U.S. patent application number 11/137360 was filed with the patent office on 2005-12-01 for rotor blade for helicopter.
This patent application is currently assigned to Fuji Jukogyo Kabushiki Kaisha. Invention is credited to Ota, Tomoki, Taguchi, Hiroshi.
Application Number | 20050265850 11/137360 |
Document ID | / |
Family ID | 35425462 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050265850 |
Kind Code |
A1 |
Ota, Tomoki ; et
al. |
December 1, 2005 |
Rotor blade for helicopter
Abstract
A rotor blade for a helicopter having: a main blade with a blade
root attached to a rotor shaft of the helicopter; and a small blade
attached to a blade tip part of the main blade, wherein a tip part
of the small blade is rectangular form in its plane shape, and has
a leading edge continuous with a leading edge of the main blade and
a chord length shorter than a chord length of the main blade.
Inventors: |
Ota, Tomoki; (Tokyo, JP)
; Taguchi, Hiroshi; (Tokyo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Fuji Jukogyo Kabushiki
Kaisha
|
Family ID: |
35425462 |
Appl. No.: |
11/137360 |
Filed: |
May 26, 2005 |
Current U.S.
Class: |
416/223R |
Current CPC
Class: |
B64C 27/463
20130101 |
Class at
Publication: |
416/223.00R |
International
Class: |
B63H 001/26 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2004 |
JP |
2004-159525 |
Claims
What is claimed is:
1. A rotor blade for a helicopter comprising: a main blade with a
blade root attached to a rotor shaft of the helicopter; and a small
blade attached to a blade tip part of the main blade, wherein a tip
part of the small blade is rectangular form in its plane shape, and
has a leading edge continuous with a leading edge of the main blade
and a chord length shorter than a chord length of the main
blade.
2. The rotor blade for a helicopter as claimed in claim 1, wherein
the chord length c1 of the small blade is set so as to satisfy a
following relational expression; .alpha..ltoreq.c1.ltoreq.0.5C
(.alpha.>0) where C denotes the chord length of the main
blade.
3. The rotor blade for a helicopter as claimed in claim 1, wherein
the chord length c1 of the small blade is set so as to satisfy a
following relational expression; 0.2C.ltoreq.c1.ltoreq.0.5C where C
denotes the chord length of the main blade.
4. The rotor blade for a helicopter as claimed in claim 1, wherein
a blade tip of the small blade protrudes outward by a specific
length relative to a tip part of the main blade, and the specific
length b1 is so set as to satisfy a following expression;
.beta..ltoreq.b1.ltoreq.0.5C (.beta.>0) where C denotes the
chord length of the main blade.
5. The rotor blade for a helicopter as claimed in claim 1, wherein
a blade tip of the small blade protrudes outward by a specific
length relative to a tip part of the main blade, and the specific
length b1 is set so as to satisfy a following expression;
0.2C.ltoreq.b1.ltoreq.0.4C where C denotes the chord length of the
main blade.
6. The rotor blade for a helicopter as claimed in claim 1, wherein
a blade tip vicinity part of the main blade is bent downward by a
predetermined anhedral angle.
7. The rotor blade for a helicopter as claimed in claim 1, wherein
the small blade has a predetermined anhedral angle relative to the
main blade.
8. The rotor blade for a helicopter as claimed in claim 1, wherein
the small blade has a predetermined angle of incidence relative to
the main blade.
9. The rotor blade for a helicopter as claimed in claim 1, wherein
a blade tip vicinity part of the main blade and the small blade
continuously joined to the blade tip vicinity part are swept back
toward the outside of the blade tip.
10. The rotor blade for a helicopter as claimed in claim 2, wherein
a blade tip part of the small blade protrudes outward by a specific
length relative to a tip part of the main blade, and the specific
length b1 is set so as to satisfy a following expression;
.beta..ltoreq.b1.ltoreq.0.5C (.beta.>0) where C denotes the
chord length of the main blade.
11. The rotor blade for a helicopter as claimed in claim 3, wherein
a blade tip of the small blade protrudes outward by a specific
length relative to a tip part of the main blade, and the specific
length b1 is set so as to satisfy a following expression;
.beta..ltoreq.b1.ltoreq.0.5C (.beta.>0) where C denotes the
chord length of the main blade.
12. The rotor blade for a helicopter as claimed in claim 2, wherein
the blade tip of the small blade protrudes outward by a specific
length relative to a tip part of the main blade, and the specific
length b1 is set so as to satisfy a following expression;
0.2C.ltoreq.b1.ltoreq.0.4C where C denotes the chord length of the
main blade.
13. The rotor blade for a helicopter as claimed in claim 3, wherein
the blade tip of the small blade protrudes outward by a specific
length relative to a tip part of the main blade, and the specific
length b1 is set so as to satisfy a following expression;
0.2C.ltoreq.b1.ltoreq.0.4C where C denotes the chord length of the
main blade.
14. The rotor blade for a helicopter as claimed in claim 8, wherein
the angle of incidence is set to be in a range of -5 to +5 degrees.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Japanese Patent
Applications No. 2004-159525 filed on May 28, 2004 respectively
which are incorporated herein by reference in its entirety.
BACKGROUD OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a rotor blade for a
helicopter.
