Key parameters of air breathing two-stroke combustion engines for integration into small scale UAVs

The advent of low cost civilian small scale UAV has resulted in the extension of the limits of range and endurance. Among the many design parameters, the selection of powerplants and propellers for optimal range and endurance is dependent upon known dynamic thrust and fuel consumption data for propeller-IC engine combinations. To date, extensive work has been done on both large aviation and wind turbine propellers as well as smaller RC electric motor configurations. This paper shows that the above data cannot be used to accurately predict the dynamic pressure and fuel consumption of propeller-IC engine combinations. This is because, the complete single cylinder engine and propeller combination is both an aerodynamic and thermodynamic process which must be considered in totality. In support of this, detailed wind tunnel tests were carried out on a representative IC engine and propeller combination. The results were non-linear and varied significantly from anticipated output. The paper summarises the outcomes, suggests changes to design strategies in light of the outcomes and concludes by proposing key areas of future investigation.