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 the numerically calculated behavior of two-spool engines. This method deepens students’ understanding of how design and control parameters affect performance and provides insight into how performance software works. It also builds on our previously published approach to teaching engine cycle design at RWTH Aachen University. We begin with an overview of the derivation of the analytical equations describing the single-spool turbojet operating line, including the effects of varying turbine and exhaust nozzle areas. We briefly extend this to transient performance by incorporating the shaft power balance. We then move to two-spool turbojets, where the operating behavior is determined by an iterative approach that captures the interaction between the low- and high-pressure compressor operating points. While students solve this iteration manually as a homework assignment to build understanding, it highlights the impracticality of such methods for complex engines. This demonstrates the need for numerical performance software to analyze two-spool engines. In the second part of the paper, we move from theory to practice, starting with an overview of how performance software works. We emphasize the role of numerical solvers that build on iteration schemes tailored to specific tasks and that incorporate compressor and turbine maps rather than making assumptions like constant efficiencies, as were needed for the analytical approach. We further present three student exercises, ranging from calculations of two-spool engine operating points to modeling specific real-world engines, evaluating their performance across the flight envelope, and analyzing transient performance. In summary, this paper presents an approach to teaching engine performance that combines analytical and numerical methods: by bridging theoretical understanding and real-world applications, future engineers are prepared to meet the challenges of designing and analyzing multi-spool aircraft engines.