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feathering does not work
By jacquesm, Section Diaries Posted on Sun Nov 28, 2004 at 08:19:30 AM MST
feathering does not work

We just shut down the machine in high winds (up to 60 mph), doing about 600...700 rpm in one very short very fast gust of wind. It was clear the feathering did not work as it was designed to do and I did not feel like doing destructive testing :)

Amazing how variable the wind is though, that burst came out of nowhere in what was otherwise a 30 mph wind...

The mill is riding idle right now - shorted windings - until the wind dies down and then we'll start it up again.

At high speeds we can still see some imbalance too, the tower starts to shake. One of my friends (Laurence) will come and shore up the one guy anchor that looks a little iffy next week.

So, todo list for when I get back:

reinforce tower with another set of guys to get rid of tower resonance or at least raise the resonance point to a frequency where it is no longer a problem

disassemble the machine, check for wear / damage

redesign governor, beef up base plate, better slide shaft, heavier weights, better blade attachement

reassemble with new governor

check blade flex for equality

build an indoor balancing rig

get another set of bearings, take seals and grease out, exchange bearings in machine with these 'balancing bearings'

rebalance the machine

disassemble (this time the governor should stay in one piece during disassembly) and remove 'balancing bearings'

reassemble with the 'real' bearings

remount on the tower, run more tests

Until then we will be running the machine in fairly low winds (up to 25 mph or so) only.

On the one hand this is a 'failure' of sorts, the feathering does not work properly, so there is a lot of work ahead of us (I think it's due to appearant wind on the 'back' of the blade stopping it from rotating freely towards coarse pitch). On the other hand it just survived a 60 mph burst of wind without feathering, which is pretty good. It gives me confidence that the design, once it's feathering properly will survive some pretty heavy winds without damage.

And, if it would not be shaking so much due to imbalance/tracking troubles then I would just let it run!

feathering does not work | 4 comments (4 topical)

Re: feathering does not work (3.00 / 0) (#1)
by gibsonfvse on Sun Nov 28, 2004 at 01:02:39 PM MST

This is pitch-based feathering, yes? Hmm... got any control theory people in your midst? :) The only thing I can think of is that any cambered airfoil producing lift also produces a pitch-down moment which is proportional to the square of the incoming airspeed. Maybe your issue has something to do with this...

Re: feathering does not work (3.00 / 0) (#2)
by nack on Sun Nov 28, 2004 at 03:20:59 PM MST

Just a few random thoughts: I might try a lighter spring before moving to heavier weights. Or maybe counter spring the weights? Also, don't know how the balancing thing worked out, but I wonder if the "common weight" in the original balancing might have contributed enough extra mass to damp some of the vibes? I also wonder if clamping some heavy split collars on top of a turn of dead tire might damp the nodes on the pole?

Re: feathering does not work (3.00 / 0) (#4)
by Flux on Tue Nov 30, 2004 at 01:22:24 AM MST

Jaques

I have been having a look at your pictures of the hub.

What type of bearings do you have for the blades to twist on? You have a lot of backward thrust and a lot of radial force so the bearings need to be free with these forces present. I couldn't tell whether you have any form of thrust bearing to keep it free with radial load.

Your weights are a fair size but not at a particularly large radius so you may not have enough force to overcome friction.

I suspect that if you spin the hub alone it will work fine.

I also agree about the slide needing improvement. To keep the blades tracking properly that slide needs to be a reasonably long sleeve on a smooth shaft. Also at the point shown in one of the pictures the linkages are only at a small angle to the allthread and the blades could twist independently quite a bit.

With your blades mounted well up to the leading edge I don't think you can do much more about blade pressure, I think its more force or less friction.

I am sure you are not far from success

Flux

[ Parent ]

Re: feathering does not work (3.00 / 0) (#3)
by jimovonz on Mon Nov 29, 2004 at 05:29:43 PM MST

Jam,

Would be really interested in more detail re: your furling mechanism. I'm gonna need something similar if I want to utilise my chopper blades.

feathering does not work | 4 comments (4 topical)

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