GB2302074A

GB2302074A - Helicopter rotor blade to hub connection

Info

Publication number: GB2302074A
Application number: GB9611539A
Authority: GB
Inventors: Santino Pancotti
Original assignee: Agusta SpA
Current assignee: Agusta SpA
Priority date: 1995-06-09
Filing date: 1996-06-03
Publication date: 1997-01-08
Anticipated expiration: 2016-06-03
Also published as: ITTO950478A0; GB9611539D0; JP2007050891A; IT1282114B1; FR2735094B1; FR2735094A1; JPH0999900A; JP4005158B2; GB2302074B; DE19622130A1; ITTO950478A1; DE19622130B4

Description

HELICOPTER ROTOR 2302074 The present invention relates to a helicopter

rotor.

More specifically, the present invention relates to an articulated rotor wherein each blade is connected to the central hub of the rotor by a fork in turn connected in articulated manner to the hub.

In articulated rotors of the aforementioned type, each blade oscillates, in relation to the hub and about the articulated joint, both vertically, in a plane perpendicular to that of the hub due to aerodynamic lift, and horizontally in the hub plane due to inertia and aerodynamic drag.

Known rotors of the above type and as described for example in US-4,808, 075, normally present a number of limiting devices for respectively maintaining the vertical and horizontal oscillation angles within relatively limited values when the angular speed of the rotor is below a given value.

Each of such devices normally comprises rocker arms fitted to the fork or hub and movable by centrifugal force between a normal idle position, wherein the rocker arms cooperate with stop surfaces on the hub or fork to limit oscillation, and an operating position wherein the blade is free to oscillate.

As regrds vertical oscillation limiting devices, i.e. for limiting oscillation in a plane crosswise to that of the hub, to ensure the trajectories of the rocker arms and respective stop surfaces coincide following pitch-change rotation of each fork in relation to the hub, US-4, 808,075 provides for connecting the rocker arms or stop surf aces to each f ork by means of a rotary supporting element made angularly integral with the hub by a transmission and f itted to the f ork so as to rotate about an axis extending substantially radially in relation to the hub.

Though normally effective, known limiting devices of the above type present several drawbacks in the event the blades are connected to the forks by respective adapting elements enabling them to be folded substantially at right angles to the forks. Which drawbacks are further aggravated in proportion to the length of the blades. That is, both when and after folding the blades, the strain generated by the weight of the blades and by any external stress on them (e. g. due to a gust of wind) tends to jam the rotary supporting elements in relation to the respective forks and/or damage the transmissions angularly connecting the supporting elements to the hub.

Moreover, known limiting devices of the above type only provide for limiting movement of the blades in the vertical plane as opposed to any direction, and must invariably be connected to further devices for limiting movement of the blades in the horizontal plane.

It is an object of the present invention to provide a rotor featuring straightforward, reliable oscillation limiting devices, each designed to maintain the oscillation angles of a respective blade, in any direction in relation to the hub, within relatively limited values when the angular speed of the rotor is below a given value.

According to the present invention, there is provided an articulated helicopter rotor comprising a central hub; a number of blades extending in a substantially radial direction from and connected in articulated manner to the hub; and a limiting assembly for limiting the transverse oscillation of each blade in relation to the hub; characterized in that said limiting assembly comprises, for each blade, a centrifugal bolt device extending in said substantially radial direction in relation to the hub and in turn comprising a seat portion and a bolt portion facing each other in said radial direction; said two portions being movable in relation to each other to and from a mutually engaged position wherein they limit within predetermined values any transverse movement of the respective blade in relation to the hub.

4 - According to a preferred embodiment of the above rotor, said two portions are respectively integral with the hub and the respective blade; said bolt portion engaging said seat portion to substantially rigidly connect the respective blade to the hub at least in a direction crosswise to said radial direction.

Preferably, one of said two portions is located outwards of the other in said radial direction; said outer portion presenting elastic means, and being movable,. in opposition to the elastic means and in said radial direction, from said mutually engaged position to a release position wherein the respective blade is free to oscillate transversely in relation to the hub in any direction.

