I do believe a way to make sure the tail doesn't lift should be in order, like a bolt through the top of the tail pivot and maybe a stop that keeps the tail out of the blade area totally.

First, nylon lock nuts do no good if the wood shrinks or gets compressed locally as WILL happen with washers.

If a cable was used to 'tie the tail on the pivot', it could also be arranged to act as a second safety. If a proper spring and a cable is used it might be able to slow the tail before it impacts the stop. I'll sketch something up on this and mail it to DanB.

I've long thought the tail should naurally furl and a cable under tension should be used to 'activate' the machine.

But - this in not my project and I am a long ways off. As it is not in my back yard, I can just yell.

also Let George know that I warned him about drinking beer while installing the blades. (forgot to tighten them, or was that me).....

I had a blast at your workshop, Learned a lot of things about building wind turbines. And how to make plasma with a microwave..lol

I hope to come buy your place sometime to visit all of you guys again, if you have a work shop at your place again, I would love to help out with it.  

The tail raising up is strange, it would have to lift up at least 2" to get past
the other side of the yaw tube. Must have had a lot of gusty winds slamming the tail around.

Keep smashing and crashing them so we don't have to. :)

Luckeydog

Nylocks or loctite will prevent things coming off even if it comes loose from compressing the wood ( which the gyroscopic forces will most likely do even if the wood doesn't shrink).

This is a silly issue and can easily be solved, same thing for the tail hinge ( only ever used that construction on 2 tiny machine.

The furling issue is a much more concerning thing to me. I really do wonder how many of these things actually furl rather than rely on stall limiting.

I don't know whether we are going below the critical offset or whether the tails are just far too heavy. I have always got away with 1/" per foot offset but I don't think there is much in hand. One machine  built as a 4ft machine with the intention of modifying the alternator to take 5ft later and I based the offset on this. I got a better result from the alternator modification than expected and went for 5'6" and it doesn't furl. The tail goes over at a fair angle but the power keeps rising. It is on a site with little real wind and hasn't come to harm but I know it wouldn't survive a normal site.

With the inclined hinge restoring force I am convinced that once it does properly furl you will see a drop in power. ( I have to try very hard not to let this drop not to become too great but fiddling with the restoring force). If it doesn't drop then I think you are not furling properly although it may be helping the stall control.

With my methods of loading where I am away from stall the drop in power may be partly due to the fact that once you overcome the seeking force it puts part of the blade in stall and the power drops. There is no real drop in power until the tail gets to about 45 deg and then it seem to defeat the seeking force and power drops.

If the seeking force is much lower with the blades stalled then the transition as it comes into furling may not be so sharp but I can't believe that the power will not drop to some extent.

It's true as you say that the tail stop was not quite right.  Looking at it closely it doesn't seem to bear squarely onto the yaw bearing.  It's surprising how tricky it is to get the position of that stop right so that it does.  In this case it is bearing onto the side of the tube in such a way that it forces the top of the tail away from the yaw much more than it needs to, and this seems to have caused the tail to lift as you pointed out.  It's like a cam action forcing the tail up on its hinge.  Unless I am not seeing it right and the ail is already lifted way beyond its normal position.

I suspect that the problem would not have occured if the stop had been further out along the tail and bearing squarely onto the yaw.  As a further safety you could design the stop to include a hook shape beyond the yaw that pulls it in rather than pushing hte tail outward.  I am reluctant to add anything to hold the tail down as this tends to make things over-complex and sometimes lets rain into the tail hinge. anyway I feel that a stop that bears both on and beyond the yaw tube would have prevented this from happening and I will look at doing this in future.

I have just been in Nicaragua building another such machine with a few modifications.  The most important mods were to the alternator mount, taking it out from 6 inches to 8 inches offset sideways (my usual offest for a 12 footer is 8 inches) and also pushing the alternator a bit forward toward the wind in its normal position.  I think this helps it to furl properly in the stronger winds.  In the last couple of years I have changed all my larger machines to sit further forward, more like the AWP frame layout.

As for whether the furling system works, I have to say that it does work pretty well, based on thirty years experience, but it does sometimes need some tweaking, and you do need to have a big enough offset.

Moving on to the blade fixings, I rely on the screws rather than bolts although I am sure that the main alternator bolts help to hold the whole thing together.  I never use a steel plate, and I have never seen a hub fail like this that I can remember.  But I will take more than usual care to lock the nut in future!

All good fun