[0004] 2. Description of the Related Art
[0005] Helicopters have been used in various fields, such as
transportation of supplies, lifesaving, and national defenses. When
a helicopter lands, as shown in FIG. 13, a succeeding rotor blade
100b interacts with tip vortices 101 generated by the blade tip of
a preceding rotor blade 100a, and generates noise. This noise is
called BVI (blade vortex interaction) noise.
[0006] In conventional rotor blades, there have been used, for
example, a rectangular blade tip part 200 shown in FIG. 14, and a
blade tip part 300 shown in FIG. 15 that has a shape of gradually
sweeping back toward the outer side of the blade tip part.
Employment of rotor blades having these shapes of blade tip parts
has not been able to reduce the BVI noise, though. For solving this
problem, various technologies have been proposed for reducing the
BVI noise, each technology adopting a rotor blade that has a
specific shape (structure) of blade tip part to weaken the tip
vortices.
[0007] For instance, as shown in FIG. 16, such technology has been
proposed that a rectangular small blade 410 is attached to a
rectangular blade tip part 400 of a rotor blade at the leading edge
side to weaken tip vortices with the tip vortices generated by the
rotor blade divided into two parts. As shown in FIG. 17, a blade
tip part 500 of a rotor blade is provided with a tip blade 510
attached thereto having a mean chord length and a span length
longer than 50% of the center-portion chord length of the rotor
blade to generate two tip vortices of substantially the same
intensity (refer to JP-Tokukaihei-4-262994A).
[0008] As another example, as shown in FIG. 18, a rotor blade
(refer to JP-Tokukai-2002-284099A) consists of a main blade 600 and
a small blade 700 that has a chord length and a span length set in
a certain range. Each of a blade tip part 610 of the main blade 600
and a blade tip part 710 of the small blade 700 has a curved shape
(for example, a parabolic shape). With this structure, tip vortices
shed from the tip part 610 interferes with tip vortices shed from
the tip part 710, and this interference can reduce the
vortices.
[0009] In the technology disclosed in JP-Tokukaihei-4-262994A,
however, generated two vortices are not positively interfered with
each other, and therefore BVI noise could not be greatly reduced.
In the technology disclosed in JP-Tokukai-2002-284099A, although
generated two vortices can be interfered with each other, a problem
arises in that designing and manufacturing of the small blade
require substantial cost and time because the blade tip part of the
small blade has a complicated shape (for example, a parabolic
shape).
SUMMARY OF THE INVENTION
[0010] An object of the invention is to greatly reduce the cost and
time necessary for designing and manufacturing a rotor blade of a
helicopter, and to remarkably reduce BVI noise generated when the
helicopter lands or descends.
[0011] For solving the problems, in accordance with the first
aspect of the present invention, the rotor blade for a helicopter
comprises:
[0012] a main blade with a blade root attached to a rotor shaft of
the helicopter; and
[0013] a small blade attached to a blade tip part of the main
blade,
[0014] wherein the small blade is rectangular in its plane shape,
and has a leading edge continuous with a leading edge of the main
blade and a chord length shorter than a chord length of the main
blade.
[0015] According to this structure, since the small blade is
attached and extended along the leading edge of the blade tip part
of the main blade, tip vortices can be shed from both the tip part
of the main blade and the blade tip part of the small blade. By
properly setting a positional relationship between the tip part of
the main blade and the blade tip part of the small blade, the tip
vortices shed from the tip part of the main blade and that shed
from the blade tip part of the small blade can be positively
interfered with each other and diffused. As a result, the tip
vortices shed from the blade tip part of the rotor blade can be
weakened, which can remarkably reduce BVI noise when the helicopter
lands or descends.
[0016] Further, since the small blade has a simple plane shape
(rectangular shape), the time and cost required for designing and
manufacturing the small blade can be greatly reduced. Further,
since the rotor blade according to the invention can be
manufactured by modifying a conventional rotor blade at its blade
tip part only, it is possible to reduce the time and cost required
for manufacturing a whole rotor blade.
[0017] Preferably, the chord length c1 of the small blade is set so
as to satisfy a following relational expression;
.alpha..ltoreq.c1.ltoreq.0.5C (.alpha.>0)
[0018] where C denotes the chord length of the main blade.
[0019] According to this structure, since the chord length of the
small blade is set to a certain length (50% or less of the chord
length of the main blade), the intensity of the tip vortices (swirl
velocity) shed from the blade tip part of the main blade and that
shed from the blade tip part of the small blade can be properly
set. Resultantly, these two tip vortices can be effectively
interfered with each other, thereby achieving superior effect of
BVI noise reduction.
[0020] Preferably, the chord length c1 of the small blade is so set
as to satisfy a following relational expression;
0.2C.ltoreq.c1.ltoreq.0.5C
[0021] where C denotes the chord length of the main blade.
[0022] With this relationship, since the chord length of the small
blade is set to a certain length (20% or more and 50% or less of
the chord length of the main blade), the intensity of the tip
vortices (swirl velocity) shed from the blade tip part of the main
blade and that shed from the blade tip part of the small blade can
be more properly set. Resultantly, these two tip vortices can be
more effectively interfered with each other, thereby achieving
superior effect of BVI noise reduction.
[0023] Preferably, a blade tip part of the small blade protrudes
outward by a specific length relative to a tip part of the main
blade, and the specific length b1 is so set as to satisfy a
following expression;
.beta..ltoreq.b1.ltoreq.0.5C (.beta.>0)
[0024] where C denotes the chord length of the main blade.
