Furling with a Twist

[Hilltopgrange]

Furling with a twist

Hi all and seasons greetings ... its been a while since I posted , just been to darn busy with to many projects all at various stages of incompleteness . The most complete is a 12 footer from Hughes latest plans but built with  parts I had to hand.

The main spec of this machine is the same as Hughes plans i.e. magnets, rotors and coil turns (48v)

However the chassis, yaw tube and tail are completely different. The yaw tube was originally a hydraulic tilt cylinder from a forklift with the ram removed and the gland nut machined to allow a 3 inch steel pipe to slip inside. The original piston was retained and acts as the bearing for the yaw. The mounting for the stub axle is a single ½ inch plate welded to the yaw tube at a 4 deg angle to give extra blade clearance and the offset for the stub axle (Renault) is 8 ½ inches. All pretty simple and not very deferent to the original plans.

I started to make the tail, again as per the plans and I had cut the steel ready to weld when I saw a few stories about tail / blade strikes and burn outs so I got to thinking! wouldn't it be handy to be able to adjust the furl point from the ground and while the wind is blowing. Wouldn't it also be useful to be able to furl as an aid to shutting down or as a fail safe.

My first thoughts was to connect a cable to the end of the standard tail, bring it over a pulley and down the centre of the tower to a winch or weights. I should say at this point my towers are all lattice work so I have easy access to the centre area within the tower for cables etc. This method would mean the cable would have to carry the full weight of the tail as it would have to lift it up behind the blades.

I then got to thinking why lift the whole tail why not just twist the tail vane through 90 deg to horizontal thus allowing the alternator offset to turn the machine out of the wind, I could set it up so that weight was needed to hold the tail vane vertical and I could control the furl point by adding or subtracting weight from the cable on the ground and while the wind is blowing. So I made many drawings and eventually a small model to test the principle.  I made the model from a few scraps of card board and a c.d. to represent the blades, the tail was made from a drinking straw with a card vane, the wind was simply the workshop airline. All very crude I know but it proved to be a useful test as proof of concept. I tried various tail configurations starting with the standard inclined hinge type, with the tail in its normal position the prop tracked the wind as normal and with it up behind the blades it furled out of the wind. So with the same model I twisted the tail vane through 90 deg and it furled as before, now I know this is not very scientific but I think it at least proved the concept.

Now it was time to go full size. I started by making a hinge system that would carry the weight of the tail and vane but I wanted to be able to adjust the angle of the tail to the wind so as to be able to correct the tracking of the wind direction without having to change the vane size. I used a ½ inch turnbuckle I had laying about. The tail itself is a steel pipe within a box section setup that allows the tail to twist via a lever at the yaw end, I also added two end stops one for vertical and the other for horizontal. The tail vane is ½ inch ply with less area than the standard plans require as the angle is adjustable I think the reduced size will be fine although time will tell

Just need to carve the blades and get it up in the air. The cable for the furling weights is on order it is 4mm 316 stainless rigging wire rope with a breaking strain of 1.75 tonnes. The cable will go over the pulley and down through the yaw bearing in a copper sleeve about 10 ft long with the power cables, I use welding cable for the first 15 ft down the tower where they then move to the outside of the tower to allow the furl cable a clear drop to ground level. The weights I intend to use are cast iron sash window weights, I have various sizes and weights to chose from. The tail vane is mounted below centre to make it top heavy so if the cable breaks or if you remove the weight the vane will fall horizontal and the machine will furl or at least that's the plan!

Im sure someone has tried this approach before but I have been unable to find it in past postings.

So there you go further updates will follow when I get it up in the air

As always all comments / ideas welcome

Seasons greetings from Ballyroney Northern Ireland

If you fancy a laugh have a look at the safety awards from our local radio station

http://downtown.bauerweb.co.uk/programmes/downtown/johnnyhero/wacky/safetyatwork.pdf

[Flux]

Be interesting to see how well it works. I have never tried it but have thought about it in a different form. If you ever see a copy of "wind power principles" or something similar by Calvert he has a scheme in there using this with a force balance on a second vane. I never fully understood it.

Similarly I have considered your idea of running a control wire and the power cables both down the centre. I believe that will work ok  especially with a lattice tower where you have more room. On my last scheme ,which has variable furling, I finally resorted to slip rings to get the control cable down the centre. Mine does not rotate the vane but uses a weight to control the furling force on a normal swinging vane.

Knowing where you live and the weather, make sure you use plenty of grease on the pivot rotating tube in the box section, that is the first thing I would expect to seize up and cause failure and was one reason why I never tried that type of thing.

Keep us updated with the results.

Flux

[Hilltopgrange]

Hi Flux

       thanks for the input! seems I am not the only one who burns the midnight oil lol.

