100W Turbine plans - blades

Dear All

I'm in the process of putting together a small turbine based upon Ben's 100w plans and have a few questions regarding the (aluminium) blades, that I'm hoping some one might have more experience with.

1. How do the blades compare with others, eg those created from plastic tubing? What are the best blades - purpose carved wooden ones? For these Ametek based turbines is there much to be gained from using a "better" blade design instead of the Ali blades (if such a thing exists)?

2. The plans are for blades 33" in diameter, with a caveat not to exceed 48". Has anyone tried other sizes, especially ones up to 48"? Any gains?

3. Presumably the part of the blade "bent up" acts as the leading edge and the turbine turns in the direction of this edge. Is this correct?

Many thanks

Paul

[Gotwind Ben]

HI Paul, welcome.
The plans are a little dated now, but still valid.
If you are attempting the 100 watt wind turbine with a DC motor, I would stay away from the folded alluminium blades I detailed for the Dynohub - too weak.

I suggest carved wooden blades as being the best, formed Alluminium blades secondly
available on eBay, but be careful, or I suggest TLG in the U.S. http://www.tlgwindpower.com/rotors/tri_mm.htm

Lastly, only due to the longevity and safety, PVC pipe blades - best for testing purposes really.

Have fun and please keep us informed on your progress.

Hi Ben

Many thanks for the reply. Couple of questions:

1. Your (possibly original) 100W plans had folded aluminium blade plans included. Has experience taught you they're not suitable?

2. You state they are too weak. By that do you mean they don't provide enough power, or that they are prone to failure?

I have enough ali to fabricate the blades (and I'm gagging to get the turbine flying) so I think I'll build some folded blades to start with and then carve some blades or buy some prefab blades as and when I can afford the time and/or money. Can you tell me:

as the blades increase in length (say from your suggested 33" to 48") what changes in terms of outputs? My understanding is that larger blades rotate slower but start in slower winds. Does that sound right?

Finally (and possibly chancing my arm here) what direction will the blades turn? In the direction of the "flat" or the "bent" edge. I assume the latter, is that correct?

Thanks for your time.

Regards

Paul

PS I'll get some foto's when it's complete and get them posted asap.

P

I've toyed with aluminum and mild steel blades bent on a folding brake these past five years. They're cheap. That's about the extent of it. Never saw one lost until it slowed down. But since they are cheap you can replace them easily if you have a brake. They eventually fatigue and fold inwards, killing your output and sticking the remaining blades in a downward position. The furthest one was thrown was about 18 inches from the pole. Of course my pole was but ten feet high, so ymmv.

Hey Matt

Many thanks for the reply. I'm going to start with the folded aluminium blades. Can you confirm which way the blades will turn? Towards the "bent" edge (as I suspect)? or towards the flat edge? I'm trying to ensure the motor turns in the correct direction for the outputs to be correctly colour coded (red/black/+/-). Probably un-necessary I know.

Regards

Paul

[Gotwind Ben]

I presume you are referring to my very old folded design, not really advised.



You are correct Paul, they rotate towards the bent edge (clockwise) in the image above if you were up wind from the turbine.

Hi Ben

Yes Ithink I must be referring to the "old plans". I bought them on 31 dec 2007 (you can see I'm a bit of a slow starter). What sort of blades do you include with the current ones? Are the plastic blades an improvement on these?

I have the Aluminium (and time) but not much else now so I'll build them to start and then look at a better alternative once the turbines up and running.

Thanks again


Paul

[Gotwind Ben]

Try folded blades if you have the material to hand.
See how they perform and maybe then look at pvc plastic pipe blades.

I've tried up to .060 aluminum and it deforms in wind over 30mph, even when using extra stiffening folds and wired hems. Sheet aluminum is too flimsy and brittle. The worst part about it is how quickly it stretches the holes where you fasten it to the hub. Stainless steel in the 20 gauge range will work up to a 30" blade; approximately a five foot diameter. And 18 gauge mild steel held up for two years before it finally bent at a fatigue point near the fasteners. I've experimented with from 26 to 16 gauges in mild steel and the bigger diameters require the heavier sheet metal. The 16 gauge was overkill for 48", but perhaps not enough for 60". I know it was doing well in severe weather (40mph-ish gusts) until the plywood rotor flexed and it struck the mount about a hundred times, so ymmv. I didn't build the turbine durable enough, I used dried kiln wood and used threaded rod held by bearings for the shaft. A better built turbine wouldn't have had that issue.

Metal blades tend to fail on the slower speeds when they do fail. I've yet to see one thrown.

Hey Guys

Many thanks for the replies. I hope to have the ali blades finished for this weekend. and then get the turbine up next week. From what's been said I'll only use them on a short term basis, replacing them as soon as possible.

From what you say Matt the key advantage over the plastic tube blades is the fact that they won't fail catastrophically. This is particularly important to me as my garden is sandwiched between two others and the turbine is right on the boundary with one of the neighbours.

As you'll see when I get the photo's posted there's not much chance of me getting 20mph winds let alone 30 or 40 :-)

Regards

Paul