Helicopter servo mounting

Abstract

The disclosure provides a helicopter rotor head assembly (100) for control of the swash plates (102a, 102b) of a coaxial counterrotating helicopter rotor head. The helicopter (1000) comprises a load-bearing gearbox (101) configured to drive the rotor head and to bear the weight of the helicopter (1000) in flight. The assembly comprises: at least one servo unit (104a-d) comprising an output shaft; a mounting structure, wherein the mounting structure is configured to be secured to the gearbox (101) and comprises an attachment element configured to releasably attach the servo unit; and an actuator, fixed to the mounting structure (106a, 106b), for connection to a control rod (108a-d) for actuating a swash plate (102a, 102b). The attachment element and the actuator are configured such that releasable attachment of the at least one servo unit (104a-d) to the attachment element engages the output shaft with the actuator.

Description

[0001] Helicopter Servo Mounting

[0002] Technical Field

[0003] The present invention relates to components for control of helicopter swash plates, and more particularly to the mounting of said components onto the body of said helicopters.

[0004] Background

[0005] Unmanned aerial vehicles (UAVs) are increasingly being used in a variety of different contexts. For example, UAVs may be used for reconnaissance purposes, or the delivery of cargo or a payload to a desired location. It is often desirable for such vehicles to have good manoeuvrability, and therefore to be as small and lightweight as possible. Some UAVs can take the form of an unmanned helicopter.

[0006] As helicopter rotor blades spin, they exert a torque on the helicopter which needs to be counteracted. This is typically achieved using a tail rotor which exerts an opposite torque to the main rotor on the helicopter. However, some helicopters instead address this by using coaxial rotors. In these aircraft, a pair of rotors are mounted one above the other on concentric shafts. The two shafts have the same axis of rotation but are configured to spin in opposite directions so that the torque is balanced.

[0007] Helicopter rotor blades are typically coupled to a swashplate, the movement and position of which can be adjusted to change the pitch of the blades and thereby control movement of the helicopter.

[0008] The movement of the swashplates can in turn be controlled by the actuation of control rods to which they are coupled, which may be actuated by one or more electric servo motors. However, due to the large weight and other forces which act upon the helicopter during flight, these servos can be subject to various loads and bending moments which can decrease their lifespan and reliability.

[0009] The servo units need to be securely carried by the helicopter in such a way that enables the actuation of the control rods whilst the helicopter is subject to large forces during flight. Additionally, the servo units may need to be removed or replaced over the lifetime of the helicopter.

[0010] Summary of Invention

[0011] Embodiments of the present invention aim to address the above problems and others. Aspects of the disclosure are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the disclosure may be provided in conjunction with each other, and features of one aspect may be applied to other aspects.

[0012] In an aspect there is provided a helicopter rotor head assembly for control of the swash plates of a coaxial counterrotating helicopter rotor head, wherein the helicopter comprises a load-bearing gearbox configured to drive the rotor head and to bear the weight of the helicopter in flight, the assembly comprising: at least one servo unit comprising an output shaft; a mounting structure, wherein the mounting structure is configured to be secured to the gearbox and comprises an attachment element configured to releasably attach the servo unit; and an actuator, fixed to the mounting structure, for connection to a control rod for actuating a swash plate; wherein the attachment element and the actuator are configured such that releasable attachment of the at least one servo unit to the attachment element engages the output shaft with the actuator.

[0013] The at least one servo unit may comprise a plurality of servo units, and the mounting structure may comprise a plurality of said attachment elements each configured to releasably attach to a corresponding one of the servo units.

[0014] The coaxial counterrotating helicopter rotor head may comprise a first swashplate coupled to a first drive shaft, and may also comprise a second swashplate coupled to a second drive shaft that is coaxial with the first drive shaft. At least one of the servo units may be configured to adjust the axial position of the first swashplate relative to the second swashplate. The at least one servo unit may comprise four servo units. Three of the servo units may be configured to control the position and / or orientation of the swashplates. A fourth one of the servo units may be configured to adjust the axial position of the first swashplate relative to the second swashplate.

[0015] The actuator may comprise a splined joint for engagement with the output shaft of the servo unit.

[0016] The actuator may comprise a surface, e.g. an outer surface, which comprises notches and / or grooves. The notches and / or grooves may be configured to engage with the mounting structure, for example with corresponding elements in an inner surface of an opening in the mounting structure (which may be a mounting plate). The actuator may be configured to engage with the output shaft of the servo unit such that it rotates with the output shaft.

