Not to mention cyclic fatigue and any funny harmonics from the blades with the longer moment arm. Those calculations are beyond me..the true test would be running to see what happens.
I can appreciate your questions. But, trust me, the shaft will be fine. I've run this stuff in a lot more severe duty applications than wind turbines. 4140 CRMO is used to make crankshafts, camshafts, agricultural equipment shafts, gearbox shafts, axle shafts, and in my case, turbine shafts. The forged bar stock that I get to build new combine shafts and whatnot where a bearing failed and chewed the shaft up or similar is stress relieved and it will take billions of torsional vibration and deflection cycles without failure. Steven tried to compare it with his electric motor shafts and there is no comparison.
I got 4140 hex shaft material that I use to build new rock trap and feeder house shafts in combines and that stuff will wear wear where it drives a rock trap beater or rear feeder house sprocket on the hexes. But I've yet to ever break one. I'll venture a bet that my turbine shaft is heavier than than your axle shafts in the rear end of you compact pickup truck (assuming you drive one) and it's the same material. So if you're really worried about my turbine shaft, then you'd better not hit any pot holes with your compact pickup.
Let's leave at this on this shaft ordeal - I'll be the first to post photos of my broken turbine shaft. But don't hold your breath waiting for them.
There is an OEM that I saw at one of the Windpower shows with a 10-20 kW scale machine that has this exact same arrangement with the prop out front. It was built like a tank and they've installed dozens. They said there are certainly advantages to putting the alternator so close to the yaw and balancing it with the prop on the other side of the tower. They were using a very large axial flux on that thing and using the casting as a huge heat sink (which got plenty of cooling wind because it was away from the prop slipstream).
I think I got the tail thing figured out on this turbine now. We just had a t-storm cell go thru and I didn't get the winds I was expecting to test it. But it did furl all the way and topped out at about 25 amps. My cheapie anemometer recorded a peak wind gust of only 33 mph but it appeared to work OK. I might have to think about it for a bit because the way I got it set up now, it furls pretty sudden like and looks like it slams the tail against the stop pretty good. A bit more progressive, but not as much as I had it before, will probably be better.
So it's drop the tower, change the angle of the spring bracket again to make it more progressive, and hope for another storm cell to see if it works. When I finally arrive at the right angle on the thing, then I can make a permanent bracket and weld it on there.
I built one other turbine once that had a rear mount generator on it. This is a photo of the thing:
That turbine would not steer. It could be running and then a side gust hit it that would fold the tail right up and it would very slowly turn and swing back into the wind. But the generator on that one was really heavy - the gen alone weighed over 50 lbs - it only had 5" of offset, and the generator hung out the back too far. This new one I built seems to steer really nice and I paid attention to getting the generator up as close to the yaw shaft as it would fit. Plus this one has 10" x 1/4" rotors in it instead of 14" x 3/8". You get two chunks of 3/8" steel whirling at 500 rpm and you got two 14" diameter flywheels hanging on there.
So I'm pleased with this "quickie turbine" that I built. If it stays below 30 amps in really strong winds now, and I can figure out an arrangement to dampen the tail a bit, I think she's going to work.
--
Chris