A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure I shows a schematic axial section of a first preferred embodiment of the rotor according to the present invention; Figure 2 shows a larger-scale section of a detail in Figure 1; Figure 3 shows a front view of a detail in Figure 2; Figure 4 shows a schematic axial section of a second preferred embodiment of the rotor according to the present invention; Figure 5 shows a larger-scale section of a detail in Figure 4; Figure 6 shows a section along line VI-VI in Figure 5.

Number 1 in Figure 1 indicates a main helicopter rotor comprising an annular hub 2 fitted to the top end of the drive shaft (not shown) of a helicopter (not shown) so as to rotate about its axis 3.

Rotor 1 also comprises a number of blades 4 (only one shown) extending outwards from hub 2 in a substantially radial direction 4a, and each connected to hub 2 by a respective connecting device 5.

Hub 2 is substantially of the type described in US Patent n. 4,808,075, to which full reference is made herein in the interest of full disclosure, and comprises an annular inner body 6 preferably made of metal and fitted to the drive shaft, and an outer frame 7 preferably made of composite material as described in US-4,808,075, and which is connected to the outer periphery of body 6 by a number of spokes 8. Spokes 8 define, on frame 7, a succession of bridge elements 9, each of which defines, with body 6 and a respective pair of adjacent spokes 8, a respective annular structure 10 connected to a respective blade 4 by a respective connecting device 5.

Each connecting device 5 comprises a substantially U-shaped fork 11 mounted with its concavity facing body 6, and which in turn comprises a top arm 12 and a bottom arm 13 made integral with each other, at the outward end in relation to body 6, by a root element 14 with a substantially horizontal, outer recess 15 defining, in element 14, two superimposed forks 16 and 17. Forks 16 and 17 face radially outwards in direction 4a in relation to body 6, and each presents two through holes 18 (only one shown) substantially parallel to axis 3, located side by side at the same distance from axis 3, and each coaxial with a respective hole 18 in the other fork 17, 16.

Each connecting device 5 also comprises an adapting element 19 comprising two integral, opposed forks 20 and 21. Fork 20, with its concavity facing outwards, houses the root of a respective blade 4 fitted to the arms of fork 20 by two through bolts 22 (only shown) substantially parallel to axis 3; and fork with its concavity facing superimposed arms 23, each axially-sliding manner inside and presenting a pair of respective holes 18.

The two pairs of coaxial holes 18 of forks 16 and 17 define, together with respective holes 24, two holes 25 (only one shown in Figure 1) presenting respective axes 26 substantially parallel to axis 3, and located side by side at the same distance from axis 3. Holes 25 house in known manner a powered device 27 for connecting relative adapting element 19 in known manner to root element 14 of relative fork 11, and which is operated to one 21, body 6, comprises two engaged in rotary and a respective fork 16, 17, holes 24 coaxial with fold element 19 and respective blade 4 squarely in relation to respective fork 11, about one of relative axes 26 and in a substantially horizontal plane. For which purpose, device 27 comprises a known motor 28 supported in a fixed position by root element 14, inside recess 15, and presenting two opposed output shafts 29 engaging the opposite ends of the hole 25 about whose axis 26 respective blade 4 is folded squarely, and each of which is fitted inside relative hole 24. Device 27 also comprises a withdrawable pin (not shown) fitted through the other hole 25.

Adapting element 19 and relative device 27 provide, in known manner, for folding relative blade 4 along the fuselage (not shown) of the helicopter, to enable compact stowage, e.g. in the hold of a ship.

Each connecting device 5 is connected to respective bridge element 9 by a wall 30 extending through the central opening of relative annular structure 10, and connected to the free inner ends of relative arms 12 and 13 by two through bolts 31 (only one shown).

Wall 30 is connected in known manner (not shown) to a pitch-change device (not shown), and presents a central hole 32 extending in a substantially radial direction in relation to axis 3 and housing a ball joint 33, the ball 34 of which is fitted to the free end of an appendix 35 extending radially outwards from hub 2 and presenting, at the other end, a flange 36 connected to the outer periphery of body 6 of hub 2.

