16 Footer fails to furl

[HaroldCR]

 I believe there is a Bergey Dealer that's a member of this forum. However, Let me put in what I remember when we were Bergey and Whirlwind, and Wincharger Dealers-Installers.

  First, as I THINK, I remember, Bergeys have an offset bend at the end of the Tail FIN. VACUUM pulls the tail around, from the wind getting stronger and rushing past the blades. A well tuned machine, will not pass any large amount of wind through the blades. It gets thrown off to the sides and around the machine. I have climbed up and BY HAND, steered machines out of the wind. You can effectively light a cigarette with a match, behind a spinning blade. Been there-done that. This is NOT BS. It was on other brand machines, including my own 4KW with 15½' Blade span. Cable down to the ground to manually furl the machine, jammed up on the side of the pulley it went through. I tried to copy Jacobs machines, as much as possible.

  Bergey also did NOT furl all the way to roughly 90°. It hit the stops at around 75°. The degree of rise of the tail, is not as exaggerated as much as the design here. That way, it furls a bit easier, but, also maintains nearly full output, without burning stators and exploding blades and such.  I'm also thinking, the tail vane JUST sticks out from the diameter of the blades, and, is quite small compared to what you guys build.

 We sold them in the late 70's-early 80's so, they MIGHT be built out of the USA for all I know, now. Haven't had contact with my x-partner for several years.

  We had our tower specs modified by Mike, owner of Bergey, so we could install their NEW 10KW machines on our towers. They were even going to put them as an option for them to sell to Dealers-Customers. My partner went out to Oklahoma City and visited the factory.

 The Motored yaw system, I would not use. We sold a Whirlwind 4KW, down in Paris, Arkansas, and had to take it down and have it factory rebuilt. It had a 4 blade metal fan that gear drove the yaw gear. It was activated by the wind and when I     S L O W L Y crawled up the tower (100'), The machine was hanging by 1 bent bolt. Anyway, I found a piece of debris that was stuck in between the fiberglass housing and the shaft that went from the fan, down into the housing. The fan would not turn, so, the machine ran away, totally shattered the 1 piece 16' blade, and about shook the machine off the tower. IF y'all try a yaw system, and it fails, yer screwed, WORSE than what y'all have now. TRUST ME ON THIS.

 We put a 24V Wincharger on a 100' tower, up on the high bluff, above Greers Ferry Lake, in Arkansas. Had to crawl up that one, with 1 guy wire broken and the blade in a jillion pieces, and THAT generator was held by a BROKEN piece of bolt. Talk about scary climbing. Managed to get it tied off to the tower, and then, lowered to the ground. Winchargers have a dual "SHOE" brake, like car drum brakes. Faster speed, more pressure applied. THIS ONE, burned through the shows, and the machine ran away.

  I could tell y'all a bunch of stories.  This IS all from experience.

[Hilltopgrange]

Hi Bob very interesting, I remember your machine well, very nice machine indeeed! I look forward to your post.

Sorry to hear your stator failed

Russell

[Hilltopgrange]

Hi Hugh The gust that caused this was very violent, I felt the tin roof on my workshop try to lift. It may have just been freak conditions that caught it, it has been a very reliable and quiet machine and have watched it furl many times. This place is no stranger to high winds so I need to get a solution.

 I hope to get up the tower this week(if the wind drops) to carry out the mod that flux suggested with an extra vane on the alternator,  I will also grease the tail pin and yaw bush while I am up there, I will also lift the tail off to see if it possibly seized or if it was binding.

Thanks for your  time (I hope you will be publishing plans for the 18 footer!)

Russell

[Flux]

I think you are right in that there is not a lot of wind behind the blades. Certainly for normal working a long tail seems a good idea and things don't yaw about so much.

In this case the tail seems more or less irrelevant, the issue seems to be that the blades stay facing into the wind against the thrust acting on the offset.

If things can run as Hugh described then I can see a case where virtually nothing will stop the thing. I suspect there is a position exactly edge on to the wind where it will stop but if it can run away on the up wind or down wind side of this you probably don't haver much chance of keeping it in the dead band.

