Propulsion model for (hybrid) unmanned aircraft systems (UAS)

Purpose - This paper deals with the estimation of the necessary masses of propulsion components for multirotor UAS. Originally, within the design process of multirotors, this is an iterative problem, as the propulsion masses contribute to the total takeoff mass. Hence, they influence themselves and cannot be directly calculated. The paper aims to estimate the needed propulsion masses with respect to the requested thrust because of payload, airframe weight and drag forces and with respect to the requested flight time. Design/methodology/approach - Analogue to the well-established design synthesis of airplanes, statistical data of existing electrical motors, propellers and rechargeable batteries are evaluated and analyzed. Applying Rankine and Froude's momentum theory and a generic model for electro motor efficiency factors on the statistical performance data provides correlations between requested performance and, therefore, needed propulsion masses. These correlations are evaluated and analyzed in the scope of buoyant-vertical-thrusted hybrid UAS. Findings - This paper provides a generic mathematical propulsion model. For given payloads, airframe structure weights and a requested flight time, appropriate motor, propeller and battery masses can be modelled that will provide appropriate thrust to lift payload, airframe and the propulsion unit itself over a requested flight time. Research limitations/implications - The model takes into account a number of motors of four and is valid for the category of nano and small UAS. Practical implications - The presented propulsion model enables a full numerical design process for vertical thrusted UAS. Hence, it is the precondition for design optimization and more efficient UAS. Originality/value - The propulsion model is unique and it is valid for pure multirotor as well as for hybrid UAS too.