Analysis and Testing of Boundary-Layer-Ingesting Pusher Propeller for High Speed Rotorcraft

Abstract

Historically, pusher propeller configurations have been rare in all aircraft due to challenges in analysis and modeling, reduced installed efficiency, difficulties with cooling, and takeoff rotation limitations. As a result of being rare, little analysis or experimental data exists on pusher propellers, and data that exists is outdated and only marginally relevant to modern rotorcraft designs. With the development of high-speed rotorcraft configurations such as the Sikorsky X2 Technology™ Demonstrator (X2TD), a better understanding is needed of the design and expected performance of a pusher propeller operating directly in the aircraft fuselage wake. This paper describes a fundamental pusher propulsion study consisting of both analysis and wind tunnel experiments that provides data to help better understand, analyze, and design pusher propeller aircraft. The study focused on capturing the interaction between an axisymmetric rotorcraft-like fuselage body with a rear-mounted pusher propeller. Analysis was conducted using Computational Fluid Dynamics (CFD). Experiments designed to capture the interaction between the fuselage and the pusher propeller were conducted using a 16 in. diameter propeller in the UTRC low speed wind tunnel. Experiments and analysis of a propeller in isolation (no fuselage), the fuselage in isolation (sans propeller), and the combined fuselage and operating propeller are presented. CFD and experimental data were in good agreement and showed similar performance trends. Data showed that for most operating conditions, the pusher propeller installed performance was significantly higher (up to 5 net efficiency points) vs. the same propeller operating in isolation. In addition, an increase in drag proportional to propeller thrust was also observed. Overall, the results demonstrated the possibility of obtaining a net propulsive efficiency benefit by using a pusher-propeller configuration which can result in improved performance of high speed rotorcraft as well as fixed-wing aircraft with similar fuselage/propeller configurations.