Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a helicopter rotor system,
in particular a rotor system which is hubless, hingeless and
bearingless.
Helicopter rotor systems constitute a highly developed
art. Especially for the larger rotor systems, and also for the
smaller, lighter rotor systems, the mounting of the blades for
their necessary motions is relatively complicated. Attempts are
being made to provide hingeless, hubless and bearingless rotor
systems, but these are presently quite complicated and extremely
critical in their construction. It is an object of this invention
to provide a hubless, hingeless and bearingless rotor system
for a light helicopter which can readily be manuEactured with
the use of conventional fiberglass fabrication techniques and
simple, strong and expedient metal components without many of
the intermediate elements between the blade and the mast which are
common in existing rotor systems.
Summary of the Invention
The invention provides a helicopter rotor system com-
prising: a rotary mast having an upright axis; three or more rotor
blades mounted to said rotary mast to be turned by said mast, each
said blade having a respective longitudinal axis directed away
from said mast, all of said rotor blades being substantially
identical to one another, and being angularly spaced apart around
said mast, each said blade comprising a skin forming an airfoil and
an internal region, a counterweight rod and a spar extending
longitudinally inside said region, said spar comprising a bundle
of aligned fibers which, inside said region are bonded to each
other, to said skin, and to said counterweight rod, said bundle
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being doubled and divided so as to form inboard of said skin a
pair of U-shaped bight portions, each with a bend and a pair of
arms, said arms being stiffly flexi~le, said fibers inside said
region constituting continuations of the fibers in said bight
portions, said fibers in bight portions being bonded together,
whereby the total cross-section area of said fibers is substant-
ially constant from the inboard end of said arms through the
major portion of the length of the spar; attachment means attaching
each of said bight portions to said mast at locations spaced apart
from one another and substantially spaced from the center of said
shaft, both on the same side of the center of the mast; a long-
itudinally-extending torque tube rigidly attached to said counter-
weight rod at a first end of each said torque tube, and a first
bearing member adjacent to the other end of said torque tube,
said torque tube having an axis; and a second bearing member
mounted to said attachment means and to said first bearing member,
whereby said torque tube is rotatable around its own axis, and can
move in any angular direction away from said longitudinal axis
around the center of said second bearing means, whereby to enable
~0 lead/lag, feathering and flapping movements.
The two bearing members are not intended to transfer
any appreciable centrifugal load from the blade to the mast. In-
stead, they function to stabilize the torque tube so it can rotate
around its own axis
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for feathering motion, and angularly in any direction from the torque tube
axis, around the center of the first bearing member for lead/lag and flapping
motion. Pitch horn means is attached to the torque tube to rotate the torque
tube around the axis of the torque tube.
According to a preferred but optional feature of this invention,
the attachment means comprises a mounting flange member, which can provide
~or an initial coning angle and for an initial camber angle, whereby to
minimize flexure of the arms in normal operations.
According to yet another preferred but optional feature of the
invention, the flexing portions of the arms are disposed outboard from the
attachment means, whereby to minimize such flexures as tend to destroy the
integrity of the bonded structure.
The above and other features of the invention will be fully under-
stood rom the following detailed description and the accompanying drawings,
in which:
Figure 1 is a partial top view of an embodiment of the invention;
Figure 2 is a side view partly in cutaway cross-section of the
system shown in Figure l;
Figures 3, 4, 5, 6 and 7 are cross-sections taken at lines 3-3,
~0 4-4, 5-5, 6-6 and 7-7, respectively, in Figure l;
Figure 8 is an enlarged view of a portion of Figure 1, partially in
cutaway cross-section;
Figure 9 is a view taken at line 9-9 in Figure 8;
Figure 10 is a fragmentary plan view showing the presently-prefer_
red embodiment of the invention;
Figures 11, 12 and 13 are cross-sections taken at lines 11-11, 12-
12 and 13-13, reapectively, in Figure lO;
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Figure 14 is a fragmentary plan view showing other features of
the embodiment of Figure 10~
Figure 15 is a partial view taken at line 15~15 in Figure 14;
Figures 16 and 17 are top and side views, respectively, of the
torque tube used in Figures lO and 14; and
Figures 18 - 25 are cross-sections ta~en at lines 18-18, 19-19,
20-20, 21-21, 22-22, 23-23, 24-24, and 25-25, respectively in Figure 14.
