NASA Technical Reports Server (NTRS) 20080004608: Blade vortex interaction noise reduction techniques for a rotorcraft

9 Pages·0.79 MB·English

by  NASA Technical Reports Server (NTRS)

United States Patent 1191 [ill Patent Number: 5,711 $5 1
Charles et al. [a] Date of Patent: *Jan. 27, 1998
BLADE VORTEX INTERACTION NOISE 2,397,132 311946 Dent, Jr. .
REDUCTION TECHNIQUES FOR A 2,892,502 6/1959 Donovan.
........................
ROTORCRAFT 3,451,644 6'1969 Marchem et al. 416RO
3209,971 511970 Gerstine et al. .
Inventors: Bruce D. Charles; Ahmed A. Hassau 3,954,229 5/1976 Wilson.
both of Mesa; Homoz Tadghighi, 4,514,143 41985 Campbell.
Gilbert; Ram D. JanakiRam, Mesa, all 4,580,210 41986 Nordstmm ........................... 2W17.13
of Ariz.; Lnkshmi N. Sankar. Atlanta, 4,706,902 11/1987 Destupder et al. .
Ga. 5,320,491 6'1994 Coleman et al. ......................... 416124
............................
5,588,800 12/1996 Chades et al. 416124
Assignee: McDonnell Douglas Helicopter
Company, Mesa, Ariz.
Primary Eraminer-John T. Kwon
Notice: The term of this patent shall not extend Attomex Agent, or FirntDonald E. Stout
beyond the expiration date of Pat. No.
5,588.800. [571 ABSTRACT
Appl. No.: 662,601 An active control device for reducing blade-vortex interac-
tions (BVI) noise generated by a rotorcraft. such as a
Filed Jun. 13,19% helicopter. comprises a trailing edge flap located near the tip
of each of the rotorcraft's rotor blades. The flap may be
Related US. Application Data
actuated in any conventional way. and is scheduled to be
Continuation of Ser. No. 251,329, May 31, 1994, Pat. No. actuated to a deflected position during rotation of the rotor
5388,800. blade through predetermined regions of the rotor azimuth,
Int C1.6 ........................................................ FOlD 5/00 and is further scheduled to be actuated to a retractedpositioo
U.S. C1. ............................................ 416/24; 244A7.13 through the remaining regions of the rotor azimuth. Through
Field of Search .................... 416L20. 24; 244117.13. the careful azimuth-dependent deployment and retraction of
the flap over the rotor disk, blade tip vortices which are the
24417.15
Primary source for BVI noise are (a) made weaker and (b)
References Cited pushed farther away from the rotor disk (that is. larger
blade-vortex separation distances are achieved).
U.S. PMENT DOCUMENTS
2,071,012 211937 Adams . 15 Claims, 1 Drawing Sheet
5,711,651
US. Patent Jan. 27,1998
5,711,651
1 2
BLADE VORTEX INTERACTION NOISE of advantages over prior art solutions. The invention, a
REDUCTION TECHNIQUES FOR A trailing edge flap located near the blade tip, is designed to be
ROTORCRAFT used as an active control device which alleviates the aero-
dynamics of the interactions and thus the impulsive BVI
This is a continuation of application Ser. No. 08D51.329 5 noise levels and signature. The trailing edge flap can be
filed May 31, 1994, and now U.S. Pat. No. 5,588,800. actuated mechanically, electrically. pneumatically, or
The invention described herein was made in the perfor- hydraulically. Through the careful azimuth-dependent
deployment and retraction of the flap over the rotor disk,
mance of work under NASA Contract No. NAS1-19136 and
blade tip vortices which are the primary source for BVI are
is subject to the provisions of Section 305 of the National
Aeronautics and Space Act of 1958 (42 U.S.C. 2457). Io made (a) weaker and (b) are pushed farther away from the
rotor disk (that is. larger blade-vortex separation distances
BACKGROUND OF THE INVENTION are achieved).
