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Current US military small unmanned aircraft systems (UAS) rely on engines and propellers sourced from the hobby radio-controlled (RC) aircraft industry. They require special fuel and in general have poor fuel efficiency. There is an urgent need to develop research capabilities to characterize and improve the efficiency of these small engines and develop the ability to operate on the available in-theater heavy fuels (JP8/kerosene). This paper describes the development of a small internal combustion (IC) propeller engine test stand capable of measuring both thrust and torque simultaneously under both static and dynamic conditions. The calculated uncertainty is found to vary from ± 10.4% to ± 1.7% for the range of interest. Torque, thrust, power, brake specific fuel consumption, (BSFC) and propeller efficiency data for a UAS engine are presented.

The engines used to power small unmanned aerial systems are often modified commercial products designed for use by hobbyists on small model aircraft at low altitude. For military applications, it is desirable to fly at high altitudes. Maintaining power from the engine at the reduced ambient air pressures associated with high altitudes requires some method of increasing air delivery to the intake manifold. Conventional turbochargers and superchargers are typically very inefficient for the low mass flows associated with small engines. Due to its unique characteristics, a pressure wave supercharger (PWS) can avoid many scaling-related losses. This project designed a small-scale PWS for turbo-normalization of a Brison 95 cc two-stroke engine for a small unmanned aerial vehicle. A larger PWS called the Comprex®, designed by Brown Boveri Company, was simulated using a quasi-one-dimensional Computational Fluid Dynamics (CFD) code developed at the NASA Glenn Research Center.