One embodiment of a helicopter rotor system 10 according to this
invention is shown in the Figures, It includes a mast 11 mounted to a fuse-
lage and driven by a fuselage-mounted engine (both not shown). The mast has
an upright axis of rotati.on 12 around which it turns to drive a plurality of
rotor blades of which two are shown, blades 13 and 14. In the example shown,
ive identical and identically mounted blades will be provided, spaced equal-
ly angularly apart from one another around axis 12. Because all of them are
identical, only blade 13 will be described in detail.
Especially in Figures 1 and 2, the size of the parts near the mast
are shown disproportionately large, the blade itself having been reduced in
size to fit it on the "sheet".
The airfoil portion 20 of blade 13 is foreshortened in the draw-
ings. It will be made of any appropriate length and dimensions, extending asfar to the left as desired, generally shaped to NACA profiles, and is driven
by the mast to exert a lifting force on the craft. The airfoil portion and
its method of manufacture are shown in detail in my United States patent No.
4,316,700. The airfoil portion includes a skin 21 which is preferably made
of a composite material, and shaped to an appropriate configuration. The skin
may be made in two parts 22, 23 (Figure 3) which can be mirror images of one
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another when the blade is symr,letrical, or can be of different shapes when
the blade is asymmetrical. 'Ihe parts meet at the leading edge 24 and trail-
ing edge 25. Bonding and joinder in this blade can readily be accomplished
with adhesives. The trailing edges could be joined together by adhesives or
fasteners.
The skin forms an internal region 26 which contains a longitudinally-
extending spacer 27 that is U-shaped so that its flanges 28, 29 abut and are
fastened to the parts 22, 23 respectively. Inside the region at the leading
edge there is a ~r~etal counterweight rod 30 which extends parallel to the
10 longitudinal axis 31 of the blade. A spar 32 is formed inside the region. It
comprises a plurality of fibers joined together in a bundle by a bonding
material to be described, and the skin, the fibers and the counten~eight
member are all mutually bonded to one another to form a monolithic construc-
tion adjacent to the leading edge. The spar is made of bundles of lengths of
fibers as ~1ill be further described below.
The skin, spar, spacer and counterweight rod are assembled in
accordance with the techniques described in more detail in the said United
States patent No. 4,316,700. Persons skilled in the art will recognize that
the bundles of fibers can be appropriately formed while the bonding material
~û is still liquid. Instead of building up the airfoil by bonding together a
group of prefabricated parts, the skin itself could be used as a mold, and
the counterweight rod, fibers and bonding material laid inside the skin, and
the skin then closed and held in a fixture so it will have the proper contour
during the curing operation. Also, the system can use the well-known 'pre-
preg" process for building up the structure.
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At the inboard end of the counterweight member there is attached a
torque tube 35 (Figure 1). This torque tube is a strong metal tube which has
a flattened portion 36 that is attached to the counterweight rod by a weld-
ment 37 so that the torque tube can rotate (feather) the airfoil portion around
its pitching axis. The fibers which form the spar continue inboard from the
airfoil portion to form a bight portion 40. When the airoil construction is
made, the bight portion will be made at the same time, and the spar consti-
tutes an extension of the bight portion itself. The purpose of the bight
portion is to mount the airfoil portion directly to the mast so as to trans-
c~.~trl f u~ I
A 1~ fer the ~e~i}gag&~ load directly to the mast, without the interposition of
bearings and clevises as are customarily used in the prior art.
The bight portion includes a flat portion 41 bent around the mast
and fitted closely thereto. When this portion is manufactured, tooling pins
~not shown) will be inserted so that the fibers do not cut across holes 42
through which bolts will later pass. In the example, because there are five
blades there are five such holes.
