We're starting a brand-new chapter now — Chapter 13, Gas Turbines —… — Page 196, Lesson 265

We're starting a brand-new chapter now — Chapter 13, Gas Turbines — Introduction. This is where we move from piston engines into the world of jet propulsion, so let's set the stage properly. First, let me give you the roadmap of what this chapter covers, because it's a big one. We begin with the history of the gas turbine engine, then we get into the principles — how it actually works. From there we look at the working cycle, and then a pressure-volume diagram of that cycle. We'll talk about constant pressure combustion, the temperature limit of the engine, and how the gas laws apply inside a gas turbine. Then we move into duct design, and after that we trace the airflow through each type of engine: a pure straight turbojet, a turboprop, a turboshaft, a low bypass ratio engine, and a high bypass ratio turbofan. We finish with propulsive efficiency and modular construction methods, and then there are questions and answers. Now, before we dive into the technical detail, I want you to notice something important about the history. The idea of using a jet reaction engine for aircraft is not new at all. In fact, in 1913 — that's over a century ago — there was a design for an aerodynamic jet engine. So the concept predates the practical realisation by decades. I want you to hold onto that thought, because it tells us that the fundamental physics of jet propulsion was understood long before the engineering caught up. Let me show you what I mean. That figure shows the 1913 design. And then we have another figure that contrasts two very different approaches. That one shows the Athodyd and the Whittle Engine, and it illustrates the principles of the gas turbine engine. The Athodyd — that's a duct that uses the forward motion of the aircraft to compress incoming air, with no moving parts in the compressor. The Whittle engine, on the other hand, is the real gas turbine — it uses a mechanical compressor driven by a turbine. That's the key distinction: one relies on ram effect, the other on a rotating compressor. Now, here's the crucial comparison I want you to understand. This figure compares the working cycles of the piston engine and the gas turbine engine. Both go through the same four fundamental processes — induction, compression, combustion, and power — but they do them very differently. In a piston engine, these happen in the same cylinder, one after another, in a reciprocating motion. In a gas turbine, they happen continuously in different sections of the engine, in a steady flow. That's the fundamental shift in thinking when you move from piston to turbine. So as we go through this chapter, keep that comparison in your mind. The gas turbine is a continuous flow machine, not an intermittent one. And that single fact drives everything else — the design, the efficiency, the limitations, and the way we operate it. Let's start with the history in detail, because understanding where this engine came from helps you understand why it's built the way it is.