Rotor drive system

Abstract

A rotor drive for a tail rotor of a helicopter is provided. The system includes a stator and a rotor mounted to the stator with a rotatable central carrier. Rotor blades are radially attached to the rotatable central carrier and each of the rotor blades is pivotable about their respective radial central axis for variation of blade pitch. At least one permanent magnet is provided on each rotor blade. A plurality of electromagnets is provided on the stator close enough to allow inductive interaction between the plurality of electromagnets and the at least one permanent magnet on each rotor blade. The permanent magnets are offset from the radial central axis in a direction perpendicular to the rotation plane for individual pitch control of the rotor blades by individual control of electric supply to the electromagnets.

Claims

1. A rotor drive system of a tail rotor of a helicopter, the rotor drive system comprising: a stator and a rotor, the rotor being mounted to the stator with a rotatable central carrier and rotor blades radially attached to the rotatable central carrier, the rotor blades defining one rotation plane with a radial central axis of each of the rotor blades and each of the rotor blades being pivotable about their respective radial central axis for variation of blade pitch, drive means for the rotor, and pitch control means for the pivotable rotor blades wherein along at least one blade radius at least one permanent magnet is fixed on each rotor blade and a plurality of electromagnets on the stator is provided coaxially on at least one stator radius to allow inductive interaction between the plurality of electromagnets and the at least one permanent magnet on each rotor blade, the at least one permanent magnet offset from the radial central axis of each rotor blade in a direction perpendicular to the rotation plane for individual pitch control of each of the rotor blades by individual control of electric supply to each of the electromagnets.

2. The rotor drive system according to claim 1, wherein the stator is a ducted fan, the rotor is mounted radially inside the ducted fan, each of the rotor blades is provided with two electrically separated permanent magnets at a tip of each rotor blade, each of the two electrically separated permanent magnets is fixed offset from the radial central axis in the direction perpendicular to the rotation plane on opposed sides to the rotation plane and the electromagnets are provided along two coaxial, electrically separate rings on an inner circumference of the ducted fan next to the tips, each of the separate rings positioned relative to the permanent magnets on one of the opposed sides to allow electrically separate induction of the permanent magnets on both of the opposed sides of each rotor blade.

3. The rotor drive system according to claim 2, wherein the ducted fan is an anti-torque system for a ducted tail rotor of a helicopter, in a shroud and the drive means for the rotor are the electromagnets of the two coaxial, electrically separate rings on the inner circumference of the ducted fan operated as individually controlled motors.

4. The rotor drive system according to claim 2, wherein the rotatable central carrier is a driven hub and the electromagnets provided along the two separate rings on the inner circumference of the ducted fan are operated as electrically separated generators for supply of power to electric consumers.

5. The rotor drive system according to claim 3, wherein the electromagnets are respectively supplied with three phase alternating current.

6. The rotor drive system according to claim 1, wherein each rotor blade is provided with a magnet blade connector having bilateral ends spaced apart in a direction of rotation with one permanent magnet at each of its bilateral ends, each of the permanent magnets being coincident with the one of the plurality of electromagnets to define at least two separate motors.

7. The rotor drive system according to claim 1, wherein a shifting system is provided for shifting the electromagnets in a Y.sub.HC-direction.

8. The rotor drive system according to claim 1, wherein the permanent magnets are mounted at the end of a lever rotatable in an axis parallel to a pitch axis wherein the lever is hinged at the permanent magnets.

9. The rotor drive system according to claim 1, wherein the two permanent magnets define individual tips of the rotor blades.

10. A rotor drive system of a tail rotor of a helicopter, the system comprising: a shroud defining a circular duct; a central carrier mounted in the circular duct; a plurality of rotor blades extending radially from the central carrier and rotatable within the circular duct, a rotation plane defined by a radial central axis of each of the rotor blades, each of the rotor blades being pivotable about a respective radial central axis to vary a blade pitch, at least one permanent magnet fixed to each of the plurality of rotor blades, and offset from the radial central axis of each blade in a direction perpendicular to the rotation plane; and a plurality of electromagnets provided on at least one of the shroud and the central carrier and positioned relative to the at least one permanent magnet to allow inductive interaction between the plurality of electromagnets and the at least one permanent magnet on each rotor blade, wherein electric supply to each of the plurality of electromagnets is controlled individually to vary the blade pitch of each of the plurality of rotor blades individually.