The bight portion includes a pair of arms 43, 44 which extend from
the 1at portion toward the airfoil portion, and are progressively shaped at
flrst to provide a pair of channels 45, 46 on opposite sides of the torque
tube (Figures 4 and 5). The channels are identical so that only channel 45
will be discussed in detail. It has a flat bottom member 47 and a pair of
flanges 4~, 49. The flanges are directed away from the torque tube, which
passes between the channels. These channels progressively change their shape
as shown in the drawings and finally merge to form a bundle 50, parts of
which pass on each side of the flattened portion of the torque tube and then
continue into the region to form the spar.
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At least arms 43 and 44 are stiffly flexible, as would be expected
of a bundle of glass fibers bonded together. They have substantial tensile
strength to resist centrifugal forces, and sufficient flexibility to accom-
modate feathering, lead/lag and flapping movements.
The torque tube extends inboard toward the mast and has a pitch horn
51 connected thereto. The torque tube of each of the blades will have its own
respective pitch horn. The pitch horns are connected to a swash plate (not
shown) to control the angle of attack of the blades. Turning the pitch horn
will rotate the blade around its axis 31 for feathering motion.
A first bearing member 52 (Figure 8~ is formed inside the torque
l-~;s
t~be at its inward end. ~ bearing member includes a cylindrical passage
adapted to receive a second bearing member 53 in the shape of a bàll which
closely fits inside bearing member 52. Thus the torque tube can be rotated
aro~md its own axis, and can be angularly moved in any direction from its
axis around the center of bearing member 53. It also has limited freedon for
longitudinal movement, as limited by the bight portion and by arms 43 and 44.
The bearing comprising members 52 and 53 is not intended to transfer any
appreciable centrifugal load. The centrifugal load is transferred by flat
portion 41 which constitutes a flexible continuation of the spar itself.
~0 Instead, the bearing acts to stabilize the inboard end of the blade at the
torque tube. It enables the blade (and torque tube) to move angularly in any
direction from axis 31 of the blade, around bearing member 53 as a center.
This enables lead/lag and flapping movement.
Second bearing member 53 is mounted to a mounting plate 54 which
fits between the two arms of the bight portion, and has a hole 55 to pass
attachment means yet to be described.
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As best shown in Figure 2, a small angle 60 (perhaps
2 up from the horizontal) is formed in the arms in the bight
portion to give a built-ln coning angle to the structure.
Attachment means 65 is provided to mount the flat
portions of the bight portions to the mast. The attachment means
includes an upper plate 66 which is attached near the top of the
mast and is connected thereto by a cross bolt 67. It behaves
as a flange on the mast. Five attachment bolts 68 extend
downwardly through holes in a bottom plate 69, below which nuts
70 are applied to compress the flat portions and the mounting
plates in a stack and to hold them to the mast. Attachment means
65 comprises plates 66 and 69, and bolts 67 and 68. It will now
be seen that upward forces exerted by the blades on the mast when
the mast is turned will be exerted through the attachment means,
and that centrifugal loads will be transmitted directly to the
mast by the bights of the blades.
As to materials of construction, the skin section will
usuallybeof glass fibre orcomposite type construction.The fibers
will usually be S-glass or some other form of glass fibers, with
the correct cross-section area and in a sufficient number to
provide the properties required for the blade. The bonding
material is preferably an initialIy liquid curable resin.
Preferably it is a vinyl ester resin rather than a thermal setting
epoxy. When glass fiber is used, polyester resin can be used.
While polyester resin will mix well, it has relatively poor
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2599-138
strength. However ! vinyl ester has the strength of epoxy and
the workability of polyester. A wet layup procedure can be
utilized, which is very convenient. One can squeeze and pat out
excess resins to room temperatures while shaping the material
to the desired configuration. Instead, a ~'pre-preg" system can
be used, which is well-known
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in the art. In all of the processes, the bonding material (the resin) fills
out the structure to a smooth and continuous configuration by seepage and by
abutment with a mold surface, or by mechanical smoothing
The term "bonding material" is used for the resin, even though it
provides much or most of the structure, and the materials in it act primarily
as structure elements or reinforcement. However, it does adhere to the other
material and joins them to form unitary constructions. For this reason, the
term "bonding" is used, although it is not intended to e~clude the meaning
of "structure'~ The bonding layers which join the sub-elements may be the same
or a different material. Using the same bonding material has the advantage
of avoiding points of discontinuity of structural properties. The techniques
of constructing the various portions will be understood by persons skilled in
the glass fiber and resin epoxy arts and require no further discussion here.
