Simplified Wind Power Systems for Experimenters

8/12/2019 Simplified Wind Power Systems for Experimenters

1/84

I,/jPublishedby.:.Helin-. % 0 \ Box 445t Browns+ille, CA 959.19 USA'5; Thi~publf~~ation is.out of print in 1983.--m-z. ,*I, ~_:,I .I _Reproduced-by permission of Helion.

Reproduction' of trhis microf iche document in anyform is subject to the same restrictions as thoseOF the original document.


2/84

3


3/84


4/84

SlMPllFiED lNo:POH(ERYSTEMSORB(PERIMfN~R$ -- .. YSecgnd Edition

- k .'-Written by Jack Park I I,/' '.Published by/:HELION ' Box 4301, Sylma?, Caliiornia 91342. . .'pCopies may be purchased 'c&m th%publisher for 6 Ipostage pak A11 .id.

@ Copyright 1975 by Jack P-ark. No portion of this book may- b$ ,reproduced without the'author's written- permission; ..'. L.~.

. .


5/84

b . ( h

Ifyou have tried to find information on windmill design ~ .amethods, if you havendesigned and buill-t a wiridmill, if ~~-- ~-~~-~~ ---~~----~~yo$'re merely interested in windmills, by now you have .discovered that,most of-the information available requires h': . .engineering training or is not complete enough to satisfy'your needs. \ ;.&.yd-, i.- cgrr &&ct> .__ .. " ,. .:'"-;*-z -. \-' Y+-=-- his is the second edition of a book writte%'by an engineer

-. *r--is>;4'ii*who-:'has spent a mojor portion of his career teachfng.inexper- :ienced aerospace technicians. This experience has assisted in .athe writing of this text.complex math&matics It is hoped that the-reduction of _into simple graphs and arithmetic problems . .will allow a greater-segment of the innovative public to use 1fhe ftidamentals an-engineer has'. To make-this book as usefulas possibl.e, a+page has been_ devoted to graph reading, and 'F -', numerous,.examples are used to8.i11ustra\te ,,each step in the .,-,windmill*design process. 'The design approa,ch ysed is not one_- .of an exact science, but rather one of approximation - takingbest guesses and estimates.' Numbers may not be exact, but, as_.with most any design problem, these numbers are usuall$. we.11'within necessary accuracy. Spme experimenters will $nderstan-d-ably need a few windmklls "under their belts'.' before these, .calculations become.sufficiently'a&%rate. Therefore, thevocabulary used.stresses conservative estima?tion vhere necessary.The windmills designed from the methods in this .m&nual may besomewhat larger than necessary, but their performance shouldsatisfy the designer's requirements. 1'1 One further item:I this manual has been, and/will be updated,expanded, and improved. The author welcomes All comments and "suggestions.


6/84

2ezeTABLE OF. CONTENTS ..a 7 ..rFOREWORD 2 \, r . ,

i Wind Energy Available, Wind Power,, Windmill Size.Windmill Efficiency, Types of Windmills, Vertical Axis Windmills,Horizontal Axis Windmills, Hybrid Windmills.rT&k~

I.

J4SECTION B, . . . ~RODYNAMIC DESIGN' 24-. Airfoils, Airfoil Aerodynamics, Windmill Blade Angle Determination,Hybrid Blade Angles, Airfoil Section, Blade Area Determination

SECTION C .,. . STRUCTURAL AND MECHANICAL DESIGN 38 I

I Structural Design, Centrifugal Force, Windmill Drag, Torque,Safety Fact'or, Load Conditions, Blade Strength, ConstructionMethods, Tube Spar. Design, Fatigue, Structural tiesign of Verticaland Hybrid \qindmills, Support Structures.Mecha'n$al Design. _ _SECT?& D- . . . POWER SYSTEMS 56EF'eTqy Storage, Storage Batteries, Fuel Cells, Flywheels, PumpedW,at,er .In-ferters.B,IBLIOGRAPHY 61APPENDIX A 62'Windmill Data


7/84

-

4

.

.

D...

mcn


8/84

/ /Wind p"ower has been used by man elude how muchwind is available,-- for some g2300 year-s. Starting where the de,,vice will be install- ,..

w$t$h, c.r~&& sail-type vanes, wind- ed, bow. fiifl Ydegign ,,&ch money the Builde'r -$ .G'proq?essed through can musterthe old Dutch four-blade horiz,or?"~~~~~~-~~-~ect, to complete the pro- 'how complex .a system is-.tal .axis machines, to veryefficient one-, two-, and three-blade high-speed machines whichuse the latest in high-lift, low-drag.airfoils, and light-weight,.high strength structural mater-ials. It is now possible for ex-'perimentor-sYto use today's advan-ced technology in the creatim ofefficient, low- cost windmills.

.planned, etc.

THE--DESIGN PRCCESS. ---_ _- eBasically, the steps one may$ollow to complete a design exer-cise are as follows: .

It is the intent of this manualto provide the reader with the,i engineering tools necessary .to- 'accomplish a respectable job of. designing and planning the con-struction of windmills (any .-ty?sof windmill device). Highly Pech-nical discussion of the theoreti-cal aspects of these tools willbe neglected in this text, since'such material 'is well documented-elsewhere. The engineering'toolsare merely highly simplified

equations and charts with exam-ples of their' uses, each reducedso that a person with minimal al-gebra experience can apply them

1. Determine the power needed.2. Determine the wind.: .enerqv>--3 the configurationwindmill requiredto obtain power required from4: the energy available. IIDesign the components of thewindmill to satisfy aerodyna-

mics and structural require- ---.ments.An alternate design process may


9/84

I

. p c

Perhaps the simplest@way to harness wind energy is to usenature's windmill, which grows in most yards- - the trees.People are harnessing ocean wave power by tying floats toanchored generators. As the floats bob up and down in thewaves, the generator is driven by the attachment cable. Youmight suppose tRat a hand-operated water pump can be tied toa swinging tree by a rope and a return spring as illustratedhere . . . . .

