GB2388095A

GB2388095A - Rotor blade control apparatus

Info

Publication number: GB2388095A
Application number: GB0210078A
Authority: GB
Inventors: Andrew Daggar
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-05-02
Filing date: 2002-05-02
Publication date: 2003-11-05
Also published as: GB0210078D0

Abstract

A rotor blade control apparatus e.g. for a model helicopter, whereby coils (10a, 10b) are mounted on a rotor assembly, turn with the rotor and are mechanically connected to control pitch of the rotor blade, and permanent magnets (11a, 11b) are mounted in a fixed position relative to the position of the rotor shaft; the pitch of the rotor blades (1) is controlled by magnetic attractive or repulsive forces between coils (10a, 10b) and respective permanent magnets (11a, 11b).The pitch of the blades may be varied cyclically or collectively. The invention avoids the need for a swash plate assembly on a helicopter.

Description

- 1 2388095

ROTOR BLADE CONTROL APPARATUS

The present invention relates to apparatus to control rotor blades particularly, but 5 not exclusively, to control helicopter rotor blades, especially, but again not exclusively, to control toy model helicopters rotor blades.

With reference to Figure I, there is shown a schematic perspective view of a conventional helicopter rotor assembly, found on both model and fullsize helicopters. The lo main rotor of a helicopter provides three Degrees Of Freedom (DOE) of control for a helicopter during flight. One is the ascent/descent of the aircraft achieved by increasing/decreasing the net lid produced by changing the speed of the rotor blades and/or by altering the pitch of the rotor blades 1, by rotating them about there pitch axis defined by blade pivot hinge 2. The other two DOF's are achieved by tilting the rotor 15 forwards/backwards and left/right. The rotor is tilted in any desired direction by changing the pitch of the blades 1 in a cyclic manner. That is, if the machine is to be directed forwards, the pitch of the blades whilst at the back of the rotor are increased and whilst at the front of the rotor are reduced. The additional lid at the rear and relative reduction in lift at the front cause the helicopter to lean forwards. The cyclic pitch changes of the rotor to blades I is achieved using a swash plate assembly 5,6.

The swash plate assembly consists of two main parts 5,6 through which the rotor mast 9 passes. One element is a disc 6, linked to the cyclic pitch control 7, 8. This disc 6 is capable of tilting in any direction but does not rotate with the rotor 9. This non-rotating disc 25 6, open referred to as the "Stationary Star", is attached by a bearing surface to a second disc 5, often referred to as the "Rotating Star". The rotating star 5 tunes with the rotor and is linked to the rotor blades I by respective control tubes 4 and pitch horns 3.

The cyclic control angles the Stationary Star 6 of the swash plate assembly in the lo desired direction. The angle of the swash plate assembly, with respect to the main shaft 9, imposes a cyclic up/down motion on the control tubes 4 as they rotate with the rotor shaft 9.

This oscillation of the control tubes is translated to cyclic pitch changes of the rotor blades 1 by the pitch horns 3.

- 2 ( In addition to providing cyclic pitch control the swash plate may also be uniformly raised or lowered to control collective pitch, that is to say to increase or decrease the lid of all rotors by an equal amount to control lift, in addition to any cyclic component.

There are several problems associated with the current swash plate assemblies. They are mechanically complex adding both drag and weight. Any failure will result in a total loss with no capability to add a secondary safety system. In large or small aircraft, where a human pilot is not capable of direct control, mechanical servos are required to move the lo push rods, which again if they fail may result in a total loss.

It is an object of the present invention to provide a rotor control system that overcomes the above-mentioned problems.

15 According to the present invention there is provided rotor blade control apparatus comprising: a rotor assembly including a rotor shaPr and at least one rotor blade connected to the shaft in a manner such that the pitch of the blade relative to the shaft may be varied; a magnetic actuator comprising a first portion and a second portion arranged to be repelled and/or attracted to each other in dependence on a magnet field between them; and control

to means for controlling the magnetic field between the two portions, wherein the first portion

of the actuator is mounted on the rotor assembly, turns with the rotor assembly and is mechanically connected to control the pitch of the rotor blade, wherein the second portion of the actuator is mounted in a fixed position relative to the position of the rotor shaft, the first and second portions being arranged such that any magnetic field between them causes

25 the first portion to be displaced restive to the second portion and causes the pitch of the blade to alter.