Normally the thing gets furled and slows and drops to a low tsr and doesn't get into this state. I can only think that the seeking force was to high for the offset at least under this rogue condition.

Flux

[HaroldCR]

 That Tin Roof trying to lift, is that Vacuum  or LIFT, as in Airplane wings LIFT, I was trying to describe.

  From all the Library research I did, and from seeing what Bergey did, I am convinced the 90° furl is not good on larger machines.

  I just dug through my "Energy Folder" of all my saved info, and found 1 copy of Bergeys Brochure. It shows a photo of the 10 KW Machine, before raising the tower. It shows the tail folded at about 80°, or so. It also says their tm Autofurl tail, which turns the rotor out of the wind, at wind speeds above 35 MPH, to protect the Excel in high winds.

  I don't have access to a scanner, so, no photo to show y'all. In the photo it does show the turned edges of the tail fin. Front edge appears to be folded over, to protect from sharp edges Can't be positive from the angle of the photo.  The rear bend is more pronounced, maybe 10" wide, figuring the fin might be 4' long  Just a guess, but, it IS a substantial area bent, maybe 15-20° from flat. The blades turn Clockwise and the bend is as you face the machine, the trailing edge is bent TO the LEFT, like it is trying to steer the mill to your left, as it is flying, with you facing the blades. ALSO, and I believe this is important, there is probably 3' of clearance from the blades to the tower. It makes for leverage to help start turning the rotor out of the wind.

  Y'all's 12" offset should be good, but, I would think putting the rotor further away from the tower would increase this advantage, also. AGAIN, this is for larger machines.

  It shows the machine nosecone of the rotor facing down, and so is the tail. This is before raising the tower up. REMEMBER, this Brochure is from 1983-84- maybe  I left Arkansas in '86. The President had already cancelled the "Energy Tax Credits", and business about died. Gotta LOVE them Politicos, EH

  When I get back to Florida, I will get on this site and maybe be able to post helpful info. Maybe what I have written, will help someone in the mean time, or, at least, give info for experiments

[bobshau]

Jonathan

Thanks for your comments on the remote control. With regard to photos on the cast blade making process, I'll need to put something together and post it. In the meantime, I'll describe the concrete mold making process, as follows:

1. I carved a 10' long, twisted, tapered wooden blade that was used to make the cavity of a two piece concrete mold.
   
   
2. The mold was made from studs and plywood forming two casket shaped box halves.  The interfaces of the boxes coencieded with the leading and trailing edges of the blade.
   
   
3. The blade was enclosed in two sheets of plastic to provide a mold release agent. In effect, one sheet covered the complete opening of one box; the other covered the opening of the other box, with the blade sandwitched between. Care was taken to prevent the plastic from wrapping around the leading and trailing edges of the blade to allow blade removal after the concrete was poured and set.
   
   
4. Re-bar was used in each box in the concrete space outside of the blade to provide strength and to help prevent cracking of concrete when the mold is moved. Metal plates were inserted to form hinge supports.
   
   
5. The blade tip and root were oriented horizontally with the trailing edge down and the leading edge up. The box halves were locked together using studs and screws.
   
   
6. Concrete was poured down into the re-bar filled cavities from the top leading edge side forcing the plastic tight against the blade surfaces.
   
   
7. After setting, the screws were removed,the two halves seperated, plastic, and blade removed.
   
   
8. Two hinges and lift arms were installed. A winch was used to lift/rotate open the top half (1400 pounds).
   
   
9. Any bubbles or other imperfections in the concrete were filled with Bondo. Blade cavity on each half was waxed.
   
   
10. The mold is now ready to receive the plywood laminated core, foam resin, glass filled resin, and non-glass filled resin. After casting, the blade core is ready to be wrapped in multiple layers of fiberglass.

    
    
    

After reading the above, I realize that pictures will be needed to show the mold and the process for casting the blade. More later in a separate post.

Blessings and peace.

Bob

[fabricator]

Great posts Harold, my offset right now is somewhere 12-13 inches, I'm seriously considering changing it to 15 inches, my tail bracket angle is 20 degrees and

I'm seriously considering changing that to 13 or 14 degrees, it is easier to make a heavier tail or add weight than it is to make a super light weight tail.

