Helicopter rotor

Helicopter rotor on which each blade is connected in articulated manner to a center hub by means of a fork PA0 the vertical plane movement of which, at rotor speeds below a given set value, is limited by a pair of limit rocker arms located between the hub and a ring nut mounted in rotary manner on the fork PA0 and rendered angularly integral with the hub by means of a compass drive.

BACKGROUND OF THE INVENTION 
The present invention relates to a helicopter rotor. In particular, the 
present invention relates to an articulated rotor on which each blade is 
connected to a center hub on the rotor by means of a fork, in turn, 
connected in articulated manner to a center hub on the said rotor. 
On articulated rotors of the aforementioned type, each blade oscillates, in 
relation to the hub and about the said articulated joint, both vertically, 
due to lift and in a plane perpendicular to the hub plane, and 
horizontally in the hub plane, due to inertia and drag. Known rotors of 
the aforementioned type are generally provided with limiting devices for 
maintaining vertical and horizontal oscillation angles within a relatively 
limited range, when the speed of the rotor is below a given set value. 
In more detail, limiting devices are known to be employed comprising rocker 
arms mounted on the said fork or hub and designed to move, due to 
centrifugal force, between a normal idle position, wherein the said rocker 
arms are designed to cooperate with contact surfaces on the said hub or, 
respectively, on the said fork, for limiting the said oscillation, and an 
operating position wherein the blade is free to oscillate. 
The main drawback on articulated rotors with limiting devices of the 
aforementioned type is that, in addition to the said vertical and 
horizontal oscillation, the said articulated joint connecting the fork and 
hub also allows the blade to turn and change pitch about its own axis. As 
such pitch-change rotation obviously results in displacement of the said 
contact surfaces and the paths of the respective rocker arms, contact 
between the said rocker arms and respective contact surfaces is impaired, 
thus resulting in rapid wear and reduced efficiency of the said limiting 
devices. 
This is extremely dangerous, especially as regards vertical oscillation 
control, in that, whereas horizontal oscillation is kept under control at 
all times by means of hydraulic dampers between the blade and hub, 
low-speed vertical oscillation is generally limited solely by the said 
rocker arms, any inefficiency of which may result, especially during 
take-off and due to both wind and "ground effect", in a sharp upward sweep 
of the blades and consequent overturning of the helicopter. 
SUMMARY OF THE INVENTION 
The aim of the present invention is to provide a rotor, the structure of 
which is such as to guarantee, at least as regards the said vertical 
oscillation limiting device, perfect contact at all times between the said 
rocker arms and respective contact surfaces, regardless of the blade pitch 
involved. 
With this aim in view, according to the present invention, there is 
provided an articulated helicopter rotor comprising a drive shaft, a 
center hub fitted onto the said drive shaft, a number of blades extending 
substantially radially from and connected in articulated manner to the 
said hub, and a device for limiting oscillation of each blade in relation 
to the said hub in a direction substantially parallel with the axis of the 
said drive shaft, characterised by the fact that, for each blade, the said 
limiting device comprises a ring nut supported on the said blade in such a 
manner as to turn about its own axis parallel with the axis of the said 
blade, compass means extending between the said ring nut and the said hub 
for rendering the same angularly integral as regards rotation about the 
axis of the said ring nut, and rocker arm means located between the said 
hub and the said ring nut and turning in a plane substantially parallel 
with the axis of the said drive shaft.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 1 and 2 show a main helicopter rotor 1 comprising a substantially 
vertical drive shaft 2 the top end of which comes out externally through a 
hole 3 (FIG. 2) formed in fuselage 4 of the helicopter. 
Rotor 1 also comprises a hub 5 fitted onto the said top end of and coaxial 
with shaft 1, and a number of blades 6 (only one of which is shown) 
extending substantially radially outwards from hub 5 and each connected to 
hub 5 by means of a respective connecting device 7. 
Hub 5 comprises a tubular inner body 8 preferably made of metal and fitted 
onto shaft 2; an outer frame 9 preferably made of composite material and 
presenting a horizontal section substantially in the form of a regular 
polygon with rounded tips equal in number to blades 6; and a number of 
annular blending elements 10 each located between tubular body 8 and a 
respective rounded tip on frame 9. 
As shown in FIG. 2, the top and bottom ends of tubular body 8 present two 
annular flanges 11, each of which is furrowed by a number of grooves 12 
curving outwards and equal in number to blades 6, each of the said grooves 
12 housing a portion of a substantially rectangular-section strap 13 made 
of composite material and presenting a substantially circular horizontal 
section. 
