Note: Descriptions are shown in the official language in which they were submitted.
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De~ lion
Pitch Adj~ "el~l Asser~ ly for Bearingless Main Rotors
Technical Field
S The present invention relates to helicopter bearingless rot~rs and,
more particularly, to such rotors having a flexbeam connector and
enveloping torque tube member for imparting pitch motion to a
helicopter rotor blade and, more particularly, to a new and useful
assembly which facilitates pitch position adjustment of the torque tube
member relative to the flexbeam connector.
Background Of The Invention
Helicopter rotor designs are increasingly utilizing a flexible
structural member, commonly termed a "flexbeam" or "flexbeam
connector", for retention of a helicopter rotor blade to a torque drive
hub member. Basic operational constraints of rotary wing flight impose
substantial functional complexity upon the rotor flexbeam necessitated
by various needs to control accurately multi-directional displacement of
the rotor blades, i.e., flapwise and edgewise bending, and torsional or
pitch change motions. As such, these configurations are termed
"Bearingless Rotors" inasmuch as they replace antiquated bearing
element rotors which accommodate motion by hinge or journal type
bearings at the rotor blade root end. The flexbeam connector, which is
typically comprised of fiber reinforced resin matrix materials, reduces
the weight, complexity, and maintenance of the rotor assembly while,
furthermore, improving the reliability and damage tolerance thereof.
Bearingless rotors of the varieties described in U.S. Patent
4,244,677, and 5,092,738 typically include a torque tube member
enveloping each of the flexbeam connectors for imparting pitch motion
- to the rotor blades. The torque tube member rigidly mounts outboard to
the root end of the rotor blade and articulately mounts inboard to the
upper and lower surfaces of the flexbeam connector. The articulate
mount is effected by a centering bearing, commonly identified by the
appellation "snubber bearing", which performs the functions of
centering the torque tube member relative to the flexbeam connector for
pitch change and flapping motion, accommodating lead-lag motion
between the torque tube member and the flexbeam connector and
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transferring pitch control and other loads therebetween. Centering
bearings, such as those described in the above-identified U.S. Patents,
are typically comprised of a plurality of spherical and flat elastomeric
laminates, which spherical laminates accommodate pitch change and
5 flapwise bending motion and which flat laminates permit a small degree
of radial and a larger degree of edgewise motion. The flat laminates are,
furthermore, comprised of high loss elastomer material for providing
edgewise, or lead-lag, vibration damping.
Pitch control inputs are imparted to the rotor blade assembly i.e.,
10 the torque tube, flexbeam connector and rotor blade, by pitch control
rods which are articulately mounted at an upper end to the torque tube
and pivotally mounted at an opposing end to a swashplate assembly.
The spatial displacement of the swashplate causes linear displacement
of the pitch control rods to effect rotational displacement of the torque
15 tube member about the pitch axes of the respective rotor blade. The
torque tube member, therefore, imparts pitch motion to the rotor blade
to vary the flight profile, e.g., speed, pitch, roll of the helicopter.
In addition to the primary function of providing pitch control
inputs to the rotor blades, the pitch control rods of the prior art provide
20 tracking correction for the corresponding rotor blade. Manufacturing
deviations and rotor blade erosion can vary the aerodynamic
characteristics of a rotor blade, which deviations can cause the rotor
blades to track dissimilar tip-plane paths when in operation. Such "out-
of-track" rotor blade condition results in increased rotor vibration and
25 degraded aerodynamic performance. Pitch change adjustments for
correcting rotor blade tracking errors are typically made by moving the
swashplate to a static reference position and adjusting the axial length of
the control rod to alter the initial pitch setting i.e., angle of attack, of therotor blade. Generally, only small adjustments are required, on the
3û order of + 1 degree, to effect the necessary corrections to properly track
the rotor blades.
