DIY Wind Turbine - Part 4 - Building Better Blades

I know this part was supposed to describe building the mounting and tail of the turbine but i had a problem with the design of the first set of blades, so this part now contains details of a revised set of blades... i do think though that the design would be ok if a stiffer plastic is used, like the proposed waste pipe, but i wanted to used the scavenged piece of guttering.

...So, the first set of blades were too flexible as i had thought, how do i know??? read on... I had mounted them to the generator and fixed the whole rig to my washing line, it was quite a windy day which made this process very difficult. Wow, it works, i got the multi-meter out and measured the output voltage, it was averaging 25V in moderate wind, and the rotor began spinning gently in very low wind giving about 3V, but when there were large gusts there was a strange noise???

I looked at the spinning turbine from the side and noticed that the tips (about 3 inches) were bending backwards under the force of the wind, and when experiencing a large gust the tips of the blades were clipping the washing line pole. Ooops, thats not good, it wouldn't take much more for the blade to get damaged... so i popped in to the house to get some tools to bring the rig back to earth, i lifted the blind for a better view of the turbine which was spinning very rapidy, and seemed to be getting quicker (damn, if only i still had the multi-meter connected). While searching for my tools and periodically checking on the turbine the clipping noise was getting louder, i could hear the wind down the chimney, an indication that the wind was indeed picking up...

... one last look before taking the tools out, BANG, failure, one of the blades hit the pole that little bit too hard, and snapped from the rotor, hurtling through the air towards the neighbours garden like a javelin. Was quite sad that the blades had failed but at the same time i was glad as the strong winds had identified a flaw in the design/material and i knew now that they would not be good enough to last as part of a permanent turbine, but i had also demonstrated that the shape of the blades was efficient enought to get the generator spinning enough to charge the 12V battery. I went out to pull the rig down to find the blade sticking vertically out of the neighbours grass... if only the cat was in the way, im fed up of it spraing on my car 

I decided to revise the design slightly in order to give the tips of the blade a little more rigidity, this would be achieved using the curvature of the guttering, the more of the curve that is used the stronger the blade. So i made the tip of the blade 75mm wide rather than the original 50mm, i also decided to extend the length of the blade by a further 50mm (to get a little bit more torque out of them). This time i produced four blades, i made the first blade and then labelled it as a template, and used this to mark out the three blades that would be required, make sure you label your template as using the wrong blade will mean each blade will get progressively larger this will seriously effect your turbines efficiency and stability. I did a quick test of the rigidity by trying to bend the blade in my hand, it was much stiffer, great... so i mounted the blades to see if they would suffer the same, problem, but alas, the wind was very low.

I did notice though that in low wind the output of the generator was around 6V not enough to charge the battery, but twice that from the old blades, so efficiency has increased, i won't be able to test any further until somone turns the wind back on. Unless these blades fail also (fingers crossed that they don't), the next part will describe the tail and mounting system... i will however make updates to this page if i am satisfied with the blades, and the output, i do need a better way of quantifying the wind speed though