Jazzy,


You would normally want both props with the top of their arc turning inward.

In this configuration, the spiral slip-stream from each prop, would hit the rudder on the same side as the prop.
This will, in case of the other engine shutting off, reduce the amount of rudder deflection needed to maintain heading on the remaining engine.

Please see the Piper PA-31-350 Navajo Chieftain, which for this reason, has one Lycoming TIO-540-J2BD on the left wing and one LTIO-540-J2BD (L - left hand rotation) on the right wing.

The Grumman Mohawk, on the other hand, had both props spinning outward, but also the triple rudders, which provide a different lateral control solution and the engines both have marked out-thrust.


On a normal model you would want both props turning inward and so the counter-rotating engine belongs on the right/starboard wing.