CA1199873A - Windmill - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A windmill for generating electricity in which each blade of the air-screw is connected to the hub by means of at least two resilient strips which are oppositely inclined both in the plane of rotation of the blade and in a plane extending through the rotational axis of the hub. This arrangement results in automatic pitch increase of the blades with higher increase air-screw rotation due to the increasing centrifugal force exerted on the blades, This regulates air-screw speed and prevents excessive speed, especially at low load. this pitch-varying mechanism can also be applied top automotive cooling fans. In accordance with another characteristic, the windmill proper consisting of the air-screw and the electric generator driven thereby, is attached to the supporting tower by a spring system, whereby any shock imparted to the windmill by wind gust, or sudden changes of direction of the wind, will be absorbed by this resilient mounting, thereby diminishing the stresses imparted to the support tower.

Description

7~3 FI~LD OF THE INVENTION
Th~ pr~nt inv0ntion r81at8~ to windmill~ and to ~ir-screw0 th~ typ~ having ~ pitch-v~rying m~chunism.
~ACKGROUN~ OF THE INUNTION
It i~ ;~no~n to provide a mech~ni~m to uary tha pitch of air-~crews, ~uch ~8 in helicopters and Mir-pl~ne~. How~v0r, euch mechani3ms Jr~ highly c, ,]~x and, th~r~ors, expen~lv0 to manuf~ctur~
and not ~uitabl~ for windmllls ~sp~cielly o~ th~ dome~tic type9 which mu~t b~ built ~t th~ lea~t co~t pn~1blN~ In win ~ t i8 lU daeirebls to provide the air-~cr0w with a v,~ri~bl~ pitch characteristic tD prevent exce~sive ape~d of th~ ~ir-scr~ in high wind cundition and ~pecially when th~ load on th~ air-3crew i3 small or nil.
Air-~erews, ~ore par~ieularly ~entilator ~an~ used in automo-biles ~or cooling th0 llquid cool~nt in the radiator, ar~ ~t tho present ti~0 not equipped with ~ variabl0 pitch f~ature; but it would b0 ~dv~nt~geou~ to 90 8qUip th~ 9~ in erd0r to automatically ~t the fan blad~ at zere pitch wh~n the ~Ut! :9~11e trlv~ls at high sp0ed ~ so ~e to conl3~r~te en~rgy . Revortin~ to windmill~ ~ the mountlng o~ thH windmill on a eupport tow0r i~ generally rigid and th~ to~er mw~t thHre~or~ b3 ~ir~ly ~upportéd in an upright posltion to re~i~t wind 9~Bt8- This coneider~bly Go~pllcat~3 the inst~llatlon wi~
O~JECTS OF THE INUENTIDN
It is th~ref ore the g~neral obJect of the pr~nt 1 nventiQn to provid0 ~n ~ir-screu, whather ol' tho pa~ ~o typ~, u~oh ~3 to b~
rot~t~d by tha wl nd ae U80CI ~n a wind~ 11, or ct tha flctiue typo ~ ~uoh a8 an air prop~llar or ~ir tan, provided with sirrpl~ meAn~ to ~ut~atleally vary the pitch oP the ~ oc~w bl~deo ln acoo~dano~
with the varlation o~ rotation01 8pe~ld of' the air-ecr~w.
It is ~noth~r m~ln ob,~act of th~ presant inventlon to pro~vide ~ln :l~ill in which the windr~ill p~oper i~ ~ttoGhod on ~ support t~w~r by reaili~nt me~n~, oo ~18 to conaider~bly dimini0h ths ~tr~a~ae~
i~part~d to ths towDr duo to ~uddan chsngea in tho:~peed or dir~ti~n