The surface of wall 30 facing root element 14 is fitted with the inner shoe 37 of an elastomeric bearing 38, the outer shoe 39 of which substantially contacts bridge element 9 and is connected, at its top and bottom ends and by means of screws 40, to the free ends of two arms 41 of a U-shaped bracket 42. Bracket 42 is f itted to bridge element 9 with its concavity f acing axis 3, and with its root element 43, by which arms 41 are joined, contacting the outer surface of bridge element 9.

Between each bridge element 9 and relative f ork 11, there is provided a limiting assembly 44 for limiting transverse oscillation of blade 4 in relation to hub 2 when this is rotated at relatively low speed or is stationary.

Assembly 44 comprises a centrifugal bolt device 45 located between two parts movable in relation to each other: the f irst comprising root element 43 of bracket 42; and the second comprising a wall 46 housed inside fork 11 and crosswise to arms 12, 13 and direction 4a, f for connecting it to the inner surf ace of arms 12 and 13. Wall 46 lies in a plane substantially parallel to the plane defined by axes 26 of respective holes 25, and presents a central through hole 48.

In the Figure 1 embodiment, and as shown more clearly in Figures 2 and 3, device 45 (indicated 45a) and presenting flanges 47 at its opposite ends comprises a seat portion 49 in a fixed position in relation to hub 2; and a bolt portion 50 movable radially in relation to hub 2 between an engaged, intermediate, and release position wherein it respectively engages, partly engages, and disengages seat portion 49.

In the Figure 4 embodiment, and as shown more clearly in Figures 5 and 6, device 45 (indicated 45b) comprises a bolt portion 51 in a fixed position in relation. to hub 2; and a seat portion 52 movable radially in relation to hub 2 between an engaged, intermediate, and release position wherein it respectively engages, partly engages, and disengages bolt portion 51.

As shown particularly in Figure 2, seat portion 49 of device 45a is formed in root element 43 of bracket 42, and comprises a cylindrical cavity 53 with its concavity facing wall 46, and presenting an axis 54 substantially radial in relation to hub 2; and a further cylindrical cavity 55 formed in element 43, in the bottom surface of cavity 53, and presenting an axis 56 parallel to and shifted downwards in relation to axis 54. Bolt portion 50 of device 45a comprises a cylindrical jacket 57 fitted coaxially through hole 48 in wall 46; and a bolt 58 defined by a cylindrical sleeve 59 fitted in axially-sliding manner through jacket 57, and presenting, at one end, a tubular head 60 of a diameter smaller than the inside diameter of cavity - 53, and of a thickness approximately equal to but no greater than the minimum distance between the inner lateral surface of cavity.55 and the inner lateral surface of cavity 53. Head 60 extends towards bracket 42 from a transverse end wall 61 of sleeve 59, which, at the opposite end to wall 61, presents an annular outer flange 62 which is pushed on to the corresponding end of jacket 57 by a spring 63 coaxial with sleeve 59 and compressed between wall 61 and a cup-shaped cover 64 fitted to the opposite surface of wall 46 to that facing bracket 42, to close the end of sleeve 59 facing respective blade 4. Head 60 is movable, in opposition to spring 63, from an engaged position, wherein it engages cavity 53 and flange 62 contacts the relative end of jacket 57, to a release position, wherein head 60 is completely outside cavity 53.

Bolt portion 50 of device 45a also comprises a further bolt 65 in turn comprising a head 66 of the same length as and fitted in sliding manner inside head 60; and a tubular rod 67 which engages in sliding manner an axial hole 68 formed through wall 61, and is fitted integral with a tubular spacer 69 cooperating with the surface of wall 61 facing blade 4, to limit the travel of head 66 - in opposition to a spring 70 fitted inside rod 67 and compressed between head 66 and cover 64 from an extracted position, wherein head 66 projects outwards of head 60 by a distance approximately equal to but no greater than the depth of cavity 55, to a withdrawn position, wherein head 66 is housed completely inside head 60 and rests on wall 61. Head 66 presents a diameter approximately equal to but no greater than the inside diameter of cavity 55, and spring 70 is less rigid than spring 63.