This invention relates to rotor blades for rotorcraft such as More specifically. the invention provides an active control
helicopters and the like, and more particularly to an device for reducing BVI noise levels generated by a
improved construction and control scheme for such rotor rotorcraft, such as a helicopter. having a rotor blade includ-
blades which permits a signifcant reduction in noise gen- ing a tip end, a root end, a leading edge. and a trailing edge.
erated by the blades. The rotor blade is attached at the root end to a rotor hub on
Conventional helicopters in descent flight conditions fre- the rotorcraft and extends radially outwardly therefrom.
quently generate an impulsive noise signature which is having a radius R and a chord C, such that when the rotor
commonly referred to as blade-vmkx interactions (BVI) hub is rotatably driven, the rotor blade rotates about the hub
noise or “blade slap”. BVI noise is generated by blade tip through a 360 degree admuth. where 0 degrees azimuth is
vortices. which interact with the rotor blades. Unfortunately. located at the downstream side of the disk, n o d yo ver the
it is typically within a frequency range which is highly tailboom. The active control device comprises a movable
important to human subjective response. Additionally, it is flap pivotally attached to the rotor blade trailing edge by a
easily detected electronically at large distances, thus increas- 25 hinge oriented generally radially along the rotor blade, with
ing the vulnerability of military rotorcraft. Consequently, a the flap having an actuator for deflecting and retracting the
reduction in the BVI noise intensity and changes in the noise flap about the hinge. Critical to the invention is that, depend-
signature, using active and/or passive noise control ing upon the particular BVI noise which is desired to be
techniques, is desirable to the rotorcraft industry. which is reduced, as will be explained infra. the flap is accordingly
challenged by today’s stringent military and civilian acous- 3o adapted to be actuated to a deflected position during rotation
tic regulations. of the rotor blade through predeterminedr egions of the rotor
There are two possible measures which may be taken to azimuth. and is further adapted to be actuated to a retracted
position through the remaining regions of the rotor azimuth.
reduce BVI noise. Namely, the tip vortex strength may be
thereby functioning to reduce BVI noise during rotorcraft
weakened, and/or the separation distance between the blade
and the tip vortex may be increased. The result of both 35 opaation.
measures is a decrease in the strength of the interaction More particularly, the rotor azimuth has flint. second
between the rotor blade and the tip vortices. Existing devices third, and fourth quadrants, the first quadrant comprising 0
which have been used for reducing BVI noise include to 90 degrees azimuth, the second quadrant comprising 90 to
Higher Harmonic blade pitch control (HHC), which seeks to 180 degrees azimuth. the third quadrant comprising 180 to
change the blade tip vortex strength, and thus the local 40 270 degrees azimuth. and the fourth quadrant comprising
aerodynamic conditions, through blade pitch changes. Other 270 to 360 degrees azimuth. In the preferred embodiment.
control means concentrate primarily on reducing the wherein it is desired to reduce advancing BVI noise (which
strength of the tip vortex through blade tip geometric is noise generated through the h t a nd second quadrants.
modifications. Typical examples are the use of leading and and is typically louder than retreating BVI noise). the
trailing edge sweep, the use of blade anhedral. and the use 45 trailing edge flap is adapted to be actuated according to a
of a subwing concept. AU of these examples, excluding schedule such that it is in a deflected position when the rotor
HHC. may be classified as passive control techniques. An blade is advancing through at least a portion of the first and
example of another active control technique would be the second quadrants. It is preferred, however. that the flap be
use of tip air mass injection, which again has the purpose of adapted to be deflected in at least portions of each of the first
weakening the blade tip vortices. 50 and second quadrants. In this preferred case, the trailing
Each of the prior art solutions to BVI noise has been at edge flap is adapted, according to the preferred schedule, to
always be in a retracted position in the third and fourth
least partially unsuccessful, either because of ineffectiveness
quadrants.
or because of the solution’s detrimental side effects with
respect to the flight characteristics and efficiency of the In some instances, it may be desirable to focus on
rotorcraft. For example, HHC methods change the aerody- 5s alleviating the strength of the retreating BVI. In such an
namic conditions along the entire blade in order to reduce instance. the opposite schedule is desirable; i.e. the trailing
BVI noise, due to the change in blade pitch. Passive BVI edge flap is adapted to be actuated according to a schedule
noise control methods are not adaptable to changing BVI such that it is in a deflected position when the rotor blade is
conditions throughout the flight regime. which are associ- retreating through at least portions of the third and fourth
ated with changes in descent rate and forward flight speed. 60 quadrants, and preferably portions of each of the third and
Additionally, most of the prior art solutions to the BVI foutth quadrants. For this case, the trailing edge flap is
problem are deployed at all times, whether or not needed, adapted. according to the preferred schedule. to always be in
often degrading flight performance unnecessarily. a retreated position in the first and second quadrants.
