U.S. patent number 3,713,750 [Application Number 05/095,643] was granted by the patent office on 1973-01-30 for circulation control rotor system.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Robert M. Williams.
United States Patent |
3,713,750 |
Williams |
January 30, 1973 |
CIRCULATION CONTROL ROTOR SYSTEM
Abstract
The rotating blades on a helicopter are in the shape of a
cambered elliptl airfoil with blunt edges. A plurality of slots are
employed on the upper surface of the air foil to blow a thin sheet
of air tangentially across the surface of the foil and around the
trailing edge. Circulation control is achieved by the tangential
blowing as the sheet of air adheres to the surface and travels
around the trailing edge, detaching beneath the trailing edge at a
location determined by the intensity of blowing. The effect of the
tangential blowing is relocation of the stagnation stream lines
producing increased lift on the foil. The air supplied to the slots
is modulated with respect to the azimuth position of the rotor and
the speed of the rotating blade so that cyclic control over the
lift of the rotor can be accomplished without altering the blade
attitude.
Inventors: |
Williams; Robert M. (Chantilly,
VA) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (N/A)
|
Family
ID: |
22252935 |
Appl.
No.: |
05/095,643 |
Filed: |
December 7, 1970 |
Current U.S.
Class: |
416/20R; 244/207;
416/90A; 416/90R |
Current CPC
Class: |
B64C
27/325 (20130101) |
Current International
Class: |
B64C
27/32 (20060101); B64c 027/72 () |
Field of
Search: |
;416/20,90 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Powell, Jr.; Everette A.
Claims
What is claimed is:
1. A circulation control helicopter rotor blade system, for varying
blade lift through a cycle of rotation, comprising:
a rotor blade having a cambered and substantially elliptical air
foil shape and blunt edges;
one of said blunt edges being a leading edge relative to blade
rotation and the other blunt edge being a trailing edge relative to
blade rotation;
said trailing edge having at least one slot adjacent to said edge
and shaped to tangentially blow fluid over said edge;
said tangentially blown fluid adhering to said trailing edge,
curving down and around said blunt edge and detaching from the
rotor at a point on its underside functionally related to the
intensity of the blowing;
control means connected to said rotor blade to control the
intensity of blown fluid from said slot for varying the blade lift
through a cycle of rotation;
said control means including a first means for modulating the
intensity of said blown fluid at a first fundamental frequency
equal to the frequency of rotor rotation and at harmonic
frequencies of the fundamental frequency;
second means for combining the blown fluid modulated at the
fundamental frequency with the blown fluid modulated at harmonics
of the fundamental, to produce a resultant blown fluid flow from
said slot, described by the relationship:
I(A.sub.1 sin .chi. + B.sub.1 cos .chi. + A.sub.2 sin 2.chi. +
B.sub.2 cos 2.chi. + . . . A.sub.n sin n.chi. + B.sub.n cos
n.chi.).
where I is the unmodulated blowing intensity;
A.sub.1, A.sub.2, . . . A.sub.n and B.sub.1, B.sub.2, . . . B.sub.n
are constants; and
.chi. is the azimuth angle of rotation with the blade zero azimuth
angle position being the polistion where the blade is parallel with
the fore-aft line of the helicopter and with the blade extending
aft from the root.
2. The system of claim 1 wherein:
said leading edge has at least one slot adjacent to said edge and
shaped to tangentially blow fluid over said edge;
said tangentially blown fluid adhering to the leading edge curving
down and around said blunt edge and detaching from the rotor at a
point on its underside functionally related to the intensity of the
blowing;
said control means blows fluid out said slot during the interval
within a cycle of rotation when said blade is in a retreating
position relative to the free-stream velocity; and
said control means includes means for deriving said fluid blown out
said leading edge slot, from said modulated fluid flow supply for
said trailing edge slot.
3. The system of claim 2 including:
means to sense negative relative wind, mounted on said blade and
connected to said control means; and
said control means including means for shutting off the modulated
fluid flow to said trailing edge and connecting the modulated fluid
flow to said leading edge in response to said sensing means sensing
negative relative wind.
4. The system of claim 3 wherein:
said means for connecting the fluid flow to said leading edge
controls the intensity of said blowing from said leading edge slot
in proportion to the magnitude of the relative wind component
sensed by said sensing means.
Description
The invention described herein may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without the payment of any royalties thereon or
therefor.
DESCRIPTION OF THE PRIOR ART
The conventional means for altering the lift of helicopter blade is
to cyclically alter the blade angle of attack and the blade speed.
