2 blade wood prop tutorial

[johnelarue]

Hi again all,

I happend upon a tutorial for carving a 2 blade WOOD prop somewhere on here but cant find it for the life of me.  Can someone point me towards one or something similar?

Thanks

[Flux]

Follow the instructions the same as for 3 blade. Just choose the characteristics to suit your intended tsr.

Why do you want 2 blades? if you want something very fast it may have some advantages but it does shudder badly in yaw. I wouldn't make anything 2 blade bigger than 8ft.

If you want something simple and fast this may do what you want if you are looking at 6ft. I hope the link still works, it's a sketch i did for someone who wanted to replace a Freelite prop. It's very simple with a flat drive face and a back curve that is part of a circle, ideal to produce with a spindle moulder.

Flux

[johnelarue]

Thanks flux,

I was thinking 2 blades for simplicity, never carved anything before.  Though am worried about the shudder effect.  I have a windblue 540 pma, that I posted about previously on hyrdro and wind.  But am considering all options.  I know it won't make a lot of watts with wind.  

So I take it 2 blades give most rpm, then 3 and so on?  I guess I could well enough make a 3 blade .

John

[Fused]

Here's my attempts at blades for a windblue 540.

Unless you are in a very high wind zone, just consider all your effort going to practice. You will be able to use what you've learned later on with a decent generator.

Good luck

Fused

[johnelarue]

Wow fused, that is a lot of work, very nice.

Even that big wood jammy didn't do it?  I'm getting 5 amps, 25 volts DC using my cordless drill at approx. 240RPM , no load of course.  With my friends drill turning 1800rpm? it lit a 100watt incandesent bulb on AC, no prob. That is what I'd get with hydro I assume, but the 240rpm I am guessing at with wind.  What kind of rpm did you get with your blades?

John

[Fused]

I had the RPM figured out back then, cant find my paperwork. The best I seen was just over 3 amps into a 12v battery with wind power, during a tropical storm. That was the only time I seen it do that much. Once these PM alts get loaded, a lot of your output watts are wasted in resistance and stator heat. Im not really in a good wind zone but the tropical storm was running 35-40 mph winds. The max blade diameter I made for it was a 6 foot. Hope it helps.

Good luck

Fused

[johnelarue]

Thanks again fused,

That is tough to hear, 3 amps in high winds.  I'm not in a high wind area but we do have moderate steady winds. Leaning more towards hydro now though, but may make a prop just to see for myself, I think you guys understand why.  Your advice is greatly appreciated, and anyone else's too. Feel free.

John

[adaml]

John,

A suggestion only - I would still consider 3 blades, if you are going to carve two then one more along the same lines.  Keep them small and fast, high tsr.  3A is about all I saw out of mine in a good wind location.  It was my first attempt at wind power and interesting learning curve.

I based my blades around this:  http://www.scoraigwind.com/selfblade/index.htm

Hope this is of some use - good luck.

[taylorp035]

My 30" two blade CNC blade set hit about 2300 rpm in 25mph + winds.  If you got 25 watts  at 240 rpm, I think you have a nice motor.  Probably a 4 - 5ft blade would be a good choice and you would see a peak around 500+ rpm.  Getting to 1800 rpm would be a stretch.

[johnelarue]

Thanks, I will consider 3 blades as well, for the balance of course.

I'll try wind first, if it doesn't put out then I'll go with hydro. Luckily we have both sources.

john

[johnelarue]

Well so far it is making 125 watts DC no load @ 240rpm.

I think with hydro it can hit 1000 rpm or better, hence the 1800 remark.

what kind of PMA are you using there Taylor?

[ghurd]

I believe you are putting too much faith in their deceptive charts.

It is not making ANY watts 'no load'.

Their own output tests say only about 200W at 2,000 RPM. (12V, 15A, 2,000RPM)

G-

[johnelarue]

I appreciate the info,

This is like riding a roller coaster.  One second I'm all pumped about using the Wind Blue 540 for wind,  the next it's like, it ain't gonna happen, better stick with hydro.  Like I said before luckily I have a hydro source, but it will be a pain in the butt financially to get the pipe, but not impossible.  

The mods required to make this a real low wind machine have me scared hatless as I've never done anything like that.... and I'm 8000 miles away from the manufacturer.

Should I open up the beast and try the mods, or buy the pipe and go with the rpms?

I'll have another beer while deciding.  

john

[taylorp035]

I was using an old 12volt bilge pump motor out of a sail boat.  12 volts no load comes at 2200 rpm and hits 35 watts at 3000 rpm.  Basically it was an easy generator that came out of a trash can      I plan on adding more coils to the motor because there is a lot of extra space inside ( which I find very odd ).