GB2077208A

GB2077208A - Controlling Helicopter Rotors

Info

Publication number: GB2077208A
Application number: GB8016889A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1980-05-22
Filing date: 1980-05-22
Publication date: 1981-12-16

Abstract

A helicopter rotor blade incidence control unit which can conveniently be constructed largely from light composite materials such as carbon fibre reinforced plastics includes two discs, (12, 16) and for each rotor blade, a connector (24), the connectors and discs being so arranged that by suitable manoeuvring of the discs relative to the rotor axis (11) the connectors can be moved circumferentially relative to the rotor to effect collective control of the rotor blade incidence, or the centre of rotation of the connectors can be moved relative to the axis of rotation of the rotor to effect cyclic control of the rotor blade incidence. Discs (12, 16) are connected together for rotation via an intermediate plate (14) and eccentric pins (15) or elastomeric means (Fig. 5, not shown) to allow transverse movement of disc (16) relative to disc (12). Collective pitch actuator (30) acting parallel to rotor axis (11) and two cyclic pitch actuators acting at right angles to one another in a plane normal to axis 11 are provided. Modified construction described (Figs. 7, 8, not shown). <IMAGE>

Description

SPECIFICATION Helicopter Rotor Blade Incidence Control The present invention relates to the control of incidence of helicopter rotor blades.

When a helicopter is in motion the relative velocity of each rotor blade relative to air through which the helicopter is flying varies throughout each cycle. The relative velocity is at a maximum when the blade is normal to the direction of helicopter motion and advancing, and is at a minimum half a cycle later. Were the angles of attack of the blades to be allowed to remain constant throughout a cycle this would result in unacceptable assymetry of lift with a helicopter in motion relative to the air. To prevent this the angle of incidence of each blade (and hence its angle of attack relative to the air flow) is varied throughout the cycle. The degree of this variation, which is referred to as cyclic variation, will depend on the speed of the helicopter relative to the air, and must therefore be variable.

It is also necessary to control the incidence of the rotor blades to vary the total lift provided by a rotor assembly (as it is a feature of helicopter design that their rotors must be run at substantially constant speed). For lift control the incidences of all blades are altered equally. Units for effecting these two types of rotor incidence variation, known as cyclic and collective respectively, conventionally use arrangements of gearing. Control of main rotor blade incidences is so vital to helicopter operation that the design of incidence control units is one of the major challenges in the design of a new helicopter. The units are unavoidably expensive and comparatively heavy.

According to the present invention a helicopter rotor blade incidence control unit includes a rotor having an axis of rotation, rotor blade attachments at positions on the rotor fixed relative to the axis of rotation, two discs mounted on and arranged to rotate with the rotor, one of the discs having secured thereto, for each rotor blade attachment, a connector for connecting the disc to a rotor blade incidence control, means for manoeuvring the discs to change the relative circumferential positions of the connectors and the attachments, and means for manoeuvring the discs to displace an axis of rotation of the connectors relative to the axis of rotation of the rotor.

The discs are preferably made from composite material, such as glass fibre or carbon fibre reinforced plastic.

In one form of the invention a first of the two discs is constrained to rotate about the axis of rotation of the rotor, and the connectors are secured to a second of the discs which is driveably connected to the first disc but has its centre of rotation eccentrically moveable relative to the centre of rotation of the first disc. The driving connection between the first and second discs may be an elastomeric coupling. When cyclic control is effected by this type of system, the first disc can conveniently be mounted on the rotor by helical splines such that axial movement of the first disc relative to the rotor results in rotational movement of both first and second discs relative to the rotor.

In another embodiment of the invention the first disc is connected to a first sleeve driven by the rotor but having an axis of rotation moveable relative to the axis of rotation of the rotor, the second disc is secured to a second sleeve slidably mounted on the first sleeve, each disc having secured thereto, for each rotor blade, one leg of an angle piece at the apex of which is carried an arm having at its free end a connector, the arrangement being such that radial movement of the apex caused by relative axial movement of the discs causes circumferential movement of the connector.

Some embodiments of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawings, of which; Fig. 1 is an elevation, partly in section, of a control unit according to the invention.

Fig. 2 is a plan view of the control unit shown in Fig. 1.

