Conceptual Design of Blended Wing Body Airliners Within a Semi-automated Design Framework

Blended wing body aircraft represent a paradigm shift in jet transport aircraft design. Stepping away from the conventional tube-and-wing philosophy, they promise benefits over existing or future conventional aircraft. The most significant challenge with the concept is the increased coupling between aircraft design disciplines that has necessitated the development and implementation of multidisciplinary design optimisation routines. A novel conceptual aircraft design program named the Initiator has been developed that is able to design conventional and unconventional passenger transport aircraft, enabling comparisons to be made which are based on the same top level requirements and analysis fidelity. It however lacks the ability to design or analyse the blended wing body. The aim of this thesis is to make comparative studies between the blended-wing-body aircraft and its conventional tube-and-wing counterpart based upon the same design requirements. To this end the work investigates the methods that are required to implement the blended wing body aircraft in a semi-automated design framework such as the Initiator. By developing a novel geometric parametrisation of the blended wing body, the design possibilities have been increased while maintaining straightforward shaping manipulation and robustness. All relevant topics of conceptual aircraft layout are considered, making the resulting aircraft feasible in terms of the integration of its components. Furthermore, methods have been implemented or developed which are capable of analysing the mass, aerodynamic performance and longitudinal stability of the aircraft to a fidelity which is suitable for conceptual design. The mass estimation methods that have been implemented are verified and validated to be within 10% of reference blended wing bodies with a smaller error of 5% being common. There is however significant scatter in reference results, making conclusive statements about accuracy difficult. Drag estimations perform less accurately with drag being overpredicted by approximately 20%. The cause of this over prediction was largely due to empirical corrections for miscellaneous and unaccounted drag sources as is done for conventional aircraft. Wave drag is considerably higher than reference cases (7 versus 1 counts). Considering the applicability of the implemented method to blended wing bodies and the limited specific transonic design that is performed, it is chosen to accept this result as a conservative estimate until higher order validations of the wave drag can be performed. Induced drag was also higher for the test cases but results are inconclusive whether this is an error or a true result of the design choices. Zero-lift drag has however been accurately estimated by the novel implementation of empirical methods. Test case blended wing body and tube and wing aircraft were formed in the 150, 250 and 400 passenger classes. The comparisons of the resulting aircraft show that the blended wing body is feasible at the fidelity level achieved. They have reduced mass, improved aerodynamic efficiency and higher fuel economy. Trends show that the improvements over tube and wing aircraft increase with aircraft size. The qualitative results contained herein should still be treated as provisional since the implementation of the concept is not complete and remaining topics could still have significant effects on the results.Aerospace EngineeringAerodynamics, Wind Energy & PropulsionFlight Performance and Propulsio

Conceptual design and evaluation of blended-wing-body aircraft

Blended wing body (BWB) aircraft represent a paradigm shift in jet transport aircraft design that promise benefits over conventional aircraft. A method is presented to enable the conceptual design of BWB aircraft, enabling comparison studies with tube-and-wing aircraft (TAW) based on the same top-level requirements and analysis fidelity. The aim of this work is to make comparative studies between the blended-wing-body aircraft and its conventional tube-and-wing counterpart based upon the same design requirements at conceptual level. By developing a novel geometric parametrisation of the blended wing body, the design possibilities have been increased while maintaining straightforward shaping manipulation and robustness. The mass estimation methods that have been implemented are verified and validated to be within approximately 5% of reference blended wing bodies. Drag estimations perform less accurately with drag being overpredicted by approximately 20%. The cause of this over prediction was largely due to empirical corrections for miscellaneous and unaccounted drag sources as well as induced drag predicted by a vortex-lattice method. Test-case BWB and TAW aircraft were formed in the 150, 250 and 400 passenger classes. The comparisons of the resulting aircraft show that the blended wing body have reduced mass, improved aerodynamic efficiency and higher fuel economy. Trends also show that the improvements over tube-and-wing aircraft increase with aircraft size.Flight Performance and Propulsio

Preliminary Sizing Method for Hybrid-Electric Distributed-Propulsion Aircraft

The use of hybrid-electric propulsion (HEP) entails several potential benefits such as the distribution of power along the airframe, which enables synergistic configurations with improved aerodynamic and propulsive efficiency. This paper presents a comprehensive preliminary sizing method suitable for the conceptual design process of hybridelectric aircraft, taking into account the powertrain architecture and associated propulsion–airframe integration effects. To this end, the flight-performance equations are modified to account for aeropropulsive interaction. A series of component-oriented constraint diagrams are used to provide a visual representation of the design space. A HEPcompatible mission analysis and weight estimation are then carried out to compute the wing area, powerplant size, and takeoff weight. The resulting method is applicable to a wide range of electric and hybrid-electric aircraft configurations and can be used to estimate the optimal power-control profiles. For demonstration purposes, the method is applied to a regional HEP aircraft featuring leading-edge distributed propulsion (DP). Three powertrain architectures are compared, showing how the aeropropulsive effects are included in the model. Results indicate that DP significantly increases wing loading and improves the cruise lift-to-drag ratio by 6%, although the growth in aircraft weight leads to an energy consumption increase of 3% for the considered mission.Flight Performance and Propulsio

Aerodynamic Model Identification of the Flying V from Sub-Scale Flight Test Data

This paper presents the identification of the aerodynamic model of the "Flying-V", a novel aircraft configuration. The aerodynamic model is estimated using flight test data from a 4.6\% sub-scale model. The dataset includes longitudinal and lateral-directional maneuvers performed by both the pilot and the autopilot to excite the aircraft dynamic modes. The so-called Two-Step Method is used to decouple and simplify the aerodynamic identification problem; the state estimation step is performed by an Iterated Extended Kalman Filter, and the parameter-estimation step using ordinary least squares. A stepwise regression technique and previous knowledge from wind-tunnel tests are combined to select the model structure, and the identified model is validated using a third of the gathered data. The estimated models are parsimonious and considered adequate in terms of model fit, with a maximum relative Root Mean Square Error of 10% for the worst validation case. For the considered location of the center of gravity and flight conditions, the estimated aerodynamic derivatives confirm that the aircraft is longitudinally stable, both statically and dynamically; and that it is also laterally and directionally statically stable. The analysis of the dynamic modes of the sub-scale model showed stable short period and roll subsidence modes, a lightly damped Dutch roll mode, and lightly damped/unstable phugoid and spiral modes.Flight Performance and PropulsionAerospace Structures & Computational Mechanic