E


10/84

POWER REQUIREDLet's 'consider two differentend uses for wind power devices.

By doing this we can see thebasic differences in thinkingneeded to design these devices.The first use is that of thewater pump. You have ,a well; youwish to tise a windmill to pumpwater up to a tank. The seconduse will be that of an electric-power generator. __ -One should keep in mind that,in most' cases, determination ofpower required will ,be a diffi-cult, if not impossible task. Insome design cases, however, itmay be as simple as looking atlast month's'electric bill to seehow much power was used. In any

case, a point which will be madeagain is that wind energy isbasically abundant and relativelyeasy to. convert. One shouldstrive to ~design a higher powerrequirement than is calculated inthe following -section of thisbook.

TIIC 'JATER Pc' ,IP

EXAMPLEYou intend to pump water from a;well 150 feet down to a tank on a50 foot high hill -thus totalheight equals 200 feet.You figure that a flow rate of400 gallons Per hour will tendall needs. 'Horsepower requiredis found by locating 200. feet on

the horizontal line, then lookingup to the 4Q.0 gallon. per hour. 'line, then across to, the verticalline to read horsepower equals0.94.

Data supplied for commerciallyavailable windmill pumps may beused for comparison with powerestimates. One should rememberthat CHART A allows estimation.Conservative-windmill design willcall for increasing the power re-quirement estimate by a factorfor safety, for eventual growth,P or both. A factor like half-again, or even twice the estimateis not unreasonable.


11/84

WATER HEIGHT

b

r FLOW RATE

HEIGHT

l,oo 200.05 .lO.09 .20.18 .40.36 .80

* 300.16.33.661.3

400.24 .47.941.9

t


12/84


13/84

EXAMPLE

For a small cabin installationwith AC wiring and utilities, thefollowing loads are sestimated:Lights 500 wattsRefrigerator 300 watts.Miscellaneous 250 iwattsTotal lQ50 watts ; . _,Accounting for line,loss:1.03 x 1050 = 108,2',watt's '*Accounting fpr inverger:-1.25 x l-Q82 = 1353 wattsAccounting for generator:1.50 x 1.353 = 2030 watts =total load. *L ,The fin,al'value do'sn't accountfor the fact that he4 300 wattmotor in the refriger tor requir-es 3 to 6 times as &-I h power fora ,few seconds each \ time 'it isstarted. We assume \that this f

hours, half of the required powereven though the generator is ca-' pable of the required watts. The+ey lies in the duration of thewind. It follows, then,pL(

thatwatt-hours ,ior kilotiatt-h rs, isthe major factor in des,igning ,awindmill. ( ' AEXAMPLE 1 -' ' i

.A cabin Jith a maximum contin-.uous load df 2.5 kilowatts is es- htimated to'require this power for50% of a d y,4 or 12 hours. Thewind averages a certain speed for,4 hours peti day (averaged over aperiod of, say, a week). The pro-blem, then, is to calculat% howmuch power the windmill must bedesigned for.Calculate kilowatt:hours:2.5 x 12 = 30Calculate windmill power required ..3Q- kilowatt-hours = 7.5 kil&atts.A ~ T..extra load will be handled by pus


14/84

* WIND ENERGY AVAILABLETo develop a common ground ofthought, we should consider theobvious, namely, that the geo-

gr.aphic area in which the winddevice is to be installed shouldbe given to neither *too little,nor too much wind. Too 1ittl"ewind, and the required amount ofpower is difficult, to get, while'too much wind may break apartyour hand-made device and depositeach component: thereof about thecountryside.,, We shall discussthese extremes shortly, but fornow let's assume enough wind..Consider, first, why you are de-signing a windmill - most impor-tantly, what YOU intend to dowith the-device, and where. Per-haps you own a-small ranch, a ca-bin spot in the hills, or someplace to use the machine. GoLhere and conduct a wind survey.

called a Dwyer Windmeter. SeePhoto $.c IHold this device into,the windand read wind speed directly. Theaccuracy of the Dwyer unit issufficien,~om~;~d;a;rnddesign pur-poses. measuringdevices Gay be considered also.A more elaborate survey is con-ducted by going the whole route

of purchasing (or building) someform of recording wind speed de-vice. Photo 2 illustrates a/weather station which is avail-able from many aircraft supplycompanies. Al& that is needed tomake a recording station is a re.-cycled movie camera modified totake a few frames of photo dataevery hour or so.

A wind sur'vey can be doneseveral ways. Start by askinglocal folks how much wind the'area gets, how fast it usuallyblows and which way. Set up yourown wind recording station. Thiscan be as elaborate, or as simpleas you wish. The lowest costmethod, sold for less ,than tenbucks at any source of supplies


15/84

i

) In most areas wnere you willlikely consider installing a windpower system you are attemptingto determine some form of averagewind speed during the period oftime the wind blows. For small,private uses of wind energy, thewind survey dataneed not be en-tirely accurate but should, sincewind energy is basically free forthe taking, be somewhat conser-vative. Keep in mind that a pore-tion of the 'usable wind energycomes from gusts, or pulses ofchanging wind speed (and direc-ti0.n') . Your windmill- will be amechanical conglomeration of>avy parts which take time toaccelerate to a different speed,and a wind pulse of short dura-tion may pass before the windmillcan speed up to take advantage ofthe increased available. windpower. Similarly, a short dura-tion slowing of the wind will not'necessarily cause a noticeablechange in the windmill, but inthis case, since the windmill ispresumably under load, it will,in fact, slow down whenever pos-sible. From this we can see thata wind device tends to averagethe short duration gust pulses

\\\HEIGHTABOVE

GROUND . \, \ \/ \ 1

WINkPEED -Figure 2 Typical Wind Profile

EXAMPLE

Using the Dwyer Windmeter (SeePhoto 1) a wind survey is conduc-ted which yields the *following,sample data: j\TIME WIIJD SPEED (MPH)

6 pm 27 pm 88 pm 149 pm 12


16/84

POWER FACTOR FOR WlNDSPEEDS FROM 10 TO SO MILES PER HQUR?

