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Question for Nando
By Goose, Section Wind Posted on Mon Feb 19, 2007 at 01:44:58 AM MST
explain the variable pitch hub??

Or anybody else that can explain how the variable pitch hub works in Nando's .pdf link
http://www.martinslade.freeserve.co.uk/Prototype%2010Kw%20Wind%20turbine.pdf
It almost looks to be a downwind design. Or does it spin CCW? I'm having a hard time grasping how it works.
Thanks

Question for Nando | 8 comments (8 topical)

Re: Question for Nando (3.00 / 0) (#1)
by Nando on Sun Feb 18, 2007 at 10:07:55 PM MST

Instead of me answering this question, I have sent the message to Simon To see if he is around and answer your question "from the Horse mouth".

Nando

Re: Question for Nando (3.00 / 0) (#2)
by Goose on Mon Feb 19, 2007 at 07:21:30 AM MST

Thanks
Goose
[ Parent ]

Re: Question for Nando (3.00 / 0) (#3)
by simonbrookes on Wed Feb 21, 2007 at 04:58:42 AM MST

Hi. I have been out of the country for some time so could not respond. I am no expert at all but enjoy making thing. I have had a turbine heating water for a few years and Nando has helped me get it working. I get an adequate power for what I want in heating. I am in an exposed location and some times I have a problem in the water system or electrics and the turbine runs away so unless I am here to shut it down on the brake it could do damage to it's self. So when I came across a drawing of a simple hub I thought I would give it a go and if it did not work well it would be fun building it. I have only had the turbine up with this hub for 3 weeks and I have been away for 2 of them. We have also had light wind since then so I have not seen it working or not as the case may be. From your comment it seems that I may have made another mistake. The turbine is an up wind and does rotate CW. If the weights and pivot are on the wrong side then all I need to do is move them. Any comment of what to do would be gratefully accepted. i.e. which way the blades have to turn, which side the weight has to be on etc.
Thanks Simon

[ Parent ]

Re: Question for Nando (3.00 / 0) (#4)
by Flux on Wed Feb 21, 2007 at 08:53:33 AM MST

For an upwind machine the safest way is to pitch to feather but this will need the blades to turn through a large angle, probably 45 deg or more to hold things on no load in a high wind.

If you pitch to stall you manage with a fairly small blade rotation but you leave the blades broadside on, developing high thrust in a storm. Several attempts at pitch to stall with up wind machines have resulted in blades striking the tower.

Pitch to feather requires the blades to rotate to increase pitch so that you are heading to the position with blades edge on to the wind with leading edges forwards.

With passive pitch you will never get that far, as long as you have enough angle to hold speed in a high wind with no load then that is good enough.

Turning through a large angle with linkages to keep blades synchronised is a challenge.

Flux

[ Parent ]

Re: Question for Nando (3.00 / 0) (#5)
by simonbrookes on Wed Feb 21, 2007 at 11:20:57 AM MST

Just to get this right when you say "Pitch to feather" you mean to reduce the speed and power the leading edge must turn into the wind. i.e. the leading edge turns away from the tower and tailing edge towards the tower in my up wind turbine.

[ Parent ]

Re: Question for Nando (3.00 / 0) (#6)
by Flux on Wed Feb 21, 2007 at 11:53:18 AM MST

correct.
Flux

[ Parent ]

Re: Question for Nando (3.00 / 0) (#7)
by simonbrookes on Wed Feb 21, 2007 at 12:04:55 PM MST

Thanks. All I have to do is rotate the root holder and do a few small changes and I will see what happens at higher wind speed.

[ Parent ]

Re: Question for Nando (3.00 / 0) (#8)
by Seaspray0 on Sat Mar 03, 2007 at 01:33:59 PM MST

The force against the blade is not on the same axis as the shaft mounted to the hub. Look at the hub. The shaft is well forward to the leading edge of the blade. This creates a torque on that shaft which would cause the blade to turn into the wind. A control cam is attached to each shaft with a pin on it. A spring pushes the plate which pushes against the pins, which provides the effort needed to counteract the torque of the wind on the blades. Adjustable bolts act as stops to keep all 3 blades in position until the torque is high enough to overcome the effort of the spring (it looks as if the spring compression can also be adjusted as well by the picture). When the blades begin to rotate, the pins on the cams will push the plate forcing the spring to compress even more. From what I see, if you let the blades rotate far enough, the cams will eventually aligning perpendicular to the plate surface where the spring plate will no longer be able to push the blades back into position (essentially, if you let the blades rotate far enough, they will lock into a feathered position). I suspect redesigning the cam shape and letting it ride directly on the plate, rather than using pins, would allow it to provide a better method of controlling the counter-torque in controlling the blade pitch.

Question for Nando | 8 comments (8 topical)

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