Fig. 1 depicts a prior art pitch control rod 200 comprising upper
and lower rod end portions 202, 204, each having threaded shaft end
portions 206, 208 which are mechanically interconnected by a threaded
3~ barrel member 210. The barrel member 210 functions similar to the
operation of a turnbuckle insofar as rotation of the barrel 210 causes
simultaneous axial displacement of the upper and lower rod end
~ . :
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portions 202, 204. Axial displacement is effected by the use of right
and left handed threads on the shaft end portions 206,208. The barrel
210 is locked in position by upper and lower jam nuts 212, 214 and
redundantly retained by a locking key 216 which engages one of a
5 plurality of circumferential castellations 218 formed along the upper end
of the barrel 210. The locking key 216, which also engages an axial slot
220 formed in the upper threaded shaft end portion 206, iS retained in
one of the circumferential castellations 218 by the upper jam nut 212
thus providing a positive anti-rotational feature for the pitch control rod
200. Accordingly, by repositioning the barrel 210 i.e., turning the barrel
clockwise or counterclockwise, the length of the pitch control rod is
varied to effect pitch position adjustments of the torque tube member
and, consequently, the rotor blade assembly.
While the prior art pitch control rod 200 described hereinabove
is functionally adequate for providing pitch control inputs to the rotor
blade assembly and for providing tracking correction therefor, the pitch
control rod has certain inherent disadvantages and limitations. For
example, the threaded and slotted components, i.e., the upper and
lower rod end portions 202, 204 of the barrel 210, and the upper and
lower jam nuts 212, 214, are not amenable to lightweight composite
material construction. As such, the control rods of the prior art are
typically fabricated from a metallic material such as steel or titanium,
which increases the overall aircraft weight. The pitch control rod is also
highly mechanically complex which results in increased fabrication and
maintenance costs, and furthermore requires additional procedural steps
to ensure that all safety requirements, i.e., proper torque loading of the
jam nuts and engagement of the locking key etc., have been attended
to. Moreover, the multiplicity of component parts incréases the number
of possible failure modes and the probability of operator error.
A need, therefore, exists to provide a pitch adjustment assembly
for rotor blade tracking which is lightweight, simple to use, and requires
fewer component parts than existing pitch adjustment mechanisms.
Disclosure Of Invention
It is an object of the invention to provide a pitch adjustment
assembly for a helicopter bearingless rotor assembly which is less
mechanically complex and incorporates fewer component parts.
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It is another object of the present invention to provide a pitch
adjustment assembly for a helicopter bearingless rotor assembly which
facilitates adjustment without the requirement for extensive disassembly
of the pitch adjustment assembly.
It is yet another object of the invention to provide a pitch
adjustment assembly for a helicopter bearingless rotor assembly which
facilitates the use of a composite-formed pitch control rod for reducing
overall system weight.
It is still another object of the present invention to provide a pitch
adjustment assembly for a helicopter bearingless rotor assembly
including a centering bearing employing elastomer material for
accommodating torque tube motion while, concomitantly, applying a
compressive preload in the elastomer material.
The present invention provides a pitch adjustment assembly for a
bearingless rotor assembly having a torque tube member enveloping a
flexbeam connector, which torque tube member defines a geometric
center and is operative to impart pitch motion to the rotor blade
assembly. The pitch adjustment assembly comprises means for
centering an inboard end of the torque tube member relative to the
flexbeam connector, wherein the centering means defines a torque tube
pivot point about which the torque tube member is rotationally
displaced relative to the flexbeam connector, means for imparting pitch
control inputs to the torque tube member, wherein the pitch control
input means defines an input pivot point, and displacement means, in
combination with the centering means, for effecting translational
displacement of the geometric center of the torque tube member relative
to the torque tube and input pivot points.
More specifically, the displacement means cooperates with the
centering means to effect translational displacement of the torque tube
inboard end while maintaining the spatial position of the input pivot
point relative to the torque tube pivot point. The preferred centering
means includes a central mounting portion, upper and lower attachment
fittings and motion accommodating elastomer disposed between the
central mounting portion and each of the attachment fittings.
Preferably, the central mounting portion connects to the flexbeam
connector while the upper an lower attachment fittings are mechanically
interconnected to the torque tube member by the displacement means.
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The displacement means may include adjustment shims or a jacking
arrangement interposed between the upper and lower attachment
fittings and the torque tube member. To provide access to the
attachment fittings, apertures are formed in the torque tube member to
S facilitate interposition of the displacement means between the
attachment fittings and the torque tube member.
