10 ft turbine blade problems ?

[halfcrazy]

Ok as most of you know i am beta testing the Classic controller on my 10 foot turbine which is an exact copy of Dans 10 footers. now i had a weird noise and checked it out to find 3 of the nuts holding the blades on missing. and we are getting 35mph winds maybe a little more and the turbine was making 1800-2200 watts i have purposely held it back power wise for now to get a feel for it. so needless to say i left it shorted and we lowered it to inspect it.

The lowering went very well in 35 mph winds i was surprised how easy it was. what i found as well as the missing nuts is the 1/4 inch steel plate behind the blades is bent back between the studs not a lot maybe 1/8 of an inch? almost like the blades where overtightened and sucked the steel into the hub right at all 4 studs if that makes any sense? my theory is that spinning this much faster there are a lot of extra forces there that we wouldn't have with the straight battery charging?

so we put new lock washers and nuts on and sent her back up 70 ft and it is again making tons of power. so my question is what would you do to make this joining of the blades and turbine better? i have 1/4 plates either side of the hub they are about 6 inches in diameter i had thought maybe going to 1/2 inch plate but that will require me installing longer studs or maybe it isn't an issue the baltic birch hub had some depressions where we used nuts and flat washers without the steel disc for a while maybe it has just formed the 1/4 plate to mach the hub?

I am not against taking it apart but i may want to change from the 1 by 2 by 1/2 mags to the 2 inch discs i think the classic could harvest a lot more power from them but that's another subject?

[Janne]

Hi, looking at the power levels you're getting from it, I'd personally sort out the furling first.. obviously it's not furling like it should, around 1000-1500W. My best bet is, that even if you get the rotor to cope with that power you will break other things too.

If the hub plates are only those 2 6 inch diameter disks, then I think the problem is with the small hub disk diameter.

[halfcrazy]

well the furling works perfect right at 18 amps in from the turbine it is fully furled. so i don't see furling helping the blades. i do see me needing to rethink the blade mount that Dan uses because of the increased rpms and the extra forces they will see.

I kinda think i may need or want to do something similar to what Dan did on his 20 ft machine for the steel plates for the blades?

[hvirtane]

I think that the main problem is that fixing wood with metal is never perfect. Wood will always reform somewhat. In your case for some reason it seems to be a large amount...

I would try first to glue the blades together in the ends and to glue on the both sides of the blades plywood disks under the metal disks.

- Hannu

[Jon Miller]

I agree, the increased forces will do things like that.  I have made plates for a 7' which make the rotor vastly stronger then wooden disks.

[halfcrazy]

yeah i do think the Baltic birch hubs where a little deformed from previous washers i am leaning towards the setup Dan used on his 20ft machine but keep the ideas coming please

[boB]

Ryan, You may want to get some wide and thick stainless Belville washers and Nylock stainless nuts. What is the bolt size? I will send you some.

Robin

[halfcrazy]

John i agree the wood discs will be a shortcoming for me with the increased power. and i think i may have started things the other day i have basically got quite a few power curves i have made and i got a special one i call "I feel lucky today" and that was where i had it the other day when we where getting 55mph winds and i could see 3kw out of this poor little turbine.

i also have a curve that mimics battery's so if i plan on being away i can have it run slower the adjustability of these things is great and will be a good asset. i am going to work on building an alternator that will be optimized for the Classic and building the steel plates like Dan uses on the 20 foot machine.

[wdyasq]

It has been my opinion there are two ways to treat wooden blades. One is to give them a coat of 'whatever' and wish for the best.

The other would be the way would be the way "Wood Epoxy Saturated Technique' boats are built.  In these boats, the wood is encapsulated and sealed in epoxy. Bolt penetrations are similarly sealed. Where bolts go through things, bushings, plugs or compression fittings are placed so the part may be fixed or loaded and not break the epoxy coating.

The method of encapsulation works. It has worked for over 40 years on boats built by the Gougeon Brothers and other wooden boat builders.

Wooden parts epoxy treated with well designed hard bolt points will not compress and the bolts can be properly tightened and locked and will not work loose.

Ron

[Crusader]

Yes, perhaps installing compression sleeves in the bolt holes on the blades would eliminate compression. I would suggest leaving a little room for some compression though. You need some for humidity expansion etc...IMO.

[clflyguy]

  Amen Ron, I have thought that so many times and just never piped up about it. Some

of the real epoxies penetrate very deeply into certain woods and you end up with a

wood-epoxy composite material that is light and incredibly strong.

 Personally, I think I would try to avoid the UV blues (sorry) I would have to cover up that

beautiful epoxied wood grain with some of that outdoor Krylon

plastic molecular bond paint -unless I have been in hibernation too long and you

can get uv inhibitor to mix into epoxy now... That would be nice, to still see the

grain under a glossy polished epoxy finish.   Gus

[Flux]

You may just have been unlucky with the bolts coming loose. There may be more gyroscopic loading when not operating in stall.

I can only comment from my own experience and that is with a different type of alternator. I have my blades sandwiched between two plywood discs but they are glued to the discs. I can't see the point of reducing the blade root width at the hub but my blades are probably narrower anyway. I think the main difference with my mounting is that the back plywood disc of the prop sits against the front of the alternator and that is a rigid 12" diameter steel object.