11. The rotor drive system according to claim 10, wherein the plurality of electromagnets is defined on an inner circumference of the circular duct and the at least one permanent magnet is positioned at a distal tip of each of the rotor blades.

12. The rotor drive system according to claim 10, wherein the plurality of electromagnets is defined on an outer circumference of the central carrier.

13. The rotor drive system according to claim 10, further comprising: two electrically permanent magnets fixed to each of the plurality of rotor blades, each of the two permanent magnets offset from the radial central axis in the direction perpendicular to the rotation plane on opposed sides to the rotation plane, two coaxial rings defined by the plurality of electromagnets provided on an inner circumference of the circular duct, each of the two coaxial rings on one of the opposed sides of each rotor blade to allow electrically separate induction of each of the two permanent magnets on both of the opposed sides of each rotor blade.

14. The rotor drive system according to claim 10, wherein the plurality of electromagnets is respectively supplied with three phase alternating current.

15. The rotor drive system according to claim 10, wherein each of the plurality of rotor blades is provided with a magnet blade connector having bilateral ends spaced apart in a direction of rotation with one permanent magnet at each of its bilateral ends, each of the permanent magnets being coincident with the one of the plurality of electromagnets to define at least two separate motors.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Preferred embodiments of the invention are presented by means of the following description with reference to the attached drawings, from which

(2) In FIG. 1 a lateral view of a tail rotor of a rotor drive system according to the invention is shown,

(3) In FIG. 2 a cross-section A-A of FIG. 1 is shown,

(4) In FIG. 3 a cross-section A-A is shown of a further rotor drive system according to the invention,

(5) In FIG. 4 a rotor blade with a positive pitch angle α in a projection of a part of the rotor drive system according to the invention is shown,

(6) In FIG. 5 a rotor blade with a pitch angle α=0° in a projection of said part of the rotor drive system according to the invention is shown,

(7) In FIG. 6 a rotor blade with a negative pitch angle α in a projection of said part of the rotor drive system according to the invention is shown,

(8) In FIG. 7-FIG. 12 different blade pitches a over one rotor revolution are shown with their respectively resulting forces and moments,

(9) In FIG. 13 a rotor blade in a further modified rotor drive system according to the invention is shown.

DETAILED DESCRIPTION OF THE INVENTION

(10) Two coordinate systems are used throughout the description:

(11) A first coordinate system with the coordinates x.sub.HC, y.sub.HC and z.sub.HC is cartesian with a helicopter's frame as reference. The x.sub.HC-axis is pointing towards the front of the helicopter in forward flight direction. The y.sub.HC-axis is pointing to the right of the helicopter clockwise in forward flight direction. The z.sub.HC-axis completes the right hand system by pointing down towards a bottom of the helicopter. The second coordinate system is a rotor fixed polar coordinate system inherent to any individual rotor blade of the rotor drive system. Relative to the helicopter's frame of reference the second system rotates with the rotational speed of the rotor about an axis of rotation y.sub.F which is parallel to y.sub.HC. Each rotor blade possesses its own second coordinate system. It is defined by the radial axis r of the rotor blade pointing from the rotor hub centre to the tip center of the rotor blade and the circumferential coordinate c.sub.F, within the rotational plane of the rotor. A revolution angle ψ describes an angular position of the rotor blade of the rotor drive system with regard to the helicopter's frame of reference. The rotation of the rotor blade around the radial axis r by the pitch angle α (i.e. FIG. 6) completes the second coordinate system.