The jacking arrangement includes housing members which
mechanically interconnect the attachment fittings to the torque tube
member and a jacking plate disposed in each housing member, which
jacking plates engage the attachment fittings and are operative to raise
or lower the torque tube center relative to the torque tube pivot point.
In addition to effecting pitch position adjustment, the jacking
arrangement is also useful for applying a compressive preload in the
motion accommodating elastomer of the preferred centering means.
The foregoing and other objects, features and advantages of the
present invention will become more apparent in light of the following
detailed description of exemplary embodiments thereof, as illustrated in
the accompanying drawings.
Brief Description Of The Drawings
A more complete understanding of the present invention and the
attendant features and advantages thereof may be had by reference to
the following detailed description of the invention when considered in
conjunction with the following drawings wherein:
Fig. 1 depicts an exploded view of a prior art adjustable pitch
control rod;
Fig. 2a is a partial side view of a helicopter bearingless rotor
assembly which is partially broken away and partially in section
showing the primary components for imparting pitch control inputs
thereto;
Fig. 2b is a partially broken away top view of the helicopter
~ bearingless rotor assembly of Fig. 2a;
Fig. 3a is a cross-sectional view substantially along line 3a-3a of
Fig. 2b;
Fig. 3b is a cross-sectional view substantially along line 3b-3b of
Fig. 2a which depicts the salient features of the present invention for
effecting pitch change adjustment and, furthermore, depicts the use of
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adjustment shims interposed between a torque tube member and a
centering bearing;
Fig. 4a depicts an alternate embodiment of the present invention
which shows a jacking arrangement for effecting pitch change
S adjustment while, concomitantly, applying a compressive preload in an
elastomeric centering bearing;
Fig. 4b is a cross-sectional view substantially along line 4b-4b of
Fig. 4a which depicts an anti-rotation key for preventing the imposition
of in-plane torsion load in the elastomeric centering bearing;
Fig. 5 is a cross-sectional view substantially along line 5-5 of Fig
3b which depicts the internal construction of a fixed-length composite
pitch control rod used in conjunction with the pitch adsustment
assembly of the present invention.
Best Mode For carrying Out The Invention
Referring now to the drawings wherein like reference characters
identify corresponding or similar elements throughout the several views,
Figs. 2a and 2b show the relevant portions of a helicopter bearingless
rotor assembly 10 which includes a drive shaft 12 which rotates about
an axis of rotation 16. A torque drive hub member 18 is mounted to the
20 drive shaft 12 and drives a plurality of rotor blade assemblies 20. Each
blade assembly 20 includes a flexbeam connector 22 which is mounted
at an inboard end thereof to the torque drive hub member 18 by
connecting bolts 23. The flexbeam connector 22 is, furthermore,
compliant about flap, lead-lag and pitch change axes 24, 26 and 28,
25 respectively, so as to accommodate multi-directional displacement of
the rotor blade assembly 20.
A torque tube member 36 envelopes the flexbeam connector 22
and is mounted thereto at its radially outer end by connecting bolts 37
and articulately mounted at an inboard end 38 by a centering bearing
30 70. The radial outer end of the torque tube member 36 also mounts to
and envelops the root end spar structure 40 of each rotor blade airfoil
42 by a series of connecting bolts 44.
A pitch contro! arm 46 is affixed to the torque tube member 36
and receives pitch control inputs from pitch control rods 48 which are
35 articulately mounted at one end to the pitch control arm 46 and
pivotally mounted at the other end to an in-plane swashplate assembly
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52. The swashplate assembly 52 includes inner stationary and outer
rotating swashplate rings 54 and 56, respectively, which receive pitch
-control inputs from at least three (3) control input members 58 to
position the swashplate assembly 52 in a desired planar orientation.