However, a more complete disclosure will be found in the aforesaid United
States patent No. 4,316,700.
In order to provide some streamlining for the system inboard of the
airfoil portion, a shroud 75 is provided which preferably has an airfoil
configuration It covers most of the bight portion of the blades. It, and
the skin in Figures 1 and 2, are shown in dashed lines in order to reduce the
~0 complexity of the drawings.
It will now be seen that the blades and the bight portions can
readily be manufactured, uniformly and quickly, using conventional molds,
fixtures, and techniques After assembly and curing, they can simply be
mounted to the mast by the attachment means, and the system is ready to
operate
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2599-138
The system flexes and twists in the arms near the mast.
The blade bends to lead and lag primarily just outboard from the
point of joinder of the torque tube to the counterweight rod.
The bearing means is forgiving of movements in directions lateral
to the blade axis (:which constitute these motions). Rotating
the pitch horn will rotate the blade to vary its angle of attack.
As many or as few blades as necessary will be provided
and will be joined in the stack at the mast. Only two are shown
for purposes of simplicity of drawings, although in the illustrated
example, three more will be provided.
It will thereby be seen that a simple, unitary rotor
system is provided which can reliably and readily be manufactured
utilizing simple metal forming techniques and glass fiber layup
techniques, resulting in a relatively inexpensive blade of a very
high quality. The construction provides for all necessary blade
motions, without requiring conventional hubs, hinges and bearings.
The blade is in effect a single, monolithic structure
without interposition of conventional elements such as clevises
and hinges.
The embodiment of Figures 10-25 overcomes some of the
shortcomings in the embodiment of Figures 1-9, Principal among
these is the fact that in the embodiment of Figures 1-9, the
bights of the individual blades must be stacked one atop the other
so that the height of the stack at the mast is determined by the
number of blades, and this of course, can limit the number of
blades. Furthermore, it would be advantageous to have the mount-
ings of all the blades in or close to the s~me plane. This
advantage is attained in the embodiment of Figures 10-25.
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In addition, by utilizing different attachment means for the blades,
it is possible to provide camber and coning angles at the attachment means
rather than as part of the structure of the blade itself.
It is a further advantage that lead/lag stresses can be taken up
in the arms themselves, distant from the attachment means so that there is
less tendency to loosening of the fabric arrangement.
This embodiment also provides means for reducing static blade droop,
and also means for obtaining more useful lift from the inboard 25% of the
rotor blade~
ln In Figure 10 there is shown rotor mast 100 which has a flange 101
to which is attached a stack of attachment plates 102. In the illustration,
there are eight of these plates in stacks of four each, which are held to the
central flange by bolts 103. All of the attachment plates are identical to
one c~mother.
The embodiment shows five rotor blades, all of which are identical,
so that only rotor blade 105 will be described in detail. Each of them has
a similar attachment and a similar pitch horn 106.
~ he blades are constructed identically to the blades in Figures
1-9, especially in the active region best shown in Figures 18 and 19, where
the skln 107 is shol~n wrapped around a counterweight member 108, and spar
109 constructed of fibers and bonding material as aforesaid. An alternate
spacer member 110 can be placed between the surfaces of the skin near the
~ s )r~ Fi~u~e, Iq
trailing edge if desired~ It is unnecessary to repeat the details of con-
struction of this blade because they have been thoroughly described above.
~y extending the "wings" of the spar, the skin can be stiffened enough that
the spacer member is unnecessary.
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A torque tube lOOa is attached to the pitch horn. It is
also welded to the counterweight member. Turning the pitch horn
therefore varies the pitch of the blade.
In figure 20, there is shown an optional stiffener
member 111 welded to the counterweight member. It extends for
a short distance along the counterweight member and is welded
thereto.