In actual use, over and above a given angular speed of hub 2, the centrifugal force acting on bolts 58, 65 is such as to overcome the resistance of respective springs 63, 70 and maintain bolt 58 in the release position, wherein head 60 cavity 53, and bolt 65 in the wherein head 66 is housed entirely With bolts 58 and 65 in the positions respectively, blade 4 is any direction in relation to hub joint 33 and bearing 38.

In the event the angular speed of hub 2 falls below said given value, the force exerted by spring 63 is sufficient to push bolt 58 into the extracted position engaging cavity 53, in which case, head 60 tends to move transversely into cavity 53 to drastically limit transverse oscillation of blade 4 in relation to hub 2. Moreover, even if the centrifugal force acting on bolt 65 falls below the thrust exerted on it by spring 70, head 66 is prevented from coming out of head 60 by encountering the bottom surface of cavity 53. Only when rotor 1 is arrested does head 60 rest on the lowest point of the lateral surface of cavity 53, thus aligning is completely outside withdrawn position, inside head 60. release and withdrawn free to oscillate in 2, in opposition to head 66 and cavity 55 to permit head 66 to move into the extracted position inside cavity 55, and so converting articulated rotor 1 into a semi-rigid rotor. In fact, when device 45a is closed, blade 4 no longer has any freedom of movement in relation to hub 2, other than rotating about its axis in opposition to bearing 38.

Device 45a therefore not only provides, alone and with the utmost reliability, for preventing blade 4 from oscillating in relation to hub 2 in any direction crosswise to the blade, but also for rendering rotor 1 sufficiently rigid to safely fold blade 4 in any weather conditions.

According to the embodiment shown in Figure 4 and particularly in Figure 5, bolt portion 51 of device 45b is formed on root element 43 of bracket 42, and comprises an appendix 71 extending from root element 43 towards respective blade 4 and presenting an axis 72 substantially radial in relation to hub 2. Seat portion 52 of device 45b comprises a cylindrical jacket 73 fitted coaxially through hole 48 in wall 46; and a cylindrical sleeve 74 fitted in axially-sliding manner through jacket 73, and presenting an inner intermediate transverse wall 75 dividing sleeve 74 internally into two opposed cavities 76 and 77. Cavity 76, facing appendix 71, is defined laterally (Figure 6) by a cylindrical surface 78 larger in diameter than appendix 71 and presenting, at a top portion, an axial groove 79 of a diameter approximately equal to but no smaller than - 13 the diameter of appendix 71. Sleeve 74 presents, at the end facing bracket 42, an annular flange 80, and, at the opposite end, a retaining ring 81 pushed on to the corresponding end of jacket 73 by a spring 82 housed partly inside cavity 77 and compressed between wall 75 and a cup- shaped cover 83 fitted to the opposite surface of wall 46 to that facing bracket 42, to close the end of sleeve 74 facing respective blade 4. Sleeve 74 is movable, in opposition to spring 82, from an engaged position., wherein cavity 76 houses appendix 7# and ring 81 contacts the relative end of jacket 73, to a release position, wherein appendix 71 is completely outside cavity 76.

Seat portion 52 also comprises a variable number of annular counterweights 84 fitted on to a threaded pin 85 extending along cavity 77 from wall 75, and which are locked on to pin 85 by a nut 86 to regulate the centrifugal force acting on sleeve 74 at a given angular speed of hub 2.

Device 45b operates in substantially the same way as device 45a, and therefore requires no further description. The only substantial difference in the operation of the two devices is that, whereas device 45a prevents any transverse oscillation of blade 4 in relation to hub 2 when rotor 1 is stationary, device 45b prevents blade 4 from oscillating in the hub 2 plane, but allows it a relatively small amount of oscillation in a vertical plane crosswise to the hub 2 plane, to reduce any stress transmitted by blade 4 to respective bridge element 9 and hence to hub 2 when rotor 1 is stationary.