[0025] According to this structure, since the blade tip of the
small blade protrudes outward by a specific length (50% or less of
the chord length of the main blade) relative to the tip part of the
main blade, the vortex center position of the tip vortices shed
from the blade tip part of the main blade can be separated apart
from that shed from the blade tip part of the small blade in the
span direction. As a result, these two tip vortices can be more
positively interfered with each other, leading to superior effect
of BVI noise reduction.
[0026] Preferably, a blade tip part of the small blade protrudes
outward by a specific length relative to a tip part of the main
blade, and the specific length b1 is so set as to satisfy a
following expression;
0.2C.ltoreq.b1.ltoreq.0.4C
[0027] where C denotes the chord length of the main blade.
[0028] With this relationship, since the blade tip of the small
blade protrudes outward by a specific length (20% or more and 40%
or less of the chord length of the main blade) relative to the tip
part of the main blade, the vortex center position of the tip
vortices shed from the blade tip part of the main blade can be
separated apart from that shed from the blade tip part of the small
blade by a proper distance in the span direction. As a result,
these two tip vortices can be more positively interfered with each
other, thereby achieving superior effect of BVI noise
reduction.
[0029] Preferably, a blade tip vicinity part of the main blade is
bent downward by a predetermined anhedral angle.
[0030] According to this structure, since the blade tip vicinity
part of the main blade is bent downward by a predetermined anhedral
angle, if the small blade does not have a predetermined anhedral
angle relative to the main blade, tip vortices generated by the
blade tip part of the main blade can be positioned under tip
vortices generated by the blade tip part of the small blade.
Therefore, these two tip vortices can be effectively interfered
with each other. Further, the tip vortices are shed downward from
the preceding rotor blade and hard to interact with the succeeding
rotor blade, which can reduce BVI noise all the more.
[0031] Additionally, since the preceding rotor blade can shed tip
vortices downward, the partial stall of the succeeding rotor blade
becomes smaller, the stall generally being caused by the current
induced by the tip vortices. Resultantly, there can be reduced
energy loss during the drive of a rotary wing, and be improved
hovering performance while the helicopter is suspended in the
air.
[0032] Preferably, the small blade has a predetermined anhedral
angle relative to the main blade.
[0033] According to this structure, since the small blade is bent
downward by a predetermined anhedral angle relative to the main
blade, the tip vortices generated by the blade tip part of the
small blade can be positioned under the tip vortices generated by
the blade tip part of the main blade. Therefore, these two tip
vortices can be effectively interfered with each other. Further,
the tip vortices are shed downward from the preceding rotor blade
and hard to interact with the succeeding rotor blade, which can
reduce BVI noise all the more.
[0034] Additionally, since the preceding rotor blade can shed tip
vortices downward, the partial stall of the succeeding rotor blade
becomes smaller, the stall generally being caused by the current
induced by the tip vortices. Resultantly, there can be reduced
energy loss during the drive of a rotary wing, and be improved
hovering performance while the helicopter is suspended in the
air.
[0035] Preferably, the small blade has a predetermined angle of
incidence relative to the main blade.
[0036] According to this structure, setting the angle of incidence
to a proper value relative to the main blade allows the tip
vortices shed from the small blade tip part to be adjusted in the
flowing direction and density thereof. Therefore, the tip vortices
shed from the main blade tip part can effectively interfere with
the tip vortices shed from the small blade tip part.
[0037] Preferably, a blade tip vicinity part of the main blade and
the small blade continuously joined to the blade tip vicinity part
are swept back toward the outside of the blade tip.
[0038] With this structure, since the tip vicinity part of the main
blade and the small blade continuously joined to the tip vicinity
part sweep back toward the tip outside, there can be reduced
airspeed in the direction perpendicular to the blade tip vicinity
part of the main blade and the extended direction of the small
blade. Consequently, this rotor blade can reduce the BVI noise, and
also improve a transonic characteristic and delay the generation of
a shock wave.
[0039] According to the invention, the small blade is attached and
extended along the leading edge of the blade tip part of the main
blade, and by properly setting a positional relationship between
the tip part of the main blade and the blade tip of the small
blade, the tip vortices shed from the blade tip part of the main
blade and that shed from the blade tip part of the small blade can
be positively interfered with each other and diffused.