Each circular strap 13 on top flange 11 is arranged facing a similar strap 
13 on bottom flange 11, and the straps in each pair of facing straps 13 
are rendered integral with each other, in such a manner as to define a 
respective annular element 10, as well as with adjacent annular elements 
10 and frame 9. The said frame 9 also consists of two straps 14 arranged 
one on top of the other and rendered integral with straps 13 of each 
annular element 10 by means of a composite material jacket 15, in such a 
maner as to define, at each rounded tip of frame 9, a bridge structure 16 
connected to connecting device 7 on respective blade 6. 
Each connecting device 7 comprises a substantially U-shaped fork 17 mounted 
with its concave side facing shaft 2. Fork 17 comprises a top arm 18 and a 
bottom arm 19 rendered integral at their respective outer ends by a root 
element 20, which, on its outward-facing side, presents a substantially 
horizontal cutout 21 defining, on element 20 itself, two arms 22 arranged 
one over the other and facing radially outwards in relation to shaft 2. 
Arms 22 each present two through axial holes, 23 and 24, and a cutout 25 
substantially parallel with cutout 21. Each connecting device 7 also 
comprises an adapting element 26 consisting of two opposed forks, 27 and 
28, the first housing the root of a respective blade 6 secured to the arms 
of fork 27 by means of two through bolts 29, and the second comprising two 
arms 30 arranged one over the other and each engaged in rotary and sliding 
manner inside a respective cutout 25, and each presenting a hole 31 
coaxial with hole 23. 
Coaxial holes 23 and 31 are fitted through with a pin 32, whereas hole 24 
houses a motor (not shown) cooperating in known manner with a drive (not 
shown) for turning respective blade 6 about the axis of hole 24, after 
first removing pin 32 housed inside holes 23 and 31. Adapting element 26 
and the said motor (not shown) provide, in known manner, for bending 
respective blade 6 along fuselage 4 and so enabling easy stowage of the 
helicopter in confined spaces, e.g. inside a ship. 
Each connecting device 7 is connected to respective bridge structure 16 by 
means of a wall 33 extending through the centre opening of respective 
annular element 10 and connected to the free inner ends of respective arms 
18 and 19 by means of two through bolts 34. 
Wall 33 presents a center hole 35 extending substantially radially in 
relation to shaft 2 and housing a ball joint 36, the ball 37 of which is 
mounted on the free end of an appendix 38. 
On the end opposite the one fitted with ball 37, appendix 38 presents a 
flange 40 for connecting appendix 38 to a flange 41 located in a plane 
substantially parallel with the axis of shaft 2 and integral with the 
outer edge of flanges 11. 
As shown in FIG. 1, wall 33 is provided with a lateral fork 42 connecting 
the end of a drive 43 controlling the pitch change of respective blade 6, 
and presents, on the side facing shaft 2, two appendices 44 designed to 
cooperate, in known manner, with the ends of respective rocker arms 45 and 
46 supported on appendix 38 and constituting, together with appendices 44, 
a device for limiting movement of respective blade 6 in relation to hub 5 
in a substantially horizontal plane perpendicular to the axis of shaft 2. 
The surface of wall 33 facing respective root element 20 is connected to 
the inner shoe 47 of a spherical elastomer bearing 48, the outer shoe 49 
of which is arranged substantially contacting respective bridge structure 
16, and is connected on its top and bottom ends, by means of screws 50, to 
the free ends of two arms, 51 and 52, on a U-shaped bracket 53 fitted onto 
the said bridge structure 16 with its concave side facing shaft 2 and its 
root element 54, by which arms 51 and 52 are joined, contacting the outer 
surface of bridge structure 16. 
Between each bracket 53 and fork 17 on respective connecting device 7, a 
device 55 is inserted for limiting oscillation of blade 6 in relation to 
hub 5 in a substantially vertical plane parallel with the axis of shaft 2. 
