This paper presents the results of the conceptual design and optimization of Hybrid Wing Body (HWB) aircraft that were designed to meet aggressive targets for fuel burn, noise, and landing / takeoff nitrogen oxide emissions for the 2030 timeframe. To address the aggressive targets, the HWB airframe design expands upon the work of the Silent Aircraft Initiative by using advanced subsystem level technological concepts with system-level, simultaneous optimization of airframe, propulsion, and operations. To assess the impact of payload and range on scalability, aircraft were designed at three scales, denoted as H1, H2, and H3, with similar payloads and range as the Boeing 737-800, 787-8, and 777-200LR, respectively. Due to cabin aisle height restrictions, the unusable "white" space for the H1 design resulted in a large empty weight fraction. Even with this, the H1 design achieved 45% lower fuel burn than the Boeing 737-800 due to the efficiencies of the all-lifting configuration, advanced propulsion system and assumed structural advancements. The H2 and H3 designs mitigated unused white space by carrying increased payload in a larger, more efficiently packaged centerbody, and their fuel burn was superior to the H1 design. The final H3 conceptual design achieved 54% lower fuel burn than the B777-200LR, noise levels 46 EPNdB below Stage 4 standards, and LTO NOX emissions that are 81.6% below CAEP 6 standards.