Flying Qualities Considerations for Relaxed Static Stability Next-Generation Civilian Aircraft

Motivated by the unsatisfactory handling qualities of a conceptual Blended-Wing-Body (BWB) aircraft uncovered during recent assessments, flying qualities requirements for relaxed static stability (RSS) civilian aircraft are investigated through a series of flight simulation experiments. The flying qualities of a MDO-based BWB design are first examined to illustrate the shortcomings of existing conceptual aircraft. A flight simulation experiment is then conducted on a large transport aircraft model with variable short-period and Dutch Roll dynamics to identify envelopes of acceptable flying qualities based on Cooper-Harper Handling Qualities Ratings, NASA Task Load Index (NASA-TLX) scores, and quantitative measures of performance. Controllability limits for RSS aircraft are suggested based on feedback from test pilots and commercial pilots, alongside Dutch Roll requirements in the presence of unstable short-period dynamics. Implications of the results for the design of next-generation aircraft are then discussed. Results represent a step towards the design of RSS aircraft with sufficient handling qualities to enable safe landings in the event of a stability augmentation system failure, thus enabling the inherent trim drag benefits of RSS while mitigating the risks of certifying civilian aircraft requiring full stability augmentation.