I made a calculation error in my previous post that I would like to correct before some sharp-eyed bugger nails me.
As I stated, the rotor diameter of this 5kw wind turbine is 5 meters (16.4 ft). And its side offset from the yaw axis is 3 1/4 inches (.271 feet). The ratio of yaw axis offset to rotor diameter is correctly calculated as 0.0165 (1.65%), rather than 0.198 as previously stated. That is about a third of the amount of offset used on the Otherpower machines.
Quoting from Flux's post:
"I strongly suspect that this is satisfactory for high wind performance but instinct tells me that once it furls it just about shuts down until the wind drops (bistable)."
The company's website is:
http://www.exmork.com/5kw-wind-turbine.htm
and it contains a curve of power vs. wind speed for this machine. The rated power of 5kw occurs at a wind speed of 10 meters/sec (22 mph), but as the wind speed increases the curve indicates that the power continues to increase up to where it reaches a maximum of 6000 watts at a wind speed of about 13 meters/sec (28.6 mph) Then the power gradually and smoothly decreases until it is less than 4000 watts at 17 meters/sec (37.4 mph), which is where the graph stops. Survival wind speed is listed as 50 meters/sec (110 mph). No signs of bistable operation there.
Of course, brochures and website claims are one thing, real world performance is another. This machine is presently resting in my workshop instead of at the top of a tower, but I hope to have it flying in a few months. Too muddy here to pour cement right now.
And Dan, by now you must be thinking that I have stolen you're thread, but hopefully what I'm about to say will convince you that I haven't. I just wanted to get Flux's comments first. All of the foregoing discussion is related to your post. I know that you are looking at alternate designs, such as bringing the alternator down the tower, etc.
There was a recent post by Hilltopgrange in which he described how his 16 footer apparently failed to furl during a storm. It appears at:
http://www.fieldlines.com/story/2010/1/21/16166/2676
In Hilltopgrange's post, he, I, and everybody else that submitted responses were extremely and totally confused about what was going on and how this could possibly happen. Total confusion. Then Hugh Piggott chimed in and cleared up the confusion.
Hugh figured it out that Hilltopgrange's 16 footer was running downwind, with the fully furled tail slammed hard against its upper stop, and held there by the wind. And it would have done that no matter how big the offset was, and no matter how light the tail.
From that day forward, I knew that I never wanted a large wind turbine with a tail boom that folds up against a hard stop. On the 5 kw machine I was talking to Flux about, the tail boom is rigidly bolted to the alternator, not hinged. That machine could never run down wind, a condition that would be extremely unstable for it. It is my hope that that discussion, along with Hilltopgrange's post, will steer your research in a new direction.
If I were going to go into a big R&D (research and development) program, as you are, that is the direction I would go. Fixed tail boom, do something with the tail feather to provide the yaw moment.
Just my two cents.
poco