Blades

[FishH2o]

Well, guys im very new to this so I wanted to say Hello and ask a couple questions. I originally started out wanting to make the otherpower 20ft turbine but i believe i bit off more then i can chew. I have one blank done that is 10ft long 13.5 inches at the widest and 6.5inches at the tip. Since i screwed up my measurements and didn't end up with the 18 inches they called for I thought heck no worries build the 17 foot.  So my question is will the .5 inch that im missing for the 17 foot turbine be that much of a difference?

[FishH2o]

Or can i still go with the 20 foot diameter and use it as 13 inches at the root and 6.5 at the tip??

[SparWeb]

I guess you mean that you started with carving the blades and haven't been working on the matching alternator.  Good, at this point a change of plan won't hurt as much.

I don't have a copy of the 17ft or 20ft plans, so I don't know specific measurements to help you with.  I'll just speak in general:
Considering the strength of the blade root needed to withstand all the radial forces of a spinning blade, plus the bending it gets from the gyroscopic effect, I would not be keen to use a blade with 2/3 the root strength. 

If your goal was a 20-ft turbine then don't be afraid of re-working a few parts to make sure you've done them right, esp if it's just one blade.
Carving the blades is a lot of work but (to me) it's the most rewarding.  I actually made 4 blades every time I have carved a set, exactly so that I could screw up one, pick the 3 best.  Having a blade left over can also be handy as a "conversation piece".   
Switching to the 17foot plan isn't a bad strategy, either, but are you sure that's what you really want? 

[FishH2o]

SparWeb,

Thank you for the reply but I decided not to go that route. I decided to go with the 10ft route since its well documented in the book and online. That will be plenty until we move top our property. Thats when I will need a 20ft.

[SparWeb]

There ya go.  Sometimes you just gotta know when you were just too ambitious.
Looking forward to seeing progress (good and bad!)

[Boondocker]

Also you will learn much flying a 10' rotor first. 
-     What are the real wind characteristics for the site
-      Is your tower adequate 

 boondocker

[finnsawyer]

     Your blade responds to the air flow past it {whatever that is} as an airfoil.  It also responds to the pressure drop {gradient} from front to back as a slab of wood.  That also creates lift {see those water pumpers, for instance}.  Its not clear which effect dominates.  Bottom line: Do not worry about the width near the root.  Do whatever you like.  Nobody knows what is happening anyway.  They just know some torque and power is produced.