5 The stationary inner swashplate ring 54 is mounted to a uniball mount
60 which permits axial and tilt translation of the swashplate assembly 52
relative to the rotational axis 16. The uniball mount 60 slides vertically
on a stationary standpipe 62 to accommodate axial motion of the
swashplate assembly 52 and includes a semispherical bearing surface 64
10 to guide and center the swashplate assembly 52 during tilt translation
thereof. Spatial displacement of the swashplate assembly 52, therefore,
causes linear displacement of the pitch control rods 48 to effect
rotational displacement of the torque tube member 36 about the pitch
axes 28 of the respective rotor blade assemblies 20.
Torque is applied to the stationary and rotating swashplate rings
54, 56 by stationary and rotating scissors linkages 66 and 68,
respectively, to maintain the necessary rotational position of the
swashplate rings 54, 56 about the rotational axis 16. That is, the
stationary scissors linkage 66 prevents rotation of the stationary
swashplate ring 54 to maintain its rotational position relative to
stationary components e.g., the control input members 58 and stationary
standpipe 62, while the rotating scissors linkage 68 drives the rotating
swashplate ring 56 to maintain its rotational position relative to the rotor
hub assembly 10.
In Fig. 3a, the torque tube member 36 is centered between and
mounted to the flexbeam connector 22 by the centering bearing 70
which performs the primary functions of centering the torque tube
member 36 about the flexbeam connector 22 and accommodating pitch
change motion of the torque tube member about the pitch axis 28.
While the centering bearing 70 can be viewed as a complementary pair
of upper and lower bearing members, it will facilitate the discussion to
describe the centering bearing 70 as a singular unit.
The centering bearing 70 is comprised of a central mounting
portion 72, upper and lower attachment fittings 74a, 74b, and motion
accommodating elastomer 76 disposed between, and preferably bonded
to, the central mounting portion 72 and each of the attachment fittings
74a, 74b. More specifically, the motion accommodating elastomer 76
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is comprised of alternating layers of resilient elastomer and non-resilient
metallic shims which form spherical and flat elastomeric laminates 78
and 80, respectively. The spherical laminates 78 primarily function to
accommodate pitch rotation of the torque tube member 36 about the
5 pitch axis 28 and the flat elastomeric laminates 80, which are disposed
between the spherical elastomeric laminates 78 and the attachment
fittings 74a, 74b, function to permit a small degree of spanwise motion
and a larger degree of edgewise or lead-lag motion. The flat laminates
80 are preferably comprised of high loss-factor elastomer to dampen
10 vibratory lead-lag motion of the rotor blade assemblies 20.
The central mounting portion 72 includes centrally disposed
bearing mounts 82 which are bonded, or otherwise affixed, to the
spherical elastomeric laminates 78. The bearing mounts 82,
furthermore, include integrally formed tabs 84 and a cylindrical reaction
pin 86 for engaging a corresponding mounting retainer 88. Each
mounting retainer 88 is bonded, or otherwise affixed, to the flexbeam
connector 22 and includes arcuate end portions 90 and a centra
aperture 92 for respectively engaging the tabs 84 and the reaction pin
86 of the bearing mounts 82 thereby transferring all centering bearing
20 loads to the flexbeam connector 22.
The upper and lower attachment fittings 74a, 74b are mounted to
an external surface 94 of the torque tube member 36 and are bonded, or
otherwise affixed, to the flat elastomeric laminates 80 of the motion
accommodating elastomer 76. The outermost end portions of the flat
25 elastomeric laminates 80 extend through apertures 96 formed in the
torque tube member 36 to permit external mounting of the attachment
fittings 74a, 74b. Such mounting location provides greater access for
attachment and preload operations (discussed in greater detail below).
The combined height dimension of the spherical and flat
30 laminates 78, 80 is prescribed such that a predetermined preload gap is
initially formed between the upper and lower attachment fittings 74a,
74b and the external torque tube surface 94. As the attachment fittings
74a, 74b are brought into mating contact with the torque tube member
36 by connecting bolts 98 (see Fig. 2a), the elastomeric centering
35 bearing 70 is compressed a select amount to effect a desired preload
within the elastomeric laminates 78, 80. It is common practice to
preload elastomeric bearings so that the elastomeric larninates thereof
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remain in compression throughout the full range of required motion.
