sirus,
I assumed that you were either joking with us, or that you had some really ambitious hydro application and just inadvertently to posted on the wind section. Anyway, here's my opinion:
If you are serious, I would encourage you to stop now, and do some research; here and thru other means (books, other sites). This is way, way too big for anything practical for wind - short of near utility scale.
Consider that with a 6' diameter prop you'd be doing very well to get 400 watts at 20 mph, and the theoretical limit at that windspeed is only about 650 watts, or .65 kW. At 400 hp, if you could drive this thing, you are up in the 300 kW range. You're looking at three orders of magnitude (1,000x) larger than what you can practically do. Beyond that, this thing is way too heavy to consider putting in the air, even on a silo, without significant engineering. Please be safe.
~ks