Jay Honeck wrote:

: It would seem logical that a third power-producing blade would be superior.

: Otherwise why would any planes have more than two blades?

At some point having 2 blades to absorb the engine power leads to blades
that are so long the tips go supersonic. This is bad, for many reasons
including the noise. (Republic Aviation actually made an airplane that had
intentionally supersonic blades: google "thunderscreech".) When you reach
this point the only solution is to use more blades. Hey, the ATR-72 has 6
blades on each prop!

In regards to your O-540, many O-540 airplanes have 3-bladers from the
factory. Commander 114, Piper 6/300, Navajo, etc. I don't know if they
use different crankshaft vibration dampers or not. My (solid crank) O-360A4A
does not have vibration dampers, perhaps the Arrow's does not either,
leading to the extra vibration with a 3-blader.

There is an excellent article in "Torque Meter" about the design of the
P&W R2800 crankshaft that describes the difficulties in crankshaft design
and handling torsional vibrations, as well as descriptions of how the vib.
dampers work. The article discusses the interplay of prop, engine, and
reduction gearbox. The article is on-line, but I don't have the link handy.
--
Aaron Coolidge