As shown, particularly in Fig.s 3 and 4, limiting device 55 comprises a 
ring nut 56 with its axis substantially parallel with that of respective 
blade 6 and mounted on fork 17 so as to turn about its own axis and in 
angularly fixed manner in relation to hub 5; a slide 57 mounted so as to 
slide along respective bridge structure 16 by virtue of a compass drive 58 
extending between slide 57 and ring nut 56; and two rocker arms, 59 and 
60, designed to turn in a plane substantially parallel with the axis of 
shaft 2, and located between slide 57 and ring nut 56 for limiting 
downward and upward displacement respectively of ring nut 56 in relation 
to slide 57, when the speed of rotor 1 is below a given preset value. In 
more detail, between the two arms, 18 and 19, of each fork 17, there 
extends a crosswise wall 61 having connecting flanges 62, on its opposite 
ends, for its own connection to arms 18 and 19. Wall 61 is located in a 
plane substantially perpendicular to the axis of respective appendix 38, 
and presents a center through hole 63 the surface of which defines a 
tapered annular seat 64 flaring towards shaft 2. Seat 64 constitutes a 
supporting and sliding seat for ring nut 56 the outer surface of which 
comprises a truncated-cone portion 65 contacting seat 64, and a 
cylindrical portion 66 extending from the smaller end of portion 65 in the 
direction of respective blade 6 and through hole 63. 
Ring nut 56 is secured axially inside hole 63 by means of a retaining ring 
67, and is provided, on the side facing blade 6, with a fork 68 for its 
own connection to one end of drive 58. 
As shown, particularly in FIG. 5, compass drive 58 lies in a plane 
substantially radial in relation to hub 5, and comprises a crank 69 the 
small end of which is inserted between the arms of fork 68 and hinged to 
the said arms by means of a through pin 70 perpendicular to the axis of 
ring nut 56. Drive 58 also comprises a connecting rod 71 consisting of two 
opposed forks, 72 and 73, the first receiving the big end of crank 69 and 
being hinged to the same by means of a through pin 74 parallel with pin 
70, and the second enclosing slide 57 and being hinged to the same by 
means of a through pin 75 parallel with pin 74. As shown, particularly in 
FIGS. 4 and 6, slide 57 is substantially U-shaped and fitted in 
crosswise-sliding manner onto bracket 53. Slide 57 comprises an end plate 
76 the inner surface of which defines a wedge 77 extending towards shaft 2 
and engaged in sliding manner inside a groove 78 formed on the outer 
surface of element 54 on bracket 53 and extending in a plane substantially 
perpendicular to the axis of shaft 2. From the top and bottom ends 
respectively of plate 76, there extend, towards shaft 2, two arms, 79 and 
80, presenting a trapezoidal plan and being tapered towards shaft 2. Close 
to its free end, each arm, 79 and 80, presents an inner groove 81 
extending over an arc of a circle with its center on the axis of shaft 2, 
and engaged in sliding manner by a respective curved guide rib 82 
extending in a plane substantially crosswise in relation to the axis of 
shaft 2, from the arm 51 or 52 of bracket 53 facing the said groove 81. As 
shown in FIG. 1, the arc over which extends each rib 82 is roughly twice 
the arc over which extends respective groove 81. 
On the side facing respective blade 6, slide 57 presents a nose 83 with a 
through hole 84 engaged by pin 75 the opposite ends of which project from 
hole 84 and are fitted respectively with a first arm 85 and a second arm 
86 of rocker arm 59. Arm 85 is located on top and comprises a head 87 
designed to cooperate with a supporting surface 88 formed on ring nut 56 
for supporting, when idle, respective blade 6 on hub 5, and to move 
towards shaft 2, releasing contact with surface 88, as a result of rocker 
arm 59 being rotated by a counterweight 89, connected to the end of bottom 
arm 86, when the speed of rotor 1 exceeds a given preset value. The said 
rocker arm 59 is rotated against the action exerted by a spring 90, a 
center portion of which is wound about pin 75, and the ends of which 
engage a slot 91 formed longitudinally along the top surface of nose 83 
and communicating with hole 84. At the bottom, nose 83 presents a 
supporting surface 92 designed to cooperate with rocker arm 60 for 
limiting, when idle, upward movement of respective blade 6. 
In actual use, the slightest movement of blade 6 in the hub 5 plane, i.e. 
crosswise in relation to the axis of shaft 2, is transmitted by fork 17 to 
slide 57 via drive 58, thus causing slide 57 to slide along respective 
bridge structure 16. Consequently, displacement of blade 6 in the hub 5 
plane causes no relative displacement of ring nut 56 and slide 57. 
Furthermore, the slightest rotation of blade 6, and consequently also of 
respective fork 17, about their respective axes, subsequent to a change in 
pitch of blade 6 imparted via drive 43, causes relative rotation of ring 
nut 56 and respective supporting wall 61; the said supporting wall 61 
rotating in relation to ring nut 56, and the said ring nut 56 being kept 
angularly fixed in relaton to slide 57 by drive 58. 
