The Oval Fuselage: A New Structural Design Concept for Blended Wing Body Cabins

Faced with the decreasing fossil fuel reserves and the need to decrease its environmental footprint, the aviation industry is searching for alternative fuels and more fuel efficient engines and aircraft. With the current designs reaching their limits, the industry has turned its attention to the family of all lifting bodies. Particularly blended wing body aircraft have received much interest, a combination of a lifting fuselage and a flying wing. It is commonly believed that this design has a high aerodynamic efficiency and lower structural weight fraction, which both contribute to a higher fuel efficiency. Though the concept has been around since World War II, no flying full-scale aircraft with a pressurized cabin currently exists. Additionally, the pressure cabins have so far been dictated by the aerodynamic design of the centre body. This thesis presents an alternative approach in blended wing body design, which has its roots in the design of conventional aircraft. For current aircraft a method called the `inside-out approach' is used, where the design of the fuselage is dictated by the requirements for the passenger and cargo compartment. Following this approach a blended wing body cabin consisting of four tangentially connected arcs, forming an oval fuselage cross-section with no need for an aerodynamic outer surface is designed. The arcs are supported by vertical and horizontal members, doubling as walls, floors and ceiling for the cabin. The research presented in this thesis describes the geometry determination and weight estimation for this new design, for pressurization, wing bending loads and longitudinal fuselage stresses. The weight estimation method that has been developed determines the thicknesses of the structural members per oval fuselage cross section, described by the four arcs and horizontal and vertical members, for a certain cabin geometry and the aforementioned loads. An imposed airfoil shape over the centre line of the cabin restricts the height of each oval cross-section. By placing these oval cross-sections in sequence, and interpolating between two neighbouring sections, a three-dimensional fuselage can be created that follows the airfoil shape. This airfoil-shaped fuselage is combined with outer wing sections, vertical tail planes, engines and landing gears to generate a complete blended wing body model. This model is analyzed by means of a Matlab optimization tool, which was adapted from a pre-existing blended wing body design tool. In this tool, the developed fuselage weight estimation is combined with a wing-weight estimation and an operative empty weight estimation to calculate the total operative empty weight. Three different conceptual design studies of blended wing body configurations, for 200, 400 and 800 passengers, have been optimized and assessed to investigate the feasibility of the new structural cabin design. These designs have been compared to another blended wing body cabin design and to conventional aircraft. In comparison to other blended wing bodies a lower fuel consumption, lower operative empty weight and longer range were found for the same maximum take-off weight and the same payload. A 400 passenger `oval-fuselage' blended wing body showed the most promising results with a 13% lower empty weight, a 6% better fuel consumption and almost 29% longer range. In comparison to the conventional airliners, this particular blended wing body showed a fuel consumption per transported kilogram that was 10% lower than that of the best performing conventional aircraft, the Boeing 777-200LR.Flight Performance and PropulsionAerospace Engineerin