Ch 5 is actually an AUX just as 6,7,8... and can be assigned as desired if you do not have retracts.

Ch 5 normally is a toggle switch with 2 positions because of its primarilly getting used for retracts... but you can use it for a bomb rlease of to operate a camera, landing lights... anything that does not need proportional control.

None of the channel assgnments are "written in stone" if its convenient for you and makes sense to you.. ailerons can be on channel 3. (I can't SEE it being convenient or making sense... but it would work.)