109

.- 8

V (MPH) P0 0

t

1 .00000692 .oooo553 .oo I19456709

1015202530g.?46505580

POWER FAC/

OR - PJPO+~ER FACTOP FOR WINO~PEEDS FROM 1~0 lo MILES PER HOUR

4IO.O.O.O0

11248

,h111

II

00440097015024035051Q6912365000797

u413264.15.50


17/84

WIND POWER EXAMPLE 1

Here, we shall discuss actuallyhow much power is available in awind of known velocity. Recallthat velocity was determined asan average value. Also, we es-tablished just how much powerwould be required to accomplishthe task for which our windmillshall be designed2 It follows,then,' that we must equate power. required to power available inorder to establish the size andshape of the wirdmill which yillaccomplish the task.

To calculate wind power, findthe wind speed value on the ver-tical line of CHART B. -Look hor-izontally to the intersectionwith the Curve, then down to reada \Talue called P, a power factor._ This value is horsepower persquare foot of frontal area ofthe windmill. Use the followingsimplified formula to calculateactual horsepower output of thewindmill. All termsof th-is for-mula will be discussed in detail.

A windmill with a frontal area(A) of 100 square feet - and anefficiency factor (E) of 0.25 isinstalled in an area with anaverage wind speed of 15 milesper hour.Problem: Calculate the horsepower;,output of this machine.Solution: Using CHART B note thatfor a 15 mile per hour wind,P=O.O23 'Then:Horsepower = 0.023 x 100 x 0.25 =0.58

EXRP4PLE..2The windmill in Example 1 c&n-erates 0.58 horsepower.

Problem: Calculate the watts ofelectrical energy this -windmillgenerates.Solution: Ivat% .i 0.58 x 746 =429+, 4


18/84

/A= .785 D2

FORMULA:

D12345

6789

1011

. 1213141520253035404550

A.79

3.147.07

12.5719.6328.2738.4850.2763.6278.5495.03

113.10132.73153.86176.71314.16490.87706:86962-l 1

12561641590.431963.50


19/84

,r:. WINDMILL EFF C/ENCY ;c

_...DIAMETER

.'ed The previous calculations call-for a value of the efficiencyfactor. Since' no manmade deviceis ever 100% efficient at.doingw,hatever it is designed for, wemust either assume a low value ofefficiency in the interest ofconservative design (a sort-ofguarantee that we'll get the pow-er we need), or -find some meansof reliably estimating a value of-;I that corresponds to our parti-cular windmill design. A windmillextracts power fromslowing the wind ,,,~$G ~~dt~~.wind could be stopped completelyby a rotating device, then 100%of the wind power could be ex,-tracted. The wind cannot bestopped: it is only slowed downby about a third of its originalwe,ed, which means that theactual theoretical maximum windpower available to a windmill is59% of the total.

Figure 3A Horizontal,'Axis Windmill

- WIDTH -( _

Now, how. much of the 59% of 'thetotal wind power is actually ex-tracted?- This -depends on the .de-I sign of the windmill, the gearlosses,,;,with which the degree of accuracythe builder of the


20/84

Windmills, as discussed in thistext, generate power while rotat- _ing. Rotation means that wind-mill components near the centeror rotation will be moving relat-ively slowly, while portions nearthe outer edges (tips) will bemoving faster, in proportion tothe distance from the center oftoration (radius). See Figure 4.

TYPE,S OF WINDMILLS

There are two primary classesof windmills:1. Those with power shafts moun-ted vertical,ly.2. Those with power shafts moun- _ted horizontally:

This gives a chance to discovera speed ratio which will be usedin future calculations: u/V ratio(called u-over-V ratio) is simplythe speed of any area of a wind-mill such as the tip of the bladedivided by the wind speed. Bothspeeds must be of the same unitslike miles per hour, or feet persecond. Obviously, the u/V ratioat the tip -written u/V(tip) is alarger number than, say, the u/Vratio halfway between the tip andthe center of rotation. Typicalwindmill calculations will usethe u/V ratio for the tip, oroutermost area of the machine.Speed ratio values you might seeare 1 to 2 for slow speed : ma-.chines, and- 5 to 7 or 8 fo~r_-the~~~~-more modern high speed-machines.


21/84

.

VERTICAL AXIS WINDMILLS

*

applications which need neither .high rotation rates or highpower. See Figure 5.