Consequently, the tip vortices shed from the blade tip part of the
rotor blade can be weakened, which can remarkably reduce the BVI
noise when the helicopter lands. Further, simple structure of the
small blade allows remarkable reduction of time and cost required
for designing and manufacturing the small blade, and resultant cost
reduction for manufacturing a whole rotor blade.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The present invention will become more fully understood from
the detailed description given hereinafter and the accompanying
drawings which are given by way of illustration only, and thus are
not intended as a definition of the limits of the present
invention, and wherein;
[0041] FIG. 1 is a plan view showing a blade tip vicinity part of a
rotor blade according to a first embodiment of the present
invention;
[0042] FIG. 2A is an explanatory diagram explaining tip vortices
generated when a conventional rotor blade is used, FIG. 2B is an
explanatory diagram explaining diffusion of tip vortices generated
in the case that the rotor blade according to the first embodiment
of the invention is used, and FIG. 2C is an explanatory diagram
showing the state of the vortices shown in FIG. 2B when viewed from
a back side;
[0043] FIG. 3A is a graph showing the state of generation of tip
vortices in the case that the chord length of a small blade on the
rotor blade is set to a length of 5% of the chord length of a main
blade, FIG. 3B is a graph showing the state of generation of tip
vortices in the case that the chord length of the small blade on
the rotor blade is set to a length of 30% of the chord length of a
main blade; and FIG. 3C is a graph showing the state of generation
of tip vortices in the case that the chord length of the small
blade on the rotor blade is set to a length of 50% of the chord
length of a main blade;
[0044] FIG. 4 is a graph showing the relationship between the chord
length of the small blade and the maximum swirl velocity of the tip
vortices shed from the rotor blade;
[0045] FIG. 5A is a graph showing the state of generation of tip
vortices in the case that the rotor blade does not have a small
blade, FIG. 5B is a graph showing the state of generation of tip
vortices in the case that the rotor blade has a small blade with a
specific length set to 20% of the chord length of the main blade,
and FIG. 5C is a graph showing the state of generation of tip
vortices in the case that the rotor blade has a small blade with a
specific length set to 40% of the chord length of the main
blade;
[0046] FIG. 6 is a graph showing the relationship between the
specific length and the maximum swirl velocity of the tip vortices
shed from the rotor blade;
[0047] FIG. 7 is a graph showing the effect of noise reduction in
the case of using the rotor blade having the main blade with the
small blade;
[0048] FIG. 8A is a plan view showing a blade tip vicinity part of
a rotor blade according to a second embodiment of the present
invention, and FIG. 8B is a diagram showing the rotor blade of FIG.
8A when viewed from a trailing edge side;
[0049] FIG. 9A is a plan view showing a blade tip vicinity part of
a rotor blade according to a third embodiment of the present
invention, and FIG. 9B is a diagram showing the rotor blade of FIG.
9A when viewed from a tip side;
[0050] FIG. 10 is a plan view showing a blade tip vicinity part of
a rotor blade according to a fourth embodiment of the present
invention;
[0051] FIG. 11 is a plan view showing a blade tip vicinity part of
a rotor blade according to a fifth embodiment of the present
invention;
[0052] FIG. 12 is a plan view showing a blade tip vicinity part of
a rotor blade according to a sixth embodiment of the present
invention;
[0053] FIG. 13 is an explanatory view for explaining a principle of
generation of BVI noise;
[0054] FIG. 14 is a plan view showing a rectangular blade tip part
of a conventional rotor blade;
[0055] FIG. 15 is a plan view showing a conventional rotor blade
with a blade tip part having a swept-back angle;
[0056] FIG. 16 is a perspective view explaining the construction of
a blade tip vicinity part of a conventional rotor blade having a
small blade;
[0057] FIG. 17 is a perspective view explaining the construction of
a blade tip vicinity part of a conventional rotor blade having a
small blade; and
[0058] FIG. 18 is a plan view explaining the construction of a
blade tip vicinity part of a conventional rotor blade having a
small blade.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0059] Embodiments of the present invention will now be described
in detail with reference to the accompanying drawings.
First Embodiment
[0060] Explanation will be given of the construction of a rotor
blade 10 according to a first embodiment of the invention with
reference to FIG. 1. A plurality of rotor blades 10 are attached to
a rotor shaft 20 of a helicopter (not shown) to constitute a rotary
wing. As shown in FIG. 1, the rotor blade 10 includes a main blade
11, a blade root 30 of which is attached to the rotor shaft 20, and
a small blade 12 attached to the blade tip part of the main blade
11.
[0061] The main blade 11 has a substantially constant chord length
C except a blade tip vicinity part, and is so formed that a
trailing edge 11b protrudes outward relative to a leading edge 11a.
The top end of the leading edge 11a of the main blade 11 is
connected to the top end of the trailing edge 11b with a blade tip
end 13 having a smoothly curved shape (parabolic shape), which
constitutes a blade tip vicinity part of the main blade 11.
[0062] A tip part of the small blade 12, as shown in FIG. 1, is a
rectangular form in its plane shape, and has a leading edge 12a
continuous with the leading edge 11a of the main blade 11 and a
chord length c1 shorter than the chord length C of the main blade
11. In this embodiment, the chord length c1 of the small blade 12
is so set as to satisfy a following relational expression:
0.2C.ltoreq.c1.ltoreq.0.5C
[0063] That is, the chord length c1 of the small blade 12 is set to
a length of 20% or more and 50% or less of the chord length C of
the main blade 11.
[0064] The blade tip part of the small blade 12, as shown in FIG.
1, protrudes outward by a specific length b1 relative to the
trailing edge end of the main blade 11. In this embodiment, the
specific length b1 is so set as to satisfy a following relational
expression:
0.2C.ltoreq.b1.ltoreq.0.4C
[0065] That is, the specific length b1 is set to a length of 20% or
more and 40% or less of the main blade chord length C.
[0066] Referring to FIG. 2, a description will be given of the
state of tip vortex diffusion for each case of using the rotor
blade 10 according to this embodiment and a conventional rotor
blade 100 having a rectangular blade tip part.
[0067] In the case that the conventional rotor blade 100 is used,
as shown in FIG. 2A, strong tip vortices 100a are shed from the
blade tip part, and the vortices 100a flow backward without being
diffused. On the contrary, if the rotor blade 10 of the embodiment
is used, as shown in FIG. 2B, first tip vortices 11c are shed from
the blade tip part of the main blade 11, and second tip vortices
12c from the blade tip part of the small blade 12. Each of two
vortices 11c and 12c flows backward.
