Author Topic: Prop Diameter Question  (Read 1047 times)

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fritzblitz

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Prop Diameter Question
« on: April 16, 2008, 07:10:06 AM »
If I change a two blade Prop with 2.8 m ( which worked well with the generator )to a 3 bladed Prop , how big must the diameter be now?
« Last Edit: April 16, 2008, 07:10:06 AM by (unknown) »

Flux

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Re: Prop Diameter Question
« Reply #1 on: April 16, 2008, 01:53:24 AM »
Who knows?


If it was ideal with a 2 blade 2.8m prop then you should change it to 2.8m. The power out is the same for a given swept area irrespective of the number of blades.


If your original blades were not an ideal match then you may benefit from a change in diameter. Also if it was correct for speed before then you need to keep the same tsr. That will mean a reduction in the chord width of each blade to keep the total chord the same.


It would take a lot of information to give you a sensible answer as we have absolutely no idea how close your original prop was.


Flux

« Last Edit: April 16, 2008, 01:53:24 AM by Flux »

fritzblitz

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Re: Prop Diameter Question
« Reply #2 on: April 16, 2008, 03:16:57 AM »
hello flux, thank you for answering so fast! The old, broken prop had a width at the root of 230 mm at the tip about 120 mm the drop at the root was 80 mm and the thickness at the tip was 30 mm! This windmill had a bad working furling system, so one day in a storm in went to the ground. I changed all the parts which I found they was wrong build. The angles of the furling system, offset etc. then I carved 3 blades, same profil as pigotts 2.4m Props but calculated to 2.8 meters diameter. Because i have build a windmill from Hughs plans, which works perfect! But now: the new blades are turning much slower than the old 2 blader , producing only 2 - 5 Amps at 24 Volts. When I let the Genny run free for a few moments and switch it back to battery load, the amp meter jumps up to 15 to 30 Amps. Depending on the wind. The Generator has an open voltage at 650 rpm of 190 Volt but I did not measure the Ohms. At now, this are all my datas! Thank you very much and excuse my english!
« Last Edit: April 16, 2008, 03:16:57 AM by fritzblitz »

Flux

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Re: Prop Diameter Question
« Reply #3 on: April 16, 2008, 09:50:09 AM »
 I think you are running stalled with the new prop. If you can get up to 650 rpm on no load I think your new prop is faster and lower solidity than the original.


I have no details of your alternator, it would be useful to know the speed for cut in at 24v. Also you say you don't know the resistance. I would either add some series resistance in the line or borrow a car battery and see how it performs into 36v as a temporary measure, that should get it out of stall.


Flux

« Last Edit: April 16, 2008, 09:50:09 AM by Flux »