I am pretty sure that Real Flight uses only Switch 2 for smoke - I am not sure if you can set that up differently, but I'm pretty sure that you can not...

Also, I don't believe that all planes offer smoke capabilities. When selecting an aircraft, if you read the description, it will usually mention something about using smoke on switch 2. I don't use it that often, so I only remember seeing it on a some of the aircraft.

Generally speaking, I had trouble getting smoke to work at all, on any plane. Eventually, I searched the knowledge base and found a suggestion to delete the RealFlight.ini file. Once I did that, and started it up again, it worked fine.