     My description may have been a little inaccurate, the box section is fixed to the inner pipe and the inner pipe rotates within the outer pipe they are both galvanized inside and out and are a sloppy fit. I was going to bush it with nylon but decided to go with slack fit instead, I was also concerned about it seizing so I have fitted 3 grease nipples (not shown) along the outer pipe and filled it with axle grease. Hopefully this should help to keep it free. As it sits it rotates very freely so fingers crossed.

It will be interesting to see how it works, time will tell.

Thanks for the book suggestion, just need to drop a few hints to the wife for Christmas lol

Thanks again

Russell

[Ungrounded Lightning Rod]

IMHO if you furl by making the tail "go away" when you furl the machine will likely flip around more than a quarter turn and start spinning backward.  Your machine becomes a downwind turbine misaligned to the wind with the blades on backward.

The blades will not be efficient in this orientation.  But a high enough wind will burn out the mill and/or cause it to self-disassemble just fine.

[zeusmorg]

 I was going to agree with Ungrounded, but while writing my post I started thinking about your difference in area of the tail on the pivot point.

 Without doing some serious thinking and a lot of math to see what would happen with the forces involved, I'm just not sure how well this system you've created will work.

 In thinking on it, you have created an interesting system. the wind wants to push the spinning blades rearward, which pushes them out of the direct path of the oncoming wind. The tail, in this instance, is pushed to the left(facing the mill head on) and then the larger area of the top of the tail would begin twisting clockwise,while the smaller bottom face is resisting that. So, once I realized this I saw the possibilities of the different furl working.

 However I do believe that allowing the tail to go totally horizontal is a mistake.

 I am interested to see just how this all works out!

[Flux]

I have to admit that I have reservations about the idea in this form but there is no harm in trying.

It is largely an adaption of the swinging vane tail fin that reduces area as it comes at a greater angle to the wind. That is a scheme that I don't like but it works. I haven't looked closely enough to see if your rope is doing the same thing as a hanging vane. If the wind forces on the vane assist the weight control it is not going to work.

You need the full vane to steer it in low wind and the vane area to decrease as it goes into furling, with the force on the centre of pressure of the vane opposing the weight.

My schemes all reduce power beyond furling point, this one probably won't so you may have to start the furling early to keep it under control in high winds.

What I like least is the fact that this scheme doesn't give you a mechanical shut off in high winds if you need it. Removing the weight removes all tail steering ability. In this condition it may decide to run down wind so you will never be able to use it other than with the weight for furling. I can't see it going down wind with the weight on but it would be nice to have a scheme that shuts down if the rope breaks rather than loose control.

Flux

[scoraigwind]

Hi Russell, It looks as if you have been busy.

Thanks for all the lovely photos.  It's ingenious, and I don't think I have ever seen a tail like that although it is not a lot different from a few that have tail vanes that swivel or tilt.  The innovation is being able to control it from the ground.

Marlec use a similar system when they deign to furl at all.  It seems to work after a fashion in low winds but the problem is that the tail and its furled vane actually do have quite a bit of drag in a strong wind, so you are not 'making it disappear' at all.  In fact the bare tail boom (especially with all that bracing) can hold the machine to face the wind to a sufficient extent to overspeed once the wind really gets going.  And at that point you have no means of shutting it down other than the brake switch.

I guess this brings me back to wondering why people always reject the stuff that works in favour of trying something that has already been tried and doesn't work :-))  But I suppose everyone has to learn the hard way.

I did make a tilt-back furling machine once that could be furled manually by pulling on the power cables, and that worked pretty well to be honest.  But it was not such a good furling system as the inclined hinge tail.  You can add a furling cable to the inclined hinge fairly easily.  Bergey do it in their Excel (as opposed to their XL) turbines, but the furling cable tends to seize and jam.

In the early years I used to adjust the furling with a windscreen wiper motor driven device that altered the spring setting and I had this driven by a circuit that sensed the battery voltage.  That was before I fully learned the golden rule: Keep it simple.

[Hilltopgrange]

Hi Guys

                Thanks for the responses even if they are negative lol to be honest I expected worse!

My intention is not to reinvent the wheel! I have found that the "normal" inclined hinge tail is far from the perfect solution to furling as the many tales of burn outs and tail/mast strikes confirm. I have tried in the past by following the plans to the letter on 6 other machines and still had problems with furling. I live in a high wind area and my machines do take a hammering maybe that is the problem but I have yet to build a machine from plans that has done exactly what it says on the tin as such, all have had to be tweaked in some way or another to bring them under control so IMHO the standard design is far from perfect.

              I don't think I will bin the idea just  yet as I have it built I might as well try it and see what happens the worst that can happen is that it wont work. Then again maybe it will work either way I will post an update in the interest of advancing the cause.