In still another scenario. it may at times be desirable, or
SUMMARY OF THE INVENTION
65 necessary, to alleviate both advancing and retreating BVI
This invention solves the aforementioned problems by simultaneously. In such a case. the trailing edge flap would
providing a BVI noise reduction device which has a number be actuated according to a schedule such that it is in a
5,7 11,65 1
3 4
deflected position as the rotor blade travels through at least reduced, and @) actuating the flap to a retracted position
portions of all four quadrants. and preferably through por- during rotation of the rotor blade through the remaining
tions of each of the four quadrants. regions of the rotor azimuth.
Although it would at fust appear that both The invention, together with additional features and
advancing and retreating BVI should
be the prefened 5 advantages thereof. may best be undato& by reference to
case, thereby maximizing noise reduction. there is a trade-
the description taken in conjunction with the
off. in terms of increased drag and consequent loss of
accompanying illustrative drawing.
efficiency of the rotor blade, for deflecting the trailing edge
flap. The created drag is greater as the blade advances
BRIEF DRSCRTPTION OF THE DRAWING
through the first two quadrants than that created as the blade
retreats through the last two quadrants. Thus, the determi- FIG. 1 is a schematicv iew of a rotor blade for a rotorcraft,
nation as to which noise to reduce must be made in con- configured in accordance with the invention, having a uni-
junction with a consideration of the resultant drag penalties. tary trailing edge flap for providing active control of BVI
Reducing only the advancing BVI is presently preferred noise;
because it is louder that the retreating B Va nd, though the 15 FIG. 2 is a schematic view sirnilas to FIG. 1 of a modified
drag penalties are higher, the flap is WiCdY deflected embodiment of a helicopter rotor blade. wherein the trailing
during descent, when power is reduced and drag is not as edge flap is segmented; and
much of a factor.
FIG. 3 is a schematic plot illustrating a preferred n o d -
In another aspect of the invention. a rotor blade is
ized flap control schedule for obtaining effective BVI noise
provided for a rotorcraft, having a tip end. a root end, a 2o reduction.
leading edge, a trailing edge. a radius R and a chord C. The
rotor blade comprises a movable flap pivotally attached to DESCRIPTION OF THE PREFERRED
the rotor blade trailing edge by a hinge oriented generally EMBODIMENT
along the rotor blade. wherein the flap has an actuator for
deflecting and retrading the flap about the hinge. The rotor 25 Referring now more PhCUlarly to FIG. 1, a rotor blade
blade is ached at the roOt end to a rotm hub on the 10 for a rotorraft. such as a helicopter. is illustrated
rotorcraft, such that when the rotor hub is rotatably driven, schematically.T he rotor blade 10 is constructed in conven-
the rotor blade rotates about the hub though a 360 degree tional fashion. and includes a leading edge 12 and a trailing
mmuy.
azimuth. the flap is scheduled to a&uated to edge 14. The blade is attached at its root end 16 to a rotor
a deflect& position d-g of the rotor blade hub 18 in a conventional fashion (not shown), so that when
bough predet-ed regionso f the rotor which 30 the rotor hub is rotationally driven by the rotorcraft engine
may comprise one or more portions, contiguous or (Or, alternatively. when it is permitted to autorotate), the
otherwise, of any of the four quadrants discussed supra, and rotor blade lo will rotate about the hub through a full rotor
is further scheduled to be actuated to a retracted position azimuth Of 360 degrees. The blade has a end 2o and
through the remaining regions of the rotor azimuth, thereby 35 a unitary trailing edge 22*I n the Preferred emb*ent.
functioning to reduce BW noised uring operation of the the flap 22 is operated using mechanical cable-driven
rotorcraft. actuators, though any conventional actuating means.
whether mechanical, electrical, pneumatic. or hydraulic,
The rotor azimuth has first, second. third and fourth
quadrants, the first quadrant comprising 0 to 90 degrees be used. The actuators be either
azimuth. the second quadrant comprising 90 to 180 degrees 40 Or using software.
azimuth, the third quadrant comprising 180 to 270 degrees Now with reference to FIG. 2. a modified rotor blade 10
azimuth, and the f& comprising 270 to 360 is illustrated which is identical in all respects to the rotor
degrees azimuth. The trailing edge flap is preferably sched- blade Of FIG. 1, except that the hailing edge flap 22 is
uled to be actuated such that it is in a deflectedposition when segmented comprising three Segments 2 k 22b, and 22C.
