Note: Descriptions are shown in the official language in which they were submitted.
-` 1059097
This is a division of copending Canadian patent
application Serial No. 226, 470 which was filed 7 May 1975.
BACKGROUND OF TI~E INVENTION
The prcsent invention relates to mounting structurcs
for the rotor blades of a rotary wing aircraft and more
particularly to a coupling system providing pitch adjustments
of the blade and providing a redundant load path effective
upon failure of the primary centrifugal load path.
It is conventional to attach the main rotor blades
of a rotary wing aircraft to the mast by means of grip-yoke
assemblies. These grip-yoke assemblies have elastomeric
bearings for allowing relative rotational movement between
the grip and yoke members while maintaining axial alignment
between these members. Such assemblies utilize conventional
tension strap and fittings or elastomeric thrust pads to
transfer the centrifugal loads between the members. Since
centrifugal blade loads are quite high, and since the main
rotor blades provide essential lift forces for rotary wing
aircraft, failure in the cen~rifugal load carrying system
can create disastrous results.
The present invention is directed to an improved
centrifugal load carrying system which provides a redundant
centrifugal load path to allow continued operation of the
aircraft if the primary centrifugal load carrying system
fails.
More particularly, in the invention, a redundant
centrifugal load structure is provided with a yoke structure
connected to the hub of the rotor and a grip attached to the
blade. The grip encloses the yoke and is held in radial
` 105909'7
alignment therewith by elastomeric radial bearings. A conven-
tional tension strap or elastomeric thrust pad is attached
between an inboard strap fitting on the inboard end of the
yoke and an outboard strap fitting on the grip. A thrust
bearing is mounted on the inboard end of the yoke and a
transverse member with a corresponding bearing surface is
provided on the grip inboard of the thrust bearing for
engagement therewith upon failure of the primary thrust support
system. In another embodiment, a bearing surface is formed
on the outboard side of the outboard strap fitting and a thrust
bearing is attached to the yoke outboard of the outboard strap
fitting for contact upon failure of the primary centrifugal
load carrying system.
In accordance with an apect of the present invention
there is provided in combination, means for connecting a
main helicopter blade to a rotor having a yoke connected
to the rotor, a grip enclosing the yoke and connected to
the blade, a strap assembly connecting the grip and yoke,
the improvement which comprises a tranverse member on said
grip, a portion of said yoke outboard of said transverse
member normally free of centrifugal forces on said grip
for contacting said transverse member upon outward
translation of said grip resulting from failure of said
strap thereby retaining said yoke in said grip upon
failure of said strap.
The present invention taken in conjunction with
the invention disclosed in copending Canadian patent application
Serial No. 226,470 which was filed on 7 May 1975, which will
be described in detail hereinbelow with the air of the
accompanying drawings which illustrate various embodiments:
1059097
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE l is a top perspective view illustrating the
rotor, grip-yoke assembly and blade of a helicopter;
FIG11RE 2 is an enlarged perspective view partially
in vertical section;
FIGURE 3 (appearing on the same sheet of drawings as
fig. l) is a vertical section of the device taken along lines
3-3 of Figure l, looking in the direction of the arrows;
FIGURE 4 is a section similar to Figure 3 illustrating
the redundant support structure in operation; and
FIGURES 5 and 6 are sections similar to Figure 3
illustrating alternative embodiments.
I 1059097
B2859 ¦ DESCRI~TI0~ 0~ ~llr: P~ R~D Erl~OnI~l~NTS
¦ Referring now to the Drawings wllerein like reerence
¦ cllaracters designate like or corresponding parts througllout
I the several vie~s, there is illustrated in Figure 1 a grip-
¦ yoke assembly for mounting a main rotor blade 10 to the
màin rotor mast 12 of the helicopter aircraft. A hub 14
mounted on the upper end of mast 12 is connected to a yoke
16 by means of bearing mountings 18. Yoke 16 extends to
. either side of main rotor mast 12. Each side of yoke 16
is rotatably attached to a grip member 20.
