenced globally at 10. The rim-driven electric thruster 10 comprises a stator 12 and a rotor 14. The stator 12 defines a nacelle with an inlet 16 and an outlet 18. In-use, air flows from the inlet 16 to the outlet 18, with air expelled through the outlet 18 providing thrust for the rim-driven electric thruster 10. In the embodiment shown, a rotor support 20 with which the rotor 14 is rotatably engageable is included in the stator 12. 5 The rear of the rim-driven electric thruster 10 is shown in Figure 2. The stator 12 comprises a plurality of stator blades 22 attached to the interior of the stator 12 to direct airflow. These stator blades 22 may preferably be rotatable about a radial axis of the stator 12, allowing some control over airflow direction. Alternatively, said stator blades 22 may be fixed in place so as to be non-moving. 10 Figure 3 depicts the rotor 14 in more detail. The rotor 14 comprises an outer rim portion 24, a plurality of magnets 26, and a plurality of rotor blades 28. The outer rim portion 24 is positioned radially outwards of a centre C of the rotor 14, and comprises a metal band 30 and a plurality of circumferentially spaced rim members 32, the rim members 32 defining a plurality of magnet receivers 26R therebetween. 15 The plurality of magnets 26 are preferably permanent dipole magnets, for example, being formed from neodymium or samarium based rare-earth magnets. Each of the plurality of magnets 26 is engaged with a said one of the plurality of magnet receivers 26R, such that the plurality of magnets 26 and the plurality of rim members 32 form an outer perimeter 34 having a continuous or substantially continuous surface; the 20 outer perimeter 34 is depicted by the double-headed arrow, but extends around the entire circumference of the rotor 14, and the arrow is indicative only. Each of the plurality of rotor blades 28 extends from the outer rim portion 24 towards the centre C of the rotor 14, and may preferably be connected to a central hub 36. It is conceivable that the central hub 36 may be excluded, with each the plurality of rotor 25 blades 28, for instance, tapering to a point. The central hub 36 may, as depicted, be annular, defining a central airflow bore 38 therethrough. This allows air to pass directly through the central hub 36, improving airflow through the nacelle. Each of the plurality of rotor blades 28 is depicted having a twisted aerodynamic profile, 30 which may taper at both ends. Other profiles are possible without deviating from the scope of the invention, including, for example and non-exhaustively, rotor blades which taper to a point, asymmetric cambered rotor blades, non-twisted rotor blades, or rotor blades having any combination of the previously mentioned features. The position of the rotor 14 within the stator 12 is shown in more detail in Figure 4, depicting the rim-driven electric thruster 10 with the stator 12 shown in cross section. An 5 optional receiving channel 40 is provided here which allows for some components of the stator 12 to be manufactured separately and then installed into a main stator body. Figure 5 depicts the rim-driven electric thruster 10 shown in cross section, with two of a plurality of winding supports 42 shown. Each of the winding supports 42 may be provided as an individual component receivably 10 engageable with the receiving channel 40 of the main stator body. There is a gap between each of the winding supports 42 and the outer perimeter 34 of the rotor 14, although the winding supports 42 may directly receive the outer perimeter 34 of the rotor 14 if the central hub 36 is not present. In such a hypothetical arrangement, the stator 12 will act as a bearing for the rotor 14. The electromagnetic drive proposal 15 disclosed herein would still be applicable. The rotor 14 is positioned in the stator 12 such that rotation is possible in a circumferential rotation channel 44, which is here defined by the plurality of winding supports 42. Each of the plurality of magnets 26 is positioned in the rotation channel 44 to permit rim-driven operation of the rotor 14. 20 Figure 6 shows a winding block 45 which is receivable within the receiving channel 40, and which includes a winding support 42 and a portion of an outer perimeter 34 of the rotor 14 in more detail. Each of the plurality of magnets 26 as depicted have an arcuate outer surface thereby creating a complete arcuate outer rotor surface 46A and a receivercontact surface which is complementarily shaped to an outward-facing surface of each 25 of the plurality of magnet receivers 26R. The winding support 42 shown here is substantially saddle shaped and has a complementarily shaped rotor-facing surface 46B to the outer perimeter 34 of the rotor 14, although each of the winding supports 42 may have a different shape, for instance an elliptic paraboloid. Figure 7 shows the winding block 47 in isolation. The winding block 45 includes the 30 winding support 42 and one of a plurality of coreless windings 48. As depicted here, the winding support 42 has a complementarily shaped rotor-facing surface 48 to the outer perimeter 34 of the rotor. The coreless winding 48 depicted here is substantially saddle shaped, which may be accomplished by, for example, each of the coreless windings 48 being wound around a surface of the winding supports 42. Such a shape permits the plurality of magnets 26 to pass through the coreless winding 48 in use, thus capturing flux circumferentially around each magnet 26. 5 The rim-driven electric thruster may be constructed by first assembling a stator 12 and forming a circumferential rotation channel 44 therein. This rotation channel 44 may be directly formed in the stator 12, or alternatively a receiving channel 40 can be formed, with the plurality of winding supports 42 installed therein to define the circumferential rotation channel 44. A plurality of windings 48 can then be arranged around the 10 circumferential rotation channel 44 as either one continuous winding or as multiple individual windings 48 which are then conductively interconnected with wires or otherwise. The circumferential rotation channel 44 may have a substantially circular planar profile, being formed around a circumference of the stator 12. The outer radial edge of the 15 circumferential rotation channel 44 is preferably complementary to the shape of the outer perimeter 34 of the rotor 14 so it matches the rotor-facing surface 46B of each of the plurality of winding supports 42. In part, the rotor-facing surface 46B may have or substantially have a saddle shaped or elliptic paraboloidal form. The rotor 14 of the rim-electric thruster 10 may preferably be constructed in parts, first 20 by assembling an outer rim portion 24 then by forming a plurality of rim members 32 thereon, which can be accomplished by, for example, circumferentially cutting out sections of the outer rim portion 24. The rim members 32 define a plurality of magnet receivers 26R therebetween into which provided magnets 26 can be engaged, forming a continuous or substantially continuous outer perimeter 34. 25 The rotor 14 can then be mounted within the stator 12, either directly rotatably engaged within the rotation channel 44 or rotatably mounted to a rotor support 20 which may be included within the stator 12. For ease of manufacturing, the stator 12 could be assembled around the rotor 14. The rotor 14 is positioned such that the plurality of magnets 26 is positioned within the rotation channel 44, permitting rim driven operation. 30 In use, each of the windings 48 can operate as an electromagnet when a current is applied therethrough. The windings 48 are described as coreless since, unlike typical electromagnets, they are not wound around a core made of a ferromagnetic material such as iron. This eliminates efficiency losses from hysteresis and from eddy currents induced in the core. The current through the windings 48 is applied such that electromagnetic interactions between the plurality of windings 48 and the plurality of magnets 26 drive the rotor 14, 5 causing it to rotate within the stator 12. The rotation of the rotor blades 28 generates thrust through expelling air from the outlet 18 of the nacelle. Different configurations of the rotor 14 are possible based on how the current is applied therethrough. For instance, the rotor can operate as a polyphase system, such as a three-phase system. It is considered that the rotor is driven by a Lorentz force between 10 the plurality of magnets 26 and the plurality of windings 48. LO CXI Each of the plurality of coreless windings 48 may be installed as individual windings 48 and then conductively connected to form a circuit, or alternatively each of the plurality of coreless windings 48 may be formed from one continuous wire, collectively forming a toroidal winding within the stator 12. 15 Figure 8 shows the plurality of magnets 26 and field lines of the corresponding magnetic field. The magnets 26 are arranged in an alternating configuration, with each of the plurality of the magnets 26 having a magnetic moment perpendicular to a radius of the rotor and such that around the outer perimeter, a north pole N of the plurality of magnets is followed by a south pole S of the plurality of magnets. This can be considered to be a 20 quasi-Halbach arrangement. This arrangement provides a suitable magnetic field for enabling rim-driven operation in conjunction with the windings 48, but the plurality of magnets 26 may be alternatively configured, for instance in a complete Halbach configuration, without deviating from the scope of the invention. A second embodiment of a rim-driven electric thruster is shown in Figures 9 to 11, and 25 referenced globally at 110. Identical or similar reference numerals will be used to refer to identical or similar components, and further detailed description is omitted for brevity. The outer rim portion 124 is shown in Figures 9 to 11. Each of the plurality of magnets 126 here are substantially cylindrical, and each of the plurality of magnet receivers 126R defined between the outer rim members 132 is dimensioned to receive one of the said 30 plurality of magnets 126. The plurality of magnets 126 may be engaged with the plurality of magnet receivers 126R using pins 148 inserted through a hole included in each of the magnets 126, with the magnet receivers 126R having corresponding slots to receive said pins 148. Alternatively, the magnets 126 may be engaged with the receivers 126R with axles instead of pins 148, 5 allowing rotation of each of the plurality of magnets 126 around an axis tangential to the rotor radius. Figure 11 shows the outer rim portion 124 and magnets 126 shown in Figures 9 and 10, and additionally includes a circumferential rotation channel 144. As can be seen, this rotation channel 144 is almost entirely captive within a winding block 145 which is 10 engagable with or part of the stator. The outer rim portion 124 is flat and substantially annular, and may for example be cut out from a flat plate. The magnet receivers 126R may for example be cut out from the edge of the outer rim portion 124. A plurality of rotor blades (not shown) may be affixed LO to an interior edge of the outer rim portion and extend towards a centre C2 of the rotor C\J 15 114. Shown in Figure 12 is a vehicle 250 comprising a pair of rim-driven electric thrusters 210. The rim-driven electric thruster may be pivotably or movably mounted to an outer surface 1 of the vehicle 250, for instance a wing of an aircraft, to permit alteration of a direction of 1— thrust provided by the rim-driven electric thruster. An aircraft is shown in the depiction of 20 Figure 12, but it will be apparent that the rim-driven electric thruster 210 could be mounted to many suitable vehicles, such as a boat or a submarine. Any number of rim-driven electric thrusters 210 could be provided, depending on the requirements of the vehicle. A second embodiment of a vehicle 350 comprising a plurality of rim-driven electric 25 thrusters 310 is shown in Figure 13. Each of the rim-driven electric thrusters is here integrated within the vehicle, with the structure of the vehicle itself defining the nacelle having an inlet and outlet. Each of the rim-driven electric thrusters 310 shown is integrated within the vehicle. This may be accomplished, for instance, by constructing the vehicle 310 so that at least one 30 nacelle is formed within a structure of the vehicle 310, and then mounting a rotor 314 within each nacelle. In this case, the structure of the vehicle itself can be considered to be a stator. 11 07 25 Pivoting could be achieved by use of a pivotable or otherwise movable or actuatable mount assembly attached to the outer surface of the vehicle 250, for example the wing of an aircraft. The rim-driven electric thruster conceivably may be pivoted or moved automatically based on data received from a gyroscope and / or an accelerometer. 5 The present invention therefore allows for the efficient generation of thrust by a rim-driven electric thruster, which may be used to propel a vehicle more efficiently and quietly than existing thrusters. The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated 10 features, integers, steps, or components, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, 15 described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