the rotor blade is advancing through at least a portion of two 45 of come, any number of =gments be dhed.d epend-
of said quadrants, and is always in a retracted position ing Upon the Control CharaCtdStiCS desired. and all other
during rotation through the remaining two quadrants. elements are identified by reference numaals identical to
,,I yet another aspect of the inventiona. method for those used in FIG. 1. Again, though mechanicsalm actuliactoirs% are
reducing BVI noise generated by a rotorcraft having a rotor preferred for their proven Pdomnce and any
blade is disclosed, wherein the rotor blade includes a tip end. 50 Of conventional actuator known in the art be
a root end. a leading edge, and a trailing edge. The rotor
blade is attached at the root end to a rotor hub on the As stated supra, the blades 10 in each of the FIGS. 1 and
rotorcraft and extends radially outwardly therefrom, such 2 embodiments are dimensionally identical. Thus, the chord
c
that when the rotor hub is rotatably driven, the rotor blade (shown in FIG. 1 and defined as a straight line, or
rotates about the hub through a 360 degree azimuth mm- 55 cross-section, between the leading and t r ~ negdg es of the
@sed of first, second. third, and fo& quadrants. the first airfoil) of each blade is the same, as is the radius (shown in
quadrant comprising 0 to 90 degrees azimuth, the second FIG. 2 and defined as the distance between the center of the
quadrant comprising 90 to 180 degrees azimuth, the third rotor hub and the blade tip) of each blade.
quadrant comprising 180 to 270 degrees azimuth, and the In the preferred embodiments. the flap 22 has a substan-
fourth quadrant comprising 270 to 360 degrees azimuth. The 60 tially constant chord dimension along its length. Thus,
rotor blade further comprises a movable flap pivotally preferably, in both blade embodiments. the trailing edge flap
attached to the trailing edge. The method comprises the steps 22 is positioned near the blade tip, in about the outboard
of (a) actuating the flap to a deflected position during 25% of the rotor blade 10. its chord width constitutes
rotation of the rotor blade through predetermined regions of approximately2 5-35% of the rotor blade chord C, and spans
the rotor azimuth, thereby reducing the strength of blade tip 65 approximately 20% of the blade radial length, or radius R.
vortices and increasing the separation of the blade tip Thus, as illustrated in FIG. 1, the distance 26 between the
vortices and the rotor blade tip. such that the BVI noise is leading edge 12 of the blade 10 and the flap hinge 28 of the
5,7 1165 1
5 6
flap 22, for both embodiments, is preferably approximately ference between the FIG. 1 and FIG. 2 embodiments is that
0.65 C to 0.75 C. Similarly, as illustrated in mG. 2. the radial the segmented trailing edge flap permits a more complex
length 30 of the flap 22. for both embodiments, is preferably control scheme, and therefore has a broadened useful range
aW*klY 0.20 R-I t has been found that a significantly of application. However, it should be noted that,
flap radial dimension engenders Other undesirable 5 occasionally, in the case of the segmented trailing edge flap,
fright effects. both embodiments, as We& the flap hinge Z8 it m yb e desirable, f ar easons of performance rather than
is Preferably oriented along a generally radial axis, and BVI reduction, for the segments to not be &=fly adjacent
free Of the the hinge. $0 one another, and perhaps to 1o-k the radially innermost
In some instances, it may be to a segment near the root end of the blade. In such an event. of
tapering trailing edge flap, Le., one which has a non-constant co~seth, e preferredc riteria of locating the entire flap in the
chord dimension along its radial length. For such an
outbomd 258 of the blade is not obsaved.
embodiment, the above preferred dimensions generally still
Some of the advantages of the inventive active control
apply. except that the only constitutes approximately
25-358 of the rotor blade chord c at its dmd evice for reducing BVI noise caused by blade tip VOdCeS
dimension, an& of come, the distance 26 bemeen the are its abxv to change the aerodynec &aracteristiCS
leading edge 12 of the blade 10 and the flq hinge 2% of the l5 locally On the through flap motions (Or
flap 22 is only approximately 0.65 C to 0.75 C at radial schedules)*t he to the trailing edge
ment schedules to changing BVI conditions which are
location of the flap’s maximum chord dimension.
