*8.2. The Design-Manufacure-Operation Continuum of the Axis of Performance—A Case Study*

Quantitative and qualitative analysis bi-directionally along the life-cycle continuum of design-manufacture-operation of an airborne system can help improving performance and safety of the system. As a case study, the authors would like to present a glimpse into a research done by them on performance enhancement of a turbofan aero-engine. The engine type used to have pre-mature withdrawals before completion of the specified time between overhaul (TBO) due to performance deterioration, manifesting in the form of higher turbine entry temperature (TET), consequent upon the higher fuel burning requirement to ge<sup>t</sup> the required engine thrust. An analysis of the engine test data of 200 engines for various engine performance parameters revealed very interesting results. Two of the typical trend graphs (for the TET and the compressor pressure ratio, with respect to the compressor mass flow rate) are shown in Figure 13.

The graphs show that the more the compressor mass flow rate, the lesser is the turbine entry temperature, and the higher is the compressor pressure ratio. Working backward along the axis of performance, the analysis of the assembly procedures revealed the various reasons for a reduction in the compressor pressure ratio, and in turn the compressor mass flow rate, leading to higher turbine entry temperature, thus making the engine susceptible to early withdrawal due to performance deterioration, like a higher blade tip run-out.

Working further backward along the axis of performance, the contributing factors at the component manufacturing stage which eventually led to the higher blade tip run-out could be found out. Improvement actions taken in the manufacturing stage on the blade realization processes and in the assembly stage on the assembly procedures, and establishing the best practice rules accordingly, helped in getting a lower turbine entry temperature and thus higher thrust at the testing stage. This could substantially reduce the susceptibility of the aero-engine for pre-mature withdrawals from the operating unit due to performance deterioration, since sufficient margin of safety was provided in the engine pass-out stage itself by aiming for an engine with lesser TET.

**Figure 13.** The Case study on Bi-directional Synthesis along the Axis of Performance.