I do have to admit though that I still do not understand exactly how the tail works if there is little wind behind the blades, it seems like offset would be more important to furling than the tail.

[HaroldCR]

Fabricator

 The 10KW Bergey has very little offset. I don't think I would change that measurement, if I were you. I also believe the pipe on a pipe furling, has enough friction, to cause that heavier tail to drag, in the beginning stages of furling. I plan to use 2 bolts as the hinge, or, a long pin, when I build my 16' mill.

  Where I got the idea of the vacuum or lift, causing the tail to swing and start furling, was, We had a Chevy Luv Pickup. The hood opened from the Windshield. The latching cable was broken, so, we just let the hood set on the rubber bumpers on the fenders.

  When we went down the road, at speed (+55 MPH), and a Semi trailer Rig went by, in the opposite direction, that hood would lift, sometimes as much as 12-15 inches off those bumpers. That's probably why you don't understand why it moves behind the blades. Also, 35 MPH or 15.7 m/s is the beginning furling wind speed. 120 MPH max wind speed design.

  The things I DO know, I learned by watching and experimenting. I'm more than happy to pass this stuff along. Just don't string me up if things go bad. heh heh

  I looked at the Bergey Site, but, did not find the photo I have in this brochure. ALSO, the whole machine is mounted maybe 8° tilted up on the rotor end. According to the photo specs. The Rotor Dia. is 7.0 meters or 23' long, so, you see, this machine DOES work well.

[windy]

Reading all of the comments make me wonder if increasing the offset may be what is causing this to happen. In a violent wind gust, the increased offset could give the wind more leverage to throw the blade downwind. Just a idea!

windy

[Flux]

You are right that the Bergey machine has little offset.It is a known fact that it only works with Bergeys blades. If you fit any other blades on a Bergey machine it will not furl.

There seems to be a lot of difference in this wind seeking effect with different blade design.

Hugh has machines working fine with 12" offset on a 16 ft rotor. Russell has 11.5" and under most conditions it works. I think it has become a noticeable fact that Dan's type blades need a bit more offset than Hugh's . I am inclined to think that for Dan's type blades you need about 13". This seems an awful lot but the evidence is there that anything less is risky.

Better to have too much than too little but then again it causes trouble keeping it in the wind if you have far too much. With the evidence available at present I don't think I would go up to 15". It would be very safe but with a normal tail you will have it running at 45deg or more to the wind below furling. I suspect many don't realise how badly these things track the wind anyway. Build one with RH furling and one with LH furling and mount them within viewing difference and you will be amazed at the tracking error.

Flux

[Ungrounded Lightning Rod]

Do what they did with cannons in the early days:  They were cast muzzle-up and longer than needed - then the extra length was cut off, taking the slag and voids with it.

You should be able to cast, say, hub-end-up with an extension (maybe with a notch) that can be cut off with a concrete saw to give you a clean end.

[Ungrounded Lightning Rod]

(Muzzle-up because pressure is highest in the chamber and lowest at the muzzle.  Cast it chamber-up and you end up with a spongy chamber and exploding cannon.)

[neilho]

Maybe I'm missing something here, but it seems to me that the furling was working properly but the tail didn't have enough moment to turn the rotor out of the wind. Increasing the moment might be one approach. Either increasing the tail area or lengthening the boom would be a way to test that surmise.

Neil

[Menelaos]

For my 13 footer that I am building these days, I was thinking about a simple mechanical way to stop the rotor when the tail is fully furled.
My idea is this:

On the back of the stator bracket, where the tail hits a peace of metal so that it cannot hit the blades when fully furled I want to install 3 small metal springs. Each spring is connected to one phase of the Alternator befor the lines go down the tower. on the tail I am planning to have a piece of stainless steel or Aluminium directly on that spot where the tail hits the springs.

Whe the tail is fully foldet, it will now automatically short the alternator. This way I see these advantages:

1. In case the tail should be fully furled but the prop still facing the wind like watched by some guys here the alternator would be shortet quickly. When the wind decreases and the tail swings back, the prop would start spinning again.

