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Date: Mon, 22 Jan 2001 23:50:50 -0800
From: tvoivozhd <tvoivozd AT roanoke.infi.net>
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To: "Homestead mailing list" <homestead AT listserv.unc.edu>
Subject: Small DIY wind turbines
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> Anyone have the old plans for an auto wind generator? Wayne

tvoivozhd---there were several plans once available from
MEN---someSensenbaugh
designs, and one I remember called the Red Baron.  As Don pointed out you
don't get
much out of an auto generator until they get up around 2000 rpm unless you
use belt
or gearbox, which  rob a high percentage of power from small generators.Auto
generators work fine in small pelton wheel microhydros though.

I don't know if MEN sells plans for these old designs---I doubt it.

The one proven DIY design is the brake drum based alternator designed byHugh
Piggott.  http://www.windmill.on.ca/   It has an excellent track record in
wear and
reliability---few other DIY's do so.

Re: Generator


Sat, 25 Oct 1997 00:20:38 +0100
hugh piggott (hugh.piggott AT mail.enterprise.net)

> eeggleston AT ag.gov wrote
>
> > The formula Hugh and I have given you comes from the energy in the
wind. You
> > CANNOT extract more energy with a wind machine than is in the wind.
> >  Actually you can't even get 60% of the energy in the wind and do 
> > useful work with it (a wall that stops the wind would therefore be 
> > near 100% efficient).

Stop there. A wall which stopped the wind totally would give no power at
all, in spite of the large force. You need force and movement. This is
the essence of the reason why we can only get a maximum possible efficiency
of 59%. As soon as we slow the wind down we divert it away from the
windmill and lose out on it. A wall diverts it all and produces no power
at all.

> I see now that when I mentioned leverage, I was using the wrong word.
>  What is the word for the force that moves a sailboat without RPM?

The bottom line is power. That is the flow of energy and that is what we
try to maximise. Power can be calculated either by multiplying foce times
distance (push times shove) as with the sailboat, or by torque times
rotational speed ('leverage' times rpm) as in a mill. Either way you look
at it, you need movement just as much as you need force.

> How is it that a rotor that sits 45 degrees to the wind is more 
> efficient than a sail that sits broadside to the wind (like the 
> wall)?

Much of the time your rotor sail is at somewhere near 45 degrees to the
wind, too.

> Im sure a slow speed generator could be designed

Yes but it has to very heavy. I specialise in low speed generators myself,
but I know my limits.

> how much usable (horse power; leverage; force; ), or whatever it is 
> called, can I expect from the wind blowing on 30 sq, ft. of sail. The
>  equation you are using starts out by dividing the air density by .5.
>  Is this done because the wind only sees half the face of a propeller
>  or is there some other reason?

It's based on the fact that the kinetci energy of a moving object is .5
times the mass times the square of the velocity.

> Do they use the same equation to estimate the potential power in the 
> sail of a boat?

yes.

> There are no boards, pipes or wires to vibrate or re-tension. The 
> paddles have an outside frame with a thin center sheet (easily 
> replacable) attached to break away in a very high wind.

I predict that the oscillating bending moments (leverages) on the blade
roots (if unsupported) will cause early fatigue failure. You will get
upward and downward loads caused by lift on tilted sails, as well as the
main, oscillating 'push'.

> Where as if I attached a 1/4 hp motor to the shaft of my windmill, I 
> know I would have no problem stalling it by holding the sail.

the reason is that electrical equipment does not work well at low speeds.
It exerts only small forces. But it can deliver very high power when the
speed is correct for its use.

> I'm not trying to be argumentitive.

appreciated :)

> I just can't understand how these things could be, if your equation 
> is correct for this windmill. What part of this don't I understand?

You still do not grasp the difference between force and power. Get a
really heavy weight and hang it there. You have a big force. It will not
power your house, however. Windmills need to give power and that requires
speed. At the sort of speed you plan to move, the forces required would
need to be much larger. You will get these forces when the wind is strong
enough, but then the sails will fall off.