This is necessary inasmuch as elastomer material is characterized by low
tensile strength and such preload or precompression prevents the
imposition of tensile loads. Byrnes et al. U.S. Patent 5,092,738
5 describes a bearingless main rotor including a centering bearing of the
type described above including an assembly procedure for effecting
preload.
Referring to Fig. 3b, the pitch adjustment assembly of the present
invention effects a translational displacement of the inboard end of the
10 torque tube member 36 relative to the flexbeam connector 22.
Translational displacement is defined herein as a displacement in a
plane which is generally normal to the pitch axis of the flexbeam
connector 22, i.e., the plane defined by the present cross-sectional view.
While a variety of mechanisms may be employed to effect such
15 translational displacement, one embodiment of the present invention
employs the use of adjustment shims 102 or spacers selectively
interposed between the upper and lower attachment fittings 74a, 74b
and the torque tube member 36. The adjustment shims 102 are retained
therebetween by the aforementioned connecting bolts 98 disposed
about the periphery of the attachment fittings 74a, 74b. Alternatively, a
jacking arrangement 140, illustrated in Fig. 4, may be employed which
facilitates pitch change adjustment while, concomitantly, applying a
compressive preload to the elastomeric laminates 78, 80.
Preferably the displacement means 102 or 140 cooperates with
the centering bearing 70 to effect translational displacement of the
torque tube inboard end while maintaining the fixity of the pitch control
rod 48, i.e., along the length thereof. More preferably, the displacement
means 102 or 140 is interposed between the upper and lower
attachment fittings 74a, 74b and the torque tube member 36. Such
30 location provides accessibility for the operator when performing pitch
position adjustments.
For the purposes of understanding the kinematics required for
effecting pitch adjustment, several spatially defined points associated
with the torque tube member 36 and the centering and pitch control
35 input means, i.e., the centering bearing 70 and the pitch control
arm/pitch control rod 46, 48, respectively, are described. The centering
bearing 70 defines a torque tube pivot point 110 about which the torque
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. . _ .
tube member 36 is rotationally displaced relative to the flexbeam
connector 22 and, furthermore, about with pitch adjustinents are made.
The pivot point 1 10, furthermore, lies in a transverse plane extending
generally normal to the pitch axis of the flexbeam connector 22. The
articulate mount 114 which connects the pitch control rod 48 and pitch
control arm 46 defines a second point, or input pivot point 116, about
which pitch control inputs and/or pitch adjustments are made.
Furthermore, the input pivot point 116 iS substantially fixed in space
relative to the torque tube pivot point and is disposed along the
longitudinal axis 118 of the pitch control rod 48 which is mechanically
connected to the swashplate assembly (bearing in mind that the
swashplate assembly is also spatially fixed when performing pitch
position adjustments). The intersection of the longitudinal axis of the
torque tube member 36 and a transverse plane, i.e., a plane which
generally corresponds with the present cross-sectional view, defines a
third point, or the geometric center 120 of the torque tube member 36.
The torque tube and input pivot points 1 10, 1 16 define a pitch
reference line 130 indicative of the current pitch position of the torque
tube member 36 relative to the flexbeam connector 22. The input pivot
point 1 16 and the geometric center 120 of the torque tube member 36
define a second line, or pitch adjustment line 132, whereby the
reference and pitch lines 130,132 form a pitch angle ~ therebetween. It
will be apparent that by displacing the torque tube center 120 relative to
the torque tube pivot point 110 and maintaining the relative spatial
position of the input pivot point 116, the pitch angle ~, varies in
accordance with the magnitude of the translational displacement (the
distance between the torque tube pivot point 1 10 and the torque tube
center 120). Accordingly, by selectively placing adjustment shims 102
between at least one of the attachment fittings 74a, 74b and the torque
tube member 36 e.g., by shifting or removing an interposed shim or
shims 102 from the lower attachment fitting 74a to the upper attachment
fitting 74b, the torque tube center 120 is shifted translarionally of the
pitch axis 28 and with respect to the torque tube pivot point 110. The
distance between the torque tube and input pivot points 1 10, 1 16 is
commonly referred to as the "arm radius" which determines the
magnitude of translational displacement necessary to effect the desired
torque tube rotational or pitch adjustment displacement. Accordingly,
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11
the pitch angle 0, which is indicative of the pitch change adjustment,
varies as a trigonometric function of the translational displacement and
the arm radius.