associated with changes in descent rate and forward flight
In operation’ careful azimuth-dependent and speed (this is not possible with passive BVI control
retraction of the flap 22 over the rotor disk are the key factors 2o methods), and the fact that of the trailing edge
for achieving the maximum possible reductions in BVI noise
flap 22 results in changes in both the tip vortex strength
and the maximum changes in the noise signature. BVI noise
(makes it weaker), andthe blade-vortex separation distances
reduction is accomplished by reducing the strength of the
(makes them larger). Devices which modify only the
blade tip vortices (which are the primary source for BVI
strength of the tip vortex generally cannot alter the separa-
noise) through significant variations in blade load
25 tion distances and vice-versa. An additional advantage
distribution,a s well as by changing the tip vortex trajectories
includes the ability to only deflect the flap when necessary
to increase the average distance the blade and the during BVI and then it when not
vortex elements causing the interactions. This is accom-
plished ,,&tions in the tip angleo f the Besides of the above enumerated advantages. another
rotor. HG. 3 is a plot of an exemplaryf lap significanta dvantage of the invention is its ability to be used
deplopent/re&,&,n schedule as a function of rotor 30 for other purposes not related to BVI noise reduction. For
-uth, 0 degrees is &fined as the point example, the flap m yb e SekdiVely deflectedt o provide lift
where the tip of the blade at issue is oriented &&Y over augmentation during maneuvering flight, vibration control.
the mbrnof the menth e same blade tip is rotor blade pitch control. aerodynamic/dynamic blade twist
dented directly over the of the the rotor modifications, and modifications to rotor acoustic signature
is 180 degrees. 35 to e m ~ t eoth er types of rotorcraft, for covert military
For both the FIG. and mG. 2 embodiments, it operations (an option certainly not available using passive
is desired to reduce advancing Bw (the presently noise control techniques) among other possibilities.
preferred embodiment), the inventors’ research has found ACCOrhdY, although an exemplary embodiment Of the
that if the flap is only deployed and rebaa4 in the first 4o invention has been shown and described m y c hanges.
quadrant of the rotor disk i.e.. between the 0 and 90 degrees ~odificatimsa.n d substitutions may be made by one having
azimuth positions, its beneficial effects on noise reduction skill in the art without dephng from the spirit and
seem to be minimal (slight changes in blade-vortex sepa- Of the invention.
ration distances occur). This is also true if the flap schedule mati s Ckihed
is Wt,=d to the second quadrant of the rotor disk, iae., 45 1. h active control device for reducing blade vortex-
between the 90 and 180 degrees positions interaction (Bvr) noise generated by a rotorcraft having a
(changes in vortex strength occur). An optimum flap s&&- rotor blade including a tip end, a root end. a leading edge.
and a trailing edge, said rotor blade being attached at said
ule has therefore henfo und to be one pennits
deflection in predetwed regions, a portions, of the root end to a rotor hub on said torc craft and extending
first and second quadrants of the rotor disk where changes in so radidY OUmardlY therefrom having a radius and a chord
c,
bhde-v-x separation distances a d strengths such that when said rotor hub is rotatably driven. said
occw simultaneously. m ef lap is retracted in the remaining rotor blade rotates about said hub through a 360 degree
regions of the including remaining portions of the azimuth. said active control device comprising:
first and second quadrants and the entire third and fourth a movable flap pivotally attached to said rotor blade
quadrants. For a given rotor, the optimum flap schedule is a 55 t r u g edge by a hinge oriented generally radially
function of the number of blades, forward flight speed, along said rotor blade. at least a portion of said flap
descent rate, flap chord length, and the geometric, and hence being positioned near said rotor blade tip, in about the
aerodynamic, characteristics of the airfoil(s) constituting the outboard 25% of the rotor blade radial length;
blades. an actuator for deflecting andretracting the flap about said
Si?uilarly, if it is desired to reduce only retreating BVI, an 60 hinge;
ophimum flap schedule would span portions of both the third wherein said flap is adapted to be actuated to a deflected
and fourth quadrants of the rotor disk If both retreating and position during rotation of said rotor blade through
advancing BVI were required to be reduced. the optimum prede-ed regions of said rotor azimuth, and is
flap schedule would preferably span portions of each of the further adapted to be actuated to a retracted position
four quadrants. 65 through the remaining regions of said rotor azimuth.
Thus, both illustrated embodiments have similar preferred thereby functioning to reduce BVI noise during opera-
operating regimes, and in most instances the primary dif- tion of said rotorcraft.
5.71 1.651
7 8
2. An active control device as recited in claim 1, wherein quadrant comprising 180 to 270 degrees azimuth, and the
said trailing edge flap is of a unitary construction. fourth quadrant comprising 270 to 360 degrees azimuth. said
3. An active control device as recited in claim 1, wherein trailing edge flap being scheduled to be actuated such that it
said trailing edge flap is comprised of a Plm&V of seg- is in a deflected position when said rotor blade is advancing
ments. 5 through at least a portion of two of said quadrants.