[0068] Since the blade tip of the small blade 12 protrudes outward
by the specific length b1 relative to the trailing edge end of the
main blade 11, the second tip vortices 12c flow backward passing
the near outside of the blade tip part of the main blade 11, and
positively interfere with the first tip vortices 11c. That is, the
right side of the first tip vortices, which rotate counterclockwise
11c in FIG. 2C, are canceled by the left side of the second tip
vortices 12c that also rotate counterclockwise, which causes the
vortices to be diffused as a whole with intensity of the vortices
weakened. As a result, the tip vortices shed from the rotor blade
10 are weakened, and the BVI noise is greatly reduced.
[0069] A description will be given of analysis on tip vortices
carried out for setting an upper limit value and a lower limit
value of the chord length c1 of the small blade 12 of the rotor
blade 10 according to this embodiment, referring to FIGS. 3 and
4.
[0070] Relating to this embodiment, tip vortices generation states
are analyzed in the case that a main blade of a rotor blade is
provided with a small blade having various chord lengths c1. Based
on the analysis result, a range of the chord length c1 (upper limit
value and lower limit value) is extracted so as to obtain an
expected diffusion effect on tip vortices, and applied the range of
the chord length c1 to the small blade 12. Here, the main blade
used in this analysis has a rectangular blade tip part.
[0071] FIGS. 3A to 3C are graphs showing tip vortices generation
states in the case that the main blade of the rectangular blade tip
part is provided with a small blade having the chord length c1 set
to (a) 5%, (b) 30% and (3) 50% of the main blade chord length C,
respectively.
[0072] The ordinate in FIG. 3 denotes values that the length,
extending from the blade tip end position of the main blade in a
span direction, is divided by the chord length C: zero represents
the blade tip end position of the main blade, positive values the
outside of the blade tip end, and negative values the blade root 30
side. The abscissa in FIG. 3 denotes the values that the length,
extending in a direction of main blade thickness from the thickness
center position to the upper and lower surface sides of the blade,
is divided by the chord length C: zero represents the thickness
center position of the main blade, positive values the upper
surface side, and negative values the lower surface side. Presented
in FIG. 3 are vorticity contour lines h and slip flow velocity
vectors v at a downstream position with one chord length of the
main blade from the main blade. The thinner vorticity contour lines
h and the shorter slip flow velocity vectors v mean the better
vortex diffusion.
[0073] In the case that the chord length c1 of the small blade is
set to 5% of the chord length C of the main blade, as shown in FIG.
3A, the contour lines h are relatively dense and the velocity
vectors v are relatively longer, therefore it is understood that
tip vortices shed from the blade are relatively strong. The reason
for this is: if the chord length c1 is short, while the swirl
velocity of tip vortices shed from the blade tip part of the small
blade is low, the swirl velocity of tip vortices shed from the
blade tip part of the main blade is high, and hence these two tip
vortices interfere relatively little with each other.
[0074] On the contrary, in the case that the chord length c1 of the
small blade is set to 30% and 50% of the chord length C of the main
blade as shown in FIGS. 3B and 3C, the contour lines h become
relatively thinner and the velocity vectors v become relatively
shorter, therefore it is understood that tip vortices shed from the
blade are relatively weaker. The reason for this is: if the chord
length c1 is set to a proper value, the lift generated by the small
blade becomes large, therefore the swirl velocity of tip vortices
shed from the blade tip part of the small blade is almost equal to
that shed from the blade tip part of the main blade, and hence
these two tip vortices effectively interfere with each other.
[0075] Incidentally, if the chord length c1 is set to more than 50%
of the chord length C, then the volume and weight of the small
blade become larger, and therefore the intensity of joint between
the small blade and the main blade unfavorably becomes lower.
[0076] In a graph of FIG. 4, the ordinate denotes the maximum swirl
velocity of tip vortices shed from the rotor blade, and the
abscissa denotes values that the chord length c1 of the small blade
is divided by the chord length C of the main blade. As shown by a
dotted line in FIG. 4, if the main blade is not provided with a
small blade, the maximum swirl velocity of tip vortices presents a
constant high value. It is understood, on the contrary, that, if
the main blade is provided with the small blade having the proper
chord length c1 (for example, 20% to 50% of the chord length C of
the main blade), the maximum swirl velocity of tip vortices is
greatly reduced due to vortex diffusion of the small blade tip
part.
[0077] Based on the analysis result described above relating to the
rotor blade 10 according to the embodiment, "0.5C" was adopted as
the upper limit value of the chord length c1 of the small blade 12,
and "0.2C" as the lower limit value.
[0078] A description will be given of analysis on tip vortices
carried out for setting an upper limit value and a lower limit
value on the specific length b1 of the rotor blade 10 according to
the embodiment, referring to FIGS. 5 and 6.
[0079] Relating to the embodiment, tip vortices generation states
are analyzed in the case that a main blade of a rotor blade is
provided with a small blade having the blade tip part protruding
outward by the specific length b1 relative to the blade tip part of
the main blade. Based on the analysis result, a range of the
specific length b1 (upper limit value and lower limit value) is
extracted so as to obtain an expected diffusion effect on tip
vortices, and applied the specific length b1 to the small blade 12
of the rotor blade 10. Here, the main blade used in this analysis
has a rectangular blade tip part.