Using your sort of arrangement I would use something like a 3/8" thick steel disc for the blades to sit on and I wouldn't consider anything less than 10" diameter. I don't think the front matters. I just have a piece of 3 mm plate rather than washers directly on to the plywood, it could be thicker and 5mm at 6" diameter may have been a better choice.

Those alternator designs started out as simple designs to be built from available parts and have evolved. It is not a form of construction I would use if starting with new components and with machining facilities available. The axial machines I have built ( smaller ones) have had the prop mounted directly on to the front magnet rotor and that is fixed rigidly to the hub. It needs a good thick plate for the front magnet rotor so that the prop forces don't warp it in operation. The rest of the alternator is built backwards behind the front disc. Even then I wouldn't hang things on allthread but you could get away with it with no prop loading being carried on it.

Obviously I am over cautious as many of these things are running successfully so the prop gyroscopic loading ( at least with stall operation) is not as great as I suspected. Considering that none of these things overhung on allthread have caused trouble I suspect you were unlucky with your blades but using a thicker and larger diameter disc to mount the blades against seems sensible.

I have to admit that my 10ft machine furls early and doesn't reach 2kW very often but it doesn't run stall operated so the blade loading is probably not so different.

Replacing the plywood discs with a fabricated metal hub may be a better way to go but I had more faith in 3 blades screwed and glued to plywood discs than individual blades fixed to steel supports although I do have an 8ft machine with adjustable pitch blades and the individual blades are mounted on to steel channel sections.

Flux

[halfcrazy]

after lots of thinking i will look it over next time it is down but i really believe a bigger steel disc will fix it the issue i think is the small disc got sucked into the old washer holes on the plywood disc. so for now my plan is to watch it and see but when i let it down i will have a new plywood disc and a bigger steel plate?

[bobshau]

My 20' rotor crashed to the ground in light winds this past summer. After inspection, I found that the all-thread bolts had become loose and had machined slightly oblong mounting holes in the wooden blade roots during operation. This extra clearance was enough for the bolts to bend back and forth with each rotation causing bolt fatigue. All six 1/2" bolts failed between the magnet rotor and blade hub. The blades were destroyed beyond repair.

As a result, my new blades have 1/2" ID pipe sleeves epoxied in the mounting holes. The hubs also have these sleeves. Now I can draw the mounting bolts tight and hopefully prevent motion during operation. I'll let you know how this works out.

Blessings and peace.

Bob S

[wdyasq]

"Some of the real epoxies penetrate very deeply into certain woods"

That is rare, in my real world experience of tens of thousands of square foot of wood/epoxy laminate. If it is critical I get a coating I use a light cloth to assure a coating thickness. The 'water resistance' is not totally in the epoxy but one of the additives, Mica, which lays flat in little layers of plates causing the water to have to work around the Mica plates AND through the epoxy.

"You need some for humidity expansion etc...IMO."

I don't share that view and neither do the formulators and proponents of full epoxy encapsulation. It is a real PITA to seal every edge of a set of blades, pre-drill then drill oversize the bolt holes that will hold the blades, inset plugs or fill the holes with a proper epoxy filler, re-drill the holes and track the blades and then finish covering the blades and coat, sand, coat, sand ........ until the blades are smooth.

Then, all of this pretty work needs to be painted. Don't worry though, if the machine is properly mounted, high enough,  it will be hard to appreciate 'bright finished' blades.

There is a LOT of labor in properly epoxy coating blades. It is also at the tail end of a project when everyone wants to get the machine flying.

Ron

[Airstream]

Just taking this back a step to clarify one point - Resins are not be used like paint - the advantage to resins is build-up to several mm thickness wholly encapsulates and strengthens the core not just act as an outer finish coat.

A good series of thinned resin base coats to promote deep penetration & adhesion, glass cloth to promote uniform thickness, strength and impact resistance, and UV blocker top coat will ONLY extend the required periodic maintenance time but nothing is fly & forget...

If you want a paint-on finish look elsewhere. Polyurethane finishes are brittle and easily damaged over redwoods and cedars - thinned base coats and many additional layers of spar varnish where it remains slightly 'gummy' or using oil finishes until the grain rejects any further absorption AND doing a religious periodic maintenance depending on your climate for refreshing of the finish is where 'paint-on' finishes lead to.

[ibeweagle]

Did you supper glue the 1,2,.5 magnets on if so easy to get of and use my magnet holder for 16 mag per rotor and make new stator of 12 coils 2 in hand # 18 70 turns for 24 volts will update new rotors soon posting and change the blades to 12 footer were are you located? have unit here almost ready. metal hub will sink into soft wood might have to also put in 1/4 20 bolts in three places on each blade for more secure hub to blade assembly also try to make sure it is sealed from water had to use rubber flashing to water proof hub to blades cheers ibeweagle

[ibeweagle]

is it a 4 bolt hub can send you some plates 1/8 10inc dim and and 1/4 in plate on top ibeweagle@hotmail.com

[hvirtane]

I think that the cure is to make the wind rotor first solid with plywood disks glued on the both sides.

When the solid wind rotor is sandwiched between the metal plates with bolts, the whole wind rotor cannot any more move easily?

- hv