Consider the fact that windturbine type devices develop pow-.er by moving in the same direc-tion as the wind. Power resultsfrom wind force acting on thesurface which is moving -with thewind. Obviously, the surface can-not moue faster than the wind orno power would result. ,Recall,however, from the discussion ofu/V ratios that the outer extrem-ities of the machine move faster a(not in revolutions per minute, .but in the mile-per-hour surfacespeed) than areas closer to thecenter of rotation. From this,we can see that the average speedratio.acrass the radius of a windturbine will be lower than ---the-----"wind, say__abou=t -Q:4-; ---while- thempu/Vratio might be, say 1 . 2;;':Th.~- ti p ~~ in this case isn't con-tributing to the generation ofpower, but the surface, on theaverage, is. .

me can determine from this


22/84

-- .__ ._e---c --. __~ .__ _-,__-.I j/


23/84

HORIZONTAL AXIS WINDMILLS

Horizontal axis windmills aretypically more' complex than ver-tical axis machines. However, thesmall circular cross-sectionalshapes of these yachines encloselarge frontal arf$as (recall thatthe vertical axgs machines haveportions of their frontal areamoving into the wind -and 'not P-KE)-ducing power), and, it followsthat horizontal axis windmillsusually produce greater amountsof power than equivalent size

HYBRID WINDMILLS

Figure 6" "Eggbeater" HybridHere, we shall depart from tra-' -

dition and dis-cuss a class ofwindmill that promises simplicity N. of design and 'construction, and


24/84

.I-

b .-_ / o- .- R

- i

--L- ;5_ ._---.__ b. ~. .=.hen all of the trade-offs have ratios may mean higher E valuesbeen studied, a designer is left- ,-and less complex due towith the finA decision as to - the" faster gearingwhich t $$k 07 windmill to turninguse in - significant effect is machine. Aa given' p$jecY. high .cen--Figure 7 ,illus-trate% the relative values' of--efficiency factor, (E) for dif-ferent types bf wind-mi&ls, .opgra- _.r_ ting at varri'ous u/V ratios. +-,'F-+&- - .%-~..am&..--..-sents actual design valuesfor specific types df-mazhines.

~. - ,,. JY5- - I-It is now possibIe to &tim&&,- '-- en0E and complete power Cal$u%,ati%ns fistarted earlier. As a methodo:f'design+ ~eeds~%S-s~lect _-c- s tional speedthe type'of windmill.th$t appears. _ I ._--*suit design"reqyi.rements, e"s- ,/

--200 RPM.1FI-~ .tin&e&he builder's ' ability toconstructa'---Yeasonable


25/84

//I

__ .

h \


26/84

Section IB . m.- .

AERbDYNAMIC DESIGN j -

.


27/84

AIRFOILS_;u-Before d?s%ussing the aerody-namic design of a windmill usingairfoils we should review the

factors which-affect airfoil per-formance. &._. _;"t -,.

*

TYPES QF AIRFOILS ,,h7% ..-_WIND

FLAT PLATEIWtND

. WIND

LIFT

Figure 8

All airfoils require 'someangle with the wind in order to d,produce lift. The more lift re- *quired, the greater the angle.The angle is measured between aline which connects the leadingedge tiith the trailing edge which ,is called a chord line, and 'thedirection. 8 The

CAMBERED AIRFOIL:


28/84

. L

4

- AIRFOIL STALL

c /J6

f.-

__NOTE:i.A. A.- FLAT PLATEB.-I SYMMETRICAL AIRFOIL

//

/ .

C. - CAMBERED AIRFOILD.- HIGHLY CAMBERED AIRFOIL.

I w5 10 15 20ANGLE OFsATTACK (DEGREFS) - *-

Figure 10 Airfoil Lift Coefficient

LIFT COEFFICIENT =ILift*r air pressure x blade area.II

where Lift is the actual forcemeasured in' duced by pounds pro-the._ airfo_ilblade.Dynamic air pressure isthe pressure acting onthe blade caused by im-

i s

1y ? :r (IBLADE STRENGTH

e We have just seen how to calcu-late blade loads. Now, let's de-termine blade strength, whioh isthe ability 'of the blade to with-


47/84

LAMINATED WOODI- COVERED WJTH FIBERGLASS

SOLID WOOD BLADE

LAMINATED WOOD/ COVERED WITH FIBERGLAkS

PARTiALLY SOLID BLADE

2. Tubular spar, with foam, balsawood, or honeycomb, or other fil-ler, covered with fiberglass andresin. The spar can be made ofaluminum, steel, or stainlesssteel.

HONEYCOMB, BALSA WOODOR FOAM FILLER BONDED. TO TUBE SPAR

The usual material fGr this&de- 'sign is aluminum, but YOU willhave to be careful inthis ty@e of planningblade to get theskin to take both the curvatureof the airfoil, and'blade twist.Try constructing al test bladewithpaper. Rivets and epoxy bon-ding ii.11 attach the skin, ribs,and spar together. Rivets may beaircraft aluminum; or steel Ilpop-rivets".4. Tubular spar, with moldedfi rglass skin.

POP-RTVETSJ -, EPOXY BOND

TUBEL. : SPAR FIBERGLASS SKIN


48/84

5. Sailwing construction' willmake fine, economical blades.,. -

TUi3ULARLEADING EDGE

SAILCLOTH 0

D-SPAR LEADING EDGE_- .

.___,_.. _. -- -- ..--_- __ . .-..CONSTRUCTION METHODS -

First, the carved wood methoduses construction skills whichare not new to experimenters.Carving wood is easy, fun, andvery rewarding. Wood, however, isnot necessarily the best materia lwith which to build a wipdmill.Iti's true that wood is the mostreadily-available, replaceableresource, but wood soaks up mois- -ture and it is mighty difficultto prevent this from happening;If one blade soaks more water.than another, 'it's' easy to seethat an oqt-of-balance conditionwill result. You can calculatethe result of 'this by changingthe weight of one blade in yourpractice calculations for centri-fugal force. In the overspeedcondition, out-of-balance isliable to cause the windmill to Lshake ,itself to death. If, on theother hand, you will take care tokeep the wooden blades sealed,this is 3 great way to build awindmill.


49/84

TUBFI&iR DESIGNdr

&e know that b lades must be Where Blade drag was previously. .strong enough to withstand ten-sion loads from centrifugal forceand bending. What follows is asimplified method of calculatinga tube size (diamete.r and wallthickness) and materia l (steel,aluminum, stainless steel, etc.),which will withstand these loads.Figure 17 illustrates the proper-ties of a tube for our calcula-tions.