4. An active control device as recited in claim 1. wherein 10. A rotor blade as recited in claim 9. wherein said
said trailing edge flap has a radial length of aPPrO-klY
trailing edge flap is scheduled to be always in a retracted
0.20 R position during rotation through the remaining two quad-
5. An active control device as recited in claim 1, said rotor
rants.
azimuth having first, second third. and fourth quadrants. the 10 ll. A rotor blade as in 9, wherein said flap
first quadrant to 90 degeeaszi muth* the
is scheduled to be deflected d h gr obtion through at least
second quadrant comp'sing 9o to 180 de@es the
portions of each of said fust and second quahts.
third quadrant cowsing lg0 to 270 azimuth* and 12. Amethod for reducing blade vomx-interaction (BVT)
the fourth quadrant 'Omsing 270 to 360 degrees noise generated by a rotorcraft having a rotor blade includ-
wherein said trailing edge is
to be actuated l5 ing a tip end, a root end, a leading edge, and a wailing edge.
according to a schedule such that it is in a deflected position
wherein said rotor blade is at said root end to a rotor
when Said rotor blade is advancing through at least a @On hub on and
of said first and second quadrants.
therefrom, such that when said rotor hub is rotatably driven,
6. An active control device as recited in claim 5. wherein said rotor blade rotates about said hub through a 360 degree
said trailing edge flap is adapted, according to said schedule. 20 azimuth comprised of second, third, and fourth
to be always in a retracted position in said third and fourth
quadrants, the first quadrant to 90 degrees
quadrants.
azimuth, the second quadrant comprising 90 to 180 degrees
7. An active control device as recited in claim 5. wherein azimuth, the third quadrant comprising 180 to 270 degrees
said flap is adapted to be deflected in at least Portions of each
azimuth, and the fourth quadrant 270 to 360
of said fust and second quadrants.
25 degrees azimuth, said rotor blade further comprising a
8. A rotor blade for a rotorcraft, having a tip end, a root
movable flap to trailing edge, said
end. a leading edge, a trailing edge. a radius R and a chord method comprising the steps of:
C and further comprising:
a) actuating said flap to a deflected position during
a movable flap pivotally attached to said rotor blade
rotation of said rotor blade through predetermined
trailing edge by a hinge oriented generally radially 30 regions of said rotor azimuth, thereby reducing the
along said rotor blade, said flap being positioned near
strength of blade tip vortices and increasing the sepa-
said rotor blade tip, in about the outboard 25% of the
ration of said blade tip vortices and the rotor blade tip.
rotor blade radial length
such that said BVI noise is reduced; and
an actuator for deflecting and retracting the flap about said 35 b) actuating said flap to a position during rota-
hinge; tion of said rotor blade through the remaining regions
said rotor blade being attached at said root end to a rotor of said rotor azimuth.
hub on said rotorcraft, such that when said rotor hub is 13. A for reducing BW noise as recited in claim
rotatably driven, Said rotor blade rotates about said hub 12. wherein said flap is actuated to a &fled position when
through a 360 degree azimuth; 40 said rotor blade is advancing through at least a portion of
wherein said flap is scheduled to be actuated to a deflected two of said quadrants.
position during rotation of said rotor blade through 14. A method for reducing BVI noise as recited in claim
predetermined regions of said rotor azimuth, and is 13, wherein said flap is actuated to a retracted position
further scheduled to be actuated to a retracted position during the entire time said rotor blade is rotating through the
through the remaining regions of said rotor azimuth. 45 remaining two quadrants.
thereby functioning to reduce blade vortex-interaction 15. A method for reducing BM noise as recited in claim
(BVI) noise during operations of said rotorcraft. 12, wherein said flap is actuated to a deflected position when
9. A rotor blade as recited in claim 8. said rotor azimuth said rotor blade is rotating through at least portions of each
having first. second. third, and fourth quadrants, the first of said first and second quadrants.