In other words, the only relative movement of each ring nut 56 and 
respective slide 57 is an oscillating movement in a plane perpendicular to 
the hub 5 plane and substantially through the axis of shaft 2. For rotor 1 
speeds below a given preset value, such oscillating movement is limited by 
rocker arms 59 and 60 which, in the absence of any relative movement of 
ring nut 56 and slide 57, other than the said oscillating movement, are 
perfectly located, at all times, facing respective supporting surfaces 88 
and 92. 
In the variation shown in Fig.s 7, 8 and 9, ring nut 56 in the embodiment 
shown in Fig.s 1 to 6 is replaced by a ring nut 93 the outer surface of 
which is substantially identical to that of ring nut 56 and is indicated 
using the same numbering system. Like ring nut 56, ring nut 93 also mates 
in rotary and sliding manner with taper seat 64 formed on wall 61, and 
presents, on the side facing hub 5, a bottom fork 94 to which rocker arm 
60 is connected in rotary manner by means of pin 95 and spring 96. Unlike 
ring nut 56, ring nut 93 presents a substantially radial appendix 97 
extending towards hub 5, over supporting surface 88. Appendix 97 presents 
a crosswise through hole 98 and engages an end fork 99 on a crank 100 
hinged to appendix 97 by means of a pin 101 extending through hole 98. 
Crank 100 forms part of a compass drive 102 also comprising a connecting 
rod 103 one end of which consists of a fork 104 connected to connecting 
rod 103 by a pin 105 engaged in a hole 106 formed through crank 100. As 
shown in Fig.s 7 and 8, connecting rod 103 consists substantially of a 
substantially trapezoidal, flat plate 107 from the opposite ends of the 
longer side of which extend the arms of fork 104, and to the shorter side 
of which, facing hub 5, slide 108 is connected integral; the said slide 
108 being mounted in sliding manner on a rail 109 supported on hub 5 and 
extending in a plane substantially crosswise in relation to the axis of 
shaft 2. Slide 108 consists of two arms 110 arranged one over the other 
and extending from the shorter side of plate 107 towards shaft 2. The said 
two arms 110 define a substantially rectangular-section passage 111 
engaged in sliding manner by rail 109. The said rail 109 comprises a rod 
112 having a curved longitudinal axis with its centre substantially 
located on the axis of shaft 2. Rod 112 presents a rectangular section of 
such size as to enable rod 112 to engage, in sliding manner, passage 111 
on slide 108, but not to turn inside the same. 
Rod 112 is provided, on its opposite ends, with two cylindrical pins 113 
coaxial with each other and each engaging in rotary manner, with a 
frictionfree bushing 114 inbetween, a hole 115 on a respective bracket 116 
connected integral with the top surface of arm 51 on bracket 53. 
Unlike the embodiment described with reference to FIGS. 1 to 6, the 
variation shown in FIGS. 7 to 9 has no slide 57 and, as shown, 
particularly in FIG. 9, bracket 53 presents an appendix 117 extending from 
its own root element 54 towards respective blade 6 and having a curved 
bottom surface constituting a supporting surface 118 (FIG. 7) for rocker 
arm 60. 
By means of a cutout 119 parallel with the axis of shaft 2, appendix 117 is 
divided into two arms 120 having crosswise through holes 121 coaxial with 
each other and engaged in rotary manner, against the action of return 
spring 122, by the opposite ends of pin 123. 
Pin 123 constitutes the fulcrum of a rocker arm 124 corresponding to rocker 
arm 59 in FIGS. 1 to 6 and comprising two counterweights 125 connected 
integral, by means of respective arms 126, to the opposite ends of pin 123 
projecting from holes 121. Rocker arm 124 also comprises a head 127 
connected to pin 123 by a centre arm 128, extending through cutout 119, 
and having a curved surface 129 substantially coaxial with shaft 2 and 
designed to cooperate with supporting surface 88. 
Both surfaces 129 and 118 extend over arcs substantially similar to the arc 
of rod 112, and greater than the arcs over which extend surface 88 and the 
end of rocker arm 60. Operation of the variation shown in FIGS. 7 to 9 is 
as already described with reference to FIGS. 1 to 6, the only difference 
being that the variation shown in FIGS. 7 to 9 has no slide 57. 
Consequently, between surfaces 88 and 118 and respective rocker arms 124 
and 60, relative movement may occur in a plane perpendicular to the axis 
of shaft 2, such movement being due to inertia and drag and being 
compensated by the size, parallel to the said plane, of surfaces 129 and 
118.