2. I will have a rope on the tail which goes down the tower to manually swing the tail to the side for whatever reasons to stop the turbine. When doing that, the alternator will be shorted as well and the prop could never start turning.

3. no sensitive sensors (for measuring wind speed or RPM) or microcontrolling is needed to activate the system. I am a friend of pure mechanical solutions as they are verry robust and reliable.

What do you think about this solution? Do you think it i practical or do you see any disadvantages?
The only disadvantage I can see is the possibility that on a stormy day the tail could be fully furled many times and thus the alternator would be shorted many times so one must make sure, that the wind speed at which the tail is fully furled and shorts the phases is not too high and thus the current is not too high when shorting.

Max

[Ungrounded Lightning Rod]

Maybe I'm missing something here, but it seems to me that the furling was working properly but the tail didn't have enough moment to turn the rotor out of the wind. Increasing the moment might be one approach. Either increasing the tail area or lengthening the boom would be a way to test that surmise.<p>
Neil

The tail doesn't turn the rotor out of the wind.  The offset of the rotor axis causes the rotor's drag forces to turn the rotor out of the wind.

The tail turns the rotor INTO the wind.  When it folds up it stops fighting the rotor's tendency to turn away from the wind - at least until the rotor gets turned around until the tail stop starts pushing the tail back out - after which the tail keeps the rotor from turning the rest of the way around to face downwind.

So if the rotor keeps facing the wind it's not a problem with the tail being too small.  It's something like the offset being too small (so the "wind seeking force" keeps the rotor pointed at the wind, the alternator load torque being too small (so the rotor overspeeds and the downwind forces on the rotor are reduced), or some other pathology (like a vertical component to the wind) keeping the rotor from being pushed away from windward.

[Ungrounded Lightning Rod]

1. In case the tail should be fully furled but the prop still facing the wind like watched by some guys here the alternator would be shortet quickly. When the wind decreases and the tail swings back, the prop would start spinning again.

Two problems here:

1)  If it's still facing the wind it's running overspeed.  Shorting it is a recipe for burnout, as it dumps the inertia of the rotor into the coils as heat, along with any additional energy collected while the rotor is still spinning.  If the alternator isn't strong enough to stall it out right away it keeps pulling more power and cooking the coils.

2)  Shorting it with contacts risks welding the contacts and holding the tail at that position.  If it doesn't turn away from the wind it cooks, as above.  If it ever does turn away it doesn't turn back until you climb the tower or pull it down and free the tail.  Wash and repeat.

2. I will have a rope on the tail which goes down the tower to manually swing the tail to the side for whatever reasons to stop the turbine. When doing that, the alternator will be shorted as well and the prop could never start turning.

You can do the same without the contacts but with a shorting switch at  the tower base.  This has the advantage that you can wait for the blades to spin down before you short it, or unshort it if it doesn't stop spinning.

[Hilltopgrange]

Shorting out to shut down is best done during a lull in the wind and not when the machine is at or close to its max power level. I always try to shut down before a storm hits! but sometimes they sneak in under the radar lol as happened here last week luckily I was at hand to shut down.
regards

Russell

[hayfarmer]

So if the rotor keeps facing the wind it's not a problem with the tail being too small.  It's something like the offset being too small (so the "wind seeking force" keeps the rotor pointed at the wind,

ungrounded lighting rod ,would a tail too small be the cause of the rotor  turning out of the wind at incision speed?
thanks hayfarmer

[Menelaos]

If it's still facing the wind it's running overspeed.  Shorting it is a recipe for burnout, as it dumps the inertia of the rotor into the coils as heat, along with any additional energy collected while the rotor is still spinning.  If the alternator isn't strong enough to stall it out right away it keeps pulling more power and cooking the coils.

I basically agree with that BUT...

...If the rotor is running on overspeed, it will due to centrifugal forces even more face the wind and if the wind is then strong enough for a longer period of time, burn out is definite as well, isn't it?
Also those centrifugal forces might lead to blades flying off the hub and causing serious damage wherever they fly!