One thing for sure standing still gets you nowhere ! Thanks again for the replies all points have been dually noted.

Merry Christmas to all

Russelll

[Old F]

How about  this start out with a  tail that will furl in a light wind

Then use a cable an weight to counter balance  the  tail

The more weight you add the higher the wind speed  it would furl at.

The weight would be at the bottom of the tower where it would be easy  to change

If the cable breaks it furls

 If you know a storm is coming  you take the weight off An it furls

  Just an odd thought after read this post.

An remembering that some of the old 32 volt machines that had blade governors

All so had manual furling tails the tails were spring loaded to the full furl an

You cranked them open to run if the cable would  break it would snap back to full furl

Oh an I got a good  chuckle out of the safety  

PDF

Old F

[Hilltopgrange]

Hi the way you have descibed is exactly the way it is set up now, the heavier the wieght the later it furls. I hope to have it flying in the next couple of weeks so we will see what happens.

I thought the bonus pic at the end with the guy holding the targetabove his head was a hoot, that guy should get a medal lol.

Russell

[Old F]

Russell I was trying to get my head wrapped  around the pics

An the twist is what threw me for a curve  LOL

All the best of the holidays to you an yours

Old F

Having so much fun it should be illegal

[Ungrounded Lightning Rod]

It is largely an adaption of the swinging vane tail fin that reduces area as it comes at a greater angle to the wind. That is a scheme that I don't like but it works. I haven't looked closely enough to see if your rope is doing the same thing as a hanging vane. If the wind forces on the vane assist the weight control it is not going to work.

You need the full vane to steer it in low wind and the vane area to decrease as it goes into furling, with the force on the centre of pressure of the vane opposing the weight.

You misunderstand the operation of the swinging-style furling tail.

The tail does not reduce it's apparent cross section to the wind, causing furling by changing a balance of forces with the offset turbine.  (There is a little angle between the tail and the wind to cancel the force from the offset turbine.  But that's a separate issue.)

Instead the tail ALWAYS points (essentially directly) downwind.  What furls the mill is changing the angle between the tail boom and the turbine axis.

The trick is the tilted pivot.  As the wind goes up (with the tail resting on a fully-unfurled stop) the turning force on the slightly offset tail and the slightly offset turbine go up in proportion.  So the preferred orientation remains the same.

Because of the tilted pivot the tail has the potential to fold up, and is held out against the stop solely by its weight acting through the pivot tilt.  But the force trying to fold the tail goes up with the wind while the weight doesn't change so the force holding it out is also unchanging.  So at some wind speed the tail-folding force becomes stronger than the unfolding force and the tail starts to fold up.  The tail remains pointed essentially downwind so the turbine turns away from the wind.  As the wind rises further it can hold the tail at a more folded angle, turning the mill further from the wind until the tail reaches the fully-furled stop.

(Yes some mills dispense with the fully-unfurled stop.  That still works about the same way, except that the tracking angle of the mill varies at wind speeds below what would be the "start of furling" wind speed on a mill with the stop.)

The issues with blade/tail collision on these mills are all about design problems:  Putting the stop too close to the pivot (i.e. just using the hinge cutaway) so that in a gust the tail can slam into it and bend or spring further toward the blades, not taking blade and tail bending under severe loads into account and so leaving too little spacing, building a pivot that lets the tail lift off the pin and miss the stop, etc.

[Flux]

"You misunderstand the operation of the swinging-style furling tail."

I have to admit that I was confused by the pictures but unless I am mistaken this can't be a furling tail. As far as I can see the tail boom is held in a fixed position by that turnbuckle. The boom angle looks to be adjustable for initial position but the thing looks like a rigid set up. I am not even sure there is any inclination on the hinge but there would be no point anyway if the thing is clamped.

The only way I can see it furling is for the boom to run at an ever increasing angle to the wind as the vane area is reduced. I am inclined to suspect that Hugh viewed it that way as well because he mentions the fact that windage on the boom alone may force it beyond safe output in very high winds. If it was a furling tail staying down wind the windage on the boom would be irrelevant.

Flux

[Ungrounded Lightning Rod]

Right, Flux.

I was describing the operation of the normal furling tail.

This one is something else - designed on the mistaken assumption that the normal furling tail furls by reducing its cross-section to the wind and the strength of its tug-of-war with the offset turbine.  This rotating tail DOES work by adjusting a tug-of-war.

Which is not to say that you couldn't design a tail that worked this other way - i.e. you might get this one to work, or "sorta work".  But it's an implementation of a different principle, not a different implementation of the same principle.

= = =

One additional downside:  This tail causes a (BIG) vertical force on the end of the boom when it's an angle between vertical and horizontal.  That might be a problem for the yaw bearing.  (You could avoid this by splitting the tail into two parts and rotating them in opposite directions.)