VTOL Concepts for Unmanned Payload Delivery Applications

Quad-rotors are widely used for unmanned VTOL missions due to simplicity and ease of control. A common civilian and military mission for a UAS is the delivery of small payloads from 5 lbs to 10 lbs. This paper compares the traditional quad-rotor configuration to a quad-rotor biplane and a tiltwing configurations for an unmanned resupply mission using the HYDRA rotorcraft design and analysis code. Physics-based blade weight models and a Finite Element Analysis module for airframe weight estimation are utilized in lieu of empirically derived trends. This analysis provides comparisons of performance, energy consumption, and empty weight breakdowns when each configuration is sized to a fixed mission profile. The two winged designs have around 14% higher payload weight fractions when sized to the same 20lb GTOW mission. The energy required to carry the additional empty weight of wings for the quad-rotor biplane and tailsitter designs is smaller than the energy consumed by the inefficient edgewise rotors of the quad-rotor design which consumes about 2.5 times the energy. Comparisons between the tiltwing and quad-rotor biplane are marginal at 20lb GTOW however at 50lb GTOW, the quad-rotor biplane has higher payload capacity. At 20lb GTOW the quad-rotor biplane has 10x the energy specific delivery productivity than the quad-rotor and about 2x higher than the tiltwing.