Shorting the blades will result in verry high currents in the coils, I agree with that and I also agree that this causes a lot of heat but this will only happen for a verry short time, not more than a few seconds.

I have once shorted my 8 feet prop in a wind of more than 60 mph when I was really scared of my life standing on the bottom of the tower. When I used the stop switch, it took about 3 seconds to stop the bades from more than 700 RPM to nearly zero.
Wouldn't the alternator most likely produce a lot more heat running on a high load for a longer period of time than on 2 or 3 seconds of shoting the phases?
Once the blades have spun down to a certain RPM, heavy stall will help braking process as then the cp decreases to nearly noting, even more if the wind speed still increases.

Or am I wrong with those thoughts???

Of course, if the alternator is not strong eough to slow down the prop, we are in trouble and burnout is defenite but this should not be the case if the alternator is of appropriate size and resistance for the size of turbine.

Shorting it with contacts risks welding the contacts and holding the tail at that position.

Good point. I did think about that but didn't really consider that an issue to worry about if the dimensions of these contacts are choosen in the right size as this is what would also happen with a normal stop switch...right?
If I for example take my 13 footer with a line resistance of 0.7 Ohms I wouldn't like it to put out more than 2.5 - maximum 3 KW for short term. As it is wound for 48 V, 3 KW would be about 50 Amps maximum, but probably less if the machine furls correctly. Do you think that would really be enough to weld the contacts over that short period of time, especially as the current is split off between the phases?

Max

[Ungrounded Lightning Rod]

ungrounded lighting rod ,would a tail too small be the cause of the rotor  turning out of the wind at incision speed?

What's "incision speed"?

[hayfarmer]

     ungrounded lightning rod ,I intended to say at  peak performance speed  .picked up that term some where. I will google it and find out. still question is reworded"

would a tail too small be the cause of the rotor  turning out of the wind at cut in speed? thanks

well googled incision and it refers to surgery procedures and rate of soil erosion,thought I saw that used as a term of cut in speed some where.

thanks in advance. hay

[electronbaby]

I sat here and read this whole post. some good things were mentioned. There are so many things at play here, it cant be pinned down to the alternator offset, or the tail size, or the turbulence intensity or shear, or whatever, its all of the above and probably a few others.

One thing I would try (in addition to Flux's recommendations) is try to lengthen the tail boom.  really try and get that tail out from behind the wash of that rotor. At high tip speeds, and with the prop pointing into the wind, there is more wind going around that turbine than through it. maybe thats interfering with the ability to furl properly at high wind speeds. Its hard to say...things happen so quickly and violently in gusty conditions.

I have never had any of these issues with my machines. Ive flown 16' as well.

hope you work it out


RoyR

[electronbaby]

Just throwing this out there.

A possible explanation for seeking force:   When a prop is spinning at a high RPM and a side furling turbine furls, to lets say a 75% reduction in swept area. There is still some swept area left exposed. It still will not let all the wind pass by and some portion of the wind will pile up, even though the majority goes by. This in essence will cause a bulge or a build up of wind in front of the prop and will  change the incoming angle of wind deflecting off the turned rotor. Could this cause there to be lift on the entire spinning disc as a whole?? and bring it back into the wind?  This will cause turbulence behind the rotor as well, possibly causing the tail to be sucked up into the furled position, even when the machine is not furled.

This theory only makes sense (to me at least) when the prop is at a high RPM.




RoyR

[walp]

Oh my.. never realized this was that big of a problem for you PMG folks.

I have a window curtain motor control with solar and wind sensors.... might build something cool out of that to prevent armageddon from happening..

But then again, I dont know if us induction motors freaks have anything to fear from slight overspeed... As far as I´ve heard, the magnetic field will collapse when taking out to much load and if not, the 10A automatic circuit breakers will go bananas above 2.5kW which is 200% of calculated generator spec. leaving the blades to it's own destiny, which brings me back on topic:

At what point will some generic tree blades eventually certainly break?

