The first model aeroplanes were free flight models and as such were not equipped with RC systems. At close inspection, the methods for launching them were much the same as those used today.
 

An Attempt at an Overview

Modern free flight glider models are either launched by hand from a slope, pulled up on a line like a kite or propelled upwards with motor-driven propellers (rubber band, combustion or electric motors). This is no different for radio-controlled gliders. As there are variants of each of the three methods, the variety is large. Let's try a very simplified overview...