The Rotor Blades

[Murlin]

Howdy folks,   Who would have known there was so much to learn when you build a wind genny...Quick update on my progress....

I have been busy lately, (seems I have a lot of Irons in the fire these days), But took some time to do some more design work this weekend.  I went ahead and modeled up the braking system.  I guess I am one of those people that Dan talked about that do too much planning....but once the design work is done, It should go a lot faster.

I love this stuff....It's what I live for

Haven't found a used planer yet, but still looking for a deal somewhere.

Have about half of my parts and will begin machining on the rotors and modifying the hub next week.

About the Rotor Blades....I am modeling up those too since I will be machining them.....besides it looks cool on the computer screen

Does the weight of the blades make any difference?

It seems the heavier of the rotors would cause a flywheel effect.

Is that good or bad?

So lighter or heavier that's the question for today.

Thanks in advance...

Murlin teh inquiring minds......

[willib]

Murlin the inquisitive, take your question to an extreme , i usually do when pondering something.

say you have a set of perfect blades angles are perfect , airfoils are perfect , everything about them is perfect.

But they are made of cast iron.

do you think they will spin in a light breeze? the amount of air needed to get them spinning will be a lot more than if they were made of Cedar or Foam ..

just my thoughts...

[Murlin]

Hrmmmm....well you got a point there....

I used to build and Fly RC aircraft.  I was just thinking if you cut some pockets to make them lighter and covered the blade with shrinkable mylar where the seam was to the trailing edge, wonder how long they would last in the elements?

Or just glass over the pockets kind of like a canvass skin airplane wing.

Just pondering the equation.

One can never get too far ahead of themselves.....NOT!!!  

Murlin teh ADHA.....

[WXYZCIENCE]

A mylar covered wing might work. It would be fun to build a scaled test model and see how it runs. Heavy blades make heavy windmills. Stronger everything would be required to hold them up in the sky. Joe

[Flux]

I am not sure taking the extreme case is helpful for this issue.

Over the weight of practical materials that would work I don't think it makes much difference.If you go stupidly heavy you need to add so much strength everywhere that it becomes impractical.

If you used a heavy timber compared with a lighter composite I doubt that there would be significant difference. Wind is never constant and you are integrating lumps of variable energy. The heavy prop would do most of the integrating with its flywheel effect and the light one would provide a much more variable current that is integrated in the battery. If the machine has a true mppt characteristic then I suspect the light one would benefit if it was closely tracking the cube law.

Most machines don't track the cube law ( nearer the square) and the flywheel follows mk^2.

Not noticed any real difference with any of my blades but I have never tried cast iron or tissue paper.

Flux

[Flux]

I am not sure taking the extreme case is helpful for this issue.

Over the weight of practical materials that would work I don't think it makes much difference.If you go stupidly heavy you need to add so much strength everywhere that it becomes impractical.

If you used a heavy timber compared with a lighter composite I doubt that there would be significant difference. Wind is never constant and you are integrating lumps of variable energy. The heavy prop would do most of the integrating with its flywheel effect and the light one would provide a much more variable current that is integrated in the battery. If the machine has a true mppt characteristic then I suspect the light one would benefit if it was closely tracking the cube law.

Most machines don't track the cube law ( nearer the square) and the flywheel follows mk^2.

Not noticed any real difference with any of my blades but I have never tried cast iron or tissue paper.

Flux

[adelaide]

i do notice difference between heavy props and light  ones, in little gusts the light ones speed up faster and make power , if something did go wrong would be safer.

my heavier ones tend to keep going bit longer in between gusts on light wind days. haven't noticed the yaw  or tracking but prob is a difference too. i prefer light but strong enuf

[whatsnext]

Lighter is better for a number of reasons but an important one is that all the kinetic energy contained within the blades prior to cutin is wasted. Blades strong enough to do the job but weightless would be best.

John..

[SamoaPower]

It seems that the fellas have covered the weight issue pretty well. I don't think it's a big point within reasonable limits.

I'm still not convinced that wood timber is the best material for blades. I'm in the process of refurbishing (new paint job) a set of aluminum blades that saw four years continous service about 20 years ago. Since I completely stripped them, I carefully examined them for fatigue cracks, which those who don't like aluminum cite as a failure mode, and found not one. These are a .040" formed skin over a tubular spar.

When you get to the issue of rotor efficiency, I may have a few more words for you.