We have been hit by 70 mph winds before, but that was before the tower was erected.
If the furling mechanism fails (I have some concerns about that now cause our blades are really heavy and probably will be full of gyroscopic forces), will that totally kill the blades?

But just as Menelaos said, we also have a rope tied to the tail boom which currently acts as the only mechanical break in the advent of a big storm... (KISS)

[freejuice]

Russell,
 I read your post, and scanned through a bit more.
More offset and maybe a bit to light on tail weight and or extend it?
 All the best,
 Gavn

[Hilltopgrange]

If you read to the end I did find the fault that caused the failure to furl, it was the the yaw tube and bush had seized on the stub mast. When I dropped the tower to rebuild the stator I had to use a sledge to get the yaw tube off the tower it was this that stopped it turning out of the wind.

Since fixing the problem it hasn't failed since, having said that I now always shut down before a storm as I don't trust it. I have had problems before with furling on smaller machines at this site. I must stress though that I do get a LOT of extreme winds I probably get more wind in a week than most folks would see in a year, some of the gusts are very vicious. These high wind events can go on for days at a time. I think any machine would struggle with these conditions.

You would think living in a high wind area is good but to be honest it is a curse to deal with.

Russell

[Ungrounded Lightning Rod]

     ungrounded lightning rod ,I intended to say at  peak performance speed  .picked up that term some where. I will google it and find out. still question is reworded"

would a tail too small be the cause of the rotor  turning out of the wind at cut in speed? thanks

well googled incision and it refers to surgery procedures and rate of soil erosion,thought I saw that used as a term of cut in speed some where.

Sounds like some automated language translator didn't understand engineering vs. medical context and turned "cut in" into "incision".  ROFL!

(Reminds me of an early English-German engineering paper translation program.  It did a surprisingly readable job except that it kept coming up with "Water Goat".  Going back to the original revealed that it was trying to translate "Hydraulic Ram".  B-)

= = = =

Regarding turning out of the wind a tad at cutin:  It's different depending on whether you have an UNfurled stop on the tail or not.  Better with the stop.

With the stop the tail normally flies a tad outward from due-leeward, providing a force offsetting the furling force on the blades.  If the forces on the tail and the forces on the rotor went up equally with wind speed this configuration would hold the same angle to the wind from nearly-calm to the point where the wind is high enough to lift the tail off the stop and start the furling process.  (After that it flies with the turbine progressively further from the wind with higher wind speed - at least until the tail is solidly at the "furled" stop.)

However a big component of the air resistance of the blades is the drag from the load of the alternator.  In a charging application this is zero up to cutin, then rises abruptly, and is approximately linear with RPM after that.  So it varies differently with wind speed than the restoring force on the tail.  This makes the equilibrium angle change somewhat and the change is most pronounced at cutin.

It's not a big deal for generation, because the reduction of the wind speed through the blades goes with the cosine of the error angle.  The cosine function is nearly flat in the region near zero degrees.  You don't get a 1% reduction until about 8 degrees, 5% about 18 degrees, 10% about 25 degrees.  So just optimize your aim for somewhere near the low end of your typical winds and don't sweat it.

If you don't have the unfurled stop, all the restoring force comes from the tail's weight working against the pivot, making the tail angle vary with the restoring force and the wind.  This makes for a bunch of variation as the wind speed and load drag vary.  Thanks to the nice properties of the cosine function it's still not a big hit to performance.  But it's less optimal and harder to precalculate than the case with the unfurled stop.

The unfurled stop also makes the mill more responsive to changes in wind direction that require a yaw in the furling direction.  This can be handy if they are the result of an added gust:  Failure to yaw to meet it quickly would slow furling to protect the mill from the increased windspeed.

[Ungrounded Lightning Rod]

If it's still facing the wind it's running overspeed.  Shorting it is a recipe for burnout, as it dumps the inertia of the rotor into the coils as heat, along with any additional energy collected while the rotor is still spinning.  If the alternator isn't strong enough to stall it out right away it keeps pulling more power and cooking the coils.

I basically agree with that BUT...

Hi, Max.  I intend to respond but don't have the time to do it properly right now.  Cheers!

