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Furling systems
By Bach On, Section Homebrewed Electricity Posted on Wed Jul 09, 2003 at 09:04:44 PM MST
Furling 101

Hi folks,
I'm in the final stages of making my generator innards. Still no prop, but I'm ready to plan and build my furling system.
One concern I have is that we are subject to occasional hurricanes that blow inland in the late Summer and early Fall. It isn't that unusual to get winds approaching 75 mph during such storms.
I've read what many have done with furling mechanisms. Yes. I did a search.
Let me check my limited understanding:
One popular method is to use a tail that is offset perhaps 20-25 degrees from the plane of the prop. I believe DanB has used this on his most recent projects. The method seems to be to have the prop turn out of the wind when the windspeeds get strong enough to push the tail and spin the alternator mount. The tail must be of an appropriate size and weight so that the furling takes place at the correct wind speed. Determing the size and weight may take some trial and error.
Seems like I've seen where some also use a movable tail. Mike, for example, uses old TV antenna rotors to adjust the tail. I'd guess this allows you to adjust the windspeed at which the prop is turned out of the wind. Does this sound correct?
Seems like I've also seen that some make their furling system so they tilt or swivel. I do not really understand the advantage to doing this.
I'd be greatful for any and all comments and advice from some of the experienced builders.
I continue to be very impressed by the collegial spirit here.
Bach On

Furling systems | 19 comments (19 topical)

Re: Furling systems (none / 0) (#1)
by iFred on Wed Jul 09, 2003 at 09:45:15 PM MST

Here is a basic pic from the tutorial I wrote on Ed's program from windstuffnow.com regarding the blade designer program he wrote...

The above pic shows what the tail is doing

The angle offset can be calculated by using Ed's program..

If you go to my web page the entire tutorial is there and at www.windstuffnow.com
www.internetfred.com

The program is cheap and is well worth the price for the headaches and calculations your going to come against..
>> all energy used to produce this comment or post came from solar and wind energy! It works!

Re: Furling systems (none / 0) (#2)
by Bach On on Wed Jul 09, 2003 at 10:07:48 PM MST

Fred,

I did go to your site and read your clearly written tutorial on blade design. I think I understand that the blades and the furling mechanism should be planned together since they are closely related.

I think what I'm really after is to better understand the various furling mechanism designs and their pros and cons. Like everyone, I want to do one that is reliable.

The one that that has me most confused is the tilt up mechanism. And I feel that locking the blades by shorting out the coils is a bad plan - especially with hurricane or tropical storm winds (Eastern North Carolina - 90 miles to the coast).

The only really safe way to handle such storms may be to take down the genny. But that is an obvious pain and carries some risk of damage. Too, safely erecting and taking down a genny usually isn't a solo endeavor. Folks around here are usually rushing around battening down the hatches and stocking up on supplies when a hurricane is eminent. I suspect there wouldn't be a oversupply of willing volunteers to help.

Bach On

- - I'm not superman, but I am very dense! -

Re: Furling systems (none / 0) (#8)
by RayW on Thu Jul 10, 2003 at 04:18:09 PM MST

Hi Bach On: What part of N.C. do you live in??? I'm near Elizabeth City.
RayW

[ Parent ]

Re: Furling systems (none / 0) (#9)
by Bach On on Thu Jul 10, 2003 at 10:26:23 PM MST

Ray,
I'm in Nashville - just West of Rocky Mount.

Elizabeth City, huh. Then you know what I mean about those storms.

Bach On

- - I'm not superman, but I am very dense! -
[ Parent ]

Re: Furling systems (none / 0) (#15)
by RayW on Sat Jul 12, 2003 at 05:37:20 AM MST

Bach On,
I've been through a few of those storms and they would make a wind jenny produce a lot of power.
RayW

[ Parent ]

Re: Furling systems (none / 0) (#16)
by Bach On on Sat Jul 12, 2003 at 06:08:12 AM MST

Ray,

Yes. Several of them have come up this way. We've had plenty of winds that topped 75 mph. My concern is that this would put a major strain on a tower and mounting system.

My back-up system consists of two deep cycle marine batteries. I have 12 volt lights around the house. I built a control box that allows me to cut the lights on or off in various parts of the house as needed. It also has digital voltage and amp meters within it so I can better monitor the batteries. I charge things with a Wal Mart charger. Not as good as one of those three step high dollar chargers. But it has a setting for Deep Cycle batts. Charging is at 2 amp, 12 amp and even short bursts of 50 amps.

The time we are most likely to lose power is during one of those storms (or a Winter storm). That's when I'd most want a back-up system to charge the batteries. Ideally, I'd like to be able to eliminate the external charger, except for maintenance. Though I doubt we have enough consistent winds during some seasons to totally do that.

I just have this horrific vision of my blades flying off and hurting somebody or the tower and genny blowing down onto a neighbor's house (or ours). Such an event wouldn't make me the most popular guy in my neighborhood. Know what I mean?

Are you out near Ahoskie and Windsor?