(12) According to FIG. 1 a rotor drive system 1 in a ducted fan as an anti-torque system, e.g. an electrical Fenestron, is mounted into a shroud 2 connected to a tail boom 3 of a helicopter (not shown). The shroud 2 is constructed as a circular open stator. Inside the shroud 2 is a rotor with a rotatable central carrier 4 and a plurality of rotor blades 5, i.e. twelve rotor blades 5, distributed around the central carrier 4 in essentially one plane perpendicular to the axis of rotation y.sub.F of the rotatable central carrier 4 and rotatable with the central carrier 4 around said axis of rotation y.sub.F. The rotor is mounted by means of the central carrier 4 into said ducted fan with said stator.

(13) Each of said rotor blades 5 is mounted by means of a rotational ball borne support for pitch with torsional spring or a flex-beam 6 with an inner end to the central carrier 4. The rotor blades 5 extend radial from said central carrier 4 with tips 7 towards the circular open stator at an inner circumference 8 of the ducted fan in the shroud 2. Said tips 7 are respectively per rotor blade 5 provided with two permanent magnets 13, 14 separate in direction of the axis of rotation y.sub.F.

(14) A plurality of electro magnets 9 of the circular open stator are provided coaxially with the central carrier 4. Said electro magnets 9 are each integrated along the inner circumference 8 of the shroud 2 encompassing the separate permanent magnets 13, 14 at the tips 7 of the rotor blades 5 without obstructing free rotation of the rotor blades 5.

(15) The electro magnets 9 with the separate permanent magnets 13, 14 provide as many linear motors as permanent magnets are provided.

(16) According to FIG. 2 corresponding features are referred to with the same references as in FIG. 1. The shroud 2 of the rotor drive system 1 with a ducted fan comprises the in direction of the axis of rotation y.sub.F circular open stator. Inside the circular open stator is the rotor with the rotatable central carrier 4 and the rotor blades 5 distributed around the central carrier 4 in the essentially one plane perpendicular to the axis of rotation y.sub.F. The rotatable central carrier 4 is mounted with unilateral radial struts 16 into said ducted fan with said stator.

(17) Each of said rotor blades 5 is mounted by means of a rotational ball borne support for pitch with torsional spring or a flex-beam 6 with the inner end to the central carrier 4. The rotor blades 5 extend radial from said central carrier 4 with tips 7 towards the inner circumference 8 of the ducted fan in the shroud 2. Said tips 7 are respectively per rotor blade 5 provided with two permanent magnets 13, 14 separate in direction of the axis of rotation y.sub.F.

(18) The electro magnets 9 of the circular open stator are aligned along the inner circumference 8 of the ducted fan in the shroud 2 in two essentially parallel rows 10, 11.

(19) According to FIG. 3 corresponding features are referred to with the same references as in FIG. 1, 2. The shroud 2 of the rotor drive system 1 with a ducted fan comprises the in direction of the axis of rotation y.sub.F circular open stator. Inside the circular open stator is the rotor with the rotatable central carrier 4 and the rotor blades 5 distributed around the central carrier 4 in the essentially one plane perpendicular to the axis of rotation y.sub.F. The rotatable central carrier 4 is mounted with bilateral radial struts 17 into said ducted fan with said stator.

(20) Each of said rotor blades 5 is mounted by means of the rotational ball borne support for pitch with torsional spring or the flex-beam 6 with the inner end to the central carrier 4. The rotor blades 5 extend radial from said central carrier 4 with tips 7 towards the inner circumference 8 of the ducted fan in the shroud 2. Respectively two permanent magnets 13, 14 per rotor blade 5 are provided at the inner end of each of said rotor blades 5 with separation of said two permanent magnets 13, 14 in direction of the axis of rotation y.sub.F.

(21) The electro magnets 9 of the circular open stator are aligned along an outer circumference 8 of the central carrier 4 in two essentially parallel rows 10, 11.

