It was just irritating me that I couldn't find it, but I finally did (sorry about the mm stuff):

micasue2... <http://groups.google.com/groups/unlock?msg=80d7d990392011ec&hl=en&_done=/group/rec.aviation.homebuilt/browse_thread/thread/4602ca1a3101d5d0/1f6d88d9d13cdf9b%3Flnk%3Dst%26q%3D%26rnum%3D33%26hl%3Den>@yahoo.com wrote:
> I want to run my engine (ford v-6) this summer for various tests and I
> want some sort of prop.  What do most people use for props when testing
> at this stage?  I was thinking of glueing together 2 or 3 fir 2x6's or
> using a laminate beam (leftovers from a remodeling project) and carving
> some airfoil shape.  Seems like it should work if it is balanced.  Of
> course I don't want to sling a blade down the taxiway or through my
> neighbors hangar door.  Anybody offer some suggestions?  Thanks.

from Michel colomban (cricri, MC100, MCR01 designer)

A square wood beam,
aera= a*a
diam=15*a

You find the power with this formula:
P=0.0532 * (diam/450)^5 * (rpm/1000)^3
with     diam in mm            rpm in revolution / mn
or
diam=((P/0.0532) * 10^9 * 450^5 / rpm^3 ))^0.2
a=diam/15

I you want check 180hp @ 3800rpm
diam = 1026mm  a = 68.4mm