[0017] The mounting structure may be configured to bear the weight of the actuator and / or the servo unit.

[0018] The mounting structure may comprise a first plate for attachment of a first pair of servo units. The mounting structure may also comprise a second plate for attachment of a second pair of servo units. The first plate and the second plate may be coupled to opposite sides of the gearbox.

[0019] The helicopter rotor head assembly may further comprise a control arm coupled to the actuator. The control arm may be arranged for coupling to the control rod, and may be configured to convert rotational motion of the actuator into linear motion of the control rod. The helicopter rotor head assembly may comprise the control rod for actuating a swash plate.

[0020] The gearbox may comprise an opening. The control rod (e.g. one of the four control rods) may be arranged to pass through the opening between the actuator and the swashplate.

[0021] The helicopter rotor head assembly may further comprise the control arm, for example it may comprise a plurality, e.g. four control arms.

[0022] The at least one servo unit may correspond to a servo unit, e.g. a single servo unit. The servo unit may be a first servo unit and the rotor head assembly may comprise a plurality of servo units, including the first servo unit. For example the rotor head assembly may comprise four servo units. Three of the servo units, e.g. three of the four servo units, may be configured to control the position and / or orientation of the swashplates.

[0023] The at least one servo unit may comprise a first pair of servo units, e.g. a first pair of the four servo units, which may be identical or substantially identical. The pair of servo units may be configured for releasable attachment to a first common element of the mounting structure, e.g. a first frame element or mounting plate. The at least one servo unit may comprise a second pair of servo units, e.g. a second pair of the four servo units, which may be substantially identical to one another and / or to the first pair of servo units and may be mountable to a second common element of the mounting structure, e.g. a second frame element or mounting plate, the first and second common elements may be arranged on opposing sides of the gearbox. Each one of a pair of servo units may be arranged to extend from the mounting structure parallel to one another.

[0024] The frame elements, e.g. mounting plates may further comprise connection points for attachment of the mounting structure to the gearbox. The connection points may comprise openings for screws to extend through and attach to the gearbox. The mounting structure, e.g. each frame elements, may comprise one or more (e.g. a pair of) protrusions comprising the connection points. The mounting structure may comprise one or more openings, for a corresponding actuator and / or output shaft to extend through.

[0025] A corresponding actuator and control rod may be provided for each servo unit. Each actuator may be or comprise an elongate element, which may extend between the servo unit output shaft and a control arm. Alternatively, the actuator may comprise the control arm. The actuator may be configured to transfer rotational movement from the servo unit output shaft to the control arm and / or the control rod. For example it may convert the rotational movement into linear movement of the control rod. The rotor head assembly may further comprise one or more bearings, e.g. annular ball bearings, which may be configured to support radial and / or axial loads e.g. on the actuator. One or more bearings may surround each actuator and / or be provided within one of the openings in the mounting structure.

[0026] The actuator may comprise a plurality of notches / ridges / grooves / splines, e.g on a portion of its surface, e.g. for engagement with the control arm 13, and / or the bearing(s). For examples the a plurality of notches / ridges / grooves / splines may be configured to engage with correspondingly shaped elements on the control arm 13, and / or the bearing(s).

[0027] The helicopter rotor head assembly may comprise the load-bearing gearbox.

[0028] The one or more servo unit may be attached to the mounting structure.

[0029] The attachment element and the actuator may be arranged to engage the output shaft of the servo unit with the actuator upon releasable attachment of the at least one servo unit to the attachment element.

[0030] The attachment element may comprise one or more screws. Each servo unit may be releasable from the mounting structure upon removal of the screws. The mounting structure may comprise one or mounting plates. In some examples the mounting structure comprises a pair of mounting plates. In some examples a first pair of servo units may be releasably attached to a first mounting plate, and a second pair of servo units may be releasably attached to a second mounting plate.

[0031] The rotor head assembly may comprise a plurality of servo units, and a corresponding plurality of actuators, where each servo unit is associated with a corresponding actuator. Each servo unit and associated actuator may further be associated with a corresponding control rod. It will be appreciated that the control rods may not form part of the rotor head assembly. In some examples there may be four sets of associated servo units and actuators (and control rods).