(22) According to FIGS. 4-6 corresponding features are referred to with the same references as in FIGS. 1-3. The plurality of electro magnets 9 are aligned to the respective rows 10, 11 along the inner circumference 8 of the ducted fan in the shroud 2, each with a distance d.sub.M to a middle rotation plane 12 through the radial central axis r of pivoting of each rotor blade 5. The respective rows 10, 11 extend along the inner circumference 8 of the ducted fan in the shroud 2. Each of the electromagnets 9 is individually connected to a phase of electrical supply from coupled individual control units (not shown).

(23) The individual control units supply at least three electromagnets 9 in the vicinity of the permanent magnets 13, 14 with at least three phase power in such a way, that a moving electromagnetic field is created which drives the permanent magnet 13, 14 like in a linear motor. Since the rotor blades 5 are individually controllable, each electromagnet 9 in the vicinity of each rotor blade 5 needs to have an own controller which creates the required magnetic field by controlling the current rating dependent on the rotor position, the actual blade pitch and the commanded forces F.sub.1 and F.sub.2.

(24) The electro magnets 9 of the respective rows 10, 11 are electrically separate, while allowing mutually at least energy transfer under the control of a common top level controller with three controller levels, namely

(25) 1. A top level controller for the whole electrical fan system. The output of the top level controller is input for level 2 blade controllers.

(26) 2. A blade controller for control of the interaction of the two linear motors of an individual rotor blade 5 dependent on the inputs of the top level controller. The blade controller commands the magnet controllers of the individual rotor blades 5.

(27) 3. The magnet controller manages the time dependent force generated by one linear motor by controlling the associated electromagnets 9 in the vicinity of the two permanent magnets 13, 14.

(28) For each permanent magnet an individual magnet controller is provided for control of the electromagnets 9 in the vicinity of said permanent magnet 13, 14 at a given time to generate a command force F.sub.1, F.sub.2 to be applied for this permanent magnet 13, 14. The magnet controller is provided with a detector for the pitch of the rotor blade 5 to which the magnet controller is connected to and detector for measurement of the azimuthal position angle ANG.DET (FIG. 1) of the rotor in order to provide control of the magnets depending on the position of the rotor blade 5 relative to the electromagnets 9. Thus each “permanent magnet”—“magnet controller”—“associated electromagnets”—combination can be considered as an individual linear motor.

(29) The two individual linear motors of the two rows 10, 11 on both sides of one rotor blade 5 are then controlled by a higher level controller with as input the pitch and blade force command in combination with the current pitch α. The azimuthal position, indicated by the revolution angle ω, is provided by means of an azimuth angle measurement system of the rotor blade 5. The input commands for the blade controllers are again generated by the top level controller which gets as command the required rotor thrust and moments, and the frequency and phase requirements from potential noise and vibration control controllers.

(30) A blade pitch axis with tip 7 of each rotor blade 5 is half way in between said two rows 10, 11 of electro magnets 9. Two permanent magnets 13, 14 are separately attached at the tips 7 of the rotor blades 5 by a magnet-blade connector plate 15. The two permanent magnets 13, 14 are offset from the radial central axis of rotation of each rotor blade 5 in direction of the rotation axis y.sub.F of the rotor to coincide with the respective rows 10, 11 of electro magnets 9 for the provision of electro magnet motors/generators depending from the electrical supply of the three phase alternating current.

(31) Two separate motors of respective permanent magnets 13, 14 and associated electro magnets 9 generate the forces F.sub.1 and F.sub.2 on each rotor blade 5 of the rotor in circumferential direction c.sub.F with the distance d.sub.m parallel to the rotation plane 12 of the rotor blades 5.