Bach On

- - I'm not superman, but I am very dense! -
[ Parent ]

Re: Furling systems (none / 0) (#19)
by RayW on Sat Jul 12, 2003 at 06:21:52 PM MST

Bach On,
I have a tape drive motor up about 35 feet above ground charging two 6 volt golfcart batteries, but it does not start charging untill the wind gets up to about 15mph and the most I've seen out of it was aboout 5 amps in some strong gusts of about 25 mph. Also I have a converted 2hp, 4 pole induction motor that I have bench tested and it will put 25 amps into the golfcart batteries at 460rpm but after about 30 minutes at this rate it gets pretty hot. With this setup I could not spin it at a slower rpm as I would like to know what it will do at 150-200rpm.
I live about 20 miles north of Elizabeth City near the northen end of Pasquotank county about 1 mile off 158.
RayW.

[ Parent ]

Re: Furling systems (none / 0) (#3)
by iFred on Wed Jul 09, 2003 at 10:22:56 PM MST

A friend of mine (Tom S) suggested a bicycle braking system that could be engaged
from the ground, I have not tried it, but it sounds like a great and cheap way to
to go. I'm not sure of the tilt you are refering to, i'll check on that as well. But
I also think that a simple resistance brake method is needed, I have been thinking the same thing, because we get some really turmendous storms two-three times a year here and was wonding about what might happen.

>> all energy used to produce this comment or post came from solar and wind energy! It works!

Re: Furling systems (none / 0) (#4)
by hvirtane on Thu Jul 10, 2003 at 06:09:37 AM MST

Hi,

at present most of the commercial small
turbines are using a system to turn the turbine
sideways. You can easily comprehend the
system if you study a small Marlec
for example (made in UK) or study Hugh Piggott's
web pages.

Germans have used at least from 1930's already
a system to turn the turbine sideways by using
a two tail system. The other smaller tail is
on the same plane as the prop. I can make a rough
drawing of the system if wanted. It incorporates
a spring and it seems to be quite easy to adjust
by trial and error.

- Hannu

Re: Furling systems (none / 0) (#5)
by Larsanderss on Thu Jul 10, 2003 at 07:19:44 AM MST

Hello..

I would be very interested in a drawing of the "springloaded two tail system" for furling.

Lars A

Re: Furling systems (none / 0) (#10)
by hvirtane on Fri Jul 11, 2003 at 06:10:24 AM MST

Here is my drawing to show
the principle.

It is made according to the explanation and
the drawing in
'Hutte'
DES INGENIEURS TASCHENBUCH
26. neuarbeitete Auflage; II Band
Berlin 1931; VERLAG VON WILHELM ERNST & SON

A remarkable fact is that book contains already
at that time also other
good explanations how to design a wind turbíne.

There are really good books concerning making
wind turbines yourself existing in German language
only. Maybe the best of the modern ones is
by Prof. Crome.

- Hannu

[ Parent ]

Re: Furling systems (none / 0) (#6)
by windstuffnow on Thu Jul 10, 2003 at 10:02:01 AM MST

I think Hugh's furling system is about the easiest to put together for us home builders. Its very basic, relatively simple to construct and very reliable.
One thing he has left out of the books is calculating the the tail angle and weight of the tail. Since all the variable's (such as tail mount angle, rotor offset and weight of the tail)interact to determine how much of the tail weight will be opposing the furling.
Below is a formula for setting up the angles and tail weight for Hugh's furling system... This can be plugged into a spreadsheet program to make it quicker also...

Input numbers:
Rotor offset (meters)
Diameter of Rotor (meters)
Wind Speed ( meters/sec)
Tail Tip Weight ( Kg)
Length of tail (meters)

Calculations:
Rotor thrust = Diameter of Rotor^2 * Windspeed^2 / 24
Tail moment = Tail tip weight * Length of tail
Rotor moment = Rotor thrust * Rotor offset
Tail mount angle = sin-1(Rotor moment / Tail moment)

To find the tail weight at a given tail mount angle ( like you already welded it on but the angle was off)( been there done that)

Tail moment = Rotor moment / (Sin(Angle in degrees)
Tail weight = Tailmoment / Length of tail

Suppose your rotor shaft is offset by 125mm and the thrust for furling is 40kg. Then the moment is 40 * .125 or 5 kg/m

Find the moment of weight of the tail by weighing the tip. If the tip weights 10kg and the tail is 2 meters long then you have 20kg moment of weight.

The angle determines how much of that weight will be opposing the furling. Furling moment is moment of weight times sine(angle). If moment of weight of the tail is 20kg/mand you want 5kg/m then the angle shoud be 14.5 degrees ( sine(5/20)= 14.5

Have Fun

Ed
Have Fun! Windstuff Ed

Re: Furling systems (none / 0) (#11)
by Hank on Fri Jul 11, 2003 at 08:29:31 AM MST

Ed,

A quick question on your formulas. How does the area of the tail vane enter into this equation? I would suspect that the area of the tail would have a great influence on overcoming the moment forces as well as the angle. Both of these appear to be related in some way.

The greater the area, the greater the side forces and vica-versa.

