Preliminary Design Study for a Blended Wing Body Seaplane

Unique customer operational and payload requirements are best met utilizing a catamaran hull design and a Blended Wing Body (BWB) that provides the most aerodynamic efficient design configuration. A conventional flying boat design isn’t suitable to deploy the large mission payloads on the water, and there isn’t an existing cargo plane capable of carrying the payloads that can be easily equipped with floats without significantly impacting performance. Since there is no suitable off-the-shelf solution, a study must be conducted into the feasibility of a BWB seaplane design. This study investigates the aerodynamic characteristics of two configurations of a BWB amphibious cargo seaplane: a baseline design and a variant equipped with catamaran-style floats. These configurations are intended for long-range offshore mission support. The primary focus is to quantify the drag penalty introduced by the floats, which was selected after evaluating three float designs, and to explore strategies for drag reduction and improved longitudinal stability on the chosen design. Experimental methods included Computational Fluid Dynamics (CFD) simulations and low-speed wind tunnel testing using a force balance. Aerodynamic performance was evaluated over a range of angles of attack at constant Reynolds numbers, yielding key metrics such as lift, drag, pitching moment coefficients, and lift-to-drag ratios. The results highlight the aerodynamic penalties of the float configuration and reveal opportunities for reducing drag while enhancing lift and stability through design refinements. These findings demonstrate the feasibility of optimizing the BWB seaplane concept for improved performance in future iterations. One of the objectives of our study is to quantify the drag penalty associated with the inclusion of catamaran-style floats. This involves comparing the aerodynamic characteristics of the aircraft model with and without the floats to identify performance trade-offs. Three different float designs were evaluated initially, with the final configuration selected based on an assessment of stability and drag minimization. The final design, chosen for its balance of reduced drag and sufficient buoyancy, was integrated into the seaplane configuration. Since the three float designs were developed so they would all exhibit near-identical buoyancy and stability characteristics, the deciding parameter for the floats was strictly magnitude of drag forces. One of the key findings of this research was drag penalty from each float design which were then compared to each other. The three float designs were identical except for the terminating edge geometry, with the first design being truncated, the second design being rounded, and the third design being sharp. SOLIDWORKS Fluid Simulation was utilized to simulate the flow around the floats at the required cruising condition (h = 10,000 ft, V = 300 kts). It was determined that the third float design, with the sharp terminating edge, had the least drag. This result was expected as the sharp trailing edge mirrors an airfoil. The float was then integrated into our first full model design. Another objective of our study is to minimize our drag and maximize our lift through design improvements. The lift-to-drag ratio, /, a critical measure of aerodynamic efficiency and one of this study’s main focus, was noticeably lower for the float-equipped design. While the floats are necessary for amphibious operations, they inherently increase drag and disrupt the airflow around the aircraft. However, optimization efforts demonstrated potential for improvement, such as reshaping the float leading edges and refining their placement relative to the fuselage, which led to our first design. A couple of methods were used to test and validate the numerical data we have collected during this study; wind tunnel testing and CFD analysis with validation. First, wind tunnel testing was carried out in the 12x12-inch open circuit University of Arizona Educational Wind Tunnel (EWT) at an approximately constant ∞ = 14.5 kPa for an angle of attack range of -10° to 10° in 2° increments for both of the plane models, one with floats and one without. With the selected experiment conditions, = 1.05 × 105 was achieved, with boundary layer transition trip strips being added to further increase the test for both models. Despite not reaching a high due to the space and velocity limitations of the EWT, the expected results and their usefulness remain unchanged. The objective was to obtain , , , and / plots as a function of for the baseline and floats-equipped models for direct comparison of their aerodynamic characteristics, with a special emphasis in the penalty of including floats. The primary objective of the CFD simulations, which were performed in ANSYS Fluent, was to assess the aerodynamic performance of the seaplane at different angles of attack (AoA), mirroring the conditions used in the wind tunnel experiments. This alignment ensured that the computational and experimental results could be directly compared, enabling validation of the numerical models and identification of any discrepancies. Additionally, the simulations provided detailed data on pressure distributions, velocity fields, and turbulent flow structures, which are challenging to measure experimentally. However, additional CFD simulations were run with different conditions, provided by our sponsor. These were meant to simulate real life scenarios during cruising or low speed conditions, meeting requirements within the scope of our study. This study successfully evaluated the aerodynamic impact of catamaran-style floats on a BWB amphibious cargo seaplane, demonstrating the trade-offs between buoyancy and aerodynamic efficiency, in addition to the feasibility of the concept as a whole. The addition of the floats increased drag and reduced the lift-to-drag ratio, but through design optimization, these penalties can be mitigated. The findings from the CFD simulations and wind tunnel tests provide a baseline from which improvements can be made. Further research is needed to explore additional design considerations in regards to the airframe structure and float geometries. By integrating these insights, the development of high-performance amphibious aircraft for long-range offshore missions can be further improved.