[0080] FIG. 5A is a graph showing a tip vortices generation states
in the case that the main blade only is used. FIGS. 5B and 5C are
graphs showing tip vortices generation states in the case that the
main blade is provided with a small blade having the blade tip part
protruding outward by the specific length b1 relative to the main
blade tip. The specific length b1 is set to 20% of the chord length
C of the main blade in FIG. 5B, and 40% in FIG. 5C.
[0081] The ordinate and abscissa in FIG. 5 are set to the same
values as in FIG. 3, respectively, and vorticity contour lines h
and slip flow velocity vectors v at a downstream position with one
chord length of the main blade from the main blade are shown as in
FIG. 3. The broader vorticity contour lines h and the shorter slip
flow velocity vectors v mean the better vortex diffusion.
[0082] In the case that the main blade only is used (without a
small blade) as shown in FIG. 5A, the contour lines h are
relatively dense and the velocity vectors v are relatively longer,
therefore it is understood that tip vortices shed from the blade
are relatively strong. Thus, if the small blade is not provided,
the tip vortices shed from the main blade are not diffused and
weakened. Even if a small blade is provided, when the specific
length b1 is almost zero with a short span length of the small
blade, a vortex center position of the tip vortices shed from the
blade tip part of the small blade is close to that shed from the
blade tip part of the main blade, therefore these two vortices can
not be effectively interfered with each other.
[0083] In the case that the specific length b1 is set to 20% and
40% of the chord length C of the main blade as shown in FIGS. 5B
and 5C, on the contrary, the contour lines h become relatively
broader and the slip flow velocity vectors v become relatively
shorter, hence it is understood that tip vortices shed from the
blade are relatively weaker. The reason for this is: if the
specific length b1 is set to a proper value, the vortex center
position of the tip vortices shed from the blade tip part of the
main blade is separated apart from that shed from the blade tip
part of the small blade by a proper distance in the span direction,
therefore these two vortices can be effectively interfered with
each other.
[0084] Incidentally, if the specific length b1 is set to more than
50% of the chord length C, the intensity of joint between the small
blade and the main blade becomes unfavorably lower.
[0085] In a graph of FIG. 6, the ordinate denotes the maximum swirl
velocity of tip vortices shed from the rotor blade, and the
abscissa denotes values that the specific length b1 is divided by
the chord length C of the main blade. As shown by a dotted line in
FIG. 6, if the main blade is not provided with a small blade, the
maximum swirl velocity of tip vortices presents a constant high
value. It is understood, on the contrary, that, if the main blade
is provided with the small blade having the blade tip part
protruding outward by the specific length b1 (for example, 20% to
40% of the chord length C of the main blade) relative to the blade
tip part of the main blade, the maximum swirl velocity of tip
vortices is greatly reduced due to vortex diffusion of the small
blade tip part.
[0086] Based on the analysis result described above relating to the
rotor blade 10 according to the embodiment, "0.4C" was adopted as
the upper limit value of the specific length b1, and "0.2C" as the
lower limit value.
[0087] Referring to FIG. 7, a description will be given of a noise
reduction effect confirmed by flight tests using an actual
helicopter.
[0088] FIG. 7 shows a measured result of landing noise for the case
that the rotor blade has a main blade only and that for the case
that the rotor blade has a main blade with a small blade. Measured
landing noise mostly comes from BVI noise. In this test, the chord
length c1 of the small blade is set to 30% of the chord length C of
the main blade. The blade tip of the small blade protrudes outward
by the specific length b1 relative to the blade tip part of the
main blade, and the specific length b1 is set to 30% of the chord
length C.
[0089] As shown in FIG. 7, the landing noise (BVI noise) for the
case that the rotor blade has the main blade with the small blade
is reduced by "2.8 EPNdB" compared with that for the case that the
rotor blade has the main blade only. It is proved that, by setting
the chord length of the small blade to a proper value and
protruding the blade tip of the small blade by the specific length
relative to the blade tip part of the main blade with the specific
length set to a proper value, the tip vortices shed from the blade
tip part of the main blade interfere with the tip vortices shed
from the blade tip part of the small blade, which weakens the tip
vortices and resultantly reduces the BVI noise.
[0090] In the rotor blade 10 according to the embodiment described
above, since the small blade 12 is attached and extended along the
straight line part of the leading edge 11a of the main blade 11,
tip vortices can be shed from both the tip part of the main blade
11 and the blade tip part of the small blade 12.
[0091] Since the chord length c1 is set to a certain length (20% or
more and 50% or less of the chord length C of the main blade 11),
the intensity of the tip vortices (swirl velocity) shed from the
blade tip part of the main blade 11 and that shed from the blade
tip part of the small blade 12 can be properly set. Further, since
the blade tip of the small blade 12 protrudes outward by the
specific length b1 (20% or more and 40% or less of the chord length
C of the main blade 11) relative to the tip part of the main blade
11, the vortex center position of the tip vortices shed from the
blade tip part of the main blade 11 can be separated apart from
that shed from the blade tip part of the small blade 12 by a proper
distance in the span direction.
[0092] Accordingly, the tip vortices shed from the tip part of the
main blade 11 and that shed from the blade tip part of the small
blade 12 can be positively interfered with each other and diffused.