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oP the win~, It 19 ~nother obJect of tha pre~ent inuention in whlch the var~able pitch msehani3m iB Co~plHt31y aUtomatiG in it~ operation-It i~ another obj~ct o~ the pr~ent inbention to provid~
a windmill of minimu~ w~ight with re~pect to the power output o~its generator,go a~ to again di~lnieh the cnst oP th~ ~upporting tower.
SUMMARY OF THE INVENTION
The variabl~ pitch ~ir-scrOEw of tha in~ntion include~ A
lD hub and at least tWD radi~l1y-extending blade~ ~ach h~ving a root radially ~paced ~rom the hub and cannscted to the sa~e by at lea~t tw~ re~ilient etrip~. The ~tr~p ar~ oppo~itely inclined in both tha plan0 of rotstion o~ th~ blades ~nd in the pl~ne oxt~ndi~g th~ough the rot~tional axi~ of the hub, Th~refore, with increaslng rotation~l spaed o~ the air-screw ~nd con~qu~nt incroa0ing centriPugal ~orc~
ex~rt~d on the blad~s7 the ~trip~ bein~ rs~ilient, gradually rl~x~
cauoing rQt~tion oP the blade3 ~bout their longitudln~l 8Xi9-In ~ccordancfi with the second ch0racteristir oP the lnuentian, tha windmill proper, including th~ ~8~ -nhly o~ the air-scr~w and o~
the el0~tric g3n~rator dri~n thereby, i~ mounted on a ~upp~rting tow3r by mean~ u~ a fl~xib1e ~pring--llke ~s~b~ or ~embaro~ which ab~orb ~ny shock c~ue0d by wind gusta on the windmill and, theroPors, the ~upporting to~0r and/or its anchoring meane can be ~ads le88 ri~id and strong than otherwi~e.
~RIEF DESCRIPTION Of THE URAWINGS
Tho foregoing will bsco~e morJ ~pparent during the fDllo~ing diaclo~wr0 hy rafqrring to the dra~ing~, in wh$chs Figur~ a per~pactlv0 ~i ew o~ part of ~ ~$rst ~ i r- ~t of tha windmlll o~ tha invention, with parts broken ~way,to ~how 3û tho interior arrang~ment;
Figurs 2 i~ an end viow of tha root of on~ blade and of tha re.silient stripe connacting tho blade to the hub ~hown ~s being above th~ blad~, th~ figure al~o showing the pitch varLat.Lon of the blade;

- 3 -t~3 Figure 3 ie a ~ide elevation of the windmil1 ~suntad en top of a supporting tow0r, pArtially shown;
Figura 4 ie a ~ront elevation o~ th0 windmillp t~ken along line 4-4 of Figur~ 3;
figura 5 i~ a partial side ~l~vation oP the hub a~d part o~
a blade and i ~3 connector etrips;
Flgur~ 6 i8 ~ eaction taksn ~long line 6-6 of Flgure 5;
Figure 7 i~ an end view of the root end o~ the blsd~ and tak~n along line 7-7 of ~i~ure 6;
Figure ~ i8 a c~oa~-section t~ken al~ng li~c 9~M o~ Figure 3;
Figure 9 i~ a perspe~tive view o~ a wind~ill in accordanc0 with a second : 'r~ nt;
Figure 10 is a paxspactivs view o~ the inner eupporting ~tructure ~or the g~nsrater ~nd alr-screw o~ the 3econd . '~ t;
and Figure 11 i an ~nd eleuation o~ the atructu~e o~ Figurs 10.
Raferring now ~ore p~rticularly to ths dra~ings in ~hich lika reference chsr~ctsra indicate like elcmente throughout, the windmill propsr, generally indicated at 1, is shown in Figure 1 and compri~es es~entia11y an alr~screw 2, which drives ~n elLctric generator 3 located ln a protectlve hou~ing 4O The windmill i8 ~upport~d by m~an~ o~ a m~ber 5 on top of a post 6, ~hoJn in Fi~ure 3, or eimilar towar, which ~ay be, for in~tanc~, 20 ~et~is hlgh; dapendlng on the loeatlon o~ the windmill.
Tha air-~crew 2 compri~es ~ hub ?~which~includeA ~ tubul~r me~ber ~, and ~p~ced flsngea or ~sllars 9 ~nd 9~ Thc ~lr~r0w ~urther include~ a plur~lity of r~dially~ext~ndin~ and angularly-~ equ~lly-ap~cod radial blados 10. In tha.ca~, illu~trat~d7 ther~
are threo blad~s, 120 degree~ apart. Each blade h~a an ~ir-~oi1 pro~ fDr l~inar sir flo~ wi~h a thick~r leading cds~ 11 end thinner trailing cdge 1~. Each blade ha~ a concaue surf~ca 13 f~cin~
the wlnd c0~ing from.the dir~ction ~hoLn by ~rraw A ~nd a conv~x face 14 upposita the wind dlrection. Each bl~da lU i~ ~ubstantially

