In the last 60 years many new technologies have entered the aerospace industry, but the overall aircraft design remained virtually unchanged. If we compare an aircraft built in the 1960's with the latest generation, they look strikingly similar. Only small evolutionary changes entered the commercial aircraft market. A lot of these changes are driven by the ever-lasting quest to reduce the amount of burned fuel. However, the reduction in fuel usage which can be gained with these small evolutionary changes decreases every aircraft generation. A revolutionary change in the aircraft design is needed to make step-change in aircraft fuel efficiency. Changing the configuration of the aircraft could create opportunities for aerodynamic and structural improvements, which will result in higher fuel efficiency. Current tools used in the field of aircraft design use a lot of empirical data obtained from the analysis of existing aircraft. These tools are not capable of correctly analysing unconventional aircraft configurations. A design tool, called the Initiator, is created which is able to synthesise a conceptual aircraft design based on a given set of top level requirements for a wide range of aircraft configurations including conventional aircraft, canard aircraft, Prandtl-planes and Blended-Wing-Body aircraft. The Initiator is verified by comparing the output of the Initiator with existing aircraft. A selection of thirteen reference aircraft varying from small regional jets to wide-body long-range jet-powered aircraft is made to verify the tool. Top level requirements are defined which match the payload, harmonic range and runway performance specifications of the reference aircraft. The aircraft generated from these top level requirements are compared to the existing aircraft. The design process is proven to work, since it converges to a feasible aircraft design which complies with the top level requirements. By comparing the maximum take-off weights and operational empty weights, it can be shown that the generated aircraft are similar to the reference aircraft. Nine out of the thirteen generated aircraft are estimated to within 10% of the reference aircraft weights. Visual inspection and comparison of external aircraft dimensions show that the implemented design rules are capable of generating an aircraft which is similar to the reference aircraft. The design tool was used to compare the different aircraft configurations. The design process works for conventional, canard, three-surface and Prandtl aircraft. Testing the design process for the Blended-Wing-Body was unfortunately not possible with the current state of the sizing methods. The canard aircraft design results in a 12% reduction in fuel mass and a 28% reduction in operational empty mass in comparison with a conventional aircraft designed for the same payload and harmonic range. However, since none of the analysis methods have been validated the confidence in the results gained from the configuration comparison in low. It can be concluded that the design tool can be used to synthesise and compare a wide range of different aircraft configurations.

Synthesis of Novel Aircraft Concepts for Future Air Travel

Hybrid wing–body configurations are currently an active field of research as potential candidates to meet NASA Environmentally Responsible Aviation N+2 goals. One characteristic of these configurations is the presence of a large number of redundant flight control surfaces. However, the design process and decision rationale for a given control surface layout is rarely discussed in the open literature. This work investigated tradeoffs between drag, control authority, actuator weight, and actuation power requirements as a function of the number and spacing of elevons. The actuators were sized based on hinge moments computed during nominal and failed control flight conditions. These effects were propagated upward to estimate changes to fuel burn, a system-level metric important to the Environmentally Responsible Aviation program, via the Breguet range equation. A model of the NASA N2A-EXTE hybrid wing–body configuration concept was used to demonstrate these tradeoffs. The study concluded that adjacent elevons...

Method for Evaluating Electrically Actuated Hybrid Wing–Body Control Surface Layouts

Hybrid Wing Body configurations are currently an active field of research as potential candidates to meet NASA ERA N+2 goals. One characteristic of these configurations is the presence of a large number of redundant flight control surfaces. However, the design process and decision rationale for a given control surface layout is rarely discussed in the open literature. This paper investigates tradeoffs between drag, control authority, actuator weight, and actuation power requirements as a function of the number and spacing of elevons. The actuators will be sized based on hinge moments measured during nominal and failed control trim analyses. These effects are propagated upwards to estimate changes to fuel burn, a system level metric important to the ERA program, via the Breguet range equation. A model of the N2A-EXTE will be used to demonstrate these tradeoffs.

