Multidisciplinary Design Optimization of Blended Wing-Body Aircraft with Lateral-Directional Stability Constraints

A persistent challenge in the design and adoption of blended-wing-body (BWB) aircraft is maintaining adequate handling qualities across the flight envelope without relying on stability augmentation. To date, many multidisciplinary design optimization (MDO) studies of the BWB have focused on longitudinal stability and control characteristics, assuming that postponing vertical surface design negligibly affects the fuel efficiency and key design features. Moreover, several measures of handling qualities depend on dynamic stability derivatives, which are difficult and expensive to compute in high-fidelity optimization studies. In this work, a handling qualities analysis on a regional-class BWB optimized without consideration of lateral-directional stability reveals an unstable Dutch roll mode. To address this deficiency, constraints are imposed on the yaw stiffness and dihedral effect derivatives in a mixed-fidelity MDO problem based on the solution of the Reynolds-averaged Navier-Stokes equations. The objectives are to determine their effects on block fuel burn and the optimal design, and to evaluate their viability as proxy constraints on Dutch roll behaviour. Imposing a minimum yaw stiffness derivative with a reduced dihedral effect derivative produces an aircraft with Level 2 Dutch roll damping, albeit with a 4.1% block fuel burn penalty. Enforcing a minimum yaw stiffness derivative alone brings the Dutch roll damping ratio to Level 3 at a 1.2% cost to block fuel burn.