Hi Guys we have had some strong winds lately with 50-70mph gusts. I normally shut my turbines down before a storm hits rather than risk damage. This morning at 4.30am the alarm on my weather station alerted me to high winds, I got up from my nice snug bed and trudged down to the workshop in the lashing rain and shut the turbines down.
Well to the point, this afternoon it calmed down a bit so I started up the 16 footer within 20 minutes there was a sudden heavy gust of 53mph and the current jumped to 96 amps almost 5kw way to much, I ran to the window and was able to see the blades where pointing straight into the wind with the tail completely folded to the furled position. The blades stayed into the wind for about 2 minutes until the gust passed and then as the wind dropped it yawed out of the wind. I was then able to shut it down and go and change my trousers, That 2 minutes felt more like a lifetime!
so I think it is safe to say that it failed to furl, I think it has survived but only just.
I have previously watched it many times furl 90 deg to the wind at about 25-30 mph, I have a streamer mounted behind the blades to show wind direction relative to the blades. Normally when it furls power peaks at about 60A 3kw for a few seconds and then drops off to 45-50A 2.5kw so I am positive that it did furl, not so sure now though.
The machine is 16 feet dia, 48v with an offset of 11.5 inches (6%) the full build can be see here
Part one http://www.fieldlines.com/story/2009/5/23/135436/243
Part two http://www.fieldlines.com/story/2009/6/21/22551/6284
Part three http://www.fieldlines.com/story/2009/7/20/11923/2353
I am putting this down to the mysterious "prop seeking" phenomenon we hear so much about and is probably the cause of many burnouts.
I went to a lot of trouble back in September to reduce the weight of the tail with aluminium and fabric sails, more detail here
http://www.fieldlines.com/story/2009/9/13/131418/233
So where do I go from here I hear you ask? And to be honest I don't know. I am now thinking the traditional furling tail design is not as reliable as many seem to think. What other options are there?
Ideally I would like to build a variable pitch hub but that's not going to be easy without a lot of machine work with machines I don't have! I have been searching past stories about variable pitch control but not a lot of working examples to go by plus a lot of the past posts are missing their pics or I get that darned upgrading message.
Other Ideas that come to mind are tilt up furling but is it going to be any better another thought was to rebuild completely but as a down wind machine with coning blades similar to Proven, not an easy option either.
This machine was built around a Land rover stub axle and hub
The stub axle originally has a half shaft running though it that fits into splines on the front plate see pic above.
I was thinking that I could fit a shortened half shaft through the alternator and out the back through a bearing to drive via gears a hydraulic pump (closed loop) max speed could then be controlled with a flow valve triggered from a speed sensor on the shaft or pressure switch in the line. Might work or might not I need to do a lot more research that's for sure.
As always I am open to any and all suggestions or ideas
Sorry for the long post and I hope you can follow my ramblings.
Russell