Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROU2~D OF INVENTlON
Wind was one of the fir~t natural energy sources
to be harnessed by man with the use of variou~ windmlll
driven apparatus. The use of wlndmllls, however,
declined drastlcally after the development of the ~team
englne, internal combustion engine, and other 08811
fueled energy conversion machine~. Recently, with the
increaslng cost of fossll and other presently widely
used energy sources, interest is again being directed
to the use of wind as a competitive source of energy.
~ For example, it has been estimated that greater
- than about 1012 kilowatt hours of electricity could
::~
be produced from practlcal wind po~7er sites in the
- - Unlted States alone, the energy available being proportional
~;~ to the air density and wind speed, the latter affecting
~ ., .
energy-by the third power. Since the amount of energy
~` available in wlnd m~y be slgnlficant when compared to
the energy needs of the world, such wlnd driven power
sources may become of lncr~sing importance, expeclally
~ ~ .
if the location at which the energy is required is remote
or where alternate energy sources require hlgh cost
fuel to produce power.
Various wind driven machines or turblnes have been
proposed or utllized, such as the well known horlzontal
- axia windmlll~. Th-ae wlndmlll~ hav~ w-d various
design~ and arrangements of rotora whlch h ve achleved
lQ4Z347
rotor tip velocity to w~nd velocity ratios of as 8reat
as 6 to 1. However, becau~e of the inherent limitation~
of such horizontal axi~ windmill~ which require the rotor
to be aligned in a particuiar direction with respect
to the wlnd direction (which of course is not canstant)
these windmills often include complex windmill rotation
drive mechanisms to m~intain the proper windmill rotor
- attitude or direction with respect to the wind direction.
These mechanisms, besides being complex, generally must be
attached to the windmill ad~acent to the axis of the rotor
and are thus supported well above ground level, at least
as hi8h a~ the radiu~ of the rotor. This also adds to
the complexity, cost and weight of the ~upporting towers
and other previously referred to mechanisms of the entlre
windmill system.
; ~
Vertic-l axis wind turbines have been proposed and
` ;tested to overcome some of these shortcomings. Most
,, .
vertical axls wind turbines, however, have very low roto~
tip velocity to wind velocity ratios and are thu~ very
lnefficient or reqùire an additional power source to
accelerate the rotor to a velocity at which the rotor
can produce positive torque. In addition, some prior
vertical axis wind turbines have utilized rather complex
. . ,
- and expensive rotor blade dQsigns or have b-en of relatlvely
low strength for practical applicatlon~. Even though
vertlcal axis wind turbines are often capable of operating
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from a wind coming from any direction and with power
generating equipment and tower structure which may be
of relatively simple construction, vertical axis wind
turbines have not been developed or widely used.
SUNNARY 0~ INVENTION
In view of the above, it i8 an ob~ect of this
invention to provide a relatively simple and low cost
wind turbine arrangement.
It is a further ob~ect of this invention to provide
,
a vertical axis wind turbine which is self-starting and
which is capable of providing a relatively high blade
tip velocity to wind velocity ratio.
It is a still further object of this invention to
provide a vestical axis wind turbine having a novel rotor
blade configuration.
It is a further ob~ect of this invention to provide
a high efficiency vertical axis wind turbine system.
This invention relates to a wind turbine having a
drive rotor including an outwardly curved, airfoil shaped
blade extending between end portions of a rotatable shaft;
and additional rotor means disposed at both end portions
of the shaft and out of registry with torque producing
portions of the drive rotor to bring the entire rotor
assembly up to a speed at which the drive rotor may
maintain a rotary driving force to the shaft and which
thereafter continueo to contribute a driving force thereto
at the higher opoeds.
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1~4;~ 7
The invention comprises a wind turbine with rotatable shaft supporting
a drive rotor that has an elongated blade with curved blade or central
curved portion of airfoil shape transverse to its curvature, and means
supporting the blade on the shaft with the airfoil shape directed along
the path of movement of the blade for exerting significant driving force
on the shaft when the curved blade portion attains a linear velocity to
wind velocity ratio greater than about three, together with starter rotor
means on the shaft having vanes out of registry with the curved portion
or curved blade of the rotor for rotatably accelerating the shaft to the
noted velocity ratio. There is coupled to the shaft some means for
utilizing the shaft rotation.
