The maneuver in aerial fight invented by Max Immelmann with the reason is to gain higher altitude while making the turn into opposite direction. This turn can be used to avoid head to head attack as it was used to surprise enemy by flying cross each other and then turning back with this maneuver to attack it from more advantaged altitude.
However the turn had already fallen somewhat into disfavor as it became obvious that the zooming aircraft presented an easy target as it hung nearly motionless at the top of the maneuver. This is a bit crack when we fly Immelmann with RC plane since we do not cut the throttle during the turn point so the speed is mainly constant.
How to make this maneuver in RC plane
Flying the plane straight on level flight then starts with 90 degree half-roll climb up using up-elevator until the plane head back to the opposite direction, just keep the plane in straight and level flight though upside down. Half-turn the plane to a normal flying position using aileron, you will heading opposite to the first direction but gaining higher altitude. This picture shows how the Immelman turn is done.
Immelman turn is not difficult to carry out, and with some practice it may become your favorite turn in most occasions. In F3A aerial competition there is also double immelman maneuver included in the rules this is the proof of how popular this turning style is widely accepted. If you can make Immelman turn there are some aerobatic maneuvers that begin with similar starting position and fun to do such as hammer head and stall turn, for instance.