(32) When, in addition to a drive force, the forces F.sub.1 and F.sub.2 generated by the two separate motors differ, a Motor Moment M.sub.B=(F.sub.1 - F.sub.2)*d.sub.m results about the blade pitch axis of the respective rotor blade 5. Said moment changes the pitch angle α of the rotor blade 5 determined by the torsional stiffness of the flexbeam 6 (see FIG. 4 or 6). When the forces F.sub.1 and F.sub.2 are equal, the torsional stiffness of the flexbeam 6 holds the rotor blade 5 in its neutral position (see FIG. 5). The pitch angle α of the rotor blade 5 leads to an aerodynamically resulting force F.sub.B (see FIG. 4 or 6) perpendicular to the rotor plane and a Drag force F.sub.D in circumferential direction c.sub.F. The sum of forces F.sub.B of all N rotor blades 5 results in the total rotor force F.sub.y in y.sub.F direction with

(33) $F_y=\underset{N}{.Math.}{F}_B.$
If any aerodynamic pitch moments are taken into account said aerodynamic pitch moments must be added to the Motor Moment M.sub.B with consequent changes of the resulting blade pitch angle α.

(34) A blade pitch sensor (not shown) is provided for each rotor blade 5 for active control of the blade pitch angle α by the control units. Said active blade pitch control system corrects any pitch angle offset by an active and preferably individual control of F.sub.1 and F.sub.2 of each rotor blade 5. An individual blade pitch control comprises the rotor azimuth angle measurement system, which determines the exact blade positions. According to the detected exact positions of the rotor blade 5 the control units supply individually the three phase alternating current to the electromagnets of the concerned rotor blade 5.

(35) According to FIG. 7 corresponding features are referred to with the same references as in FIGS. 1-6. Along one entire rotation of the rotor each rotor blade moves from the revolution angle ψ=0° to the revolution angle ψ=360° corresponding to 2π. The revolution angle ψ=0° and the revolution angle ψ=360° are aligned on the x.sub.HC-axis pointing towards the front of the helicopter in forward flight direction. The revolution angle ψ=90° and the revolution angle ψ=270° are aligned on the z.sub.HC-axis. Respective pitch angles α of one rotor blade 5 along one entire rotation of the rotor from the revolution angle ψ=0° to the revolution angle ψ=2 π are indicated with the respective revolution angle ψ. The pitch angles α of one rotor blade 5 vary from 0° at the revolution angle ψ=0° to a maximum at the revolution angle ψ=π/2, back to 0° at a revolution angle ψ=π, again to a maximum at the revolution angle ψ=3/2 π opposed to the maximum at the revolution angle ψ=π/2 and is back to 0° at the revolution angle ψ=2 π, and so on for the next revolutions of the rotor.

(36) A force F.sub.B to each rotor blade 5 is related to each pitch angle of each rotor blade 5 between the revolution angle ψ=0° to the revolution angle ψ=2 π. The sum of forces F.sub.B of all rotor blades 5 of the rotor between the revolution angle ψ=0° to the revolution angle ψ=2 π results in the total rotor force in y direction

(37) $F_y=\underset{N}{.Math.}{F}_B.$
The moment M.sub.xF is calculated by summing up the cross products of the forces F.sub.B in Cartesian vector notation and their individual radii of application r.sub.z to the rotor center in vector notation for all blades.

(38) According to FIG. 8 corresponding features are referred to with the same references as in FIGS. 1-7. The pitch angles α of one rotor blade 5 vary from a maximum at the revolution angle ψ=0° to 0° at the revolution angle ψ=π/2, back to a maximum at the revolution angle ψ=π opposed to the maximum at the revolution angle ψ=0°, again to 0° at the revolution angle ψ=3/2 π and is back to the maximum of the revolution angle ψ=0° at the revolution angle ψ=2 π, and so on for the next revolutions of the rotor.

(39) A force F.sub.B to each rotor blade 5 is related to each pitch angle of each rotor blade 5 between the revolution angle ψ=0° to the revolution angle ψ=2 π. The sum of forces F.sub.B of all rotor blades 5 of the rotor between the revolution angle ψ=0° to the revolution angle ψ=2 π results in the total rotor force in y direction

(40) $F_y=\underset{N}{.Math.}{F}_B.$
The moment M.sub.zF is calculated by summing up the cross products of the forces F.sub.B in Cartesian vector notation and their individual radii of application r.sub.x to the rotor center in vector notation for all blades.