DESCRIPTION OF DRAWINGS
~ he invention is illustrated in the accompanying drawing wherein;
Fig. 1 is a somewhat simplified perspective view of the wind turbine
assembly of this invention showing the relative positions of the rotor
ele~ents;
Fig. 2 ghows diagrammatically the preferred shape of the blades in
the main drive rotor of the wind turbine;
Fig. 3 shows diagra~matically a comparison of the blade shape of this
invention with other possible blade curvatures;
Fig. 4 is a cross-sectional view of the airfoil portion of the blade
shown in Fig. 2;
; Fig. 5 is a graph of efficiency versus velocity ratios for the
~ respective rotor portions of the present wind turbine;
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Fig. 6a and Fig. 6b illustrate by cros~ section
variou~ shapes that the straight ~egment~ may have for the
blades shown in Fig~. 1 and 2;
Fig. 7 illustrates diagrammatically in a top sectlon
view the positions of the vanes of the starter rot~r
.~
~; ueilized in the wind turbine as~embly of Fig. l;
Fig. 8 is a per~pective view of another starter
rotor arrangoment which may be used with the turbine of
Fig. l;
~i 10 Fig. 9 ~hows diagrammatically a modification to the
~ drlve rotor blade and blade shape;
-, Figs. lOa and lOb illustrate further modifications
of the drlve rotor blade to effectively increase the
, a~pect ratio of the rotor blade;
Fig. ll illustrates a modified version of the wind
?` ~ ~ ' turbine which utilizes a vertical ~tacking of drive
`~ -rotors; and
Fig. 12 is a simplified diagrammatic view of an
~1 . .
arrangement of the drive rotor blades in which the blade
segments may be folded to reduce tho wind proflle of the
turbine.
.
DETAILED DESCRIPTION
The wind turbine of thls invention lncludes a wind
driven maln power or drlve rotor 10 and a pair of wind
driven starter rotors 14 and 16 coupled to a rotatable
shaft 12, a~ indicated in Fig. 1. It is preforred that the
- 6 -
104Z347wind turbine be supported in a vertical posltion as
shown, 80 that any wind, regardless of direction, will
always cause rotation o~ the wind turbine rotors without
ad3ustment of the turbine axis. Each of the rotors
10, 14 and 16 are fixed to the shaft 12 so as to rotate
together about fixed platform or tower 18 with the shaft
12 malntained in the desired vertical pos~tlon. Shaft
12 msy be rotatably mounted on platform 18 by appropriate
rotary bearings, and the like and may be stabilized by
.
appropriate guys or other supports 19 from upper
-- portions of the shaft, if such is desirable, depenting
,~ .
on the size of the wind turbine and the wind velocitie~
~in which it i8 to be operated. In addition, shaft 12,
and consequently rotor~ 10, 14 and 16, may be coupled
dlrectly or via an appropriate drive system, such aæ
- represented by gears 20 and 22, to a suitable utilization
- means 24 which may convert or otherwise utilize the energy
. .
~; ~ produced by the rotation of shaft 12. Utilization means
24 may be any appropriate apparatus or mechanism which
may convert the rotary motion of the wind turbine into
electricity orsome other form of energy, for exsmple an
alternator or generator, or which may provide some other
operatlon or function, for example pumping of a fluid frcm
a well or operating anoth-r appsratu~ or m-chanlsm.
The main drive or power rotor 10 may include one
or more generally vertically disposed elongated bla~es,
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~04Z;~47
such as the three blades 26a, 26b and 26c shown, which are fastened or
coupled to shaft 12 at their extremities through an appropriate collar or
other support. The blade or blades may be po~itioned around ghaft 12
so as to balance each other or may be provided with appropriate counter-
weights, or the like to provide this balance. Each blade, as indicated
by blade 26a, may include a central outwardly curvet, arcuate portion
28 connected through straight segment 30 to an upper portion of shaft
12 and through another straight segment 32 to a lower portion of shaft
12, for convenience the portion 28 msy be referred to as the curved blade
and the portions 30~ 32 as means for supporting the curved blade. More
or less blades than the three shown may be utilized in rotor 10 but with
some lowering of efficiency and/or inordinate increase in cost, the
efficiency of drive rotor 10 being a function of the ratio of blade area
to the blade swept area. The shaft 12 may be a single solid or hollow
rot, concentric rods rotatable with respect to each other, or a lattice
or truss-like structure, depending on its proposed strength and size and
the apparatus w ed to support the same.