Claims

1) An articulated helicopter rotor comprising a central hub; a number of blades extending in a substantially radial direction from and connected in articulated manner to the hub; and a limiting assembly for limiting the transverse oscillation of each blade in relation to the hub; characterized in that said limiting assembly comprises, for each blade, a centrifugal bolt device extending in said substantially radial direction in relation to the hub and in turn comprising a seat portion and a bolt portion facing each other in said radial direction; said two portions being movable in relation to each other to and from a mutually engaged position wherein they limit within predetermined values any transverse movement of the respective blade in relation to the hub.

2) A rotor as claimed in Claim 1, characterized in that said two portions are respectively integral with the hub and the respective blade; said bolt portion engaging said seat portion to substantially rigidly connect the respective blade to the hub at least in a direction crosswise to said radial direction.

3) A rotor as claimed in Claim 1 or 2, characterized in that one of said two portions is located outwards of the other in said radial direction; said outer portion presenting elastic means, and being movable, in opposition to the elastic means and in said 16 - radial direction, from said mutually engaged position to a release position wherein the respective blade is f ree to oscillate transversely in relation to the hub in any direction.

4) A rotor as claimed in Claim 3, characterized in that it comprises, for each said blade, a fork connecting the blade to the hub; the fork comprising two arms respectively above and below the hub; the relative said limiting assembly being located between said two arms; the relative said outer portion being integral with the fork; and the other relative said portion being an inner portion and being integral with the hub.

5) A rotor as claimed in Claim 4, characterized in that each said f ork comprises a wall extending between said two arms and crosswise to the respective said blade; said transverse wall supporting the relative said outer portion.

6) A rotor as claimed in any one of the foregoing Claims from 3 to 5, characterized in that said seat portion is an inner portion in said radial direction and in relation to the relative outer portion, and comprises a f irst cavity formed on the hub, with its concavity facing outwards and substantially in said radial direction, and of a given inside transverse dimension; said outer portion comprising a first bolt fitted in axially-sliding manner through said transverse wall and substantially in said radial direction, and first elastic means for pushing the first bolt towards said f irst cavity; the first bolt presenting, on the said facing said first cavity, a head of a smaller transverse dimension than the inside transverse dimension of the first cavity.

7) A rotor as claimed in Claim 6, characterized in that said inner portion also comprises a second cavity formed through the bottom surface of the relative first cavity and presenting a given section; the head of the first bolt being tubular; said outer portion comprising a second bolt fitted in axially-sliding manner along the first bolt and along said tubular head, and second elastic means for pushing the second bolt towards said second cavity; and the second bolt presenting, on the side facing said second cavity, a head of a section approximately equal to but no larger than the section of the second cavity.

8) A rotor as claimed in Claim 7, characterized in that the first and second elastic means present a first and different second rigidity; the second rigidity being less than the first.

9) A rotor as claimed in Claim 7 or 8, characterized in that said tubular head is of such a thickness that, when it is positioned, in use, contacting an inner lateral surface of the first cavity by virtue of the weight of the relative blade, the second bolt is positioned substantially coaxial with the second cavity.

10) A rotor as claimed in any one of the foregoing Claims from 3 to 5, characterized in that said bolt portion is an inner portion comprising an appendix of a given transverse dimension, integral with the hub, and extending from the hub substantially in said radial direction; said outer portion comprising a movable element fitted in axially-sliding manner through said transverse wall and substantially in said radial direction, and elastic means for pushing the movable element towards said appendix; the movable element presenting, on the side facing said appendix, an axial cavity with its concavity facing said appendix substantially in said radial direction, and of an inside transverse dimension larger than the transverse dimension of said appendix.

11) A rotor as claimed in Claim 10, characterized in that the movable element presents an annular flange extending outwards from the end of the movable element facing said appendix.

12) A rotor as claimed in Claim 10 or 11, characterized in that said cavity presents an upper axial groove of a transverse dimension approximately equal to but no smaller than the transverse dimension of said appendix.

13) A helicopter rotor, substantially as described and illustrated herein with reference to the accompanying drawings.