EQUATION 10 IBLADE BENDING LOAD =Blade drag x-radius x 12 .' '

determined in pounds offorceradius = distance measur- \ed in feet to the centerof the blade from rota-tion center

EXAMPLE -Windmill diameter = 12'feetBlade drag = 10 pouna~sBlade bending load/=,.;r 10 x 12 x 12/4 =,,a60 inch-pounds

IUsing da& methods presented inAppendix/E, you can select a tubesize which is strong enough totake/the bending load./'i

I,/FATIGUE//


50/84

One way to prevent fatiguefailure (which claimed the lifeof one ,of the blades on the SmithPutnam windmill) is to keep theloads low in relation to thestructural strength. This is thebasis for conservative structuraldesign.

Basically, w,e havq'consideredstructural design as a '&i\,mplifiedapproximate problem. If you wishto persue structural design to anexact level -which I recommend -check the bibliography in thistext for an excellent referenceon this subject.STRUCTURAL DESIGN OF VERTICALAND HYBRID WINDMILLS

Structural design of ve-rticalaxis machines such as the Savo-nious Rotor involves making 'themachine stro enough for centri-fugal force. The tower and sup-port structures must be strongenough to prevent, toppling overin high winds.Hybrids, which are verticalaxis machines using high-speed,high efficiency airfoil blades

SUPPORT STRUCTURES

Coslete windmill design invol-ves planning the support struc-ture. This structure can be 3ssimple as a short pipe, or ascomplex as a cable supportedtower. Two loads must be suppor-ted by your tower: the weight ofthe entire windmill assembly; andthe total drag, which includeswindmill drag and tower drag. Asan approximation, simply doublethe windmill drag load to get thetotal. The guy wires you use mustsupport these drag loads.

The tower must be rigid. Anyfl.exibility will result in lessefficient wi"ndmil1 operation;particularly in-the case of ver-tical axis.machines.


51/84

I CENTRIFIGAL FORCE/BLADE .BENDING OF HYBRID WINDFjlrlLLS b_- Figure 18 ' Photo 3 Hybrid-V'Protocype -7>

iBLADE NOT BENT

BLADE ILLUSTRATED CABLE SUPPQRT ..


52/84

Problem: To control windmillspeed in gale winds.

Solution: There are several. The.-. solution you arrive. at."depends onthe windmill, -the expectedstrength qf tempest winds , andyour ingenuity. Here are a fewsolutions'already used:A- Aiming the windmill out of thewind, two ways: turn it sideways,-or tilt it up. See Figure 21.

B-' Coning -_, allowing the bladesto form a cone in the downwinddirection which reduces- thefron-tal area, thus--reducing the powerand-rotary-speed. Blades (can .be--freely hinged wlith, perhaps, asmall spring to hold them out forstrating. Centrifugal force holdsthem out during normal rot,ation,but tempest..winds increase blade D- Aerodynamic control - this is

BWindmill Aiming '


53/84

r-YIND ,

Figure 22 Windmill Coning


54/84

Y

CENTER OF ROTATION

DRIVE SHAFT

WIND9

, .CENTRI FIJGAL\

EXTENSIONAGAINST SPRING o

CAM CAUSESBLADE ANGLE

--


55/84

c r

COMPRESSIONSPRING# *I.

5

\

e4

BLADE HUBicSLIDES DOWNWI NDI LINK FIXED TO SHAFT AND BLADECHANGES BLADE ANGLE AS HUB :MOVES L _

BLADE MoTloN

..

-, ,, _; , -- o

: 3 .,i, 5

It should be * noted that withany of tahe methods discussed he-re-- alt blades and blade.control de -------.-\vices md&t.be linked together sothat all blades react together..Any time one blade geometry ispermitted to vary from the confi-guration of other blades during.- high-speed rotation, severe vi-&ration and balance problems will


56/84

A-Tail feathers. Look at Photo 4.The tail-mounted fin acts like anairplane's rudder to keep thewindmill aimed into the wind.

Types of vanes&used are illus-trated in Figures 2G A, B, and C.Design A is a bit,of nostalgia,but it works. Des::$gn B is a greatimprovement, and C is the best. .)The reason is simple. You wantthe tail vane which is most sen-sit'ive and responsive to changesin wind direction. Design C hast le hig lest ratio of vane span,which is t le distance from top tojbottom 02 the vane, to vane chordthe distance from leading edge totrailing edge. Such vane5 arelike glider wings which are de-signed to make the most use oflight up-drafts to support thesecraft aloft without benefit of :$motor. Practical ratios of spandivided by chord for the vanemight be between 'two and ten. Inother words, a typical vane mightbe five times as tall as it iswide.

'b

Photo 4 :

WIND -

WIND V


57/84

behind this area. This 'vibrationcan enhance fatigue problems, andshould be. reduced by streamliningthe tower in the blade region.Problem - Your windmill doesn'tturn fast enough for the genera-tor you want to use.Solution - Gears or pulleys andbelts to increase the speed.Gears are great, but expensive,and they require a box to housethem and their oil or, grease.Some experimenters have recycledautomotive "rear ends" completewith gear trains inside for suchpurposes. Bicycle chains andsprockets can be recycled fromjunk parts. Pulleys and belts ofall types are available but auto-motive V-belts should be avoided.because of high belt friction andslippage problems. cog belts,while expensive at first, .last along time and work well with lowfriction.

The starting point'for any de-m sigh is to calculate the gear ra-tio you need.