[0032] Each servo unit and / or actuator may be configured to actuate its corresponding control rod to control the rotor blades of the helicopter, e.g. to provide collective and / or cyclic pitch control.

[0033] In another aspect there is provided a method of replacing a servo unit of a helicopter rotor head assembly. The method comprises detaching a first servo unit from the attachment element, and attaching a second servo unit to the attachment element.

[0034] Brief Description of Figures

[0035] Some examples of the present disclosure will now be described with reference to the figures, in which:

[0036] Figure 1 gives a schematic view of an example coaxial helicopter.

[0037] Figure 2a shows a schematic side view of an example helicopter rotor head assembly. Figure 2b shows a schematic front view of the example helicopter rotor head assembly.

[0038] Figure 3 illustrates a portion of an example mounting structure for the servo units of a helicopter rotor head assembly.

[0039] In the drawings like reference numerals are used to indicate like elements.

[0040] Detailed Description of Figures

[0041] The present disclosure relates to a mounting arrangement which enables the servo units which actuate the swashplates of a coaxial helicopter to be attached to the helicopter without substantially bearing the load of the helicopter. This in turn enables the servo units to be easily removed and replaced. The servo units are releasably attached to a mounting frame which is connected to the gearbox of the helicopter, where the gearbox bears the weight of the helicopter in flight. Attachment of the servo units to the mounting structure also engages the servo units with the control rod mechanism, thereby enabling control of the helicopter swashplates and rotor blades.

[0042] Figure 1 shows a schematic side view of an example coaxial helicopter 1000. The coaxial helicopter 1000 comprises a first rotor 1002 which comprises a plurality (e.g. 3) rotor blades. The helicopter 1000 further comprises a second rotor 1004 comprising a corresponding plurality of rotor blades.

[0043] The helicopter 1000 further comprises a gearbox or transmission 101. The gearbox 101 is coupled to an engine or other power source (not shown), and is configured to drive each of the rotors 1002, 1004. As shown in the figure, in operation the first rotor 1002 and the second rotor 1004 are configured to spin in opposite directions, to provide lift to the helicopter 1000 whilst balancing torque.

[0044] The gearbox 101 is mechanically coupled to drive the first rotor 1002 via a first drive shaft 1006, and is mechanically coupled to drive the second rotor 1004 via a second drive shaft 1008. The first drive shaft 1006 and the second drive shaft 1008 are concentric, e.g. concentric cylinders, with the second drive shaft 1008 arranged inside the first drive shaft 1006. The first 1006 and second 1008 drive shafts and the first 1002 and second 1004 rotors are coaxial, i.e. they share an axis of rotation.

[0045] Figure 2a shows a schematic side view of an example helicopter rotor head assembly 100, for a coaxial helicopter having a pair of counterrotating rotors such as the helicopter 1000 of Figure 1. Figure 2b shows a front-on view of the same assembly 100. To aid clarity, the coaxial drive shafts and rotor blades are not shown in these figures. The assembly 100 comprises a gearbox 101 such as the gearbox 101 described above. The gearbox is configured to be bear the weight of the helicopter during flight. That is, during flight, the weight of the helicopter acts through the gearbox 101.

[0046] The assembly 100 further comprises first and second swashplates 102a, 102b. The first and second swashplates 102a, 102b are each configured to control the movement of the first 1002 and second 1004 rotors respectively, e.g. to adjust the pitch of the rotor blades of said rotors, and thereby to control the movement of the helicopter. The movement of the swash plates 102a, 102b is controlled by a plurality of servo units 104a-d. Each of the servo units 104a-d are mechanically coupled to one or both of the swashplates 102a, 102b, via corresponding control rods 108a-d. The servo units 104a-d are operable to actuate their corresponding control rod 108a-d to adjust the movement, position and / or orientation of the swash plates 102a, 102b. The servo units 104a-d are configured to actuate the control rods 108a-d in response to a control signal, which may be received from a controller (not shown) to which the servo units 104a-d are connected. The servo units 104a-d comprise a servomotor and a position sensor configured to provide position feedback to the motor.