> OK, Hugh, I'll bite - what in the world is Eigg? Not some new 
> European designer drug, I hope :>

It's a place (a Hebridean Island) where I go to install small hydro
turbines. They are much more cost-effective than the small wind turbines.
My latest one gives 2.7kW of direct AC power.

Hugh
Scoraig off the grid
Scotland



The tower is as important as the generator---you have to get well off the
ground to
avoid ground effect dampening of available wind.  Nice if you have terrain
which
funnels wind to the wind turbine site
 http://www.windpower.dk/tour/wres/powdensi.htm   (power varies with the
cube of the
wind)
.  http://www.windpower.dk/tour/wres/siting.htm
http://www.windpower.dk/tour/wres/speedup.htm
 http://www.aermotorwindmills.com/tower_instructions.htm   (erecting one)

 http://www.e-marine-inc.com/windmap.html   (wind map to see if it is
worthwhile)

 http://www.wood-carver.com/gemini.html   (you have to buy or make a prop)
 http://www.awea.org/faq/bladefab.html
 http://beadec1.ea.bs.dlr.de/Airfoils/propdes.htm   (design with computer)
 http://www.ulflight.com/   (balancing)
 http://www.windpower.dk/tour/wtrb/stall.htm   (propeller stall and drag)
 http://www.windpower.dk/tour/wtrb/safety.htm   (anything turning this
fastis
dangerous)




 This FAQ entry was
 developed from an
 online message
 exchange.





                  Small Wind Turbine Blade Fabrication

                  Has anyone out there carved a wooden prop with both
twist and
                  taper, or at least twist? I'm working on a windcharger
project
using
                  a low-rpm DC generator. I've built a two-blade prop with
no twist
                  and am now machining a hub with manually-adjustable
pitch, but
                  suspect that I won't get the TSR I'd like without some
twist. I've
                  read all the references that I can find in my local
library, but I
have
                  not found anything that even hints at the
fixturing/jigging that
                  might produce the correct profile for a twisted/tapered
airfoil
using
                  conventional tools such as routers and saws. Also,
nobody says
                  much about actual design of the hub, torque shaft, and
thrust
                  bearing.

                  I built my non-twisted airfoil by copying and scaling
the profile
of a
                  Cessna wing. I used a flat 1x4x6' plank of clear douglas
fir, and
                  made a stairstep approximation to the shape by machining
                  longitudinal grooves with a router. I then "finished"
the shaping
by
                  knocking off the steps with a hand- held belt sander.
Finally, I
                  trimmed the ends (where my shaping control was
sloppiest) and cut
                  the wing into two 30-inch blades. Actual width of my
blades is 3.2
                  inches, with a thickness equal to about 15% of the chord.

                  The generator is a multipole permanent-magnet "servo
motor", with
                  a measured generator constant of 27.5 rpm/volt and a
measured
                  source resistance of 1.24 ohms. I'm looking for a
charging current
                  of 5 amps at 15 volts (to overcome the drop of a single
                  reverse-blocking diode), which means my loaded prop
speed will
                  need to be 583 rpm. Cut-in to begin charging (approx. 12
V + 0.7 V
                  open-circuit) will occur at about 350 rpm.

                  Swept area of the rotor is about 27.5 square feet, in a
"donut"
                  shape because of 6-inch hub extensions. Even with a
conservative
                  efficiency estimate for the generator, a 15 mph wind
meets my
                  requirements. TSR at rated output will be 8.33 (124.88
MPH). This
                  may well require a L/D in excess of what such a crude
propeller
                  design can deliver, so my options will be:

                     1.trim the propeller tips to reduce TSR, down to the
limit
                       imposed by area and efficiency;
                     2.increase my windspeed for rated output; or
                     3.build a more complex (twisted/tapered) airfoil.

                  Option 1 is the preferred result, as it is easily
accomplished and
                  results in a more compact finished product. Getting to a
TSR of 6,
                  however, will require trimming about 10 inches from the
blade tips,

                  leaving a swept area of 13.88 square feet. The required
system
                  efficiency is still within reason, but now optimistic
instead of
                  conservative.

