furling problems with hugh piggot 10' generator

[getterdone]

ok iv'e built a 10' generator by the book of hugh piggot. iv'e been testing it by flying it on the back of a truck. it does not start to furl until we hit 40 miles per hr. at this speed its producing about 40 amps. were using 2 12v batteries wired for 24v. our system is 24v. i've read where we needed about 12,lbs of pressure to make it furl at 30amps,about max or you might have a melt down. this being said.,i cut a 1/2' section out of the tail pivit support to lesson the weight to about 12# of force and switched from 8sq.foot of 1/2' plywood to 5sq.'of 3/8 to get 12lbs of pressure to make it furl. put it to the test truck and furled about at 26 to 28 amps. speed of truck was 28 miles per hr. took the truck up to 40 miles per hr. and amps dropped to 8 to 12 amps. what am i doing wrong? tail tracked wind ok. where might be my problem with piggot's design on that tail? dimensions were exactly by the book. thanks for any and all help. it'll work ok the way it is; but i know it's wrong.also in high winds i'll be loseing amperage.

[Warrior]

I'm no expert but it seems to be running OK after the tail mod.

28 amps @ 28 mph is about 672 watts. At 40 mph you get less amps because the furling is doing it's job, protecting the machine from mechanical and electrical overload.

Warrior

[Flux]

I am completely confused by your terminology. I don't understand what you mean by cut 1/2' section out of the tail hinge to lessen the weight. I also have no idea what you mean by 12 lbs of pressure.

What matters here is the moment of the tail about its hinge. The weight of the tail at the pivot point is totally irrelevant .

If you lay the machine on its side so that the tail can pivot vertically about its hinge you can find the moment by weighing the tail at a known radius.

Assuming the tail was 4 ft long from the pivot and it weighed 12 lb at the end you would have a moment of 12 x 4 = 48lb-ft.

If you weighed it at a point 2 ft from the pivot it would weigh 24lb. The moment would be the same 24 x 2 = 48lb-ft.

You would probably have achieved what you wanted by reducing the plywood from 1/2" to 3/8" and keeping the area the same.

What you have observed is perfectly normal, despite the thoughts of some, furling is not a precise process and it is quite normal for the output to fall in the higher wind speeds.( many don't find this and burn things out, making me suspect that they are not actually furling)

Your 40A was probably on the high side, Your new value is probably on the low side but safe.

No significant reduction in output will take place for the first 30 deg or so of movement of the tail from its stop. You can probably take the current when the tail is about 45deg as a sensible furling value. You may exceed this current in lower winds during gusts but it will not be sustained and shouldn't hurt. During very high winds it will tend to drop below this current and under those conditions it will likely be so turbulent that a lower output will make life easier.

Your best bet is to play with the plywood thickness, starting with the original area and you may have to reduce the area a little if you need to get the tail moment lower. There is no point in messing about with metal at the pivot point.

I am sure Hugh gives a figure for the tail moment, but it may be just a weight at a known distance ( end or c of g).

It would be interesting to see your current at different wind speeds ( and angle of tail at each speed if possible). Vehicle testing tends to give high output figures so the wind speed may not be exactly as the vehicle spedo suggests but it will be interesting. The furling will react rather differently to real wind with gusts and turbulence but it will be interesting all the same.

Flux

[TomW]

flux;

I think he means the pressure against the prop hub that turns it into furling?

Not positive, but I do know DanB provided that information at one time although I cannot say for sure what value he stated.

Terminology can get confusing at times, indeed.

Cheers.

TomW

[Ungrounded Lightning Rod]

Was the turbine actually wired to a load so that it was producing 40 amps?  Or was it spinning unloaded?  (It's not clear from your writeup.)

If the latter, try it again with the diodes and batteries hooked up so it's actually charging the batteries with whatever amps it will drive.

The furling is driven by drag, and the drag is mostly fallout from load on the shaft.  A mill that isn't under load furls at a much higher wind speed than one that is under load.

