The roll requires ailerons but if your airplane only has rudder then you might be able to pull off a larger, somewhat untidier ‘barrel roll’. A roll with ailerons is a very smooth maneuver and not too difficult to pull off.
How to fly it: Same start as the inside loop; fly straight and level on at least half throttle. To begin a roll, apply a very small amount of up elevator and left or right aileron a split second afterwards. No need for full power this time, keep the throttle stick where it is throughout the roll. If you are using rudder alone you’ll need to apply much more up elevator and put the plane in to a small climb before rolling.
As you apply elevator and aileron, the airplane will start to roll over. Keep the aileron stick in the same position but you will probably have to adjust the elevator to keep the roll tidy. As the plane inverts, release elevator and apply a tiny amount of down elevator when the airplane is fully inverted, this will prevent any loss of altitude during the roll (generally speaking…).
Once the airplane is right-side up again, return the sticks to neutral and resume straight and level flying.
Above is the roll on video (on the RealFlight rc flight simulator), including close-ups of the Tx stick inputs and the airplane’s response.