On the Performance of Common-Core Turboprops

Abstract

Turboprops offer a promising pathway for sustainable aviation, as they can achieve high levels of propulsive efficiency and reduced installed drag compared to high bypass ratio turbofans. Turboprop engine cores, though, are rarely designed from scratch; instead, they remain geometrically similar and can be used across several engine variants, which is known as the concept of growth engines or core commonality. This paper investigates the impact of core commonality on the installed performance of the next generation small-core turboprops. Firstly, a turboprop cycle design optimization is carried out based on a multi-point synthesis approach for 2035 entry into service assumptions. The propeller, nozzle and engine core are individually designed and analyzed. Preliminary design studies of the core compressor are performed using a 2D streamline curvature algorithm, providing insights into the aerodynamic trade-offs of highly loaded all-axial multistage compressors. The second part of this study examines the performance of growth engine variants by applying the common-core approach to the designed 2035 baseline turboprop engine. In this context, “growth” refers to increasing equivalent shaft power to meet the thrust demands of a derivative aircraft designed for higher passenger capacity and/or extended range. A common-core design methodology is developed and proposed, enabling power growth through zero-staging of the core compressor and power off-take from the free-power turbine to drive electric motors, which in turn power additional e-propellers in electrified turboprop variants. Three optimal growth engine designs are identified, achieving up to 34.8% power growth relative to the baseline turboprop while maintaining design constraints, including high-pressure spool overspeed limits, a fixed propeller design, and considerations for cooled or uncooled free-power turbines. Overall, this study systematically analyzes the common-core concept, reflecting the approach followed by engine manufacturers over the years.