Stefan wrote:

Of course the effects of the P-factor can be overcome by appropriate
design. The most simple solution would be the possibility to trim all
three axis.

Yaw damping does wonders in the Pilatus. Of course your typical GA
aircraft doesn't have 1200hp - and doesn't cost $3.5M.

On the more expensive level (much more expensive, I would guess), you
can overcome the P-factor effects by using two contra-rotating coaxial
propellors. This would not only overcome the effects of the P-factor,
but also those caused by torque. Kamov helicopters are an example of
such a design.

Effective, yes, but very complex, heavy and expensive. I recall seeing
an ad for Breitling watches that had a P-51 with contra-rotating props.
I think it was a one-off aircraft with a RR Griffon engine?

Contra-rotating coaxial propellors not only solve the P-factor and
torque, but they make the propellor more efficient, too. Probably too
little effect compared to the additional cost and complexity, so it has
been realized only rarely. Tupolev 114 is an example.

IIRC Tu-95/114 was the fastest prop aircraft of its category. I think
the cruise speed was near 500mph? I think that was a combination of
high-shp Kuznetsov turboshafts and the efficiency of the contra props.
Pretty amazing aircraft IMO.