Rotation
I think this is a very important factor. Handing the props helps in terms of equalling the torque effect but as you say its the slipstream vortex in reality. However this proved not to be as straightforward in practice as at first expected by Aerodynamicists. The process of evening out the slipstream vortex proved to cause all sorts of other less predictable aerodynamic problems mostly on take off and landing when airflow was slower as well as additional cooling problems. The Whirlwind with true handed Peregrines had serious rudder ineffectiveness while landing in particular, which delayed it and led to a bigger fin being fitted but landing speed was always high.
The Hornet with handed (via gear) Merlins tried to learn from this but had very similar problems in Mk 1 form which was never experienced with its predecessor the Mossie (not handed) until a long strake was fitted in front of the tail. Until that change it was never able to exploit its full power on take off without fishtailing.
Last edited by Screenworx; 25th Sep 2012 at 13:57.
Reason: typo