                  At 30" blade length (6 foot overall diameter), rotor
solidity is
                  4.85%; 2.83% at the blade tips. This is in the
acceptable range for

                  the working TSRs, but obviously I could improve my
starting torque
                  by tapering the blades wider at the root.

                  So - who's done this already? Design is the easy part,
fabrication
                  hints for a repeatable twist/taper seem hard to come by!

                  - Marty Jones, mjones AT ms3.dseg.ti.com



                  Q.
                  Has anyone out there carved a wooden prop with both
twist and
                  taper, or at least twist?

                  A.
                  I think you'd find that the use of composites (i.e.
foamand
                  fibreglass/kevlar/carbon-fibre) might be simpler and more
                  effective. It wouldn't take much work to figure out
thebest
                  taper to put on a blade so that if it were twisted, the
result
                  would be a (near) true pitch from root to tip.

                  If you use expanded polystyrene then you can build
yourcore
                  by simply using a home-made hot-wire cutter and a 
coupleof
                  plywood rib templates - this technology is 
extensivelyused
                  by model aircraft enthusiasts.

                  Once the blade cores are cut, put a twist in them 
andglass
                  them.

                  If you're looking for a prop that will provide good
torque at low
                  revs then you'll need quite a bit of chord at the root
of the
                  blades. In light winds it's the root section of the
blade which
                  will get things spinning. If you don't have enough
root-section
                  then your prop will simply sit there with stalled
blades:-(

                  You should also be aware that once you build a true-pitch
                  propellor, attempting to adjust the pitch by rotating the
                  blades on their length-wise axis will result 
insignificant
                  efficiency drop. Reducing the pitch in this way can even
result
                  in the tips going into a negative-pitch condition and
                  increasing it will potentiall send the roots into a
negative pitch
                  condition.

                  If variable pitch is what you're looking for then you'll
probably
                  have better luck using shorter blades on longer shaftsand
                  more of them. Your main goal should always be to get
                  maximum efficiency at the bottom-half of the wind range.
                  Once the wind exceeds a certain level the
efficienciesdon't
                  really matter since you're probably creating more torque
than
                  you can easily use. The other most important thing is a
                  method of preventing over-reving in very high winds.
                  Low-twist variable pitch props can do this quite well by
                  feathering but longer (higher twist) props can exhibit
                  tremendous levels of stress on the hub even when stopped
                  due to their not insigificant drag.

                  bruce AT faxmail.co.nz



                  A.
                  Harold Davis of Midland, Texas makes blades for 
turbinesas
                  well as small airplane props using a special machine
that is a
                  cross between a "stereo" table saw and a copy lathe.
Withit
                  he can copy a twisted, tapered nonstructural blade onto a
                  good wood blank as many times as he might want. All you
                  need is to come up with one blade of the correct profile
using
                  wood and bondo, then make all you need. Highly chambered
                  airfoils might require special care and extra finishing
steps.

                  Admittedly it is an exotic, custom made machine. Still a
                  non-engineer made it in his shop -- could be a
goodwaypoint
                  in the search for information.

                  Eric Eggleston



                  A.
                  Rotor design for best performance requires somewhat more
                  work. One can make performance predictions using PROP93
                  from the Alternative Energy Institute (AEI) at West Texas
                  A&M (806) 656-2295 or PO Box 248, Canyon, TX 79016-0001.
                  One usually makes templates incorporating the desired
                  shape, chord, & twist at selected radii, and then carvesa
                  pattern. Harold Davis of Aerotec Propeller can make a
pattern
                  and carve out a blade for you rather quickly. He may
evenbe
                  able to make you one from scratch. You can reach Haroldat
                  (915) 685-0867. He manufactures small wind turbine
rotorsin
                  his shop in E. Midland, TX.

                  You can get all the engineering details in our book,"WIND
                  TURBINE ENGINEERING DESIGN, by D.M. Eggleston & F. S.
                  Stoddard, Van Nostrand Reinhold, 1987, ISBN0-442-22195-9.