,Chain DriveEXAMPLE

Your windmill has a rotationrate in a mild wind of, say, 303revolutions per minute. The gen-erator you plan to use begins to


58/84

DESIG Section D q . . POWER SYSTEMS


59/84

s

Consider the fact that, man him-self 'as a means a ,of mechanicalpower can contributie only aboutone horespower hour; of work inany given day. When energy ismade available to relieve manfrom using only his own power in/performing useful&asks real pro-gress is made. \

Conversion of energy\, in a truealternative sense, otiqht not tocontribute to the .-~hea$z -lo-ad Q-fthe e'arth as a whole.,Wind energyis an obvious source of .powerwhich does not liberate energy inthe form of heat not already inthe atmosphere, since the primemover of wind is solar heat.

It's an interesting fact thatwind and solar heat--are comple-mentary in nature which allowspractical utilization of theseenergy sources at a grass rc?otslevel. Tests have shown that,averaged over a five year period,solar energy peaks at about 28watts per square foot of collec-

t \ \

tor surface in July, and drops toabout 9 watts per square foot t\;inJanuary, wile wind energy peaksat about 35 watts per square footin February, and drops to about 7watts in August - depending onwhere you live. Thus, the twosources can provide aconstant reasonably= -,amount .o f bower whenused together.

The point. to remember about thetwp energy-hurces-, used together-r--- -or separately, is that there are3 short-time variations in poweravailable. Thus, energy storageis. required to guaran,tee poweravailability when needed. A wind-mill installed in an area of vir-tually constant winds (mountainpasses, and some beach areas, forexample) twill likely not need ex-tensive energy storage, while awindmill in areas given to exten-ded periods of no wind need largestorage systems, or other energy.: sources. Figure 27 illustrates,'the elements of a complete powersystem. .

a


60/84

ENERGY ;Four poss;ible system: will bediscussed here. These;*are:

-1 . Storage Batteries '.2. Fuel Cells ;3. Flywheels i.4. Pumped TL7ater

-\An ideal wind power systemfwould use combinations of thesestorage systems. For example, onwindy days when an exce55 ofenergy is available the batterieswill be charged to their fullstorage capacity. When the bat-teries are charged a simple swit-ching device might divert elec-

tricity to a water pump to storewater as will be discussed shor-tly. In any case no single methodof energy storage is ideal. .

STORAGE BATTi?QIESStorage batteries are commonand readily available. Automotivebatteries are perhaps the mostcommon units today. These units

WATTS = Amps x VoltsorWATT-HOURS = Amp-hours x Volts

EXAMPLE

For a-2 volt automotive batterywhich is rated at 63 amp-hours,Watt-hours = GO x 12 = 723.

Now if the power required esti-mate (from earlier windmill cal-culations) indicates a require-ment of, say, five kilowatt-hoursper day (that's 5900 watt-hours)and the power available on a par-ticular day from your windmill isthree kilowatt-hours, a storagecapacity of the difference: ortwo kilowatt-hours is needed. Asmuch as the entire power require-ment may be. required, dependingon the duration of the wind. Ifthe battery to be used is capableof storing, say, 720 watt-hours,then 5039 divided by 720 equals

_ c ii

i . t-.-IL --$, ---r;------. ~----~~~


61/84

^F

* Batteries that are designed forpurposes more compatible withwind energy storage are used inelectric golf-carts and nrecrea-tion vehicles like motor-homes.These batteries are larger, andu more costly than automotive units*c but their increased capacity andlife may offset the hassles YOU--migh-t experience nsi?ng~Pcheap -autobatteries. 4-c. ' .FUEL CELLS 0

.Fuel cells are not new devices,as one might think. An experimen-9 ter named Davy built one in 1801,and by 1839,. cells which use* gaseous fuels were being tested.-Today it is possible to constructY a fuel cell which uses gaseoushydrogen land oxygen to generateelectrical energy, and do so at. i conversion efficiencies grea$er,,than possible with hny other sys-atem. LI I-__ B,&ically, a fuel cell is a-form of battery in that electri--'-- city-is geEFated by a c&&mica1_~- ~~reaction within the device. Dry*~~~~..--~cel-+ a-s -used in ordinary flash-, LIlights and transistor radios are

.-. _jj :c l --:.:

>

wh.Gh must :.,be'stored.tricity banzbe used This elec- -:-dire,otly to Jconvert water into gaseous oxygenand hydrbgep. These bases can $estored (separately, mind you) andeventual'ly brought together in afuel cell to' be reconverted to 'electricalThis- process en e r gy, :-and- 'waker.is polluti-bn- free,but-, for now, not entirelytical'due, to* the 'price of prac-fuel ,cell. Ultima-tely , thewill ge made fuel ~cells'practical asare further.developedN. /

they.

* L'-FL&EELS . **\Flywheels sto+>e?ehergy-by meansof high-speed rot&ion of a heavydisc, or wheel. It's a simplematter,.to design a system whichuses windmill supplied electricalenergy to .spin-up a fly heel.This flywheel energy will i-x con-verted back4 to electricity asneeded ..because the same motor'that spins the flywheel can -actas a generator.

By,using newly create.d strut-,


62/84

PUMPED WATER q JStorage batteries and pumped

water are perhaps the most likelyto be used methods of ener-gystorage by experimenters. In thecase of pumped water all you needto do is, say, build two waterstorage ponds, one much higher upa hill , than the other.Earlier discussion showed how

to calculate power required topump water at a certain flow rate .up a desired heig.ht . The samechart shows how much pcswer YOUcan get back bL allowing waterfrom the upper pond to flow backto the lower pond.To store really;'. large -.arnounts--.of enerqy your ponds will lookmore like lakes"; and there willbe an altitude' difference o-fseveral hundred feet: Ratherlarge pipes in the return linewill be needed to get as large aflow rate as possible, but thewindmill can fill the. upper pond

slowly, if necessary.