quadrant comprising 0 to 90 degrees azimuth. the second
* * * * *
quadrant comprising 90 to 180 degrees azimuth. the third
I11111 1111111l11 l1llI11 lIl1 IIIII 11111 IIIII IIIII IIIII IIIII 111l11l111111l11l1
US005711651Bl
REEXAMINATION CERTIFICATE
(4222nd)
United States Patent
B1 5,711,651
[19] [ill
Charles et al. [45] Certificate Issued *Nov. 28,2000
[54] BLADE VORTEX INTERACTION NOISE 2,776,718 111957 Zuck ......................................... 416123
REDUCTION TECHNIQUES FOR A 3,588,273 611971 Kizilos ...................................... 416123
ROTORCRAFT 3,952,601 411976 Galli et al. ................................ 416123
4,789,305 1211988 Vaughen .................................. 4161131
1751 Inventors: Bruce D. Charles; Ahmed A. Hassan, 5,366,176 1111994 Loewy et al. ......................... 244175 R
both of Mesa; Hormoz Tadghighi,
FOREIGN PATENT DOCUMENTS
Gilbert; Ram D. JanakiRam, Mesa, all
of Ariz.; Lakshmi N. Sankar, Atlanta, 482607 1211942 Germany ................................. 416123
Ga. 252442 511926 United Kingdom ..................... 416123
758338 1011956 United Kingdom ..................... 416124
[73] Assignee: McDonnell Douglas Helicopter Co.,
Inc., Mesa, Ariz. OTHER PUBLICATIONS
Reexamination Request: DGLRiAIAA 14th Aeroacoustics Conference, Eurogress
No. 901005,193, Dec. 16, 1998 Center Aachen, Federal Republic of Germany May 11-14,
1992-9242425-"Effects of a Trailing Edge Flap on the
Reexamination Certificate for:
Aerodynamics and Acoustics of Rotor Blade Vortex Inter-
Patent No.: 5,711,651
actions" by B. Charles, H. Tadghighi, A.A. Hanssan,
Issued: Jan. 27, 1998
McDonnell Douglas Helicopter.
Appl. No.: 08/662,601
Filed: Jun. 13,1996
Primary Examiner-John T. Kwon
[ * ] Notice: This patent is subject to a terminal dis-
[571 ABSTRACT
claimer.
An active control device for reducing blade-vortex interac-
Related U.S. Application Data
tions (BVI) noise generated by a rotorcraft, such as a
helicopter, comprises a trailing edge flap located near the tip
[63] Continuation of application No. 081251,329, May 31, 1994,
of each of the rotorcraft's rotor blades. The flap may be
Pat. No. 5,588,800.
actuated in any conventional way, and is scheduled to be
[51] Int. C1.7 ........................................................ FOlD 5/00 actuated to a deflected position during rotation of the rotor
[52] U.S. C1. ............................................ 416/24; 244117.13 blade through predetermined regions of the rotor azimuth,
[58] Field of Search .................................. 416120, 24, 23; and is further scheduled to be actuated to a retracted position
244117.13, 17.15 through the remaining regions of the rotor azimuth. Through
the careful azimuth-dependent deployment and retraction of
~561 References Cited the flap over the rotor disk, blade tip vortices which are the
primary source for BVI noise are (a) made weaker and (b)
U.S. PATENT DOCUMENTS
pushed farther away from the rotor disk (that is, larger
2,622,686 1211952 Chevreau et al. ........................ 416123 blade-vortex separation distances are achieved).
B1 5,73 1,651
1 2
REEXAMINATION CERTIFICATE 7. An active control device as recited in claim 5, wherein
ISSUED UNDER 35 U.S.C. 307 at least segments of said flap [is] are adapted to be deflected
in at least portions of each of said first and second quadrants.
THE PATENT IS HEREBY AMENDED AS 8. A rotor blade for a rotorcraft, having a tip end, a root
INDICATED BELOW. S end, a leading edge, a trailing edge, a radius R and a chord
r and further comprising:
Matter enclosed in heavy brackets [ ] appeared in the
patent, but has been deleted and is no longer a part of the a movable flap Comprising a plurality of segments and
patent; matter printed in italics indicates additions made pivotally attached to said rotor blade trailing edge by a
to the patent. hinge oriented generally radially along said rotor blade,
10
said flap being positioned near said rotor blade tip, in
AS A RESULT OF REEXAMINATION, IT HAS BEEN only about the outboard 25% of the rotor blade radial
DETERMINED THAT length;
Claims 2 and 3 are cancelled. an actuator for deflecting and retracting each segment of
1s the flap about said hinge while the rotor blade is
Claims 1, 4, 5, 7, 8 and 12-15 are determined to be rotating;
patentable as amended. said rotor blade being attached at said root end to a rotor
hub on said rotorcraft, such that when said rotor hub is
Claims 6 and 9-11, dependent on an amended claim, are rotatably driven, said rotor blade rotates about said hub
determined to be patentable. 20 through a 360 degree azimuth;
wherein said flap is scheduled to be actuated to a deflected
New claims 16 and 17 are added and determined to be
patentable. position during rotation of said rotor blade through
predetermined regions of said rotor azimuth, and is
1. An active control device for reducing blade vortex- 2s further scheduled to be actuated to a retracted position
interaction (BVI) noise generated by a rotorcraft having a
through the remaining regions of said rotor azimuth,
rotor blade including a tip end, a root end, a leading edge,
thereby functioning to reduce blade vortex-interaction
and a trailing edge, said rotor blade being attached at said
root end to a rotor hub on said rotorcraft and extending (BVI) noise during operations of said rotorcraft.
