Constant Chord Constant Pitch

[klsmurf]

Hi All,
Last Sunday I had an urge to make a new set of blades for my hobby mill. I normally run PVC blades on it as it has no furling. The PVC will spin up nicely, depending on the length, and then stall in higher winds, thus somewhat protecting the mill from burnout.

This time I thought I’d try a set of constant chord, constant pitch wood blades. I looked in my scrap pile of wood. Not much there of any thickness, so I decided to experiment.

I found 3 pieces of very dry cedar 1x4's. Did some lay-out and got to planing. The boards were not choice, but in about an hour I came up with these.


Since I used the face of the 1x4, I had to make some wedges to pitch the blades. I chose 10* as a starting point.



Over the next couple evenings I was able to get everything drilled, balanced, sanded and mounted. The weather was going to cooperate, so I decided to test run them unfinished.


I am real pleased with how the blades did. The mill was up for 2 days, seeing winds from 7-15 mph during the sunlight hours. The rotor is 6 ft. (too much for my mount), and it hit 900 rpm in a 20+ mph gust. The start-up was 6-7 mph and cut in was 8-9 mph. I've got some options to consider now.
Some help now please.
1) If I cut the diameter down a few inches I should get higher speed, but what effect would this have on my cut in?
2) What effect should I see if I keep the length, but change the angle from 10 to 7*

[bj]

   They turned out pretty nice.   I'm no blade expert, except on how to do the wrong things, but I would go with
the angle change first.  If for no other reason than if you cut them off, it's pretty hard to put it back on.  But
you can experiment with the angle 'til the cows come home.
   Just how I see it.   Good luck, either way.

[A of J]

Firstly they are good looking blades, I too did as you did with no regrets, you say the diameter is too large for your mount, do you mean tower?

You would have to supply more information on your tower & generator before anybody can post a meaningful reply.

Allan

[klsmurf]

Thanks for the replies guys.

bj...
I was planning to mess with the angle first. I don't have one of those "board stretchers" in my work trailer.

A of J...
My mill is just a DC motor. I call it a 200W mill. There is no nameplate, but was told it was rated at 14A, 150V and 2000rpm. I run it on a 12V system. I've seen a couple peaks at about 300W. The tower is a tilt-able, Rohn 25g antenna tower at 40 ft. with 1 set of guys at the top. I should have been more specific than "mount". My main concern is actually my wimpy mast stub. I have pipe to upgrade that, but if I proceed with these blades, (rather than using PVC) I need to redo the whole mount and include furling capabilities.