"A fixed position relative to the rotor shaft" is defined for the purposes of this specification as a position fixed relative to the rotor shaft, not necessarily rotating with the

30 rotor shaft, such that a force exerted between the two portions of the actuator will cause the upper portion to be displaced whilst the lower portion is retained in place relative to the rotor shall. The definition does not preclude arrangements where the "fixed position" may

- 3 ( be changed by some secondary mechanism, provided that a reaction force can still be applied to the actuator.

The present invention, employing a magnetic actuator unit capable of attracting or 5 repelling, enables the rotor blades to be controlled without the need for a swash plate arrangement associated with a conventional helicopter. This enables an arrangement having no mechanical linkages between rotary and stationary parts, which is simpler in design, -

lighter and which has less drag.

loPreferably, the rotor assembly comprises two rotor blades mounted to the rotor shaft, each blade being free to pivot relative to the rotor shaft about a pitch axis associated with the blade, wherein the first portion of the actuator is mounted to a rotor blade and located at a point horizontally spaced from the pitch axis of the rotor blade such that any displacement of said first portion caused by the interaction with the second portion of the Is actuator alters the pitch ofthe blade.

In an alternative arrangement, each rotor blade may have a first portion of an actuator connected to it by mechanical linkage. This may be convenient if it is desired to locate the first portion at some particular desired location for either aerodynamic or balance 20 considerations.

In a another alternative arrangement the apparatus may further comprise a fly-bar for controlling the pitch of the rotors, wherein the first portion of the actuator is mechanically connected to control the pitch of the rotor blade by being mechanically linked as to the fly bar, to control the position of the fly-bar which in turn controls the pitch of the rotor blades. This achieves the same benefit by replacing the mechanical linkage to the fly-

bar in those rotor assemblies where previously the swash plate was mechanically linked to a fly bar instead of directly to the rotors. The fly-bar simply being a small rotor blade having a pivot axis at 90 degrees to that of the main rotors and linked to the main rotors such that so lift exerted by the fly-bar tilts the main rotors about their pitch axis so as to cyclically control the pitch of the main rotor blades.

- 4 The apparatus may comprise two rotor blades and two actuators mounted either side of the axis of the rotor blades wherein the means for controlling the current apply the current cyclically causing the actuator to be in anti-phase, this providing a balanced design whereby the total force applied via the actuators is maintained constant.

The two rotors may be fixed together so that they can only pivot together relative to the shaft and they may share a common pivot axis. In this arrangement an actuator may act on both rotor blades. This can also simplify the pivot linkage with the rotor shad.

However, with this arrangement net lift can only be changed with blade speed, as the lo collective pitch of the blade cannot be altered.

In an alternative arrangement, the two rotor blades may be free to pivot relative to each other, with a first portion of an actuator associated with each rotor blade. This arrangement enables the collective pitch to be controlled.

A plurality of second portions of the actuators may be fixed to a fuselage of an aircraft on which the rotor assembly is mounted, the second portions being in close proximity to the first portions during at least part of a revolution of the rotor assembly.

Where the second portions are electromagnetic coils and the first portions mounted to the 20 rotors are permanent magnets this arrangement avoids the need for any electrical power supply to first portions mounted on the rotor assembly. With this arrangement it is preferable that the actuators are only energised by the control means when the first and second portions are close enough for the electromagnetic field generated by at least one

portion to interact with the other portion, this saving electrical power.

It may be preferable that each magnetic actuator is an electromagnetic actuator, wherein the first and second portions are arranged to be repelled and/or attracted to each other in dependence on an electric current passed through at least one of the portions, the control means controlling the electric current. This arrangement is very flexible as the so magnetic field can be controlled almost instantaneously by the current passed through it and

may be controlled to oscillate in synchronism with rotation of the rotor assembly.