1. A rim-driven electric thruster for vehicle propulsion, the rim-driven electric thruster comprising:a stator defining a nacelle with an inlet and an outlet, a circumferential5 rotation channel being formed in the stator, and the stator including a plurality ofcoreless windings arranged around the circumferential rotation channel, the stator comprising a plurality of winding supports around which the plurality of windings is wound;a rotor comprising;10 an outer rim portion positioned radially outwards of a centre of therotor, the outer rim portion having a plurality of circumferentially spaced rim members defining a plurality of magnet receivers therebetween;a plurality of magnets, each of the plurality of magnets being engaged with a said one of the plurality of magnet receivers such that the plurality 15 of magnets and the plurality of rim members form an outer perimeter having acontinuous or substantially continuous surface; anda plurality of rotor blades extending from the outer rim portion towards the centre of the rotor;the rotor being positioned in the stator such that the plurality of magnets20 is received in the rotation channel in-use to permit rim-driven operation of therotor; andfurther comprising at least one stator blade attached to an inner surface of the nacelle,wherein the rotor further comprises a central hub positioned at the centre25 of the rotor connected with each of the plurality of rotor blades, and wherein thecentral hub is, or is substantially, annular,wherein each of the plurality of winding supports has a complementarily shaped rotor-facing surface to the outer perimeter of the rotor.