[0047] The assembly 100 comprises four such servo units. The four servo units 104a-d are attached, in particular mounted-on, the gearbox 101 via a mounting structure 105. The mounting structure 105 comprises a first mounting plate 106a and a second mounting plate 106b. The first and second servo units 104a,b are attached to the first mounting plate 106a, and the second and third servo units 104b,c are attached to the second mounting plate 106b. The first 106a and second 106b mounting plates are attached to opposite sides e.g. opposite surfaces of the gearbox 101. The first mounting plate 106a is connected to the second mounting plate 106b via a rigid frame 107. Each of the servo units 104a-d are releasably attached to their corresponding mounting plate 106a-b, as described in more detail below.

[0048] As shown in Figures 2a-b, the servo units 104a-d are attached to the gearbox 101 such that they are positioned on the opposite side of the gearbox 101 from the swashplates 102a-b. In particular, the servo units 104a-d are provided on what constitutes the underside of the gearbox 101 in flight. Each of the control rods 108a-d therefore need to extend around or through the gearbox 101. As shown in Figures 2a-b, in the assembly 100 three of the control rods 108a-c extend around the outside of the gearbox 101. The fourth control rod 108d is configured to extend through an opening in the gearbox, wherein the opening extends axially from the under surface of the gearbox to its top surface.

[0049] The first three of the servo units 104a-c and control rods 108a may be configured to adjust the movement, position and / or orientation of the swash plates 102a, 102b, whilst the fourth servo unit 104d and control rod 104d may be configured to provide differential control, that is to adjust the position of the first swash plate 102a relative to the second swashplate 102b. Figure 3 is an exploded view of a portion of the assembly 100, which illustrates an example of the connection between the servo units and mounting structure in more detail. The assembly 100 in Fig. 3 is shown flipped vertically with respect to Figures 2a-b.

[0050] As shown, each of a pair of servo units 104 comprise an output shaft 302, which is configured to rotate upon activation of the servo unit 104. The pair of servo units 104 are also configured to be mechanically connected to one another at their outer ends (i.e. the end opposite the end which engages with themounting plate 106, via connecting means in the form of screws 15.

[0051] The mounting plate 106 comprises a pair of openings for the respective output shafts 302 of the two servo units 104 to extend into. The mounting plate 106 further comprises connection points (e.g. holes) for connecting to aligned connection points on each of the servo units 104 via an attachment element, in particular a pair of screws 14. The mounting plate 106 further comprises a pair of protrusions comprising connection points in the form of openings for connection to the gearbox, via a pair of screws 17 per protrusion.

[0052] Each of the servo units 104 are attached to the mounting plate 106 via the screws 14, and are releasable from the mounting plate 106 upon removal of the screws 14. In this way the servo units 104 can be removed or replaced in the assembly. As such, the screws 14, either individually or collectively, can be considered an attachment element configured to releasably attach their corresponding servo unit 104 to the mounting structure (e.g. mounting plate 106).

[0053] Upon attachment of the servo units 104 to the mounting plate 106, each of the output shafts 302 are configured to engage with an actuator, in the form of actuating element 9. The actuating element 9 is fixed to the mounting plate 106. For example, a portion of the actuating element 9 comprises a surface having notches and grooves configured to engage with corresponding elements in the inner surface of the openings in the mounting plate 106. The actuating element 9 is an elongate element that is configured to engage with the output shaft 302 such that it rotates with the output shaft 302. The actuating element 9 extends from the mounting plate 106 and is configured to transfer rotational movement from the output shaft 302 to the control rods (e.g. those shown in Figures 2a- b). In particular the actuating elements 9 are each configured to engage with a control arm 13. Each control arm 13 is arranged to couple to one of the control rods which actuate the swash plates of the helicopter. The control arm 13 is configured to translate the rotational movement of the actuating element 9 into linear movement of the control rod to which it is attached. In particular, the control arm 13 comprises a circular portion which is engaged with the end of the actuating element 9 and is configured to rotate about the axis of the actuating element 9, and a substantially rectangular portion extending from one side of the circular portion. The rectangular portion is coupled to the control rod such that rotational movement of the control arm 13 to provides linear movement of the control rod.

[0054] The control arm 13 is supported within a support element 8. The support element 8 is affixed to the mounting plate 106. In particular it is affixed to the opposing face of the mounting plate 106 from the servo units 104, via screws 4. The support element 8 substantially surrounds the control arm 13, but comprises an opening through which the rectangular portion extends, and which enables rotation of the control arm 13 about the axis of the actuating element 9. The support element 8 comprises a supporting rim 6 with a larger diameter than the main body of the support element 8. The supporting rim 6 is coupled to the mounting plate 106 via a plurality, e.g. six, screws 4.