There is a substantial difference in the blade, as shown
progressively from Figures 21-25. The skin, it will be noted,
begins to have a camber at its trailing end, and as can be seen,
the lower rear edge 112 beginstodroop fartherand fartherbelow the
horizontal axis 113. This gives a greater angle of attack, the
closer the skin approaches to the horizontal axis 113. This
provides an increase angle of attack closer to the mast, which
with the enhanced stiffness of the llp will give some lift in this
area which usuall~v does not provide any substantial lift. Also,
the chord of the blade can increase as it extends toward the mast,
also increasing the lift at the inboard section. While the
increase might seem small, still in a machine weighing perhaps
2,000 pounds, even 125 pounds of lift can be a considerable
assistance and can lift the weight of the blades themselves.
To attain certain of the advantages of this invention,
the fibers of the spar are taken from the spar in two bundles
instead of one. As before, each bundle 115, 116 is doubled so as
to form a bight portion 117, 118 with a pair of arms 119, 120,
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121, 122 and a respective bend 123~ 124c These bends are wrapped
around respective bolts 125, 126 on the attachment plates
whereby to mount the b.lade to the mast, The fibers wrapped
around the bend return the full len~th of the blade. Because
the fibers are bonded together, and so are the arms, they appear
to be simple bundles.
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It should be recognized hexe that the attachment plates
are intended to be quite rigid and take no part in ~lexure or
control of the attitude of the blade. They are intended to
constitute an extension of the rotor mast and constitute
direct attachment means for the blade,
Each blade has a respective counterweight member as
aforesaid, which extends to a first hearing member 127 (Figure 12
in the nature of a hollow longitudinal tube fitting over a
second bearing 128 mounted to the attachment means, i~e., to the
attachment plates~ This enables longitudinal motion and rotary
motion around the center of the ball-like second bearing member
as has already been described.
It will now be seen that each blade has two points of
attachment to the attachment plates instead of only one,and thatit
is attached to the plate rather than being directly wrapped around
the mast. Therefore, all attachments can be at the same elevation.
The bundles are shown as they progress from adjacent to
the plate, to adjacent to the a-ttachment means in Figures 21-25.
It will be seen that they progress from a pair of relatively
squat, constructions through U-shaped constructions and then to
modified hat-shaped constructions, the most significant of which
are shown in Figures 24 and 25 to include stiffener lip 130, which
e~tends normally to the horizontal axis It will be appreciated
that this can give substantial rigidity against droop. ~t the
bolts, the fibers have been bent to form the bend.
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In the use of these blades, it transpires that the lead/
lag effects occur at approximately sections 20~20 through 22-22.
It will be observed that at this point it is quite distant from
the attachment means and that there is no discontinuity at this
location which could work to destroy or degrade the
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bonded structure, In conventional structures, attachment means are provided
at this location, which is disadvantageous.
The use of attachment plates enables substantial advantages to be
attained because these plates can be shaped to provide various angles. For
example, in Figure 12 the plates are shown with a coning angle 131 stamped
into them at the center so as to reduce the excursion required of the bight
itself to achieve this angle, Similarly, the plates can be stamped with a
` ~3 2 /~ ~
air of joggles~ to establish a positive basic pitch angle for the
blades with the same objective and advantage. Thus, by merely shaping the
plates, it is possible to reduce cyclic stresses on the blades themselves.
Again, it is emphasized that the attachment plates form merely an
extension of the mast itself and take no part in the flexure of the blades
during operation, neither as to feathering, nor flapping, nor lead/lag motion.
Another advantage of this class of blade is that wider cross-
sections of the blade 44~ can be provided at its root than at its tip so as
to take greater advantage of the inboard portion of the blade, and that the
total cross-section of the fibers is constant throughout the entire blade and
its attachment, thereby avoiding discontinuities of transition points between
the various shapes. This is a tremendous assistance in lay up of the device
in manufacture,
Although each blade is attached to two points instead of one, it
is hubless in the same sense as the embodiment of Figures 1-9. A rotor hub
is a mechanism which provides not only for retention of the blade, but also
for movement of the blade lead/lag, flapping and feathering modes.
Because the at~achment plates do not provide for any of this, they
are hubless in the same sense as before,
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This invention is not to limited by the embodiments shown in the
drawings and described in the description, which are given by way of example
and not of limitation, but only in accordance with the scope of the appended
claims.
