Note: Descriptions are shown in the official language in which they were submitted.
CA 02348677 2001-08-09
1 ROTOR FOR ROTARY WING AIRCRAFT
2 Cross-Reference to Related Applications
3 [0001] This application claims the priority of U.S. Provisional patent
application serial
4 no. 60/206,661 filed May 24, 2000.
BACKGROUND OF THE INVENTION
6 Field of the Invention
7 [0002] The present invention relates generally to rotors for rotary wing
aircraft.
8 Description of the Related Art
9 [0003] One type of rotor used for rotary wing aircraft is a single
structural blade
assembly made up of outer blades and internal spar caps. The rotor has a tip
at either
11 extreme end. Each side of the blade of the rotor has a leading edge, that
is moved into
12 the wind during rotation of the rotor and a trailing edge that lies
opposite the leading
13 edge. Prior rotors, such as the one shown in U.S. Patent No. 6,024,325
encase two flex-
14 beam spars within the rotor. Manipulation of the location and orientation
of the spars
alters the pitch of the rotor, thus permitting control of the aircraft's lift.
16 [0004] Centrifugal force tends to move all rotating masses toward the plane
of rotation
17 because the plane of rotation represents the maximum distance that a mass
can attain
18 from the axis of rotation. When a symmetrical rotor blade is at zero pitch
relative to the
19 plane of rotation, every mass above the plane of rotation is matched by an
equal mass on
the lower side, so no pitch control forces are applied. However, when the
rotor blade is
21 pitched up, such as when the pilot pulls up on the collective, masses near
the leading edge
22 are moved above the plane of rotation and masses near the trailing edge are
moved below
23 the plane of rotation. Centrifugal force tends to urge both masses toward
the plane of
24 rotation, causing the blade to want to move toward zero pitch. Therefore,
to minimize
pitch control forces, all masses should be as close to the pitch change axis
as possible.
26 (0005] U.S. Patent No. 6,024,325 describes a rotor for rotary wing
aircraft. That patent
27 is incorporated herein by reference. The rotor described in the '325 patent
provides a
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CA 02348677 2001-08-09
1 tremendous improvement over prior ant rotors. However, some improvements are
2 desirable.
3 [0006] A prototype constructed in accordance with the '325 patent flew well,
but the
4 collective forces were high. The large separation of the spar caps at the
point of
attachment to the blade increased collective control forces because
centrifugal force
6 urged the spar caps toward the plane of rotation. Also, the rotor blade of
the rotor
7 described in the '325 patent is swept back moving the outboard tip weights
rearward to
8 eliminate compressive stresses in the trailing edge, thus, moving the center
of gravity of
9 the tip weights toward the structural axis of the rotor. This sweep
increases collective
control forces because it increases the average distance of the tip weights
away from the
11 pitch change axis as centrifugal force tends to push the weights toward the
plane of
12 rotation. The sweep results in an aerodynamic "arrow" effect wherein the
airstream on
13 the swept tip tends to force the blade toward zero pitch.
14 [0007] The present invention provides improvements over the prior art.
SUMMARY OF THE INVENTION
16 [0008] An object of the invention is to provide an improved rotor having
lower
17 collective control forces while maintaining the advantages provided by
prior art rotors.
18 A number of features are used to achieve this. First, the spar caps of the
spar become
19 joined to one another at the same point where bonding begins between the
blade and the
spar. The tendency of blade to want to flatten out is minimized since
centrifugal force
21 acting on the spar caps tries to force the caps to stay in the plane of
rotation and by
22 placing the caps as close to the pitch axis as possible, reduces the moment
arm and the
23 moment resisting the spar from twisting. Tip weights are located at or near
the pitch
24 change axis as well. In a preferred embodiment, the tip weights are located
evenly in
front of and behind the structural center of the inboard section of the spar.
The blade of
26 the rotor and the tip are not swept back.
27 BRIEF DESCRIPTION OF THE DRAWINGS
28 (0009] Figure 1 is a plan view of a portion of a prior art rotor. Figure 1
A (inset) is a
29 detail view of tip weights 16.
[0010] Figure 2 is a plan view of an exemplary rotor constructed in accordance
with the
31 present invention. Figure 2A (inset) is a detail view of tip weights 80.
32 [0011] Figure 3 is a partial cut-away isometric view of the rotor shown in
Figure 2.
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1 [0012] Figure 4 is a cross-sectional view taken along lines 4-4 in Figure 3.
2 [0013] Figure 5 is a cross-sectional view taken along lines 5-5 in Figure 3.
3 [0014) Figure 6 is a cross-sectional view taken along lines 6-6 in Figure 3.
4 [0015) Figure 7 is a cross-sectional view taken along lines 7-7 in Figure 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
6 [0016) Referring first to Figure 1, half of prior art rotor 10 is shown of
the type
7 described in U.S. Patent No. 6,024,325. The rotor 10 has an outer blade 12
with a spar
8 14 disposed therein. The blade 12 forms the aerodynamic housing of the rotor
10. Tip
9 weights 16 are located along the forward edge of a portion of the rotor I 0.
The spar 14
comprises two spar caps 18, 20 that are separated from one another proximate
the root
11 of the rotor 10 and become joined to one another at approximately station
136. However,
12 bonding of the spar caps 18, 20 to the blade 12 occurs at station 84.5 and
continues
13 outboard of that point. Therefore, the bonding occurs inboard of the point
where the spar
14 caps 18, 20 become joined to one another. In addition, a structural rib 22
is disposed
within the blades 12 at the point where bonding begins to further stiffen the
rotor 10.