As earlier discussed, prior art pitch adjustment mechanisms are
S configured to vary the axial length of the control rod to effect pitch
position adjustment. Applying the same descriptive geometry to the
prior art, it will be apparent that the torque tube pivot point 110, torque
tube center 120 and input pivot point 116 are co-linear, i.e., disposed
along the above-defined pitch reference line 130, and furthermore, the
torque center 120 and torque tube pivot point 110 are, at all times,
coincident. In contrast, the present invention variably displaces the
torque tube center 120 relative to the torque tube pivot point 110, and,
consequently, varies the pitch angle ~ between the pitch reference and
pitch adjustment lines 130, 132.
In Fig. 4a a jacking arrangement 140 functionally replaces the
adjustment shims 102 described hereinabove for effecting translational
displacement of the torque tube center 120. Furthermore, the
attachment fittings 74a, 74b are reconfigured for mateably engaging the
jacking arrangement 140. The jacking arrangement 140 includes upper
and lower housing members 142a, 142b having respective jacking
plates 144 disposed therein. Connecting bolts 98 mount the upper and
lower housing members 142a, 142b to the torque tube member 36 in
areas corresponding to the torque tube apertures 96. Each of the
housing members 142a, 142b, furthermore, includes a pilot surface 146
for accepting a peripheral bearing surface 148 defined by each of the
upper and lower attachment fittings 74a, 74b, which pilot surface 146
mechanically interconnects the centering bearing 70 to the torque tube
member 36 while, furthermore, permitting axial translation thereof.
Each of the housing members 142a, 142b also includes a threaded
30 ~ portion 150 for threadably engaging the corresponding jacking plate
144, whereby rotation thereof effects linear displacement within each of
the housing members 142a, 142b. The jacking plates 144 engage the
outer surfaces 152 defined by each of the attachment fittings 74a, 74b
and, are operative to reposition the fittings 74a, 74b relative to the
housing members 142a, 142b, thereby raising or lowering the torque
tube center 120 relative to the torque tube pivot point 110. That is, for
example, by rotating the jacking plates 144 in equal amounts in
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12
opposite directions about rotational axis 154 i.e., in clockwise and
counterclockwise directions, the torque tube center 120 is raised or
lowered with respect to the torque tube pivot point 110.
The pilot and peripheral bearing surfaces 146, 148 are sufficient
in length to permit the necessary translational displacement of the
torque tube member 36 relative to the attachment fittings 74a, 74b
while maintaining the necessary coupled engagement therebetween.
For example, to effect the maximum pitch adjustment of + 1 degree, the
translational displacement is approximately + 3.8 cm (.15 inches) for a
torque tube member 36 having an arm radius of 216 cm ( 8.5 inches).
Accordingly, the pilot-peripheral bearing interfaces sh~;Jld be greater
than about 20.3 cm (.8 inches) in length to accommodate translational
displacement and properly capture the attachment fittings 74a, 74b.
To avoid the imposition of torsional loads in the elastomer 76 of
the centering bearing 70, a means 160 (see Fig. 4b) may be employed
for preventing rotation of the attachment fittings 74a, 74b relative to the
housing members 142a, 142b and about rotational axis 154. Preferably,
an anti-rotation key 162 is formed in the attachment fittings 74a,-74b
along the peripheral bearing surfaces thereof, which key 162 engages a
slot 164 formed in the housing members 142a, 142b along the pilot
surfaces 146 thereof. While any means for preventing rotation may be
incorporated, such as a polygonal shaped interface between the pilot
and peripheral bearing surfaces 146, 148, the anti-rotation means must
accommodate axial translation of the attachment fittings 74a, 74b.
In addition to providing pitch position adjustment, the jacking
arrangement 140 concomitantly functions as a preload device to apply a
compressive preload in the elastomer 76 of the centering bearing 70.
