Abstract: A model internal-combustion engine having a rotatable shaft driven by an engine, a propeller secured to said shaft, and a self-starting mechanism in the form of a cylindrical hub mounted coaxially on the shaft against the propeller and having at one end an axially extending drive element at its periphery by means of which it drives the propeller and ramp-defining walls adjacent a spring-engaging element at its other end, and a helically wound spring surrounding the shaft, anchored at one end to a stationary part of the engine, and having a free end bearing against the hub with a hook formed thereon to automatically engage the spring-engaging element of the cylindrical hub and energize the spring when the propeller and hub are rotated in a contra-normal direction and to otherwise ride on the ramps of the hub in non-engaging relation to its spring-engaging element.