16 The rotor 10 may be considered to have an inboard portion 24 that lies
radially inward
17 of the point where bonding begins. There is also an outboard portion 26. In
the inboard
18 portion, the spar caps 14 are readily moveable upwardly and downwardly
within the
19 blade 12 to one another in order to alter the pitch of the blade 12. In the
outboard portion
26, the blade 12 is bonded to the spar caps 14. As a result, the spar caps 14
do not move
21 with respect to one another within the housing of the blade 12 in the
outboard portion 26.
22 It should be appreciated that forces affecting pitch of the blade 12 are
largely imparted
23 to the blade 12 at the point 28 where the outboard section 24 and inboard
section 26 meet.
24 As can be seen, the spar caps 14 are widely separated from one another at
point 28. Also,
the tip of the blade 12 and spar are swept back.
26 [0017] The pitch change axis 30 for rotor 10 is shown on Figure 1. The
pitch change
27 axis 30 is the axis around which the blade 12 will rotate when the pitch is
changed by
28 movement of the spars 14. As can be seen, the majority of the tip weights
16, particularly
29 those proximate station 192, lie some distance behind the pitch change axis
30. Further,
the nearer one gets to the blade tip 32, the further behind the axis 30 the
weights 16 are
31 located. During rotation of the rotor 10, centrifugal forces acting on the
mass of the
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I weights 16 will cause the weights 16 to want to move into the plane of
rotation, thereby
2 increasing the collective forces necessary to increase the pitch of the
blade 10.
3 [0018] Turning now to Figures 2, 3, 4, 5, 6 and 7 there is shown an
exemplary rotor 50
4 that is constructed in accordance with the present invention. The pitch
change axis 52
for rotor 50 is shown in Figure 2. The rotor 50 has two blade assemblies 54
and 56 that
6 extend outwardly from spinner 58. Because construction of the two blade
assemblies 54,
7 56 is identical, only the construction of blade assembly 54 will be
described in detail.
8 Stations along the blade assembly 54 are indicated by numerals in Figure 2.
As discussed
9 herein, stations refer to that position measured in inches from the axis of
rotation 60 for
the rotor 50. Dimensions given are for illustrative purposes only. The rotor
50 has a
11 unitary spar 62 that extends nearly tip-to-tip. The spar 62 is separated
along its central
12 section into two spar caps 64, 66. The spar caps 64, 66 merge with one
another to form
13 a single outboard spar portion 68. A blade cuff 69 is used to transfer
pitch control forces
14 to the blade assembly 54 to twist the spar caps 64, 66. The blade assembly
54 has an
outer blade housing 70 that is made up of an upper skin 72 and a lower skin 74
that,
16 collectively, form the airfoil surface for the rotor 50. The blade housing
70 is not swept
17 back, but the very outboard section is swept back like a shark fin to
reduce noise. The
18 spar portion 68 is swept back a few degrees within the housing 70 proximate
the tip 51.
19 (0019] Separation of the spar caps 64, 66 from one another is gradually
reduced from
the root, or axis of rotation 60 toward the station 114 of the rotor blade
assembly 54. The
21 spar caps 64, 66 become joined to one another at approximately station 114.
A
22 reinforcing rib 76 is located at that station as well. Inboard of the rib
76, along inboard
23 portion 77, the spar caps 64, 66 are not bonded to the blade housing 70 so
that they may
24 be moved upwardly and downwardly within the housing 70. Outboard of the rib
76,
along outboard portion 79, the spar portion 68 is bonded to the blade housing
70 using
26 bonding material 78. As best shown in Figures 5, 6 and 7, bonding material
78 fills the
27 space between the spar portion 68 and the outer blade housing 70.
28 [0020] Tip weights 80 are disposed along the leading edge 82 of the blade
assembly 54.
29 In the described embodiment, the tip weights 80 extend from station 184
outwardly to
station 252. As can be seen with reference to Figure 2, the location of the
tip weights 80
31 approximates the pitch change axis 52. In other words, the weights 80 are
located to
32 minimize the average distance between the weights 80 and the pitch change
axis 52. The
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1 rearward sweep of the spar portion 68 proximate the tip 51 allows for this
placement. The
2 rotor tip weights 80 are positioned near the leading edge 82 to keep the
center of mass
3 ahead of the blade aerodynamic center. In a preferred embodiment, the tip
weights 80
4 are located evenly in front of and behind the structural center of the
inboard section of
the spar 62.
6 [0021] In operation, the exemplary rotor 50 uses three primary features to
reduce
7 collective control forces. First, separation of the spar caps 64, 66
gradually reduced from
8 the root 60 toward the tip 51 until the spar caps 64, 66 marry one another
at the point
9 where the blade housing 70 is attached to the spar 62. Second, rotor tip
weights 80 are
attached to minimize the average distance between the weights 80 and the pitch
change
11 axis 52 of the blade assembly 54. Third, the spar 62 is swept back
proximate the tip 51
12 to follow the trailing edge of the tip weights 80. The aerodynamic shell of
the blade
13 housing 70 is not swept.
14 [0022] While the invention has been described with reference to a preferred
embodiment, it should be apparent to those skilled in the art that it is not
so limited, but
16 is susceptible to various modifications and changes without departing from
the scope of
17 the invention.
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