This has been accomplished by mechanical means, introducing extreme
mechanical complexity and increased dynamic weight. Other methods
use cylindrical air foils with circulation control or lifting foils
combined with a blown jet flap. However, the cylindrical foil and
jet flap concepts are limited and cannot attain the efficiency of
the circulation control rotor which is capable of higher lift
coefficients and higher lift to drag ratios.
SUMMARY OF THE INVENTION
The rotating blades in a helicopter are formed from a basic air
foil shape selected from potential flow theory calculations and may
be cambered elliptical shape, having a blunt or rounded leading and
trailing edge. A number of slots are disposed in a line
substantially parallel to the edge and adjacent the edge. As the
blade is rotated air is blown out these slots in a thin sheet. The
thin sheet adheres to the trailing edge and remains attached, by
the Coanda effect, until it reaches the separation point on the
blade under side, beneath the trailing edge. The point of
separation beneath the trailing edge is determined by the intensity
of blowing. The effect of the circulation control is to relocate
the stagnation stream lines and produce a higher lift on the foil,
the lift on the air foil being functionally related to the ratio of
the velocity of the blown air to the free stream velocity blowing
over the rotating wing.
In addition, the air blown through the slots and over the trailing
edge is modulated proportionally to the sine and cosine of the
rotor azimuth angle and at harmonics thereof to permit the rotor to
distribute the lift cyclically in any desired manner, and to reduce
power consumption and vibration.
Each blade tapers from a predetermined thickness at its root to a
more narrow thickness at its tip. In addition, the cross-section of
the rotor is structured with a plurality of individual plenum
chambers to supply air to each of the slots. The plenum chambers
supply air to the upper blade surface to produce the tangential
flow as needed on leading and trailing edges and to a slot on the
underside of the blade, producing a jet flap or blown flap so the
effects of the blown flap and circulation control tangential flow
may be combined to produce the widest variation in lift on the
rotor.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a rotor system according to the principles of this
invention, mounted for rotation on a hub, having a slot on the
underside of the rotor adjacent its tip to produce the jet flap and
tangential slots for circulation control.
FIGS. 2a-2d relate to FIG. 1 and shows cross-sections of the blade
of FIG. 1 at various distances along the blade length.
FIGS. 3a and 3b are cross-sectional views of the blade showing
other possible arrangements of the slots, according to the
principles of this invention.
FIGS. 4a-4c show the relative wind profile across the blades of
FIG. 1.
FIG. 5 shows the blade of FIG. 1 with sectioned slots for
increasing the control over blade lift.
FIG. 6 is a top view of the blade of FIG. 1 with slots arranged to
be overlapping on one edge for increasing the control over blade
lift.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a blade is shown connected to a hub for
rotation and having tangential slots for circulation control
blowing as seen.
Blade 11 is attached for rotation to hub 13. A second matching
rotor 10, partially shown, is attached to hub 13, 180.degree. out
of phase with rotor 11. Conduits 15 within hub 13, supply air for
circulation control blowing to blades 10 and 11, respectively.
Arranged on blade 11 is a slot 19 extending from the hub 13 for a
portion of the distance along the length of the blade. Slot 19 is
substantially parallel to the longitudinal axis of blade 11. A
second slot 21 is arranged substantially parallel to the
longitudinal axis of the rotor between the trailing edge 20 and
slot 19 and below slot 19 relative to the top surface of the blade
11. Slot 21 extends from the hub 13 to the tip of the blade, marked
by stage D. A slot 23 substantially parallel to the longitudinal
axis of the blade 11 and on its underside, adjacent to the edge 22
extends from the blade tip a partial distance of the length of
rotor 11 towards the hub 13. Slot 23, connected to conduit 15,
produces a jet flap when air is expelled through it. Additional
slots 26 and 27 are arranged substantially parallel to the
longitudinal axis of blade 11 and are located on edge 22 of blade
11. Slot 26 extends from the hub a partial distance along the
length of blade 11 and slot 27 extends from the hub 13 along the
length of edge 22. It can be seen as blade 11 rotates 180.degree.
in the direction of arrow 25, slots 21 and 19 will become leading
edge slots in relation to the free stream velocity, while slot 27
will become a trailing edge slot. With blade 11, as shown in FIG.
1, edge 20 is trailing and edge 22 is leading with respect to the
direction of the free stream velocity.
