Rodney first you might learn how to spell "definitely". Rudder only turns aren't decent turn. You are making the model turn by a series of skids in the air. Remember the rudder controls the yaw axis. Next dihedral is a stabilizing influence primarily used on trainers. The purpose of dihedral is to keep the wings level. If a wing drops in a turn, its lift increases due to a better angle of attack. Here is some reading to help you out of your confusion:

http://www.mindspring.com/~cramskill/dihedral.htm

In regard to rudder only turns, you might try to understand the following:

http://avstop.com/AC/FlightTraingHandbook/Rudder.html

The aircraft will turn using only the rudder, but the nose will drop unless up elevator is used. Essentially using the rudder to turn is a series of skids.

The primary purpose of the rudder is to make a coordinated turn using both it and the ailerons. With an aileron turn, the lift vector is tilted. The lift vector is resolved into its two components: the vertical and horizontal parts. The latter is what turns the aircraft while the former supports the aircraft in the air or overcomes the force of gravity. Notice that the vertical component is decreased compared to when the aircraft was flying straight and level. To increase the vertical component, the nose of the aircraft has to be slightly raised in the turn.

And what role does the rudder play in this? The ailerons create adverse yaw or drag that prevents the nose of the aircraft from perfectly tracking the path of the turn. The rudder counteracts this yaw and keeps the turn smooth or coordinated.

When you're flying a rudder only model with or without dihedral, you must use the rudder and elevators. The rudder to yaw the aircraft, and then the elevators to correct the slipping nose. Otherwise, the plane will spiral out of control.

Ciao,

Eagle Al