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rigid but of light weight construction9 auch as a resin impragnatod with glase ~ibrae ~or tho skin an~ a cor~ o~ foam plastic. The root 15 o~ each blade ie thickened and i radially spaced frnm the hub 7. Each blad~ i8 conn~cted to the ~langa~, or collarc 9~ o~ the hub by ~eans of a p~ir of reeilient conn~ctor stripa 16 and 1~. The~
connactor 8trip8 ar8 ~ade o~ apring steel or the like r~0ili~nt material ~nd ara bent at the desired angle n~ar their end purtion~.
Conn0ctor strip 16 o~ esch blade~ which i8 the laading strip ~i~
r~p~ct to the direction of rotation o~ the blad~ hown by arro~a ~, und~r the action o~ ths wind, i8 rigidly conn~cted at one end to th0 collar 9~ and at its othar end to the root 15 o~ tha blado 10 at th~
convex Yace 14 of th0 bl~de and n~ar the le~ding ~dg~ 11. Connector ~krip 17, which i~ the trailing strip ~ith reapect to eir-screw rotation, i~ rigidly conn~ctad at it~ radially inner and to thc collar 9, and at it~ radially outer end to the root 15 ot th~ blade 10~ on the concave ~c0 13 thereo~ snd near the trailing edge 12 o~ aaid blad~.
It i8 tharefDre ~een thflt the two connector ~trips 16 and 17 ar~ opposit~ly inclined to each other~ both in tha plans o~
rotstion of the blados and ln a pl~ne extending through tha rDtatisn~
axis of th~ hub 7 (8~e Figur0~ 5 and 6). In the exa~ple shown~ th~
attach~nt polnts of the ~wo connector strip~ 16, 17 to the collara 9 and 9~ Bre po~ition~d in ~ common pluna ~xtonding through tho long axi~ o~ the hub~ ~hlle the attaoh~ant poi~t~ of the connector etrips 16 and 17 to the ro~t 15 of the bl~d~ iD are connectod to ~aid root at ~p~c~d polnts tr~naverae tu the blade and al~o acro~s the thickne~a o~ the root 15. The arrang0~0nt i8 such that with increa~
~ng c~ntri~ugal ~orce exert~d on tha blado ~ith incre~e in th~ ~ir~cr~
rotational ~peed~ th~ connoct~r etrips 16, 17 b~ing r~ailient, tend to tak~ a radial po~ition with respect to the$r re~psctive attaohment U~int to the collar~ 9 and 9', end th~ cauaes r~tation of th~ ~e~pect-ive bladea lO about their longitudinal ~xi~, re~u1ting in a vari~tion of pitch. More particularly9 th0re i~ produc~d an :lncreaae of pitch with ~ 5 -incr0a e of th0 ~psed o~ tha air-~crew. Thi~ i8 cleerly shown in fi~ura 2~ wherein at low alr-screw rot~tional spasd, the pitch o~
tha blade with respect to tha dire~tion o~ travol of the blRd0 1~
small at low air-screw speed and, roneaquently, at low ~ind ~pe~d, and incre~eee with the increasa of the sir-ecrew speed ~nd~r higher wind uelocity. For instanca, the pltch may incr~ee Prom -5 to -35. Thi~ automatic.pitoh lncreaee e~feotivaly controle the p0ed of rotatlon of thY sir~screw to obtain c 3ubstantially uniforo spsed and exc889iu~ speed will be prevented, even in very high wind conditlon and at low load. ~lade pitch increaee i~ al8~ caueed by the fDrce o~ the wind acting on each blade no~mal to lt when the~
location of the re~ultant of said ~orce transuer~ely of said hlade i8 nearer the sttachment point o~ 3trip 17 Shan nf atrip 16. Thie cDntribute~ to the speed li~itation of the air~screw.
It ia clear that the location o~ the attachment point~ o~ the connector Rtrips to the hub and blades, the distance between flenges 9, 9' and/or th~ eti~ne~c of the strips cQn be v~ried to vary ths ratc of pitch incr0ase ~nd -~iT ' pitch with wlnd velocity. Obviouely, to increase eti~ne~e, the number o~ sl;rips can ba doubled, a~ ~hown at 16~ and 17' in Figure 5.
It i~ noted that the two connector etrips ~erue not only a~
