Replacing a 2 blade prop with a 3 blade - how to choose?

[RknRusty]

I'm finally getting to the point on my Sterling profile Yak-9 build to start thinking about the power plant. I'll be using a Fox Stunt .35 and would like to use a 3 blade prop, mostly for aesthetics, but I've never used one before. For instance if I find that a 2 blade 10x5 Power point or Master Airscrew works best, how do I choose a 3 blade prop to replace it?
Thanks.
Rusty

[Steve Thomas]

A commonly-quoted rule of thumb is to go down an inch in diameter and up an inch in pitch - so in your case, you'd be looking at something like a 9x6 3-blade. Obviously that's not a hard-and-fast rule and individual mileage may vary.

The problem I have is actually getting hold of them.  The Tornado 9x6 was popular, but I wouldn't know if or where you could still buy any. MA make them in certain sizes (usually with 1-2" less pitch than advertised, by all accounts), but there's not much by way of the more upmarket options.  Neither Bolly nor Brian Eather are making them any more, and last time I tried to get a Majik one from Randy, he was out of stock. Are there any other options out there, anyone?

[RknRusty]

Thanks, Steve. A rule of thumb is all I need. Once I get her trimmed up with a two blade prop, I'll know what to start experimenting with.
Rusty 

[Igor Burger]

Equivalent 3 bl prop is

90% of the orriginal 2 bl diameter if prop blades are of the same geometry (shape, aspect ratio)

or

87% if blades have orriginal width ( orriginal prop blades with cut tips)

or

100% (the same) of diameter if blades are narrower by 2/3

in all cases pitch is the same as orriginal

[RknRusty]

Excellent. I cut and pasted that information into my notes. Thanks, Igor.
Rusty