It is my understanding that with variable pitch blades you can design it to go EITHER direction with the pitching. You can pitch forward ,or like you did, you can pitch the blades backward all the way to straight up and down which is what I always called zero degrees like you do. It seems to me it would be easier to design the pitching to go back like yours does instead of forward, BUT Flux and others have told me in the past that pitching Forward is more reliable for controlling in high winds and less 'Tower loading'. (Stress on the pole/tower)
However, to be honest, I worry about the 'stiction' problem pitching forward. It Seems to me it would be MUCH less of a problem pitching backward. But I could be wrong.
Perhaps you could start at less of an agressive angle-- like perhaps 25 degrees. It just makes me wonder if it isn't getting somewhat stuck at 45 degrees or so in very low wind, and it can't turn fast enough to begin to furl back (pitch) toward the steeper angles to really get going???
Can you tell us if you used the common method with 'Arm Weights' in order to pitch the blades using gravity as the rpm increases,, or did you use something different like your 'slide mechanism pitching'? Can you quess what the fastest rpm it has acheived so far in the winds??
I was also wondering: Did you purposely WANT to make a big, slower (visually 'controlled and safe looking')mill? And is this why you chose to make the variable pitch control blades? Or did you do this because you thought it would make more power in lower winds? Was it simply "Looks"? It makes me curious as to why you chose this design and method of control.
- Very good work. Thanks for showing us your progress with pictures. -Sorry for so many questions. It is just very interesting to me.
Yes i built it to be a slow machine,..I use to live in palm springs Ca. and we have huge windfarms...they all turned very slow and slow = less vibration, noise, damage etc. at least thats my 2 cents...
as far as variable pitch ive had that idea for more than 10 years maybe finally i can get it to work....its a very simple design using the blades as counter weights with centrifugal force, im trying to make it as failsafe as possible...
i made a model its here in the board somewhere its exactly how i made the mill,...but its kinda fun testing this thing out it has its flaws but this is just a prototype thats why the blades are just flat plywood, the nice fiberglass blades come later when i get some more info on what is needed maybe tapered for more speed like flux and tom w have mentioned...its a work in progress....
as far as pitching what ill probably end up doing is have it start at 5 degrees and as it speeds up, have the pitch go to 0 placing the bottom of the blades into the wind (which is more stress on the tower and blades) right now they pitch from about 5 degrees and as they go faster the pitch increases,...(less stress on the tower and blades) it's all trial and error now...
Thx
Rob[ Parent ]
Those commercial machines are likely to be faster than this, but because of the large diameter the rotational speed will be low.
Going much lower than tsr5 makes the alternator big and costly and the blade solidity rises rapidly and stress may not fall much.
If you pitch to stall I doubt that going to 0 will be sufficient unless you have a large stalling load from the alternator. Most blades will run well at 0 but may not start well. I suspect you may need to go negative, but the angular movement is way less than pitching to feather.
Flux[ Parent ]
Well theres some more pics...it's binding a little where the nut presses onto the spring,...i think i may need a bearing there but lets see how this works, after re adjusting and greasing everything the pitch bounced back pretty well, the good thing about using threaded rod is that i can reverse the blades very easy, gonna make some lighter airfoiled blades next after i see how it behaves,....what kinda taper would you guys recommend?
I wanted to stay with straight angles so i was thinkin maybe at 1/3 the way down taper to 6".....
Rob [ Parent ]