Fig. 3 is side elevation in section along Line Ill-Ill of Fig 2, of a detail of the unit of Fig. 1.

Fig. 4 is a plan view showing details of the means. for displacing the axis of rotation of the connectors in the unit illustrated in Fig 1.

Fig. 5 is an elevation, partly in section, of an alternative version of the unit illustrated in Fig 1.

Fig 6 is a plan of part of the unit illustrated in Fig 5.

Fig 7 is an elevation, partly in section, of another embodiment of the invention, and Fig 8 is a plan view of part of the unit illustrated in Fig 7.

A helicopter rotor blade incidence control unit (Figs 1-4) has a rotor (10) having an axis of rotation (1 1). Secured to an end of the rotor (10) is a rotor head (20) to which rotor blades (21) are secured by attachments (22). The rotor blades (22) are rotatable about spanwise axes (23).

Mounted on the rotor (10) by a splined coupling (13), is a first disc (12) which is constrained to rotate with the rotor (10) but has some degree of axial and circumferential freedom of movement relative to the rotor (10) allowed by the splined coupling (13). An intermediate disc (14) is connected to the first disc (12) by an array of at least three eccentric pins, of which one is shown at (1 5) and similar pins (not shown) connect the intermediate plate (14) to a second disc (16).The second disc (16) is therefore constrained to rotate with the first disc (12) and rotor (10) but its centre of rotation (17) (Fig 2) can be moved relative to the rotor axis (11) up to a limit imposed by the degree of eccentricity of the pins (1 5). The second disc (16) is mounted on a sleeve (18) on which is rotatably mounted a collar (19). An actuator (30) operable in a direction parallel to the rotor axis (11) is connected by a scissors linkage (31) to the collar (19) and actuators (32, 33) (Fig 4), operable normal to the rotor axis (11) and to each other are also connected to the collar (19).For each rotor blade (21) the second disc (16) carries a connector (24) which connects the second disc (16) to an incidence control lever (25) such that motion of the disc (1 6) relative to the rotor (10) moves the incidence control lever (25) and hence alters the incidence of the rotor blade (21). As illustrated in Fig 1 the connector includes a T-pin (26) which is free to rotate in the disc (16) and to slide parallel to the rotor axis (11) and a fork pin (27) which is free to rotate and slide in a boss of the T-pin and to rotate at the fork end relative to the incidence control lever.

In operation with the rotor (10), and hence all associated items including the rotor blades (21) rotating, the incidence of each blade will be the same at each point in a cycle when the axis of rotation (17) of the second disc (16) is the rotor axis (11). Movement of the actuator (30) causes the collar (19), sleeve (18), second disc (16), intermediate disc (14) and first disc (12) to move axially relative to the rotor (10), and due to the helical connection (13) this causes rotation of the whole assembly relative to the rotor (10). This relative rotation is transmitted by the connectors (24) to the incidence control levers (25) and hence the incidences of all blades are altered by an equal amount.Movement of either actuator (32), actuator (33), or both acts via the collar (19) and sleeve (18) to move the second disc (16), as permitted by the eccentric pins (15), to displace the axis of rotation (17) of the second disc (16) from the rotor axis (11) as illustrated in Fig. 2, and introduces a cyclic variation in the incidence of each blade as it rotates. Blade (21) incidence can therefore be controlled as required according to flight conditions, cyclically by actuators (32, 33) and collectively by actuator (3). The freedom of the T-pin and the fork pin of the connector to rotate and slide accommodates the motions of disc (1 6) and also accommodates motions of the incidence lever (25) due to blade flap or coning.

In an alternative version of the above described embodiment of the invention (Figs 5 s 6) an elastomeric coupling (40) replaces the intermediate disc (14) and the eccentric pins (15).

Arms (41) secured to the second disc (16) include elastic hinges (42, 43) which allow the arms (41) to deflect normal to the plane of disc (1 6) whilst remaining rigid in the plane of disc (16). Arms (41) are connected to incidence control levers (25) by self-aligning bearings (44). Other details of this arrangement are as described above with references to Figs 1-4. This arrangement is potentially considerably lighter and cheaper to construct than the embodiment described with reference to Figs 1-4.