Hank

[ Parent ]

Re: Furling systems (none / 0) (#12)
by windstuffnow on Fri Jul 11, 2003 at 10:48:53 AM MST

The area of the tail really doesn't effect the furling system, unless of course its much to small. The furling system works on weight ( or gravity ). Basically uses the same theory of the caster angle in the front end of your car. The caster angle tends to hold the wheels straight because of the weight of the car. When the wheels are turned one way or the other the weight of the car wants to move them straight again. When you turn the wheels it actually lifts the car on one side. The same with hugh's furling system. When the pressure on the prop exceeds the weight of the tail it lifts the tail. The tail actually remains aligned with the wind for the most part.

Have Fun!
Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: Furling systems (none / 0) (#13)
by Hank on Fri Jul 11, 2003 at 01:47:14 PM MST

Ed,

That part I understand (caster angle and all of that) but I think it must be the wind acting on the vane that actually overcomes the gravity force and moment in which case area becomes very important.

The reason I'm asking all these questions is that I'm all built and set to go (tower needs to go up) but when I run your calculations I find that I'll furl at about 9 M/sec wind speed.

My rotor is 8 ft., my rotor offset is 3.8 inches, my vane area is 2 ft squared, boom is 5 ft. and my tilt angle is in the order of 22 degrees, and the tail tip weight is about 8 pounds.

By tilt angle it is the angle from verticle as in Hugh's books (of course each book has a different angle from 15 to about 27 degrees). Perhaps we are talking different angles.

Don't want to get everything up and running to find that the system will furl just when it should produce some power.

Perhaps I should add some weight to the tail!

All help is greatly appreciated,

Hank

[ Parent ]

Re: Furling systems (none / 0) (#14)
by windstuffnow on Fri Jul 11, 2003 at 04:14:09 PM MST

Hank,
Thats why I added "unless it was to small" part. To big wouldn't matter because your working with both forces... the force trying to rotate the prop around the pole and the weight trying to hold it in place (tail).
You can install a moveable weight on the tail and set your furling based on the formula. If it seems to furl to soon move the weight back a bit.
Since you already have the angle in place use the bottom formula to find the tail tip weight and add the moveable weight set toward the front. Don't set it all the way forward to leave some movement for adjustment. Add the weight you need and you should be set ( don't forget to lock the weight down though... does strange things )

Have Fun
Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: Furling systems (none / 0) (#17)
by scoraigwind on Sat Jul 12, 2003 at 07:35:14 AM MST

Hank don't worry too much. You aren't going to get it right first time but you are in the ballpark. I prefer to use a light tail at first until I see how things go and then add some weight to it later when I get confident that the machine is fit to run harder.

I use similar calculations to work out the tail weight etc but I do find that it pays to make the tail a little lighter. The blades will actually seek the wind to an extent and you don't have to hold them into the wind as hard as the calculations imply.

The tail hinge angle can be anything, depending on the weight of the tail. For bigger machines with heavier tails I use a smaller angle. This is fine so long as the tower is accurately vertical. For small machines I use a larger angle. That's fine so long as the tail does not fall off (vibration can cause it to climb off).

The area of the vane just has to be enough to be able to hold the blades into the wind. This will be the same in any windspeed. If in doubt make it too big. (Yours sounds a wee bit small) And give it a slight offset side angle into the wind (to the side). Then it will grip the wind and hold the blades straight on. If it is bigger it needs less side angle (angle of attack). If it is too small then the machine may yaw away even in low winds. The tail will fail to hold it into the wind.

The area of the vane will determine the angle it makes to the wind but the difference is small. The weight will determine the force required to furl the machine, by lifting the tail and allowing the machine to yaw out. So the weight is more important.
Hugh Piggott http://www.scoraigwind.co.uk
[ Parent ]

Re: Furling systems (none / 0) (#18)
by Hank on Sat Jul 12, 2003 at 01:32:49 PM MST

Thanks for the respose Hugh,

I followed your books (for the most part) so I'm sure it will work. Tweaking sounds like part of the game here. I just don't want a disaster first time up.
I also want to understand the math and logic a bit better.
It keeps up nights (what a weirdo).

All you guys have been immensly helpful and I appreciate your advice and comments.

Keep them coming,
Hank

[ Parent ]

Re: Furling systems (none / 0) (#7)
by Mike on Thu Jul 10, 2003 at 03:51:14 PM MST

Just to clarify... I suppose I could use the rotor to angle the tail and
regulate the output, but that's not how I'm using it. The rotor-mounted
tail is on my test genny, which I use mostly for experiments with different
alternators. I just unfurl the tail when I'm running it, and otherwise I keep
the tail furled, so the prop is 90 degrees to the wind. Since we've been
getting severe storms here on a daily basis, I'd rather not have to worry
about it. The two small gennies ride the storms fine with no furling, and
I can get 30 - 35 amps out of the pair when a storm comes through,
which is more than I need. I've seen 70 amps with all three gennies flying,
but it's more important to make sure the big one makes it through the night
than to get the extra current.

- Mike

http://www.bioelectrifier.com

Furling systems | 19 comments (19 topical)

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