In this article by Fly Staff for Fly RC Magazine, they describe what conventional fuel systems and unflow fuel systems are. They also discuss the conventional tank theory, pressure differential, fuel mass, the unflow theory of operation, why it is important to check a valve, tips for having a successful fuel system, and how to tune for maximum performance.
Sir George Cayley, often called the Father of Aeronautics, designed a helicopter powered by a bow-string mechanism with feather blades (similar to the reproduction shown here). Later, he experimented by flying a model with multiple adjustable surfaces, allowing him to understand how every change affected the model’s flight. This model is a ½ scale replica of his original 1804 model. Cayley used the data from these experiments to publish his On Aerial Navigation in 1809.