p~tch-verying mechanism but al~o as a connecting mean~ betwe~n the blade and the hub, Furthermore, this cDnnecting ~s~ns being re3ilient9 any euddsn wlnd gu~t exarted on the bl~des will re~ult in the flex~nQ
of th~ oonneotor ~trips and, therefore, inclination o~ th~ blado away ~rom the ~ind direc~ionO
~h~ oth0r parts o~ th~ windmill are ~1DO OP vary ~imple snd lightwetght construction. Ths tubular memb~r ~ c~ th~ hub 7 tQ 8i~ply mount~d for retation ~bout an inn~r st~tion~ry ~h~ft 1~ ~upport~d sub~tantially horizontally. Th~ sloctrlc gen~rator 3 i9 8U9pOnded from ~ha~t 1~ by ~e~nH ef str~p~ 20. The body a~ the electric g~n~rator 19 is slid~bl~ guid~d in th~ atraps 20, more particularly in t~a trame 21 form0d by seid ~tr~ps. A mul~i-grDove pulley 22 i~ dly mount3d on tho tubul~r m~mher ~ o~ th~ hub 7 flnd drivo~ a ~llor dia~ot~r 3't~ ~
pull~y 23 ~ d to th~ lnput Rha~t o~ th~ sl~tric g~ner~tor 19 thro~gh a plurality of ~-b~lt~ 25. ~ec~u~e th~ electric g~nerator i3 ~reely su~p~nded9 it act~ a3 9 balt tighten0r undsr it~ own welght.
Tha 3upport shaft lB al~o support~ tha housing, gener~lly lndicat~d at 4, which pre~rsbly consicts o~ a rigid framework 26 which ~upports a flexible lightweight ~kin 27 mads, ~or lnstance, o~
wat~r~proo~ ~abric, and which ~ompl~t~ly cover~ th0 01ectric generator 3 and the pulleya 22, 23 and b~lt~ 25.
I~lembar 5, which elJppe~rts the ~ntire wind~ill 1, msy cDnsist ~i0ply of a resili~nt rod ~emb0r~ ~sde of ~pring ~aterial, such spring st~el, and b~nt to have a horizontally-~xtending uppcr 13nd p~rtion 28 which i8 welded, ~r o~her~i~s ~ecured,to tha sh~t 1~ of tha ~i~dmill. This h~rizontal and portion i~ follow~d by an integral vartical portion 2~ ~ in turn ~ol 1 CW_L' by e ucrtic~lly~- downwardly~
inclined portion 30, in turn termlnat~d by a vsrtical portion 31, which iB secur~d at its lower ond to a vertical tubular sp~ 32 ~ountcd ~or free rotation about a vsrtical axis in a cylindrical body 33,which for~s part of a br~cket! generally indicatad at 34~ for ~tt~ching tho wlndmill on the top of a po~t 6~ Tlhi0 po~t ~sy con~ist o~ ~n ordin~ry t01Hphone wooden po~t. Th~ bri3ckst 34 h~ h~n se~n l~
top pl~n uiew, thr~ p~rall01 ar~s 3S ~acured ~nd downwardly depending frnm khe cylindrical body 33 and ~ach oP U-shape cross-~ction~ a~ shown in Fi~ure ~. Ths~e ~rms 3S aro adaptad to ~urround and be sscur~d to the top portiQn oY woode~ post 6. Each sr~ 35 is provi~od with hol~ 36 to which guy wire~ 37 sre attaohed At their top end ~nd ~hich ars sd~pted to be nchorcd in the ground or oth~r sult~bl~ ground lovel ~tructure ~or ~aintaining the po~t 6 in uertical po~ition and, con~equently~ th~
~x19 0~ the hub 7 normal.ly in sub~t~nti~lly horizontal position~
A~ sbown in Fi~ure 3, and 8~ pr~uiou~ly not~d, the ~irmill 1~ o~ the downwlnd type. Since tho uertlcally-inclined portion 30 o~ ths supporting ~ember 5 provides aufficiant lateral o~f~et of the rotationsl plsno of the ~ir-sor0~ in downwind direction with ra~pect to the vartical 8Xi9 ~f rotation of the support m~bar, there iB obtain~d automatic eri~ntation o~ the windmill ln the wind directlon, ~c clearly ~hcwn in Figure 3, without ræquiring a tail ~in. The windmill ia ~ree to rotete continuou~ly about the axig a~ apindle 52.
The output wira~ 38 of tha el~ctric gon~r~tor 3 run do~n th~ ~upport msmber 5, whil~ being suitably protected ag~in~t ~eathar, and ent0r tha.hollow ~pindle 32, which i~ provldsd at it~ lower ~nd with rotary connactor ~8~ ' ly~ g~ner~lly indic~ted ~t 39, tor continuou~ conn~ctlon with th~ oetput wir~ 40 running down the pG~t