A motor (not shown) is connected to hub 13 to rotate blade 11 and
its matching blade 10. This motor can be any suitable type and need
not necessarily be attached or drive the rotor through the hub 13
and may be a jet of air blown outward from the rotor along an area
adjacent the top of the rotor blade.
Referring now to FIG. 2, cross-sections of the blade 11 at stages
A, B, C and D are shown. As shown in FIGS. 2a and 2b, the
cross-sectional shape of the blade 11 at its root at stage A is a
cambered and substantially elliptical air foil with blunt edges 22
and 20, tangential slots 26 and 27 along one edge and tangential
slots 19 and 21 along the other edge and with a typical air foil,
being 50 percent thick at stage A and 30 percent at stage B. The
section at stage C is shown at FIG. 2c, is in the shape of a
cambered and substantially elliptical airfoil with slots 27 and 21
disposed on the opposite edges 22 and 20 respectively, and with the
thickness of the blade narrowed to approximately 15 percent while
FIG. 2d shows the tip of the rotor at stage D narrowed to 10
percent with slot 21 in edge 20 and 27 in the opposite edge 22 with
jet slot 23 in the under side of blade 11 adjacent edge 22 for
producing a jet flap.
Extending the length of rotor 11 and dividing it into three plenum
chambers is a continuous divider structure 29. Plenum chamber 1
supplies air for tangential slot 27. Plenum chamber 2 similarly
provides air for tangential slots 19 and 21. Plenum chamber 3
provides air for jet flap slot 23. Air for the three plenum
chambers 1, 2 and 3 is provided through conduit 15, mounted within
the hub 13 and connected to control box 17. Control box 17 contains
a series of valves, is tied in with the pilots controls, and
modulates the air supplied to the plenum chambers in a functional
relationship to the azimuth position of the blade, as will be
explained in the following. Conduit 15 and control box 17, may be
any suitable and known means for supplying air to the rotating
blade.
Referring now to FIG. 3, wherein is shown other possible
arrangements of slots and plenum chambers within the rotor. FIG. 3a
shows a blade 31 in cross-section with a double plenum chamber
having tangential slots 33 and 35 arranged in each blunt edge and
designed to tangentially blow air around each blunt edge. In
addition, a jet slot 34 may be included in this rotor blade. In
FIG. 3b, rotor 37 contains a double plenum chamber with the
tangential slot 39 arranged in one blunt edge and the other edge
having a jet flap slot arranged in the under side of the rotor.
OPERATION
The operation of the blade will be explained in reference to the
angular or azimuth position of the blade, relative to the fore-aft
line of the helicopter fuselage. For explanation purposes, it is
assumed the helicopter is in a vector direction, 180.degree.
opposite to the free stream velocity direction. Blade 11 is
rotating in the direction of arrow 25 and as shown in FIG. 1, is in
the retreating position relative to helicopter forward motion. The
free stream velocity vector is as shown by the arrow in FIG. 1. The
zero azimuth position is designated as the position where blade 11
is aligned in the fore-aft direction of the helicopter fuselage and
with rotor 11 extending from the hub towards the aft portion of the
helicopter fuselage. The 90.degree. azimuth position of the
helicopter rotor 11 would then be with rotor 11, perpendicular to
the fore-aft line of the fuselage and extending from the hub away
from the port side of the helicopter, the 180.degree. position of
the rotor blade 11 would be with rotor blade extending from the hub
assembly to the forward part of the fuselage and with the tip
pointed into the vector of the free stream velocity, the
270.degree. position would be with the rotor 11 perpendicular to
the fore-aft line of the fuselage and extending from the hub
assembly away from the starboard side of the helicopter
fuselage.
HOVER OPERATION
First, the operation of the blades will be explained in reference
to a hovering condition where the free stream velocity is zero. In
hovering, the free stream is equal to zero, the relative wind
velocity over the helicopter blade 11 in each quadrant is constant,
the first quadrant being zero to 90.degree., the second quadrant
being 90.degree. to 180.degree., the third quadrant being
180.degree. to 270.degree. and the fourth quadrant being
270.degree. to 360.degree. of rotor 11 rotation.
Air pressure to plenum 2 is cut-off while the air supply to plenum
1 and 3 is pressurized, forcing air out tangential slots 26 and 27,
causing it to flow along the trailing edge 22. Pressure within
plenum chamber 1 is maintained through 360.degree. of blade
rotation. As the free stream velocity is zero at hover, edge 20
will always be the trailing edge.