It has beèn found that if a perfectly flexible cable of uniform
~` :
density and cross section is attached at its ends to two points on a
vertical axis and is then spun at a constant angular velocity about the
veroical axis, the cable will assume the curvature indicated by the dotted
, ~ .
line 34 shown in Fig. 2, referred to hereinafter as a troposkien shape,
regardle-s of the angular velocity.
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When the cable assumes this shape and i8 rotated about
the vertlcal axis, the stresses produced in the cable
sre essentlally tenslle stresses. It has further been
found that for purposos of this lnvention, the tropo~kien
; shape can be approximated by a clrcular src 34a, at the
outermost portion of the troposkien shape, and a pair of
stralght segments 34b and 34c coupled between the ends
of the circular arc 34a and the rotation axis. With this
approxlmation, the cable is still sub~ected to essentially
10~ tensile stresses with only negligible bending ~tresses.
TbiJ approximatlon i8 utilized as the desired shape for
the power rotor 10 blades illustrated in Fig. 1.
., ~
~ Flg. 3 illustrates the diffèrences between a
:
; ; tropo~kien-shaped curve 34 and that of a circular arc
36 and a catenary-shaped curve 38~ The catenary-shaped
k.
curve 38 -pproximates the shape assumed by a perfectly
flexible cable of uniform den8ity and cross section hanging
freely from two fi~ed points. A rotated blade having
elth-r of-the shape~ 36 or 38 will produce greater
-~ ~ 20bending stresses than the shape 34 or its approximation.
. ~
described above, the troposkien-shaped curve 34
-- minimiz the bending stresses produced in the vertical
.
blade when sub~ected to rotary motion, while the approxima-
tion of a tropo~kien ahape, as illu~trated by the circular
arc ~-gment 34a nd th- tra$8ht ~egment sectlons 34b
and 34c in Flg. 2 and the correspondlng curved portion
28 and straight segments 30 and 32 of the blade 26a in
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- Fig 1, provide minimized bendlng stresses while insuring
a blsde configuratlon which may be manufactured with
a relatively simpl- shape at relatively low cost The
blade configuration shown may be selected to provide a
close; approximQtion of the troposkien shape to minimize
~ bending`~tresses by minimizing the maximum separation
.. . ~. . .
~` di-t nce'beeween curve 34 and the pproximatlon segments
: 34a,'34b and 34C? or by otherwlse ad3usting thë approximation
hap~ In additlon, since th~ rotors 14 and 16 are
~ located ln po-ition where they may normally interfere
with an sir sèream or wind directed against the blades
of rotor I0 t the upper nd lo~er tr_ities th-reof
the trsight segm~nts 30 and 32 of the rotor lO'blades
'' ' c~n be"i'or èd a8 structur 1 members with little or no
rod~nu ic lift or touque producing effects Further,
Inc- the torque or rotary force produced by the blades
of rotor 10 increà~-~ a~ the blade distance from the
rot tion a is -ncr a-es, the U8- of tho curved portion
28 as th- principal or only drive section m~kes more
eff tiv- u~e of wind nergy as other portions of the
blade~ o ely the ~traight s-gmcnts, inherently produce
.
- lower torque levels fro~ equal wind energy
~- Th- curved portion 28 of th- blad-s 26a, 26b and
~:
'~ 26c r provid-d with an irfoil ~hap or cros~ 8 ction
~' tranfv-r~- to th- blad- curv tur and facing tha
dlr ction of rot-tion of rotor 10 ~o ~ to provide li~t
10 -
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104Z;~47
force when the rotor 10 turns in a wind. A typical
cross section is shown in Fig. 4 which i8 selected to
provide an optimum Lift-to-Drag ratio, thus increasing
power producing performance.