(41) According to FIG. 9 corresponding features are referred to with the same references as in FIGS. 1-8. The pitch angle α of one rotor blade 5 is constantly at a maximum over the whole revolution of the rotor. Each pitch angle α of each respectively next rotor blade 5 in circumferential direction is constantly at a maximum opposed to the pitch angle α of the one rotor blade 5 over the whole revolution of the rotor. Thus all of the rotor blades 5 are fixed in alternately opposed maxima relative to each other over the whole revolution of the rotor.

(42) A force F.sub.B to each rotor blade 5 related to each pitch angle of each rotor blade 5 is compensated by the force F.sub.B related to the pitch angle of the next rotor blade 5 in circumferential direction between the revolution angle ψ=0° to the revolution angle ψ=2 π, while a drag force F.sub.D from each rotor blade 5 results. The moment M.sub.yF is calculated by summing up the cross products of the drag forces F.sub.D in Cartesian vector notation and their individual radii of application r to the rotor center in vector notation for all blades.

(43) According to FIG. 10 corresponding features are referred to with the same references as in FIGS. 1-9. Pitch angles α of one rotor blade 5 vary continuously from 0° at the revolution angle ψ=0° to a maximum at the revolution angle ψ=π/2 and back to 0° at a revolution angle ψ=π. Each pitch angle α of each next rotor blade 5 in circumferential direction between 0° and π varies a given revolution angle ψ of the neighbouring rotor blade 5 to the respectively opposite direction. Thus the rotor blades 5 between 0° and π in circumferential direction of the rotor move continuously to pitch angles α alternately opposed relative to each other while the rotor blades 5 between π and 2 π stay respectively in neutral position. The variation of the pitch angles α of the one rotor blade 5 is shown with one curve of the diagram of FIG. 10 while the variation of the pitch angles α of each next rotor blade 5 in circumferential direction is shown with the opposed curve of said diagram.

(44) A force F.sub.B to each rotor blade 5 related to each pitch angle α of each rotor blade 5 is compensated by the force F.sub.B related to the pitch angle α of the next rotor blade 5 in circumferential direction between the revolution angle ψ=0 to the revolution angle ψ=2 π, while a drag force F.sub.D from each rotor blade 5 results. The drag forces F.sub.D are just generated between the revolution angle ψ=0 and angle ψ=π. Consequently the part of any circumferential drag force F.sub.D which acts in x.sub.HC direction between angle ψ=0 and angle ψ=π is not compensated by an equivalent force between angle ψ=π and angle ψ=2 π, which leads in total to a force F.sub.x in x.sub.HC direction.

(45) According to FIG. 11 corresponding features are referred to with the same references as in FIGS. 1-10. Pitch angles α of one rotor blade 5 vary from 0° from the revolution angle ψ=π/2 to a maximum at the revolution angle ψ=π and back to 0° at a revolution angle ψ=3/2 π. Each pitch angle α of each next rotor blade 5 in circumferential direction varies a given revolution angle ψ to the respectively opposite direction. Thus the rotor blades 5 between ½ π and 3/2 π in circumferential direction of the rotor move continuously to pitch angles α alternately opposed relative to each other while the rotor blades 5 between 0° to ½ π and ¾ π to 2 π stay respectively in neutral position. The variation of the pitch angles α of the one rotor blade 5 is shown with one curve of the diagram of FIG. 11 while the variation of the pitch angles α of each next rotor blade 5 in circumferential direction is shown with the opposed curve of said diagram.

(46) A force F.sub.B to each rotor blade 5 related to each pitch angle of each rotor blade 5 is compensated by the force F.sub.B related to the pitch angle of the next rotor blade 5 in circumferential direction between the revolution angle ψ=0 to the revolution angle ψ=2 π, while a drag force F.sub.D from each rotor blade 5 results. The drag forces F.sub.D are just generated between the revolution angle ψ=π/2 and angle ψ=3/2 π. Consequently the part of any circumferential drag force F.sub.D which acts in z.sub.HC direction between angle ψ=π/2 and angle ψ=3/2 π is not compensated by an equivalent force between angle ψ=3/2 π and angle ψ=π/2, which leads in total to a force F.sub.z in z.sub.HC direction.

