wind turbine question

[damoc]

hi and thanks to all the people from otherpower for all the imformation

and inspiration they have given me.

i have only a little bit of expierience with home brew wind power

3 different turbines so far nothing that has produced more than 100 watts

peak.

i am working on a 16 foot wood laminate turbine running automotive

alternators i understand the problems and limitations with  auto

alternators and have read the faq section but its what i want to do.

the questions i have are

1 what is the main advantage of a 3 prop designe as opposed to a more simple

and stronger two prop is it balancing or low wind start up?

i have already started the two prop designe but am now starting to

second guess myself.

2 how does the designe from hugh piggot and otherpower prevent twisting

of the cable down to the bottom of tower and batteries.

i fitted a "lock bolt" to the tower which prevented 360 degree movement

so the cable did not twist but it would often "jam" in a position which

did not allow the turbine to turn into the wind and hence produce power.

thanks in advance for any help

don

[Flux]

I hope you are not trying to hang a 16ft prop on the spindle of an automotive alternator. OK if you are using gearing and a decent shaft.

Two blade props are fine if you have some means of steering them into the wind very slowly. During yaw they produce a vibration and a rapidly yawing 16ft machine with a tail will cause a lot of undesirable forces on the machine. Things are not too bad up to about 8ft but beyond that I would keep well away from 2 blades. There is no real difference in running performance with 2 or 3 blades but the shudder during yaw is absent on the 3 blade prop. Unless you have some form of steering other than a tail best to avoid 2 blades.

With the exception of a very few strange sites the cable doesn't twist up much. You may have to unwind it every few months or years depending on the site. With a good drop it can tolerate many turns and there are not many sites where you don't have plenty of time and warning to untwist it. Many use a plug and socket at the bottom of the tower to save having to rotate the yaw head to untwist it.

Don't fit a physical stop as you suggest, if you rely on any form of furling you have a recipe for disaster as it will fail to control when it hits the stop.

Flux

[wpowokal]

If I may add a little info to Flux's answer, the shudder occurs when the blades are in the horizontal plane and the machine try's to chase the wind, ie move from side to side (yaw).

In 3 blade machines 2 are never in the horizontal plane.

So take an angle grinder in your hands turn it on and try to twist it from side to side, it resists, same forces apply to a two blade turbine.

allan down under

[damoc]

thanks for your help .the 16 foot will be fixed in position on a

freestanding tower because i have a decent prevailing wind through the summer and building a yaw mechanism on to it was a little to intimidating.

[electronbaby]

If you will have the machine in a fixed, prevailing wind direction, why did you ask about the things you did? If its in a fixed orientation, then two blade approach (presuming upwind) would be fine. If the machine does not yaw, the no need to worry about your feed line getting twisted.

If its in a fixed position, your main bearings will take a beating during all other times of the year when the wind wanders off of its prevailing direction, as the prop will be unevenly loaded. This is especially true the larger prop diameter you go, and amplified by turbulent wind found close to the ground if the tower is short.

[TomW]

Roy;

I suspect he has a misconception / confusion here between furling and yawing.

One is to track the wind the other is to protect the turbine by offsetting the prop from the wind, as I am certain you know.

He sure seems confused with his added comments completely contrary to his initially stated needs.

Another case of the facts seeming to change as the helpers try to help?

Or not?

As usually is the case, the devil is in the details.

Tom

[damoc]

questions were for 2 different turbines and towers one tower is running a small home brew turbine already but is only producing about 100 watts and has no furling

/safety built in i want to replace the turbine with one of the otherpower turbines

this april.

the 16 foot to be finished turbine is only going to be on a 20 foot tower

so it will be susceptable to ground disturbance but i only realy need this

turbine working 2 to 3 days a month for electrical/water pumping to a pond

and storage tanks so i am not as concerned with efficiency as long as it does

a good job on an intermitant basis

[damoc]

just wanted to add  i plan to mount the 16 foot on a light truck differential

and use the brakes as a braking device during times of wrong direction or unneeded

wind.

thanks for all your help you answered all my questions.

don

[wooferhound]

Another note about the difference between 2 and 3 bladed props...

 2 blades will spin faster than 3 blade props in the same wind. More blades equals slower spin rate.