                  David M. Eggleston, Dmeengr AT aol.com DME Enginering 1605W.
                  Tennessee, Midland, TX 79701, (915) 683-5735 FAX
(915)570-4956



                  A.
                  We carve twisted and non-linear tapered airfoil using a
                  pantagraph router copying a pattern (see comment). We
                  learned our skills from the great John Kraft formallywith
                  Winpower in Newton, IA.

                  Two patterns are required; one for the round
(downwide)side
                  and one for the flat. The patterns and propeller
blankshave
                  the tape cut in the trailing edge. The trick is to
design the
                  round side of the propeller with a reference line downthe
                  highpoint from tip to butt along which no material is
removed.

                  First, the round side of the propeller blank is carved
on the
                  router. Next the propeller blank is truned over and
nowsits
                  and is clamped on the reference line on the router table.
                  Finally, the flat side is made from the flat side fo the
pattern.

                  The big job is hand sanding the two patterns 
fromtemplates
                  describing the flat and round sides of the propeller at
stations
                  generally no more than 3 to 6 inches apart. The 
leadingand
                  trailing edges are carefully marked on the corresponding
                  edges of the patterns before sanding is begun.
Thetemplates
                  are generated from a design program like Propfile.

                  Other manufacturers us different procedures. Harold
Davisat
                  Aerotec uses a gunstock or aircraft propeller typecarving
                  machine and Mick Sagrillo uses a varying tilt planer
like Art
                  Randolf used to have at Santa Rosa Machine.

                  Elliott Bayly, wpt AT cp.duluth.mn.us  World Power
Technologies,
                  Duluth, Minnesota



                  Q.
                  Has anyone out there carved a wooden prop with both
twist and
                  taper, or at least twist?

                  I do it quite often, usually with hand tools, but can 
usea
                  bandsaw for big blades to make life easier. There arefull
                  details in my books. I do not use a precise section
assuch,
                  and I do not find that the blade performance suffers much
                  compared to those who do (attempt to). I specify certain
                  dimensions at each of a series of equally spaced stations
                  along the span, and simply interpolate straight lines
between
                  these.

                  the important variables are

                       chord width
                       setting or twist angle
                       thickness
                       angle of trailing edge bevel

                  The front (windward face) can simply be flat (but
twistedif
                  you follow me), and the back is curved into a smoothcurve
                  within the above constraints. It is well worth 
taperingand
                  twisting the blade, as this permits you to make a strong
job at
                  a high tip speed ratio, with good efficiency.

                  Q.
                  . . . a 15 mph wind meets my requirements. TSR at rated
output
                  will be 8.33 (124.88 MPH). This may well require a L/D
in excess of

                  what such a crude propeller design can deliver . . .

                  A.
                  No, that is not too ambitious at all, with a 
taperedblade.
                  Rather noisy is the only problem. Important to use the
correct
                  tip pitch, and not make the section too thick, or it will
                  'whisper' very loudly.

                  Q.
                  . . . so my options will be: 1. trim the propeller tips
to reduce
TSR,
                  down to the limit imposed by area and efficiency;

                  A.
                  You are losing all your wind! Bad idea.

                  Q.
                  2. increase my windspeed for rated output. . .

                  A.
                  same again

                  Q.
                  . . . or 3. build a more complex 
(twisted/tapered)airfoil.

                  A.
                  Well worth it. Not hard to do.

                  Q.
                  So - who's done this already? Design is the easy part,
fabrication
                  hints for a repeatable twist/taper seem hard to come by!

                  A.
                  You can get full details from my books as I said, but if
anyone
                  is interested I can try to expand in the text format on
this list.
                  Pictures help a lot, though.

                  Comment on: "We carve twisted and non-linear
taperedairfoil
                  using a pantagraph router copying a pattern."

                  This approach is no doubt excellent for mass
production,but
                  rather daunting for those who want to produce
smallbatches,
                  and keep changing the spec.

                  Hugh Piggott, Scoraig Wind Electric, Dundonnell, Ross
shire, IV23
                  2RE, Scotland. email: hugh.piggott AT enterprise.net

                        Wind FAQ | AWEA Home Page
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--
Bevanron of EarthNSky Farm   Sleep well tonight, for somewhere in the
ocean's depths, MY son is protecting YOUR freedom.