- 5 ( Preferably one portion of the, or each, actuator is a coil and advantageously the first portion of the actuator is a coil and the second portion of the actuator is a permanent i magnet. The mass of the coil will normally be greater than that of the permanent magnetic and it may be necessary to incorporate a mass onto the rotor assembly for stability, or if the 5 rotor blade has a blade neutral position generated by the centripetal force acting on the first portion. A blade neutral position is required because there is no mechanical linkage to the blade and therefore the mean position of the rotor blade has to be controlled in some way.

lo An alternative way of achieving this is by having spring bias on the pivot axis to the neutral point. Alternatively a pivot axis for the blade pitch may be aligned such that centre of lid of the blade lags the axis sufficiently for aerodynamic forces to hold the blade in this neutral position. ]5 It is particularly advantageous if the apparatus additionally comprises a detector for generating a signal relating to the position of the rotor shaft, the signal being received by the control molars, wherein the actuator is controlled is dependence on the received signal.

However, in an alternative arrangement a motor style commutator or an arrangement of brushes could achieve this.

Alternatively one portion of the, or each, actuator may comprise a permanent magnet the position of which is controlled by the control means to control the strength of the magnetic field between the two portions of the actuator.

25 Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like numerals are used throughout to indicate like parts, of which: Figure I is a schematic diagram of a prior art helicopter rotor blade control

30 apparatus; Figure 2 illustrates the principal of the present invention; Figure 3 schematically illustrates a first embodiment in accordance with the present invention;

- 6 ( Figure 4 is a schematic perspective view of a second embodiment in accordance with the present invention; Figure 5 is a schematic view of a third embodiment in accordance with the present invention; 5 Figure 6 is a schematic perspective view of a fourth embodiment in accordance with the present invention; Figure 7 is a schematic perspective view of a fifth embodiment in accordance with the present inventions and Figure 8 is a schematic perspective view of a sixth embodiment in accordance with lo the present invention.

The operation of the prior art rotor apparatus of Figure 1 has been described above

in the introduction to the present application.

Is Referring now to Figure 2, rotor apparatus in accordance with the present invention is illustrated where the control tube and swash plate assembly of the Figure I prior art

arrangement has been replaced by a magnetic actuator. The actuator comprises a first portion 10, attached to rotor blade 1 by pitch horn 3, and a second portion I I attached in a fixed position relative to the rotor blade 1.

The actuator 10, 1 I will typically comprise a permanent magnetic and a coil (but may comprise two coils) whereby an electric current passing through at least one coil causes the first portion 10 to be attracted or repelled relative to the second portion 1 1. The arrows indicate this. This action will rotate the blade I about its pivot axis 2.

Referring now to Figure 3, there is illustrated a first embodiment of in accordance with the present invention. In this embodiment. two rotors I are fixed to a common blade pivot hinge 2, which hinge pivots relative to the top of the rotor shaft 9. Attached to pitch horns 3 are respective electromagnetic coils I Oa and I Ob mounted in front and behind blade JO pivot hinge 2, respectively. Also, attached to the rotor shaft 9 are supports 26a and 26b for permanent magnets 11a and 11b. The magnets 1 la, 1 lb are positioned below coils lOa and fob and the coils 10a and lOb electrically connected such that any cyclic electric current passing through them will cause the coils I Oa and 1 Ob to be attracted and repelled in anti

- 7 f phase towards their respective permanent magnets I I a or 1 1 b. The coils 1 Oa and 1 Ob are connected in series via slip rings 13, 14 and wires I S. 16, 17 and 18 to controller 19.

Ignoring any requirement to trim the rotor assembly then in a "hover" position no 5 current is supplied through the coils and the centrifugal force experienced by the coils biases the rotor blades 1 to their blade neutral position. In this arrangement, the blade neutral position will have the desired amount of lid preset by the pitch being preset because with this arrangement it is not possible to alter the collective pitch as the two rotors blades 1 are fixed relative to each other.

Although in the embodiment illustrated the permanent magnets are shown mounted to the shaft with coils mounted to the rotors, these could be swapped. However, in the case of small model aircraft, it may be preferable to have the coils mounted to the rotors. The mass of coils is normally greater than the mass of magnets and therefore this mass can be 15 utilised to increase the moment of inertia of the rotors and thus increases the stability of the helicopter. When it is desired to move the helicopter in a particular direction, backwards, forwards, left or right, the cyclic control stick 25 is moved in the desired position. In the 20 case of a piloted aircraft, this will be mounted within the aircraft and generates an appropriate signal via line 20 to the controller 19. The principal is exactly the same in respect of a remote controlled aircraft, except in this case the signal from the cyclic control stick 10 is passed to transmitter 24. The signal is then transmitted to receiver 23 on the aircraft for transmission via wire 21 to the controller 19.

