Unmanned Wingless Rotorcraft Scaling

The work addresses the allometric scaling of unmanned rotorcraft. Compound unmanned rotorcraft are not considered in this study. A population of 93 unmanned rotorcraft are compiled into a single dataset comprising size and performance parameters, including the maximum takeoff weight, maximum payload weight, battery mass, battery capacity, rotor diameter, endurance, range, maximum speed, and operational ceiling. Rotorcraft are grouped based on rotor configuration, propulsion type, and perceived application to study the clustering of the data points. An apparent performance limit for unmanned electric rotorcraft is found at 120 min of endurance and in the 70 km range; a higher range and endurance are currently only achievable using thermal propulsion systems. Furthermore, the regression analysis links size and performance parameters in easy-to-use expressions for the preliminary design of unmanned rotorcraft. It is determined that size parameters have a stronger correlation with the maximum takeoff weight than performance parameters. Comparative analysis suggests that unmanned rotorcraft cannot be treated as a subclass of conventional helicopters due to distinct scaling behaviors. A comparison with theoretical models based on first-order physics principles highlights the major role of low-Reynolds-number aerodynamic effects in rotorcraft scaling.