In the hover condition, a thin sheet of air will be blown out slots
26 and 27. The thin sheet having a uniform velocity along its
length and a uniform density. The thin sheet of air produced by the
tangential blowing adheres to the blunt trailing edge 22, curving
around the edge and detaching itself from the blade at some point
below the trailing edge determined by the intensity of blowing.
Circulation control around the trailing edge 22, through tangential
blowing results in increased lift on rotor 11. Matching blade 10,
arranged to rotate with blade 11 would be similarly ducted and
circulation control would be similarly maintained over the trailing
edge of blade 10, to balance the lift produced by blade 11. The
lift produced is proportional to the velocity of the jet issuing
out of the tangential slot. The effect of the tangential blowing is
to relocate the stagnation stream lines further aft along the blade
and to increase the pressure distribution along the top surface of
the blade so that the overall lift along the blade is
increased.
Air blown out of slot 23 produces a jet flap at the tip of blade 11
and relocates the stagnation stream line further aft, at the tip
area.
FORWARD FLIGHT
In forward flight all plenum chambers are cyclically pressurized.
In forward flight, the free stream velocity over the rotors is a
value greater than zero. In conventional helicopters, the blade 11
produces a greater lift in the first and second quadrants than is
produced in the third and fourth quadrants. In the first and second
quadrants the relative wind over the advancing blade is in the
direction of the free stream velocity and produces a higher lift
than when the blade is retreating in the third and fourth quadrant
and the relative wind is negative over a portion of the blade. In
this forward flight condition to equalize the higher lifting forces
produced when the blade is in quadrants 1 and 2 with the lower
lifting forces produced when the blade is in quadrants 3 and 4, the
lift in quadrants 3 and 4 is increased by blowing air out through
slots 19 and 21 when edge 20 becomes the trailing edge relative to
the free stream velocity. The lift on the rotor in quadrants 3 and
4 will be proportional to the ratio of the tangential slot jet
velocity to the free stream velocity.
As shown in FIG. 4, the relative wind across the blade will depend
upon the quadrant in which the blade is moving and with the
distance along the blade from the hub.
As shown in FIG. 4a, the relative velocity along the rotor blades
is shown by the envelope 60 connected to the relative wind vectors
across the advancing blade 61 and the retreating blade 63. The
advancing blade is at the 90.degree. position and the retreating
blade is in the 270.degree. position. As shown, reverse wind
denoted by arrow 69 is being experienced along the retreating blade
between points 65 and 67. Point 67 being the axis of rotation with
an increase in free stream velocity, as shown in FIG. 4b, the
distance along the retreating rotor experiencing reverse flow,
denoted by the distance between points 71 and 67, is increased.
While as shown in FIG. 4c, for a maximum free stream velocity and a
maximum forward helicopter velocity the reverse flow is experienced
along the entire length of the retreating blade 63. Where reverse
flow occurs, the lift along the blade will be decreased
proportionally to the distance along the blade experiencing reverse
flow. As this condition of reverse flow becomes excessive, the lift
in quadrants 3 and 4 of blade 11 will be reduced to the point where
a couple develops to rotate the helicopter about its longitudinal
center line resulting in a flipping of the helicopter. However,
with circulation control through tangential blowing, lift is
increased on the blade, in quadrants 3 and 4 by blowing along the
blade approximately where the reverse flow is occuring. Where the
free stream velocity is relatively low as shown in FIG. 4a and the
reverse flow occurs between the rotating hub and a point short
distance from the rotating hub, the slot 19 is used independently
to blow over the inside portion of the rotor and increase the lift
over that portion. As the free stream velocity increases, the
reverse flow at any point along the retreating blade will be an
increasing function of the free stream velocity and will be
inversely proportional to its distance from the hub 13. As shown in
FIG. 4c, where a relative wind across the retreating blade causes
the retreating blade to be completely in reverse flow, the reverse
flow will be maximum at the hub and in this condition, tangential
slots 19 and 21 are used together to increase the lift on the
retreating blade, the flow from slots 19 and 21 combine to maximize
the blowing intensity when the reverse flow magnitude is greatest.
In forward flight, to maximize the lift on the blade through a full
cycle of rotation, air is cyclically blown through slots 26, 27 and
23 when the blade 11 is in the first and second quadrants and air
is cyclically blown through slots 19 and 21, where the blade is
experiencing reverse flow in the third and fourth quadrants.
