Teaching Aero-Engine Performance: Performance Analysis of Single-Spool and Two-Spool Engines

Abstract In this paper, we present an approach to teaching aircraft engine performance analysis that progresses from analytical models of single-spool engines to numerically calculated behavior of two-spool engines. Building on our previously published approach to teaching engine cycle design at RWTH Aachen University, this method deepens students' understanding of how design and control parameters affect performance and provides insight into how performance software works. We begin with the derivation of the analytical equations describing the single-spool turbojet operating line, including the effects of varying turbine and exhaust nozzle areas. We then address two-spool turbojets, where operating behavior is determined by an iterative approach capturing the interaction between the low- and high-pressure compressor operating points. Students manually solve this iteration to build understanding, which highlights the impracticality of such methods for complex engines and the need for numerical performance software. In the second part of the paper, we move from theory to practice, starting with an overview of how performance software works. We emphasize that numerical solvers use iteration schemes and incorporate compressor and turbine maps, rather than relying on assumptions like constant efficiencies. We also present three student exercises, from calculating two-spool engine operating points to modeling real engines, evaluating performance across the flight envelope, and analyzing transient performance. In summary, this paper presents a teaching approach that combines analytical and numerical methods: bridging theoretical understanding with real-world applications prepares engineers to meet the challenges in designing and analyzing multispool aircraft engines.