In addition to the input signal from the cyclic control stick 25, the controller 19 additionally receives an input signal on wire 29 from position feedback sensor 27. The sensor29 detects the position of the rotor 9 through via detecting the presence of indicator 28 mounted to the rotor shalt 9. The sensor 27can be any normal positioning sensor, for so example a potentiometer, a magnetic or optical index pulse device or a mechanical commutation index pulse.

- 8 - ( The controller 19, determining the position of the rotor shaft 9, energises coils 1 Oa, 1 Ob to cause the rotor blades 1 to be tilted about blade pivot hinge 2 such that one rotor blade will produce more lift than the other. This causes the aircraft to tilt and subsequently veer towards the point of lowest lid. As the rotor assembly rotates, the signal applied to the 5 coils lea, lob via the controller is cyclically reversed in synchronism with the speed of ntation of the rotor. Thus as the rotors change position with each other the lift characteristics are swapped so that the point of highest lift is maintained in the same position relative to the aircraft. Controller 19 determines where this point should be from the position of the rotor shaft 9 and the input received from the cyclic control stick 25.

Although not shown, it is possible to provide a duplicate control system along side that shown including duplicate coils, such that should any component fail the auxiliary system may be used to control the pitch of the rotor blades 1. In such an arrangement it may be possible for some components least likely to fail to be shared by the two contrary.

t5 systems, for example magnets I la and I lb. The above description of Figure 3 describes the main components of the invention,

and their relative interaction. However, there are various ways these components may be arranged and four further embodiments are described below with reference to Figures 4 to to 7. The principal of operation is essentially the same in each embodiment and therefore the embodiments will only be described in so far as they vary from the embodiment described with reference to Figure 3.

Referring to the embodiment shown in Figure 4, each rotor blade I is free to pivot 25 independently about its pivot axis defined by blade pivot hinge 2. Permanent magnets 1 la and l I b are again mounted on the rotor shad but in this embodiment coils 1 Oa and l Ob are connected, via respective feed horns 3, independently to corresponding rotor blades 1. The pitch of each blade is controlled in exactly the same manner as described above with reference to Figure 3 with the exception that each blade 1 can be pivoted independently of 30 the other. This enables a collective pitch control to be applied, in addition to the cyclic pitch control previously described. Thus if the lid produced by the complete rotor assembly is to be increased then, in addition to the cyclic forces applied between the coils l Oa, I Ob and respective magnets I l a, l I b, an additional collective repulsive force can be applied to

increase the combined lift, or attractive force to decrease the combined lid, of the rotor blades 1.

Referring to Figure 5, there is shown an embodiment where the principal of 5 operation is identical to that described above with reference to Figure 4. However in this embodiment the location of the actuators, comprising coils 1 Oa, lOb and permanent magnets 1 la, I lb, has changed. Here the coils lea, lob are mounted on respective support arms 31 a, 31 b that in turn are connected to a pivot point 30 on the rotor shaft 9. When the coils lea, lOb are energised, they are deflected causing respective support arms 3 la, 31b to lo move and in turn displace respective linkage members 32a, 32b connected to respective rotor blades 1, altering the pitch of the blades 1. The arrangement illustrated in this figure enables the coils and magnets I Oa, 1 Ob, 1 1 a, 1 1 b to mounted very close to the shaft 9 reducing the moment of inertia which will make the aircraft more responsive. This may be desirable on larger aircraft. This also minimises the drag generated by the coils and 15 magnets. Reterring now to Figure 6, an arrangement is illustrated where a number of permanent magnets 34 to 37 are mounted to the fuselage 33 of the aircraft. The principal of operation is identical to that described with reference to the earlier figures. The controller 20 19, knowing the location of the magnets 34 to 37, controls the current through the coils 1 Oa, 1 Ob when the coils are above the magnets, to provide the desired pitch control for each rotor blade 1. This arrangement has the advantage of reducing the mass attached to the rotor shad 9 thereby increasing the response of the aircraft to any input signal. It is also possible, as with all embodiments, to swap the coils lea, lOb for the magnets, and vice 25 versa. This may be advantageous in this embodiment for only permanent magnets would then be mounted to the rotor assembly and thus no electrical signal would need to be applied to the rotor shaft 9, avoiding the need for slip rings 13, 14 disclosed in the earlier Figures 3 and 5.