Because of the nature of rotor 10 and the circular
movemont of the blades, each blade curved airfoil section
28 will experience both positive and negative angles of
attack during a revolution 60 that there i~ no apparent
atvantage in ~sing a nonsymmetrical airfoil. In addition,
the lift for airfoil~ increases with increasing angle of
attàck up to the point where the flow separates from the
airfoil, which condition may cau~e a stall and is gen rally
to be avoided, the maximum lift being higher for increa~ing
~ spect ratios (the ratio of airfoil length to airfoil
; chord length). However, with the rotor 10, the wind
felt on curved portion 28 is not simply the ab~olute wind
~peed or velocity but rather the absolute wind velocity
minus vectorially the absolute blade velocity. Also, in
a rotating airfoil, the angle of attack i~ the angle
between the relative wind speed (that is the apparont
wind direction) and the chord line of the airfoil blade,
the angle of attack being dependent on wind velocity,
rotational blade velocity and the blade position with
re~pect to the turbine. For a given blade position, the
angle of attack decrea~es with increasing blade velocity
to wind velocity ratio. Therofore, for a sufficiently
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104Z347
high ratio, the airfoil may never stall during a revolution
while at low ratios the airfoil may be stalled ovcr an
àppreciable portion of the blade revolution. At high
ratios, the angle of attack decrease~ consequently decreasing
the chord-wise component of lift. There is thus maximum
rotor efficiency at some tip velocity (linear velocity
; of blade or vane at its maximum diameter) to wind velocity
ratio as indicated by curve 40 in Fig. 5, as detenmined
by analytical studies and wind-tunnel testing. It has
been found that the most efficient velocity ratios for
; ~ - the rotor 10 of this invention to produce maximum power
~ is from about 5 to 7, typically with a msximum at about 6.
"`'`J` A symmetrical airfoil shape which has a large lift-
- to-drag ratio msy be the NACA 0012 airfoil (National Advisory
Committee for Aeronautics). Such an airfoil or similar
irfoil may be formed, as shown in Fig. 4, with a high-
- strength backbone or tensile stress element 42 surrounded
by a rigid foam core 44. The stress element 42 may be a
steel, aluminum or fiber composite leaf or strap which is
roll or otherwise formed in the desired arcuate curvature
shown in Fig. 2 by curve 34a 80 as to act as the supporting
: ~ :
element for the curved portion 28 and as the strength
member to withstand the tensile force~ produced in the
blade from tho rotatlon of rotor 10. The rigld foam
core 44 may be formed from lightweight polyurethane or
the like foam bodies, as described below. Suitsble
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104Z347
fa~teners or attachments, such as hinges or pin~ (not
shown), may be affixed to the ends of element 42 at thi~
time for convenience in connecting the curved portion 28
of the blade to the straight segments 30 and 32. The
rigid core 44 may be shaped in the desired airfoil
conflguration and suitably adhered to the stress element
42, such as by forming the core 44 by machining ~r the
like two separate ri8id foam body balves from sultable
foam blades into the de~ired complementary shapes or
-~ 10 ~ections 44a and 44b and then attaching the sections on
either side of the curved stress element 42. The outer
surf~ce of the core 44 may then be appropriately coated,
' :
~ ~ such as with a fiberglass resin skln 46 in either m~t,
: ;
cloth or sprayed form, to provide a s~ooth and erosion
resistant surface around the core 44 which will protect
~; ~ the same from impacts by ob~ects carried by the wind
nd from rain, hail, or the like. The skin 46 may be
~ .
smoothed and polished and further coated to minimize
fricion and other aerodynamic losses and to provide
:
~ 20 the desired final shaping and balancing of the airfoil.
.,:
~`~ The straight segments 30 and 32 of the blades 26a,
-~ 26b and 26c may be formed of any convenient shape which
, :
- provides minimal wind resistance and which has sufficient
;;- tensile strength to support the curved portion 28 undsr
; maxlmum otress condltions and are attached ln an approprlate
manner to the fasteners connected to curved portion 28.
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For example, the straight segments may be fonmed with an
airfoil shape to aid in providing a drive force or to
minimize drag resi6tance to rotor 10 by bending a sheet
into an airfo~l shape and welding ~he trailing edge~
of the sheet, a~ shown by the straight segment cross
section 50a in Fig. 6a. Howevsr, since the str~ight
segments may contribute very little drive force due to
thelr position wlth respect to the rotors 14 and 16 and
with respect to shaft 12, economy may dictate the use of
.
a s~mple circular hollow or solid rod or other sh~pe as
indicated by the cross section 50b in Fig. 6b. The
straight segments are generally made of rigid msterials
to support the blades when the turbine is at rest and may
include suitable supports (not shown) from shaft 12 to
; aid in this support. There may also be applications
where it would be desirable to form the segments 30 and
32 out of a flexible material, such as a steel cable, which
. would assume the troposkien shape upon rotation of the
turblne. In these arrangoments, some other support of
the airfoil portions may have to be provided, as needed,
when the turbine is at rest.