As discussed earlier, the conventional approach for preloading an
elastomeric centering bearing 70 involves the predetermination of a
preload gap between the attachment fittings 74a, 74b and the torque
tube member 36 such that a predictable compressive preload is applied
to the elastomer 76. The parameters which are evaluated to determine
the size of the preload gap generally include the predicted spring rate
stiffness of the centering bearing 70, the predicted spring rate stiffness of
the torque tube member 36, and manufacturing tolerances associated
with the centering bearing 70, the torque tube member 36 and the
flexbeam connector 22. Insofar as material differences and
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13
manufacturing deviations will vary slightly from one blade assembly 20
to another, it is not possible to ensure that the proper preload has been
applied using conventional approaches. The jacking arrangement 140
of the present invention, on the other hand, ensures that the proper
compressive preload is applied irrespective of material differences and
manufacturing deviations. That is, for example, once the jacking plates
144 are properly positioned for establishing the desired pitch po~sition,
torque is equally applied to the jacking plates 144 e.g., rotating both
jacking plates in a clockwise direction, so as to cause convergence
thereof toward the torque tube pivot point 110. Accordingly, the
jacking plates 144 engage the attachment fittings 74a, 74b to establish
the desired preload in the elastomeric laminates. This operation should
be performed without influencing the earlier established pitch setting.
Alternatively, pitch adjustment operations may be performed
subsequent to the application of preload, however, a steady torque
value must be maintained during the pitch adjustment procedure.
The preload may be measured using a load measurement device
such as a torque wrench 166 wherein the jacking plates 144 provide
feedback thereto for indicating the applied preload. The following
method/analysis is useful for calculating the torque necessary to produce
a desired preload of 10752 N (2400 Ibs.) in the elastomeric centering
bearing 70. First, the centering bearing 70 is placed in a holding fixture
(not shown) to determine the spring rate stiffness of the bearing wherein
a load is applied and recorded to produce a deflection of .127 cm (.05
inches). Second, the spring rate stiffness of the elastomeric centering
bearing 70 is calculated in accordance with equation (1):
K= P/.127cm (1)
wherein K is the spring rate stiffness of the elastomeric centering bearing
70, and P is the applied load. Next, the deflection ~ required to
produce a desired preload of 10752 N (2400 Ibs.) is determined by
equation (2):
â = 10752 N/K (2)
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14
The final step requires measurement of the torque required to produce
the deflection ~ in the centering bearing 70 which can then be applied
to future rotor blade assemblies in applying the proper preload. The
jacking arrangement is therefore unaffected by material differences and
manufacturing deviations insofar as the preload is measurable with each
instal lation.
By combining the displacement means 102 or 140 with the
torque tube centering means i.e., the centering bearing 70, the control
rod 48 may be fixed in length and/or fabricated from lightweight
composite material. Referring again to Fig. 3b, the preferred fixed
length composite control rod 48 is comprised of high strength
reinforcing composite fibers, such as graphite, fiberglass or aramid
fibers, disposed in a binding resin matrix. The control rod 48 includes
upper and lower rod end portions 170 and a center body portion 174
disposed therebetween. The primary load carrying element of the
control rod 48 is a composite winding having looped end portions 176
which circumscribe metallic or elastomeric rod end bearings 178 to
form the upper and lower rod end portions 170. The looped end
portions 176 furthermore, transition to form longitudinal strap members
180, 182 which are the primary load carrying elements of the center
body portion 174. Referring to Fig. 5, the center body portion 174
additionally comprises a chopped fiber matrix filler 184 i.e., randomly
oriented fibers in a binding matrix, disposed between and integrally
formed with the strap members 180, 182, and a transverse composite
wrap 186 which is circumferentially wound about the filler 184 and
strap members 180,182. The transverse wrap 186 functions to
strengthen the bond between the filler 184 and strap members 180,182
and provide buckling stability therefor.