In another embodiment of the invention (Figs 7 and 8) a rotor (50) has secured thereto a rotor head (70) on which a number of attachments such as those shown at (71) each carries a rotor blade (72). A first disc (51) is mounted on an inner sleeve (52) which has an inner diameter greater than that of the rotor (50) and which is constrained (by means not shown) to rotate with the rotor (50). A second disc (53) is secured to an outer sleeve (54) which is slidably mounted on the inner sleeve (52). Collars (55, 56) are rotatably mounted on inner and outer sleeves (52, 54) respectively, and are constrained to move axially with the sleeves.An actuator (57) is connected to the collars (55, 56) such that its operation alters the axial separation of the collars and hence the separation of the first and second discs (51, 53). Actuators (58), of which one only is illustrated in Fig 7, operate at right angles to each other on the collar (56) to alter the axis of rotation of the inner sleeve (52) relative to an axis (59) of the rotor (50) in a manner analogous to the operation of actuators (32, 33) in Fig 4. A control star (60) (Fig 8) has, for each rotor blade (72), a control arm (61) mounted at the apex of an angle piece (62) having a leg secured to each of the discs (51, 53). Each control arm (61) has a connector (63) which lies substantially on a radius 90 displaced from the radius of the angle piece (62) to which the arm is attached.With this arrangement radial movement of the apex of the angle piece (62) results in circumferential movement of the connector (63). Each connector (63) is connected to an incidence control lever (64) (Fig 7). The connection may be by means as illustrated, of a fork end pin (65) slidably and rotatably mounted in the connector (63).

In use, with this embodiment of the invention, collective control of rotor blade (72) incidence is effected by operation of actuator (57), and cyclic control of the rotor blade (72) incidence is controlled by actuators (58), control being similar to that of the embodiments described above with reference to Figs 1-6.

It will be realised that many alternative embodiments of the invention will be possible. In particular details of the attachment of connectors (24, 63) to incidence control levers (25, 64) respectively may be varied considerably without affecting the scope of the invention.

Claims

1. A helicopter rotor blade incidence control unit including a rotor having an axis of rotation, rotor blade attachments at positions on the rotor fixed relative to the axis of rotation, two discs mounted on and arranged to rotate with the rotor, one of the discs having secured thereto, for each rotor blade attachment, a connector for connecting the disc to a rotor blade incidence control, means for manoeuvring the discs to change the relative circumferential positions of the connectors and the attachments, and means for manoeuvring the discs to displace an axis of rotation of the connectors relative to the axis of rotation of the rotor.

2. A helicoptor rotor blade incidence control unit as claimed in Claim 1 wherein the discs are formed from a composite material.

3. A helicopter rotor blade incidence control unit as claimed in Claim 2 wherein the composite material is carbon fibre reinforced plastic.

4. A helicopter rotor blade incidence control unit as claimed in any one of Claims 1-3 wherein a first of the two discs is constrained to rotate about the axis of rotation of the rotor, and the connectors are secured to a second of the discs which is driveably connected to the first disc but has its centre of rotation eccentrically moveable relative to the centre of the first disc.

5. A helicopter rotor blade incidence control unit as claimed in Claim 4 wherein the driving connection between the first and second discs includes an intermediate disc and eccentric pins.

6. A helicopter rotor blade incidence control unit as claimed in Claim 4 wherein the driving connection between the first and second discs is elastomeric.

7. A helicopter rotor blade incidence control unit as claimed in any one of claims 4-6 wherein the first disc is mounted on the rotor on helical splines.

8. A helicopter rotor blade incidence control unit as claimed in Claim 1 wherein a first disc is connected to a first sleeve which is driven by the rotor but has an axis of rotation moveable relative to the axis of rotation of the rotor, a second disc is secured to a second sleeve slidably mounted on the first sleeve, each disc having secured thereto, for each rotor blade, one leg of an angle piece at the apex of which is carried an arm having at its free end a connector, the arrangement being such that radial movement of the apex caused by relative axial movement of the discs causes circumferential movement of the connector.

9. A helicopter rotor blade incidence control unit substantially as herein described with reference to Figs 1-8.

10. A helicopter rotor having an incidence control unit as claimed in any one of Claims 1-9.

11. A helicopter having a rotor as claimed in Claim 10.