Grip member 20 is provided with four tangs 22. Bolts
24 are used to attach the inboard end of blade 10 to tangs
22. A pitch horn 26 extends from the trailing side of grip
. 20 and is attached to a control tube 28 for controlling the
pitch of blade 10.
Figure 2 illustrates in detail the primary centrifugal
load supporting system interconnecting yoke 16 and grip 20
to allow pitch rotation of blade 10. Grip 20 is provided
with a longitudinally extending chamber 30 in which is ~ounted
yoke 16. Yoke 16 has inboard and outboard clearance openings
32 and 34, respectively, extending completely therethrough.
An axially extending chamber 36 is formed in the yoke 16
between openings 32 and 34. Chamber 36 forms a covering for
. the strap assembly of the primary centrifugal load supporting
system.
1059097
B2859 ¦ An inboard bearing fitting ~8 is fixed to grip 20
¦ at the inboard cnd thereof. Fitting 38 extends through
¦ opening 32 and across the inboard ends of chambers 30 and
¦ 36. Fitting 38 is fixed in place by bolts 40 on grip 20.
¦ Fitting 38 is bonded to the exterior cylindrical surface
of an elastomeric bearing 42. Bearing 42 is a conventional
elastomeric bearing formed from alternating concentric
cylindrical members of elastomer and metallic materials
bonded together. Fitting 38 has a dust seal cap 44 to
protect bearing 42.
Inboard strap fitting 50 has a cylindrical portion
52 bonded to the interior cylindrical surface of elastomeric
bearing 42. Strap fitting 50 has a conical portion 54
extending between portion 52 and a large cylindrical portion
56. Portion 56 of fitting 50 is of a sîze to fit into an
annular groove 58 formed at the inboard end of chamber 36.
A chamber 60 is formed in the interior of cylindrical
portion 56. Radially extending aligned bores 62 extend
through portion 56. A cylindrical inboard strap spool 64
is of a size to fit into chamber 60. A central bore 66
extends through the spool 64 for alignment with bores 62.
An inboard strap pin 68 is inserted through bores 62 and
66 to fix spool 64 in place within chamber 60.
Groove 58 has a shoulder 70 against which fitting 50
rests when the primary load carrying system is loaded. In
this manner, fitting 50 is attached at one end to yoke 16
1059097
~2859 ¦ and has its othcr end supportcd by bearing 42. Bearing 42 is
¦ in turn attached to grip 20 to maintain axial alignment
between the grip and yoke. Limited rotation between grip 20
and yoke 16 for blade pitch adjustments is provided by
distortion of bearing 42.
` A similar bearing structure is positioned at the
outboard end of chamber 30. An outboard bearing support
fitting 80 is attached to grip 20 to extend across the outboard
ends of chambers 30 and 36. Fasteners 82 extend through
grip 20 and fix fitting 80 in place. An elastomeric bearing
84 similar in construction to bearing 42 has its exterior
cylindrical surface bonded to fitting 80.
According to one aspect of the present invention,
an improved radial bearing support and combined redundant
load path member 86 is supported from and attached to the
outboard end of yoke 16. Member 86 has flanges (not shown)
bolted to yoke 16 at points outboard of opening 34. Member
86 has a cylindrical portion 88 which extends in an outboard
direction and is bonded to the interior of bearing 84. A
conical portion 90 connects portion 88 to an enlarged
cylindrical portion 92. Enlarged cylindrical portion 92
extends in an inboard direction and uniquely has a thrust
bearing 94 mounted on the inboard side thereof.
An outboard strap spool 100 is positioned to extend
transversely across the interior of chamber 30 to extend
through opening 34. Spool 100 is fixed in position in the
1059al9~
B2859 ¦ chamber by means of an outboard strap pin 102. Pin 102 extends
¦ through a bore 104 in spool 100 and through aligned bores
106 in the walls of grip 20. Pin 102 is fixed in position
l by fastener 107 in the ends thereof. Spool 100 has a planar
outboard facing surface 108 which is spaced a short distance
"A" from the inboard side of bearing 94.
