My first set of blades (part 1 of ?)

[icicle]

This is my first attempt yes they are skinny and thin but for a learning set they didn't cost much

the fuzzy white lines you see is cigarette smoke my boards are 1" thick x 3" wide x 8 feet long

this picture I was trying to show how far I went up before I started my taper which was 8" from bottom

this one was my airfoil so far at the tip, Still need to trim it down another 1/4"

This on is why you don't cut with a dremel tool I also have the saws all attachment

most of the wood is knot free I tried but I have to live with a few knots

After two hours by my dremel tool and the planner attachment I gave up

my tip angle was or still is at 7 dregees

as I get all my hand tools and more money I get them done. Two rough cut four more to go

I plan on making a 6 blader

Cody

[sdscott]

Cody, this may just be a practice-run for you, however, you should be aware that your dimensions are way-off of a production grade set of blades.  Eight-foot blades will render a 16-foot sweep-area, and with a 3" by 1" Root, you will have too much flexing and too little strength along the Cord of the blades to support the turning forces in moderate winds (not to mention strong winds).  The structural integrity of this rotor will fail quickly, and be very dangerous.  I suggest that you read more on this forum about blade-carving and understand the basic design and concepts of good blade design a little better before you continue in the direction you seem to be headed.  P.s. Why are you are planning a six-blade rotor?

Cheers!

[icicle]

First as I live in the country and this is going to be in my bottom field I'm not worried about the flexing.

Second I figured with a little more flexible the blades would bend rather to snapping off in high winds.

third the old saying a little is good, lot has to be better

I also realize that to balance 6 blades will be a pain

[finnsawyer]

You know, you could have gone with a zero degree angle when carving at the tip and put in a seven degree wedge at the root.  This is one way to gain a little more effective twist from thin lumber.  One also could laminate the blades.  Each layer of lamination only needs extend far enough to give the desired twist to that radius.

As far as bending is concerned, putting a rim like a those little plastic toys around the blade tips will stiffen the blades considerably.  When the blades bend back the distance around the tips gets shorter.  The rim prevents this shortening since its length is fixed.  With six blades it might be doable.  You do, of course, increase stresses in the blades.    

[icicle]

Thanks GeoM.

  Never thought about putting a fiberglass coat over then to give a better twist.

I think if I did coat them with a layer of fiberglass it will also strengthen a little bit

[finnsawyer]

You misunderstood.  I was talking about a rim like a bicycle rim, kind of like an extension of the winglets they put on airplane wings now.  It would also reduce the vortices.  Think about it.

[icicle]

I read most forms regarding blade carving and I understand where you are coming from, But if one makes a extremly stiff blade it has no give and will tear down the whole tower. On the other hand if you make them A little bit ( or my case extermly) weaker, the blades should bend and relive some of the stress on the tower before it fails, It would seem nobody want's there system to crash and burn. I would rather my blades break in flight than the whole tower failing.

What is cheaper the blades or the tower?

[icicle]

GeoM,

  The only problem I see in the rim idea is what happens when the blades pop out of the center it will throw every thing off balance and will lead to a melt down.

[finnsawyer]

The blades don't pop out of the center unless you have a catastrophic failure, as the rim is fastened to the blades by glue, which is stronger than the wood, or by some mechanical means.  The whole point of the rim is to prevent the bending of the blades, which requires the blade tips to be securely fastened to the rim.  While any structure will fail if the stresses become strong enough, you should also consider that the blade tips hitting the tower or simply breaking is also a catastrophic failure, and it does happen.

[icicle]

GeoM,

not to change the subject, but would it be better to go with a 2 or 3 degrees at the tip and a 7 to 10 degrees by the hub.

I will have to think on the rim ideal for a while.

I never looked into the max. tilt For mounting of the genny. If my blades do fold back 2 to 4 feet with out the rim should I make the pitch around 8 to 12 degrees

 

[finnsawyer]

I'd say go with around 4 degrees.  With a TSR of seven the angle between the apparent wind and the plane of rotation of the blades is 8.13 degrees.  With a twist toward the wind of four degrees off of that plane you will have an attack angle of four degrees.  The larger the attack angle the greater the lift, but the lower the fraction of the lift that will be in the direction of rotation, as that fraction is dependent on the difference between 8.13 degrees and the angle of attack.  It turns out to be pretty much a wash.  I'll stay with my recommendation that you carve the blades with zero degrees twist at the tip and increase the twist toward the root as determined by the angle of the apparent wind as long as you can.  Then use a wedge at the root to get the desired twist at the tip.  As you can see, this gets pretty complicated.  Drawing diagrams might help.  Note that the flat or cambered side of the blade is always toward the wind.  I hope this helps.

[nothing to lose]

"But if one makes a extremly stiff blade it has no give and will tear down the whole tower. On the other hand if you make them A little bit ( or my case extermly) weaker, the blades should bend and relive some of the stress on the tower before it fails, It would seem nobody want's there system to crash and burn. I would rather my blades break in flight than the whole tower failing."

I would think that is basically wrong!

Kinda like saying if I punch holes in my tires now I don't have to worry later about getting flats.

If you build the tower correctly and use a working furling system to turn out of major storm winds, or some type of braking system or shut down the genny in major storms, etc... the tower should never come down. It only comes down if you don't build it correct to beging with.

If you snap off a blade your going to be out of balance, figuring the blade will snap in the hardest of winds, not lowest, you are going to severly stress the tower as the genny tries to bounce around every which way with only 5 blades instead of the 6 it should have. Break off 2 in a row, more problems!

If you check out the site, I don't recall any tower failures because blades were stiff, the posted failures were like not securing turn buckles and they worked loose unscrewing themselfs. Weak blades don't help that. And once a genny I think broke a blade and bounced right off the tower, was supported only by the power leads I think, but tower was fine.

Other things like placing the saddle onthe wrong end of the guy wire and the cable sliped and let tower fall I think.

There are some tower failures, but I don't think any involved stiff non-flexing blades.