lo A further embodiment is illustrated in Figure 7 where the rotors I are again fixed relative to each other, as in the Figure 3 embodiment. A permanent magnet 43 is suspended from a link arm 38 between the two rotor blades 1, which link arm 38 is supported by flexible pins 39, 40 which extend to the top ofthe shaft 9. Two coils 41, 42 are mounted to

- 10 ( the aircraft fuselage 33 such as to attract or repel permanent magnet 43 as it rotates with the rotor bWes 1. Energising either of coils 41, 42 causes the permanent magnet 43 to be deflected from its normal position which will cause pins 39, 40 to flex and the link arm 38 to be tilted over. This increases the lift of one rotor blade relative to that of the other in the 5 same manner as described with reference to the Figure 3 embodiment. In the Figure 7 embodiment, however, the mass of the moving magnet cannot be used as a stabilization mass. It is to be noted that in this arrangement a constant current can be applied to the coils as the cyclic action is achieved by the effective reversing of the polarity of the magnet as it rotates through 180 degrees.

A final embodiment is illustrated in Figure 8. This is essentially the same as the embodiment described above with reference to figure 6. However in the figure 8 embodiment the magnets lea and lob are now permanent magnets and the fixed magnets 34 to 37 of figure 6 have been replaced by magnets 44 to 47, each supported by a respective IS actuator 48 toSI Each actuator is controlled by the control means such that a respective magnet may be rotated to expose either a North face or a South face to magnets 1 Oa and 1 Ob. Thus each magnet 44 to 47 may either attract or repel magnets I Oa and I Ob by an amount dependent 20 on the angle of the face of the magnet 44 to 47 relative to magnets 1 Oa and 1 Ob. When it is desired to provide a differential lift each opposed pair of magnets 44, 46 and 47, 49 will be out of phase, such that one will cause an increase in lid on a rotor blade 1 whilst the other causes a decrease in lift on that blade. This arrangement may also be used to control collective pitch.

Several embodiments have been described above and it will be appreciated that further embodiments may be implemented within the scope of the appended claims. For example in the embodiment of figure 6 the same effect could be achieved by raising or lowering magnets 44 to 57, with the rotors I biased by spring means, or centripetal action so to a first limit of pitch. Additionally the magnets on the rotors could then be replaced by ferrous material. Also only one, or perhaps two opposed magnets 44, 46 could be employed, mounted on a frame, which frame could be rotated in order to provide the differential liR in the desired direction. Also it will be realised that instead of the actuators

- 11 direclY control the rotor blades the actuators could equally control a fly-bar bled to the rotor blades in the same man entiOnal swash plates can control the few examples of the Y di fly or by means of the fly-bar. These j t tions withy the scope of the append

Claims

À. - - - - - 12 CLAIMS

1. Rotor blade control apparatus comprising: a rotor assembly including a rotor shaft and at least one rotor blade connected to the shaft in a manner such that the pitch of the s blade relative to the shaft may be varied; a magnetic actuator comprising a first portion and a second portion arranged to be repelled and/or attracted to each other in dependence on a magnet field between them; and control means for controlling the magnetic field between

the two portions, wherein the first portion of the actuator is mounted on the rotor assembly, turns with the rotor assembly and is mechanically connected to control the pitch of the rotor lo blade, wherein the second portion ofthe actuator is mounted in a Eked position relative to the position of the rotor shaft, the first and second portions being arranged such that any magnetic field between them causes the first portion to be displaced relative to the second

portion and causes the pitch of the blade to alter.

l5

2. Apparatus as claimed in Claiml, wherein the rotor assembly comprises two rotor

blades mounted to the rotor shaft' each blade being free to pivot relative to the rotor shaft about a pitch axis associated with the blade, wherein the first portion of the actuator is mounted to a rotor blade and located at a point horizontally spaced from the pitch axis of the rotor blade such that any displacement of said first portion caused by the interaction 3 to with the second portion of the actuator alters the pitch of the blade.

