There is a lot of discussion here somewhere about loading with two machines but like you I wouldn't be able to find it. The idea will work up to a point. If you wind one section to load normally up to a certain wind speed you can bring the second stage in and hold things down to higher wind speeds. You would need to make the second alternator stage very powerful to be able to hold it to much higher wind speeds and you would never be able to make anything much bigger than 8ft work in this mode without furling.
The second stage has to be very powerful and efficient to effectively clamp the blades to constant speed so you are working in blade stall. Choosing the correct blade profile for stall operation like the early grid machines with induction generators did would help.
The whole thing is wasteful of copper and magnet and in the end it is better to use one winding with the extra magnets and copper arranged in a different way but you then have to have some control scheme that keeps you from stalling in the normal working wind speeds. To do what you propose you would have to use about 1/3 of your alternator for normal working and the other 2/3 just for stall operation in high winds. Not an efficient use of materials at any wind speed but certainly you would be able to raise furling speed to perhaps 40 mph if you got it right.
Second point, any 10 ft prop making helicopter noises at 150 rpm has serious problems. I suspect you are way off with your speed predictions. If you managed to rewind your stator with 2 in hand wire when the original specified single I can't believe you have kept the same number of turns. If you have got the winding in the same space then I suspect you have halved the number of turns. One turn will be a complete loop of 2 wires and you can't have got twice as much wire in there. If you have got this extra wire in with turns as you describe you will have to have increased stator thickness to near double and the increased magnet spacing will have lowered the flux and what I mention below about cut in speed will still apply.
If this is the case you will have doubled the cut in speed. The thing will perform very much better in high winds but the prop will run faster and be noisy. You will need to take more care with trailing edges and blade tips if you want to keep noise reasonable at higher speeds. I would expect a 10ft prop to start reaching helicopter type noises somewhere above 500rpm depending on the actual blade construction.
If you really have these noises above 150 rpm I suspect you have got your drop figures confused and the pitch angle is way too high.Or your trailing edges are over 1/8" thick.
Flux