A Scalability Study of the Multirotor Biplane Tailsitter using Conceptual Sizing

This paper presents a methodology for preliminary sizing of unconventional rotorcraft using a physics-based approach to size and estimate the weight of primary load-carrying members. The methodology is demonstrated for a Quadrotor Bi-plane Tailsitter (QBiT), a tilt-body configuration that can operate in both helicopter and airplane mode. A beam lattice framework for the airframe structure, and the spar geometry in the rotor blade are iteratively adjusted during design sizing to accommodate the expected wing loads and rotor blade loads. Using this analysis, a consistent combination of vehicle macro-dimensions (rotor radius, tip speed, wing span) as well as detailed design parameters (spar height, skin thickness and cross-section weight) are obtained simultaneously. To compare the effectiveness of various powerplants within a weight class, the sizing methodology was modified to identify the payload for three different vehicle take-off weights: 20 lb, 50 lb and 1000 lb. To enable operation within constrained urban canyons, the effect of restricting maximum vehicle dimensions to 10 ft for the 1000-lb designs is also examined. An electric transmission model is used in these designs owing to its relative insensitivity of transmission efficiency to the operating RPM.