The use of a fixed-length composite control rod 48 in
combination with the displacement means 102 or 104 described herein
provides substantial weight savings when compared to prior art pitch
adjustment mechanisms. In a weight-critical vehicle such as a rotorcraft,
weight economy, on the order of a few kilograms, can yield significant
cost savings and performance benefits. For example, when comparing
the weight associated with a ship-set of pitch control rods 48 (a ship-set
is 5 control rods for a five-bladed rotor assembly), a fixed-length
composite control rod 48 offers a weight savings of 25% to 30% or
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approximately 6.13 kg. (13.5 Ibs) for a five bladed rotor assembly as
compared to adjustable metal control rods. The additional weigt~t of,
for example, the adjustment shims 102 i.e., reclaims approximately 1.6
kg. (3.5 Ibs) of the weight savings, thereby resulting in a positive weight
5 savings of about 4.54 kg. (10 Ibs.) The weight associated with the
jacking arrangement 140 reclaims a larger portion of the total weight
savings, i.e., approximately 5.44 kg. (12 Ibs), however, a positive
weight savings is, nevertheless, reaiized. While the weight savings
~ associated with the jacking arrangement 140 is less dramatic, the ease of
performing pitch adjustment, coupled with the ability to properly
preload the elastomeric centering bearing 70, makes the use of the
jacking arrangement 140 an attractive alternative to the use of
adjustment shims 102.
The displacement means 102 or 140 described herein provides a
lS simple and reliable method for effecting pitch change adjustment. The
adjustment shims 102 reduce the complexity and multiplicity of
component parts associated with prior art pitch adjustment mechanisms
while, furthermore, providing enhanced fail-safe reliability. With regard
to the latter, fail-safe retention is provided by the plurality of connecting
bolts 98, which are employed for connecting the attachment fittings
74a, 74b to the torque tube member 36. The jacking arrangement 140
facilitates pitch change adjustment while furthermore, applying a
compressive preload in the elastomeric centering bearing 70. The
jacking arrangement 140 obviates the need for painstaking and
laborious disassembly required by prior art pitch adjustment
mechanisms, while furthermore, enabling the relaxation of costly
manufacturing requirements e.g., material specifications and highly
precise manufacturing tolerances, necessitated by preload
devices/methods of the prior art.
Although the invention has been described with respect to the
use of adjustment shims 102 or a jacking arrangement 140 to effect
translational displacement of the torque tube member 36, it willbe
appreciated that other adjustment schemes utilizing or modifying the
centering bearing 70 to cause such displacement can be employed.
Furthermore, while the invention as described herein employs an
elastomeric centering bearing 70 to effect an articulate mount between
the torque tube member 36 and the flexbeam connector 22, it should be
CA 02204901 1997-0~-08
W O 96/15029 PCTrUS95tl31S6
understood that any centering arrangement which accommodates pitch
motion of the torque tube member 36 relative to the flexbeam
connector 22 can be employed while remaining within the spirit and
scope of the invention. For example, a centering bearing which
S provides pure rotational displacement of the torque tube member 36
can be employed. Furthermore, while the invention preferably utilizes a
fixed-iength composite control rod 48, a metallic pitch control rod of the
fixed or variable length variety may be incorporated. Regarding the use
of a variable length pitch control rod, the present invention is useful to
provide a broader range of pitch adjustment than is currently available.
Moreover, those skilled in the art will recognize that the
foregoing and other changes, omissions and additions may be made to
the exemplary embodiments described herein without departing from
the spirit and scope of the present invention.
What is claimed is:
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' CA 02204901 1997-0~-08
understood that any centering arrangement which accommodates pitch
2 motion of the torque tube member 36 relative to the flexbeam 22 can
3 be employed while remaining within the scope of the invention. For
4 example, a centering bearing which provides pure rotational
displacement of the torque tube member 36 can be employed.
6 Furthermore, while the invention preferably utilizes a fixed-length
7 composite control rod 48, a metallic pitch control rod of the fixed or
8 variable length variety may be incorporated. Regarding the use of a
9 variable length pitch control rod, the present invention is useful to
provide a broader range of pitch adjustment than is currently available.
11 Moreover, those skilled in the art will recognize that the
12 foregoing and other changes, omissions and additions may be made
13 to the exen~plary embodiments described herein without departing
14 from the scope of the present invention.
What is claimed is:
S-4994 16 p~ ;} S