~ As illustrated by the curve 40 in Fig. 5, rotor 10
- mu~t be driven to a blade tip speed to wind velocity
- ratlo of about 3 before the rotor 10 blados bogin to
e~ort or provld- a slgniflcant driving forco sufflcient
to offset drag, inertia, and othor 108808 and to accelorate
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the turb~ne to peak operating lèvels. In order to achleve
this velocity, starter rotor~ 14 and 16 are appr~prlately
supported at upper and lower portions of rotor 10 coupled
to tha common shaft 12 and out of registry with curved
portions 28 of the drive rotor 10. A particularly effective
starter rotor ie illustrated in Fig. 7 in which a pair
of arcuate or semicircular ~haped rectangular vanes 52
and 54 are supported on shaft 12 with hollowed portions
facing in opposite directions with a portion of each
vane overlapping the shaft 12 and the other vane in a
generally S-~hape fashion. With the vanes 80 positioned,
. .
wind directed against the hollow portion or chamber on
the inside of one of the vanes, such as the portion 56
of vane 52, will apply a driving force against vane g2
In the direction-of the arrow 58 and will be directed
through the channel 60 between vane 52 and shaft 12
against the hollow portion of vane 54, again producing
a driving force in the direction of arrow 58. Such a
rotor e~hibits an efficiency to rotational velocity ratio
charscteristic as indicated by the curve 62 in Fig. 5
-~ showing that the peak performsnce of the rotor shown in
`f~ Fig. 7 occurs at a ratio of approximately one. The ratio
of the diameter of rotor 10 to rotors 14 and 16 should
, . . .
-~ thus be sized to be from about 5 to 6 to 1, 80 that both
the starting and drlv~ rotors ar~ op-rating at th-ir
peak perfor~ance at about th- same rotatlonal velocities.
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1~4Z347
It has also been found that the starter rotors 14 and
16 may be provided with a height which i8 approximately
the same as their diameter to minimize blocking of the
most effective portion, that ~8 the curved portlon 28 of
rotor 10 as indicated in Fig. 1, or they may extend from
said curved portion 28 to beyond the ends of the drive
rotor 10 blades. The vaneæ 52 and 54 of the starter
... .
rotors may be made in the fonm shown or with variable
thlckness in an airfoil shape to provide increased
efficiency. For purpose of economy, and since the
additional aerodynamic perfonmance may not be significantly
greater to warrant the additional fabrication cost~, the
vanes 52 and 54 are preferably fonmed from sheet metal
with the~vane chamber or hollow portion forming a se~ment
of an arc having constant radius. The vanes of the
upper starter rotor 14 should be positioned, as shown in
Flg. 2, 80 as to be out of phase with the vanes of the
lower startor rotor 16, that is, interdigitated or
perpendicular one with re~pect to the other, 80 that
., .
-~ 20 the wind turbine is self-starting from wind coming from
- any direction and 80 as to ~mooth out the starting torque
produced by the starting rotors. Other types of starter
; rotors, such as certain drag-type rotors msy be utilizod
but with lower over all effici-nci-s and drive power,
such as the type ~hown in Fig. 8 utilizing thre8 bucket8
;~ 62a, 62b and 62c appropriately connected to shaft 12.
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104Z347
The respect~ve rotors 10, ~4 and 16 connected to the
common shaft 12 may be rotated in a wlnd to a velocity
; of from 3 to 4 times that of the wind by the proper
proportioning of the size and radiu~ of the starter
rotors and the power rotor, as described above. The
stsrter rotors will self-start without any external
application of power (other than wind) and will automatically
regulate the correct airfoil starting velocity as a
function of any wind velocity within the operating range
0 and limitations of the turbine. The starter rotor may
continue to produce driving power even at the operating
.
velocity of the power rotor witbout degrading the latter
~`- operation. With the blade design described above, the
- forces produced in the blade are substantially tensile
`In nature and readily absorbed by the system. The
~- utillzation means 24 may then be operated to provide
;
- ` whatever power, energy or operation desired from the
rotation of the wind turbine in a highly efficient,
simple and low cost system.