radially outwardly therefrom, having a radius R and a chord 12. A method for reducing blade vortex-interaction (BVI)
30
C, such that when said rotor hub is rotatably driven, said noise generated by a rotorcraft having a rotor blade extend-
rotor blade rotates about said hub through a 360 degree
ing radially and having a predetermined radial length, said
azimuth, said active control device comprising:
rotor blade including a tip end, a root end, a leading edge,
a movable flap pivotally attached to said rotor blade
and a trailing edge, wherein said rotor blade is attached at
trailing edge by a hinge oriented generally radially
3s
along said rotor blade, at least a portion of said flap said root end to a rotor hub on said rotorcraft and extends
being positioned near said rotor blade tip, in about the radially outwardly therefrom, such that when said rotor hub
outboard 25% of the rotor blade radial length, said is rotatably driven, said rotor blade rotates about said hub
trailing edge flap being comprised of a plurality of through a 360 degree azimuth comprised of first, second,
segments, and an entire length of said trailing edge 40 third, and fourth quadrants, the first quadrant comprising 0
flap, including combined lengths of all of said plurality
to 90 degrees azimuth, the second quadrant comprising 90 to
of segments, Comprising less than % of the rotor blade
180 degrees azimuth, the third quadrant comprising 180 to
radial length; and
an actuator for deflecting and retracting each segment of 270 degrees azimuth, and the fourth quadrant comprising
the flap about said hinge while said rotor blade is 4s 270 to 360 degrees azimuth, [said rotor blade further com-
rotating; prising a movable flap pivotally attached to said trailing
wherein said flap is adapted to be actuated to a deflected edge,] said method comprising the steps of
position during rotation of said rotor blade through
a) providing a movable segmented flap which is pivotally
predetermined regions of said rotor azimuth, and is
attached to said trailing edge of said rotor blade, said
further adapted to be actuated to a retracted position so
flap having a radial length which is less than % of said
through the remaining regions of said rotor azimuth,
rotor blade radial length;
thereby functioning to reduce BVI noise during opera-
tion of said rotorcraft. b) actuating aportion of said segmented flap to a deflected
4. An active control device as recited in claim 1, wherein position during rotation of said rotor blade through
said trailing edge flap has a combined radial length of 5s predetermined regions of said rotor azimuth, thereby
approximately 0.20 R. reducing the strength of blade tip vortices and increas-
5. An active control device as recited in claim 1, said rotor
ing the separation of said blade tip vortices and the
azimuth having first, second, third, and fourth quadrants, the
rotor blade tip, such that said BVI noise is reduced; and
first quadrant comprising 0 to 90 degrees azimuth, the
second quadrant comprising 90 to 180 degrees azimuth, the 60 [blc) actuating said deflected portion of said segmented
third quadrant comprising 180 to 270 degrees azimuth, and flap to a retracted position during rotation of said rotor
the fourth quadrant comprising 270 to 360 degrees azimuth, blade through the remaining regions of said rotor
wherein said trailing edge flap is adapted to be actuated azimuth.
according to a schedule such that [it is] at least segments 13. A method for reducing BVI noise as recited in claim
thereof are in a deflected position when said rotor blade is 65 12, wherein said portion of said segmented flap is actuated
advancing through at least a portion of said first and second to a deflected position when said rotor blade is advancing
quadrants. through at least a portion of two of said quadrants.
B1 5,711,651
3 4
14. A method for reducing BVI noise as recited in claim 16.A n active control device as recited in claim 1, wherein
13, wherein said portion of said segmented flap is actuated said trailing edge pap has a radial length and has a
to a retracted position during the entire time said rotor blade
non-constant chord dimension along said radial length,
is rotating through the remaining two quadrants.
17. A method for reducing BVI noise as recited in claim
15. A method for reducing BVI noise as recited in claim s
12, wherein said portion of said segmented flap is actuated 12, wherein in step b)fewe" than all of said segments of said
to a deflected position when said rotor blade is rotating segmented flap are actuated to said deflected position.
through at least portions of each of said first and second
quadrants. * * * * *