Charlie P has it right. Regardless of any kit's directions otherwise, in a high wing trainer type, differential can be a real helper and save a model especially from a lesser experienced flier. Another item that helps even the experienced flier (NOT 3D, Pattern, etc. which has different needs) is the use of setting ailerons - on flat bottom wings and scale models - UP about 3-5 degrees. I know it doesn't "look" right, but it saves many a model from a snap roll on take-off and/or a landing, since that left hand on rudder seems to freeze up!!!