[Menelaos]

Ok, I can wait ;-)

In the mean time I was thinking about the problem of a fully furled wind facing machine again. Even though teh solution was found in this case and seemd to be mechanical, there are plenty folks who have watched this happen.

I have another option that might have some influence...no it defeitively has some Influence, the question is just if it is big enough to be noticed or not... :
It seems this effect happens mostly when the prop is spinning very fast and thus centrifugak forces of the blades are verry big.

Try this experiment:

Take a wheel from a pedal bike and hold it in your hands with the axle parallel to the ground. Make it spin fast and sit down on an office chair (those with wheels). Everything is under controll unless u now try to "spin" the chair and turn it around. You will not be able to hold the bike wheel straight up anymore as there are enormous forces pushing it to the side.

Now imagine our earth to be that chair and I guess you now know what I am up to...

If the Hub of the prop shows directly north or south, everythings works fine but when it shows east or west, there will always be a force trying to make it show north or south and this effect is not directly linked to the rotor speed but to the centrifugal forces of the blades which of course are the higher the faster the prop spins.

So when the prop turns out of the wind, there will be a lot of force on the hub, a lot more than we might thing depending on the direction in which the turbine shows....

maybe there is some kind of influence....maybe, if the direction of the wind changes quickly in a gust and the tail moves up and furles, the prop is just too slowly moving around, partly also because of the efect I just discribed....

This should be worse, the mor diameter the prop has so that furling at some point just cannot work properly anymore...

Am I pverestimating this or would you consider this to be a "relevant" factor?

Anyway this is the principle how the gyro compass on ships work as they contain verry fast spinning disks that aline withe the earth axle.

This also means that the effect would be of different strenghts, depending on how far noth or east of the equatot you are located.

Max

[niall2]

hi Menelaos

i,ve wondered about this effect as well....i think others have posted about this a long time back
as far as i can tell the bike wheel and chair experiment depends on adding another another field of axis
i.e. your hands allow the wheel to travel vertical ...or downward ...this i think brings in the gyro (or precession effect)
if your hands could lock the wheel the precession wouldnt be there ....erm...ish....i think  

tilt up furling mills seem to have issue with this effect  ..it depends on the direction of rotation ,some have offset in the tail to get around this , a survivor mill is
i think a good example of how to get around the problem



 pic  provided by allen


i did see the gyro rotation effect in a tilt up furl machine i tried based on some previous posts on the forum .... others  gratefully pointed out my versions  inherit flaw.....  



mine was just a big gyroscope pretending to be a mill.........but i,d defiantly agree , it interesting to think about ....


 

[jlt]

The survivor mill has a good track record.I think that i will try to come up with a design  like it for a large truck alternator i converted to permanent magnet alt. I haven't seen many home built designs .   

[scoraigwind]

The survivor mill has a good track record.I think that i will try to come up with a design  like it for a large truck alternator i converted to permanent magnet alt. I haven't seen many home built designs .   

I have/had one of those.  It flew off the tower top! 

To be honest it did work for a few years but ran very fast and noisy.  Also the blade plate suffered fatigue due to bending.  But yes that furling system does just about work, so long as the wind doesn't get too strong.  It get's harder and harder to lift the weight up.

[SparWeb]

So when the prop turns out of the wind, there will be a lot of force on the hub, a lot more than we might thing depending on the direction in which the turbine shows....
...
Am I pverestimating this or would you consider this to be a "relevant" factor?
Max

Actually, I bet people tend to underestimate this, not overestimate.
Not a lot of home-builders pay much attention to the mass of their blades and rotor, however with increasing mass that inertia becomes greater, too.

You're describing a gyroscope, and if you're keen on engineering math, you could estimate the angular momentum of your own turbine and then calculate the torque it puts on your tower when it yaws.  You have to make some assumptions, not difficult ones, though.  I've found that it is possible for the pitching moment on my 8-foot turbine to be many hundreds of newton-meters!  I factor these things into my tower loads - though I notice nobody else does...

Niall,
Was it you who, a few years ago, watched your turbine do a "walk around the block" in a storm?