EASA/GCAA Part-66 · Module 15 — Gas Turbine Engine · B1

Gas Turbine — the Running Engine

Objective: start the engine, follow air through it, and read the cockpit gauges. The Brayton cycle (compress → burn → expand → accelerate) turns fuel energy into thrust; see where pressure, temperature and velocity peak, and how the two spools (N1 fan, N2 core) behave.

3-D cutaway — airflow through the engine

Engine instruments

Brayton cycle (P–v)

Shut down

Thrust lever 0 %

Compressor pressure ratio 30

Turbine inlet temp (TIT) 1400 °C

Bypass ratio (turbofan) 5 : 1

N1 · fan spool

N2 · core spool

EGT

0°C

Net thrust (rel.)

0kN

Brayton cycle: Intake → Compress → Burn → Expand (turbine) → Accelerate (nozzle) · Thrust ≈ ṁ(V_exit − V_inlet)

A gas turbine runs on the Brayton cycle. The compressor raises pressure (and temperature); fuel burns at roughly constant pressure to add heat; the turbine extracts just enough energy from the hot gas to drive the compressor. Whatever is left accelerates out of the nozzle — and that jump in velocity is the thrust. Pressure peaks after the compressor, temperature peaks in the combustor, velocity peaks at the nozzle. A turbofan sends most of its air around the core (bypass) for efficient, quieter thrust.

Try this: Press Start and watch the N2 core spool lead, then N1 follow, with an EGT light-up spike.
Try this: Move the thrust lever to Takeoff. Watch the gauges, exhaust velocity and the Brayton loop grow.
Try this: Switch Turbojet ⇄ Turbofan and change bypass ratio — see the bypass duct and thrust change.
Try this: Raise TIT toward the red arc — real engines are limited by how hot the turbine can survive.