Build, learn, repeat...

[Merv]

I have a ft tiny trainer, and would like to switch between 3ch (right stick rudder) and 4ch (right stick aileron) without physically switching the servo leads.

Why not set up a mix, aileron to rudder?

 

[Jeffo]

Would that achieve what I want? What would the values be?

 

[Merv]

I would suggest bumping both valves from 50% to 100%. You may need to change one to -100%
If I recall the rudder is channel 4, not channel 2.
If I recall mixes 5 & 6, could be controlled with a switch.