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Need blade carving help
By force9BOAT, Section Wind Posted on Tue Apr 18, 2006 at 06:25:47 AM MST
What is the best reference?

Realizing I need to make a new set of (better) blades for my machine I'm reading everything I can find but feel like I'm getting more confused? Can someone point me to a good reference for blade design and development? I'm having trouble understanding what angle of attack, TSR, chord width, etc. should be and how to form the correct shape.
Thank you,
Rob

Need blade carving help | 7 comments (7 topical)

Re: Need blade carving help (3.00 / 0) (#1)
by Flux on Tue Apr 18, 2006 at 01:31:55 AM MST

Try Hugh's site.
http://www.scoraigwind.com/index.htm About half way down you will find blade theory and blade carving instructions.

I think Windstuffnow will help if you load the pdf about building the 6ft kit.

http://www.thebackshed.com/Windmill/Articles/DonBrown1.asp
This will give you a lot of basic ideas on angle of attack, tsr etc.

Hugh's Windpower Workshop also has this covered and lots more.

Dan has the basic simple construction he uses on Otherpower in various places but it is a bit tricky to find.

It is very confusing until you get the basic idea of the shape, then all the construction methods make sense. I prefer to work from drop from the front face as Hugh does, but Dan and others prefer to measure angles. It comes to the same thing, if you know the chord width and the angle you can use the inverse tan on your calculator to find the drop.
Flux

Re: Need blade carving help (3.00 / 0) (#2)
by adelaide on Tue Apr 18, 2006 at 01:49:09 AM MST

play with Alton's wind calculator or similar http://www.alton-moore.net/wind_calculations.html
try changing the diameter and the tsr and see what happens to the rpm/ power on paper would recommend 3 blades for balance reasons.
i usually go bigger diameter and higher tsr to make up the rpm with lager cord (with for strength)follow angle is important.
what are the specs of your alt and do u have hi or lo wind?

Re: Need blade carving help (3.00 / 0) (#3)
by force9BOAT on Tue Apr 18, 2006 at 09:42:21 AM MST

I have low wind most of the time. My alternator is dual rotor, 24 polls, 9 coils (90 wraps each) of 16 gage wire. As of now the coils are connected in Star format but I'm going to change it to delta for higher RPM. Target voltage is 24V.

Construction photos are here: http://www.atm-international.com/RenewableEnergy/Wind/axial_flux_alternator_project1.htm

[ Parent ]

Re: Need blade carving help (3.00 / 0) (#4)
by DanB on Tue Apr 18, 2006 at 10:29:22 AM MST

Hi Rob --
I think your running 8' blades there... and I expect your cutin speed is probably down somewhere around 120 rpm or so with 90 turns in ea. coil. If you can change it to Delta, that will help. You might also experiment with opening the airgap up a bunch. Low windspeed doesnt matter - you're blades wont capture any energy unless you allow them to spin up to an efficient speed. I cant find pictures of your blades that tell me if they're good - or bad, so that may or may not be the problem so far as I can tell, but your cutin speed has to be way too low for an 8' machine. If you do get the cutin speed up by opening the airgap (shoot for 24V cutin around 170 rpm perhaps.. give or take a bit) then I expect itll be much improved - but Im a bit worried about the resistance in the stator then. You'll want it to furl very early and even that may not help. I expect the blades may overspeed... or the stator may overheat - or both. You could improve this by wiring in Delta if you can make that change. Either way itll be fun to experiment! Getting the cutin speed up a bunch will also help you determine if the blades are decent or not.

[ Parent ]

Re: Need blade carving help (3.00 / 0) (#5)
by DanB on Tue Apr 18, 2006 at 10:34:29 AM MST

Perhaps I should've posted in response to your earlier story on all this. I just think it's important that - if your planning an 8' machine you get the alternator more inline with that before you worry about carving another set of blades. On your webpage you talk about the blades free-spinning @1000 rpm - to me that suggests they may not be all that bad, but your low cutin speed on teh alternator is surely killing you.

[ Parent ]

Re: Need blade carving help (3.00 / 0) (#6)
by force9BOAT on Tue Apr 18, 2006 at 11:50:27 AM MST

Thank you for the feedback Dan. To be clear, I dropped the 8 blade idea along time ago and went with 3 blades.

The coil connections in the stator are external to the mold so I can change them. The first thing I'm going to do before making new blades is to change to delta. I'm actually thinking of changing to the "Jerry rig" Flux suggested. For that I'll need to purchase at least one more 35A rectifier from Forcefield.com. I'm hoping that making that change in the stator will raise the cut-in speed enough to help.

Another thing I'm thinking about is making the jump from 24v to 48V. I could do that for the price of one more solar panel but I'll have to save that idea for the future.

Rob

[ Parent ]

Re: Need blade carving help (3.00 / 0) (#7)
by tecker on Tue Apr 18, 2006 at 02:24:31 PM MST

I'd bet that if you measure the output from one of the 90 turn coils at 100 rpm your going to get close to half of the potiential your lookin for .If that's the case rectify indevidually and add up mix and match for the highest power curve .

Need blade carving help | 7 comments (7 topical)

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