Radios installed in older auto-mobiles used a vibrator (mechani-cal inverter) which made a hum-'ming sound while a vibrating reed"relay inside a little silver canoscillated back-and-forth tointerrupt DC current and causeAC. Modern inverters use high-powered transistors as electronicoscillators ,to make this change.Inverters are usually

efficient, asquite

man-made devices(30 -ox* the order of 33 to 90peircent of the electric energythey take in will come 'back out.Their highest.' efficiency is ob-tained when. inverters are opera-ting near the maximum power capa-bility. See Figure 28.

100%

EFFICIENCY


63/84

BIBLIOG x- . . .--0

Excellent bibliographies on//- SCARING MAGAZINE;------ January 1964,various alternative energy sub-jects 4are alremvailable. Thefollowing items are listed to addto, rather than dupl,imte thework of others,.. ".,mn

and November 1973. Data on highperformance Wortmann airfoils.Available from Soaring Societv of

*

PLANS ,Savonious RotorHackleman, Michael+?A., ' WIND &WINDSPINNERS, available for $7.50from Earthmind, 26510 Jose1 DriveSaugus, Calif. 91350.Horizontal Axis . /Helion - 12/16 Plans - optionalsize, construction methods, andalternators. Aluminum blades.Complete plans and instructionsfor $10 ' from Helion Box 4301,Sylmar, Calif. 91342.Hybrid

America,Calif. Box 66071,~ Los Angeies,90066.Abbott and Von Doenhoff, THEORY"OF 1ilING SECTIONS, Dover Publica-tions, 180 Varick -*Street, NewYork, 14, N.Y. Data-on all ofthe major NA,CA Airfoils.GENERALWIND ENERGY'BIBLIOGRAPHY, avail-able from. Windworks,Route 3,- Box 329,Mukwonago, Wise.for $3'. 53149;

Write to Helion - address above. 1/

CATALOG OF AIRCSUPPLIES,

CON-STRUCTIONfor 25c from16673 Roscoe


64/84

Appendix A\\ WINDMILL DATA\

1 -t

,

P _I

I


65/84

i

\

.

.4

a


66/84

,I :

- 4

\\ SINGLE TIER

I .SAVONJ& ROTORf- *_,\ I\ 1-1 \b,NUMB/ ER OF VANES\\,

A \

ir

,ePSPECT RA;IO

J


67/84

+


68/84

.

f


69/84


70/84

TWO BLADEI...- _ -

I - ~----..-HIGH-S>- 'T"-.,_-< .-_--G-yHORIZONTAL AXIS WINDMILLS--.-_.

E .2-


71/84

C.

.4

HIGH-SPEEDHORIZONTAL AXIS WINDMILLS


72/84

Aprjendix B AIRFOIL DATA .A( \ .c

Following is a discus&ion of the method ~by which you can ilay out an exact airfoil shape according-to some numberswhich are presented Tn this section of the book. A graphis presented which shows the lift coefficient performancefor each of the airfoils listed. This 'graph will helpyou in Blade Angle computations.* Other airfoils areavailable, some better than those listed here, many less -..suitable. Check the.bibliography in this.book for sources -Fof further airfoil information. _ ,,. r,HOW TO LAY OUT AN AIRFOIL' A-

The numbers p'resented..for each type of airfoil are percent-ages of the airfoil\'s chord length. When you have determinedchord lengths, youCcan calculate dimensions from which to'develop the exact airfoil shape much as you would plot a 'grhph.

A few of these numbers for the Clark Y airfoil are: IStation

0 *l/252.5

. Upper3.50.5.456.50.

n


73/84

i-./

Now you simply plot the airfoil on a large sheet of graph paper.:, c.Start on a straight horizontal.-line. Always measure from Station =0 to the right to each next station point, then measure up or down _to the upper or lower p~oints. Measure up from this -line by theupper value. Make adot at this point. Then, at the same station,measure from the.hoiizontal line to the lower value. If the lowervalue has a minus (-1 sign, measure'.below the line. If 'not, thelower value-is &eastt-red- above the line. Some sources of airfoilinformation will have different station values for the upper point'than for the lower value. 'For these airfoils , you will have to 1.compute the different additional station values. Keep them.separate. :"&z' d

By making all $hes:dots for the upper and lower values, you willgenerate a series of dot targets wpich, when connepted with'scurved line, will form the airfoil shape;.The "LR" value is the leading edge radius. Again, it's a,percentage of the chord. For the Clark Y, LR = J-5%,- or 0.015.For a JO inch chord, zileading edge radius = 10 x- .015 = -15 inches.

Use this value to shape the curve at the leading edge with acompass or draftsman's circle guide. Some..airfoils wilb not 'show the leading edge radius value'. This is really a referencenumber. You can'draw the curve without it. I


74/84

: \ i2.1 1 I I I I I


75/84

5cr.A.01.252.55.07.51020304cr506070

CLARK Y- St. CYR 234 NACA 0012 NACA 0,015 NACA 4412JPPER LOWER UPPER LOWER UPPER LOWER UPPER LOWER UPPER LOWEi*3.5 3.5 6.42 6.42 0 '0 0 0 0 05.45 1.93 9.55 3.75 1.89 -1.89 2.37 -2.37 2.44 -1.435.5 1.47 11.0 2.7 2.62 -2.62 3.27 -3.27 3.39 -1.957.9 .93 12.7 1.4 3.56 -3.56 .4.44 -4.44 4.73 -2.498.85 .63 13.8 .85 4.2 ,-4.2 5.25 -5.25 5.76 -2.74

*.6 .42 14.6 .5 4.68, -4.68 5.85 -.5.85 6.59 -2.8611.36 .03 16.2 .2 5.74 -5.74 7.17 -7.17 8.8 -2.7411.7 0 16.55 . 6 5 6 .;O -6.0 7.5 -7.5 9.76 -2.2611.4 '0 16.1 1.1 5.8 -5.8 7.25 -7.25 9.8 -1.-EI10.52 0. 15.2 1.35 5.29 -5.29 6.62 -6.62 9.19 -1.49.15 0 .13.3 1.9 4.56 -4.56 5.7 -5.7 8.14 -1.07.35 0 10.8 1.35 3.66 -3.66 4.58 -4.58 6.69 -.650


76/84

_.

m - r

STA JPPER LOWER JPPER LOWER0 1 01.7 t.77 -1.372.65. 3.44 -1,E

i.-050, :

m-l.-23-1.24

5.16 1.81 -2.486.69 5.46 -2.7610.3319.56

5.59 -3.26

-1.14-1.03-.7?