(47) According to FIG. 12 corresponding features are referred to with the same references as in FIGS. 1-11. The pitch angles α of one rotor blade 5 vary between a maximum at the revolution angle ψ=π/2 and a maximum at the revolution angle ψ=3/2 π opposed to and half of the maximum at the revolution angle ψ=π/2 and so on for the next revolutions of the rotor.

(48) Alternatively forces in x.sub.HC and z.sub.HC direction can be generated by the superposition of a moment generation perpendicular to the rotors rotational axis y.sub.F with an anti-torque-thrust F.sub.y. One half of the rotor creates a high thrust in one direction, while the other half creates a low thrust in the other direction. The low thrust flow is used to redirect the high thrust flow, resulting in total in a force F.sub.z in z.sub.HC-direction. Also a force F.sub.x and again a moment M.sub.yF is generated supplemental to a desired force F.sub.z

(49) With the respective halves of high thrust and low thrust shifted each with π/2 relative to the pitch angles α shown—a force F.sub.x in x.sub.HC-direction results correspondingly. Supplemental to the desired force F.sub.x, a force F.sub.z and a moment M.sub.yF is generated.

(50) Thus the moments M.sub.xF, M.sub.yF and M.sub.zF are calculated by summing up the cross products of the forces F.sub.B and F.sub.D in Cartesian vector notation and their individual radii of application r.sub.F (see FIG. 9) to the rotor center in vector notation for all blades. FIG. 12 depicts the generation of a desired force F.sub.z.

(51) ${\stackrel{.fwdarw.}{M}}_{\mathrm{xyzF}}=\underset{N}{.Math.}\left({\stackrel{.fwdarw.}{F}}_B\times {\stackrel{.fwdarw.}{r}}_F\right),\mathrm{with}{\stackrel{.fwdarw.}{M}}_{\mathrm{xyzF}}=\left(\begin{array}{c}{M}_{\mathrm{xF}}\\ M_{\mathrm{yF}}\\ M_{\mathrm{zF}}\end{array}\right),{\stackrel{.fwdarw.}{F}}_B=\left(\begin{array}{c}{F}_{\mathrm{Dx}}\\ F_B\\ F_{\mathrm{Dz}}\end{array}\right)\mathrm{and}{\stackrel{.fwdarw.}{r}}_F=\left(\begin{array}{c}{r}_{\mathrm{Fx}}\\ 0\\ r_{\mathrm{Fz}}\end{array}\right).$

(52) According to FIG. 13 corresponding features are referred to with the same references as in FIGS. 1-12. With pitch variation, the distance of the permanent magnets 13, 14 on the rotor relative to the rotor plane 12 and relative to the electromagnets 9 in the shroud 2 changes, which can lead to a non-optimal location for inductive interaction. A shifting system shifting the electromagnets in y.sub.HC-direction is provided. Alternatively a width y.sub.M and/or a length x.sub.M of the permanent magnets 13, 14 is increased, so that the permanent magnets 13, 14 cover the electromagnets 9 at all pitch angles α. Or, further alternatively, the permanent magnets 13, 14 are mounted on an end of a lever 18 rotatable relative to an axis parallel to the pitch axis with its hinge at the position of the permanent magnets 13, 14, while a system is provided preventing the permanent magnets 13, 14 to leave the rotational plane 12 of the electromagnets 9.

(53) The rotor drive system 1 can be used to control blade pitch in any thrust generating rotational system or systems which draw power from the movement of the surrounding air like wind turbines.

REFERENCE LIST

(54) 1 rotor drive system 2 shroud 3 tail boom 4 rotatable central carrier 5 rotor blades 6 flex-beam 7 tips 8 inner circumference 9 electro magnets 10 row 11 row 12 rotation plane 13 permanent magnet 14 permanent magnet 15 magnet-blade connector plate 16 unilateral radial strut 17 bilateral radial strut 18 lever