Flying-V Family Design

Abstract

The Flying-V is a novel aircraft configuration that promises a large improvement in fuel burn performance compared to conventional aircraft, integrating the passenger cabin and cargo volume into the lifting surface. The Flying-V is a V-shaped flying wing with an oval cabin and engines over the trailing edge. The aircraft does not have high-lift devices, and fins and elevons provide stability and control. The Flying-V has been studied on several aspects such as aerodynamics and structures, confirming its large potential fuel burn reduction. This study focuses on the feasibility of developing a family of Flying-V aircraft, which is a crucial step in passenger aircraft development offering multiple aircraft variants at limited development and production cost. The ability to design a family of Flying-V aircraft can be a large advantage with respect to blended wing body designs, of which earlier research suggests that developing a family is difficult due to its lack of a constant cross-section. On a higher level, this research is one of the few focusing on family design of an unconventional aircraft configuration in the conceptual design phase. The Flying-V family is optimised for minimal fuel burn, ensuring commonality in terms of common variables and common components between family members. Fuel burn is calculated using fuel fractions and the Breguet range equation. A vortex-lattice method is employed to study the aerodynamic characteristics of the aircraft, enhanced with a viscous module to estimate its lift-to-drag ratio. The weight of the aircraft is estimated using empirical relations, a semi-analytical oval fuselage weight estimation method and a quasi-analytical conventional aircraft wing weight estimation method. The fuel burn model is validated using the reference aircraft family, resulting in a fuel burn within 0.9% of the data provided by the aircraft manufacturer. Feasibility of the Flying-V family design is ensured by including a range of top-level aircraft requirements on payload, range, cruise speed and altitude, low-speed performance, stability and control and airport regulations. The complete model is built within a ParaPy framework, which is a Knowledge-Based Engineering environment programmed in Python. Optimisation of the Flying-V aircraft family is performed using an iterative procedure, optimising variables that describe the planform and cross-section of the aircraft. The only unique variable for each aircraft variant is the length of the untapered part of the cabin, maximising commonality in the aircraft family. The optimised Flying-V (FV) family consists of three aircraft with a passenger capacity of 293, 328 and 361 for the FV-800, FV-900 and FV-1000 respectively. The design ranges of the Flying-V family members at maximum passenger capacity are 11.2x103 km, 14.8x103 km and 15.4x103 km. The range of the FV-800 is smaller than the other two aircraft family members because no requirement was imposed on this range, determining the range implicitly from the available fuel volume resulting from optimisation of a two-member aircraft family. The optimised design suggests a 20% and 22% lower fuel burn than the modelled reference aircraft family for the FV-900 and FV-1000 on the design mission, proving the feasibility in terms of fuel burn of a Flying-V aircraft family. The penalty in fuel burn compared to individually optimised aircraft is 8.9%, 7.1% and 4.2% for the FV-800, FV-900 and FV-1000 respectively. The takeoff mass of the Flying-V family members is 185x103 kg, 234x103 kg and 266x103 kg respectively. With respect to the modelled A350 family, this is a reduction of 17% and 15% for the -900 and -1000 variant. The approach speed of the FV-900 and FV-1000 is estimated at 136 and 137 kts, much lower than the specified approach speed of the reference aircraft of 140 and 147 kts. Besides constraints on payload and commonality, driving requirements in Flying-V family design are the shift in centre of gravity during flight, the wingspan and the fuel tank volume. Feasibility of the design is ensured by drawing a floor plan of the aircraft fitting its payload and furnishing. Additionally, a sensitivity analysis on the obtained design vector confirms its optimality.