Furling problem

[phil b]

Strong gusting,shifting winds has made an upwind genny into a downwind one twice in 2 years.

What did the mill do? It turned away from the wind, started rotating the blades backwards and producing power! Not much, just enough to keep my batteries fully charged when not in use.

It is based on Hugh's 8 ft, with dual rotor 12 magnets/9 coils. The angles for the tail attachment were by the book until the tail came off the first time. I welded it back with a 10 degree angle because it furled at 40 mph.

See if you can determine what caused the failure.

[stephent]

Looks like the gusty winds just beat and banged the tail furling limits against the "stops" until the tail pivot axle broke....use double strength pipe or better, solid rod to hang tail assembly on. Weld another reinforcing section at cut furl limit edge like the added side to  keep it from bending--and it looks like it climbed up before coming/breaking off.

Use retainer rod through middle of pipe axle or weld stud at top if using solid axle.

[DanB]

Id have made the pivot and especially the bearing (the pipe that fits over it with the notch) longer.  If the tail bearing came all the way to the bottom of the pivot then the force at the weld (where it broke) would be much less.

I also always weld a 'stop' on the tail boom that hits the yaw bearing to keep the tail out of the blades - this eliminates the force on the notch itself when fully furled.  We've had those get beat up/seen them get spread open (like yours) up here before - the result is the tail hits the blades and sometimes the tail bearing cracks.  

So if you stick with the same design, using the same size pipes etc... those are possible improvements.  The alternative is to use solid shaft - larger pipe - make it all much stronger.  I've never seen one snap off like that but I've worried about it - now perhaps I'll worry more!

[scoraigwind]

I have never seen this before but it is the logical place for the thing to fail.

The simplest way to beef it up is to use the same pipe sizes as the yaw.  Clumsy but very strong.  No downside that I can see (in fact I would probably use it in my plans to simplify finding all the pipes if I were to start again).

However i think there is something wrong.  The arrangement should be strong enough.  The blades may be out of balance.  Or what about the weird alternator mount.  It might be causing a resonance of some sort.  Watch the machine running and you will probably see what is causing the extreme fatigue loading you must be getting.  The big overhang will certainly put more load on the high end tail stop.

It appears that vibration is causing the tail to climb up on its support and this would accentuate the fatigue hammering on the bit that broke.

[phil b]

The blades are static and dynamically balanced very well and are tracking within 1/8" of true. Rotors are balanced as well.

The stator will get hot at times and rubs unevenly against the all thread holding the rotors. This causes the unit to squeek and to become unbalanced in high winds.

I think the "weird" configuration may be amplifying vibration of the unit.

It's time for a total rebuild.

Instead of using pipe bearings in the tail, I'll try catagory I (1/2") tractor hitch pins. Snug steel bushings are available to convert from catagory I to cat II. A clip is also included with the pin to keep it in place. They should be available at any tractor supply store for less than $10.

 I must say the unit has taken 60+ mph gusty winds, 12 to 108 degree temperatures, blowing sand and 2 dust devils. I'm still very impressed with the extreemly ruggedness and durability of the design.

Thanks Hugh, DanB and stephant for your comments. They are appreciated.

[WXYZCIENCE]

Phil , nice first picture. Looks good even as a down wind design set against an awesome sky.
Joseph.