Gas Turbines - Introduction — Page 196, Lesson 268

Let’s start at the very beginning of the gas turbine story, because the whole subject hangs on one simple idea: jet propulsion. I want you to picture a lawn sprinkler. Water flows through it, and the force of that water escaping makes the sprinkler spin. That spinning is jet propulsion in action. Now, the formal definition I want you to hold onto: jet propulsion is the force generated in the opposite direction to the flow of gas or liquid under pressure that is escaping through an opening or hole. So the gas or liquid is under pressure, it escapes through an opening, and the force pushes back in the opposite direction to that flow. That’s the core of it. And here’s the key principle that makes all of this work. Whatever device uses jet propulsion, it is essentially a Reaction Engine. That means it operates on the Third Law of Motion, stated by the English physicist Sir Isaac Newton in 1687. For every action, there is an equal and opposite reaction. The escaping gas is the action, and the forward thrust is the reaction. That’s why we call it a reaction engine. Now, this isn’t a modern idea. The first known use of a reaction engine was by Hero of Alexandria in 250 BC. Hero’s engine was a sphere into which steam was introduced under pressure. The steam came in through apertures, and those apertures also formed the bearings on which the sphere was allowed to rotate. So the same holes that let the steam in also let the sphere spin. When the steam was allowed to escape through two bent tubes mounted opposite one another on the surface of the sphere, it created a thrust that caused the sphere to rotate around its axis. That’s the same principle as the lawn sprinkler, just with steam. Now, the idea of using a jet reaction engine for aircraft is not new either. In 1913, a French engineer named Lorin suggested a design for an Aerodynamic Thermal Duct, which we call an Athodyd for short. But it wasn’t until 1941 that Sir Frank Whittle’s jet engine actually powered an aircraft in flight. So we have the theory from Newton in 1687, the first reaction engine from Hero in 250 BC, the Athodyd concept from Lorin in 1913, and then Whittle’s engine flying in 1941. So when we talk about a gas turbine engine, we’re talking about a reaction engine that uses this exact principle. The thrust comes from gas under pressure escaping through an opening, and the reaction to that escape is the force that propels the aircraft forward. That’s the foundation we’ll build everything else on.