3.33 -3.75

1.01.j.l?7 .$


77/84

I

Graphs are used.to simplifycalculations. I have pre-sented many graphs in thismanual so that computationswhich are normally,difficultwill be made easily. Sothat all users of this texthave graph reading ability,this page is presented.

CONDITION 1 - You know VALUE Aand you wan&to find VALUE B onSample Graph 1.

4XAMPLE b .If VALUE'A equals 8, start onthe horizontal line a t 8 andlook (or draw a line) vertic-ally up to the curve: Next,look (or draw a line) hori-zontally to the scale at theleft. Notice that the answerVALUE B equals 4.

&OTE - You may have more than onecurve which applies to your pro-

10, 9

87

m6

21

lb2 34 5 6 7 8 910

.E A

VALUE ASAMPLE GRAPH 1 .

*

*Appendix D I - ,


78/84

. . DiTAlLED WINDMILL PERFORMANCE F,

- Power = Force x Velocityu.

1 bI:2 - Force = Pressure- x Area I3 - Pressure = J PxV3/2 ,4 'where p = Mass denj,jty of air =a0.0024 .slugs / foot3at,sea level

V = wind speed measured in. feet p'er second4 - Power = . 0012 x V3 x A. ,where A = windmill frontal- area measured in-square feet ,

V = wind speed measured in feet per secondThis is the't.heoretical power availa'ble in a wind of-speed = V,acting across a windmill of frontal area = A..Power units hereare foot-pounds per second.5 - One Horsepower ='550 foot-pounds per second6 = Horse Pow-er = .6012 x V3 x A '/ 550 '= 0.0000022 x V3 x A .bAgain, this is theoretical horsepower.7 - The mathematical horsepower which a windmill can extract 'fr m the above val;ue is 59.3% of the total. However, no wind-

Appendix E .--;-. * ._, ._


79/84

STRENGTH OF CONSTRUCTION MATERIALS . -iiTUBE 'TENSILE STRENGTH ;.' ., (i

To compute t'ube tensile strength, measured in pounds of force,multiply tension area from Graph A below times the tensile strengthfactor for &&he metal alloy of the tube. See next page for tensilestrength factors.-EXAMPLE /-

0 A 2-inch diameter by . 065 inch wall thickness tube of Aluminumalloy 2024 T-4 is selected. Calculate the tensile strength. FromGraph A, note that tension area equals .39. Tensile strength factorfor this alloy is 60,000. Then Tensile Strength = .39 x 60,000 =23,400 pounds.

.9I?

.8

.7

7

\


80/84

, .;b c ITUBE BENDING STRENGTH ' Ic ,',

1. . . To compute approximate tube bending strength, measured in in&T+._ pounds, multiply K-value from Gr'aph B below times the tensile zF. 'Lstrength factor. *. " " . 1EXAMPLE ' .'. _._--.._._ -..A 2-inch diameter-by . 065 inch wall thickness tube of Aluminumalloy 2024 T'4 is selected-,,_ Calculate the bending strength. FromGraph B, note that K = 0 .19 ..~~~~~'ensile strength factor for this alloyequals 60,000. Then Bending Strengtk,r; 0.19 x 60,000 = 11,400 inch-'..

.6

.

\,

.7 TENSILE STRENGTH FACTORSAlloy Tensile StrengthFactorAlurniyn2024 T-46061 T-67075 T-6

60,00042,000 I'75,000 J I

*


81/84

-. 9,TENSILE STRENGTH OF WOOD BLADES.Wood blades - as discussed earlier in this manual - are laminatedand carved from quality materials like aircraft grade'spruce. ,TheTensile Strength Factor for wood varies between 7000 to about 12,000pounds per square inch. This value depends on the type of wood used,and the moisture content. Wood strength increases rapidly as'themater ial dries out. For avera'ge.wood used in the 10% to 15% moisturecontent range, a safe check of blade strength can be made with atensile strength factor of 8,000. You need to know the tensile area (of the blade. Then multip ly this area times the strength factorto compute blade tensile strength. \

EXAMPLEThe blade sketched has a tensile area for the structural woodforward portion (you can disregard any strength value in the-balsa or foam trailing edge in this example) of approximately 12square inches. Blade strength = 12 x 8,000 = 96,000 pounds. Thisis the maximum'centrifugal tension load this blade can withstand.

, i -~ -P

.=

iI.

CABLE STRENGTH I-Cables are used for tower guy wires, windmill br*acing, and so on.

Data presented is for 7 x 19 flexible aircraft stranded-cable----,m~P .-available in surplus outlets, or the source listed in the Biblio-: cgraphy o;f this book. ,


82/84

d -Y wf BOLT STRENGTH

J..

P Data presented are for airc,raft qua8

9 BOLT DIAMETER.(inches)3.# 3/16 .':y\

511'6- 3/a

Simplified Wind Power Systems for Experimenters

Documents

Transcript of Simplified Wind Power Systems for Experimenters