Assessment of Electrically Actuated Redundant Control Surface Layouts for a Hybrid Wing Body Concept

This paper presents a semi-analytical method for the weight estimation of fuselages with an oval cross-section, applied to blended wing body aircraft. The weight estimation of the fuselage primary structure is based on a structural analysis of two-dimensional crosssections and it is completed by a set of empirical relations for the weight estimation of the secondary structure and non-structural items. A conceptual design study on a stable (5% static margin), 400-passenger blended wing body aircraft has been performed with the weight estimation method implemented in an aircraft conceptual-design program. A top level requirement for the harmonic range of 15,200km was imposed on the design. From the anaylis a maximum take-off weight of 395 metric tons has been found, with an operative empty weight fraction of 45% and a fuselage airframe weight of 47.3 metric tons (amounting to 26% of the operative empty weight). The results of this study are presented in comparison to the Boeing 777-200LR airliner, showing a slightly higher operative empty weight fraction, a lower fuel consumption of 2.05kg per passenger per 100km.

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Semi-Analytical Weight Estimation Method for Fuselages with Oval Cross-Section

In today’s highly competitive aviation industry, continuous efforts are being directed towards reducing design time and simplifying systems. One of the prime aspects of aircraft design is the development of high-lift systems, which are used to obtain satisfactory performance in low-speed flight. The associated design and integration of high-lift systems is highly multi-disciplinary and iterative in nature, due to tight dependencies between aerodynamics, mechanism kinematics and structures. Therefore, these systems should be considered early in the design process. Current methods for weight and power estimation of high-lift systems rely on empirical methods which are not sensitive to design variables and load cases. To improve the current design process, a new methodology has been developed, employing a Knowledge Based Engineering (KBE) application (inGDL) that integrates the preliminary wing designwith trailing edge high-lift systems and accounts for three-dimensional flap kinematics. The high-lift system in the developed application includes the kinematic synthesis of four commonmechanisms, an initial actuation architecture, weight and power estimate. The development scope has been limited to single-slotted flaps. The developed application works as follows: a clean wing geometry is first generated, after which the designer can assume an initial trailing edge flap layout. By subsequently specifying the required flap settings, the kinematic mechanisms are synthesized. When a feasible design is obtained, a SimMechanics multi-bodymechanism model is generated and then simulated to obtain the internal loads and actuation torque. An initial aerodynamic load of the flap has been determined using an empirical normal load estimation method by ESDU. Next, the mechanisms and actuating drive train are sized, leading to a determination of system weight and drive motor power. The link between the application and sizing module is completely automatized. After a design cycle has beenmade, an automatically generated report presents the obtained feasible design. In order to get an indication of the applied sizing method accuracy, a measurement of the outboard hooked-track mechanism of a VFW-614 flap has been carried out. The measured weight is compared to a modeled hookedtrack mechanism, synthesized and sized specifically for the VFW-614 wing. The results show a 13% underestimation ofmechanism weight, which is caused by modeling simplifications, assumption during sizing and likely the normal load prediction error. The developed application provides designers with the possibility to combine the aerodynamic, kinematic and mechanical aspects in one design environment. By quickly obtaining geometrical and sizing estimates, in addition to identifying design sensitivities, trade-offs can be made earlier in the design process. The application has been made such, that it can be expanded with higher-fidelity analysismodules and additional functionalities. By improving the current modeling concept and sizing method, more accurate results can be obtained and more load cases accounted for.

Design Framework for Trailing Edge High-Lift Systems: A Knowledge Based Engineering Application

This paper details a new software tool to aid in the conceptual design of blended-wingbody aircraft. The tool consists of four main modules. In the preliminary sizing model a class I estimate of the maximum take-off weight, wing loading, and thrust-to-weight ratio is calculated. This information is used together with an initial guess of the 30 design variables that to form a geometric model of the aircraft. From this geometric model four disciplinary models are derived: an aerodynamic model, a model of the wing box structure, a model for the cabin, and a model for the fuel tank. In the subsequent analysis module refined weight estimation for the operating-empty weight is being calculated, as well as the center-of-gravity shift during loading, the static margin, the main stability and control derivatives, and the harmonic range. In the last module, these analysis results are compared to 27 nonlinear constraints stemming from the top-level requirements and the aviation regulations. A gradient-based optimization routine is employed to find a combination of the design variables that satisfies all constraints while optimizing for harmonic range at constant maximum take-off weight. Between 20 and 60 iterations are required to achieve convergence. The tool has been set up to allow for maximum configurational flexibility such as forward-swept outer wings, under-the-wing engines, and twin vertical tails.

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J. Van Dommelen

Papers

A Conceptual Design and Optimization Method for Blended-Wing-Body Aircraft

A Conceptual Design and Optimization Method for Blended-Wing-Body Aircraft