Generalized Sizing Methodology for Hybrid Aircraft Using Integrated Performance Constraints

Abstract

Hybrid aircraft are systems capable of flying as either fixed-wing aircraft or rotorcraft, as well as transition between these modes. Nowadays, hybrid aircraft have many potential applications as they consolidate some of the advantages of fixed-wing aircraft and rotorcraft. Despite the abundant knowledge on designing fixed-wing aircraft, designing hybrid aircraft is a challenging process and considerable design work yet needs to be developed. Diverse hybrid aircraft preliminary design studies have focused on presenting new configurations using traditional design methods for fixed-wing aircraft and/or historical data. Although such approach is practically possible, it may lead to having either insufficient or unneeded excess engine power. Insufficient power prevents aircraft from achieving the desired performance requirements and increases transition flight time. On the other hand, excess power penalizes the design by increasing the aircraft cost and weight, resulting in diverse performance deficiencies. Thus, to obtain adequate power, wing, and rotor disc loadings, this paper presents a formal sizing methodology for hybrid propeller-driven aircraft with the necessary mathematical formulations based on integrating the performance requirements in the fixed-wing, rotorcraft, and transition flight modes. The methodology is verified by estimating the XV-15 tiltrotor sizing parameters with errors less than 3% compared with the real aircraft parameters.