The intensity of the blown air through the slots, is modulated with
respect to the azimuth position of the blade, as expressed by the
following relationship. Intensity = A.sub.1 Sin .chi. + B.sub.1 Cos
.chi. + A.sub.2 Sin.sub.2 .chi. + B.sub.2 Cos.sub.2 .chi. + A.sub.3
Sin.sub.3 .chi. + B.sub.3 Cos.sub.3 .chi. + . . . A.sub.n Sin.sub.n
.chi. + B.sub.n Cos.sub.n .chi.
Where A.sub.1, A.sub.2, A.sub.3 . . . A.sub.n and
B.sub.1, B.sub.2, B.sub.3 . . . B.sub.n are constants
and .chi. is the azimuth angle of blade 11.
The modulated blowing, related to the blade angle and its
harmonics, reduces vibration and decreases rotational power
requirements.
The blowing and the blade lift may be further controlled by blowing
air only over the length of edge 20, experiencing negative relative
flow, while restricting the blowing to over that portion of edge
22, not in negative flow. This can easily be accomplished by
utilizing pressure transducers 34 and 36, placed along edge 20, and
dividing slot 27 into two distinct slots 35 and 37, as shown in
FIG. 5, separated by stage B by divider 32. Each slot, 35 and 27,
is separately supplied with air.
The pressure transducers 34 and 36, are placed on edge 20 and are
tied into air control 17. When blade 11 experiences negative
relative wind at transducer 34, the transducer will signal an
absence of positive air pressure to control 17. Control 17
responsive to transducer 34 then will cut off the supply of air to
slot 26 and slot section 35 and supply air to slot 19. When the
portion of blade 11 experiencing negative relative wind extends to
transducer 36, it will signal an absence of positive air pressure
to control 17, causing control 17 to cut off the supply of air to
slot section 37 and to supply air to slot 21. In this described
manner, the lift on the blade in quadrants 3 and 4 can be more
precisely controlled by blowing air over the portion of edge 20
experiencing negative relative flow while supplying air to the
portion of edge 22 not in negative relative flow. Referring now to
FIG. 6, it is shown how this control concept can be extended by
increasing the number of slots on edge 20, each slot extending from
hub 13, a unique distance along the length of the blade 11 and
sectioning the slots on edge 22 to correspond to the lengths of
each slot on edge 20. In FIG. 6, blade 11 is shown in a top view as
having slots 41, 43 and 45, each slot extending for a unique length
along edge 20. One slot 47 is shown on edge 22, sectioned by
dividers 55 and 57 into distinct slot sections 49, 51 and 53. The
position of dividers 55 and 57 are opposite the ends of slots 41
and 43, respectively, so the length of slot 49 corresponds to the
length of slot 41, the combined length of slot 49 and 51
corresponds to the length of slot 43 and the combined length of
slots 49, 51 and 53 corresponds to the length of slot 45. Pressure
transducers 61, 63 and 65 are tied to control box 17 and sense an
absence of positive air pressure corresponding to negative relative
wind. The control box 17, in response to the signals received from
the pressure transducers controls the air to the slots.
Referring now to FIG. 4, the control of tangential blowing along
the length of blade 11 is described. When the negative relative
wind extends along a small length of blade 11, as in FIG. 4a, only
transducer 61 will sense an absence of positive air pressure.
Control 17, is response to the transducer signal, will cut off the
supply of air to slot 49 and supply air to slot 41. When the
portion of blade 11 experiencing negative relative wind increases,
as shown in FIG. 4b, transducer 63, will sense an absence of
positive air pressure causing air to be cut off from slots 49 and
51 and causing air to be supplied to slots 41 and 43. Similarly,
when the length of blade 11 is experiencing negative relative wind,
as shown in FIG. 4c, transducer 65 senses an absence of positive
air pressure and causes air to be cut off slots 49, 51 and 53 and
causes air to be supplied to slots 41, 43 and 45. As slots 41, 43
and 45 overlap, causing the air flow to combine in the overlapped
portions, the intensity of blowing will be proportional to the
intensity of the negative relative wind along the length of blade
11.
Although three slots and three plenum chambers are shown, for the
helicopter rotor 11, additional slots of varying length can be
added and plenum chambers 1 and 2 can be additionally subdivided to
separately maintain air supplies to the additional slots as may be
desirable to more accurately control the lift along the blades.
In addition, the pressure transducers can be used which can sense
the magnitude of the negative relative wind and control 17,
responsive to the magnitude sensed, can proportionally control the
intensity of blowing.
Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
* * * * *