Date of Award


Document Type


Degree Name

Master of Science in Aeronautical Engineering


Department of Aeronautics and Astronautics

First Advisor

Marc D. Polanka, PhD.


Three analysis techniques were used to measure the heat rejection of a 55 cc air-cooled two-stroke engine. This study was performed as part of a larger effort aimed at extending range and endurance limitations of Group 1 & 2 Remotely Piloted Aircraft (RPA). The engine selected for the study was a 55 cc gasoline-fueled, carbureted, spark-ignition engine made by 3W-Modellmotoren and is representative of RPA engines in these groups. With a surface area to volume ratio of 1.48 1/cm, the engine is in a size region where thermal losses begin to dominate engine efficiency and thermal efficiencies of less than 20% are common. The first measurement method was an energy balance between the fuel energy entering the system and the various avenues for energy to leave the system. The second method used an enclosure around the engine and measured the enthalpy increase of the air owing past the cooling ns. The third method used heat flux gauges placed on the cylinder head to measure the heat flux at those locations. The energy balance method estimated heat rejection at approximately 30-40% of the total fuel energy for full and partial power settings. As part of the energy balance method, the engines tested achieved a maximum thermal efficiency of 13.7% and a maximum brake power value of 2.9 kW. The engine enclosure method measured heat rejection values to be approximately 2 kW at full and partial power settings. This equates to 8-11% of the fuel energy at full power and 20-26% at a 25% power setting. The heat flux gauge method measured heat flux values of up to 33 kW m2 . Applying the heat flux values over the surface area of the cylinder resulted in 1.2-2.1 kW of heat loss. As a percent of total fuel energy this represents 7-13% at full power and 22-30% at a 25% power setting.

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