Complex sentence: They soon started development of one of the first purpose-designed aircraft engines, which emerged in the spring of 1909 as the 7-cylinder rotary Gnome Omega, delivering 50hp from 75kg.
Split into simpler sentences: They soon started development of one of the first purpose-designed aircraft engines, combining several Gnone cylinders into a rotary engine. The design emerged in the spring of 1909 as the 7-cylinder rotary Gnome Omega, delivering 50hp from 75kg.