"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."
I actually would rather choose FORWARD pitching for numerous reasons as Flux and others have said. I've seen numerous commercial mills pitch forward, so it must have advantages. -Hope your design works out well!
I was sorta thinking that a coarse 25 degree angle would help in start-offs and 'take-offs'. (getting to the point of cut-in)
But now I see that starting at 4 or 5 degree (blades almost straight up and down) as the other's say would allow the prop to 'coast' (keep spinning a decent rpm) very well when the small wind breezes go down to almost nothing. Which is what you want for low wind performance.
I did not know that at zero degrees the blades can keep going. That is good to know.
So the backward pitching goes from the 'normal set starting point' of 4 or 5 degrees to, say, NEGETIVE 5 degrees to basically 'air brake' when a big wind gust comes.
I am thinking of trying to do this for my small 6 footer. (but at a 700rpm or so since it is small)
- I had one small observation though--
I could be wrong, but I was looking at where the blade pitch axis is on his blades (up near the top upper side of each blade), and it seems to me that that placement would be more suitable for blades that pitch to feather forward. Could that axis placement actually counter resist pitching backwards?? I would've probably put the pitch axis a little BELOW the center of the blade to pitch backwards easier. (maybe I'm looking at it backwards?/ It turns Counterclockwise right?)
[ Parent ]
It even gets more "fun" when you discover terms like apparent wind. Suddenly your pitch isn't really relative to the true wind. And its constantly changing.
In order to get a grip on prop pitch I had to think in terms of screw threads. a fine pitch takes more turns on a screw to go into the material than a coarse pitch. The wind being the "material" a prop screws through. Finer pitch on prop [more flat] lets it rotate more times and faster for a given "length" of wind.
Not very refined but helps keep it strate for me.
Tom
"Education consists mainly of what we have unlearned."--Mark Twain[ Parent ]
Thx
Rob[ Parent ]