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Blended-wing-body aircraft are typically more energy efficient than conventional tube-and-wing aircraft due to higher aerodynamic efficiency and lower weight; thus, they could mitigate environmental concerns and lower operating costs. The wing-body blending and absent conventional empennage make the remaining components highly multifunctional, interdependent, and sensitive. In this work, a mixed-fidelity multidisciplinary design optimization framework with a Reynolds-averaged Navier-Stokes aerodynamics model and high design freedom realizes much of the potential of a blended-wing-body regional aircraft. Minimum necessary model fidelity is used. Critical design requirements are identified, efficient design features are explained, and relative fuel efficiency is calculated.
In a first investigation, design requirements include sizing, cruise trim, one-engine-inoperative directional trim, takeoff rotation and field length, initial climb performance, low-speed trim and static margin, and cruise rate of climb. Results show how optimal design features vary and performance is overpredicted if critical design requirements and key geometric freedoms are excluded. A 4.8% block fuel burn reduction is enabled by variable-length landing gear. Non-cruise requirements penalize block fuel burn by 3.2%, the penalty reaching 7.6% if lower geometric freedom that inhibits tight cabin contouring and the creation of a novel forebody ridge is used. Leading-edge carving is optimal, which, like the ridge, front-loads the center body, helping efficiently trim a nose-heavy aircraft with minimal trailing-edge lift reduction; moreover, low-mounted engines reduce the frontloading required. The high design freedom acting through a high-fidelity aerodynamics model generally helps efficiently satisfy design requirements, resulting in a cruise lift-to-drag ratio of 21.7 at 36 000 ft and Mach 0.78 (nacelle and excrescence drag is considered).
The competitiveness of blended-wing-body aircraft for low-payload, short-range missions is subsequently investigated. All mission capabilities of the Embraer E190-E2 best-in-class regional jet are matched, and the requirement of near-stall trim at center of gravity extremes is added, yet 9.9% less fuel is consumed by the blended-wing-body aircraft over a 500 nmi mission just above 44 500 ft. The 23.7 cruise lift-to-drag ratio is 24.7% higher than that of the E190-E2, and the maximum takeoff weight is 5.6% lower. For longer missions, fuel savings conservatively reach 16.4% to 22.6%. Moreover, a strut-braced-wing aircraft is nominally outperformed by 2.4%, and 4.7% to 9.1% for longer missions.
