Hi Guys
I have finally got to the stage of carving blades and am a little confused. I have an alternater very similar to the old Otherpower 10 footers with 24 2" x 1/2" magnets, 9 coils with 60 turns and I am getting a cutin rpm of around 150 for 24V in Star. If I need to increase the cutin speed I will either widen the air gap or make another stator with a couple fewer turns as I may need to remake it anyway. More details are in my Diary
My question is this
I have bought some timber (just cheap softwood for £20) which is 1800mm (5'11") long x 220mm (8 5/8") wide by 45mm (1 3/4") thick
How wide should I make it at the tip and how far out from the centre should I start the taper?
If I follow the blade plans in Hugh Piggots book "How to Build a Wind Turbine" it would be 100mm (4") at the tip whereas in the blade theory page at Otherpower the tips (for a 3600mm, 10 foot blade) are 75mm (3") which I guess would be 90mm (3.5") for 3600mm (11'10") diameter blade. I know 1/2 an inch isn't much but it is near enough 22% of the width at the tip (I think) which makes it sound a lot more when looked at like that.
The second point probably makes more of a difference. Where to start the cut? In Hugh Piggots book the cut starts 600mm (24") from the centre whereas The Otherpower blades start at 300mm (12") for a 3600mm, 10 foot blade so I guess that would be 365mm (14.4"). Or could it remain at 300mm (12")?
It seems to me that the Hugh Piggot blades are wider and heavier with a higher drag and therefore slower which means a lower TSR. Is that correct? He says in the book they have a TSR of 6. Did I read somewhere that the DanB blades have a TSR of 7?
If everything I have said above is correct then I have finally hammered into my brain what TSR really means and how to change it. If not could someone please try to explain it again.
I want my turbine to be on the safe side of ideal as I have seen blades spinning very fast and it was a scary sight, so should I make it more like Hughs or more like Dans?
Or will it really matter?
Many thanks
AliBro