. .
If it is desired to provide increased driving torque
but with somewhat higher tensile stresses, the blades of
: ,.. .
~-~ rotor 10 may be modified by positioning appropriate mas~
~- or weight members at the ~unctlon between the straight
segments and the curv-d portion of the blade, such as
shown by weight mo~bers 64 nd 66 in Flg. 9. These masses
will tend to straighten out and change the arc of the
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104Z347
curved portion of the blades of the previous troposkien
descrlption into a new arc ~hape or curved portion 2&
whlch increases the swept area of the rotor 10 blado~.
In other words, the airfoil portion of the blades are
more vertical and thus provide a greater average rad~u~
from the rotor ~haft to the drive portion of the power
blade and a greater area of blade ~weep. Sin~e the
blade curved portion is still in the form of an arc, the
stres-ses within the curved portion will still be tensile
but m~y require a higher strength ~oint or iunction between
the curve portion 28a and the straight segments of ehe
blade.
The blades of rotor 10 may be further modified by
installing tip plates of larger dimension than the blade
C~88 section at the 3unction be~ween the curved po~tion
., ~ .
28 and the straight segments 30 and 32 of the power
blades of rotor 10. These tip plates are most effective
when the angles of attack are high to increase the
~,~
effective aspect ratio (ratio of blade length to blade
chord length) of the blade airfoil by preventing the
higher pressure air inside the airfoil from "spilling"
around the end of the airfoil into the low pressure ~ide.
The tip plates may be installed perpendicular to the
blade a~ sho~n in Fig. lOa by tip 68a or perpendicular
to th- vertlcsl axls or shaft 12 of the turbine as
indlcated by tip 68b in Fig. lOb. In the latter configur-
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1~4Z347ation, the tip plate 68b wo;uld minlmize interference
with the alr flow over the blade itself and would not
have to rotate against the air stream at the rotstional
velocity of rotor 10.
Since the fabrication cost of a wind turbine of the
type described above may increase ~ubstantlally as the
size of the wind turbine is increased and since wind
velocities often increase with distance above ground
level, it may be desirable to stack wind turbines one
`-10: bove the other on a common shaft 72, as indicated
in Fig. 11 by turbines 70a and 70b. Because of this
increase in wlnd velocity with height, it may also be
desirable that the upper wind turbine 70b be provided
; ;
~ with a diameter greater than lower t~rbines to provide
.; :
more efficient ut~lization of the wind energy. The
turbines 70a and 70b (and additional stacked turbines)
and their common sbaft 72 may be appropriately supported
i ~
at the ground and with suitable guy and collar arrange-
ments 74a and 74b at intermediate and upper positions of
- 20 ~ the turbines. The turbines can thus be positioned 80
`~ - as to occupy a limited area of ground without any wind
-1 intererence between turbines. It will be understood
-`:that these turbines may be provided with one or more
similar starter rotors as doscribed above.
In ord-r to prot-ct tho wind turbines of thi~
invention from excessive winds, tho turbinos may be providod
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104Z347
with demount~ble or foldable ~unction~ or fasteners at
the connection between the curved portion~ and strsight
segments of the blades and between the blades and shaft
12 ~o that the blades may be folded or collap~ed to a
much smaller dlameter which will have significantly
lower wind reslstance and which may be suitably c~vered,
if desired. For example, if the blades of rotor 10 are
provided, as shown in Fig. 12 with a hinge-like connector
between each of the upper straight blade segment~ 30'
and 30" and curved portions 28' and 28" and between the
,; .
lower straight ~egments 32' and 32" and the vertical
shaft 12', and if the lbwer straight segments are demountable
from the curved portion, the lower straight segments may
be detached from the curved portion of the blade and
folded against the ~haft while the upper straight segment
and curved portion are pivoted against the shaft and
:
appropriately fastened or strapped thereto. A~ can be
~` seen, the wind profile of the turbine is thus drastically
- reduced.
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':,' -
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