[getterdone]

yes tom ,danb said you needed about 15# of pressure aginst the hub. at this point it should start to furl. with 1/2' ply wood at 8sq ft of the stuff it would not, impossible to furl. so thats when we went to 3/8 plywood. at that it still was in the 20lb range. the only thing to do was change the angle of the tail hinge. [the piece of metal between the hinge and the main pipe.] that reduced the amount of force it takes to furl.i did state it took 12#, it really takes about 15# to start it to furl. we put it up today. wind will blow this week end. i'll let youall know how it works.

[getterdone]

yes it was hooked to a load [two 12v batteries hooked up in series. with all the good stuff and time you all put into this board it needs to be stressed to new comers like me the importance of furling at the right amprage, if not they will burn up their hard work. i just about burned mine up. it really got hot. i dont know what temp it was but i couldn't touch it for any length of time. the thing was not designed to put out 40 amps. guess that in my short time of building, resurching about a little over a year know, testing when your wind generator furls; at the proper design [amps] is the most important thing you can do to insure that your windgen has a long life.

[getterdone]

its up so time will tell if it works according to design. i'll be watching it for a month or so, then i'll be taking it to sothern central missouri. close to ntl's place. this along with a listroid and some solor pannels will be all my electric power. when all this comes together i'll move. i'm in illinois now.

[getterdone]

thank all for comments. thaught danb would have something to say. kind'a would like to know his thoughts on the subject.

[Countryboy]

How much offset do you have from the yaw axis?  You should be offset about 5 inches.  If your offset is less than that, it will furl later.

Shortening the tail boom may help you too.

[Flux]

I had assumed that the figures were not force directly from the prop  because the figures seem far too low.

I have now found a figure from Dan suggesting that his 10 ft machine needs a force of about 25lb to furl at 1kW output. This is interesting and seems to indicate that the prop seeking force is much greater than I imagined on Dan's machines.

Firstly I have no idea what wind speed Dan's 10ft machine needs to produce 1kW but it must be up in the 30 mph region.

I have found some figures for my 10 ft machine, which furls about 25mph.

The thrust on a disc is found from 1/2 rho A V^2. The thrust on a rotating prop will be less than this and depends a lot on the power coefficient at that point but I seem to have assumed that .7 x the disc thrust would be near.

At 25mph this gives just under 100lb. In my case the offset is 5" so the torque trying to turn the thing out of the wind is 100 x 5/12 = 41 lb-ft

The moment of the tail against its stop would need to produce this torque to balance it.

I found that the seeking force on my prop produces a torque of about 18 lb-ft  so the tail needs to balance 41-18 or 23 lb-ft.

This torque equates to a thrust of 23 x 12/5 = 55lb of thrust on the prop.

This is much higher than Dan's figure and I suspect Dan's figure is at a higher wind speed, making the difference even greater.

I do know that the seeking torque is very dependent on the prop design and loading conditions and it is all to easy to muck things up and never be able to overcome that seeking force ( it will never furl). It looks as though Dan's seeking torque is rather higher than in my case ( I have been caught and play very safe now).

I have no idea how these figures relate to Hugh's design, and again prop construction and alternator loading would vary from one machine to another, with different line resistance etc.

None of the details of my tail would help, it uses sheet metal rather than plywood and doesn't use an inclined hinge but uses a wire rope round a drum to convert weight to restoring torque. The restoring torque is about 23 lb-ft as I mentioned so you could compare that with a hinged tail quite easily. ( torque needed to move tail from its stop measured horizontally).

I always seem to have to add weight to the tails of my machines to raise the furling speed, which is safe. I still wonder if some of the machines mentioned here really do furl at a safe speed, room for more investigation.