3. Apparatus as claimed in Claim 1, comprising two rotor blades mounted either side of the rotor shaft each having the first portion of an actuator connected to it by a mechanical linkage.

4. Apparatus as claimed in claiml further comprising a fly-bar for controlling the pitch of the rotors, wherein the first portion of the actuator is mechanically connected to control the pitch of the rotor blade by being mechanically linked to the fly bar, to control the position of the fly-bar which in turn controls the pitch of the rotor blades.

5. Apparatus as claimed in any preceding claim, comprising two rotor blades and two actuators mounted either side of the axis of the rotor blades wherein the magnetic fields

associated with respective actuators is in anti-phase.

- 13 (

6. Apparatus as claimed in any preceding claim, comprising two rotor blades fixed together so they can only pivot together relative to the rotor shaft.

s

7. Apparatus as claimed in any one of Claims 1 to 5 comprising at least two rotor blades free to pivot relative to each other, each rotor blade having a first portion of an actuator associated therewith.

8. Apparatus as claimed in any preceding claim' wherein each rotor blade has a blade lo neutral position.

9. Apparatus as claimed in Claim 8, wherein the blade neutral position is generated, at least in part, by the centripetal force acting on the first portion of the actuator.

s

1 O. Apparatus as claimed in Claim 8, wherein blade neutral position is generated by the pivot axis for the blade pitch being aligned such that the centre of lift of the blade lags the axis sufficiently for aerodynamic forces to hold the blade in its neutral position.

11. Apparatus as claimed in any preceding claim, comprising a detector for generating a to signal related to the position of the rotor shaft, the signal being received by the control means which controls the actuators in dependence on the received signal.

12. Apparatus as claimed in any preceding claim, wherein the control means receives feedback from the actuators.

13 Apparatus as claimed in any preceding claim wherein the magnetic actuator is an electromagnetic actuator and wherein the first and second portions are arranged to be repelled and/or attracted to each other in dependence on an electric current passed through at least one of the portions, the control means controlling the electric current.

14. Apparatus as claimed in claim 13, wherein the first portion of the actuator is a coil and the second portion of the actuator is a permanent magnet.

- 14 1 S. Apparatus as claimed in claim 13 or 14, wherein the second portion of one or more actuators is fixed to the rotor shaft and mounted adjacent the corresponding first portion.

16. Apparatus as claimed in claim 15 wherein the control means is arranged to 5 cyclically control the magnetic field in synchronism with the rotation of the rotor assembly.

17. Apparatus as claimed in anyone of claims 13 or 14, comprising a plurality of actuator second portions fixed to a fuselage of an aircraft on which the rotor assembly is mounted, the second portions being in close proximity to the first portions during at least lo part of a revolution of the rotor assembly wherein the actuators are only energised by the control means when the first portions are in close proximity to the second portions.

18. Apparatus as claimed in anyone of claims I to 12, wherein one portion of the or each actuator comprises a permanent magnet the position of which is controlled by the Is control means to control the strength of the magnetic field between the two portions of the

actuator.

19. Apparatus as claimed in claim 18, comprising means to rotate the magnet to control the magnetic field strength.

20. Apparatus as claimed in claim 18, comprising means to raise or lower the magnet towards or away from the other portion of the actuator to control the magnetic field

strength. 25

21. Apparatus as claimed in claim 18, 19 or 20 wherein the first portion of each actuator comprises a permanent magnet mounted to the rotor assembly and a second portion comprises a permanent magnet mounted relative to the fuselage of an aircraft to which the rotor assembly is attached.

aa

22. Apparatus as claimed in claim 21 wherein the second portion is arranged to be rotated whereby an attractive field between the magnets can be reversed such that the

magnets are repelled.

- 15 (

23. Apparatus as claimed in any one of claims 1 to 20 wherein one portion of the actuator comprises a ferrous material.

24. Apparatus as claimed so any preceding claim, wherein the first portions are 5 vertically spaced from the second portions.

25. Rotor control apparatus substantially as hereinbefore described with reference to, and/or as illustrated in, one or more of Figures 2 to 8 of the accompanying drawings.