Making wooden blades with Max

A well made video by Max ‘Menelaus’ of www.kleinwindanlagen.de showing how to shape blades using a bandsaw and power sander.  It’s also interesting to note the reduced number of steps in the process compared to the procedure in my Recipe Book.

I like making things simpler although I have some doubts about the thickness of the result.  And I also have doubts about whether I would enjoy all the noise and the dust.  I like to use a sharp plane and I enjoy ‘surfing’ the wood with a draw knife, but if you want a quick result then this may be the best solution for you as for Max.

 

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11 Responses to Making wooden blades with Max

  1. Roger Brown says:

    even with the best procedures is there any way to get close with wood to the aerodynamic precision of an engineered composite?

    • admin says:

      You don’t have to get perfect precision at all and the process is actually quite forgiving. Blade efficiency is generally pretty acceptable even with a rough job. But I like to spend just a little time making the best job I can just for the satisfaction of it.

  2. Hi Roger, yes I totally believe you can get absolutely aerodynamically precise with wood and I’ve just updated my construction blog on the subject:
    http://thewindinthewires.wordpress.com/little-jenny/blades-2/
    I agree with Hugh generally, most carved blades give great efficiency for the effort put in and are achievable by many people with simple tools which is so important.
    My interest is in working towards better wooden/composite blades that won’t stall as quickly as the simple carved blades when the alternator slows them at higher wind speeds. I’ll be working on a hybrid carved/composite method later in the summer.

  3. Roger Brown says:

    thanks Jan – very good point – wood blades are very achievable and offer a real sense of satisfaction in their completion.

  4. David Simms says:

    I would like to ask both Jan and Hugh, given their experience in making blades and the fact that I’ve only made a few sets, how effective they have been at maintaining balance through the process. Try as I may, I still have to resort to weights, once the blade set is made.
    In the future, I intend to monitor the balance at different stages in the construction process hoping that it will point to whichever blade has been allowed to get a bit too “fat”.

    re. efficiency. It has often been said that the difference in efficiency, between straight-no-twist blades and those with as much taper and twist as a piece of wood will allow (which hardly approaches the theoretical, over the length of the blade) is inconsequential when one considers the overall “system” efficiency. just for fun, do either of you know of any testing that compares a “taper-and-twist” set of blades with a “no-taper-or-twist” set, on the same generator ?

  5. David Simms says:

    Thanks for pointing me toward that paper, Hugh. I read the conclusions and saved a copy for further study. It appears that the advantages of a twist-taper blade is fairly small. You’ve probably seen some of the old Wincharger blades. They used a highly cambered Wortmann profile and a straight blade without any taper. it’s an interesting approach but, personally, I like the twisted and tapered blades, not only for the slightly improved performance (and, probably better starting ability) but for the artistry involved.
    i note, also, the improved performance of the rounded leading edge, as with the 4415 profile.
    it is reassuring to hear that you find it necessary to pack on the lead, sometimes, despite using great care in care in carving the blades. i won’t feel so bad, now, that my last set would have required a fair chunk of metal to balance them.
    The next time, I’ll take great pains to plane and cut the raw planks so they are as close to the same dimension as possible. Then, I’ll check the balance at the outset. Maybe getting better uniformity can be achieved by flipping the planks, if needs be. Then, I’ll check the balance as i move along in the process, just for fun. There’s something esthetically displeasing about chunks of lead.

    • admin says:

      If you are happy with a low tip speed ratio, then the advantages are fairly small, yes. However if you want to make a slender blade for high speed then I would question whether the constant chord approach is wise. Such blades tend to flex and hit the tower.

      The machine they tested in the paper is a small one with low tip speed ratio to provide good starting torque for the stiffness in the bearings. My larger designs have faster blades with relatively narrower chords.

  6. Jan Wolstenholme says:

    I like twisted & tapered blades for all the technical reasons and for the sheer beauty and the fun in making them. Not only have I seen a Wincharger blade, I have heard them in operation and I have an old one here. It was obviously an economical production strategy, very good use of lumber. I was looking at a real antique glider (sailplane) last week and wondered if we can’t make blades in the same way as glider and model wings are made, modern materials or wood veneer/epoxy should be strong enough…. stay tuned

    • David Simms says:

      I think that Wincharger designed those blades for the ease of production; they could take the plank and run it through a shaper and, presto, out comes a blade.
      I have heard of the blades hitting towers but that may be due to several factors; since the blades didn’t feather, the wind force kept on increasing. With some models, the blades were 12′ long and this would allow for more bending in the blade, as wind speeds increased.
      I will soon make a set for a 2.4 meter, 500w Chinese unit that I picked up a couple of years ago. I think I’ll try your method, Jan, just for fun. I’m a bit concerned about the aggressive sanding but, I guess that if one is very careful it should be ok.

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