5 fur connection to an eLectric load and sl~ctr~c control ey~te~.
The eupporting ~rr~ng~ment for~d by re~ilient ~e~ber 5 i~
such th~t, ~on th~re i~ no wind, the ~ir-~crew axia i~ slightly vertically :Lnclined upw~rdly with re~pect to ~ha horizont~l; with ~oderate wind v~locity of about 15 to 18 ~iles por hour~ th~ r~
~xl~ ~ouo~ do~n to b~oo~ bst~ntially horizontal D ~ith th~ result that th~ oP wlnd en0rgy Lta oapturad., Und~r hlgh wind or exr-e~sivæ wind torct3, th0 air prnpt~ller ~xia ~ill tend to movo down ~rom tho h~rizont~l~"Jheraby the ~3ir-w~w will preiaent a smallar r~elatanc~ area to th~ wind~ Thi~ arr~n3 ~nt al30 11f'l'13CtiV~lly hslps 2D in prcventing rsxce~si ve air-sorl3w rot~tlonal~pe0d under high wind cDndition. In a wind burst~ t~ aUppQrt ~embt3r 15 will 8iil~ply bond in a rasilit3nt manner. Therefors;, any audden ~hock which ~ight be otharwlse tran~mlttl3d to thc po~t 6~. i8 oonsidarably reduced, ~hertaby th~ post its~lf, and al~o it8 tanchorag~ ~ystem, ~ay bta mado le~t~ ~trong th~r; otherwils~ -FigLIres 9 to ll how a ~tacond '-Qd1r- nt of th~ ~upporting gyatam ~or ths3 windmill dssign~d ~or windmills having a greatsr power OUtptlt capacity than that of tht3 ~ir~t ambodiment.
In tha sacond ~ n'r ~d~ nt~ ths windmill proper ia exactly the sami3 ~3~ in thl3 ~ir~t t3r~od1--nt and includet3 tha air-scr~w 2, tha s31sctric gentarator 3, not ehown, the housing 4 wlth tha hub9 not shown~
o~ thl3 air-~crsw rotatably mounted on a ~Support or shsft lB, such as in ths Pirst 0mbodim~3nt. Th~3 shEI~t lB in ths ~cond ~mbodimant 19 fixsd by U~shaped clamps 41 kD ths c~nter oP tWD fl~9embliea 0~
conventional leaf springs 42, such ao u~sd for sutomobil0 ~uspen~inn~.
The two leaf spring aeeemblie~ 42 are freely ~uspend~d at th~ir outar ends by meana of ordinary ~utomotive shackl~s 43 to th~ top o~ inuerted L-ahap0d brackats 449 the~selve~ ~p~tanding from and rigidly necur0d to gensrally rectangular frame 45 provid~d with diagonal reinforcing bars ~6 9 to the under3ide of which i9 sscur~d a whssl member 47 rotatably mountsd on a vertical rod 4~ for free rotation about a vertical axi3. T~ low~r end o~ rod 48 i9 secured i~ any ~uitsble manner~ ~uch as by tha bracket eyst~m 34 of tha first -bo~ nt~ to the top of the ~upport tower 6~ Suitable ~rr~ngemont, ag in the first embodiment including rotary slectric contact~, i0-Prouided, as in the first ~-~odir ~t, for ren~action of th6-slsctric gensrator suspend~d ~rom th~ shaft 18. Shaft 18 can be ~u~ficiontly ext0ndad ~rom the end of ths frsme 45, so th~t tha plane o~ rotation of tha air-scrsw will be laterally offset a ~u~iaient distance ~rom the vertical pi~otal axis of th~ windmill arrang0mant on post 6, 80 that ths ~ind-mill will automatically orisnt its01f in the wind.
It will be undarstood th~t with the arrangem~nt o~ the l~af ~pring a~amblie~ 42 re~ilientlysUpporting the shaft 18 of` the windmill, any sudd6n change in wind direction, eithar v~rtically or hori~ontally, will psrmlt the air-scrsw 2 to immediately orient ltself pro~orly into the wind. Shaft 1~ can move up and down, with the leaf spring a~semblies 42 flexing accordingly. The shackie~ 43 permit a later~l angular mov2m0nt in a horizontal plane in either direction o~ the ~h~t 1~. Here again, any 3hock by ~udden oh~nge~ in the wlnd direction or by wind gu~t~ ~ill be ab~orbed by the re~ilient Bupporting 3y8tem~ ~0 that ~ny etrains on the ~upporting po~t will be gr~atly decreased.
Reu~rting again to th0 pitch-Yarying ~echani~ illu~trated in Figures 1 to 7, it will be noted that the ~ame can bs appli0d not only to air-s~rews ~0Dd ~or win' Lll 8 in which the air-~crew i~ dri~n by the wind, but for air-Rcrews u~ed a~ propeller~ in applicationc where it is desirable So va~y the pitch o~ the propall0r blade~
in accor~anca wi~h the spesd of rot~tion. 5uch an application may b0 found, for in~tance~ in v0ntilator fflns ~or th0 liquid-~oolant of automatiue qngines. In such an application, th0 ~pe0d o~ rotation of the ~an incraases proportionally to the engine ~peed.
At high-engine revnlutlon, the car or automobile normally travel~
.at suf~icisnt ~peed, 80 that cooling i8 nut n~c~s~ary. It i~
th~refore ~esirable,in or~ar to eliminate ~n~ine dr~g, to reduce ths blada pltch to zsro at high~engine speed. There~ore, in ordsr to achieve thi~, the arrangement of the pr~ent invention can ba provlded7 in which ths pitch o~ the blade i~ initially set ~t ~
xirl poeitive pitch ~or no rotation of th~ air-screw or propaller, and tD gradually d~crsasa to zero at a predetermined hlgh sp~ed (~or inot~nce, rs~3rr~ng tu Fig. 2~ the pitch ~ight dacrease fro~ ~ 35 to zero~.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
PRIVILEGE IS CLAIMED, ARE DEFINED AS FOLLOWS:

1. A variable pitch air-screw comprising a hub, at least two blades, each radially extending from said hub and having its root radially spaced from said hub and at least two resilient strips for each blade rigidly attached to said blade root and to said hub at their opposite ends, said strips being oppositely inclined both in the plane of rotation of said blades and in a plane extending through the rotational axis of said hub, whereby increase of the centrifugal force exerted on said blades will decrease said inclination of said strips and cause rotation of each blade about its longitudinal axis relative to said hub, to thereby vary the pitch of the blades with variation of the rotational speed of said air-screw.

2. A variable pitch air-screw as defined in claim 1, wherein said strips are attached to said blade root at spaced points transverse to said blade and also across the thickness of said root and said strips are attached to said hub at spaced points axially of said hub.

3. A variable pitch air-screw as claimed in claim 2, wherein said strips cross each other when seen in a plane passing through the rotational axis of said hub.

4. A variable pitch air-screw as claimed in claim 3, wherein said strips are attached to said hub at spaced points lying in a plane containing the longitudinal axis of said hub.

5. In a windmill comprising the variable pitch air-screw as defined in claim 2, and further including a generally horizontally-supported stationary shaft on which said hub is mounted for free rotation, an electric generator suspended from said shaft, a pulley-and-belt drive connected between said hub and said generator for driving the latter by said air-screw, and a resilient support for connecting said shaft to a sup-porting tower for said windmill.

6. In a windmill as claimed in claim 5, wherein said resilient support is in one piece and has an upper portion rigidly secured to said shaft, a vertically-extending lower portion rotatably mounted for free rotation about a vertical axis with respect to said supporting tower and an intermediate vertically-inclined portion for supporting said windmill in a laterally-offset position with respect to said tower, whereby pressure exerted on said air-screw will cause automatic orientation of said air-screw in the wind direction by rotation of said resilient support about its vertical axis.

7. In a windmill as claimed in claim 5 or 6, wherein said electric generator is suspended from said shaft for guided vertical movement, whereby the belt of said drive is kept taut under the weight of said electric generator.

8. In a windmill including the variable pitch air-screw as claimed in claim 1, 2 or 3, further including a generally horizontally-disposed shaft on which said hub is mounted for free rotation, a supporting tower for said windmill, guy wire means for maintaining said tower in upright position to support the windmill at a distance above ground, and a resilient connection between said support shaft and said tower acting as a shock-absorber for the stresses transmitted by said air-screw to said tower, such as caused by wind gusts.