I set my flaps on my 3 position switch on the transmitter... so I had up, partially down and full down. The real plane lands using either Flaps 30 or 40 degrees.

I never measured on my model, but for the middle position I used about 3/4" and max extended was about 1.25".

Experiment flying the plane with flaps down at altitude so you can get a feel for using them during landing. When I flew my Cessna, I always used rudder to make coordinated turns - you'll need the rudder even more at low speed.

Hope this helps,
Scott