[0055] The actuating element 9 comprises a portion which extends into the support element 8 for engagement with the control arm. A pair of annular ball bearings 2, 7, surround this portion of the support element 8 which are coupled together via a circlip 25. The bearing 2 closest to the control arm 13 may have a greater diameter than the bearing 7 closest to the mounting plate 106. The bearing 7 and / or the bearing 2 are mounted on the actuating element 9.

[0056] The actuating element 9 may comprise a plurality of notches / ridges / grooves / splines on a portion of its surface, for engagement with the control arm 13, and / or the bearing(s) 2, 7.

[0057] A further annular ball bearing 7’ may be mounted on the actuating element 9 on an opposite side of the control arm 13 from the bearings 7, 2. A further coupling arrangement is provided for each control arm 13, comprising a screw 20, a nut 21 and a pin 23 are provided, wherein the screw 20 extends through a hole in the rectangular portion of the control arm 13, such that the control arm 13 is secured between the head of the screw 20 and the nut 21 , and may be used for rigidly connecting the control arm 13 to a corresponding control rod 108. The hole / opening in the control arm is provided at the end of the control arm 13 furthest from the pivoting connection to the actuating element 9.

[0058] It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein.

[0059] As will be appreciated by the skilled reader in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Any features of any aspects of the disclosure may be combined with any of the other aspects of the disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the examples is intended to be separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the examples in which it is described, or with any of the other features or combination of features of any of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the invention.

[0060] Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

CLAIMS1. A helicopter rotor head assembly for control of the swash plates of a coaxial counterrotating helicopter rotor head, wherein the helicopter comprises a load-bearing gearbox configured to drive the rotor head and to bear the weight of the helicopter in flight, the assembly comprising: at least one servo unit comprising an output shaft; a mounting structure, wherein the mounting structure is configured to be secured to the gearbox and comprises an attachment element configured to releasably attach the servo unit; and an actuator, fixed to the mounting structure, for connection to a control rod for actuating a swash plate; wherein the attachment element and the actuator are configured such that releasable attachment of the at least one servo unit to the attachment element engages the output shaft with the actuator.

2. The helicopter rotor head assembly of claim 1 , wherein the at least one servo unit comprises a plurality of servo units, and wherein the mounting structure comprises a plurality of said attachment elements each configured to releasably attach to a corresponding one of the servo units.

3. The helicopter rotor head assembly of any preceding claim, wherein the coaxial counterrotating helicopter rotor head comprises a first swashplate coupled to a first drive shaft, and a second swashplate coupled to a second drive shaft that is coaxial with the first drive shaft, wherein at least one of the servo units is configured to adjust the axial position of the first swashplate relative to the second swashplate.

4. The helicopter rotor head assembly of any preceding claim, wherein the at least one servo unit comprises four servo units, and wherein three of the servo units are configured to control the position and / or orientation of the swashplates.

5. The helicopter rotor head assembly of claim 4 as dependent on claim 3, wherein the other one of the servo units is configured to adjust the axial position of the firstswashplate relative to the second swashplate.

6. The helicopter rotor head assembly of any preceding claim, wherein the actuator comprises a splined joint for engagement with the output shaft of the servo unit.

7. The helicopter rotor head assembly of any preceding claim, wherein the mounting structure is configured to bear the weight of the actuator and / or the servo unit.

8. The helicopter rotor head assembly of any preceding claim, wherein the mounting structure comprises a first plate for attachment of a first pair of servo units, and a second plate for attachment of a second pair of servo units, wherein the first plate and the second plate are coupled to opposite sides of the gearbox.

9. The helicopter rotor head assembly of any preceding claim, further comprising a control arm coupled to the actuator, and arranged for coupling to the control rod, wherein the control arm is configured to convert rotational motion of the actuator into linear motion of the control rod.

10. The helicopter rotor head assembly of any preceding claim, wherein the gearbox comprises an opening, wherein the control rod is arranged to pass through the opening between the actuator and the swashplate.11 . The helicopter rotor head assembly of any preceding claim, further comprising the control arm.

12. A method of replacing a servo unit of a helicopter rotor head assembly according to any of the preceding claims, the method comprising detaching a first servo unit from the attachment element, and attaching a second servo unit to the attachment element.

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