A tension strap 110 extends through chamber 36. Strap
110 is connected between inboard strap spool 64 and outboard
. strap fitting 100 to provide a primary centrifugal load
path between the grip and yoke. Strap 110 is of a conventional
construction and can be twisted along its length to allow
pitch adjustment of helicopter blade 10. In addition,
elastomeric bearings 84 and 42 maintain radial alignment-
between the grip and yoke.
Conventionally upon failure of tension strap 110 or
its mounting, grip 20 will translate with respect to yoke
16 to a point where either blade 10 falls completely of
the mast or pitch control is lost. Either one of these
results can cause the aircraft to crash.
In the present invention a unique secondary or
redundant load path is provided which is effective in the
event of a failure of the primary load carrying system.
This redundant load path is effective in the event, for
example, strap 110 breaks at 120, as illustrated in Figure
4. Break 120 frees grip 20 to move in the direction of
arrow 122 with respect to yoke 16. This in turn causes
bearings 84 and 42 to deform, as illustrated, and moves
1059097
B2859 ¦ bearing 94 a distancc "A" into contact with surface 108 of
outboard strap spool 100. Since bearing 94 is supported
by member 86 which is in turn connected to yoke 16, relative
movement of grip 20 with respcct to yoke 16 will be limited
S to the dimension "A". In addition, the engagement of
bearing 94 on surface 108 will allow pitch adjustments of
blade 10. This allows blade 10 to continue to operate for
a short period of time to allow safe landing of the aircraft.
In addition, this redundant system operates upon
failure of members such as the pin 68 or fitting 50.
In this manner, a redunaant centrifugal load supporting
system is provided which allows pitch adjustments of the
blade and which presents aircraft crash upon failure of
the primary system. - -
In Figure S, a second embodiment of a redundant
centrifugal load path is illustrated. In this embodiment
thrust bearing 94 is not present on outboard member 86'.
HoweYer, a bearing 130 is mounted on the inboard end of
portion 52 of fitting 50. An inboard radial support
fitting 132 is provided with an end cap 134 which extends
transversely across grip 2~. Cap 134 encloses bearing 130
and has a planar surface 136 which is normally spaced away
from bearing 130 a short distance. Cap 134 is designed
to carry axial loads upon failure of the primary system.
. Upon failure of either strap 110, fitting 100, or pin 102,
bearing 130 will move into contact with surface 136 and
will provide for pitch adjustment of the blade.
1059(1 97
B2859 ¦ A third cmbodinient of a redundant ccntrifugal load
path is illustrated in Figure 6, wllere instead of a tension
strap the primary load supporting system includes an
elastomeric thrust pad 137 of construction similar to bearings
42 and 84. Pad 137 is laterally supported on the inboard
side by fitting 138 fixed to pin 139 on grip 20'. The outboard
side of pad 137 is laterally supported by a fitting 140
with flanges 141 fixed in place by bolts 142 extending
through yoke 16'. In addition, the redundant load path
includes inboard fitting 50' with outboard flanges 51' fixed
to yoke 16' by means of bolts 143. Upon failure of either
thrust pad 137 or pin 139, bearing 130 will move into contact
with surface 136 as described in the embodiment illustrated
in Figure S.
Although three embodiments of the secondary load
path have been illustrated, it is to be understood, of course,
that other configurations could be utilized to provide a
secondary load path which is effective upon failure of the
primary load path without departing from the spirit and
scope of the invention. These other configurations could
involve other types of friction reducing elements other
than thrust bearings positioned to selectively engage a
transverse member upon failure of the primary system.
Having described the invention in connection with
certain specific embodiments thereof, it is to be understood
that further modifications may now suggest themselves to
those skilled in the art and it is intended to cover such
modifications as fall within the scope of the appendcd claims.