As a result, the tip vortices shed from the blade tip part of the
rotor blade 10 can be weakened, which allows remarkable reduction
of BVI noise when the helicopter lands.
[0093] Moreover, the small blade 12.of the rotor blade 10 according
to the embodiment described above has a simple plane shape
(rectangular shape), therefore the time and cost required for
designing and manufacturing the small blade 12 can be greatly
reduced. Further, since the rotor blade 10 according to the
invention can be manufactured by modifying a conventional rotor
blade at its blade tip part only, it is possible to reduce the time
and cost required for manufacturing a whole rotor blade.
[0094] Furthermore, the rotor blade 10 according to this embodiment
has a blade tip end 13 of the main blade 11 formed in a parabolic
shape, which makes airspeed in a direction perpendicular to the
blade tip end 13 of the main blade 11 smaller toward the leading
edge side. Accordingly, the rotor blade 10 according to the
embodiment is superior in a transonic characteristic and delays the
generation of a shock wave, thereby avoiding a sharp increase of
resistance.
Second Embodiment
[0095] A description will be given of a rotor blade 10A according
to a second embodiment of the present invention with reference to
FIG. 8. The rotor blade 10A is substantially the same as that of
the first embodiment with the exception that the blade tip vicinity
part of the main blade and the construction of the small blade of
the rotor blade 10 in the first embodiment are slightly modified.
Therefore, those elements which are the same as corresponding
elements in the first embodiment are designated by the same
reference numerals as of the first embodiment, and the modified
structure only will be described.
[0096] As shown in FIG. 8, the rotor blade 10A according to this
embodiment has a blade tip vicinity part 11A of the main blade 11
bent downward by a predetermined anhedral angle .delta.1, and has a
small blade 12A attached to the main blade 11 by a predetermined
anhedral angle .delta.2 with respect to the main blade 11. These
anhedral angles .delta.1 and .delta.2 can be properly determined
according to the size and rotating velocity of the rotor blade 10A,
the flying speed of the helicopter, etc., and can be set to, for
example, within a range of 0-30 degrees.
[0097] In this embodiment, the anhedral angle .delta.1 of the blade
tip vicinity part 11A of the main blade 11 is set to larger angle
than the anhedral angle .delta.2 of the small blade 12A as shown in
FIG. 8B. With this structure, tip vortices generated by the blade
tip part of the main blade 11 is positioned under tip vortices
generated by the blade tip part of the small blade 12A, and these
two tip vortices can be effectively interfered with each other.
Further, since the tip vortices are shed downward from the rotor
blade 10A, these vortices are hard to interact with the succeeding
rotor blade, which can reduce BVI noise all the more.
[0098] The rotor blade 10A of the embodiment can shed tip vortices
downward, and therefore can control the partial stall of the
succeeding rotor, the stall generally being caused by the current
induced by the tip vortices. Resultantly, there can be reduced
energy loss during the drive of a rotary wing, and be improved
hovering performance while the helicopter is suspended in the
air.
Third Embodiment
[0099] A description will be given of a rotor blade 10B according
to a third embodiment of the present invention with reference to
FIG. 9. The rotor blade 10B is substantially the same as that of
the first embodiment with the exception that the construction of
the small blade of the rotor blade 10 in the first embodiment is
slightly modified. Therefore, those elements which are the same as
corresponding elements in the first embodiment are designated by
the same reference numerals as of the first embodiment, and the
modified structure only will be described.
[0100] As shown in FIG. 9, the rotor blade 10B has a small blade
12B attached to the main blade 11 by a predetermined angle of
incidence .theta.. The angle of incidence .theta. can be properly
determined according to the size and rotating velocity of the rotor
blade 10A, the flying speed of the helicopter, etc., and can be set
to, for example, within a range of -5 to +5 degrees. By setting the
angle of incidence .theta. to a proper value, tip vortices shed
from the blade tip part of the small blade 12B can be adjusted in
the flowing direction and intensity thereof so that the tip
vortices shed from the blade tip part of the main blade 11 can
effectively interfere with the tip vortices shed from the blade tip
part of the small blade 12B.
Fourth Embodiment
[0101] A description will be given of a rotor blade 10C according
to a fourth embodiment of the present invention with reference to
FIG. 10. The rotor blade 10C is substantially the same as that of
the first embodiment with the exception that the construction of
the joined potion between the main blade and the small blade of the
rotor blade 10 in the first embodiment is slightly modified.
Therefore, those elements which are the same as corresponding
elements in the first embodiment are designated by the same
reference numerals as of the first embodiment, and the modified
structure only will be described.
[0102] As shown in FIG. 10, the rotor blade 10C has a joined potion
14C formed of a smooth surface (plane or curved surface) between
the main blade 11 and the small blade 12. The joined portion 14C
having a smooth surface can reduce air resistance acting thereon,
which can improve a transonic characteristic and delay the
generation of a shock wave.
Fifth Embodiment
[0103] A description will be given of a rotor blade 10D according
to a fifth embodiment of the present invention with reference to
FIG. 11. The rotor blade 10D is substantially the same as that of
the first embodiment with the exception that the construction of
the blade tip vicinity part of the main blade of the rotor blade 10
in the first embodiment is slightly modified. Therefore, those
elements which are the same as corresponding elements in the first
embodiment are designated by the same reference numerals as of the
first embodiment, and the modified structure only will be
described.