Flux

[getterdone]

i made it 5" according to piggots directons with 4deg offset to the yaw bearing [keep blades from hitting the tower]. the angle of the hinge is 35degrees from the rotor plane. ok what i did to change the force it takes to move the hub, i cut a piece of metal out of the tail hinge support and changed the 2o deg, the design called for. that hinge support was 4" in length,and that wasn"t changed. at the top it measured 2 3/16" at the bottom it measured 3/4", this gives your 20degres offset from the yaw bearing. after cutting a tryangler piece out, from the top and then closing the gap, and rewelding; this changed the 20degrees. the 2 3/16 measurment now is about 1 15/16. hope you understand what i'm tring to say. in doing that it takes less force to furl.

                           

[Flux]

I follow what you have done now, I have not seen the 10ft design, it must be like the 12 ft with a very different tail construction from the 8ft.

Yes indeed reducing the inclination below 20 deg will make it furl earlier. I was under the impression that you just removed metal to reduce weight, which has no effect at the hinge point, but saving weight on the metalwork at a point beyond the hinge would help.

I am not entirely sure why the changes were needed, things that survive on Scoraig should survive anywhere, but there is a fair bit of difference between real wind and simulated wind from a truck test.

At least you have made it safe and all should be well.

The loss of output in high wind is normally of no consequence as the batteries are usually full under storm conditions and early furling gives the whole machine an easier life.

Flux

[getterdone]

when measuring the force at a given point,to start the furl. that point has to be the same. in other words no matter exact design shouldn't matter that much. danb's 10' machine is different than piggot's machine. using different materials. what needs to be cleared up is at what point should you take the lbs reading. [from the center of the hub shaft?] i took mi reading from the stater end bracket using a fish scale.

i like danb's design a little better than hugh piggots. the next one i build will be patterned after them. i wish danb would produce a book on each size and market it. hugh's book is great, the only down side is that he skips around and combines several sises in one book. this gets confusing for the newcommer. DanB read this, please!

[Flux]

getterdone

I agree with much of your comments.

Dan has some excellent designs and people starting from scratch would be well advised to look at the latest details on Otherpower. Mixing up earlier versions and making some sort of hybrid will cause confusion and trouble. As the designs have evolved things have been changed to take care of new ideas. Trying to use older designs with different magnets or windings with later mechanical ideas may lead to trouble.

I find it hard to keep up with changes but as I never build these things it doesn't matter.

A complete set of plans would be a good idea but it takes time and Dan may not have that in excess.

Hugh's earlier plans were very easy to follow, I haven't seen the later versions and it may be that by including various other sizes it may have muddled the issue. I am familiar with the 4 ft and 8ft. I have also seen the 12ft but not in the plans. I am not familiar with the 10ft so I am unable to comment.

Regarding the furling issue, the most useful piece of information would be to give the torque needed to pull the tail boom from its stop. This will include the effects of the tail moment about its pivot and also the hinge angle, errors in either would show up in this moment.

Measuring the thrust as Dan does it comes up with exactly the same information in a very indirect way. It is awkward to do and includes much uncertainty from the yaw pivot friction.

I would strongly advise against trying to use information on one design intended for another.

Hugh's blades will not have the same self seeking force as Dan's and the correct tail moment for one may be way off for the other.

Flux

[ZooT]

Er uh.......would it be useful to add a machined weight that would fit around the main tail tube/pipe, with a couple of setscrews in it and slide that weight further from or closer to the the yaw bearing to adjust the wind speed at which furling occurs?

[getterdone]

yea an adjustable weight would work nice, but in my case i started out with too much weight to begin with. flux said it right in doing what i did to make it furl. better to be safe than sorry. it should work just fine. no sizable wind yet. need 40 or so miles per hr to really see if it furls at the rated amps,with out it burning up. the truck test showed it would go up to 28amps and that was about all. this was at 30 miles per hr. any faster say 40 miles per hr,it would be fully furled and the amp reading would drop. it varied. the average was around 10 or so amps. it seemed you could tell how fast you were going by how many amps it was producing. 10amps[10miles per hr.],15amps[15mph],,,20amps[20mph],and so on. when you got to 30mph it would hold steady at 28amps.any faster truck speed, and it would drop from 28amps[fully furled].