2. The rim-driven electric thruster as claimed in claim 1 3, wherein the stator 30 comprises a rotor support with which the central hub of the rotor is rotatablyengageable.

3. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein each of the plurality of magnets has a cylindrical or substantially cylindrical shape.

4. The rim-driven electric thruster as claimed in claim 1 or claim 2, wherein each of5 the plurality of magnets has an arcuate outer surface and a receiver-contactsurface which is complementarily shaped to an outward-facing surface of each of the plurality of magnet receivers.

5. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein the at least one stator blade is rotatable about a radial axis of the stator.10 6. The rim-driven electric thruster as claimed in any one of the preceding claims,wherein each of the plurality of winding supports is, or is substantially, an elliptic paraboloid shape or a saddle shape.

7. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein each of the plurality of winding supports is provided as an individual 15 component receivably engageable with a main stator body of the stator.

8. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein each of the plurality of windings has, or has substantially, an elliptic paraboloid shape or saddle shape.

9. The rim-driven electric thruster as claimed in any one of the preceding claims, 20 wherein the plurality of windings collectively forms a toroidal winding in the stator.

10. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein at least one of the plurality of rotor blades includes a serrated edge portion.

11. The rim-driven electric thruster as claimed in any one of the preceding claims, 25 wherein at least one of the plurality of rotor blades has a twisted aerodynamicprofile.

12. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein the plurality of magnets is arranged such that a polarity of adjacent magnets alternates in a circumferential direction of the outer rim portion.30 13. The rim-driven electric thruster as claimed in any one of the preceding claims,wherein each of the plurality of windings is a polyphase winding.07 2514. The rim-driven electric thruster as claimed in any one of the preceding claims, wherein a plurality of said rotors is provided, the stator having a complementary number of circumferential rotation channels therein.

15. A vehicle comprising a rim-driven electric thruster as claimed in any one of the 5 preceding claims.

16. The vehicle as claimed in claim 15, in the form of an aircraft.

17. The vehicle as claimed in claim 15 or 16, wherein the rim-driven electric thruster is integrated within the vehicle.

18. The vehicle as claimed in claim 15 or claim 16, wherein the rim-driven electric 10 thruster is pivotably or movably mounted to an outer surface of the vehicle topermit alteration of a direction of thrust provided by the rim-driven electric thruster.

19. A method of providing an efficient aircraft drive system, the method comprising the steps of:a] providing a vehicle as claimed in any one of claims 16 to 18; and15 b] providing a drive current to the plurality of windings to provide a rimlessdrive for the rim-driven electric thruster.

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