[0104] As shown in FIG. 11, the rotor blade 10D has a straight
blade tip end 13D connecting between tips of the leading edge 11a
and the trailing edge 11b of the main blade 11. In the rotor blade
10D of this embodiment, the trailing edge 11b protrudes outward
relative to the leading edge 11a, then the straight blade tip end
13D has a large swept-back angle .LAMBDA., thereby airspeed
perpendicular to the blade tip end 13D is reduced due to the effect
of the swept-back angle .LAMBDA.. That is, if a constant flow
velocity is given by V.infin., the airspeed perpendicular to the
blade tip end 13D is V.infin.cos.LAMBDA. (<V.infin.).
Accordingly, the rotor blade 10D according to this embodiment is
superior in a transonic characteristic and delays the generation of
a shock wave, allowing avoidance of a sharp increase of
resistance.
Sixth Embodiment
[0105] A description will be given of a rotor blade 10E according
to a sixth embodiment of the present invention with reference to
FIG. 12. The rotor blade 10E is substantially the same as that of
the first embodiment with the exception that the construction of
the blade tip vicinity part of the main blade of the rotor blade 10
in the first embodiment is slightly modified. Therefore, those
elements which are the same as corresponding elements in the first
embodiment are designated by the same reference numerals as of the
first embodiment, and the modified structure only will be
described.
[0106] As shown in FIG. 12, in the rotor blade 10E according to
this embodiment, a leading edge blade tip vicinity part 15E is
swept back by a certain swept-back angle, a trailing edge blade tip
vicinity part 16E is swept back by the certain swept-back angle to
be in parallel with the leading edge blade tip vicinity part 15E,
the trailing edge blade tip vicinity part 16E is extended outward,
and the tip of the leading edge blade tip vicinity part 15E is
connected with the tip of the trailing edge blade tip vicinity part
16E with a blade tip end 13E having a smooth parabolic shape. The
small blade 12 has a leading edge 12a continuous with the leading
edge blade tip vicinity part 15E. That is, the rotor blade 10E
according to this embodiment has a blade tip vicinity part 11E of
the main blade 11 and the small blade 12 continuously joined to the
blade tip vicinity part 11E so as to sweep back toward the blade
tip outside.
[0107] In the rotor blade 10E according to this embodiment, the
structure is such that the blade tip vicinity part 11E of the main
blade 11 and the small blade 12 continuously joined to the blade
tip vicinity part 11E sweep back toward the blade tip outside.
Thus, airspeed in the direction perpendicular to the blade tip
vicinity part 11E and the small blade 12 of the main blade 11 can
be reduced. Consequently, the rotor blade 10E according to this
embodiment is superior in a transonic characteristic and delays the
generation of a shock wave, allowing avoidance of a sharp increase
of resistance.
[0108] In the embodiments described above, the trailing edge of the
main blade of the rotor blade exemplarily protrudes outward
relative to the leading edge, but it is not always necessary to
protrude the trailing edge outward than the leading edge. A main
blade having a rectangular blade tip part can be employed. Even
when the main blade having a rectangular blade tip part is
employed, aforementioned effects of the vortex diffusion and the
noise reduction can be achieved, as long as the chord length c1 of
the small blade is set to a particular length (for example,
0.2C.ltoreq.c1.ltoreq.0.5C), and the blade tip of the small blade
protrudes outward by the specific length b1 relative to the blade
tip part of the main blade, with the specific length b1 set to a
certain length (for example, 0.2C.ltoreq.b1.ltoreq.0.4C).
[0109] In the embodiments described above, the chord length c1 of
the small blade of the rotor blade is exemplarily set to 0.5C (50%
of the main blade chord length C) as the upper limit value, and
0.2C (20% of the main blade chord length C) as the lower limit
value. However, these upper and lower limit values can be
appropriately changed according to the size and shape of a rotor
blade, if desired tip vortex diffusion could be attained. In this
case, the lower limit value of the chord length c1 of a small blade
should be set to not less than a minimum necessitated value .alpha.
(>0) to function as a small blade.
[0110] In the embodiments described above, the specific length b1
of the rotor blade is exemplarily set to 0.4C (40% of the main
blade chord length C) as the upper limit value, and 0.2C (20% of
the main blade chord length C) as the lower limit value. However,
these upper and lower limit values can be appropriately changed
according to the size and shape of a rotor blade, if desired tip
vortex diffusion could be attained. For example, the upper limit
value of the specific length b1 can be set to 0.5C (50% of the main
blade chord length C), and the lower limit value to a positive
constant value .beta. (>0) less than 0.2C.
[0111] In the second embodiment, the anhedral angle .delta.1 of the
blade tip vicinity part 11A of the main blade 11 is exemplarily set
to larger than the anhedral angle .delta.2 of the small blade 12A
(.delta.1>.delta.2), but the anhedral angle .delta.2 may be set
to larger than the anhedral angle .delta.1 (.delta.2>.delta.1).
In this case, the tip vortices shed from the blade tip part of the
small blade 12A can be positioned under that shed from the blade
tip part of the main blade 11, and these two tip vortices can be
effectively interfered with each other.
[0112] While there has been described in connection with the
preferred embodiments of the present invention, it is to be
understood to those skilled in the art that various changes and
modifications may be made therein without departing from the
present invention, and it is aimed, therefore, to cover in the
appended claims all such changes and modifications as fall within
the true spirit and scope of the present invention.
* * * * *